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*USMLE* > Micro > Flashcards

Micro Flashcards

1
Q

P. jiroveci

CD4 count, risk factor, prophylaxis

A

CD4 <200/mm3

oropharyngeal candidiasis increases risk

TMP-SMX

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2
Q

Toxoplasma gondii

CD4 count, risk factor, prophylaxis

A

CD4 <100/mm3

positive Toxoplasma IgG is a risk factor

TMP-SMX

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3
Q

Mycobacterium avium complex

CD4, prophylaxis, pathogenesis in HIV, signs/symptoms, biopsy

A

CD4 <50/mm3, prevent with Azithromycin

ingestion/inhalation > prevents phagolysosome formation > insufficient IFN-y to activate macrophages in CD4 defic.

nonspecific sx (fever, weight loss, D); anemia, HSmegaly, high ALP/LDH with RES involvement

dx by blood culture (but slow); biopsy shows granulomas of foamy epitheliod cells + giant cells with IC acid-fast bacilli

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4
Q

Congenital Toxoplasmosis: when does baby get it and what it do

A

in utero transplacental infection

triad = intracranial calcifications, chorioretinitis, hydrocephalus

also hepatosplenomegaly, neuro issues (seizure, eye movement problems, altered muscle tone) and rash

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5
Q

Congenital HSV: when does baby get it and what it do

A

intrapartum infection

causes ophthalmia neonatorum (also via Chlamydia or Neisseria, conjunctivitis)

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6
Q

Clostridium septicum

what does it cause? in whom specifically?

A

gram-pos, spore-forming, exotoxin-producing normal flora

spontaneous gas gangrene in patients with underlying COLON CANCER, IBD or immunosuppression (is normal gut flora that can get into circulation when mucosa is compromised

RAPID ONSET MUSCLE PAIN, fever, HEMORRHAGIC BULLAE, dusky skin, edema + CREPITUS

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7
Q

Vibrio vulnificus

A

gram-negative

increased risk for fulminant infection in HEMOCHROMATOSIS b/c needs free iron for growth

rapid-onset sepsis and bullous skin lesions

shellfish consumption or wound infection with seawater

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8
Q

fungal infection from indwelling catheter

what microbe + what sx?

A

candidemia

sepsis, abscess, and pustular skin lesions with red base

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9
Q

multiple myeloma-related common infections

A

lung - S. pneumo or H. flu

UTI - E. coli

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10
Q

differentiation of EBV vs. non-EBV infectious mononucleosis

causes of non-EBV IM

A

non-EBV IM often does NOT have sore throat or lymphadenopathy or heterophile Ab positivity

CMV IM can come from blood transfusions (irradiation of blood products reduces risk)

other causes of IM-like syndromes are HHV-6, HIV and toxoplasmosis

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11
Q

a glycosylated HIV polyprotein that is cleaved into 2 smaller proteins

what is it? what are the 2 smaller proteins? functions of resulting proteins and why are they glycosylated?

A

GP160 is cleaved into GP120 and GP41 (Gp160 glycosylated in rER and Golgi)

gp120 is an envelope protein that mediates viral attachment

gp41 is an envelope protein that mediates fusion

glycosylation helps with immune evasion (masks antigens), host cell binding + proper protein folding

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12
Q

main mechanism of aminoglycoside resistance

how does this mechanism arise in microbes?

A

antibiotic-modifying enzymes (acetylases, kinases, etc.)

aminoglycosides altered by acetylation, etc. have reduced binding of the 30S ribosomal subunit (16S component)

usually via PLASMID or TRANSPOSON transfer, not chromosomal mutation

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13
Q

3 infections assoc. with acute pancreatitis

A

mumps
Coxsackie
Mycoplasma

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14
Q

Staph epidermidis

biochem tests + microbiological characteristics

A

catalase-positive (as are all Staph)
coagulase negative (differentiates it from aureus)
gamma-hemolytic (no hemolysis)
novobiocin sensitive (diff from saprophyticus)

gram-positive cocci in clusters
adhesion + biofilm proteins > infects prosthetics

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15
Q

Histoplasma capsulatum

general characteristics, transmission + pathogenesis

dx (culture, labs + characteristic signs)

A

dimorphic, transmitted by inhalation > transforms to yeast in lungs

replicates in phagosomes of macrophages > oval/round yeast cells in macros

intact immunity > asymptomatic or self-limited pulmonary infection (cell-mediated immunity)

impaired immunity > RES dissemination with HSmegaly, LAP, and PANCYTOPENIA

dx by BLOOD/URINE Ags, hyphae on Sabouraud culture and characteristic TONGUE ULCERS

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16
Q

Schistosoma haematobium

where? how? what it do?

A

Africa and Middle East - URINARY schistosomiasis

freshwater snails release larvae > penetrate skin > migrate to + mature in liver > travel to bladder venous plexus

terminal hematuria, dysuria + frequent pissing

hydronephrosis, pyelonephritis and bladder SCC

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17
Q

Schistosoma mansoni / japonicum

where? how? what it do?

A

Mansoni - Africa, Middle East, S. America + Carribean
Japonicum - Asia, Philippines, Japan

same pathogenesis as haemotobium, but travels thru portal veins to GI

intestinal schisto - D and pain, ulceration with IDA
hepatic schisto - HSmegaly, periportal fibrosis + portal htn

all 3 spp. have Th2 granulomatous response with eosinophils and M2 macrophages

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18
Q

Echinococcus granulosus

transmission + disease

A

DOG TAPEWORM - dog host (sheep intermediate)

food contaminated with dog poop > hydatid cysts

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19
Q

Diphyllobothrium latum

transmission + disease

A

FISH TAPEWORM - raw freshwater fish

vitamin B12 deficiency and megaloblastic anemia

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20
Q

Taenia solium

transmission + 2 diseases

A

PIG TAPEWORM - undercooked pork (worm infection) or eggs in carrier feces (cysticercosis)

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21
Q

Parvovirus B19

type of virus? transmission?

