MICROBIOLOGY PART 2 Flashcards
Which Staph are resistant/sensitive to Novobiocin?
NOvobiocin—Saprophyticus is Resistant; Epidermidis is Sensitive.
“On the office’s “staph” retreat, there was NO StRESs.”
Which Strep are resistant/sensitive to Bacitracin and Optochin?
Optochin—Viridans is Resistant; Pneumoniae is Sensitive.
OVRPS (overpass).
Bacitracin—group B strep are Resistant; group A strep are Sensitive.
B-BRAS.
α-hemolytic bacteria
Form green ring around colonies on blood agar.
Include the following organisms: Streptococcus pneumoniae Viridans streptococci
β-hemolytic bacteria
Form clear area of hemolysis on blood agar. Include the following organisms:
Staphylococcus aureus Streptococcus pyogenes—group A strep )
Streptococcus agalactiae—group B strep
Listeria monocytogenes
Morphology and virulence factors of staphylococcus aureus
Gram-positive cocci in clusters
Protein A (virulence factor) binds Fc-IgG, inhibiting complement activation and phagocytosis.
“Staph make catalase because they have more “staff.”
Staphylococcus aureus Commonly colonizes ________.
the nose
Staphylococcus aureus causes
Inflammatory disease—skin infections, organ abscesses, pneumonia (often after influenza virus infection), endocarditis, and osteomyelitis
Toxin-mediated disease—toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin), rapid-onset food poisoning (enterotoxins)
S. aureus food poisoning due to ingestion of preformed toxin –> short incubation period (2–6 hr). Enterotoxin is heat stable –> not destroyed by cooking.
Bad staph (aureus) make coagulase and toxins.” Forms fibrin clot around self abscess.
What is MRSA?
(methicillin-resistant S. aureus) infection—important cause of serious nosocomial and community-acquired infections; resistant to methicillin and nafcillin because of altered penicillinbinding protein
What is TSST (S. aerues)?
TSST is a superantigen that binds to MHC II and T-cell receptor, resulting in polyclonal T-cell activation. Presents as fever, vomiting, rash, desquamation, shock, end-organ failure. Use of vaginal or nasal tampons predisposes to toxic shock syndrome.
Staphylococcus epidermidis
Infects prosthetic devices and intravenous catheters by producing adherent biofilms. Component of normal skin flora; contaminates blood cultures. Novobiocin sensitive.
Staphylococcus saprophyticus
Second most common cause of uncomplicated UTI in young women (first is E. coli). Novobiocin resistant
Streptococcus pneumoniae causes
Most common cause of: Meningitis
Otitis media (in childhren) Pneumonia
Sinusitis
“S. pneumoniae MOPS are Most OPtochin Sensitive. “
Pneumococcus is associated with “rusty” sputum, sepsis in sickle cell anemia and splenectomy
Streptococcuss pneumonae morphology, virulence factors
Lancet-shaped, gram-positive diplococci A. Encapsulated. IgA protease.
No virulence without capsule.
Bile soluble (lysed by bile)
alfa - partial hemolysis (green)
Catalase + vs. Catalase -
+ = clusters –> Staphylococcus
- = chains –> Streptococcus
Viridans group streptococci
normal flora, causes, how to differentiate
Viridans streptococci are α-hemolytic. They are normal flora of the oropharynx and cause dental caries (Streptococcus mutans) and subacute bacterial endocarditis at damaged valves (S. sanguinis). Resistant to optochin, differentiating them from S. pneumoniae, which is α-hemolytic but is optochin sensitive
“Viridans group strep live in the mouth because they are not afraid of-the-chin (op-to-chin resistant).”
Streptococcus sanguinis
Sanguis = blood. There is lots of blood in the heart (endocarditis). S. sanguinis makes dextrans, which bind to fibrin-platelet aggregates on damaged heart valves.
Streptococcus pyogenes (group A) Causes..
