Gram + Micro Flashcards by Steffanie Nelson

Alpha hemolytic bacteria

Streptococcus pneumoniae
Viridans streptococci (S. mutans, S. mitis)

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Beta hemolytic bacteria

Staphylococcus aureus
Streptococcus pyogenes (group A strep)
Streptococcus agalactiae (group B strep)

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Gram +, beta hemolytic, catalase +, coagulase + cocci in clusters

Staphylococcus aureus

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Protein A

Staph aureus. Binds Fc-IgG, inhibiting complement activation and phagocytosis

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TSST-1

Superantigen that binds to MHC II and T cell receptor, resulting in polyclonal T-cell activation

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Staph aureus food poisoning

Due to ingestion of preformed toxin (2-6 hr)

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Diseases caused by staph aureus

Inflammatory disease - skin infections, pneumonia (often after influenza), organ abscesses, endocarditis, septic arthritis, osteomyelitis.
Toxin mediated disease - toxic shock syndrome, scalded skin syndrome, rapid onset food poisoning.
MRSA

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Gram +, catalase +, coagulase -, urease + cocci in clusters. Novobiocin sensitive. Does not ferment mannitol.

Staphylococcus epidermidis

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Gram +, catalase +, coagulase -, urease + cocci in clusters. Novobiocin resistant.

Staphylococcus saprophyticus

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Gram +, catalase -, alpha hemolytic, lancet shaped diplococci. Encapsulated. IgA protease. Optochin sensitive

Streptococcus pneumonia

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Strep pneumo is the most common cause of which conditions?

Meningitis
Otitis media (in children)
Pneumonia
Sinusitis

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Gram +, catalase -, alpha hemolytic cocci. Resistant to optochin.

Viridans group streptococci

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Where are viridans group streptococci located? What can they cause?

Normal flora of the oropharynx. Streptococcus mutans and S mitis cause dental caries. S. sanguinis causes subacute bacterial endocarditis.

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Gram +, catalase -, beta hemolytic cocci in chains. Bacitracin sensitive. PYR +.

Streptococcus pyogenes (group A streptococci)

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What kind of infections are caused by group A strep?

Pyogenic - pharyngitis, cellulitis, impetigo, erysipelas
Toxigenic - scarlet fever, toxic shock-like syndrome, necrotizing fasciitis
Immunologic - rheumatic fever, glomerulonephritis

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Virulence factors for group A strep

Hyaluronic acid capsule and M protein inhibit phagocytosis

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Blanching, sandpaper like body rash, strawberry tongue, and circumoral pallor in setting of group A strep pharyngitis (Erythrogenic toxin +)

Scarlet fever

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Gram + cocci, beta hemolytic, bacitracin resistant. Produces CAMP factor, which enlarges the area of hemolysis by S. aureus. Hippurate test +. PYR -

Streptococcus agalactiae (group B strep)

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What infections does group B strep cause?

Colonizes vagina. Causes pneumonia, meningitis, and sepsis, mainly in babies

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When are pregnant women screen for group B strep? What is done if they are positive?

Screen at 35-37 weeks gestation. Pts with + culture receive intrapartum penicillin prophylaxis

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Gram + cocci, catalase -, no hemolysis, does not grow in 6.5% NaCl

Streptococcus bovis

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S. bovis is associated with?

Colon cancer

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Gram + cocci, catalase -, grows in 6.5% NaCl, PYR+, variable hemolysis

Enterococci

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What infections do enterococci cause?

Normal colonic flora. Penicillin G resistant and cause UTI, biliary tract infections, and subacute endocarditis (following GI/GU procedures). VRE are an important cause of nosocomial infection

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Gram + spore forming rod. Produces anthrax toxin. Aerobic

Bacillus anthracis

Only bacterium with a polypeptide capsule (contains D-glutamate)

Bacillus anthracis

Bacillus cereus

Causes food poisoning. Emetic type usually seen with rice and pasta, nausea and vomiting within 1-5 hr, caused by cereulide (preformed toxin). Diarrheal type - watery, nonbloody diarrhea and GI pain within 8-18 hrs.

Gram + facultative intracellular rod. Aerobic.

Listeria monocytogenes

How is listeria acquired

Ingestion of unpasteurized dairy products and cold deli meats, via transplacental transmission, or by vaginal transmission during birth

What conditions can listeria cause?

Amnionitis, septicemia, and spontaneous abortion in pregnant women; granulomatosis infantiseptica; neonatal meningitis; meningitis in immunocompromised; mild, self limited gastroenteiritis in healthy individuals

How is infection with listeria treated?

Ampicillin

Gram +, spore forming, obligate anaerobic rods

Clostridia

Tetanospasmin

An exotoxin causing tetanus

Tetanus toxin mechanism

Protease that cleaves SNARE proteins for neurotransmitters. Blocks release of inhibitory neurotransmitters, GABA and glycine, from Renshaw cells in spinal cord

Spastic paralysis, trismus, risus sardonicus, opisthotonus

Tetanus

How is tetanus treated?

Antitoxin +/- vaccine booster, antibiotics, diazepam (for muscle spasms), and wound debridement

Heat labile toxin that inhibits ACh release at the neuromuscular junction

C botulinum

Diplopia, dysarthria, dysphagia, dyspnea

Botulism

alpha toxin

Lecithinase, a phospholipase. Toxin produced by C perfringens that can cause myonecrosis and hemolysis.

Toxins produced by C difficile

Toxin A, an enterotoxin, binds to brush border of gut and alters fluid secretion. Toxin B, a cytotoxin, disrupts cytoskeleton via actin depolymerization. Both toxins lead to diarrhea and pseudomembranous colitis.

Which antibiotics commonly cause C difficile?

Clindamycin or ampicillin

How is C difficile treated?

Metronidazole or oral vancomycin

Gram + rod; transmitted via respiratory droplets

Corynebacterium diphtheriae

How does C. diphtheriae cause diphtheria

Via exotoxin encoded by beta-prophage. Inhibits protein synthesis via ADP-ribosylation of EF-2.

Symptoms of diphtheria

Pseudomembranous pharnygitis, with lymphadenopathy, myocarditis, and arrhytmias

Gram + long branching filaments, weakly acid fast, aerobe

Nocardia

What does nocardia cause?

Pulmonary infections in immunocompromised; cutaneous infections after trauma in immunocompetent; can spread to CNS

How is infection with Nocardia treated?

Sulfonimides (TMP-SMX)

Where is Nocardia found?

Soil

Gram + long branching filaments, anaerobe, not acid fast

Actinomyces

Where is Actinomyces found?

Normal oral, reproductive, and GI flora

What can Actinomyces cause?

Oral/facial abscesses that drain through sinus tracts; often associated with dental caries/extraction and other maxillofacial trauma. Can cause PID with IUDs

How is Actinomyces treated?

Penicillin

Mycobacterium avium

Causes disseminated, non-TB disease in AIDS. Often resistant to multiple drugs

Prophylaxis for M avium

Azithromycin when CD4+ count <50 cells/mm3

Mycobacteria scrofulaceum

Cervical lymphadenitis in children

Mycobacteria marinum

Hand infection in aquarium handlers

Cord factor

Virulence factor in M tuberculosis strains; activates macrophages (promoting granuloma formation) and induces release of TNF-alpha

Sulfatides

Surface glycolipids. Inhibit phagolysosomal fusion. Present in M tuberculosis

Yellow sulfur granules

Actinomyces

Gram + Micro Flashcards

(60 cards)