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USMLE - Microbiology


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virulence factor of staph aureus - binds Fc-IgG, inhibiting complement fixation and phagocytosis
protein A
superantigen that binds to MHC II and TCR, resulting in polyclonal T cell activation
TSST - (staph aureus)
what makes coagulase?
staph aureus
antibody to what enhances host defenses against strep pyogenes?
M protein
group A beta-hemolytic strep?
strep pyogenes
what detects recent strep pyogenes infections?
ASO titer
associated with rusty sputum, sepsis in sickle cell, and splenectomy?
strep pneumo
most common cause of meningitis, otitis, pneumonia, sinusitis?
strep pneumo
what gives immunity to strep pneumo?
IgG antibodies to surface acidic polysaccharide
causes pneumonia, meningitis, and sepsis mainly in babies
group B strep (agalactiae) - beta hemolytic, bacitracin resistant
what is Lancefield grouping based on?
differences in the C carbohydrate on the bacterial cell wall
what can grow in 6.5% NaCl
enterococci can cause what?
UTI, subacute endocarditis, biliary tract infections
bacteria related to colon cancer?
strep bovis
type of strep viridans that can cause subacute bacterial endocarditis?
strep sanguis
what does C. perfringens produce?
alpha toxin
gram-positive rods with metachromatic granules?
corynebacterium diphtheriae
woolsorter's disease?
bacillus anthracis
inhalation of anthrax spores?
flulike symptoms that rapidly progress to fever, pulmonary hemorrhage, and shock
gram-positive anaerobe that causes oral/facial abscesses that may drain through sinus tracks in skin
gram positive, weakly-acid fast aerobe that causes pulmonary infection in immunocomprimised patients
nocardia asteroides
sulfur granules
gram-positive rods forming long branching filaments resembling fungi
actinomyces & nocardia
most invasive disease of H. flu is caused by what capsular type?
treatment for H. flu meningitis?
treatment for neisseria gonorrhea?
ceftriaxone - also z pack or doxycycline because 50% will also be infected with chlamydia
why don't you want to culture if pt. has epiglottitis?
manipulation cause laryngeal spasm
members of enterobacter family (7)
e. coli, salmonella, shigella, klebsiella, enterobacter, serratia, proteus
what antigen is related to the virulence of enterobacter?
K antigen
all of these ferment glucose and are oxidase negative
these bacteria grow pink colonies on MacConkey's agar
klebsiella, e. coli, enterobacter (KEE), citrobacter
salmonella or shigella: motile and can disseminate hematogenously?
salmonella or shigella: which is more virulent?
salmonella or shigella: symptoms may be prolonged with antibiotic treatments
salmonella or shigella: animal reservoir
this is usually transmitted from pet feces, contaminated milk, or pork; outbreaks common in daycare centers
yersinia enterocolitica
this can mimic Crohn's or appendicitis & can disseminate to produce lymphadenitis
yersinia enterocolitica
arthritis can develop with yersinia infection in patients with what?
vibrio parahaemolyticus and v. vulnificus
contaminated seafood
reheated rice
B. cereus
meats, mayonase, custard
s. aureus
reheated meat dishes
c. perfringens
undercooked meat
e. coli 0157:H7
poultry, meat, eggs
bloody diarrhea; comma or S-shaped organisms
is campylobacter motile?
e. coli producing shiga-like toxin; can cause HUS
day-care outbreaks, pseudoappendicitis
protazoan causing bloody diarrhea
entamoeba histolytica
protaozoa causing watery diarrhea
giardia, cryptosporidium (in immunocompromised)
treatment for legionella?
UTI - urine with alkaline pH
proteus - very motile - able to break down urea
pneumonia in CF
wound and burn infections
treatment for pseudomonas?
amnoglycoside plus extended-spectrum penicillin (piperacillin, ticarcillin)
aerobic gram-negative rod; oxidase positive, non-lactose fermenting; pyocyanin pigment
hot tub folliculitis
pneumonia, sepsis, UTI, drug use and diabetic osteomyelitis
cellulitis from animal bite, cats, dogs
dairy products, contact with animals
ghon complex
TB granulomas (Ghon focus) with lobar and perihilar LN involvement; reflects primary infection or exposure
mycobacterium scrofulaceum
cervical lymphadenitis in kids
mycobacterium kansasii
pulmonary TB-like symptoms
acid-fast bacillus that likes cold temperatures and cannot be grown in vitro
mycobacterium leprae
reservoir for m. leprae in U.S.?
what does m. leprae infect?
skin and superficial nerves
treatment for leprosy?
long-term oral dapsone - toxicity is hemolysis and methemoglobinemia
which type of Hanson's diseaseiis worse?
