Bacteriology Flashcards
Staphylococcus
- Gram positive cocci in clusters
- Protein A binds Fc-IgG, inhibiting complement activation and phygocytosis
- causes
- inflammatory disease: skin infection, organ abscesses, pneumonia, endocarditis, osteomyelitis
- Toxin mediatad disease: TOSS-1, scalded skin syndrome ( exfoliative toxin), rapid onset of food poisoning (enterotoxin)
- MRSA: serious nosocomial and community acquired infections. Resistant to methicillin d/t altered penicilin binding protein
- Toxins
- TSST: super antigen that binds MHC II and TCR leading to polycolonal T cell activation ( fever, vomiting, shock, end organ failure
- Food poisoning: ingestion of preformed toxins ( 2-6 hr incubation). Heat stable toxin is not destroyed by cooking
Staphylococcus Epidermidis
- Gram positive, cocci, catalase positive, coagulase (-), novobiocin sensitive
- infects prostatic devices and intravenous catheters by producing an adherent biofilm
- component of normal skin flora
- contaminates blood culture
Staphylococcus Saprophyticus
- Gram positive, Cocci, Catalase positive, Coagulase negative
- novobiocin resistant
- second most common cause of UTI in young women ( after E. coli)
Streptococcus pneumoniae
- Gram positive, diplococci, catalase negative, alpha hemolytic
- Causes
- Meningitis
- Otiti media (children)
- Pneumonia
- sinusitis
- encapsulated (no virulence without capsule)
- IgA protease
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Viridans streptococci
- Gram positive, Cocci, catalase negative, alpha hemolysis
- no capsule, optochin resistant, bile insoluble
- normal flora of oropharynx and cause dental carries (S. mutans) and subcute bacterial endocarditis at damaged valves
Streptococcus pyogenes
Gram positive, Cocci, Catalase negative, Beta hemolysis
- bacitracin sensitive
- Causes
- Pyogenic: pharyntitis, cellulitis, impetigo
- Toxigenic: scarlet fever, toxic shock syndrome, necrotizing faciitis
- Immunologic: rheumatic fever, acute glomerulonephritis
- Antibodies to M proteins enhance host defenses but can give rise to rheumatic fever
- JONES criteria
- joints
- carditis
- nodules
- erythema nodosum
- syndenham chorea
- impetigo more commonly preceeds glomerulonephitis than pharyngitis
- Scarlet fever: scarlet rash with sandpaper like texture, straberry tongue, circumoral pallor
Streptococcus agalactiae
Group B strep
Gram positive, Cocci, chains, catalase (-), beta hemolytic
- Bacitracin resistant
- Colonizes vagina
- Causes ( mainly in babies)
- penumonia
- meningitis
- sepsis
- Produces CAMP factor which enlarges the area of hemolysis formed by S. aureus.
- Hippurate test positve
- screen pregnant women at 35-57 weeks: positive cultures requires intrapartum penicillin prophylaxis
Enterococci
Gram positive, Cocci, catalase negative, no hemolysis, grown in 6.5% NaCl and bile
- E. faecalis and E. faecium
- normal colonic flora that are penicillin G resistant
- cause UTI, biliary tract infections, subacute endocarditis
- VRE: cause nosocomial infection
Streptococcus bovis
Gram positive, cocci, catalase negative, grows in bile, does not grow in 6.5% NaCl
- colonizes the gut
- can cause bactermia and subacute endocarditis in colon cancer patients
- Bovis in the blood= cancer in the colon
Corynebacterium dipthaeriae
- Diphtheria
- exotoxin encoded by beta prophage
- inhibits protein synthesis via ADP- ribosylation of EF-2
- Symptoms
- pseudomembranous pharyngitis
- lymphadenopathy
- myocarditis
- arrythmia
- Gram postive rod
- metachromatic (red and blue) granules
- Elek test for toxin
- black colonies on cystine tellurite agar
ABCDEFG
- ADP ribosylation
- Beta prophage
- Corynbacterium
- Diptheriae
- Elongation factor 2
- Granules
Spore forming bacteria
- Bacillus anthracis (G+)
- Clostridium perfringens (G+)
- C. tetani (G+)
- B. cereus
- C. botulinum
- Coxiella burnetii
Clostridium Tetani
G (+), spore-forming, obligate anaerobic bacilli
- Produces tetanospasmin
- exotoxin cause tetanus
- tetanus toxin are proteases that cleave releasing proteins for neurotransmitters
- Induces tetanic paralysis
- blocks glycine and GABA release from Renshaw cells in spinal cord
- causes spastic paralysis, trismus (lockjaw), risus sardonicus
Clostridium Botulinum
G (+), spore-forming, obligate anaerobic bacilli
- Produces preformed, heat labile toxin that inhibits ACh receptor release at NMJ
- causes botulism
- Disease in adults: ingetion of preformed toxin
- Disease in babies: ingestion of spores ( floppy baby syndrome)
