Micro Basics (media, microscopy, etc) Flashcards
AST results are dependent on:
1) Inoculum density
–standard density should be used
2) pH of media
3) Cation concentration of media
4) Supplements / abx in media
–NaCl
–lysed blood
5) Thymidine content in media
6) Incubation conditions
–CO2, O2, temp
7) Incubation length
8) Concentration of abx
Media cation concentration that is too high results in __ zone sizes
Smaller
Cefoxitin is a surrogate for __ in S. aureus testing?
mecA mediated oxicillin R
Media that is too thin results in __ zone sizes
too large
Antibiotic concentration gets smaller/larger as distance from the disk increases
Smaller. The highest concentration is next to the disk (abx diffuses out).
What is the most common reason for antibiotic conditions to fail?
1) Bag/jar not sealed
2) Catalyst inactive
SPS is used for blood culture collection because…
1) anticoagulase
2) inactivates neutrophils
3) inactivates some abx
4) precipitates some complement
Waiting more than 15 minutes to incubate the plate after dropping abx disks leads to larger / smaller zone sizes?
Larger
Campy need what gas concentrations to grow?
5% O2, 10% CO2, 85% Nitrogen
Bacteria with capsules
Some Killers Have Pretty Nice Capsules Yo Bebe
Strep pneumo
Kleb
H flu b
Pseudo aeruginosa
Neisseria men
Crypto neoformans / Cholera
Yersinia pestis
Bacillus anthracis
Bordetella pertussis
Bacteria with cAMP toxins
CAMP
Cholera
Anthrax
E coli (M turned sideways)
Pertussis
Bacteria with phage vir factors
Urease pos orgs
PUNCH KISS
Proteus
Ureaplasma
Nocardia
Cryptococcus
Helicobacter
Klebsiella
Staph saprophyticus
Staph epidermidis
Oxidase pos orgs
VP CHEN LAMB
V. cholera
Pasteurella / Pseudomonas / Plesiomonas
Campylobacter
H. pylori
Exclude Enterobacteriaceae
Neisseria
Legionella
Aeromonas
Moraxella
Brucella
Eikenella
Kingella
IMViC
Indole/Methyl Red/Vogues Proskauer/Citrate
1) Indole
–Peptone broth + Kovac’s reagent = red on top of tube
2) MR
–5.0 ml buffered peptone broth
–Acid from glucose fermentation
–48 hour incubation then Methyl Red indicator = Red+
3) VP
–Peptone broth from MR test (before MR added)
–Mixed acid fermentation from glucse
–48 hour incubation then alpha-naphthol + KOH = Red on top+
4) Citrate
–Bromothymol blue + Simmons agar
–Blue after incubation = +
Indole+ = Ecoli / P. vulgaris / K. oxytoca
MR= = Kleb / Enterobacter
MR+/VP+ = S. aureus
VP+= Kleb/Enterobacter/Moraxella
Cit+ = Salmonella / Kleb / P. mirabilis / Citrobacter / Enterobacter / Serratia
Citrate positive
VPPPECKSS
Vibrio cholera
P. mirabilis / Providencia / Pseudomonas
Enterobacter
Citrobacter
Kleb
Salmonella / Serratia
Citrate negative
SEEY
Shigella
Ecoli
Edwardsiella
Yersinia
Purpose of GNR enrichment media
-Extend lag phase of normal flora and decrease lab phase of pathogens
Examples:
GN broth
Tetrathionate
Selenite-F broth
EMB
Eosin Methylene Blue
-inhibits GP
–Holt-Harris (lactose + sucrose)
–Levine’s (sucrose only)
NLF = clear (except for sucrose fermenters P. vul and Serratia)
LF = black/purple metalic
MAC
-More inhibitory than EMB
-Neutral red, crystal violet, bile salts
-Lactose
SS Agar
-Neutral red, bile salts, brilliant green, sodium citrate
-H2S indicators = sodium thiosulfate + ferric citrate
-Lactose
–LF = red
–NLF = clear
XLD agar
-Phenol red, deoxycholate, citrate
-Xylose, lactose, sucrose
-H2S indicator = ferric ammonium citrate + sodium thiosulfate
–Salmonella = red w/ black center
–Shigella = red
HEK
-Bromothymol blue, acid fuchsin, bile salts
-Lactose, sucrose, salicin
-H2S indicator = ferric ammonium citrate + sodium thiosulfate
–Salmonella = blue-green w/ black center
–Shigella = clear/gree
-Proteus = yellow
-Other GNR = orange/pink
BS Agar
-Bismuth Sulfite, dextrose, ferrous sulfate
-Best for S. typhi and lac+ Salmonella
-S. typhi = black colony w/ black zone and metallic sheen
-Other Salmonella = green
