Antimicrobial Resistance Genes In Porcinepasteurella Multocidaare Not Associated With Its Antimicrobial Susceptibility Pattern

Forty-eightPasteurella multocidaisolates were recovered from porcine pneumonic lungs collected from farms in "Castilla y Leon" (north-western Spain) in 2017-2019. These isolates were characterized for their minimal inhibition concentrations to twelve antimicrobial agents and for the appearance of eight resistance genes:tetA,tetB,bla(ROB1),bla(TEM),ermA,ermC,mphEandmsrE. Relevant resistance percentages were shown against tetracyclines (52.1% for doxycycline, 68.7% for oxytetracycline), sulphamethoxazole/trimethoprim (43.7%) and tiamulin (25.0%), thus suggesting thatP. multocidaisolates were mostly susceptible to amoxicillin, ceftiofur, enrofloxacin, florfenicol, marbofloxacin and macrolides. Overall, 29.2% of isolates were resistant to more than two antimicrobials. The tetracycline resistance genes (tetAandtetB) were detected in 22.9% of the isolates, but none were positive to both simultaneously;bla(ROB1)andbla(TEM)genes were found in one third of isolates but both genes were detected simultaneously in only one isolate. TheermCgene was observed in 41.7% of isolates, a percentage that decreased to 22.9% formsrE; finally,ermAwas harbored by 16.7% andmphE was not found in any of them. Six clusters were established based on hierarchical clustering analysis on antimicrobial susceptibility for the twelve antimicrobials. Generally, it was unable to foresee the antimicrobial susceptibility pattern for each family and the association of each particular isolate inside the clusters established from the presence or absence of the resistance genes analyzed.