Identification of transferable DHA-1 type AmpC β-lactamases and two mutations in quinolone resistance-determining regions of Salmonella enterica serovar Thompson

Emergence and genomic characteristics of multi-drug-resistant Salmonella in pet turtles and children with diarrhoea

Pet turtles are a well-recognized source of human salmonellosis, posing a threat to human health, particularly children who commonly keep pet turtles. To date, the genomic characteristics of Salmonella among pet turtles and children has not been well described. We investigated the prevalence, antimicrobial resistance (AMR) and genomic characteristics of Salmonella from pet turtles in Beijing, China. In total, 9.6 % (46/480) of pet turtles were positive for Salmonella with S. Thompson being the dominant serovar (19/46) in 2019. Moreover, 80.4 % of Salmonella were multi-drug resistant (MDR) and 60.7 % were resistant to ampicillin, streptomycin, sulfonamides and tetracycline (ASSuT). We further compared the genomes of S. Thompson isolates from pet turtles (n=19) with those from children with diarrhoea (n=28) in the same region and year, most of which were sequence type (ST)26, with one novel ST7937 identified from a child-associated isolate. S. Thompson isolates from children with diarrhoea exhibited less resistance than isolates from pet turtles. Most MDR isolates possessed multiple AMR genes, including the AmpC β-lactamase-encoding genes bla DHA-15 and bla DHA-1 which co-occurred with the IncA/C and IncHI plasmid replicon types. To the best of our knowledge, this is the first time that the bla DHA-15 gene has been detected from Salmonella. Several pet turtle-associated S. Thompson isolates comprised phylogenetically close clusters with those from children with diarrhoea (<20 SNP differences). Bayesian analysis demonstrated that the Chinese ST26 S. Thompson strains had a recent evolutionary history and evolved into two major clades, with one clade acquiring various resistant plasmids. Our findings revealed the emergence of MDR Salmonella among pet turtles in China and provided evidence for the interspecies transmission of S. Thompson.

First Clinical Case of In Vivo Acquisition of DHA-1 Plasmid-Mediated AmpC in a Salmonella enterica subsp. enterica Isolate

A pan-susceptible Salmonella enterica serovar Worthington isolate was detected in the stool of a man returning from Sri Lanka. Under ceftriaxone treatment, a third-generation cephalosporin (3GC)-resistant Salmonella Worthington was isolated after 8 days. Molecular analyses indicated that the two isolates were identical. However, the latter strain acquired a blaDHA-1-carrying IncFII plasmid probably from a Citrobacter amalonaticus isolate colonizing the gut. This is the first report of in vivo acquisition of plasmid-mediated resistance to 3GCs in S. enterica.

Plasmids carrying DHA-1 β-lactamases

The aim of this review is to provide an update on the plasmids mediating DHA-1 cephalosporinase in Klebsiella pneumoniae. These plasmids have been mainly found in this bacterium but not only. The first was isolated from Salmonella sp. in France in the early 1990s. They are currently reported worldwide. Bla_DHA-1 beta-lactamase gene is usually co-expressed with many other antibiotic resistance genes such as extended-spectrum β-lactamases (bla_CTX-M-, bla _SHV -types), oxacillinases (bla_OXA-1, bla_OXA-30), penicillinases (bla _TEM -type), carbapenemases (bla _OXA48 , bla_KPC-2), aminoglycosides (aacA, aadA, armA), fluoroquinolones (qnrB4, aac6'-1b-cr), and sulfonamide (sul1) resistance genes. Plasmids carrying DHA-1 cephalosporinase have different sizes (22 to 313 kb), belong to diverse groups of incompatibility (R, L/M, FII(k), FIB, A/C2, HI2, HIB), and are self-transferable or not. The multidrug resistance region consists of a mosaic structure composed of resistance genes, insertion sequences, composite transposon, and integrons.