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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. Highly opportunistic pathogen.
Many normal flora, some strict pathogens, some cause disease by sensitization. Entry may be through skin or respiratory tract. Growth in chains or pairs.
Toxins and enzymes of Streptococcus spp.
Streptokinase (fibrinolysin), streptodornase (DNAse), Hyalronidase, Erythrogenic toxin (scarlet fever rash only in lysogenic strains), Hemolysins (toxins that lyse red blood cells)
Combines with teichoic acids to form pili that aid in attachment and impede pagocytosis. Determines type specificity of group A; correlates with virulence. Host antibodies determine immune status.
A frank pathogen. Pharyngeal infections, tonsilitis strep sequelae, "flesh-eating bacteria." Transmission may be via infected carriers.
Group A (Streptococcus pyogenes)
Normal flora in female GU tract. Neonatal sepsis and meningitis.
Group B (Streptococcus agalactiae)
Normal gut flora. UTI, cardiovascular infections and meningitis.
Group D (Enterococci)
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.
Pneumococci (Streptococcus pneumoniae)
most are saprophytes of soil, water, and vegetation.
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)
may be normal gut flora, but occasionally causes food poisoning.
Worldwide inhabitants of soils and animal feces. Large, anaerobic, motile rods.
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).
Agent of tetanus. Produces a potent neurotoxin which is released on death of the organisms. Noninvasive, infection strictly localized in dead or injured tissue into which spores are introduced.
can be invasive if introduced to damaged tissue. causes gas gangrene, myonecrosis. produces an enterotoxin that can cause diarrhea.
may be normal gut flora. Pseudomembranous colitis(inflammation of colon) and antibiotic associaated diarrhea.
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 b-hemolysin that probably contributes to pathogenicity Intrauterine ninfections- May lead to abortion
Bacteremias and meningitis in compromised adults- Insidious to fulminant
(Coryne = club-shaped). Pleomorphic (highly varied and irregular
- Irregular, non-sporing rods
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.
- Corynebacterium diphtheriae
Acid-fast aerobic rods
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.
- Mycobacterium tuberculosis
Agent of leprosy. Very slowly invasive in cooler peripheral tissues. Disease results in a marked immunosuppression
- Mycobacterium leprae
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)
Placed bacteria in 4 divisions, based on cell wall type- 3 are of clinical interest (thick, thin, none)
For identification of bacteria grown in the laboratory
Assessing presence or absence of specific biochemical markers allows precise identification
Bergey's Manual of Determinative Bacteriology (1923)
Classification based on genetics (rRNA; DNA homology)
Bergey’s Manual of Systematic Bacteriology (1984)
Criteria for classification and identification (practical and clinically relevant)
- Morphology- what it looks like. Shape and other structural features.
- Differential staining- based on chemical composition of cell wall.
- Biochemistry- enzymatic reactivity
- Serology- reactivity with animal sera
- Phage typing- sensitivity to infection with various virus types
contribute to a pathogen's invasiveness or toxigenicity.