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Int J Food Microbiol. 2016 Jun 16;227:1-5. doi: 10.1016/j.ijfoodmicro.2016.03.017. Epub 2016 Mar 17.

Antimicrobial susceptibility of Clostridium difficile isolated from food animals on farms.

Author information

1
Bacterial Epidemiology and Antimicrobial Resistance Research Unit, United States Department of Agriculture, Agricultural Research Service, 950 College Station Rd, Athens, GA 30605, USA. Electronic address: sutawee.thitaram@fsis.usda.gov.
2
Department of Food Science and Technology, University of Georgia, Athens, GA 30602, USA.
3
Poultry Microbiological Safety and Processing Research Unit, United States Department of Agriculture, Agricultural Research Service, 950 College Station Rd, Athens, GA 30605, USA.
4
Bacterial Epidemiology and Antimicrobial Resistance Research Unit, United States Department of Agriculture, Agricultural Research Service, 950 College Station Rd, Athens, GA 30605, USA.
5
Center for Epidemiology and Animal Health, United States Department of Agriculture, Animal and Plant Health Inspection Service, 2150 Centre Ave, Building B, Fort Collins, CO, 80526, USA.

Abstract

Clostridium difficile is commonly associated with a spectrum of disease in humans referred to as C. difficile-associated disease (CDAD) and use of antimicrobials is considered a risk factor for development of disease in humans. C. difficile can also inhabit healthy food animals and transmission to humans is possible. As a result of the complexity and cost of testing, C. difficile is rarely tested for antimicrobial susceptibility. A total of 376 C. difficile strains (94 each from swine and dairy feces, and 188 from beef cattle feces) were isolated from healthy food animals on farms during studies conducted by the National Animal Health Monitoring System. Using the Etest (AB Biodisk, Solna, Sweden), samples were tested for susceptibility to nine antimicrobials implicated as risk factors for CDAD (linezolid, amoxicillin-clavulanic acid, ampicillin, clindamycin, erythromycin, levofloxacin, metronidazole, rifampicin, and vancomycin). Vancomycin was active against all isolates of C. difficile (MIC90=3.0μg/ml) while almost all isolates (n=369; 98.1%) were resistant to levofloxacin. With the exception of vancomycin, resistance varied by animal species as follows: linezolid (8.5% resistance among swine versus 2.1 and 1.1% resistance among dairy and beef, respectively), clindamycin (56.4% resistance among swine versus 80% and 90.9% resistance among dairy and beef, respectively), and rifampicin (2.1% and 0% resistance among swine and dairy cattle isolates, respectively versus 14.3% resistance among beef isolates). Regardless of species, multiple drug resistance was observed most often to combinations of clindamycin and levofloxacin (n=195; 51.9%) and ampicillin, clindamycin and levofloxacin (n=41; 10.9%). The reason for the variability of resistance between animal species is unknown and requires further research.

KEYWORDS:

Antimicrobial susceptibility; Beef cattle; Clostridium difficile; Dairy cattle; Swine

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