Vertical and horizontal dissemination of an IncC plasmid harbouring rmtB 16S rRNA methylase gene, conferring resistance to plazomicin, among invasive ST258 and ST16 KPC-producing Klebsiella pneumoniae.

OBJECTIVES: Carbapenem resistance in Klebsiella pneumoniae is a major clinical challenge. Aminoglycosides remain an important asset in the current therapeutic arsenal to treat these infections. We examined aminoglycoside resistance phenotypes and genomics in a collection of 100 invasive KPC-producing K. pneumoniae isolates sequentially collected in a Brazilian tertiary hospital between 2014 and 2016. METHODS: Aminoglycoside susceptibility testing was performed. We used a combined long-read (MinION) and short-read (Illumina) whole-genome sequencing strategy to provide a genomic picture of aminoglycoside resistance genes, with particular emphasis on 16S rRNA methyltransferases and related plasmids. RESULTS: 68% of the strains were resistant to gentamicin and 42% to amikacin, with 35% resistant to both of these commonly used aminoglycosides. We identified the 16S rRNA methyltransferase gene rmtB in 30% of these isolates: 97% (29/30) belonged to sequence type 258 (ST258) and a single isolate to the emergent ST16 clone. In ST258 and ST16 the rmtB gene was located on large IncC plasmids of 177 kb and 174 kb, respectively, highly similar to a plasmid previously identified in Proteus mirabilis in the same hospital. Moreover, 99% of the isolates remained susceptible to the veterinary-approved drug apramycin, currently under clinical development for human medicine. CONCLUSION: Such findings in geographically and temporally related isolates suggest a combination of vertical clonal spread as well as horizontal interspecies and intraspecies plasmid transfer. This broad rmtB dissemination in an endemic setting for KPC-producing clones is worrisome since it provides resistance to most clinically available aminoglycosides, including the novel aminoglycoside-modifying enzyme-resistant plazomicin.

Tracking methicillin-resistant Staphylococcus aureus clones in Colombian hospitals over 7 years (1996-2003): emergence of a new dominant clone.

Worldwide dissemination of methicillin-resistant Staphylococcus aureus (MRSA) clones is a well-characterised phenomenon. Two hundred isolates of MRSA recovered from 17 Colombian hospitals collected between 2001 and 2003 were characterised by pulsed-field gel electrophoresis (PFGE). A new dominant electrophoretic pattern unrelated to previously characterised clones in Colombia was detected in 137 (68.5%) of these isolates. Only 40 (20%) isolates still showed a pattern closely related to a previously described dominant clone. The new electrophoretic pattern was indistinguishable from a cluster of isolates recovered in Chile between 1996 and 1998. Isolates from this clonal cluster exhibited multidrug resistance but were susceptible to linezolid and glycopeptides. The results indicate a shift in the population genetics of Colombian MRSA and confirm dissemination of the Chilean clone for the first time.