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Questions and Answers
What is the primary function of teichoic acid in staphylococci?
What is the primary function of teichoic acid in staphylococci?
Which statement best describes coagulase-positive staphylococci?
Which statement best describes coagulase-positive staphylococci?
Which of the following surface proteins is NOT associated with adherence in staphylococci?
Which of the following surface proteins is NOT associated with adherence in staphylococci?
What differentiates coagulase-negative staphylococci from coagulase-positive ones?
What differentiates coagulase-negative staphylococci from coagulase-positive ones?
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What is the role of the capsule in staphylococci?
What is the role of the capsule in staphylococci?
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Which disease is primarily associated with S. mutans?
Which disease is primarily associated with S. mutans?
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What virulence factor of Streptococcus is considered major and promotes adherence?
What virulence factor of Streptococcus is considered major and promotes adherence?
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Which of the following species is classified as a β-hemolytic streptococcus?
Which of the following species is classified as a β-hemolytic streptococcus?
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What is a distinguishing feature of viridans streptococci compared to other streptococci?
What is a distinguishing feature of viridans streptococci compared to other streptococci?
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E. faecalis and E. faecium are primarily associated with which type of infections?
E. faecalis and E. faecium are primarily associated with which type of infections?
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Which statement about Streptolysin O and Streptolysin S is correct?
Which statement about Streptolysin O and Streptolysin S is correct?
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What role does lipoteichoic acid play in pathogenesis?
What role does lipoteichoic acid play in pathogenesis?
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Which characteristic is true for both S. salivarius and other species of streptococci listed?
Which characteristic is true for both S. salivarius and other species of streptococci listed?
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Which capsular serotypes of S. aureus are primarily associated with infections?
Which capsular serotypes of S. aureus are primarily associated with infections?
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What role does the capsule of Staphylococcus play in its pathogenicity?
What role does the capsule of Staphylococcus play in its pathogenicity?
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Which enzyme produced by S. aureus is responsible for dissolving fibrin threads in blood clots?
Which enzyme produced by S. aureus is responsible for dissolving fibrin threads in blood clots?
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What is the primary function of the enzyme coagulase in S. aureus?
What is the primary function of the enzyme coagulase in S. aureus?
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Which toxin produced by S. aureus is known to cause tissue necrosis and is active against neutrophils?
Which toxin produced by S. aureus is known to cause tissue necrosis and is active against neutrophils?
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What is the primary consequence of the action of exfoliative toxins A and B in infants?
What is the primary consequence of the action of exfoliative toxins A and B in infants?
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Which characteristic of S. aureus cytoplasmic membrane is critical for its biosynthetic functions?
Which characteristic of S. aureus cytoplasmic membrane is critical for its biosynthetic functions?
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Which enzyme allows S. aureus to survive treatment with β-lactam antimicrobial drugs?
Which enzyme allows S. aureus to survive treatment with β-lactam antimicrobial drugs?
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Which of the following is a membrane-damaging toxin produced by S. aureus?
Which of the following is a membrane-damaging toxin produced by S. aureus?
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What is the effect of hyaluronidase produced by S. aureus?
What is the effect of hyaluronidase produced by S. aureus?
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Which virulence factor of Streptococcus pyogenes contributes to its resistance to phagocytosis?
Which virulence factor of Streptococcus pyogenes contributes to its resistance to phagocytosis?
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What condition is directly associated with the poststreptococcal sequela of acute rheumatic fever?
What condition is directly associated with the poststreptococcal sequela of acute rheumatic fever?
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Which disease is considered the most common infection caused by Neisseriae gonorrhoeae?
Which disease is considered the most common infection caused by Neisseriae gonorrhoeae?
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Which of the following is NOT a consequence of infections caused by Streptococcus pyogenes?
Which of the following is NOT a consequence of infections caused by Streptococcus pyogenes?
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What is the primary action of the C5a protease produced by Streptococcus pyogenes?
What is the primary action of the C5a protease produced by Streptococcus pyogenes?
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What is a characteristic feature of Neisseriae meningitidis that enhances its virulence?
What is a characteristic feature of Neisseriae meningitidis that enhances its virulence?
