Serotypes, Antimicrobial Susceptibility, and Potential Mechanisms of Resistance Gene Transfer in Erysipelothrix rhusiopathiae Strains from Waterfowl in Poland

Abstract

Erysipelas is a significant problem in the waterfowl farming in Poland, and information on the characteristics of the Erysipelothrix rhusiopathiae strains causing this disease is limited. In this study, we determined the serotypes, antimicrobial susceptibility, and potential mechanisms of resistance gene transfer in E. rhusiopathiae isolates (n = 60) from domestic geese and ducks. We also developed a multiplex PCR for the detection of resistance genes. The antimicrobial susceptibility of the isolates was assessed using the broth microdilution method. Resistance genes, integrative conjugative element (ICE)-specific genes, phage-specific genes, and serotype determinants were detected by PCR. Multilocus sequence typing (MLST) was performed for selected resistant strains. The comparative analyses included 260 E. rhusiopathiae strains whose whole genome sequences (WGSs) are publicly available. E. rhusiopathiae isolates represented 7 serotypes, among which serotypes 5 (38.3%) and 1b (28.3%) were the most common. All strains were susceptible to β-lactams, and the vast majority of them were resistant to tetracycline (85%) and enrofloxacin (80%). The percentages of isolates resistant to other antimicrobials used ranged from 3.3% to 16.7%. Ten isolates (16.7%) were found to be multidrug resistant (MDR). The genotypic resistance profiles of the E. rhusiopathiae strains corresponded to their phenotypic resistance, and the amplification patterns obtained using the 10-plex PCR developed in this study were fully consistent with the results of single PCRs. The most prevalent resistance gene was tetM. In enrofloxacin-resistant strains, nonsynonymous mutations in the gyrA and parC genes were identified. The presence of ICE-specific genes was confirmed in resistant strains, and in MDR isolates of serotype 8 that represented sequence type (ST) 113, prophage DNA (Javan630-like) linked to the lsaE gene was additionally detected. The results indicate that β-lactam antibiotics should be the first choice for the treatment of waterfowl erysipelas in Poland. ICEs, including a transposon from the Tn916/Tn1545 family, and bacteriophages are most likely responsible for the transfer of resistance genes in E. rhusiopathiae.