Profile of Salmonella Isolates in Bullfrog Production: PFGE, MLST, and Antimicrobial Resistance

Abstract

The continued development of bullfrog farming holds great potential for expansion. However, these animals serve as reservoirs for various pathogens, including Salmonella, posing a risk to food safety and public health. Therefore, the primary objective of this study was to identify potential sources of Salmonella contamination in a bullfrog production facility in Minas Gerais, Brazil, by characterizing isolates through Pulsed-Field Gel Electrophoresis (PFGE), Multilocus Sequence Typing (MLST), and antimicrobial resistance profiling. A total of eight Salmonella isolates were analyzed, comprising six isolates from bullfrog carcasses and two from breeding tanks. PFGE characterization revealed four distinct profiles, with a clonal relationship among isolates belonging to the same serovar, except for S. Newport, where the profile of the breeding tank isolate differed from that of the carcass isolates. MLST analysis identified three sequence types (STs): ST 32, ST 614, and ST 6855, corresponding to S. Infantis, S. Newport, and S. 6,8:i:-, respectively. Regarding antimicrobial resistance, one isolate was resistant to azithromycin, two were resistant to neomycin, and three were resistant to ciprofloxacin. All isolates were susceptible to cephalexin, meropenem, cefotaxime, ceftriaxone, ampicillin, tobramycin, and cephalothin. The presence of distinct PFGE profiles among isolates of the same serovar suggests multiple sources of pathogen contamination within the production chain, raising significant sanitary concerns. The identified sequence types (STs) are of public health relevance, highlighting the pathogenic potential of these isolates. While most isolates were susceptible to the tested antimicrobials, the detection of azithromycin resistance is particularly concerning. The combined PFGE and MLST data indicate potential cross-contamination within the production chain, emphasizing the need for stringent control measures.