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Which toxin produced by Streptococcus pyogenes is a pore-forming toxin that damages membranes?
Which toxin produced by Streptococcus pyogenes is a pore-forming toxin that damages membranes?
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Which condition is linked to Streptococcal Toxic Shock Syndrome (STSS)?
Which condition is linked to Streptococcal Toxic Shock Syndrome (STSS)?
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Which of the following skin conditions is caused by Streptococcus pyogenes?
Which of the following skin conditions is caused by Streptococcus pyogenes?
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How does the hyaluronic acid capsule of Streptococcus pyogenes affect immune response?
How does the hyaluronic acid capsule of Streptococcus pyogenes affect immune response?
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Which type of infections are primarily associated with Streptococcus pyogenes?
Which type of infections are primarily associated with Streptococcus pyogenes?
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What virulence factor is primarily associated with Streptococcus agalactiae?
What virulence factor is primarily associated with Streptococcus agalactiae?
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What is a major difference between α-hemolytic and β-hemolytic streptococci?
What is a major difference between α-hemolytic and β-hemolytic streptococci?
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Which Streptococcus species is known for its association with pneumonia and meningitis?
Which Streptococcus species is known for its association with pneumonia and meningitis?
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What surface protein is characteristic of Streptococcus pyogenes?
What surface protein is characteristic of Streptococcus pyogenes?
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Which organism is known for its bile resistance and fecal origin?
Which organism is known for its bile resistance and fecal origin?
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What disease is particularly associated with Streptococcus agalactiae in neonates?
What disease is particularly associated with Streptococcus agalactiae in neonates?
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What virulence factor does Streptococcus pneumoniae use to evade the immune response?
What virulence factor does Streptococcus pneumoniae use to evade the immune response?
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Which type of hemolysis is exhibited by Streptococcus bovis?
Which type of hemolysis is exhibited by Streptococcus bovis?
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What is a typical clinical significance of viridans streptococci?
What is a typical clinical significance of viridans streptococci?
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Study Notes
Lecture 6: Cocci
- Cocci are spherical-shaped bacteria.
- Staphylococci are pyogenic cocci and coagulase-negative staphylococci.
- Staphylococcus aureus characteristics include morphology, culture, and biological characteristics.
- Staphylococcus aureus virulence factors include: SPA, coagulase, hemolysin, and enterotoxin.
- Diagnostic tests for S. aureus include laboratory tests and principles of controlling staphylococcus infections.
- Streptococcus characteristics include morphology, culture, and biological characteristics.
- Streptococcus virulence includes group A streptococcus infections, pyogenic and non-pyogenic infections caused by group A, diseases caused by group B, D streptococcus and enterococcus, streptolysin, pyrogenic exotoxin, invasive enzymes.
- Diagnostic tests for streptococcus and pneumococcus include antistreptolysin O (ASO) test.
- Neisseria classification includes Neisseria meningitides and Neisseria gonorrhoeae.
- Neisseria characteristics include biological characteristics, pathogenicity, immune response, diagnostic laboratory tests, prevention, and treatment of diseases.
Classification
- Family: Micrococcaceae
- Genus: Staphylococcus, Micrococcus
- Species: S. aureus, S. saprophyticus, S. epidermidis
- Other species: Micrococcus luteus, etc.
Staphylococcus
- Discovered by Sir Alexander Ogston in 1880.
- Cluster-forming micro-organisms.
- Facultative anaerobes, catalase-positive, Gram-positive cocci.
- The genus Staphylococcus contains about forty species and subspecies today.
- Important human pathogens: S. aureus, S. epidermidis, S. hominis, S. haemolyticus, S. saprophyticus, and others.
Structure and Physiology
- Gram-positive cocci.
- Non-motile, facultative anaerobes.
- Cells occur in grape-like clusters due to cell division along different planes. Daughter cells remain attached to one another.
- Salt-tolerant, allows survival in human skin.
- Tolerant of desiccation, allowing survival on environmental surfaces.
Staphylococcus aureus - Morphology
- Polysaccharide capsule is rarely found in cells.