Causes: Pyogenic—pharyngitis, cellulitis, impetigo Toxigenic—scarlet fever, toxic shock–like syndrome, necrotizing fasciitis Immunologic—rheumatic fever, acute glomerulonephritis
Impetigo more commonly precedes glomerulonephritis than pharyngitis.
“Pharyngitis can result in rheumatic “phever” and glomerulonephritis. “
Criteria for rheumatic fever
J♥NES criteria for rheumatic fever: Joints—polyarthritis ♥—carditis Nodules (subcutaneous) Erythema marginatum Sydenham chorea Pharyngitis can result in rheumatic “phever” and glomerulonephritis.
Scarlet fever criteria
Scarlet fever: scarlet rash with sandpaper-like texture, strawberry tongue, circumoral pallor.
Antibodies + Streptococcus pyogenes (group A)
Bacitracin sensitive.
Antibodies to M protein enhance host defenses against S. pyogenes but can give rise to rheumatic fever.
ASO titer detects recent S. pyogenes infection
Streptococcus agalactiae (group B) characteristics, normal flora, causes
B == Babies!
Bacitracin resistant, β-hemolytic, colonizes vagina; causes pneumonia, meningitis, and sepsis, mainly in babies.
When should you screen pregnant women for S. agalactiae? If +?
Screen pregnant women at 35–37 weeks.
Patients with culture receive intrapartum penicillin prophylaxis.
S. agalactiae produces ____ factor
Produces CAMP factor, which enlarges the area of hemolysis formed by S. aureus. (Note: CAMP stands for the authors of the test, not cyclic AMP.)
Hippurate test +
Enterococci (group D)
Enterococci (Enterococcus faecalis and E. faecium) are normal colonic flora that are penicillin G resistant and cause UTI, biliary tract infections, and subacute endocarditis (following GI/GU procedures).
Lancefield group D includes the enterococci and the nonenterococcal group D streptococci.
“Enterococci, hardier than nonenterococcal group D, can grow in 6.5% NaCl and bile (lab test).”
Entero = intestine,
faecalis = feces,
strepto = twisted (chains),
coccus = berry
Lancefield grouping
Lancefield grouping is based on differences in the C carbohydrate on the bacterial cell wall.
VRE
vancomycin-resistant enterococci) are an important cause of nosocomial infection.
Streptococcus bovis (group D)
Colonizes the gut. Can cause bacteremia and subacute endocarditis in colon cancer patients.
“Bovis in the blood = cancer in the colon”
Cornyebacterium diphtheriae
causes
Causes diphtheria via exotoxin encoded by β-prophage. Potent exotoxin inhibits protein synthesis via ADP-ribosylation of EF-2. Symptoms include pseudomembranous pharyngitis (grayish-white membrane A) with lymphadenopathy, myocarditis, and arrhythmias.
Coryne= clubshaped
Lab diagnosis of Cornyebacterium diphtheriae
Lab diagnosis based on gram-positive rods with metachromatic (blue and red) granules and Elek test for toxin.
Black colonies on cystine-tellurite agar.
Corynebacterium diphtheriae ABCDEFG
ABCDEFG: ADP-ribosylation Beta-prophage Corynebacterium Diphtheriae Elongation Factor 2 Granules
Vaccine for C. diphtheriae?
Toxoid vaccine prevents diphtheria.
Spores: bacterial
Some bacteria can form spores at the end of the stationary phase when nutrients are limited. Spores are highly resistant to heat and chemicals.
Have dipicolinic acid in their core. Have no metabolic activity.
How to kill spores?
Must autoclave to kill spores (as is done to surgical equipment) by steaming at 121°C for 15 minutes.
Spore-forming gram-positive bacteria found in soil
Bacillus anthracis, Clostridium perfringens, C. tetani
Other spore formers
B. cereus, C. botulinum, Coxiella burnetii.
Clostridia (with exotoxins)
Gram-positive, spore-forming, obligate anaerobic bacilli
C. tetani exotoxin and causes
Produces tetanospasmin, an exotoxin causing tetanus. Tetanus toxin (and botulinum toxin) are proteases that cleave releasing proteins for neurotransmitters.
