BackgroundThe emergence of carbapenem-resistant Klebsiella pneumoniae poses a serious problem to antibiotic management. We investigated the β-lactamases in a group of carbapenem-resistant K. pneumoniae clinical isolates from Turkey.MethodsThirty-seven strains of K. pneumoniae isolated from various clinical specimens were analyzed by antimicrobial susceptibility testing, PCR for the detection of β-lactamase genes, DNA sequencing, and repetitive extragenic palindronic (REP)-PCR analysis.ResultsAll 37 isolates were resistant to ampicillin, ampicillin/sulbactam, piperacillin, piperacillin/tazobactam, ceftazidime, cefoperazone/sulbactam, cefepime, imipenem, and meropenem. The lowest resistance rates were observed for colistin (2.7%), tigecycline (11%), and amikacin (19%). According to PCR and sequencing results, 98% (36/37) of strains carried at least one carbapenemase gene, with 32 (86%) carrying OXA-48 and 7 (19%) carrying NDM-1. No other carbapenemase genes were identified. All strains carried a CTX-M-2-like β-lactamase, and some carried SHV- (97%), TEM- (9%), and CTX-M-1-like (62%) β-lactamases. Sequence analysis of blaTEM genes identified a blaTEM-166 with an amino acid change at position 53 (Arg53Gly) from blaTEM-1b, the first report of a mutation in this region. REP-PCR analysis revealed that there were seven different clonal groups, and temporo-spatial links were identified within these groups.ConclusionsCombinations of β-lactamases were found in all strains, with the most common being OXA-48, SHV, TEM, and CTX-M-type (76% of strains). We have reported, for the first time, a high prevalence of the NDM-1 (19%) carbapenemase in carbapenem-resistant K. pneumoniae from Turkey. These enzymes often co-exist with other β-lactamases, such as TEM, SHV, and CTX-M β-lactamases.

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IntroductionXylose isomerase (XI) (D-xylose ketol-isomerase E.C 5.3.1.5) catalyzes the isomerization of D-xylose into xylulose as the first step of xylose metabolism in many microorganisms (Wovcha et al., 1983). It is also responsible for catalyzing the isomerization of glucose to fructose in vitro, and is an important enzyme in the food industry, used in the production of high fructose corn syrup. This is the reason why XI is also known as glucose isomerase (Jensen and Rugh, 1987;De Raadt et al., 1994). The fact that the enzyme isomerizes xylose to xylulose means that it could be used industrially for producing ethanol from hemicellulose (Wang et al., 1980;Ertunga et al., 2007;Karaoglu et al., 2013). Xylose, one of the major fermentable sugars in nature, is, after glucose, the second most abundant sugar in lignocellulosic biomass. Efficient fermentation of xylose is a necessary step in developing economically viable processes for producing biofuels, such as ethanol, from biomass (Zeikus, 1996;Schenck, 2000). For this reason, many XI genes appropriate for industrial applications were transferred to Saccharomyces cerevisiae