microbio/ immuno usmle

staph pneumonia

bronchopneumonia

• 2nd most common secondary pneumonia

• risk of abscess

• grape cluster gram +

• yellow colonies

• catalase/ mannitol +

• group A proteins

• tx; penicillin (MSSA)/ vanco or  linezolid (MRSA)

H influenza pneumonia

bronchopneumonia

• common secondary pneumonia / COPD 

• chocolate agar

• IgA protease

• tx; amoxiclav/ 2nd-3rd gen cephalo

P aerogunosa pneumonia

bronchopneumonia

• seen in CF pts

• humid environments

• catalase/ oxydase +

• non lactose fermenting

• blue- green pus/ sweet odour 

• tx; pip tazo/ 3-4th gen cephalo

moraxella catarrhalis pneumonia

bronchopneumonia

• CAP- COPD

• diplococci

• non maltose fermenter

• biofilm

• tx; amoxiclav/ 2nd gen cephalo

legionella pneumonia

bronchopneumonia

• CAP

• COPD/ immunosupressed

• water

• silver stain / gram negative

• tx; fluriquinolone/ macrolides

strep pneumonia

lobar pneumonia

• most common overall

• adults/ elders

• encapsulated diplococci in chains

• optochin sensitive

• catalase -

• tx; penicillin/ 3rd gen cephalo

kleb pneumonia

lobar pneumonia

• enteric flora aspiration

• immunosuppressed/ alcoholics

• risk of abscess 

• lactose fermenter

• tx; fluoroquinolones/ 3rd gen cephalo

mycoplasma pneumonia

atypical pneumonia

• most common atypical

• young adults living in crowded spaces

• no gram stain

• papular rash

• tx; macrolide/ doxy/ fluroquinolones

chlam pneumonia

atypical pneumonia

• young adults

• cytoplasmic inclusion bodies

• tx; doxy/ macros

RSV pneumonia

atypical pneumonia

infants

CMV pneumonia

atypical pneumonia

• double stand dna virus

• immunosupp

• tx; ganciclovir/ foscarnet

influenza pneumonia

atypical pneumonia

• elderly/ immunosupp/ COPD

• helical ssRNA

coxiella pneumonia

atypical pneumonia

• animals exposure/ farmers 

• gram negative

• tx; doxy/ erythromycin

bacterial meningitis characteristics

cloudy CSF w/ raised wbc/protein/ pressure but low glucose

group b strep meningitis

• neonates

• aka strep galactiae 

• gram + in chains

• bacitracin resistant

• hippurate +

• tx; penicillin/ 1st-2nd gen cephalo

e coli meningitis

• neonates

• lactose fermenter

• k1 polysaccharide capsule

• tx; ampicillin/ 3rd gen cephalo

listeria monocytogenes meningitis

• neonates

• gram +

• spore forming

• tumbling motility

• cold resistant

• tx; ampicillin

strep pneumonia meningitis

• chained diplococci

• bile soluble

• optochin sensitive 

• tx; penicillin/ 3rd gen cephalo

neisseria meningitis

• infants- young adults/ people living in close quarters

• gram - diplococci

• maltose/ glucose fermenter

• adhesins, IgA 1 protease and capsular polysaccharide 

• tx; 3rd gen cephalo/ penicillin G

meningitis gram - rods

• immunosupp

• e coli/pseudomonas/ kleb

viral meningitis charcateristics

clear csf w/ raised wbc and

raised to normal pressure and protein

HSV2 meningitis

• infants/ immunosupp

• tx; acyclovir

enterovirus meningitis

• esp cocksackie for infants

• most common cause of viral meningitis

• linear isohedral

mumps meningitis

• unvaccinated infants

• parotid swelling

• self limiting

CMV meningitis

• aka herpes 5

• immunosupp

• similar presentation to EBV but - monospot test

• large atypical cells with owl eye appearance 

• tx; ganciclovir

unique feature parvo B19

single strand DNA virus

unique feature reovirus

double stand rna virus

unique feature listeria

tumbling motility

intracellular

unique feature histoplasma capsulatum

intracellular yeast within macrophagessmaller than rbc

unique feature coccidioides immitis

spherule filled with endospore

larger than rbc

unique feature blastomyces dermatididis

broad based budding yeast

unique feature coccidioides immitis

spherules filled with endospores

unique feature clostriodium perfringens

double zone hemolysis blood agar

list of encapsulated organisms

SHINE SKIS

• strep pneumo

• h influenza b

• neisseria meningitis 

• e coli (sometimes)

• salmonella

• kleb pneumonia

• group b strep (agalactiae)

type 1 hypersensitivity

immediate- IgE/ basophils/ mast cells/ histamine

later- cytokines/ ige

anaphylaxis/ asthma

type 2 hypersensitivity

atb vs self

thyroiditis, goodpasture syndrome, pernicious anemia, rheumatic fever, myastenia gravis

type 3 hypersensitivity

atb vs antigen

post strep glomerulonephritis, SLE, polyarteritis nodosa

type IV hypersensitivity

T cell response (CD4/8)

