Absence of high priority critically important antimicrobial resistance in Salmonella sp. isolated from Australian commercial egg layer environments

The development of antimicrobial resistance in foodborne pathogens is a growing public health concern. This study was undertaken to determine the susceptibility Salmonella enterica subspecies isolated from Australian commercial egg layer industry. S. (n=307) flock environments (2015–2018) were obtained reference, research and State Government laboratories six states. All isolates serotyped. Antimicrobial testing (AST) for 16 agents performed by broth microdilution. genes sequence types (STs) identified significant whole genome sequencing (WGS). Three main serotypes detected, Typhimurium (n=61, 19.9%), Senftenburg (n=45, 14.7%) Agona (n=37, 12.1%). AST showed 293/307 (95.4%) susceptible all tested amoxicillin-clavulanate, azithromycin, ceftiofur, ceftriaxone, ciprofloxacin, colistin, florfenicol, gentamicin, kanamycin trimethoprim-sulfamethoxazole. Low levels non-susceptibility observed streptomycin (2.3%, n=7), sulfisoxazole (2.0%, n=6), chloramphenicol (1.3%, n=4) tetracycline (1.0%, n=3). Very low ampicillin (2/307; 0.7%) cefoxitin 0.7%). Two (S. Havana Montevideo), exhibited multidrug-resistant phenotypes streptomycin, possessed corresponding (aadA4, aac(6?)-Iaa, sul1, tetB). One isolate resistant tetracycline, both tetA blaTEM-1B. WGS also these as belonging ST4 ST578 Havana) ST19 Typhimurium). absence highest priority critically important antimicrobials well extremely level AMR generally among likely reflect Australia's conservative registration policy food-producing animals rates use within