|Headrick, Marcia - FDA - CVM|
Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: March 18, 2003
Publication Date: May 18, 2003
Citation: Cray, P.J., Headrick, M. 2003. Phenotype affects antimicrobial resistance profiles of escherichia coli isolated from chicken rinsates. American Society for Microbiology. Abstract. Z-040. P. 193. Technical Abstract: Introduction: Isolation of Escherichia coli can be facilitated by the use of selective or chromogenic media. According to the manufacturer, E. coli colonies appear blue-green (BG) on Chromagar ECC. We found that E. coli can also appear as cream (C) or blue-cream (BC) colonies. In this study, we examined these three different colony phenotypes that appeared on Chromagar ECC and their associated antimicrobial resistance profiles. Methods: E. coli was isolated from chicken carcass rinses after direct plating of rinsate (n=627) onto Chromagar ECC and overnight incubation at 37C. One BG colony was selected per plate if a C and/or BC isolate could also be selected from the same plate until 100 BG colonies were obtained. Isolates were confirmed as E. coli by Vitek. Antimicrobial resistance profiles were obtained by use of broth microdilution as per manufacturer's direction (SensititreTM) using a custom made plate. Additionally, PCR was used to detect the presence of E. coli O157:H7 strains and the virulence markers stx2 and eae. Results: Forty-eight C and 63 BC E. coli confirmed isolates were obtained from the 100 BG plates for comparison. There was little or no resistance to amikacin, ceftriaxone, chloramphenicol, ciprofloxacin, or nalidixic acid for any of the 3 colony phenotypes. Resistance to other antimicrobials differed between the colony phenotypes but the only significant (p<0.05) difference in resistance was seen between the BG (16.0%), C (10.4%), and BC (1.6%) colonies to trimethoprim/sulfamethoxazole. No E. coli O157:H7 was detected, however, 29 BG, 11 C and 12 BC isolates carried the gene for biosynthesis of the H7 antigen. Only one BG isolate was positive for eae, but none of the isolates were positive for stx2. Conclusions: The data indicate that chromogenic media may be used to select different populations of E. coli within the same sample. Further, antimicrobial resistance profiles differ between these populations indicating that care must be taken when interpreting results.