An investigation of resistance to β-lactam antimicrobials among staphylococci isolated from pigs with exudative epidermitis

摘要

Background A high proportion of staphylococci isolated from pigs affected with exudative epidermitis were found to be resistant to β-lactam antimicrobials. The primary objective of this research was to investigate and characterize β-lactam resistance in Staphylococcus hyicus , Staphylococcus aureus and other staphylococci isolated from these pigs. Results The antimicrobial resistance patterns of 240 staphylococci isolates were determined by disk diffusion, of which 176 (73.3%) of the isolates were resistant to 3 β-lactams (penicillin G, ampicillin, and ceftiofur). The presence of mec A gene was identified in 63 staphylococci isolates from skin samples by PCR. The mec A gene was identified in 19 S . aureus , 31 S . hyicus , 9 Staphylococcus chromogenes , 2 Staphylococcus pseudintermedius isolates, and in 1 isolate each of Staphylococcus arlettae , and Staphylococcus cohnii subspecies urealyticus . From SCC mec typing results, the majority (45/63, 71.4%) were shown to be SCC mec type V. One isolate was SCC mec III. Fourteen isolates were detected as mec class A, mec class C or ccr type 5. The ccr complex and mec complex was not detected in 3 isolates of methicillin resistant S . hyicus (MRSH) based on multiplex PCR. Of the 30 isolates of MRSA identified from nasal samples of the pigs, 29 isolates were SCC mec type V and 1 isolate was SCC mec type II. Staphyloccoci isolates that were mec A negative but resistant to β-lactam antimicrobials were further examined by screening for mec C, however all were negative. Furthermore, the majority of mec A negative β-lactam resistant staphylococci isolates were susceptible to oxacillin and amoxicillin-clavulanic acid in a double disk diffusion test. Conclusions Methicillin resistance can be identified in a variety of staphylococcal species isolated from pigs. In this study there was a great deal of similarity in the SCC mec types between staphylococcal species, suggesting that resistance may be passed from one species of staphylococci to another species of staphylococci. While this has been reported for acquisition of methicillin-resistance from coagulase negative staphylococci to S . aureus , these data suggest that transmission to or from the porcine pathogen S. hyicus may also occur. The identification of methicillin resistance in a variety of staphylococcal species in pigs does raise concerns about the spread of serious multi-drug resistance in food producing animals and warrants further study.