A

naked ssDNA

respiratory, hematogenous or congenital transmission

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22
Q

Parvovirus B19

prodrome and 2 clinical manifestations in normal patients

A

Prodrome - HA, coryza, GI sx (heavy viremia + shedding)

Erythema Infectiosum - in KIDS; bright red cheek rash, circumoral pallor, fever +/- reticular rash on arms, legs, trunk

Acute arthropathy - in ADULTS; polyarthritis that is SYMMETRIC on PIP, knee and ankle joints; self-limited + non-destructive

(both have immune complexes + low shedding)

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23
Q

Parvovirus B19

2 clinical manifestations in unique types of patients

A

Aplastic crisis - “reticulocytopenia” in pts with pre-existing RBC issues such as sickle cell or spherocytosis

Hydrops fetalis - pregnant woman infected > hydrops in baby is common; direct hemolysis + precursor interruption

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24
Q

Asplenic patient

more susceptible to infection with which bacteria? (general type + species examples)

A

encapsulated bacteria

group B strep (agalactiae)
H. flu
Strep pneumo
Meningococcus
Salmonella typhi
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25
Q

Malarial life cycle

this card is a nightmare, just for review

A

Anopheles bite > SPOROZOITEs infect hepatocytes

in liver - dormant infection with HYPNOZOITEs or a SCHIZONT of many MEROZOITES forms in liver cell > schizont rupture releases merozoites to blood

in blood - merozoites infect RBCs and form TROPHOZOITES > asexual formation of more schizonts in RBCS with further merozoite release or…

gametocyte formation > picked back up by mosquitos

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26
Q

Toxocara canis

manifestations? dx?

A

DOG ROUNDWORM - incidental infection in humans

eosinophilic GRANULOMATOUS inflammation
visceral LARVA MIGRANS
ocular larva migrans

dx by serology

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27
Q

Oncogenesis by HBV vs. HCV

1 mechanism for both, 2 mechanisms unique to only 1 of them

A
  1. Increased Hepatocyte Turnover - with local inflammation > incr. mutation risk (both HBV + HCV)
  2. Genome Integration - only HBV! partial dsDNA integration into host genome via topoisomerase I can cause insertional mutagenesis
  3. Oncogenic Viral Proteins - viral protein “HBx” activates cell growth genes + interferes with p53 (HBV only!)
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28
Q

MCC of sepsis in asplenic pt?

MCC of osteomyelitis in asplenic pt?

prevention?

A

Sepsis - S. PNEUMO > H. flu > (E. coli, pseudomonas, staph, other strep)

Osteomyelitis (in sickle cell) - SALMONELLA > (S. aureus, E. coli)

penicillin prophylaxis and pneumococcal vaccination

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29
Q

Mefloquine

active against what phase of malarial life cycle? clinical consequence?

A

a SCHIZONTICIDE that kills replicating parasites IN RBCS

does NOT kill hepatic schizonts (is inactivated in liver)

must take for 4 WEEKS after return (liver schizonts rupture after 8-30 days)

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30
Q

Plasmodium in Africa is often which species?

Resistant to what?

Treated with what?

A

Falciparum

chloroquine-resistant

mefloquine, doxycycline or atovaquone-proguanil

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31
Q

Zika virus

pathogenesis? clinical? dx?

A

ssRNA Flavivirus; TRANSPLACENTAL transmission; targets NEURAL PROGENITORS

microcephaly, craniofacial disproportion; SPASTICITY + SEIZURE; ocular issues

imaging - calcifications, ventriculomegaly, cortical thinning

RNA detection by PCR of urine, serum or CSF

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32
Q

Shigellosis

infects which type of cells? then what?

(most common species? other species)

A

infects “MICROFOLD (M) CELLS” of GI mucosa (at base of villi in Peyer’s patch in ileum)

is endocytosed, lyses the endosome, multiplies and spreads laterally to other cells > denuding + ulceration of mucosa > bloody D

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33
Q

HIV biding, fusion + entry process

A

gp120 binds CD4 plus CCR5 or CXCR4 co-receptors

gp120 undergoes conformational change to expose gp41 which mediates fusion

(Maraviroc blocks CCR5; enfuvirtide blocks gp41)

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34
Q

Two HIV regulatory genes

not gag, pol, env

A

Nef - regulates MHC-I expression on infected cells

Tat - transcriptional activator, promotes viral gene expression

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35
Q

MCC viral meningitis in children

what else can it cause, more rarely?

A

Enterovirus, specifically Coxsackie B

more rarely, encephalitis with flaccid paralysis

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36
Q

What kind of organisms are CGD patients susceptible to?

A

CGD = NADPH oxidase inactivation > no ROS formation

CATALASE-POSITIVE MICROBES - without catalase, microbes can’t prevent H2O2 accumulation from THEIR OWN metabolism in phagosomes > hypochlorite is formed + damages microbe; with catalase, H2O2 is broken down

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37
Q

What are the 5 most common organisms that infect CGD patients?

A

CATALASE-POSITIVES:

S. aureus
Burkholderia cepacia
Serratia marcescens
Nocardia
Aspergillus
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38
Q

Molecule linked to PG wall in Gram-positive microbes only

A

Teichoic acid

Ag determinant for microbe ID and Ag target for immune system

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39
Q

Which bacteria produce IgA protease? (4)

what does it do?

