To the best of our knowledge, this is the first report describing K. pneumonia and S. marcescens clinical isolates co-harboring blaKPC and blaNDM-1, including K. pneumonia ST258 and ST340, which were not previously described.
The ST258 emerged during the early 2000s as a hybrid clone created by recombination between ST11, ST442 and the ST340, which is a single-locus variant of ST11 as well [19]. These isolates tend to be pan-resistant, restricting the therapeutic options, particularly to high resistant S. marcescens isolates, since they are intrinsic resistance to polymyxins [20].
The dissemination of NDM-1 and KPC-2 in Brazil is of great concern since a Providencia rettgeri isolate carrying NDM-1 was described in the South region in 2013 [18] and, subsequently, Rozales et al, 2014 [21], published a study analyzing 1134 isolates of Enterobacteriaceae, among which 11 isolates (0.97%) harbored blaNDM-1. Noteworthy, none of these cases had a history of traveling outside Brazil, which suggest a local acquisition. The isolates analysed in the present study were collected from patients who fulfill the risk factors contributing to infection by co-resistant agents, e.g. low socioeconomic class, low educacional backgroung, severe clinical conditions and poor functional status [8,21,22]. Even outside of the hospital setting there are concerns about KPC-2 producing K. pneumoniae isolates (ST340), as demonstrated by the presence of such samples on the waters of urban rives in Sao Paulo, Brazil [23]. Such a finding has as one possible explanation the inproper treatment of hospital sewage being discarded on the rivers.
Outside the hospital setting, another concern is the lack of basic sanitation. Under this circumstance, Klebsiella pneumoniae isolates (ST340) harbouring KPC-2 has been reported in urban areas, in the city of Sao Paulo, Brazil, during a local surveillance study (15).
Our isolates displaye a high-level of resistance to β-lactams, aminoglycosides, and fluoroquinolones. A possible reason for these results is that carbapenem-resistant enterobacteria isolates carrying blaNDM-1 are more likely to be resistant to several antibiotics. They are often accompanied by other genes, which are resistant to β-lactams, fluoroquinolones and aminoglycosides [7].
The isolate which was colistin resistant did not harbor plasmidial mediated resistance genes nor chromosomal mutation on the WGS analyzes. We speculate that the resistance derived from virulence genes encoded at Lipopolysaccharide (LPS) rfb locus, wzm and wzt codify the proteins to form an ATP-binding cassette (ABC) transporter responsible for export O-antigenic polysaccharide (O-PS), a glycan necessary to synthetize cell surface LPS. The ABC transporters are formed to a specific O-PS [24]. The Wzt protein dictates the specificity of the substrate and the glycan chain length, which serves as an export signal recognized by the ABC transporter. The K. pneumoniae isolate 1581 carries just the wzm gene therefore our hypothesis is that lacking wzt trapped the transporter in a state incapable to complete the O-PS export. It might explain the colistin resistance, specifically because in K. pneumoniae the cytosolic glycan synthesis and export are obligatorily coupled [25].
According to table 1, the patient clinical conditions were severe, therefore, the presence of blaKPC-2 and bla NDM-1 might contributed to unfavorable clinical outcome, considering that four of the patients died in this same hospitalization without blood culture clearance. Based on the evidence presented here, significant effort is required to identify these isolates with both resistance genes in the routine and research laboratory. To complicate matters further, we are rising an hypothesis regarding the correlation between high-resistance bacteria found in survilance assays in urban rivers in Sao Paulo, performed by Pereira et al, 2014 and those found in hospitals[23]. The detection of samples co-harboring KPC-2 and NDM-1 remains unsatisfactory with phenotypic tests. As a result, routine microbiology laboratories must be on alert for samples co-harboring these mechanisms. Early detection becomes extremely important for the implementation of infection control measures and epidemiological surveillance, tests as a direct multiplex-PCR from the sample for example would be helpful if performed.