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Title: Isolation method (direct plating or enrichment) does not affect antimicrobial susceptibility of Campylobacter from chicken carcasses

Author
item LADELY, SCOTT - Food Safety Inspection Service (FSIS)
item Meinersmann, Richard - Rick
item Plumblee Lawrence, Jodie
item FEDORKA-CRAY, PAULA - Former ARS Employee

Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2016
Publication Date: 3/21/2016
Citation: Ladely, S.R., Meinersmann, R.J., Plumblee, J., Fedorka-Cray, P.J. 2016. Isolation method (direct plating or enrichment) does not affect antimicrobial susceptibility of Campylobacter from chicken carcasses. Journal of Food Safety. doi: 10.1111/jfs.12279.

Interpretive Summary: The Food Safety and Inspection Service recently changed their protocol for isolating Campylobacter for use in the National Antimicrobial Resistance Monitoring System. We were able to compare results from poultry carcasses in which both methods - direct plating or enrichment culturing - were compared. There were 291 carcasses in which Campylobacter was isolated by both methods. C. coli was recovered more frequently using enrichment. Even though C. coli tended to be more resistant to antimicrobials, the overall resistance patterns were not significantly different between the two culture methods.

Technical Abstract: To determine if Campylobacter isolation method influenced antimicrobial susceptibility results, the minimum inhibitory concentrations (MIC) of nine antimicrobials were compared for 291 pairs of Campylobacter isolates recovered from chicken carcass rinse samples using direct plating and an enrichment method. Among the isolates 64.1% were C. jejuni, 35.7% were C. coli, and 0.2% were C. lari. Direct plating yielded significantly less (P< 0.05) C. coli (21.3%) compared to sample enrichment (50.2%). Antimicrobial resistance was most common for tetracycline (41.4%), nalidixic acid (26.3%), and ciprofloxacin (25.9%). Significantly more (P<0.05) C. coli were resistant to nalidixic acid, ciprofloxacin, gentamicin, azithromycin, and erythromycin as compared to C. jejuni isolates. Nonparametric bootstrap analysis of antimicrobial MICs showed no significant differences between direct plating and the enrichment method for any of the antimicrobials tested. These data indicate that bacterial isolation method can bias Campylobacter species recovery. However, isolation method did not significantly affect antimicrobial susceptibility results of C. jejuni or C. coli recovered from broiler carcasses.