3Antimicrobial resistance of Pasteurella multocida isolates recovered from swine pneumonia in Spain throughout 2017 and 2018

Abstract A total of 32 Pasteurella multocida isolates were obtained from 60 cases of swine pneumonic lungs collected in “Castilla y Leon” (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 erm C, bla ROB1 , tet B and msr E 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.