Specimen Processing

Question 1

what are two fastidious organisms that would grow on CHOC?

Answer 1

Haemophilus and Neisseria spp

Question 2

What does CHOC contain that BAP doesn’t and why?

Answer 2

It has the V factor, NAD, released from blood cells because they are lysed in the medium; required by H. influenzae and haemolyticus along with factor X, and alone by parainfluenza

Question 3

What is CNA and what is it selective for?

Answer 3

Colistin Nalidixic acid; for gram positive cocci

Question 4

what do colistin and nalidixic acid suppress the growth of, so that other organisms can grow?

Answer 4

gram negative bacilli

Question 5

what is MTM and what is it selective for?

Answer 5

Modified Thayer-Martin; for gonococci (Neiserria), a gram negative diplococci

Question 6

what are the four components of MTM?

Answer 6

Vanc, Colistin, Nystatin, and TMP

Question 7

what do each of the components of MTM inhibit?

Answer 7

Vanc- inhibits gram positives
Colistin- inhibits GNB
Nystatin- inhibits yeast
TMP- inhibits swarming of Proteus

Question 8

IS EMB selective or differential or both? what for if so?

Answer 8

Eosin Methylene Blue is selective for gram negatives and differential for lactose fermenters and non

Question 9

What is inhibited on EMB and how?

Answer 9

gram positives, by the pH INDICATORS, the eosin and methylene

Question 10

How do lactose fermenters appear on EMB?

Answer 10

black/purple, maybe with metallic sheen

Question 11

Is MAC selective or differential and how?

Answer 11

Both; selective for gram negatives bc the crystal violet and bile salts inhibits gram positives
Differential for lactose fermentation: bright pink or pink colonies

Question 12

what is SMAC and how different from MAC?

Answer 12

Sorbitol MacConkey, it has sorbitol instead of lactose which verotoxin-producing E. coli o157 cannot ferment, producing colorless colonies; Normal E. Coli can ferment sorbitol and produces pink colonies

Question 13

what is the pH indicator in SMAC?

Answer 13

neutral red

Question 14

what is XLD media and its use?

Answer 14

Xylose-lysine deoxycholate; it is selective for enteric gram negative bacilli but not E. coli or Proteus

Question 15

what is inhibited on XLD? by what?

Answer 15

gram positives- by deoxycholate

E. coli and Proteus by citrate

Question 16

What does Shigella look like on XLD and why?

Answer 16

colorless bc it doesn’t ferment xylose or produce H2S

Question 17

Describe Salmonella on XLD

Answer 17

because it ferments xylose then metabolizes peptone, and produces H2S, it produces red colonies with black centers

Question 18

What media is selective and differential for Vibrio?

Answer 18

TCBS: Thiosulfate citrate bile salts & sucrose

Question 19

What in TCBS inhibits gram positives?

Answer 19

bile salts; Vibrio can grow in them

Question 20

How is TCBS differential?

Answer 20

V. cholerae produces yellow colonies, V. parahaemolyticus produces green

Question 21

what color are Salmonella enterica on MAC?

Answer 21

colorless

Question 22

Give the 4 media of choice for processing stool specimens at this facility

Answer 22

BAP, XLD, CAMPY, SMAC

Question 23

Name the media of choice for recovering Vibrio from stool

Answer 23

TCBS: Thiosulfate- Citrate- Bile Salts-Sucrose

Question 24

WHat media best supports Yersinia enterocolitica?

Answer 24

CIN: cefsulodin irgasan novobiocin

Question 25

how does Yersinia enterocolitica appear on CIN?

Answer 25

red bull’s eye

Question 26

Name the selective anaerobic media for Bacteroides spp?

Answer 26

ANA LKV (Laked Kanamycin Vanc)

Question 27

what should be inoculated onto EMB to readily detect E. coli?

Answer 27

urine

Question 28

what transport media is used for stool cultures that will be delayed in receipt at the lab?

Answer 28

Cary-Blair transport medium for outpatient specimens

Question 29

How are Chlamydia species cultured from genital specimens? WHy? How else can they be identified?

Answer 29

using cycloheximide-treated McCoy cells, bc they are obligate intracellular parasites; the most common way to diagnose is with NAATs. Fluorescein-conjugated antibodies can also be used, or cytology can detect chlamydia inclusions in epithelials

Question 30

How are specimens for viral culture best transported?

Answer 30

they require antibiotics to keep bacteria from proliferating and additional nutrient such as fetal calf serum or albumin; refrigerate until can inoculate culture media

Question 31

when should CSF be cultured and what if there is a delay?

Answer 31

Immediately; can place in 3 to 7% CO2 at 37 C but process as soon as possible