T11&12 Medical Bacteriology & Bacterial Identification

endospore - found in what gram

gram positive

conjugation

sex pili

transformation

uptake free DNA

transduction

bacteriophage

vesiduction

extracellular vesicles

gram-negative bacteria characteristics

• LPS endotoxin lipid A (heat-stable)

• thin peptidoglycan

• outer and inner membrane

gram-positive bacteria characteristics

• thick peptidoglycan → sensitive to antibiotic

• teichoic acid

acid-fast bacteria - characteristics

mycolic acid

LPS recognized by what TLR

TLR4

best pH for organism growth

6-8

best temperature for pathogenic growth

37 degrees

average generation time for bacteria

1-3 hours

generation time for E. coli

20 minutes

selective media

suppress unwanted microbes

differential media

distinguish colonies

enrichment media

encourage growth of desired

hemoculture

• gray tab: aerobic for adults

• gold tab: anaerobic

• pink tab: aerobic for kids

• red tab: TB/fungus

gram staining procedure

crystal violet → iodine → alcohol → safranin

acid-fast staining types

• ziehl-neelsen (hot)

• kinyoun (cold)

• auramine-rhodamine (fluorescence)

chlamydiae - stain to use

H&E

rickettsiae - stain to use

giemsa

mycoplasma - stain to use

DAPI/Hoechst

legionella - stain to use

silver

auramine-rhodamine staining - used for

M. tuberculosis

horizontal transmission

contact, sex, respiratory drops

vertical transmission

placenta, delivery, breastfeeding

fomites transmission

tetanus

vehicle transmission

food, water, aerosol

vector transmission

• mechanical: no bite

• biological: bite

examples of sterile sites

blood, CSF

possible normal skin flora contaminations

Bacillus, Corynebacterium, P. acnes, Coagulase negative Staphylococci

transient bacteremia

caused by medical staff but immune fights back

intermittent bacteremia

chronic lesion → eliminate bacteria → re-enter blood until chronic lesion healed (pneumonia)

continuous bacteremia

low levels of bacteria always in blood (infective endocarditis, gout)

transport within how many hours

2 hours

transport media

• carry blair

• stuart’s/amies without charcoal

• thioglycolate

• purple tube (EDTA)

carry blair transport media

stool sample

stuart’s/amies without charcoal transport media

• for all

• add inert gas for anaerobe

thioglycolate transport media

anaerobe

suprapubic aspirate

suspect anaerobe

catheter urine sample

bedridden

transport of aerobic samples

4 degrees except CSF and hemoculture

transport of anaerobic samples

room temperature with nitrogen, carbon dioxide, soft agar

hemoculture guidelines

adults 5-10 mL per bottle 2 bottles within 24 hours

why can’t the green blood tube be used

heparin inhibits PCR → false negative

nonselective culture media examples

• blood agar

• chocolate agar

• mueller-hinton agar

• thioglycolate broth

selective, differential culture media examples

• MacConkey agar: selective for gram-negative, differential for lactose-fermenting

• Mannitol salt agar: selective for Staphylococci, differential for S. aureus

• Xylose lysine deoxycholate agar: selective and differential for Salmonella and Shigella

• Lowestein-Jensen medium: selective for mycobacteria

• Middlebrook agar: selective for mycobacteria

urine specimen bacterial colony interpretation

• colony less than 10^4 CFU → no further test

• unless: S. saprophyticus, Salmonella, Burkholderia pseudomallei → antibiotic susceptibility test and identification

urine find 1 species - ignore when

• 10^4 in midstream

urine fine 2 species - ignore when

• second species < 10^5 in midstream

• first species greater than equal to 10^5 in catheter

urine find 3 species - ignore when

• second species < 10^5 in midstream

• ignore if all three are pathogen in catheter

urine find 3 species - test again when

• all three >/< 10^5 both midstream and catheter

catalase test

• positive: Staphylococcus

• negative: Streptococcus

• produce gas bubble

oxidase test

• positive: Vibrionaceae

• negative: Enterobactericeae

• produce indophenol blue

coagulase test

• positive: S. aureus

• negative: Staphylococcus spp.

• produce thrombin

antibiotic susceptibility test - diffusion method

select drug to treat bacteria

antibiotic susceptibility test - dilution method

to find drug concentration