Antimicrobial Susceptibility and Clonal Relationship of Tetracycline Resistance Genes in netF-Positive Clostridium perfringens.

NetF-producing type A Clostridium perfringens, a pathotype of C. perfringens, causes necrotizing enteritis in neonatal foals and necrotizing and hemorrhagic enteritis in dogs. Recent core genome multilocus sequence typing study revealed that netF+ C. perfringens strains belong to two distinct clonal populations (clonal complexes I and II). There are no reports on susceptibility to antimicrobial drugs of isolates from this pathotype. The susceptibility to 13 different antimicrobial drugs of 49 netF+ strains recovered from foals or dogs with necrotizing enteritis in Canada, the United States, and Switzerland was assessed using a commercial microdilution panel designed for anaerobic human pathogens. All isolates were highly susceptible to 12 antimicrobial agents, including all beta-lactams tested, such as penicillin G and ampicillin, as well as clindamycin, chloramphenicol, and metronidazole. The isolates consistently presented a reduced susceptibility or resistance to tetracycline, which was associated with previously described tetracycline resistance genes. Clonal complex I isolates (n = 41) possessed the tetA408(P) gene, whereas clonal complex II isolates (n = 8) possessed the tetA(P)-tetB(P) genes and were more likely to be fully resistant.