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Title: Antimicrobial susceptibility of Clostridium difficile isolated from food animals on farms

Author
item THITARAM, SUTAWEE - Former ARS Employee
item FRANK, JOSEPH - University Of Georgia
item SIRAGUSA, GREGORY - Former ARS Employee
item BAILEY, STAN - Former ARS Employee
item DARGATZ, DAVID - Animal And Plant Health Inspection Service (APHIS)
item LOMBARD, JASON - Animal And Plant Health Inspection Service (APHIS)
item HALEY, CHARLES - Animal And Plant Health Inspection Service (APHIS)
item LYON, STEVEN - Former ARS Employee
item Cray, Paula

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2016
Publication Date: 6/16/2016
Citation: Thitaram, S.N., Frank, J.F., Siragusa, G.R., Bailey, S.J., Dargatz, D.A., Lombard, J.E., Haley, C.A., Lyon, S.A., Cray, P.J. 2016. Antimicrobial susceptibility of Clostridium difficile isolated from food animals on farms. International Journal of Food Microbiology. 227:1-5. doi: 10.1016/j.ijfoodmicro.2016.03.017.

Interpretive Summary: Clostridium difficile is an anaerobic bacterium commonly associated with disease in humans referred to as C. difficile-associated disease (CDAD). Illness can range from mild diarrhea to life-threatening conditions involving the bowel. One of the major risks for infection with C. difficile is use of an antimicrobial for an illness other than infection with C. difficile. The use of antibiotics can disrupt the normal balance of microorganisms in the gastrointestinal tract and allow C. difficile to become established and colonize an empty bowel. Monitoring the development of antimicrobial resistance in bacteria isolated from animals as well as humans is necessary to assess risk, facilitate proper use of antimicrobials and prolong their useful lifespan. The objective of this study was to investigate the susceptibility of C. difficile isolated from swine, beef and dairy cattle feces to common antimicrobials used in human and veterinary medicine. 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 USDA-Animal Plant Health Inspection Services National Animal Health Monitoring System. Using the Etest (AB Biodisk, Solna, Sweden), bacteria 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 = 3.0 µg/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. The Etest proved to be a reliable method for determining antimicrobial phenotypes among animal isolates. These data are important for epidemiologists, public health officials including physicians and veterinarians as well as researchers studying treatment and control options.

Technical 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. Clostridium 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 = 3.0 µg/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. The Etest proved to be a reliable method for determining antimicrobial phenotypes among animal isolates.