Antimicrobial resistance of Pasteurella multocida isolates recovered from swine pneumonia in Spain throughout 2017 and 2018

A total of 32 Pasteurella multocida isolates were obtained from 60 cases of swine pneumonic lungs collected in “Castilla y León” (northwestern Spain) between November 2017 and April 2018. Capsular type A isolates were isolated from 96.9% cases and capsular type D from the remaining 3.1%. All isolates were characterized for their susceptibilities to eight antimicrobial agents and the presence of eight resistance genes. The frequency of susceptibility was lower than 60% in four of the drugs, 84.4% of the isolates showed resistance to at least two compounds, and 46.9% to a combination of three drugs. The resistance patterns suggested that enrofloxacin, chloramphenicol, tetracycline and cefotaxime were the compounds most likely active to P. multocida. The usage of PCR revealed that ermC, blaROB1, tetB and msrE genes occurred in more than 37.0% isolates, that suggested its putative accountability in the resistance of the strains harbor them. However, most were detected in susceptible strains and only a genetic explanation for the resistance could be linked to erythromycin. Therefore, the resistances to clyndamicin, cotrimoxazol, β-lactams and tetracyclin observed by phenotypic testing remains genetically unexplained and further investigations are required. Keywords: Pasteurella multocida, Swine pneumonia, Antimicrobial agents, Disk diffusion testing, Resistance genes