Poma Microbiology

Microbe and disease:

• Microbes:
- Bacteria: prokaryotes with singe cell with no specialized protein synthesis organelle and mitochondria. It is classified by gram stain (cell wall structure), aerobic/anaerobic, genetic and biochemical features. Example is streptococcus pneumoniae
- Virus: subcellular entities with no organelles and contains packaged nucleic acid that proliferating using other cells. Classified by nucleic acid type, capsid structure, biological and genetic features. Example is varicella Chickenpox
- Fungi: eukaryotes that can be unicellular or multicellular (moulds). Disease inducing at right opportunity can be either superficial or deep
- Parasite: eukaryotes that can be multicellular ranging from protozoas to tapeworms
- Prions: infectious proteins
• Infective manifestation:
- Colonization vs infection: micro-organisms are normal colonizers of skin gut or even wound but do not cause infection. However when the circumstances is presented, the microbes may breach the anatomical protection and become pathogen and infect the body
- Endogenous vs exogenous: infecting organism may be within the host flora (endogenous) or acquired from another individual or environment (exogenous)
- Symptomatic vs asymptomatic: infection may not cause physical problems such as herpes (which infects for life), or produce symptomatic in which a disease occurs. Pathogen may become latent and inactive while transmitted by later present complications after years. Example are polio that’s asymptomatic but some gets headache and paralysis
- Acute vs chronic: short term infection such as influenza or longer term such as hepatitis C virus
- Signs and symptoms: systemic effects such as fever, chills, fatigues, rigor and rash while locally inflammation will be swelling, redness, heat, soreness, tenderness, pus etc. diarrhea with gastroenteritis.
• Pathogenesis: disease occurs due to an imbalance of host and pathogen interaction. While pathogen aims to proliferate, transmit, invade, survive in host, the host counteract with immune defense such as PMN, antibody, T cells and even diarrhea to expel toxins etc.
• Pathogenesis of fever:
- Infection is very common cause with other ones including tissue injury, malignancy, drugs and other inflammatory immune disease.
- Temperature is controlled by hypothalamus. However during infection, monocytes and macrophages are activated to liberate various cytokines such as TNF or IL which cause the hypothalamus to alter the body temperature point. Heat also generated by vasoconstriction and shivering
- Increased temperature allows for advantage in fighting infection as condition is less favorable to pathogen and more preferable by immune proteins
- High fever can be harmful thus anti-pyretics such as paracetamol and aspirin is used to avoid complications.
• Major advances in medicine: understanding the knowledge of pathogens and their transmission and pathogenesis, control of disease have much improved. Health initiatives promoting hygiene, use of vaccination and antibiotics have decreased mortality of infectious disease greatly.
- However problems such as antibiotic resistance by microbes is becoming more important

