Third-generation cephalosporin resistance (3GC-R) in Escherichia coli is a rising problem in human and farmed animal populations. We conducted whole genome sequencing analysis of 138 representative 3GC-R isolates previously collected from dairy farms in South West England and confirmed by PCR to carry acquired 3GC-R genes. This analysis identified blaCTX-M (131 isolates: encoding CTX-M-1, -14, -15, -32 and the novel variant, CTX-M-214), blaCMY-2 (6 isolates) and blaDHA-1 (one isolate). A highly conserved plasmid was identified in 73 isolates, representing 27 E. coli sequence types. This novel ∼220 kb IncHI2 plasmid carrying blaCTX-M-32 was sequenced to closure and designated pMOO-32. It was found experimentally to be stable in cattle and human transconjugant E. coli even in the absence of selective pressure and was found by multiplex PCR to be present on 26 study farms representing a remarkable range of transmission over 1500 square kilometres. However, the plasmid was not found amongst human urinary E. coli we have recently characterised from people living in the same geographical location, collected in parallel with farm sampling. There were close relatives of two blaCTX-M plasmids circulating amongst eight human and two cattle isolates, and a closely related blaCMY-2 plasmid found in one cattle and one human isolate. However, phylogenetic evidence of recent sharing of 3GC-R strains between farms and humans in the same region was not found. Importance Third-generation cephalosporins (3GCs) are critically important antibacterials and 3GC-resistance (3GC-R) threatens human health, particularly in the context of opportunistic pathogens such as Escherichia coli. There is some evidence for zoonotic transmission of 3GC-R E. coli through food, but little work has been done examining possible transmission (e.g. via interaction of people with the local near-farm environment). We characterised acquired 3GC-R E. coli found on dairy farms in a geographically restricted region of the United Kingdom and compared these with E. coli from people living in the same region, collected in parallel. Whilst there is strong evidence for recent farm-to-farm transmission of 3GC-R strains and plasmids – including one epidemic plasmid that has a remarkable capacity to transmit – there was no evidence that 3GC-R found on study farms had a significant impact on circulating 3GC-R E. coli strains or plasmids in the local human population.

Rapid and accurate differentiation of Salmonella spp. causing enteric fever from nontyphoidal Salmonella is essential for clinical management of cases, laboratory risk management, and implementation of public health measures. Current methods used for confirmation of identification, including biochemistry and serotyping as well as whole-genome sequencing analyses, take several days. Here we report the development and evaluation of a real-time PCR assay that can be performed directly on crude DNA extracts from bacterial colonies for the rapid identification of typhoidal and nontyphoidal Salmonella.

Salmonella enterica serovar Infantis is the fifth most common Salmonella serovar isolated in England and Wales. Epidemiological, genotyping and antimicrobial-resistance data for S . enterica Infantis isolates were used to analyse English and Welsh demographics over a 5 year period. Travel cases associated with S . enterica Infantis were mainly from Asia, followed by cases from Europe and North America. Since 2000, increasing numbers of S . enterica Infantis had multidrug resistance determinants harboured on a large plasmid termed ‘plasmid of emerging S . enterica Infantis’ (pESI). Between 2013 and 2018, 42 S . enterica Infantis isolates were isolated from humans and food that harboured resistance determinants to multiple antimicrobial classes present on a pESI-like plasmid, including extended-spectrum β-lactamases (ESBLs; bla CTX-M-65). Nanopore sequencing of an ESBL-producing human S . enterica Infantis isolate indicated the presence of two regions on an IncFIB pESI-like plasmid harbouring multiple resistance genes. Phylogenetic analysis of the English and Welsh S . enterica Infantis population indicated that the majority of multidrug-resistant isolates harbouring the pESI-like plasmid belonged to a single clade maintained within the population. The bla CTX-M-65 ESBL isolates first isolated in 2013 comprise a lineage within this clade, which was mainly associated with South America. Our data, therefore, show the emergence of a stable resistant clone that has been in circulation for some time in the human population in England and Wales, highlighting the necessity of monitoring resistance in this serovar.

ObjectivesThe objective of this study was to identify the mechanisms of cefotaxime resistance (CTX-R) in 1226 Escherichia coli from 4581 environmental samples collected on 53 dairy farms over a 2-year period in South West England and to characterise a blaCTX-M-32-producing plasmid, pMOO-32, found to be widely distributed.MethodsCTX-R isolates were identified using MIC breakpoint agar plates. β-lactamase genes of interest (GOIs) were detected by PCR. WGS was performed and analysed using the Center for Genomic Epidemiology platform. A plasmid-specific multiplex PCR was designed to indicate the presence of plasmid pMOO-32.ResultsAmongst 1226 CTX-R isolates, PCR identified blaCTX-M group 1 (549 isolates), blaCTX-M group 9 (100 isolates), blaCMY (12 isolates), blaDHA (1 isolate) and no GOI (566 isolates). WGS analysis of 184 representative isolates identified blaCTX-M (131 isolates; encoding CTX-M-1, -14, -15, -32 and the novel variant, CTX-M-214), blaCMY-2 (6 isolates), blaDHA-1 (one isolate) and presumed AmpC-hyperproduction in 46 isolates that were PCR negative for GOIs. A highly conserved plasmid was identified in 73 isolates, representing 27 E. coli STs. This ∼220 kb IncHI2 plasmid carrying blaCTX-M-32 was designated pMOO-32, was found to be stable in cattle and human transconjugant E. coli even in the absence of selective pressure, and was found by multiplex PCR to be present on 26/53 study farms.Conclusionsβ-lactamases capable of conferring resistance to third generation cephalosporins were evident on 47/53 farms within this study. This was largely because of the widespread dissemination of an IncHI2 plasmid carrying blaCTX-M-32.