A

Neisseria (both), S. pneumo, H. flu

Cleaves IgA at its hinge region > Fab and Fc fragment

facilitates bacterial mucosa adherence

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40
Q

Bacillus anthracis

antiphagocytic feature

A

D-glutamic acid capsule

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41
Q

B. anthracis

toxins

A

edema factor - adenylate cyclase

lethal factor - hydrolyzes MAPK kinases

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42
Q

B anthracis

culture + micro characteristics

A

large, nonmotile, spore-former

nonhemolytic, gram-positive rod

cultures grow curled edges with “MEDUSA HEAD” shape

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43
Q

B anthracis

severe form of disease + its signs

A

Hemorrhagic Mediastinitis in “Pulmonary Anthrax”

prodrome > widened mediastinum on x-ray

can cause shock, brain edema/hemorrhage + death

seen in woolsorters and mail sorters

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44
Q

“Genetic Reassortment” in viruses

what happens? what kind of viruses / example?

another name for the result

A

2 strains infect same cell > SEGMENTS reassort > progeny with reassorted genomes (since genome is changed, progeny of the progeny will retain same changes)

SEGMENTED viruses only

in cause of INFLUENZA viruses, NA and HA are on different segments > novel strain created by reassortment = ANTIGENIC SHIFT

(drift is just point mutations)

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45
Q

segmented viruses

4

A

all are RNA viruses

Orthomyxo - INFLUENZA

Arena - LASSA FEVER virus

Bunya - HANTA virus

Reo - ROTAvirus

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46
Q

typical HEP B histo picture

A

“GROUND GLASS” hepatocytes have finely GRANULAR, diffusely homogeneous PALE PINK cytoplasm

due to accumulation of HBsAg in cells

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47
Q

typical Hep C histo picture

A

less specific picture than Hep B (no ground glass)

LYMPHOID AGGREGATES in portal tracts and MACROVESICULAR STEATOSIS

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48
Q

Strongyloides stercoralis infection

two larvae types? special infectious mechanism?

A

roundworm

infection - infectious FILARIFORM larvae in feces soil > penetrate skin > lungs > swallowed > adults lay eggs in GI mucosa > non-infectious RHABDITIFORM larvae release in poo

AUTOINFECTION - some rhabdi larvae molt into filari larvae and auto-infect host > widespread dissemination = HYPERINFECTION

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49
Q

Strongyloides stercoralis

hyperinfection in which patients (general answer is obvious but be more specific)

A

immunocompromised

specif. on drugs or HTLV-1 infection > impaired Th2

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50
Q

Strongyloides

s/s? specific findings? tx?

A

asymptomatic, or…
chronic GI and pulmonary sx

“LARVA CURRENS” - red itchy linear streaks on thigh/butt via subcutaneous larval migration away from butt

Dx - RHABDITIFORM larvae in stool; O+P on GI biopsy

Tx - IVERMECTIN

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51
Q

polysaccharide component of Hib capsule

A

polyribosylribitol phosphate

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52
Q

how does PRP capsule of Hib prevent phagocytosis?

A

binds “FACTOR H” in host circulation

factor H normally degrades C3b deposited on host cells > prevention of C3b deposition on Hib > no opsonization / complement mediated lysis

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53
Q

M protein

which microbe? function?

A

in cell wall of Strep pyogenes

binds factor H > prevents opsonization / complement mediated lysis

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54
Q

Protein A

which microbe? function?

A

cell wall of S. aureus

prevents opsonization by binding Fc region of Igs

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55
Q

Aeromonas hydrophila

micro characteristics?
disease?
risks?

A

oxidase-positive
non-lactose-fermenting
Gram-negative rod

gastroenteritis, wound infection, bacteremia

exposure to contaminated water

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56
Q

Pyrrolidonyl arylamidase test (PYR)

S. pyogenes?
S. aureus?

A

S. pyogenes is PYR POSITIVE

S. aureus is PYR NEGATIVE

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57
Q

Best method for confirmatory dx of Trichomonas

A

Saline microscopy for MOTILE TRICHOMONADS

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58
Q

Diff. dx of vaginal infections by vaginal pH

3 infections

A

Bacterial vaginosis and trichomonas show HIGH pH (>4.5)

Candidiasis shows NORMAL pH (3.8-4.5)

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59
Q

How to diff btwn two types of gram positive cocci?

A

Catalase

Staph - cat pos
Strep - cat neg

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60
Q

How to differentiate Strep by hemolysis?

A

alpha hemolytic - slight zone, greenish > S. pneumo + viridans

beta hemolytic - S. agalactiae or S. pyogenes

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61
Q

Which 2 types of cat-neg Gram+ cocci are gamma-hemolytic (no hemolysis)?

A

Enterococci

Strep gallolyticus (bacteremia/infective endocarditis assoc. with colon cancer)

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62
Q

How to diff btwn alpha hemolytic strep?

A

bile and optochin sensitive - S pneumo

bile and optochin resistant - S. viridans

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63
Q

How to diff btwn beta hemolytic strep?

A

S pyo - bacitracin-sensitive and PYR positive

S agalact - bacitracin resistant, PYR negative, and CAMP positive

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64
Q

How to diff btwn gamma hemolytic gram+ cocci?

A

Enterococcus - grow in 6.5% NaCl and bile, PYR positive

S. galloyl - grow in BILE BUT NOT SALT and are PYR negative

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65
Q

which two bacteria are PYR positive?

A

S. pyogenes

Enterococci spp.

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66
Q

Campylobacter jejuni

source other than contaminated food?