lepromatous worse than tuberculoid
the chlamydial petidoglycan wall is unusual in that it lacks what?
muramic acid
treatment for chlamydia?
erythromycin or tetracycline
cytoplasmic inclusions seen on Giemsa or fluorescent antibody-stained smear
infection of liver capsule with RUQ pain; associated with chlamydial or gonococcal infection
Fitz-Hugh-Curtis syndrome
how do the reticulate bodies of chlamydia replicate?
binary fission
types A, B, and C of chlamydia
Africa/Blindness/Chronic infection
types D-K of chlamydia
urethritis/PID, ectopic pregnancy, neonatal pneumonia or conjunctivitis
types L1, L2, and L3 of chlamydia
lymphogranuloma venereum (acute lymphadenitis - positive Frei test)
treatment for neonate after passage through chlamydia-infected birth canal?
erythromycin eye drops
most common STD in U.S.?
only spirochete that can be visualized using analine dyes (Wright's or Giemsa stan) in light microscopy
shepherd's crook-shaped spirochete
Wal's disease
fatal from of leptospira infection - jaundice, bleeding, renal failure, skeletal muscle necrosis
treatment for Borrelia recurrentis?
doxycycline, erythromycin
treatment for Lyme disease?
what causes yaws?
tremonema pertenue - tropical infection that is not an STD, although VDRL test is positive
what are important reservoirs for ixodes? what is required for tick life cycle?
mice; deer
signs of tertiary syphilis?
broad-based ataxia; positive Romberg; Charcot joints; stroke without hypertension
congenital syphilis?
saber shins, saddle nose, deafness
primary syphilis?
painless chancre
secondary syphilis?
disseminated isease with constitutional symptoms, maculopapular rash (palms and soles), condylomata lata
VDRL positive, FTA positive?
active infection
VDRL positive, FTA negative?
probably false positive
VDRL negative, FTA positive?
successfully treated
VDRL false positives?
viruses (mono, hep), drugs, rhematic fever, RA, SLE, leprosy
Weil-Felix reaction?
classic test that uses cross-linking proteus antigens to confirm diagnosis of rickettsia
strep associated with pharyngitis, cellulitis, impetigo, scarlet fever, TSS, rheumatic fever, glomerulonephritis?
strep pyogenes (group A beta hemolytic)
characteristics of rheumatic fever?
subcutaneous nodules, erythema marginatum, chorea, carditis
tumbling motility, menigitis in newborns, unpasteurized milk
listeria monocytogenes
virulence factor of staph aureus?
protein A
what does c. difficile produce?
a cytotoxin, an exotoxin that kills enterocytes, causing pseudomembranous colitis
what encodes the exotoxin of corynebacterium diphtheriae?
vesicular papules covered y black eschar
bacillus anthracis
what part of gram-negative bugs inhibits entry of penicillin and vancomycin?
the outer membrane layer
this vaccine contains type B capsular polysaccharide conjugated to diphtheria toxoid or other protein
h. flu
flagellar antigen of enterobacter?
H antigen
somatic antigen of enterobacter?
O antigen (polysaccharide of endotoxin)
viruses causing watery diarrhea?
rotavirus, adenovirus, norwalk virus
pertussis toxin permanently disables what?
cholera toxin permanently activates what?
how does pertussis toxin promote lymphocytosis?
by inhibiting chemokine receptors
treatment of choice for most rickettsial infections?
classic triad of rickettsiae?
headache, fever, rash (vasculitis)
rickettsiae are obligate intracellular parasites and need what?
CoA and NAD
all rickettsiae except what are transmitted by an arthropod vector and cause headache, fever, and rash?
why is coxiella an atypical rickettsia?
because it is transmitted by aerosol and causes pneumonia
what causes rocky mountain spotted fever? to where is it endemic?
rickettsia rickettsii; endemic to east coast
vector for rocky mountain spotted fever?
tick; rickettsia rickettsii
vector for endemic typhus?
fleas; rickettsia typhi
vector for epidemic typhus?
human body louse; rickettsia prowazekii
what causes Q fever?
coxiella burnetii
rickettsial disease with no rash, no vector, negative Wiel-Felix, and casative organism can survive outside for a long time
coxiella burnetii
what does the Weil-Felix reaction assay for?
antirickettsial antibodies, which cross-react with proteus antigen
what is the only bacterial membrane containing cholesterol?
mycoplasma pneumoniae
growth on Eaton's agar?
