A chromogenic plating medium for isolating Escherichia coli O157:H7 from beef.
There was no significant difference (P > 0.05) in the percentages of Escherichia coli O157:H7 cells recovered on BCM O157:H7 (+) agar (69.7%) and MacConkey sorbitol agar containing 5-bromo-4-chloro-3-indoxyl-beta-D-glucuronic acid (MSA-BCIG) (76.8%) vs Tryptic soy agar. Three E. coli O157:H7 strains (ATCC 35150, 43890 and 43894) were separately inoculated into raw ground beef at low (mean 0.32 cfu g-1) and high (mean 3.12 cfu g-1) levels. Using the United States Department of Agriculture (USDA) m-EC + novobiocin enrichment broth, BCM O157:H7 (+) medium surpassed MSA-BCIG agar with overall percentage sensitivities for BCM O157:H7 (+) of 92.1 and 94.4 compared with 52.6 and 84.7 for MSA-BCIG at low and high levels, respectively. A comparison of BCM O157:H7 (+) and MSA-BCIG agars using naturally contaminated beef samples was made utilizing presumptively positive enrichment broths previously identified by rapid methods. The E. coli O157:H7 cells in these broths were concentrated with Dynabeads anti-E. coli O157 before inoculating the agars. The respective percentage sensitivity and specificity values were 90.0 and 78.5 for BCM O157:H7 (+) and 70.0 and 46.4 for MSA-BCIG. Thus, under identical pre-plating conditions, BCM O157:H7 (+) medium displayed a greater sensitivity than MSA-BCIG for detecting E. coli O157:H7 in artificially inoculated beef, and both greater sensitivity and specificity upon examining naturally contaminated beef samples.
Restaino
L
L
R & F Laboratories, West Chicago, IL 60185, USA.
Frampton
E W
EW
Turner
K M
KM
Allison
D R
DR
D000818:Animals; D001431:Bacteriological Techniques; D002417:Cattle; D002863:Chromogenic Compounds; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry; D019453:Escherichia coli O157 / Q000254:growth & development* / Q000302:isolation & purification*; D006801:Humans; D008461:Meat Products / Q000382:microbiology*; D012680:Sensitivity and Specificity
D002863:Chromogenic Compounds; D003470:Culture Media