Bacterial Growth, Structure and Function

• Bacterial growth phases:
- In the beginning, replication of bacteria is slow as the enzymes and metabolism are adjusted to new condition and hence a lag phase
- Later on, growth is exponential with asexual cell division. Growing cells require energy source and ability to acquire and synthesize cellular components. Iron is the only nutrient not freely available in the body.
- As nutrients are exhausted and toxic waste accumulation, bacteria enter stationary or even death phase where all division are completed. Adaptation is needed for harsh conditions and in species of Bacillus, DNA is copied and encased in a endospore which is released to enhance survival.
• Features: bacteria are diverse in their habitat and growth is largely dependent on ability to obtain nutrient and generate ATP, e.g. psuodomonas is highly versatile and can grow in many conditions while Chlamydia is only intracellular. The more adaptive a bacteria is to growing in host, the more specialized nutrient it requires.
- Chlamydia can’t produce its own ATP so must reside intracellularly. Thus culturing colony must use live animal cells and antibiotic must pass into cells, e.g. tetracycline
- Some bacteria require to be cultured on heated blood (chocolate agar) with NAD and/or hemin supplied. This feature is useful to identify bacteria type.
- Anaerobic bacteria is only a risk for deep wounds but not superficial wounds as it dies with oxygen exposure, e.g. clostridium
- Bacteria with slow growth require longer antibiotic course to kill, e.g. tuberculosis
- pH changes
• Importance of oxygen: in presence of oxygen, carbon source is fully utilized while in anaerobic respiration ferments carbohydrate to acid and use other compounds as terminal electron acceptor, e.g. SO42-
- Obligate aerobes: oxygen is essential for these bacteria, e.g. mycobacterium tuberculosis
- Obligate anaerobes: oxygen is toxic for these bacteria, e.g. clostridium
- Facultative anaerobes: can growth in either oxygen or no oxygen environment, e.g. Escherichia coli
• Bacterial structure:
- polysaccharide capsule surrounding a cell wall which is thick in gram positive bacteria and thin in gram negative.
- Inner cell membrane lines the cell wall intracellularly and houses the electron transport chain apparatus and provide osmotic barrier.
- In the cytoplasm are 70s prokaryotic ribosome for protein synthesis
• Gram-staining:
- Using crystal violet to stain the bacterium
- Iodine forms a complex with crustal violet and trapping it in the thick PG layer of the Gram positive cell
- Subsequent addition of acetone or alcohol will not wash the crystal violet/iodine for gram-positive, but will for gram negative and thus decolourize the cell
- To reinforce, saffranin is added. For Gram-positive, purple predominates but for gram negative, dye is taken up and become red stained.z
• Differences in structure of gram positive and gram negative:
- Gram-positive: has adhesion/wall protein
- Gram-negative: has periplasm, porin, pilus, OMP, and outer membrane
• Function of structures and drug target:
- Chromosome: genetic material - targeted by DNA inhibiting drug
- Plasmids: circular non-essential material coding for virulence function or antibiotic resistance
- Cytosol: contains enzymes – targeted by metabolic inhibiting drugs
- Ribosomes: protein synthesis - target by synthesis inhibiting drugs
- Inclusion body: storage
- Inner membrane: osmotic barrier – complement or bacteriophage that puncture IM
- Peptidoglycan: support and strength – target by antibiotics that inhibit synthesis to produce cell lysis
- Wall protein(+): adhesion and nutrient uptake – antibody target
- Outer membrane(-): permeability barrier
- Outer membrane proteins (-): porins allowing small molecules into periplasms and nutrient uptake – antibody and antibiotics
- Teichoic acid: causes inflammation and endotoxin-like shock – antibody target
- Periplasm: contain degradative enzyme and transport protein
- Capsule: anti phagocytic and decoy – antibody target
- Pili: adhesion and DNA transfer – antibody target
- Flagellae: motility, adhesion – antibody target
- Endospore: highly resistance structure that carry DNA – using high heat and pressure treatment
• Peptidoglycan: a single macromolecule making up the cell wall that surrounds the cytoplasmic membrane.
- It is comprised of chains of alternation amino sugar of N-acetylglucosamine and N-acetylmuramic acid crosslinked by glycine peptides cross-bridge between the 5 amino acid residue of NAMA units.
- Provides the bacteria with shape and rigity and is necessary for growth and cell division. Bacteria will lyse if this layer is disrupted.
- In gram-positive, other compounds such as teichoic acid, glycoproteins and lipoprotein may be covalently attached
- Drugs: lysozyme can degrade the glycan backbone between NAMA and NAG; penicillin containing a beta-lactam bond forms a structural antagonist and binds to transpeptidase preventing cross-linkage; vancomysin binds to the amino acid residue and also prevent cross-linkage.
• Lipopolysaccharide: the outer leaflet of the outer membrane of gram-negative bacteria consisting of three section – lipid A, core polysaccharide, and O-antigen. Present in E.coli
- Lipid A is responsible for viability and endotoxin activity which can cause strong immune response, fever, shock
- Core polysaccharide is branched consisting of 9-12 sugars important for viability
- O-antigen is a linear polysaccharide of 50-100 repeating units of 4-7 sugars non-essential but used to distinguish different strains within bacterial species
• Lipooligosaccharride: similar structure to LPS but without the O-antigen
• Role of LOS and LPS: bacteria such as meningococcus when lyses release blebs of OM containing LOS and outer membrane proteins with LPS. These act as immune decoys and directly stimulate the TLR4 (toll-like receptors) on macrophages to secrete cytokines to mediate immune response.
• Immune response:
- Acute inflammation: neutrophils attracted to the site of infection and phagocytose the pathogen. Process enhanced by complements and antibodies. Release of cytokine by macrophages and neutrophils attrach more leukocytes and increase permeability of vessel.
- result can either be destruction of organism or survival of organism which will lead to morbidity and mortality
- survival of bacteria such as meningitis using a capsule to avoid tagging proteins will release more OM blebs and stimulate further cytokine release. Overstimulated immune response is harmful causing fever, vasodilation of vessel and loss of blood into tissues (hypotension), bleeding under skin (rash) and further necrosis and dead phagocytic enzymes.
• Capsule: poorly immunogenic polysaccharide that masks the antigenic protein on the bacteria surface and prevents recognition by complement and antibodies. Even so vaccine can be developed that target the polysaccharide of the capsule.

