New Delhi metallo-β-lactamase and OXA-48 carbapenemases in Gram-negative bacilli isolates in Libya

To the Editor Carbapenems (i.e. ertapenem, imipenem, meropenem, and doripenem) are second line antimicrobials reserved to treat serious infections, including those caused by Gramnegative bacilli (GNB) producing extended-spectrum b-lactamses (ESBLs). ESBLs mediate resistance among GNB to b-lactam drugs, including third generation cephalosporins. Emergence of carbapenemases-producing GNB (mainly Acinetobacter baumanii, Pseudomonas aeruginosa, and members of the family Enterobacteriaceae) in the last decade is a serious health problem globally. Carbapenemases are members of three molecular groups of b-lactamases, Ambler class A, B (i.e. metallo b-lactamases [MBLs]), and D (i.e. oxacillinases) (1, 2). Recently, the novel carbapenemase New Delhi MBL (NDM) was reported for the first time in Tunisia in Klebsiella pneumoniae isolated from a female patient transferred from Libya (3). However, there is little information regarding genes associated with carbapenem resistance among GNB in Libya. Included in the study were eight GNB isolates that are resistant to at least one carbapenem (i.e. ertapenem) obtained in 2013 and 2014 from different clinical specimens from patients at the time an infection occurred. Patients were aged between 10 and 87 years (mean 37.1 years). Information about patients and the organisms isolated from them included in the study are shown in Table 1. In this prospective investigation, clinical specimens were collected under approved ethical standards, and the study was reviewed and approved by the Academy of Graduate Studies, Tripoli, Libya. All specimens were cultured on plates of blood agar and MacConkey agar (Oxoid Ltd., Basingstoke, Hampshire, UK) and incubated at 378C for 24 48 h. Isolated organisms were identified to the species level and tested for their susceptibility to avariety of antimicrobial agents by the BD Phoenix Automated Microbiology System (PAMS, MSBD Biosciences, Sparks, MD, USA) as recommended by the manufacturer. PAMS provides antimicrobial susceptibility results as susceptible (S), intermediate susceptible (I), or resistant (R) and are interpreted according to Clinical and Laboratory Standards Institute criteria (4). Quality control strains used included Escherichia coli ATCC 25922, K. pneumoniae ATCC 700603, and P. aeruginosa ATCC 27853 (ATCC, LGC Standards S.r.l., Italy). Furthermore, six of the GNB isolates were tested phenotypically for the production of MBLs by the MIC Test Strip MBL (Liofilchem, Rosetodegli Abruzzi, Italy) as recommended by the manufacturer. All eight isolateswere examined forgenes encoding ESBLs blaCTX-M, blaGES, blaVEB, blaPER, or blaBES and carbapenemases blaKPC, blaVIM, blaNDM, or blaOXA-48 by polymerase chain reaction (PCR) using primers and conditions described previously (5, 6). In addition, both A. baumanii isolates were further tested for carbapenemase genes blaOXA-23-like, blaOXA-24/40-like, blaOXA-143-like, blaOXA-51-like, and blaOXA-58-like using PCR as above. All A. baumanii and Pseudomonas sp. isolates were resistant to the three carbapenems as well as to nearly all other antimicrobials that were used. Only colisitin showed excellent activity against the GNB isolates investigated (100% susceptible) followed by amikacin (50% susceptible). Furthermore, all organisms were multidrug resistant (MDR; resistance to three or more antimicrobial groups). Table 2 shows the antimicrobial susceptibility of the investigated GNB isolates. Of the ESBLs genes examined, blaCTX-M was detected in one K. pneumoniae and in the Enterobacter gergoviae isolate, and blaGES in the P. aeruginosa isolate. Other ESBL genes examined were not detected in all eight GNB isolates. Of the carbapenemase genes investigated, blaNDM was detected in one K. pneumoniae, and blaOXA-48 in E. gergoviae and in another K. pneumoniae isolate. On the other hand, the carbapenemase gene blaKPC was not detected in all isolates investigated. Table 3 shows genes encoding ESBLs and carbapenemases in the GNB isolates from Tripoli, Libya. Oxacillinases are mainly present in Acinetobacter sp. (7), and some of them are intrinsic to the organism (e.g. OXA51) while others are acquired (e.g. OXA-23). blaOXA-23-like and blaOXA-51-like were found in both A. baumanii isolates. Recently, Mathlouthi et al. (8) reported MDR A. baumannii isolates harboring blaOXA-23-like, blaOXA-24-like, and blaOXA-48-like genes in Libya. On the other hand, we identified OXA-48 in one K. pneumoniae as well as in the E. gergoviae isolate. Kocsis et al. (9) reported K. pneumoniae harboring OXA-48 carbapenemase in a Libyan refugee in Italy. In addition, several studies reported OXA-48 carbapenemaseproducing K. pneumoniae in patients transferred from Libyan Journal of Medicine