- Peptidoglycan (murein) is the major structural component of the cell wall, important in staphylococcal infections.
- Teichoic acid is another important component of the cell wall.
Peptidoglycan
- Half of the cell wall is peptidoglycan, common in gram-positive bacteria.
- Subunits are N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG).
- Gram-positive bacteria has many cross-linked layers, making the cell wall more rigid, unlike gram-negative bacteria.
Protein A
- Protein A is a major component of the cell wall located on the cell surface.
- Also released into the culture medium during growth.
- Binds to the Fc part of all IgG molecules, except IgG3, not an antigen-antibody reaction.
- The surface of most S. aureus strains (but not coagulase-negative staphylococci) is uniformly coated with protein A.
- Used in serological tests as a carrier for antibodies directed against other antigens.
Antigenic Structure
- Capsule or polysaccharide slime layer.
- Peptidoglycan layer.
- Polysaccharide A (teichoic acid).
- Protein A.
- Cytoplasmic membrane.
- Clumping factor.
Teichoic Acid
- Species-specific, phosphate-containing polymers.
- Bound covalently to the peptidoglycan layer or through lipophilic linkage to cytoplasmic membrane (lipoteichoic acid - LPA).
- Mediates the attachment of staphylococci to mucosal surfaces through its specific binding to fibronectin.
Coagulase and Other Surface Proteins
- Outer surface of most S. aureus strains contains clumping factor (coagulase).
- Binds fibrinogen, converting it to insoluble fibrin, causing staphylococci to clump or aggregate.
- Detection of this protein is a primary test for identifying S. aureus.
- Coagulase: Causes blood to coagulate, protecting bacteria from phagocytosis.
- Staphylococci are often coagulase-positive.
- Coagulase-positive: S. aureus
- Coagulase-negative: S. epidermidis, S. hominis, S. haemolyticus, S. saprophyticus.
Other Surface Proteins
- Important for adherence to host tissues, include collagen-binding protein, elastin-binding protein, fibronectin-binding protein.
Capsule
- A loose-fitting polysaccharide layer (slime layer) is only occasionally found in staphylococci cultured in vitro, believed more common in vivo.
- Eleven capsular serotypes have been identified in S. aureus. Serotypes 5 and 7 are associated with the majority of infections.
- Helps by inhibiting chemotaxis and phagocytosis of staphylococci.
- Promotes adherence to catheters and synthetic materials.
Cytoplasmic Membrane
- Complex of proteins, lipids, and small amounts of carbohydrates.
- Serves as osmotic barrier for the cell.
- Anchorage for cellular biosynthetic and respiratory enzymes.
Enzymes
- Staphylococcal enzymes: Coagulase, Catalase, Hyaluronidase, Fibrinolysin, Lipases, Nuclease, Penicillinase.
Role of Enzymes
- Coagulase: Triggers blood clotting.
- Hyaluronidase: Breaks down hyaluronic acid, enabling bacterial spread.
- Staphylokinase (Fibrinolysin): Dissolves fibrin threads in blood clots.
- Lipases: Digest lipids, allowing growth on skin's surface and in cutaneous oil glands.
- β-lactamase: Breaks down penicillin. Allows bacterial survival with beta-lactam antimicrobial drugs..
Virulence Factors
- Cell wall-associated structures: Peptidoglycan, Capsule, Protein A, Clumping factor (bound coagulase).
- Extracellular toxins: Haemolysin, Leukocidin, Enterotoxin, TSST, Exfoliatin toxin,.
- Coagulase: Staphylokinase, DNAase, Phosphatase, Lipase, Phospholipase, Hyaluronidase, Serokinase, Protease.
Staphylococcal Toxins
- S. aureus produces many virulence factors; at least five cytolytic or membrane-damaging toxins (alpha toxin, beta toxin, delta toxin, gamma toxin, Panton-Valentine leukocidin).
- Exfoliative toxins A and B cause staphylococcal scalded skin syndrome (SSSS).
- Eight enterotoxins (A-E, G-I) cause food poisoning.
- Toxic Shock Syndrome Toxin 1 (TSST-1)
Exfoliative Toxins
- Exfoliative toxins A and B cause staphylococcal scalded skin syndrome (SSSS).