mycoplasma pneumoniae
normal flora dominant in nose
staph aureus
normal flora dominant in skin
staph epidermidis
normal flora dominant in oropharynx
strep viridans
normal flora dominant in dental plaque
strep mutans
normal flora dominant in colon
bacteriodes fragilis > e. coli
normal flora dominant in vagina
lactobacillus, colonized by e. coli and group B strep
common causes of pneumonia in kids (6 wks. - 18 yrs)
viruses (RSV), mycoplasma, c.pneumonia, s.pneumo
common causes of pneumonia in adults (18-40)
mycoplasma, c.pneumo, s. pneumo
common causes of pneumonia in adults (40-65)
s. pneumo, h. flu, anarobes, viruses, mycoplasma
common causes of pneumonia in elderly
s. pneumo, viruses, anaerobes, h.flu, g-rods
common causes of pneumonia in nosocomial
staph, gram-negative rods
common causes of pneumonia in immunocomprimised
staph, gram-negative rods, fungi, viruses, PCP (HIV)
common causes of pneumonia in aspiration
common causes of pneumonia in alcoholic/IV drug user
strep pneumo, klebsiella, staph
common causes of pneumonia in postviral
staph, h. flu
common causes of pneumonia in neonate
group B strep, e. coli
common causes of atypical pneumonia
mycoplasma, legionella, chlamydia
causes of meningitis in newborn (0-6 mos)
GBS, e.coli, listeria
causes of meningitis in children (6 mos - 6 yrs)
s. pneumo, n.meningitidis, h.flu B, enterovirus
causes of meningitis in 6-60 year olds
n.meningitidis, enterovirus, s.pneumo, hsv
causes of meningitis in elderly (over 60)
s.pneumo, g-rods, listeria
causes of meningitis in HIV
cryptococcus, CMV, toxoplasmosis (brain abscess), JC virus (PML)
CSF findings in bacterial meningitis
increased pressure, neutrophils, protein - decreased sugar
CSF findings in fungal/TB meningitis
increased pressure, lymphocytes, protein - decreased sugar
CSF findings in viral meningitis
n/+pressure, + lymphocytes, normal protein and sugar
cause of osteomyelitis in most people
staph aureus
cause of osteomyelitis in sexually active
neisseria gonorrhoeae (rare), septic arthritis more common
cause of osteomyelitis in diabetics and drug addicts
cause of osteomyelitis in sickle cell
cause of osteomyelitis in prosthetic replacement
staph aureus and staph epidermidis
cause of vertebral osteomyelitis
TB (Pott's disease)
UTI in ambulatory patients
e. coli (50-80%), klebsiella (8-10%)
second most common cause of UTI in young ambulatory women
staph saprophyticus
cause of UTI in hospital?
e. coli, proteus, klebsiella, serratia, pseudomonas
UTI - colonies show metallic sheen on EMB agar
e. coli
UTI - large mucoid capsule and viscous colonies
UTI - swarming on agar (motility); produces urease
vaginitis, strawberry-colored mucosa
trichomonas vaginalis
noninflammatory, malodorous discharge; positive whiff test; clue cells
gardnerella vaginalis
risk factor: newborn nursery
risk factor: urinary catheterization
e. coli, proteus
risk factor: respiratory therapy equipment
pseudomonas aeruginosa
risk factor: work in renal dialysis unit
risk factor: hyperalimentation
candida albicans
risk factor: water aerosols
infections dangerous in pregnancy
ToRCHeS: toxo, rubella, CMV, HSV, HIV, syphillis
traumatic open wound
c. perfringens
surgical wound
staph aureus
sepsis/meningitis in newborn
group B strep
neutrophils in CSF?
bacterial meningitis
normal protein and sugar in meningitis?
teichoic acid is unique to what type of organisms?
endotoxin/LPS (outer membrane) is unique to what type of organisms?
what do teichoic acid and lipid A induce?
TNF and IL-1
space between the cytoplasmic membrane in gram-negative bacteria
periplasm - contains many hydrolytic enzymes, including beta lactamases
this mediates adherence to surfaces, especially foreign surfaces, e.g. indwelling catheters
glycocalyx - made of polysaccharide
this contains a variety of genes for antibiotic resistance, enzymes, and toxins
plasmid - made of DNA
what is the only gram-positive with endotoxin?
what is exotoxin made of?
what is endotoxin made of?
typical diseases with exotoxin?
tetanus, botulism, diphtheria
tpical diseases with endotoxin?
meningococcemia, sepsis by gram-negative rods
gram-negative cocci?
these have a gram-negative cell wall but are too small to be seen with light microscope
spirochetes - must be visualized with darkfield microscope
no cell wall; neither gram-positive or gram-negative
lipopolysaccharide found in cell wall of gram-negative bacteria
endotoxin - heat stable
this bug inactivates elongation factor (EF-2), causes pharyngitis and pseudomembrane in throat
corynebacterium diphtheriae
ADP ribosylation of G protein stimulates adenylyl cyclase, increasing pumping of Cl- and H20 into gut
what does e. coli heat-labile toxin stimulate?
adenylate cyclase
what does e. coli heat-stable toxin stimulate?
guanylate cyclase
name the 6 classic gram-positives
strep, staph, bacillius, clostridium, corneybacterium, listeria
what does bordatella pertussis stimulate?
adenylate cyclase; also inhibits chemokine receptor
double zone of hemolysis on blood agar?