Introduction to Virus

• Virus:
- Virus contains nucleic acid RNA or DNA but not both.
- Virus can survive outside but to proliferate it must infect a host cell (obligate intracellular parasite) as it does not have its own ribosome, e.g. hepatitis A in sewer for weeks but herpes dies.
- Respond to antiviral but not antibiotics
• Classification:
- Structure of the virus: shape of capsid (helical, icosahedral etc), nucleic acid composition, acquired envelop
- Transmission route: respiratory, enteric (ingestion) or arbovirus (carriers)
- Disease: hepatitis or respiratory illness etc.
- For example: hepatitis B is a blood transmitted virus consisting of DNA with an envelop whereas hepatitis A is obtained by ingestion and contains RNA without an envelop.
• Structure:
- Nucleic acid: single or double stranded DNA or RNA. The RNA maybe be positive (can be directly synthesized into viral protein) or negative (must be transcripted into mRNA then into protein) and segmented, e.g. influenza A has 8 segments of RNA allowing resortment
- Envelop: a layer of plasma membrane modified with viral factors and acquired from the host cell when the virus leaves.
• Transmission:
- Respiratory: coughing and aerosol droplets
- Faecal-oral: unhygienic hands
- Blood-borne: contact with blood
- Arthropod: carried by insect and passes on when bitten
- Close contact/sexual: body fluid such as breast milk or saliva
• Pathogenesis and replication: disease caused by virus varies according to virus itself, target organs and immune response of host. Virus can cause direct damage through infection or due to immune response.
- Attachment and penetration: surface protein of the virus interacts with cell surface receptor of host cells and attempts entrance by either fusing with the cell membrane or endocytosed as a vacuole.
- Replication of nucleic acid and production of viral factors: the virus hijacks the cellular replication systems. DNA virus replicates usually in the nucleus while RNA virus in the cytoplasm. RNA virus requires to be reverse transcribed into DNA by intrinsic reverse transcriptase to allow replication. In both cases, viral proteins are synthesized either by viral enzymes that contained with the virus or cellular enzymes. Proteins are then transported to cell membrane.
- Incorporation: at times, the viral DNA maybe incorporated into the genome of the host cell and lay dormant to be activated later, e.g. HIV.
- Assembly: the structural components of the virus assemble into a capsid around the newly formed viral nucleic acid.
- Release: the virus escapes the cells by cell lysis or exocytosis in which the viruses obtain their envelope with the attached proteins on the membrane. They are free to infect adjacent cells or transmit to new host.
• Viral tropism: attraction of viral to a cell and cause infection mediated by specific protein the surface of the viral capsid or envelop. Different virus will target different receptor for attachment and penetration:
- Influenza on sialic acid on glycoprotein
- Rabies to acetylcholine receptor
- HIV to CD4 receptors
• Difference in pathogenesis:
- Method of entrance
- How patient present
- Cell interaction with virus
- Target organ
• Outcome of virus infection:
- Cell lysis and death
- Latency/persistence in which a virus remain with the cell genome and there is no expression of viral protein in the infected cell
- Transformation causing host cell to become tumour cell
- Non-permissive
• Viral diagnosis:
- Microscopy: observe the histology of affected cell
- Antigen/antibody detection: presence of viral antibody in the body by blood sampling, e.g. HIV
- Culture: cultivate the cells with the viruses in laboratory
- Molecular: using PCR to amplify viral DNA to identify
• Treatment and prevention:
- Antiviral: target enzymes at any steps from attachment to replication to release of virus, e.g. protease inhibitors, nucleoside analogues to halt replication
- Vaccination: injection of harmless viral proteins or analogue into the body to stimulate immune response and antibody production
• Prions: rare abnormal protein, when in the body, subverts and leads to production of more abnormal proteins and death of the host.
- Variant CJD
- BSE

