USMLE Step 1: Microbiology

organisms known for causing endocarditis

Staphylococcus aureus
Staph epididermis
viridans strep
VRE
Strep. bovis
HACEK organisms

Mycobacterium tuberculosis
4 drug treatment regimen

isoniazid, ethambutol, rifampin, pyrazinamide

used to treat Trichomonas or Gardnerella

Metronidazole

used to treat Plasmodium vivax or ovale

chloroquine + primaquine

used to treat Pediculosis capitis or pubus

permethrin, pyrethrin

organisms most commonly responsible for otitis media

Strep pneumoniae
Haemophilus influenzae
Moraxella catarrhalis

Otitis Externa
Most Common Cause

Pseudomonas aeruginosa

fungus that causes San Joaquin Valley fever

Coccidioides

fungus found in rural Latin America

Paracoccidioides

fungus associated with plant thorns and cutaneous injury

Sporothrix

fungus found in states east of the Mississippi River

Blastomycoses

fungus found in bird and bat droppings

Histoplasmosis

mold form contains barrel-shaped arthroconidia

Coccidioides

encapsulated bacteria (8)

E. coli
Strep pneumoniae
N. meningitidis
Klebsiella pneumoniae
Haemophilus influenae
Pseudomonas aeruginosa
Salmonella
group B Strep

steeple sign on X-ray

Parainfluenza
Croup

thumb sign on x-ray

Epiglottitis
Haemophilus influenza

treatment of chronic hepatitis B and C

IFN-alpha, ribavirin

most abundant bacteria in the colon of most individuals

Bacteroides fragilis

likely organisms in a patient with chronic granulomatous disease

Staphylococcus aureus
E. coli
K. pneumoniae
Aspergillus
Candida
(all are catalase +)

organisms that cause infections in the mouth of AIDS patients

HSV, C. albicans, EBV, CMV

three structural genes that code for HIV proteins

gag (p24)
pol (reverse transcriptase, integrase)
env (gp120, gp41)

dark purple nodules on the skin in an HIV patient

HHV-8, Kaposi sarcoma

CMV treatment

Ganciclovir

Opportunistic infection in HIV patients
Most Common

Pneumocystis jirovecii

drug used to prevent Pneumocystis pneumonia

TMP-SMX

causes hemolytic-uremic syndrome

EHEC: 0157:H7

medications used to treat C. diff colitis

Metronidazole
oral Vancomycin

food poisoning as a result of mayonnaise sitting out too long

Staphylococcus aureus

diarrhea caused by Gram (-) nonmotile organism that does not ferment lactose

Shigella

Rice-water stools

Vibrio cholera

Diarrhea caused by an S-shaped organism

Campylobacter jejuni

Diarrhea
transmitted from pet feces

Yersinia enterocolitica

Food poisoning resulting from reheated rice

Bacillus cereus

Diarrhea caused by Gram (-) motile organism that doesn't ferment lactorse

Salmonella

Travelers' Diarrhea
Most Common Cause

ETEC

diarrhea after a course of antibiotics

C. difficile

diarrhea caused by Gram (-) lactose fermenting bacteria, no fever

E. coli

Diarrhea caused by Gram (-) comma-shaped organism, no fever

Vibrio cholera

Diarrhea and recent ingestion of water from a stream (2)

Giardia lamblia, Entamoeba histolytica

food poisoning from undercooked hamburger meat

0157:H7
E.coli

food poisoning due to exotoxin (2)

Staphylococcus aureus
Bacillus cereus

osteomyelitis in sickle cell disease

Salmonella

Most Common protozoal infection in the US

Toxoplasma gondii

Amoebic dystentery

Entamoeba histolytica

African sleeping sickness

Trypanosoma brucei

protozoal diarrhea in campers and hikers

Giardia lamblia

protozoa transmitted in raw meat or infected cat feces

Toxoplasma gondii

protozoa transmitted by sandflies

Leishmania

causes vaginitis

Trichosomiasis

found in the stool of a patient who visited Mexico and presents with bloody diarrhea

cysts of Entamoeba histolytica

stage of malaria life cycle: looks like a diamond ring

trophozoite

stage of malaria life cycle: ruptures the cell host

merozoite

stage of malaria life cycle: replicating intracellularly

early schizont

stage of malaria life cycle: form injected from the anopheles mosquito

sporozoite

stage of malaria life cycle: banana-shaped

gametocyte

mechanism responsible for recurrent fever in malaria

cyclic rupture of RBCs

Most Common helminth infection in the US

Enerobius vermicularis

helminth infecting 1/4 of the world

Ascaris lumbricoides

Snail host
"swimmer's itch"

Schistosoma

Most Common predisposing factor to bladder cancer in 3rd world countries

Schistosoma haematobium

contracted by eating undercooked fish and causes an inflammation of the biliary tract

Clonorchis inensis

Hookwork

Ancylostoma, nacator

Giant roundworm

Ascaris lumbricoides

contracted by eating undercooked crabmeat and causes inflammation of the lung

Paragonimus

Pork tapework

Taenia solium

Adult patient from Mexico with new onset seizures and brain calcifications

Taenia solium

Hematuria in patient from 3rd world country (especially Egypt)

Schistosoma haematobium

mediates adherence of bacteria to the surface of a cell

Pilus
Pili

protects against phagocytosis

Capsule

forms attachment between two bacteria during transfer of DNA material (AKA conjugation)

Sex Pilus

stain required to see Cryptococcus neoformans

India ink

stain required to see Pneumocystis jirovecii

silver stain

stain required to see chalmydia

Giemsa

method by which plasmids are exchanged between bacteria

conjugation

exotoxin inhibits Ach release, leading to flaccid paralysis

Botulinum toxin

exotoxin lecithinase that causes gas gangrene

alpha toxin
of C. perfringens

exotoxin inhibits the inhibitor of adenylate cyclase

Pertussis toxin
Bortadella pertussis

exotoxin stimulates adenylate cyclase, causing chloride and water to move into the gut

heat labile Toxin - E. coli
Cholera Toxin - Vibrio cholera

exotoxin destroys leukocytes

Leukocidin toxin
Staphylococcus aureus

exotoxin composed of edema factor, lethal factor, and protective antigen

Toxin
Bacillus anthracis

exotoxin causing rice-water diarrhea

heat labile Toxin E. coli
Cholera Toxin - Vibrio cholera

exotoxin causes scarlet fever

Erythrogen, Pyrogen
Streptococcus pyogenes

exotoxin causes toxic shock syndrome

TSST-1
Staphylococcus aureus

exotoxin inactivates EF-2

Diptheria Toxin

exotoxin blocks the release of the inhibitory neurotransmitter glycine

Tetanus Toxin

Most Common aerobic skin flora

S. epidermidis

organisms most commonly implicated in subacute endocarditis (3)

viridans Strep
enterococci
coagulase negative Staph, espeically S. epidermidis

causes scalded skin syndrome

Staphylococcus aureus

white membrane on pharynx

C. diphteriae

pharyngitis --> glomerulonephritis

S. pyogenes (group A)

Meningitis
Most Common Cause

S. pneumoniae

Osteomyelitis
Most Common Cause

Staphylococcus aureus

serious newborn infections

E. coli
group B Strep
Listeria

infant with poor muscle tone

C. botulinim

diarrhea after using antibiotics

C. difficile

Respiratory distress in a postal worker

B. anthracis

Otitis media in children

S. pneumoniae

cellulitis (2)

Staphylococcus aureus
Staphylococcus pyogenes

spore-forming bacteria (3)

Clostridium, Bacillus, Coxiella

Argylle-Robertson pupil

Syphilis