GRAM POSITIVE BACTERIA Flashcards
(5 cards)
Streptococcus spp.:
Many species, hard to classify. Many normal flora, some strict pathogens, some cause disease by sensitization. Entry may be through skin or respiratory tract. Growth in chains or pairs.
Many toxins and enzymes:
Streptokinase- fibrinolysin
Streptodornase- DNAse
Hyaluronidase
Erythrogenic toxin- scarlet fever rash (only in lysogenic strains) Hemolysins-
M protein- Combines with teichoic acids to form pili that aid in attachment and impede phagocytosis. Determines type specificity of group A; correlates with virulence. Host antibodies determine immune status.
No single classification system is completely satisfactory. Most widely accepted is the Lancefield system. Group A (S. pyogenes): A frank pathogen. Pharyngeal infections, tonsillitis strep sequelae,
“flesh-eating bacteria”. Transmission may be via infected carriers.
Group B (S. agalactiae): Normal flora in female GU tract. Neonatal sepsis and meningitis.
Group D Enterococci. Normal gut flora. UTI, cardiovascular infections and meningitis. Pneumococci (S. pneumoniae)- Normal inhabitant of upper respiratory tract. No significant toxins.
Causes disease by multiplying in tissues. Capsule is a virulence factor; protects from phagocytosis. The condition of particular patients predisposes them to disease.
Staphylococcus aureus-
Yellow-pigmented colonies; grows in irregular grape-like clusters.
Ubiquitous human parasite; present on skin and mucous membranes of 25-50% of human populations.
Can be invasive, or highly toxigenic, or both. Produces a wide spectrum of diseases, with much tissue damage. Suppurative wounds (abscesses), and pyogenic wounds (pus).
Highest risk is in newborn nursery, intensive care unit, operating room, and cancer chemotherapy wards. Multiple virulence factors
Toxic shock syndrome toxin- Fever, shock, multi-organ involvement
Heat stable enterotoxin- Food poisoning, vomiting
Exfoliative toxin- scalded skin syndrome, desquamation
Coagulase- coagulates plasma, forms a protective wall. Coagulase correlates with invasiveness Catalase, hyaluronidase (digest connective tissue), staphylokinase (fibrinolysis), proteases, lipases Hemolysins, leukocidins- blood cell toxins
Produces β-lactamase, which metabolizes penicillin, and develops multi-drug resistance Very active metabolically and a highly opportunistic pathogen
Other Staphylococcus spp. may be normal flora that cause opportunistic infections
Endospore-forming rods
Bacillus spp. - most are saprophytes of soil, water, and vegetation
B. anthracis- Agent of anthrax. Infection through injured skin or mucous membranes, or, rarely, by inhalation.
Requires contact with infected animals. Invasive (disseminates rapidly through blood and lymphatics) and toxigenic (a capsule protein is highly toxic).
B. cereus- May be normal gut flora, but occasionally causes food poisoning
Clostridium spp.- Worldwide inhabitants of soils and animal feces. Large, anaerobic, motile rods.
Clostridium botulinum- Agent of botulism. Illness not a result of infection, but rather, an intoxication following
ingestion of food in which bacteria have grown (usually germinated from spores).
C. tetani- Agent of tetanus. Produces a potent neurotoxin which is released on death of the organisms.
Non-invasive, infection strictly localized in dead or injured tissue into which spores are introduced. C. perfringens- Can be invasive if introduced to damaged tissue.
Causes gas gangrene, myonecrosis. Produces an enterotoxin that can cause diarrhea.
C. dificile- May be normal gut flora. Pseudomembranous colitis and antibiotic associated diarrhea.
Regular, non-sporing rods
Listeria monocytogenes- Can cause a wide spectrum of diseases
Most common route of infection is oral, in contaminated foods.
Invasive- Multiplies intracellularly in intestinal epithelial cells and monocyte/macrophages. Toxigenic- A β-hemolysin that probably contributes to pathogenicity
Intrauterine infections- May lead to abortion
Bacteremia and meningitis in compromised adults- Insidious to fulminant
Irregular, non-sporing rods
Corynebacterium spp. (Coryne = club-shaped). Pleomorphic (highly varied and irregular shapes). Corynebacterium diphtheriae- Causative agent of diphtheria. Spread by droplets or contact.
May be present in respiratory tract, in wounds or on skin of infected individuals and carriers.
Bacteria colonize wounds or mucous membranes and produce a potent toxin that inhibits protein synthesis.
Toxin causes marked inflammation of respiratory epithelial cells.
Damage may later be seen in heart, liver and other distant sites.
Only lysogenized bacteria produce diphtheria toxin, but non-toxigenic forms may be invasive.
Bacilli colonizing the throat produce a pseudomembrane that restricts airway. Breaking membrane causes
bleeding and release of more toxin.
Mycobacterium- Acid-fast aerobic rods
Mycobacterium tuberculosis: No recognized toxins. Disease is from establishment and proliferation, and
interactions with the host. Can be very invasive- lesions grow and spread. Resides principally in macrophages. M. leprae: Agent of leprosy. Very slowly invasive in cooler peripheral tissues.
Disease results in a marked immunosuppression
Nocardia asteroides- An aerobic soil dweller. Resembles a fungus (hyphal growth).
Disease begins as a respiratory infection and spreads to other parts of the body, including brain and kidney. Most often seen in immunocompromised patients (leukemia, AIDS, or drug-induced)