Viral examples of pathogenesis: Herpes complex

• Herpes simplex: DNA viruses with an icosahedral shaped capsid belonging to the herpes viruses that are able to become latent in the host with each bacteria having tropism for a particular cell target. HSV-1 usually causes orolabial herpes while HSV-2 usually causes genital herpes.
- Viruses emerged from the host cell is encapsulated with a glycoprotein capsule
- infections for herpes can not be treated but the clinical manifestations can
- HSV types 1 and type 2 are extremely similar and although they have different preference for location of infection. HSV-1 infects during childhood while HSV-2 infects when you become sexually active
• Diseases caused by herpes virus:
- varicella: respiratory route and dissemination to the skin. Has a latency period
- varicella zoster: reaction of varicella and spread through the skin
- glandular fever
• Cytomegalovirus: a specific genus of the Herpes virus called HSV-5 in which infection of immunocompotent individual are usually produced asymptomatic but can be deadly to patients who are immunocompromised.
• Survival and transmission:
- HSV being an enveloped virus is more fragile to deactivation by desiccation and chemical agents than non-enveloped viruses such as hepatitis. Thus it is unable to survive long outside the human body and build a very close relationship with the host, surviving within the body of 80-95% population in the case of HSV-1.
- Transmission: achieved by directly inoculation of infect material on to abraded skin or mucous membrane, e.g. kissing, sexual intercourse during birth. The virus usually passes asymptomatically from host to host and infection goes unrecognized.
- Babies can be badly infected in the birth canal and after several days of incubation, the virus will activate and cause serious damage and there is no immune system for the baby, neural encephalopathy
• Attachment and penetration: activities depend on the glycoprotein molecules that exist on the surface of the bacteria.
- HSV preferentially infects certain cells of the body such as epithelial cells such as those that line mucous membranes or skin and nerve cells.
- Adherence: after deposition the virus adheres to the surface of the cells by specific receptors on the viral envelop (glycoproteins). This process is called cell tropism.
- Penetration: fusion of the envelope with the cell membrane allows penetration of the viral capsid into the cell.
• Virus Entry and Cell Fate
- After entry into the cell it moves from the surface to the nucleus. This process appears to be mediated by normal cellular traffic proteins such as dynein that transport intracellular material on the microtubule on the cells.
- On the nuclear membrane the DNA of the virus is injected into the nucleus
- Cell fate: the fate of the cell depends on the cell type. For an epithelial cell the virus begins to replicate using the cells own transcriptional and translational mechanisms to produce genome copies as well as mRNA for translation of protein.
- Replication: replication of the virus occurs in the nucleus and the viral capsid is also assembled. The nucleocapsid then leaves the nucleus and acquires an envelop from the host’s cell membrane which have had specialized viral glycoproteins inserted (synthesized before)
• Consequences: after primary infection the virus enters the axon of the sensory neuron using the interaction of the glycoprotein capsule and the cell axon terminal. The virus’s cell body is in the dorsal root ganglion. The virus ascends the axon by retrograde transport mechanism such as protein dynein and enters the nucleus. The viral DNA circularizes and become latent.
- Usually in response to stress (virus detects very light stress such as menstruation) the virus can be reactivates and travels down the axon to the periphery by kinesin which is the cells own axonal transport. At the axon terminus, the virus can either bud off and pass to epithelium cells or a vacuole is formed and it is endocytosed. At this points it can either be excreted asymptomatically or infect epithelial cells to case clinically apparent lesions
- some viruses do not become latent but cause chronic persistent infections at a low level which may not be clinically evident, e.g. hepatitis B and C
• Immune evasion:
- down regulation expression of MHC class molecules so the immune systems does not react so immediately
- glycoprotein in its envelope act as a Fc receptor potentially thwarting antibody recognition of the virus and infected cells
- resides normally in dorsal root ganglia which is an immunological privileged site
- intracellular location in the sensory cell which makes it difficult to eradicate the virus as sensory neurons does not regenerate as easily
• Treatment: mimick normal base of DNA material, e.g. analogues and when used by virus to replicate, the material is integrated into the genome and cause termination of the replication. As the virus is needed to be phosphorylated to cause material to active, it is only specific to the infected cells.

