Genomic characterisation and epidemiology of nosocomial Serratia marcescens isolates resistant to ceftazidime and their plasmids mediating rare blaTEM-61

ABSTRACT Objectives We determined the whole DNA sequences of plasmids carrying a rare extended-spectrum β-lactamase gene (blaTEM-61) to precisely understand spread resistance among nosocomial Serratia marcescens populations. Methods Twenty non-duplicate ceftazidime-resistant S. isolates (ceftazidime MICs, 32 >128 mg/L) collected over 1 year were pulsotyped and nucleotide blaTEM-61 its promoter region determined. Twelve representative analysed by whole-genome sequencing. Results The 20 comprised two distinct pulsotypes: I (14 isolates) II (6 isolates). They all contained gene. A polymorphism in repeat number 15-nucleotide sequence (5′-ATGTCATGATAATAA-3′) was found blaTEM-61; two, three four units 6, 12 2 isolates, respectively. Single (SNP)-based phylogenetic analysis revealed that 7 pulsotype (12–44 SNP differences) 5 (15–55 formed clusters genotypes 2, All harboured plasmid Tn1–blaTEM-61 element, although they slightly different size (78 883 bp, 78 898 bp 913 bp) owing differences 15-bp repetitive sequences. 42 542-bp broad-host-range element also one isolates. Conclusions characterised plasmid-encoded novel transposon-dependent mechanisms underlying propagation antibiotic resistance, together with repeated new polymorphic blaTEM-61.