C. perfringens
what does C. tetani block the release of?
inhibitory NT glycine
what does C. botulinum block the release of?
what does shiga toxin do?
cleaves host cell rRNA; also enhances cytokine release, causing HUS
what type of bugs are rickettsia and chlamydia?
intracellular parasites
neisseria meningitidis ferments what?
maltose and glucose
neisseria gonorrhea ferments what?
what produces a blue-green pigment?
what produces a red pigmetn?
serratia maracescens
IgA proteases allow what organisms to colonize mucosal surfaces?
strep pneumo, neisseria meningitidis, neisseria gonorrhoeae, h. flu
silver stain?
fungi, PCP, legionella
india ink?
cryptococcus neofromans
Ziehl-Neelsen stain?
acid-fast baceria
PAS stain?
stains glycogen, mucopolysaccharides; used to diagnose Whipple's disease
Giemsa's stain?
borrelia, Plasmodium, trypanosomes, chlamydia
congo red?
amyloid; apple-green birefringence in polarized light (because of beta-pleated sheets)
chocolate agar with factors V and X?
H. influenzae
Thayer-Martin (VCN) agar?
N. gonorrhoeae
Bordet-Gengou (potato) agar?
B. pertussis
tellurite plate, Loffler's medium, blood agar?
C. diphtheriae
Lowenstein-Jensen agar?
M. tuberculosis
pink colonies on MacConkey's agar?
lactose-fermenting enterics - Klebsiella, e. coli, enterobacter (fast); citrobacer, serratia (slow)
charcoal yeast agar buffered with increased iron and cysteine?
Sabouraud's agar?
obligate aerobes (4)
Nagging Pests Must Breathe: nocardia, pseudomonas, mycobacterium, TB, bacillius
obligate anaerobes (3)
clostridium, bacteriodes, actinomyces - lack catylase and/or superoxide dismutase, and thus are susceptible to oxidative damage; generally foul smelling, difficult to culture, and produce gas in tissue (CO2 and H2)
obligate intracellular bugs (2)
rickettsia, chlamydia (stay inside when it's Really Cold)
facultative intracellular (8)
Some Nasty Bugs May Live FacultativeLY:
salmonella, neisseria, brucella, mycobacterium, listeria, francisella, legionella, yersinia
encapsulated bugs (4)
strep pneumo, H. flu, neisseria meningitidis, klebsiella - positive quellung reaction
bacillus anthracis, c. perfringens, and c. tetani form what?
spores (gram positive soil bugs)
alpha hemolytic bacteria?
s.pneumo(cat-, optS), s.viridans (cat-, optR)
beta hemolytic bacteria?
s. aureus (cat+, coag+), GAS (cat-, bacS), GBS (cat-,bacR), listeria
how do you differentiate strep pyogenes form strep agalactiae?
strep agalactiae (bacitracin S), strep agalactiae (bacitracin R)
DNA transferred from 1 bacterium to another
nature of DNA transferred in conjugation
chromosomal or plasmid
DNA transferred by a virus from 1 cell to another
nature of DNA transferred in transduction
any gene in generalized transduction; only certain genes in specialized transduction
purified DNA taken up by a cell
transformation (any DNA)
most capsules are made out of polysaccharide except bacillus anthracis, which contains what?
chemical composition of spore?
keratin-like coat; dipicolinic acid - provides resistance to heat, dehydration, and chemicals
what is a pilus made out of?
location of exotoxin genes?
plasmid or bacteriophage
location of endotoxin genes?
bacterial chromosome
which is antigenic - exotoxin or endotoxin?
both of these bugs activate EF-2
corynebacterium, pseudomonas (exotoxin A)
how do you distinguish staph epidermidis from staph saprophyticus
s. epidermidis is novabiacin S, s. saprophyticus is novabiacin R
another name for group A beta hemolytic strep?
strep pyogenes
another name for group B beta hemolytic strep?
strep agalactiae
which is bile soluble - strep pneumo or strep viridans?
strep pneumo

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