Activities of Pathogens in Vivo

• Pathogens: microbes capable of causing damage to the host
• Infection: colonization of a host by a pathogen while evading the hosts defense and proliferate to cause damage (sign and symptoms of disease). However a bacteria does not have to be present in order to cause damage, e.g. by exotoxins.
• Sources of infectious agents: food, animal, people
• Routes of infection: airbourne, contact, respiratory, animal bite
• Risk factors: surgery and trauma, increased contact with pathogens, compromised or immature immune system (young children and patient that have undergone chemotherapy)
• Colonization: requires adherence of the bacteria. Large bacteria organelles allow attachment and initiate invasion such as indicate the cell to endocytose.
- Adherence of bacteria is important as it prevent the bacteria from being washed away and be anchored to its preferred niche and begin cellular invasion or toxin production
• Mechanism of adherence:
- Non-specific adhesion molecules: teichoic acid
- Specific adhesin
• Specific adhesin:
- Gram negative bacteria: use pili and fimbriae and outer membrane adhesin. One examples is H. pylorus, a rod bacterium uses strong flagellum to propel through the thick alkaline mucus on stomach epithelium and attaches via pili and outer membrane adhesions. Another example is the N. meningitis which uses pili to attach to the receptors of the nasopharyngeal cell surface and then retraction of the pili allows outer membrane adhesin to attaches to the receptors as well.
- Gram positive bacteria: uses cell wall proteins, e.g. MSCRAMMs (microbial surface components recognizing adhesive matrix molecules) bind matrix proteins. For examples streptococcus pyogenes uses lipoteichoic acids to mediate initiate attachment to the cell surface and then MSCRAMM facilitate stronger interaction with matrix proteins such as fibronectin or fibrinogen.
• Mechanism of bypassing the physical barrier: bacteria infection occurs through wounds in the skin as it can not penetrate the skin, or it can enter through insect bites or by cellular invasion of the outer mucosal cells.
• Mechanisms of resisting antibacterial compound in secretion:
- Altering surface charge so as to repel cationic peptides
- Producing proteases to cleave sIgA
- Producing a physical barrier, e.g. capsule, S-layer, outer membrane.
• Mechanism of resisting complement:
- Producing a low immunogenicity barrier such as a capsules that prevents antibody binding and hence the activation of classical pathway.
- By preventing formation of C3 convertase on bacterial surface again with capsule that has low affinity for protein B
- Mimicking host cells so that any C3b formed is degraded. Sialic acid capsules have a high affinity for serum protein H which targets C3b for proteolytic destruction
- Enzymes that degrades complement factors
- Fixing complement away from the membrane, e.g. long O-antigens
• Mechanism of resisting phagocytosis:
- Prevent recognition using a capsule
- Bind layer of host proteins so bacterium is recognized as a self
- Escape from the phagosome or prevent phagosome/lysosome fusion
- Prevent attraction of phagocytes by cleaving of C5a
- Produce toxins that kill the phagocyte
- Invasion of host cell
• Mechanism of resisting antibodies:
- Prevent binding use a protective capsule
- Prevent binding by altering antigenicity of surface
- Degrade antibodies such as IgA protease
- Bind the antibodies in a non-functional manner which can be used as a covering of host proteins
- Invasion of the host cells as antibodies can not penetrate
- Release blebs of antigenic membrane that acts as a decoy of the immune systems
• Mechanism of obtaining iron: iron is the only nutrient that is difficult for the bacteria to obtain and is essential as a co-factor for replication. Iron is not in free circulation in the blood but instead stored as ferritin or transferred with transferrin.
- Adapting in a iron rich niche of a phagosome
- Release proteases such as haemolysin to increase supply of iron,
- Specific binding proteins to bind and obtain iron, e.g. for transferrin
• Mechanism of bacterial damage:
- Exotoxin: proteins secreted with specific activities as enzymes or receptors agonists. Toxin may stop a cells from functioning such as prevent protein synthesis leading to cell death, or it can modify cellular activities. E,g, cholera toxin increase cAMP levels within intestinal cells resulting in chloride secretion and diarrhea. Toxin delivery not necessary requires the presence of the bacteria but can be previously secreted and ingested later.
- Enzyme damage: bacteria may secrete degradative enzymes that destroy proteins and connective tissue such as streptococcus pyogenes causing necrotizing faciitis. These enzymes also allow the bacteria to penetrate deeper into tissues.
- Co-lateral damage from inflammatory response: the immune response may involve the white blood cells to release degradative enzymes and reactive molecules such as hydrogen peroxide and damage surrounding tissues.
- Acute inflammation: excessive cytokines response to bacterial endotoxin (e.g. LOS, LPS, teichoic acid in peptidoglycan) or exotoxin can results in high fever, increases vascular permeability and intravascular coagulation and lead to embolism of capillaries in extremities. Loss of blood volume can lead to shock.
- Chronic inflammation: tissue damage by persistent antigens derived from persistent bacteria such as granuloma formation in Mycobacterium infections and gastric ulcer induced by H. Pylori.
- Blockages and space limitation: growth and mass of the bacteria or associated inflammation can cause problems of blockages. For examples vegetations of S. aureus from endocarditis being sloughed off can be carried into the vessels where they cause embolism. Granuloma from skin lesion can block sensory nerves.
- Post infection sequelle: autoimmunity response after bacterial infection, e.g. rheumatic fever where antibodies produced against antigens of streptococcus pyogenes strains target heart valve epitopes. Repeated exposure to the infecting strain type can induce recurring damaging episodes.
• Diagnosis:
- Culturing of the colony: gram staining the bacteria and microscopic examination for shape and colour can help identify strain, e.g. checking CSF of patients for gram negative bacteria which is meningitis. If you can’t see bacteria, then could be virus or intracellular such as Chlamydia.
- Detection of DNA: PCR can detect intracellular bacteria such as Chlamydia as DNA is amplifed
- Analysis: looking at the overall symptoms, location of infection will provide useful information
- Antigens: look for products or presence of bacteria such as antigens or antibodies can indicate infection
• Prevention:
- Vaccinate against many disease, sp immune system can recognize and destroy infection
- Eradicate sources of infectious agent such as hand washing
- Isolation of patients with contagious airbourne disease, e.g. leprosy
- Surgery put deeper fissure at risk so therefore provide antibodies and sterilize equipment
• Treatment:
- Killing antibiotics and avoid effect on normal flora
- Treat symptoms such as suppress high temperature, replace fluid due to diarrhea. Though antibiotics can reduce chlora infection period but it is not as effective as fluid electrolyte provision.
- Remove dead tissue but not disrupt blood supply so less leukocytes and healing.