- causes flaccid paralysis
Clostridium perfringens
G (+), spore-forming, obligate anaerobic bacilli
- produces alpha toxin (lecithinase) a phospholipase that causes myonecrosis and hemolysis
- gas gangrene
Clostridium difficile
G (+), spore-forming, obligate anaerobic bacilli
- Toxin A
- enterotoxin
- binds to brush border of gut
- Toxin B
- cytotoxin
- cytoskeletal disruption via actin depolarization
- pseudomembranous colitis
- diarrhea
- often secondary to antibiotic use
- Diagnosed by detection of one or both toxins in stool
- Tx: metronidazole (Flagyl) or PO vancomycin
Bacillus anthracis
- Gram positive, spore forming rod
- produces anthrax toxin
- polypeptide capsule (containing D-glutamate)
Cutaneous anthrax
- Boil like lesion–> ulcer with back eschar
- painless, necrotic
- uncommonly progresses to bacteremia and death
Pulmonary anthrax
- inhalation of spores
- flu like symptoms that rapidly progresses to fever, pulmonary hemorrhage, mediastinitis and shock
- woolsorter’s disease: inhalation of spores from contaminated wool
Listeria monocytogenes
- Facultative intracellular microbe
- acquired by ingestion of unpasteurized dairy produces and deli meats via transplacental transmission or by vaginal transmission at birth
- “Rocket tails”: actin polymerization that allow them to move through cytoplasm and into cell membrane
- Gram positive, produces LPS
- Pregnant women: septicemia, spontaneous abortion
- granulomatosis infantiseptica, neonatal meningitis, meningitis in immunocompromised, mild gastroenteritis in healthy
- Tx: ampicillin in infants, immunocompromised and elderly for meningitis
Actinomyces
- Gram positive anaerobic
- not acid fast
- normal oral flora
- causes oral/facial abscesses that drain through sinus tracts, forms yellow “sulfur granules”
- Tx: penicillin
Norcadia
- Gram positive aerobe
- acid fast (weak)
- found in soil
- causes pulmonary infections in immunocompromised and cutaneous infection after trauma in immunocompromised
- Tx: sulfonamides
Mycobacterium tuberculosis
- acid fast
- sxs: fever, night sweats, weight loss, hemoptysis
- cord factor in virulent strains inhibits macrophage maturation and induces release of TNF-z
- Sulfatides (surface glycolipids) inhibit phagolysosomal fusion
Mycobacterium leprae
- acid fast bacillus
- infects skin and superficial nerves ( glove and stocking loss of sensation)
- reservoir in US: armadillos
Lepromatous
- diffusely over skin with leonine facies
- communicable
- low cell mediated immunity with humoral Th2 response
- Tx: Dapsone + rifampin+ clofazimine for 2-5 years
Tuberculoid
- limited to few hypoesthetic hairless skin plaques
- high cell mediated immunity with a TH1 type immune response
- Tx: dapson + rifampin for 6 mo
Neisseria
- Gram negative
- diplococci
- ferment glucose and produce IgA proteases
- N. gonorrhoaea is often intracellular
Neisseria
Gonococci
- gram negative, diplococci
- no polysaccharide capsule
- no maltose fermentaiton
- no vaccine
- sexually transmitted
- causes
- gonorrhea
- septic arthritis
- neonatal conjunctivitis
- pelvic inflammatory disease (PID)
- Fitz-Hugh-Curtis syndrome
- Condoms prevent sexual transmission
- Erythromycin ointment prevents neonatal transmission
- Tx: ceftriaxone ( azithromycin or doxycycline) for possible chlamdia co-infection
Neisseria
Meningococci
- Gram negative, diplococci
- Polysaccharide capsule
- maltose fermentation
- vaccine
- respiratory and oral secretion transmission
- causes
- meningococcemia
- meningitis
- Waterhouse-Friderichsen syndrome
- Prophylaxis: Rifampin, ciprofloxicin, ceftriaxone
- Tx: Ceftriaxone or penicillin G
Haemophilus influenzae
- gram negative rod (coccobacillus)
- aerosol transmission
- produces IgA protease
- Culture on chocolate agar requires factors V (NAD+) and X (hematin) for growth
- causes
- epiglottitis
- meningitis
- otitis media
- pneumonia
- Tx:
- mucosal infections: amoxicillin +/- clavulanate
- meningitis: cetriaxone
- Prophylaxis: Rifampin
- Vaccine: type B capsule polysaccharide conjugated to diptheria toxoid (given between 2-18 mo)
Legionella pneumophilia
- gram negative rod
- silver stain
- grows on charcoal yeast extract culture with iron and cysteine
- detected by presence of antigen in urine
- aerosol tranmission from environmental water sources habitat ( air conditioning, hot water tanks)
- No person to person transmission
- Tx: macrolide or quinolone
Legionnaire’s disease
- severe pneumonia, fever, GI and CNS symptoms
Pontiac Fever
- mild flu like symptoms