- Usually in infants and newborns.
- Spectrum of diseases characterized by exfoliative dermatitis, mediated by exfoliative toxins.
- Prevalence varies geographically, generally less than 5% to 10% in S. aureus strains.
Food Poisoning Enterotoxins
- Eight serologically distinct staphylococcal enterotoxins (A-E, G-I) and three subtypes of enterotoxin C.
- Stable to heating at 100°C for 30 minutes, resistant to hydrolysis by gastric and jejunal enzymes.
- Preformed food, heat-resistant enterotoxin, usually self-limiting in 2-6 hours.
- Symptoms include nausea, abdominal cramping, vomiting, and diarrhea.
- Foods particularly effective carriers: custard, cream-filled bakery goods, processed meat, chicken, salads with mayonnaise, ice cream, milk, and dairy products.
Food Poisoning Enterotoxins
- Once a food product is contaminated, neither reheating the food nor digestive process will be effective in protecting against the toxin.
- These toxins are produced by 30–50% of S. aureus strains.
- Enterotoxin A is most commonly associated with disease.
- Enterotoxins C and D found in contaminated milk products, enterotoxin B causes staphylococcal pseudomembranous enterocolitis.
Toxic Shock Syndrome Toxin (TSST) and Other Toxins
- TSST-1: Superantigen (SAG).
- Non-specific binding of toxin to receptors triggers excessive immune response.
- S. aureus strains produce other extracellular, biologically active substances like proteases, phosphatases, lipases, lysozyme.
Toxin-mediated Infections
- Toxic shock syndrome (TSST-1).
- Superantigen (SAg) activates a large number of T cells.
- Associated with use of tampons but also postoperative wound/tissue infections.
- Symptoms: high fever, vomiting, diarrhea, sore throat, muscle pain, severe shock.
- Skin rash may develop, followed by desquamation. Blood cultures typically negative.
Toxic Shock Syndrome Toxin -1
- TSST-1, also called pyrogenic exotoxin C and enterotoxin F.
- A heat-and proteolysis-resistant, chromosomally mediated exotoxin.
- Ability to penetrate mucosal barriers, causing systemic effects.
- Death in patients with TSS is usually due to hypovolemic shock, a life-threatening condition.
Epidemiology of Staphylococcus aureus
- Ubiquitous; all people have coagulase-negative staphylococci.
- Transient colonization of common moist folds of skin with S. aureus is common.
- Colonization of newborns' umbilical stumps and perineal areas with S. aureus is common.
- Also found in the oro-pharynx, gastrointestinal, and genitourinary tracts.
- Shedding of bacteria is common, responsible for many hospital-acquired infections.
- Colonizes anterior nares of 20%–30% of healthy people, strains with increased virulence are hard to distinguish.
- Community infections are endogenous.
- Spread within hospitals often via hands of medical personnel, outbreaks involve nasal carriers.
Clinical Manifestations
- Clinical manifestations of some staphylococcal diseases are almost exclusively a result of toxin activity (e.g., staphylococcal food poisoning and Toxic Shock Syndrome).
- Other diseases result from proliferation, leading to abscess formation and tissue destruction.
Staphylococcal Diseases
- Systemic disease: Toxic shock syndrome (TSS toxin), bacteremia, endocarditis, pneumonia, osteomyelitis.
- Local pyogenic infections: folliculitis, furuncle, carbuncle,bullous impetigo, panaritia/paronychia, wound infections, mastitis, osteomyelitis, staphylococcal pneumonia.
Staphylococcus epidermidis
- Common skin commensal.
- Has a predilection for plastic material.
- Associated with infections of IV lines, prosthetic heart valves, and shunts.
- Causes urinary tract infections in catheterized patients.
- Variable antibiotic sensitivity pattern.
- Treatment aided by antibiotic susceptibility tests.
Infections caused by S. epidermidis
- Bloodstream infection, endocarditis, cerebrospinal fluid (CSF) shunt infection, peritoneal dialysis catheter infection, urinary tract infections, prosthetics joint infections, infection of vascular grafts.
