Characterization of multidrug-resistant Klebsiella pneumoniae from Australia carrying bla_NDM-1

Abstract

bla_NDM genes, encoding metallo-β-lactamases providing resistance to carbapenems, have been reported in many locations since the initial report in 2008, including in several Enterobacteriaceae isolates in Australia/New Zealand. Here, we compare 4 additional carbapenem-resistant Klebsiella pneumoniae carrying bla_NDM-1 isolated in Australia. Two are sequence type ST147, previously associated with bla_NDM in Australia and elsewhere. They carry bla_NDM-1 and different 16S rRNA methylase genes (armA or rmtC) on different conjugative plasmids, in 1 case with an IncFII_Y replicon. One isolate belongs to the globally important ST11 but did not transfer a plasmid to Escherichia coli. The fourth isolate belongs to the novel ST1068 and transferred bla_NDM-1, armA, and an IncA/C plasmid. Amplification and sequencing of ompK porin genes suggest that, unlike the case for other carbapenemase genes, ompK36 defects may not be required for NDM to cause clinically relevant levels of carbapenem resistance.

Introduction

The NDM-1 metallo-β-lactamase is able to hydrolyze carbapenems, along with most other β-lactams. bla_NDM-1 was first identified in a Swedish patient of Indian origin in 2008 (Yong et al., 2009), although it was later found in Enterobacteriaceae from 2006 (Castanheira et al., 2011). Clinical isolates carrying bla_NDM-1 or minor variants have now been reported in most parts of the world in a number of different species, most commonly Enterobacteriaceae such as Klebsiella pneumoniae, but also in Acinetobacter spp. bla_NDM genes have been identified in a variety of different sequence types (ST) of both K. pneumoniae and E. coli (Johnson and Woodford, 2013). bla_NDM genes have also been identified in a variety of different plasmid types, mostly belonging to the IncA/C and IncF groups (Johnson and Woodford, 2013), but not all plasmids identified as carrying bla_NDM-1 have been typed.

Defects in K. pneumoniae outer membrane porins (OmpK) appear to be required for clinically relevant levels of carbapenem resistance in isolates expressing many carbapenemase enzymes, such as Klebsiella pneumoniae carbapenemase (KPC) (Nordmann et al., 2009). ompK35 defects are common in isolates carrying genes encoding extended-spectrum β-lactamases (ESBL) (Martínez-Martínez, 2008), while defects in ompK36 (Wang et al., 2009) or in both of these porins may be more important for carbapenem resistance (Martínez-Martínez, 2008). The importance of the minor porin, OmpK37, in carbapenem resistance is less clear (Martínez-Martínez, 2008). While ompK genes of K. pneumoniae isolates carrying carbapenemases such as KPC are often characterised, only 1 previous study of K. pneumoniae with bla_NDM (an ST231 isolate from Spain) appears to have examined ompK genes, finding an early stop codon in ompK35, while ompK36 could not be amplified (Oteo et al., 2012).

bla_NDM genes have been sporadically reported in clinical isolates from Australia and New Zealand since 2009, from several different members of the Enterobacteriaceae (E. coli, K. pneumoniae, Proteus mirabilis, Providencia rettgeri, Enterobacter cloacae) (Fernando et al., 2010, Poirel et al., 2010, Rogers et al., 2013, Sidjabat et al., 2011, Williamson et al., 2012). All isolates were from people recently returned from the Indian subcontinent, and all but one reported recent medical care, including hospitalisations. Most isolates carried bla_NDM-1, but minor variants with conservative substitutions, bla_NDM-3 (D95N) and bla_NDM-6 (A233V), were also present. Here, we describe 4 further K. pneumoniae with bla_NDM-1 isolated in Australia, 2010–2012.