Streptococcus pyogenes

• Streptococcus pyogenes: a positive gram stained coccus bacteria that prefer to reside in anaerobic locations with rich nutrients supply.
- Capable of haemolysing RBC to obtain iron
- Disease associated with streptococcus pyogenes is responsible a variety of conditions, ranging form superficial skin and throat infection to life threatening invasive disease.
- Colonizes either the pharynx or the skin through wounds
• Cutaneous infections: bacteria gain access to subcutaneous tissues through minor cuts, trauma, burns or surgery
- Pyoderma: a confined purulent infection of skin that leads to pus filled vesicles. Contagious, spread through touch.
- Erysipelas: an acute inflammation of the infected skin with local skin with local pain and systemic signs
- Cellulitis: infections of deeper subcutaneous layers of the skin. Local inflammation and system signs.
- Necrotising fasciitis: extensive and rapid destruction of muscle and fat.
• Throat infections:
- Pharyngitis: sore throat, with fever and headache. Throat likely to be inflamed and may have an exudates.
- Scarlet fever: a complication of pharyngeal infection by a subset of strains that produces pyrogenic exotoxin. The toxin spreads in the blood and spread over the body from the chest causing diffused rashes. A yellow coating covers the a red raw surface of the tongue (strawberry tongue)
• Intoxification: scarlet fever and streptococcal toxic shock syndrome which is produced through excessive cytokine induced by superantigen toxin or bacteria. Response is augumented by presence of lipoteichoic acids.
• Invasive disease:
- Bacteriaemia/septicaemia: excessive inflammatory responses to bacterial components, e.g. lipotechoic acid leading to shock
- Necrotizing fasciitis
- Streptococcal toxic shock syndrome
• Sequella: after infection complications
- Rheumatic fever: caused by M-types of S. pyogenes and associated with prior streptococcal throat infection. Antibodies created against the bacterium recognizes human proteins as pathogenic (this is because M-protein variation can sometimes produce an analogue of the host cells), e.g. of heart joints targeting inflammatory responses and associated damage of these cells.
- Acute Glomerulonephritis: associated with prior streptococcal throat and skin infection. Antibody-streptococcal antigens complexs are deposited in the renal glomeruli targeting inflammatory responses and associated damages to these cells.
• Transmission routes: person to person, respiratory droplets (pharyngitis), touch (skin infection)
• Mechanism of S pyogene adherence:
- Contains MSCRAMM that bind to human cells and blood proteins
- M- and M-like proteins that bind extracellular matrix proteins such as collagen and fibrinogen
- F-proteins that bind to fibronectin
- Epa binds to collagen
- Lipoteichoic acids which is non-specific surface adhesion
- LipoTA is negatively charged and so attracted to the positive charge of the tissue.
• Mechanism of mobility and dissemination: secreted exoenzymes
- DNAse: when bacteria kills a cells, the release of DNA forms a very sticky and viscous gel that stop bacteria from moving so secreted DNAse degrades the DNA to break free
- Streptokinase: activates plasminogen to plasmin to dissolves fibrin clots, allowing escape from abscesses etc.
- Cysteine protease: destruction of tissue allowing passage
- Hyaluronidase: destroys connective tissue
• Mechanism of resisting antibacterial compounds:
- Capsule of hyaluronic acid that is similar to connective tissue used to mask antigenic protein on surface of the bacteria.
