Antimicrobial susceptibility of Clostridium difficile isolated from neonatal pigs with enteritis

April 1, 2005 — Adam Moeser (ed. David Burch)
  [ES]

Clostridium difficile is the primary agent responsible for antibiotic-associated diarrhea and pseudomembranous colitis in humans, horses, and laboratory rodents. Recently, C. difficile has been recognized as an important etiologic agent of enteritis in neonatal piglets in which sows may be a source of infection. The objective of this study was to determine the antimicrobial susceptibility of porcine C. difficile strains.

Eighty isolates of C. difficile from feces or colonic contents of neonatal pigs with enteritis were obtained for determination of MIC for 8 antimicrobial agents using the agar dilution method.

Erythromycin, tilmicosin, and tylosin had relatively low MIC50 values that ranged between 0.25-0.5ug/mL. However, MIC90 values for these antimicrobials were 64ug/mL (for tylosin) and greater or equal to 256ug/mL (for tilmicosin and erythromycin) suggesting in-vivo resistance of a proportion of isolates. Tiamulin MIC values ranged from 0.125 to 256ug/mL and virginiamycin MIC values ranged from 0.125 to 16ug/mL. Tiamulin and virginiamycin MIC90 values were 8 and 16ug/mL, respectively suggesting a moderate susceptibility. Tetracycline had a MIC50 of 8ug/mL and a MIC90 of 32 ug/mL. Bacitracin and ceftiofur had MIC90 values greater than 256ug/mL suggesting little activity against C. difficile.

Tiamulin and virginiamycin are available only in feed or water formulations and thus are expected to reach higher concentrations in gut and therefore would be more efficacious in reducing fecal shedding in sows as compared with parenteral treatment. Erythromycin and tylosin are available in injectable form thus allowing treatment of infected piglets suckling the sow. However, in-vitro MIC data should be interpreted with caution, as it may not translate to in-vivo efficacy. Clinical trials are needed to determine the efficacy of these antimicrobial agents in the field.

Reference:

Post, KW, Songer JG. Antimicrobial susceptibility of Clostridium difficile isolated from neonatal pigs with enteritis. Anaerobe. 10:47-50, 2004.