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Title: Antimicrobial resistance of Listeria monocytogenes isolated from a poultry further processing plant

item Lyon, Steven
item Berrang, Mark
item Cray, Paula
item Meinersmann, Richard - Rick

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2008
Publication Date: 6/1/2008
Citation: Lyon, S.A., Berrang, M.E., Cray, P.J., Fletcher, D.L., Meinersmann, R.J. 2008. Antimicrobial resistance of Listeria monocytogenes isolated from a poultry further processing plant. Foodborne Pathogens and Disease. 5(3):253-259.

Interpretive Summary: Listeria monocytogenes is a human pathogen that can be found on chicken meat and chicken meat products. In an earlier study, 157 L. monocytogenes isolates were recovered from a commercial chicken cooking plant. These isolates were subjected to a molecular subtyping technique which subdivided them into 14 distinct subtypes; some subtypes wee repeatedly detected in the plant and therefore labeled as persistent in that environment. The antimicrobial resistance of L. monocytogenes has not been widely reported and the relationship of antimicrobial resistance to molecular subtype or persistence in a chicken cooking plant has not been explored. We measured the resistance of all 157 isolates to a panel of 19 antimicrobial drugs and compared the reistotypes within and across molecular subtypes. All isolates were susceptible to antibiotics except for ceftriaxone (153 isolates, 97%), oxacillin with 2% NaCl (142 isolates, 90%), ciprofloxacin (59 isolates, 37%), clindamycin (43 isolates, 27%), tetracycline (5 isolates, 3%), linezolid (3 isolates, 2%) and trimethoprim/sulphamethoxazole (1 isolate, 0.06%). Aside from drugs to which L. monocytogenes is innately resistant, resistance to antimicrobials was not highly prevalent. With the exception of tetracycline resistance, the different antimicrobial resistance patterns were scattered across several molecular subtypes. Tetracycline resistance was only found in isolates from one particular molecular subtype. No relationship was noted between the persistence of an isolate in the chicken cooking plant and antimicrobial resistance. These results show that antimicrobial resistance does not seem to be correlated with molecular subtype or increased survival and persistence within a chicken cooking plant.

Technical Abstract: The objective of this study was to compare antimicrobial resistance profiles of distinct types of Listeria monocytogenes isolated from a commercial poultry cooking plant. One hundred fifty seven L. monocytogenes isolates representing 14 different ActA types were tested for susceptibility to 19 antimicrobial drugs using the broth microdilution method. All isolates were susceptible to antibiotics except for ceftriaxone (153 isolates intermediate or resistant), oxacillin with 2% NaCl (142 isolates resistant), ciprofloxacin (59 isolates intermediate or resistant), tetracycline (5 isolates resistant), clindamycin (43 isolates intermediate), linezolid (3 isolates intermediate) and trimethoprim/sulphamethoxazole (1 isolate intermediate). Prevalence of antimicrobial resistance was low among all the 14 types. There was a low amount of diversity of resistotypes, which were defined in this study as subdivisions of ActA types according to antimicrobial resistance profiles of the isolates. The 5 tetracycline resistant isolates represented all the members of one ActA type in Lineage II. Antimicrobial resistance is not highly prevalent in L. monocytogenes from a poultry further processing environment. Types of L. monocytogenes as distinguished by ActA sequencing do not predict antimicrobial resistance except possibly for tetracycline resistance. L. monocytogenes types that persist in a poultry cook plant are not related to antimicrobial resistance and excluding tetracycline resistance, antimicrobial resistance does not seem to differ according to ActA type or lineage.