Staphylococcus intermedius is the most common coagulase-positive staphylococci isolated from dogs. Debate continues about whether this organism is transient on the skin and hair coat, having transferred from a reservoir site, such as the oral cavity or the nasal cavity. In this study, 35 dogs in a "pet pals" program had bacterial culture of the hair coat and oral cavity performed at least 4 times a year. Over a 5-year period, 562 cultures revealed 125 isolates of Staphylococcus intermedius. An isolate was found at least once from each dog and several times from at least 25 dogs. Staphylococcus intermedius was isolated from the oral cavities of 31 of 35 (89%) of dogs. It was isolated from the hair coat in 19 of 35 (54%) dogs. In addition, 32% of the oral cavity cultures (n = 284) grew S. intermedius compared with only 13% of the 278 hair coat samples. Arbitrary primed polymerase chain reaction testing showed that a single major type was isolated from 91% of dogs (n = 22) and that S. intermedius of this type was isolated more than once. However, in persistently colonized dogs, a genetic shift was observed. Colonization of the hair coat and oral cavity was similar in dogs that were transiently colonized (S. intermedius isolated only once). In contrast, in dogs that were persistently colonized the oral cavity was the predominant site of colonization, with 73% of isolates coming from the oral cavity compared with 27% from the hair coat. When antimicrobial sensitivity patterns of these commensal strains were compared with the results of other studies on cultures from healthy dogs, similar sensitivity patterns were observed. However, when these commensal strains from pet dogs were compared with clinical isolates from dogs with pyoderma, significant culture differences were observed for macrolide and trimethoprim-sulfamethoxazole antibiotics.

COMMENTARY: This study clearly demonstrates that S. intermedius can be isolated from healthy pet dogs and, in many dogs, isolated repeatedly. The authors showed that the "reservoir site" is not the hair coat but the oral cavity. Another important finding was that in persistently infected dogs, there may be more than 1 genetic strain and that these strains may have different antimicrobial sensitivity patterns. Many laboratories "pool" samples for antibacterial testing, and this may not be appropriate for dogs with bacterial pyoderma that recurs or is difficult to treat. In the end, it may be more cost-effective to have the reference laboratory perform separate antimicrobial testing on individual strains.

Molecular characterization of Staphylococcus intermedius carriage by healthy dogs and comparison of antimicrobial susceptibility patterns to isolates from dogs with pyoderma. Hartman FA, White DG, West SHE, et al. VET MICROBIOL 108:119-131, 2005