2016/06/27 by DAE Dayao, JS Gibson, PJ Blackall +1
paper · doi:10.1111/avj.12458
crossref issued 2016/06/27 · crossref published 2016/06/27 · crossref published-online 2016/06/27 · crossref created 2016/06/29 · crossref published-print 2016/07/01 · crossref deposited 2023/09/26 · crossref indexed 2026/07/24
Objective To identify genes associated with the observed antimicrobial resistance in Actinobacillus pleuropneumoniae , Haemophilus parasuis and Pasteurella multocida isolated from Australian pigs. Design Isolates with known phenotypic resistance to β‐lactams, macrolides and tetracycline were screened for the presence of antimicrobial resistance genes. Procedure A total of 68 A. pleuropneumoniae , 62 H. parasuis and 20 P. multocida isolates exhibiting phenotypic antimicrobial resistance ( A. pleuropneumoniae and P. multocida ) or elevated minimal inhibitory concentrations ( MICs ) ( H. parasuis ) to any of the following antimicrobial agents − ampicillin, erythromycin, penicillin, tetracycline, tilmicosin and tulathromycin − were screened for a total of 19 associated antimicrobial resistance genes ( ARGs ) by PCR . Results The gene bla ROB‐1 was found in all ampicillin‐ and penicillin‐resistant isolates, but none harboured the bla TEM‐1 gene. The tet B gene was found in 76% (74/97) of tetracycline‐resistant isolates, 49/53 A. pleuropneumoniae, 17/30 H. parasuis and 8/14 P. multocida . One A. pleuropneumoniae isolate harboured the tet H gene, but none of the 97 isolates had tet A, tet C, tet D, tet E, tet L, tet M or tet O. A total of 92 isolates were screened for the presence of macrolide resistance genes. None was found to have erm A, erm B, erm C, erm 42, mph E, mef A, msr A or msr E. Conclusion The current study has provided a genetic explanation for the resistance or elevated MIC of the majority of isolates of Australian porcine respiratory pathogens to ampicillin, penicillin and tetracycline. However, the macrolide resistance observed by phenotypic testing remains genetically unexplained and further studies are required.