- Carbohydrate layers used to identify streptococcus by their unique arrangement of saccharides (an antigenic target) but does not involve in resistance
• Mechanism of resisting complement:
- M-protein binds serum protein H, which favors C3b degradation
- M-proteins binds Fc region of the IgG preventing initiation of the classical complement pathway
- Capsule is a barrier to complement binding
- SIC (streptococcal inhibitor of complement) interferes with membrane attack complex of the complements
- C5a peptidase to reduce the concentration of the chemotactic signal C3a to prevent attraction of neutrophils
• Mechanism of resisting phagocytosis:
- M-protein binds Fc region of IgG preventing recognition
- M-protein binds fibrinogen and covering bacterial cells with proteins that will be recognizes as self
- M-protein bind the protease inhibitor alpha-macroglobulin giving protection against phagocyte proteases.
- C5a peptidase reduces concentration of chemotactic signal
- Hyaluronic acid capsule is recognized as self – so it is antiphagocytic
- Streptolysin lyses leukoctyes
• Mechanism of resisting antibodies:
- Capsule is low immunogenicity hyaluronic acid that is a component of the intercellular matrix and is recognized as self
- Antigenic variation with highly variable regions in the gene coding for antigen, e.g. M-protein protrudes through the capsules and varies and avoid identification
• Mechanism of acquiring iron: beta haemolysin is very effective at lysing blood so when cultured on a blood agar produce a clear halo while alpha haemolysin does not destroy RBC so a translucent halo
- Haemolysin release haemoglobin from red blood cells and myoglobin from muscles cells
- Protein of the cell wall have a high affinity for heme and intake
- Ferritin is also released from lysed cells and are primary sources of iron for S pyogene and does not acquire iron from lactoferrin or transferring
- Once nutrients in a local area is depleted, the bacteria degrades protein to release amino acids as nutrients
• Mechanism of damage:
- Exotoxin: SpeA toxic shock involves super antigen induces T-cells to secrete damaging cytokines leading to shock while SpeB is cysteine protease that lead to destruction of tissue and spread of bacteria. Streptolysin O and S cause lysis of erythrocytes platelets and leukocytes and release of lysosomal enzymes.
- Enzyme damage: SpeB can cause destruction of tissue while streptolysin with their release of lysosomal enzyme can kill phagocytes after engulfment. Hyaluronidase degrades tissue.
- Acute inflammation: lipoTA and endotoxin activates inflammatory cascade that leads to sepsis and work synergistically with super antigen toxins
- Post infection: cross reacting antibodies produces rheumatic fever and acute glomerulonephrititis
• Diagnosis:
- Culturing the S. pyogenes colony and then analyzed with gram stain and microscopy. Any gram positive coccus bacteria must either be straphylococci or streptococci. Adding a drop of H2O2 to the colony can allow distinguish as streptococcus can not break down H2O2 so no bubble is formed while straphylococci can.
- On blood agar, high levels of streptolysin indicate recent infection.
- Look for antibodies against antigenic S. pyogenes such as anti-streptolysin O, anti DNAse, anti-hyaluronidase
• Control of S. Pyogene infection:
- bacitracin: a streptococcus specific drug that inhibit the production of cell wall and causes death of the bacteria
- penicillin: peptidase transferase is inactivated by penicillin
- protein synthesis inhibitors: clindamycin, erythromycin
- competition: colonize the bacteria wit ha colony of a different streptococcus to out compete