TB, contact dermatitis, GvHD

vibrio cholera

watery non bloody diarrhea

• gram -  bacilli

• contaminated water/ uncooked sea food

• acid labile/ oxidase +

• choleratoxin

• raised cAMP

• rice water stool

• tx; doxy/ azithromycin

ETEC

watery non bloody diarrhea

• aka e coli 

• heat labile toxin ->raised cAMP-> loss of Cl and NaCl 

• travellers diarrhea

• supportive tx

giardia lamblia

watery non bloody diarrhea

• foul fatty stool

• camping

• malabsorption/ weight loss

• water borne

• Direct fluorescent antibody testing 

• tx; tinidazole

rotavirus

watery non bloody diarrhea

• peds/ cruise ships

• dehydration

• linear isocahedral (double/ triple layer)

• double strand rna virus

norovirus

watery non bloody diarrhea

• peds/ cruise ships

• rna calcivirus

shigella

bloody diarrhea

• gram - bacilli

• low ID50 -> low dose required to cause infections

• shiga toxin

• invasion fo M cells

• HUS (hemolytic uremic syndrome)

• reactive arthritis

• tx; supportive or fluriquinolones/ 3rd gen cepahlo if severe

salmonella

bloody diarrhea

• non typhoid- poultry/ turtle, osteomyelitis in sickle cell pts

• gram -

• non lactose fermenter

• produce hyrogen sulfide

• vomiting

• tx; fluoroquinolone if non typhi

campylobacter jejuni

bloody diarrhea

• gram - bacilli

• undercooked poultry/ unpasteurized milk

• can trigger GBS

• reactive arthritis

• oxidase +

• tx; macrolides

EHEC

bloody diarrhea

O157 H7

• shiga like toxin

• no sorbitol fermentation

• hamburger + HUS (kids)

• gram - bacilli

• flagellated

• indole +

• lactose fermenter

• fecal oral (raw meat/ water/ produce)

• LS/ST toxins

• rbc destruction -> can progress to bloody diarrhea O157 H7/ AKI

• ↑ Schistocytes on blood smear

• tx; eculizumab/ supportive

entamoeba histolytica

bloody diarrhea

• flask shaped ulcer

• liver abscess

• fecal oral protozoan

• water borne

• incubation period up to a month

• tx; nitromidazole

staph aureus diarrhea

toxin mediated/ preformed

• meats/ mayo

• rapid onset

• coagulase +

• gram + cocci in cluster

• tx; flucoxacillin

bacillus cereus diarrhea

toxin mediated/ preformed

• rice

• emetic/ diarrheal

• gram + bacilli

• spore/ enetrotoxin

• supportive care

vibri/ hep A diarrhea

shellfish

c diff

hospitalized/ antibio

• toxic megacolon

entamoeba histolytica

liver abscess + RUQ pain

diarrhea

vibrio vulnificans/ para haemoliticus

wound infection/ septicemia associated with shellfish

B lactams atb

• pneicillin

• cephalo

• carbapenems

• monobactams

penicillin

• “ -illin”

• bind to penicillin binding proteins -> crosslink peptidoglycan layer

cepahlosporins

5 gen

bind to penicillin binding proteins -> crosslink peptidoglycan layer

1st gen cephalo

• cephalexin, cefazolin

• vs gram +

• B lactamase sensitive

2nd gen cephalo

cefuroxime, cefaclor

3rd gen cephalo

• ceftriaxone, cefixime

• vs gram -

• B lactamase resistant

4th gen cephalo

cefepime

5th gen cephalo

ceftaroline

carbapenems

• imipenem, meropenem…

• bind to penicillin binding proteins -> crosslink peptidoglycan layer

monobactams

• aztreonam

• bind to penicillin binding proteins -> crosslink peptidoglycan layer

glycopeptides

• vancomycin, bacitracin

• Bind to D-alanyl-D-alanine section of peptidoglycan precursor → inhibited peptidoglycan synthesis

• bacteriostatic vs c diff

lipopetide

• daptomycin

Lipid portion binds to bacterial cytoplasmic membrane -> intracellular K+ efflux -> depolarization membrane

aminoglycosides

• gentamicin/ “icin”

• inhibit initiation complex -> protein mistranslation

tetracycline

• doxy/ “cycline)

• Block incoming aminoacyl-tRNA with amino acids → ↓ protein synthesis

macrolides

• eryhtromycin, clarythromycin, erythromycin

• Bind to 23S rRNA → inhibition of transpeptidation, translocation, and chain elongation → ↓ protein synthesis

lincosamides

• clindamycin

• Impair transpeptidation → inhibition of chain elongation → ↓ protein synthesis

• Increase opsonization and phagocytosis

Inhibit alpha toxin expression

oxazolidinones

• linezolid

• Prevent association of 50S with 30S subunit (23S RNA)→ impairment of initiation complex formation → early interruption of protein synthesis

• bacteriostatic except strep

fluoroquinolones

• “-xacin”

• Prevent association of 50S with 30S subunit (23S RNA)→ impairment of initiation complex formation → early interruption of protein synthesis

• bacteriostatic except strep

nitroimidazoles

• metronidazole/ tinidazole

• free radical formation-> single strand breaks in DNA molecules

• pro drug

sulfonamides

• sulfadiazine

• decrease DNA methylation

rifamycin

• rifampin, rifabutin, rifaximin

• Block mRNA synthesis via inhibition of bacterial DNA-dependent RNA-polymerase → ↓ protein synthesis

• bacteriostatic and bactericidal

measles

incubation period up to 2 weeks

koplik spots + 3Cs

rash starting at hair line

tx vit A

mumps

no rash

parotitis

rubella

longest incubation

rash face then down

arthralgia/ arthritis