A

domesticated animals

especially puppies from kennels

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67
Q

1 cause viral gastroenteritis

transmission? presentation?

A

Norovirus

feces-contaminated food/water

vomit-predominant illness with pain and moderate amt diarrhea (non-inflammatory, no blood/WBCs in stool)

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68
Q

Vibrio parahaemolyticus

where + from what? presentation? worse in whom?

A

marine environments; contaminated shellfish

diarrhea-predominant gastroenteritis

sepsis in liver disease / HEMOCHROMATOSIS

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69
Q

dx for Giardia

3 things, first 2 most important

A
  1. Stool O + P
  2. Fecal immunoassay for antigens
    (3. SI biopsy - villus atrophy + crypt hyperplasia dependent on disease severity)
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70
Q

main mechanism for Giardia immunity

considering this, who gets Giardia more?

A

CD4 function and SECRETORY IgA (binds trophozoites > impaired adherence to upper small bowel wall)

Kids with IgA deficiency, X-linked agammaglobulinemia or COMMON VARIABLE IMMUNODEFICIENCY get giardia more

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71
Q

M protein

which microbe? structural homology with what?

A

S pyogenes

homologous to human tropomyosin and myosin (both have many alpha helices + coiled coils)

cross-rxn with heart myosin > rheumatic carditis

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72
Q

prophylaxis for Strep agalactiae

A

universal screening by maternal vaginal + rectal culture at 35-37 weeks

any woman who is CULTURE POSITIVE or has PAST CHILD AFFECTED should take…

INTRA-PARTUM PENICILLIN (or ampicillin alternative) will prevent sepsis, pneumonia + meningitis in baby

(prepartum penicillin has a risk of re-colonization before birth)

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73
Q

Primaquine

unique use in malaria?

A

kills HYPNOZOITES dormant in liver > prevents disease relapse

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74
Q

what 2 plasmodium spp. tend to create hypnozoites?

consequence? tx?

A

P. vivax and ovale

can cause disease recurrence after hypnozoite rupture from liver; tx with primaquine

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75
Q

how can LACTOSE-FERMENTING GRAM-NEGATIVE RODS be differentiated in UTIs in women?

differentiates what species?

A

Indole test - conversion of Trp to indole

E. Coli - indole-positive

Enterobacter cloacae - indole-negative

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76
Q

What is FIRST used to differentiate gram-negative rods biochemically?

A

MacConkey agar

Lactose fermenters form PINK colonies (Klebs, E coli, Enterobacter, Citrobacter, Serratia)

Non-fermenters form WHITE colonies (Pseudomonas, Shigella, Salmonella, Proteus)

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77
Q

Among lactose fermenting gram negative rods, how are they differentiated by fermentation speed?

A

Fast fermenters - Klebs, E. coli, Enterobacter

Slow fermenters - Citrobacter, Serratia

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78
Q

Among non-lactose fermenting gram-neg rods, what is the FIRST step in differentiation?

A

oxidase test

oxidase positive - Pseudomonas

oxidase negative - Shigella, Salmonella, Proteus

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79
Q

Among oxidase-negative non-lactose fermenting gram-negatives, how is differentiation performed?

A

TSI agar (“triple sugar iron”)

assesses H2S production (creates BLACK color)

No H2S - Shigella

H2S production (black) - salmonella, proteus

80
Q

1 COD in patient hospitalized for acute rheumatic fever

A

PANCARDITIS

mitral stenosis and its complications come much later

81
Q

HIV increases chances of EBV causing what?

A

EBV antigen-induced B-CELL PROLIFERATION resulting in Burkitt lymphoma

“immunodeficiency-related” Burkitt is not necessarily in the jaw like endemic… can arise in the GI tract etc.

(“starry sky” histo, high Ki-67 fraction, diffuse medium-sized lymphos + a t(8;14) causing c-MYC overexpression)

82
Q

flu vaccines

what 2 types + routes of admin?
who is recommended to get it?

A

Parenteral inactivated
Nasal spray live-attenuated

anyone over 6; especially health care workers, elderly, chronically diseased or immunocompromised

83
Q

main effect of INACTIVATED flu vaccine on viral function?

A

induces production of NEUTRALIZING ANTIBODIES against the HEMAGGLUTININ antigen

this inhibits binding of HA to sialylated receptors on host cells and thus INHIBITS VIRAL ENTRY via endocytosis

84
Q

main effect of LIVE ATTENUATED flu vaccines on viral function?

A

stimulate MHC-I pathway > generate CD8+ cells that kill infected cells

85
Q

Cephalosporin resistant organisms (5 things)

3 via one mechanism; 2 via another

A

Altered PBPs:

  1. Listeria monocytogenes - but ampicillin works
  2. Enterococcus
  3. MRSA

No cell wall:

  1. Chlamydia
  2. Mycoplasma
86
Q

Congenital Rubella Syndrome

classic triad

2 other possibilities

A
  1. CATARACTS - present as white pupils
  2. Sensorineural DEAFNESS
  3. PATENT DUCTUS ARTERIOSUS

CV defect can also be peripheral pulmonic stenosis

head defects including microcephaly and retardation

87
Q

What kind of vaccine is MMR?

A

live attenuated

88
Q

Besides kids 12-15 months and booster at 4-6 years…

who should get MMR vaccine?

A

non-pregnant women of childbearing age with low/no rubella antibody titer

give MMR and advise to avoid pregnancy for 4 weeks

89
Q

wet mount of CSF of meningitis pt shows MOTILE TROPHOZOITES

what is it? tx?

