Feeding pets raw meat-based diets (RMBDs) has become increasingly popular but may constitute a risk due to the contamination with pathogenic and antimicrobial-resistant (AMR) bacteria. The aim of this study was to evaluate commercially available RMBDs with regard to microbiological quality and occurrence of AMR Enterobacteriaceae. Of 51 RMBD samples, 72.5% did not meet the microbiological standards for Enterobacteriaceae set out by EU regulations for animal by-products intended for pet food. Furthermore, Salmonella was detected in 3.9% of the samples. AMR bacteria were found in 62.7% of the samples, the majority thereof were resistant to third-generation cephalosporins due to the production of extended-spectrum β-lactamases (ESBLs) including CTX-M-1, which is widespread in livestock, and CTX-M-15, which is the most common ESBL variant worldwide. Colistin- and aminoglycoside-resistant isolates, producing MCR-1 and RMTB, were identified in 3.9 and 2% of the samples, respectively. The majority of the AMR Escherichia coli belonged to commensal groups A or B1 and were associated with clonal complexes CC155 and CC10. Two belonged to the emerging extraintestinal pathogenic CC648, and one to the globally disseminated uropathogenic E. coli sequence type ST69, suggesting zoonotic potential. The microbiological quality and the high prevalence of AMR producing Enterobacteriaceae in RMBDs raise concerns for animal and public health.

Fosfomycin, originally known as phosphonomycin, was discovered five decades ago and has been approved for the treatment of uncomplicated urinary tract infections (UTI) since early 1970 (Silver, 2017). The phosphonic acid-derived antibiotic containing an epoxide and a propyl group possesses a unique chemical structure and the mechanism of action comprising broad-spectrum activity against Gram-negative and Gram-positive aerobic bacteria is unrelated to any other antibiotic family (Castañeda-García et al., 2013; Silver,

The use of florfenicol in farm animals may select enterococci that carry resistance genes which confer resistance to linezolid, a critically important oxazolidinone antibiotic used in human medicine.  This cross-sectional study aimed to assess the occurrence of oxazolidinone resistance genes in florfenicol resistant enterococci from fattening pigs in Switzerland, and to characterize a subset of the isolates using whole genome sequencing (WGS). A total of 31 florfenicol-resistant enterococcal isolates were obtained from 27 (5%) of 565 cecal samples of fattening pigs from seven (11%) of 62 farms. Screening by PCR revealed the presence of cfr/poxtA in 1/31, optrA in 15/31 and poxtA in 15/31 enterococcal isolates, respectively. One randomly selected isolate per PCR-positive Enterococcus species and positive farm was selected for further analysis (n=10). In nine of the ten isolates, the presence of oxazolidinone resistance genes did not result in phenotypic resistance. WGS analysis showed the presence of E. faecalis (n=1), E. faecium (n=1), and E. hirae (n=1), harboring optrA18, optrA7 and a new optrA allele, respectively. E. durans (n=1), E. faecium (n=4), and E. hirae (n=1), carried the wild-type poxtA , and E. faecalis (n=1) co-harbored cfr(D) and poxtA2 . Except for optrA7, all oxazolidinone resistance genes were found on plasmids. MLST analysis identified E. faecalis ST19 and ST376, E. faecium ST80 belonging to hospital-adapted clade A1, and  E. faecium ST21, ST55, ST269 and ST416, belonging to clade A2 which represents human commensals and animal strains. The occurrence of cfr(D, optrA and poxtA in various porcine Enterococcus spp. demonstrates the spread of oxazolidinone resistance genes among enterococci from fattening pigs in Switzerland. The presence in one sample of poxtA-carrying E. faecium  ST80 emphasizes the potential risk to human health through dissemination of strains carrying oxazolidinone resistance genes into the food chain.

Objectives Fosfomycin is an important antibiotic for the treatment of MDR Enterobacteriaceae infections. High susceptibility rates are, however, threatened by the spread of plasmids encoding fosfomycin-modifying enzymes. In this study, we sought to characterize the genetic context of fosA in plasmids from Escherichia coli and Klebsiella spp. isolates recovered from food, wastewater and surface water in Switzerland. Methods E. coli and Klebsiella spp. isolates collected between 2012 and 2019 in Switzerland were screened for fosfomycin resistance. Presence of fosA was verified by PCR and sodium phosphonoformate (PPF) disc potentiation testing, and transferability was tested using conjugation assays. Whole-genome sequences including complete fosA-containing plasmids were determined using long- and short-read sequencing. Results In 11 E. coli and two Klebsiella spp. isolates, high-level fosfomycin resistance was mediated by plasmids containing fosA3 (n = 12) or fosA8 (n = 1). Four isolates harboured a near-identical 45 kb IncN plasmid with fosA3, while replicon types varied in the remaining plasmids. The fosA genes were typically embedded in IS26-bounded transposition units and frequently located in the proximity of blaCTX-M transposition units. Conclusions Although fosfomycin resistance rates are currently low, the presence of fosA-encoding plasmids circulating in the Enterobacteriaceae population suggests that fosfomycin resistance may rapidly spread upon increased selection pressure. Transposition mobility of fosA and co-location on plasmids with other resistance genes may further promote its dissemination.

Feeding pets raw meat-based diets (RMBDs) is becoming increasingly popular but comes with a risk of pathogenic bacteria, including Shiga toxin-producing Escherichia coli (STEC). In humans, STEC may cause gastrointestinal illnesses, including diarrhea, hemorrhagic colitis (HC), and the hemolytic uremic syndrome (HUS). The aim of this study was to evaluate commercially available RMBDs with regard to the occurrence of STEC. Of 59 RMBD samples, 59% tested positive by real-time PCR for the presence of Shiga toxin genes stx1 and/or stx2. STECs were recovered from 41% of the 59 samples, and strains were subjected to serotyping and virulence gene profiling, using whole genome sequencing (WGS)-based methods. Of 28 strains, 29% carried stx2a or stx2d, which are linked to STEC with high pathogenic potential. Twenty different serotypes were identified, including STEC O26:H11, O91:H10, O91:H14, O145:H28, O146:H21, and O146:H28, which are within the most common non-O157 serogroups associated with human STEC-related illnesses worldwide. Considering the low infectious dose and potential severity of disease manifestations, the high occurrence of STEC in RMBDs poses an important health risk for persons handling raw pet food and persons with close contact to pets fed on RMBDs, and is of concern in the field of public health.