Companion Animal Gastrointestinal Laboratory
School of Veterinary Medicine University of California, Davis


Isospora felis oocysts (400X)
Current Projects


  • Clostridium perfringens and Clostridium difficile-associated diarrhea.
    Current research projects primarily focus on furthering our understanding of the pathogenesis of clostridial-associated diarrhea in dogs, cats and horses. Specific research projects involve the evaluation of diagnostic assays, virulence factors that may be involved in disease, antimicrobial susceptibility profiles of bacterial isolates, and disease characterization.

  • Determination of antimicrobial susceptibility profiles of canine Clostridium perfringens and Clostridium difficile isolates.
    Clostridium perfringens is one of the most widespread pathogenic bacteria, and has been associated with a wide range of diarrheal diseases in both humans and animals. In the dog, C. perfringens has been associated with 28-34% of diarrheic cases, ranging in severity from a mild self-limiting diarrhea to a potentially fatal acute hemorrhagic diarrheal syndrome. The recommended treatment for dogs with suspected C. perfringens-associated diarrhea includes administration of antibiotics such as ampicillin, erythromycin, metronidazole, tylosin, and tetracycline. However, there is a paucity of information regarding the antibiotic susceptibility profiles of canine C. perfringens to these commonly utilized antibiotics. This information is particularly important in the face of increasing reports of resistance among anaerobic bacteria isolates from both humans and animals. We have recently completed a study evaluating the in vitro antibiotic susceptibilities of 131 canine C. perfringens isoaltes to the antibiotics mentioned above. Results are being published in an upcoming issue of Veterinary Microbiology. Most isolates were susceptible at relatively low concentrations of antibiotics, however, several multiple-antibiotic resistant strains were found. We are currently evaluating genetic resistance determinants in these isolates for the presence of resistance genes associated with the antibiotics erythromycin, tetracycline, and tylosin.
  • Determination of the incidence of beta2-toxigenic C. perfringens in diarrheic and nondiarrheic dogs and characterization of gene sequence.
    Canine diarrhea associated with Clostridium perfringens has principally been though to involve the activity of Clostridium perfringens enterotoxin (CPE). However, the pathogenesis of the organism is not fully understood, as CPE is also detected in healthy nondiarrheic dogs. The role that other virulence factors may play, therefore, needs further investigation. A recently described virulence factor, the beta2-toxin, has been associated with enteritis in piglets and typhlocolitis in horses. We are currently evaluating what role this toxin may play in the pathogenesis of canine C. perfringens-associated diarrhea by assessing the incidence of beta2-toxigenic C. perfringens in both nondiarrheic and diarrheic dogs, as well as in vitro toxin production by these isolates. Preliminary results have revealed a large number of mutated sequences that do not produce the beta2-toxin in vitro.
  • Determination of antimicrobial susceptibility profiles of foal Clostridium perfringens isolates.
    Clostridium perfringens-associated diarrhea in the foal is frequently characterized as a rapidly progressive disease that often has a fatal outcome, despite the use of intensive care measures. Because the clinical condition of foals can deteriorate rapidly, therapeutic intervention with antibiotics is often warranted. However, there is a paucity of information about the antibiotic susceptibilities of foal C. perfringens isolates to commonly administered antibiotics. Furthermore, many orally administered antibiotics can cause diarrhea as a result of intestinal overgrowth by resistant bacteria. The main objective of this study is to assess the susceptibility of C. perfringens isolates obtained from foals to commonly utilized antibiotics. This study entails three specific goals:
    1) evaluate susceptibilities to antibiotics used to treat foals with C. perfringens-associated diarrhea,
    2) evaluate susceptibilities to antibiotics that may predispose foals to intestinal overgrowth of C. perfringens
    3) compare the distribution of antibiotic resistance between two geographically distinct populations of foals from two universities that are presented with large caseloads of foal diarrhea.


School of Veterinary Medicine-University of Califoria Davis