A

Primary Amebic Meningoencephalitis

Naegleria fowleri; amphotericin B

90
Q

4 causes of necrotizing fasciitis

A
  1. Strep pyogenes
  2. Staph aureus
  3. Clostridium perfringens
  4. Polymicrobial
91
Q

Aeromonas hydrophila

microbial characteristics
3 diseases via spread by what?

A

oxidase-positive, non-lactose-fermenting gram negative rod

gastroenteritis, wound infections, or bacteremia after exposure to contaminated water

92
Q

Typhoidal salmonella infection

cause + epidemiology

A

S typhi and paratyphi

source is HUMANS (unlike S enterica) via contaminated water/food in DEVELOPING countries

93
Q

Typhoidal salmonella infection

pathophys of infection

A

enterocyte invasion > CAPSULAR ANTIGEN Vi blunts neutrophil response > extensive replication in MACROPHAGES > spreads thru lymph and RES

94
Q

Typhoid fever

s/s

A
  • Progressive fever with PULSE-TEMP DISSOCIATION (relative bradycardia)
  • maculopapular “ROSE SPOTS” on trunk
  • abdominal pain, HSmegaly, GI bleeds + perforation
95
Q

Other than self-limited diarrhea, what can be some rare complications (3) of non-typhoidal Salmonella?

A
  1. Osteomyelitis
  2. Mycotic aneurysm
  3. Endocarditis
96
Q

Mechanism of host cell death caused by E. histolytica

A

contact btwn microbe + host cell inserts an AMEBIC CHANNEL-FORMING PROTEIN in the host cell membrane

97
Q

anti-Campy Abs cross react with what host molecule to cause Guillain-Barre syndrome?

A

GM1 Ganglioside

98
Q

Babesiosis

s/s (general, and more severe ones)

A

fever, fatigue, MYALGIA, HA + flu-like sx

if severe:
ARDS
CHF
DIC
SPLENIC RUPTURE
99
Q

Babesiosis

diagnostic histo (stain + 2 signs)

A

wright giemsa stain of blood smear

intra-RBC “RING FORMS” - pleomorphic

occasional “MALTESE CROSS” forms

100
Q

Aedes mosquito

what two viruses?

A

dengue fever + chikungunya

<14 day incubation

101
Q

3 viruses which can cause dilated cardiomyopathy

A

Coxsackie B

Adenovirus

Influenza

102
Q

Neurocysticercosis

organism? transmission?

A

Taenia solium (pork tapeworm)

EGGS excreted in human feces > ingested in contaminated food

(as opposed to eating LARVAE in pork causing normal infection)

103
Q

Neurocysticercosis

where? presentation?

A

central + south america, sub-saharan africa, asia

LONG INCUBATION (months-years)

seizures, focal neuro sx + intracranial hypertension via CSF OBSTRUCTION

104
Q

Neurocysticercosis

Dx? Tx?

A

CT/MRI - show cysts + scolex (head of tapeworm with hooklets)

Eosinophilia
high ESR

albendazole

105
Q

What pathophysiological mechanism is responsible for the neural effects of rheumatic fever? (Sydenham’s chorea)

A

cross reactivity between antibodies against microbial N-ACETYL-BETA-D-GLUCOSAMINE, and..

host neuronal LYSOGANGLIOSIDE

106
Q

In utero CMV infection

consequences?

(think senses, CNS and RES)

A

up to 5% women get primary CMV in preg - 1/3 of these transmit to fetus in utero (mostly 1st trimester)

  • Chorioretinitis
  • Sensorineural deafness
  • Microcephaly + seizures
  • HSmegaly + jaundice
107
Q

Causes of reactive arthritis other than C. trachomatis

A

Enteritis via…

Salmonella, shigella, yersinia, campy or c diff

108
Q

Joint aspirates show what in reactive arthritis?

A

NO MICROBES - it is not a disseminated infection, but rather an inflammatory reaction caused by the infection

109
Q

Triad for botulism

A

Diplopia, dysphagia and dysphonia (hoarseness)

both nicotinic and muscarinic blockade via ACh release inhibition

110
Q

How does botulism affect muscle contraction?

How can this be tested?

A

Flaccid paralysis via decreased ACh release at NMJ

Results in decreased CMAP (compound muscle action potentials) that can be increased again by RAPID REPETITIVE NERVE STIMULATION

111
Q

Where + how should lumbar puncture be performed?

A

pt recumbent or sitting bent forward

needle inserted btwn L3/L4 or L4/L5 (well below end of SC)

palpate ILIAC CRESTS and find body of L4 between the 2 crests

(goes through interspinous ligament, ligamentum flavum and dura into space containing cauda equina)

112
Q

what do serovars A-C of C. trachomatis cause?

A

“Trachoma” - ocular infection in children

113
Q

PG precursor disaccharide is made of what 2 molecules?

A

N-acetylmuramic acid

N-acetylglucosamine

114
Q

What PG cell wall component do penicillins structurally resemble?

A

D-Ala-D-Ala

facilitates their binding to TRANSPEPTIDASE > inhibits final “cross-linking” step of wall synth

115
Q

Dengue fever

virus type? primary vs. secondary infection differences?