- Infection in newborns, eye infection, pacemakers or implantable cardioverter-defibrillators, infection of breast implants
Importance of S. saprophyticus
- Skin commensal frequently isolated in rectum and genitourinary tract of young women.
- Can be the causative agent of UTIs in young healthy women.
- 2nd most common urinary pathogen (after E. coli) in uncomplicated cystitis in young women.
- Colony counts ≥10⁵ CFU/ml usually indicate significant bacteriuria.
- Usually sensitive to a wide range of antibiotics.
Prevention
- Hand antisepsis is the most important measure in preventing nosocomial infections.
- Proper wound and surgical openings cleansing, aseptic use of catheters or indwelling needles and suitable antiseptic use is important.
Streptococcus
- Gram-positive cocci, occurring in pairs or short chains.
- Non-motile, non-spore-forming. Some strains are encapsulated.
- Strict anaerobes and facultative anaerobes..
- Catalase-negative.
Streptococcus Species Classification
- Classified based on hemolytic activity.
- α-hemolytic: partial hemolysis (green), e.g., Streptococcus pneumoniae, Viridans.
- β-hemolytic: complete hemolysis (clear), e.g., Streptococcus pyogenes.
- γ-hemolytic: no hemolysis, e.g., Enterococcus faecalis, Enterococcus faecium.
Rebecca Lancefield's Classification
- Lancefield antigens are cell wall carbohydrates.
- Group A — rhamnose-N-acetylglucosamine.
- Group B — rhamnose-glucosamine polysaccharide.
- Group C — rhamnose-N-acetylglucosamine and some other carbohydrates.
- Group D — glycerol teichoic acid containing alanine and glucose.
- Group F — glucopyrasonyl-N-acetylgalactosamine.
- Only pyogenic streptococci are β-hemolytic. Hemolysis is used for practical classification.
Streptococcus Species Classification (cont.)
- Lancefield realized that all species in each group generally (and conveniently) shared similar properties (e.g., clinically significant properties, type of hemolysis, normal host, relevant body system or tissue).
- Examples: Group A (human upper respiratory tract / S. pyogenes); Group B (human urogenital tract / S. agalactiae); Group C (S. zooepidemicus, from animal products); Group D (S. faecalis, bile-resistant, fecal origin).
Streptococcus species (cont). Common Characteristics
- See page 59 and 60 for specific characteristics and details of different Streptococcus species.
S. pneumoniae and S. viridans
- Pneumococcus: has an antigenic polysaccharide capsule.
- Viridans: lack Lancefield antigens or capsules.
- Streptolysin O and S cause β-hemolysis.
- Streptolysin S is only active in aerobic conditions.
- Streptolysin O is only active in anaerobic conditions.
Classification Based on O2 Requirement
- Classification determined by oxygen requirement and hemolysis: aerobes, anaerobes, α-hemolysis, β-hemolysis, γ-hemolysis.
- Enterococcus faecalis is an example.
Virulence Factors of β-Hemolytic S. pyogenes
- Surface antigens: Protects against lysozyme, responsible for adherence, resistance to phagocytosis.
- C-carbohydrates: Protect against lysozyme.
- Fimbriae: Responsible for adherence.
- M-protein: Contributes to resistance to phagocytosis.
- Hyaluronic acid capsule: Causes no immune response.
- C5a protease: Hinders complement and neutrophil response, degrades complement.
Extracellular Virulence Factors
- Streptolysin O: Pore-forming toxin damages membranes.
- StrepSAgs (Erythrogenic toxins): Produced by some strains; causes rash of scarlet fever, pyrogenicity, acute rheumatic fever (ARF), and lethal shock (Streptococcal Toxic Shock Syndrome (STSS)).
Clinical Significance of Streptococcus pyogenes
- Acute pharyngitis and tonsilitis.
- Impetigo and deep skin infection.
- Acute rheumatic fever.
- Acute nephritis.
Poststreptococcal Sequelae
- Acute rheumatic fever (ARF): Follows respiratory infection, recurrent ARF produces rheumatic heart disease.
- Glomerulonephritis: Follows respiratory or skin disease. "Nephritogenic" strains are involved.