Tetanus is tetanic paralysis (blocks glycine and GABA release [both are inhibitory neurotransmitters] from Renshaw cells in spinal cord). Causes spastic paralysis, trismus (lockjaw), and risus sardonicus.
C. botulinum exotoxin and causes
Produces a preformed, heat-labile toxin that inhibits ACh release at the neuromuscular junction, causing botulism. In adults, disease is caused by ingestion of preformed toxin. In babies, ingestion of spores in honey causes disease (floppy baby syndrome).
“Botulinum is from bad bottles of food and honey (causes a flaccid paralysis). “
C. perfringens exotoxin and causes
Produces α toxin (“lecithinase,” a phospholipase) that can cause myonecrosis (gas gangrene) and hemolysis.
“Perfringens perforates a gangrenous leg.”
Clostridia difficile exotoxin and causes
Produces 2 toxins. Toxin A, enterotoxin, binds to the brush border of the gut. Toxin B, cytotoxin, causes cytoskeletal disruption via actin depolymerization –> pseudomembranous colitis –>diarrhea. Often 2° to antibiotic use, especially clindamycin or ampicillin.
‘Difficile causes diarrhea”
How to diagnose C. difficile?
Diagnosed by detection of one or both toxins in stool.
Treatment for C. difficile?
metronidazole or oral vancomycin. For recurring cases, fecal transplant may prevent relapse.
Anthrax is caused by what bug
Caused by Bacillus anthracis, a gram-positive, spore-forming rod
morphology of B. anthracis and toxin
produces anthrax toxin. The only bacterium with a polypeptide capsule (contains d-glutamate).
Cutaneous anthrax vs. Pulmonary antrhraz
C: Boil-like lesion –> ulcer with black eschar ( right) (painless, necrotic) –> uncommonly progresses to bacteremia and death.
P: Inhalation of spores –> flu-like symptoms that rapidly progress to fever, pulmonary hemorrhage, mediastinitis, and shock.
Woolsorters’ disease—inhalation of spores from contaminated wood.
Bacillus cereus
Causes food poisoning. Spores survive cooking rice. Keeping rice warm results in germination of spores and enterotoxin formation.
Emetic type usually seen with rice and pasta.
Nausea and vomiting within 1–5 hr. Caused by cereulide, a preformed toxin. Diarrheal type causes watery, nonbloody diarrhea and GI pain within 8–18 hr.
Reheated rice syndrome.
Listeria monocytogenes transmission
Facultative intracellular microbe; acquired by ingestion of unpasteurized dairy products and deli meats, via transplacental transmission, or by vaginal transmission during birth.
Listeria monocytogenes morpholoy and virulence factors
Form “rocket tails” (via actin polymerization) that allow them to move through the cytoplasm and into the cell membrane, thereby avoiding antibody. Characteristic tumbling motility; is only gram-positive organism to produce LPS.
Listeria monocytogenes causes…
Can cause amnionitis, septicemia, and spontaneous abortion in pregnant women; granulomatosis infantiseptica; neonatal meningitis; meningitis in immunocompromised patients; mild gastroenteritis in healthy individuals.
Listeria monocytogenes treatment
Treatment: gastroenteritis usually self-limited; ampicillin in infants, immunocompromised patients, and the elderly in empirical treatment of meningitis.
Actinomyces
long branching filaments resembling fungi.
gram-positive anaerobe
not acid fast
Causes oral/facial abscesses that drain through sinus tracts, forms yellow “sulfur granules”
acintomyces normal flora
normal oral flora
actinomyces treatment
penicillin
nocardiaä
long, branching filaments resembling fungi.
gram-positive aerobe
acid fast(weak)
Causes pulmonary infections in immunocompromised and cutaneous infections after trauma in immunocompetent
Nocardia normal flora
found in soil
Nocardia treatment
treat with sulfonamides