A

positive-sense ssRNA flavivirus

4 serotypes DENV1-4

primary infection is often asymptomatic or self-limited + results in immunity to same serotype

secondary infection with DIFFERENT serotype results in MORE SEVERE illness (via Ab-dependent enhancement, more complexes and enhanced T-cell activity)

116
Q

S/S of “classic dengue fever”

A
  • “Break bone fever” - fever with severe myalgia + joint pain
  • RETRO-ORBITAL PAIN
  • DIFFUSE MACULAR RASH - “white islands in sea of red”
  • Leukopenia, thrombocytopenia (EPISTAXIS, PETECHIAE, PURPURA)
117
Q

S/S of “dengue hemorrhagic fever”

especially 1 special sign

A
  • high capillary permeability > worse bleeding than classic form with SHOCK, RESP/CIRC FAILURE
  • TOURNIQUET SIGN - petechiae form after 5 minutes of cuff inflation
  • thrombocytopenia, prolonged fever
118
Q

What 2 cell types does EBV have tropism for?

Via what receptor?

A

B cells and nasopharyngeal epithelium

binds to CD21 (aka CR2) on these cells

(this is the receptor for complement C3d; EBV binds it with its gp350)

119
Q

Most common adult meningitis vs. neonate meningitis

A

Adult - S. pneumo and N. meningitidis

Neonate - S. agalactiae and GRAM-NEG RODS

120
Q

3 most common viral meningitis causes

A
  1. ENTEROVIRUS - most common (coxsackie, echo + polio)
  2. Arboviruses
  3. HSV - type 2 more common than type 1
121
Q

Difference in WBC count in CSF btwn bacterial and viral meningitis

A

viral - often <500/mm3 (lymphos)

bacterial - often >1,000/mm3 (neutrophils)

122
Q

Difference in glucose and proteins in CSF btwn bacterial + viral meningitis

A

Viral - glucose is normal or slightly low; protein is mildly elevated (<150 mg/dl)

Bacterial - glucose is always low (<45) and protein is highly elevated (>250)

123
Q

What are the segmented viruses?

4 classes

A
  1. Orthomyxoviruses - influenza
  2. Reoviruses - rotavirus, colorado tick virus
  3. Bunyavirus
  4. Arenavirus

ORBA

124
Q

What can segmented viruses do if 2 different ones co-infect a cell?

A

REASSORTMENT - genetic shift

genetic segments reassort and create progeny with reassorted genomes (can go on to make more progeny with same genome, unlike when only surface molecules are exchanged)

125
Q

what toxin causes the symptoms of Rotavirus infection? how?

A

NSP4 - increases chloride permeability in gut > watery diarrhea

126
Q

MacConkey agar

what does it differentiate and how?

A

lactose fermenters vs. non in gram-neg enteric rods

lactose fermenters lower agar pH and create PINK colonies (E. coli, Enterobacter, Klebs)

non do not create pink (Pseudomonas, Proteus, Salmonella, Yersinia)

(has bile salts + crystal violet to inhibit gram-pos)

127
Q

What can be added to MacConkey to differentiate a certain E. coli strain?

A

sorbitol - differentiates O157:H7 (enterohemorrhagic)

sorbitol replaces lactose; O157:H7 can’t ferment sorbitol > no pink colonies

128
Q

What might the microbe be if it produces pink colonies on MacConkey after a LONG fermentation?

A

Shigella sonnei

129
Q

What might the microbe be if it produces pink colonies on MacConkey that look moist and sticky?

A

Klebsiella or Enterobacter

due to polysacch capsule

130
Q

What is EMB agar and what does it differentiate?

A

eosin methylene blue

isolates enteric pathogens from contaminated specimens; looks for lactose fermentation

lactose fermenters bind dye and produce GREEN METALLIC SHEEN

131
Q

What kind of hemolysis due E. coli produce?

A

beta hemolysis

132
Q

What is the virulence factor in E. coli for neonatal meningitis?

A

K1 capsular antigen

133
Q

What is the main treatment for TREATMENT-RESISTANT SCHIZOPHRENIA?

(poor response to at least 2 meds; continued sx)

134
Q

What are the side effects of clozapine? (4)

A
  • Neutropenia - must monitor CBC
  • Seizures
  • Myocarditis
  • Metabolic syndrome
135
Q

Rubella (“German measles”)

vs.

Measles (Rubeola) … rash differences

A

both are maculopapular, start on face + spread to trunk + limbs

Rubella SPREADS FASTER, but DOES NOT DARKEN OR COALESCE as much as measles

(Rubella also has postauricular/occipital lap)

136
Q

3 viruses with atypical lymphocytes on peripheral smear

A
  1. EBV
  2. CMV
  3. Hepatitis B
137
Q

How long do antibody responses sometimes take to develop in syphilis?

A

4 weeks

so RPR, VDRL and fluorescent treponemal Ab absorption tests can be negative

nontreponemal (RPR and VDRL) are more commonly false-negative during this time

138
Q

What is the “skin snip” test used to diagnose?

A

Onchocerciasis

river blindness via black fly bite

139
Q

Main clostridium perfringens toxin involved in gas gangrene?

A

alpha toxin

has phospholipase/lecithinase activity > activates DAG and arachidonic acid pathways > TXA2, PAF, IL-8 and edema

140
Q

What is RSV’s virulence factor for cell entry?

A

a fusion protein

141
Q

2 tx for RSV infection

A

Palivizumab - anti-fusion protein

Ribavirin - guanosine analog halts RNA synth

142
Q

Bacterial infections in patients with LOW B CELLS

A

Anything encapsulated: picture all the sketchy capsules…

“Please SHiNE SKiS”

Pseudomonas
S. pneumo
Hib
Neisseria
E coli
Salmonella
Klebsiella
Strep group B (agalactiae)
143
Q

Bacterial infections in patients with LOW GRANULOCYTES

A 
Staph
Burkholderia cepacia
Pseudomonas
Serratia
Nocardia

are all CATALASE+ … affect CGD pts without NADPH oxidase bc break down the H2O2 they produce

144
Q

2 bacteria described as “branching + filamentous”

differentiation + tx?