Streptococcal Erysipelas
- A streptococcal skin infection.
Neisseria
- Gram-negative diplococci: Neisseria meningitidis, Neisseria gonorrhoeae.
- Kidney-shaped, occurs in pairs, present inside polymorphonuclear cells.
Clinical Significance of Neisseria
-
Neisseria meningitidis:
- Meningitis, meningococcemia (septic poisoning).
-
Neisseria gonorrheae:
- Urinary tract infection (most common): gonococcal urethritis, pelvic inflammatory disease.
Neisseria infections
- N. meningitidis: Causes meningitis and meningococcemia; leading cause of death from infection in children.
- Prominent polysaccharide capsule enhances virulence by its antiphagocytic action.
Neisseria gonorrhoeae vs. N. meningitidis
- N. gonorrhoeae: lacks polysaccharide capsule, has three outer membrane proteins (I, II, III); protein II plays a role in attachment, and varies antigenically.
- N. meningitidis: Endotoxin is a lipopolysaccharide; endotoxin of N. gonorrhoeae is a lipo-oligosaccharide.
Characteristics of Neisseria
- See page 76 for a detailed comparison of characteristics between Neisseria gonorrhoeae and Neisseria meningitidis.
Neisseria Meningitidis - Pathogenesis and Epidemiology
- Humans are the only hosts.
- Transmitted by airborne droplets, colonize nasopharyngeal membranes in upper respiratory tract (transient flora).
- Polysaccharide capsule enables the organism to resist phagocytosis by PMNs.
- From nasopharynx, enter bloodstream and spread to specific sites (e.g. meninges or joints).
Meningococci
- 3 virulence factors: Endotoxin (LPS) causes fever and shock; immunoglobulin A protease helps the bacteria attach to the membrane of the upper respiratory tract; a polysaccharide capsule.
Diagnostic Laboratory Tests
- Specimens (blood, spinal fluid) taken for smear, culture, chemical determinations.
- Nasopharyngeal swab cultures are used for carrier surveys.
- Smears: Gram-stained smears of centrifuged spinal fluid show typical neisseriae within PMNs or extracellularly.
Laboratory Tests (cont.)
- Cerebrospinal fluid (CSF) specimens plated on chocolate agar, incubated at 37°C in 5% CO2.
- Presumptive colonies identified by Gram stain and oxidase test.
- Serology: Antibodies to meningococcal polysaccharides measured by latex agglutination or hemagglutination tests.
- Fermentation tests: N. meningitidis ferments glucose and maltose.
Growth of Neisseria Meningitis
- Blood Agar, Chocolate Agar
Neisseria Gonorrheae - Pathogenesis and Epidemiology
- Only infects humans.
- Usually sexually transmitted; newborns can be infected during birth.
- Usually symptomatic in men but often asymptomatic in women.
Neisseria Gonorrhoeae
- Genital tract infections are most common.
- Pili are major virulence factors; mediate attachment to mucosal cell surfaces; antiphagocytic.
- Endotoxin of gonococci is weaker than that of meningococci.
- Lacks a capsule.
Infections Caused by Neisseria gonorrheae
- Anorectal area, throat, eyes. - Anorectal infections in women and homosexual men. - In the throat: pharyngitis. - In newborns: purulent conjunctivitis (ophthalmia neonatorum).
Diagnostic Laboratory Tests (cont.)
- Specimens (pus and secretions) from urethra, cervix, rectum, conjunctiva, or throat.
- Smears: Gram-stained smears of urethral or endocervical exudates reveal many diplococci within pus cells.
Neisseria Gonorrhoeae (details)
- Culture is performed immediately after collection on enriched (e.g., modified Thayer-Martin) selective media incubated in 5% CO2 at 37° C.
- Neisseria gonorrheae ferments glucose only.
Neisseria gonorrheae (Growth)
- Best growth is on Thayer-Martin, Chocolate agar supplemented with vancomycin and nystatin.
- Factor X and V (hemoglobin, NAD) are required for species cultivation.
- A 5-10% CO2 atmosphere is required for primary cultivation.
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