Patient with tuberculosis

• Symptoms: tiredness, fever, sweats and weights loss and cough productive of bloody sputum
• Clinical diagnosis:
- X-ray: infiltration in both lungs apices and a cavity in the left lung apex. Abscess in the upper lobe
- Sampling: sputum samples examined with ZN stains under the microscope reveals large numbers of acid-fast bacilli (acid-fast because they resist decolourisation by acid after staining)
- Cultures: TB grows slowly in the laboratory taking almost 24 hours to double in numbers thus it requires up to 4 weeks to grow enough bacteria from the sample to start analysis and testing treatments
• Epidemiology:
- increased incidence of tuberculosis in people from third world countries
- most of the tuberculosis in European NZers occurs in elderly people
- it may take many years from arrival in NZ for tuberculosis to become apparent
- immigrants from 3rd world countries have high tuberculosis rates
• Time of infection: impossibly to know for precisely but most likely that the patients was infected in her home country perhaps as a child or young adult.
• Transmission: pus spilling out of the abscess into the airways will stimulate her to cough and every times she coughs she will create an aerosol with large numbers of mycobacterium tuberculosis containing droplets. Potential radius is 1m and while large droplets hits the ground, smaller droplets containing an average of 3 bacili will drift in the air and eventually inhaled by another person
• Primary response of the body:
- After the Mycobacterium tuberculosis containing aerosol is breathed into an alveolus the organisms are ingested by alveolar macrophages. However the TB releases chemicals to resist the killing of lyzozyme and superoxide while it escapes the lyzosome and replicate inside the cytoplasm.
- The macrophages are eventually killed and the TB bacteria are released. The cycle continues
• Reinforced response of the body: During this period, neutrophils and antibodies are all useless with only T-helper cells and macrophages the important types.
- Macrophages releases cytokines and present antigen to activate T-helper cells
- T helper cells releases cytokines including IL and TNF to enhance immune response
- T Helper cells are attracted to the site of infection and a granuloma forms with dead mycobacterium tuberculosis and dead macrophages in the center, surrounded by live infected macrophages, and in the outer region activated helper lymphocytes.
- The organism at the site of the infection may continue to replicate but remain controlled by the immune system for years. The person remains asymptomatic
• Expression of the tuberculosis:
- It is difficult to explain why the immune system fails to control the infection and allows aymptomatic tiny granulomas to enlarge to form tuberculosis disease
- A theory for the minority is due to HV infection which deteriorate the immune systems and hence thriving of the mycobacterium tuberculosis
• Processes in the lung:
- When the immune system loses control of the infection at any of the sites where a granuloma is present then tuberculosis disease develops in that tissue.
- For this patient, a granuloma has steadily enlarged and eroded through her bronchioles or other airway resulting in exposures of the organisms to high oxygen levels and rapid multiplication of bacteria and formation of a liquefied abscess
• Risk to other people: depends on
- duration of her cough
- closeness of her contact with others
- number of organism in her sputum
- condition of others that may impair their immunity
• Criteria of mycobacterium tuberculosis: used to evaluate patients and whether they need treatment
- mycobacterium tuberculosis disease: already unwell with evidence of significant infectious pathology as shown by symptoms of pneumonia and abnormal chest X-ray
- asymptomatic mycobacterium tuberculosis: infected but no progression to disease
- absent of mycobacterium
• Mantoux test: able to demonstrate the presence of circulating lymphocytes with specific activity against mycobacterium tuberculosis antigens and use this to determine whether a person has been exposed to TB or not.
- injection of the surface antigen of TB into the skin and if T lymphocytes for the disease is present will cause an inflammatory response
- the test is positive for people with the infection or disease but it is also positive in people who has been given BCG vaccine thus making it hard to interpret
- the test is negative for non-infected and non-vaccinated people
• Treatment:
- isolation to prevent transmission to others is important before treatment has reduced the patient’s infectivity
- patients with TB have large numbers of bacteria at the site of infection and requires treatment with a combination of anti-microbial agents for many month
- patients with TB infection without disease have relatively small numbers of bacteria at the site of infection and are usually treated with on anti-microbial (isoniazid) agents for 6 month
- TB drugs call kill liver
- Mycobacterium bovis is a bacteria that affect cow but similar to that of TB. Thus it can be grown on agar and injected into humans safely as it is not adapted to human host to gain immunity

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