A

both NOCARDIA and ACTINOMYCES (both Gram+)

nocardia = aerobe in soil
actinomyces = anaerobe in oral, GI, repro tract

for tx remember “SNAP”

Sulfonamides > Nocardia (TMP-SMX)
Actinomyces > Penicillin

145
Q

What stain for acid-fast bacteria is cheaper + more sensitive for screening than Ziehl Neelsen?

A

Auramine-Rhodamine

146
Q

What are the 3 aerobic bacteria to remember?

picture the bellows from sketchy

A

Nocardia
Pseudomonas
MycoBacterium

“Nagging Pests Must Breathe”

147
Q

What are the urease positive microbes?

for the mnemonic, think of what happens when you have struvite stones

A

Pee CHUNKSS

Proteus
CRYPTOCOCCUS (1 fungi!)
H pylori
Ureaplasma
Nocardia
Klebs
S epidermidis + S saprophyticus
148
Q

Catalase+ organisms (10)

A

CATS Need PLACESS to Belch Hairballs

Pseudomonas
Listeria
Aspergillus (fungi!)
Candida (fungi!)
E coli
Staph
Serratia
Burkholderia cepacia
H pylori

picture the cats in sketchy; degrades H202 to water and O2 BUBBLES

149
Q

Aside from the orofacial abscesses w/ sinus tracts…

what kind of infection can Actinomyces cause?

A

can cause infections in pts with IUDs leading to PID

tx with penicillin

(remember yellow “sulfur granules”)

150
Q

What microbe can mimic TB infection in immunocompromised pts? Differential?

A

Nocardia > cavitary lung lesions

will be negative on skin PPD test

151
Q

cell wall mutation conveying resistance to vancomycin

A

D-Ala becomes D-LACTATE in vanc-resistant microbes

152
Q

What is TRANSFORMATION in bacterial genetics?

Which bacteria do it, mostly? What can prevent it?

A

a bacterium BINDS + IMPORTS short pieces of naked bacterial chromosomal DNA (from other lysed bacteria) and then expresses its genes

SHiN bacteria (S pneumo, H. flu, Neisseria)

DNase degrades naked DNA + prevents

153
Q

What type of CONJUGATION in bacterial genetics results in NO transfer of CHROMOSOMAL DNA?

what is transferred and how?

A

F+ x F- conjugation

F+ plasmid with genes for SEX PILUS allows an “F+” bacterium connect to an “F-“ bacterium without the plasmid

a SINGLE STRAND of the double-stranded plasmid is transferred across the “mating/conjugal bridge” + then made double-stranded

(no transfer of chromosomal DNA)

154
Q

What type of CONJUGATION in bacterial genetics results in transfer of some CHROMOSOMAL DNA?

what is transferred and how?

A

Hfr x F-

  • F+ plasmid incorporates into the DNA of the F+ cell forming an “Hfr” (high-freq recombination) cell
  • plasmid DNA plus a few flanking chromosomal genes are then transferred from the Hfr cell to an F- cell
  • previously F- cell is still considered F- bc doesn’t have a plasmid, but now has RECOMBINANT dna containing plasmid genes
155
Q

What is TRANSDUCTION in bacterial genetics?

A

transfer of genes via a phage

156
Q

What is GENERALIZED TRANSDUCTION in phage transfer of bacterial DNA?

via what type of phage?

A

a “packaging error” via LYTIC phages

phage infects bacterium > cleaves its DNA > new phage capsids are produced in infected bacterium (some contain phage DNA, some bacterial DNA) > phages are released > phage with bacterial DNA infects new bacterium and transfers old bacterium’s genes to it

157
Q

What is SPECIALIZED TRANSDUCTION in phage transfer of bacterial DNA?

via what type of phage?

A

an “excision” event via LYSOGENIC phages

  1. lysogenic phage infects bacterium and INCORPORATES DNA into bacterial chrom.
  2. phage DNA is EXCISED WITH FLANKING BACTERIAL GENES
  3. new phage capsids can infect other bacteria with PHAGE/BACTERIAL DNA COMBO
158
Q

what 5 BACTERIAL TOXIN genes are transferred via LYSOGENIC PHAGES?

A

ABCD’S

group A strep ERYTHROGENIC toxin
Botulinum toxin
Cholera toxin
Diphtheria toxin
Shiga toxin
159
Q

what sterilization method is used to kill spores?

A

autoclave at 121 C for 15 minutes

160
Q

what molecule does the core of a bacterial spore contain?

A

dipicolinic acid

161
Q

What is TRANSPOSITION in bacterial genetics?

what bacterial process does this play a major role in?

A

a segment of DNA called a TRANSPOSON that can jump from one location to another (from plasmid to chromosome + vice versa)

role in plasmid-mediated transfer of MULTIPLE-ABX RESISTANCE GENES btwn bacteria

ex: Tn1546 carrying vanA gene from VRE to S. aureus

162
Q

what kind of lymphocytes are the atypical lymphocytes in EBV?

A

T-lymphocytes

specifically CD8+

163
Q

Coccidioides immitis

morphology

A

thick-walled spherules with endospores

much LARGER than RBC

(don’t confuse the thick walls for the capsule of Cryptococcus! look for the endospores)

164
Q

Coccidioides immitis

where? causes what?

A

SW united states

transient pulmonary sx in normal pts

progress SKIN, BONE and MENINGES in immunocompromised; “desert rheumatism” ARTHRALGIAS

can cause ERYTHEMA NODOSUM or MULTIFORME

165
Q

Blastomyces dermatitidis

morphology

A

broad-based budding

SAME size as RBC

166
Q

Blastomyces dermatitidis

s/s

A

lung disease can disseminate to…
SKIN / BONE

VERRUCOUS skin lesions look like SCC
forms GRANULOMATOUS nodules

167
Q

special medium for Neisseria gonorrhoeae

its contents and what they inhibit (4)

A

Thayer Martin - chocolate sheep blood agar with…

  1. Vancomycin - gram+
  2. Colistin - gram-
  3. Trimethoprim - gram-
  4. Nystatin - yeast

(VCTN “vacation” from contaminating microbes)

168
Q

Malarial form that is initially transferred by mosquito?

A

Sporozoite

goes to liver and forms a schizont of merozoites

169
Q

Dormant liver malarial form?

A

Hypnozoite

170
Q

Malarial structure containing many merozoites?

In what two places do they form?

A

SCHIZONTS are round collections of merozoites that form in the LIVER and RBCs and rupture to infect more RBCs

(liver schizonts are mefloquine resistant due to mefloquine inactivation in liver; RBC schizonts are killed by mefloquine)

171
Q

Form of malaria that is released into circulation and infects RBCs

172
Q

Which fungi form “SPORANGIA”?

A

Mold fungi such as RHIZOPUS

173
Q

Aside from being round/oval cells with a noticeable polysaccharide capsule…

what is a characteristic of Cryptococcus microscopy?

A

NARROW-based BUDDING

opposed to broad-based in Blasto

174
Q

What prevents SUPERFICIAL Candida infection vs. HEMATOGENOUS spread of Candida?

A

superficial - T-CELLS … so more superficial infections in HIV or similar immune disorder

hematogenous - NEUTROPHILS … so more fungemia/endocarditis in pts with neutropenia (eg, leukemia pt)

175
Q

Whipple disease

microbe, microbial characteristics

A

Tropheryma whippelii

intracellular Gram+ rods (actinomycetes)

176
Q

Whipple disease

s/s

A

Older white male with…

C - Cardiac sx
A - Arthralgias - multiple joints
N - Neurologic sx - incl. psychiatric

Diarrhea/steatorrhea later

(FOAMY WHIPPed cream CAN; macros are foamy)

177
Q

Whipple disease

histo (2 special features of affected cells)

A

SI mucosa with FOAMY macrophages that contain GRAM+ RODS and GRANULES that are…

1) PAS-positive
2) DIASTASE-resistant

(granules = lysosomes + partially digested microbes)

178
Q

Tx of diphtheria (2 things)

A
  1. Diphtheria antitoxin - preformed Ab

2. Abx - penicillin / erythromycin to decrease toxin formation

179
Q

MCC of community acquired pneumonia

what about in HIV pts?

A

S. pneumo

SAME in HIV pts!

180
Q

HPV strains for skin warts (verruca vulgaris)

181
Q

HPV strains for anogenital warts

182
Q

How do NEURAMINIDASE inhibitors affect viral function?

A

inhibit VIRION RELEASE

183
Q

Abx tx of Salmonella enterica causes what?

A

prolonged fecal excretion of the organism

184
Q

What is a TYPE III SECRETION SYSTEM?

which microbes have it?

A

“injectisome”

needle like protein appendage that facilitates direct delivery of toxins from certain GRAM-NEG microbes

PESS - Pseudomonas, E coli, Shigella, Salmonella

185
Q

Mechanism of Staph Scalded Skin Syndrome

A

epidermolytic exotoxins “EXFOLIATIN A + B”

cleave desmoglein-1 > similar sx to pemph vulgaris

(one is chromosomally encoded, other is plasmid)

186
Q

Possible CV consequence of croup?

A

Pulsus paradoxus secondary to severe upper airway obstruction

187
Q

Action of hemagglutinin

A

binds sialic acid and promotes viral ENTRY

188
Q

surface molecule in ALL paramyxoviruses + its function

A

F (fusion) protein

causes resp. epithelial cells to fuse and form multinucleated giant cells

189
Q

Enterococcal endocarditis

in whom? how?

A

OLDER MEN after CYSTOSCOPY

can also be by colonoscopy, or obstetrics procedures

190
Q

Enterococci

main types of infections (4)

A
  1. UTI
  2. Endocarditis - after cystoscopy in old man
  3. Intraabdominal
  4. Pelvic
  5. Wound
191
Q

What is viral recombination?

What kind of viruses can do it?

A

NON-SEGMENTED dsDNA viruses (eg, HSV)

exchange of genes by CROSSOVER within homologous regions

progeny AND ALL SUBSEQUENT progeny will have recombined genomes w/ traits from both parents

192
Q

What is phenotypic mixing in viruses?

A

when viruses co-infecting a cell exchange NUCLEOCAPSID / ENVELOPE proteins only

immediate progeny will have different outer surface proteins, but subsequent progeny will not because no genomic change

193
Q

what’s transformation in VIROLOGY (not bacterial genetics)?

A

incorporation of viral DNA into host chromosome (“lysogeny”)

194
Q

What microbe enhances Staph aureus hemolysis?

How?

A

Strep agalactiae

CAMP factor - a phospholipase that enhances beta-hemolysins

195
Q

Disseminated gonococcal infection

triad

A
  1. Polyarthralgia - moves around, resolving spontaneously in one joint and then appearing in others
  2. TenoSynovitis - tenderness along tendons
  3. Dermatitis - PAINLESS PUSTULES on limbs

(remember it’s a triad but it’s PTSD = Polyarthralgia (or purulent arthritis), TenoSynovitis and Dermatitis)

*USMLE* (28 decks)

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