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Molecular Diversity of NDM-1, NDM-5, NDM-6, and NDM-7 Variants of New Delhi Metallo-β-Lactamases and Their Impact on Drug Resistance by Kashaf Junaid

Background: The emergence of multidrug-resistant bacteria has become a serious healthcare problem worldwide.
Methods: In this study, 192 clinical specimens collected from a tertiary hospital in Al Jouf, Saudi Arabia were processed in order to isolate gram-negative bacteria. Bacterial isolation was performed using standard microbiological techniques and the MicroScan WalkAway Plus automated analyzer. Phenotypic methods and PCR were done to characterize bacterial strains, and DNA sequencing was used for the molecular characterization of new Delhi metallo-β-lactamases NDM genes.
Results: This study reports the presence of the blaNDM gene in 95 gram-negative bacterial isolates. Among the iso-lates, 71 (74%) carried blaNDM-1 and 24 (25%) carried blaNDM gene variants. Different specimen analyses revealed that the samples from the intensive care unit (ICU) showed the highest percentage (38%) of NDM-1 positive isolates. Molecular identification revealed 87% belonged to the Enterobacteriaceae family. The species profiling showed that 41% of the clinical isolates were Klebsiella pneumoniae, 25.3% of isolates were E. coli, and 9.5% were Enterobacter cloacae. Thirteen percent of the gram-negative isolates, Pseudomonas aeruginosa and Acinetobacter baumannii, belonged to the Pseudomonadaceae family and Gammaproteobacteria family, respectively. The antibiotic sensitivity profile of the 95 isolates revealed that all the isolates harboring the NDM gene showed resistance against ampicillin. Among the NDM-harboring isolates, the highest resistance was found against cefuroxime and co-amoxiclav antibiotics. The isolates were the most sensitive to tigecycline and amikacin. However, the ability of some NDM-harboring gram-negative isolates to grow in the presence of amikacin and tigecycline suggests that these NDM-producing strains carry an additional drug-resistance mechanism.
Conclusions: The prevalence of NDM-harboring gram-negative bacterial isolates in hospital settings is an alarming situation. The Enterobacteriaceae family was found to be the most common carrier of the NDM gene, which indicates a need for more stringent use of antibiotics and better control in hospitals to minimize the risk of cross contamination and spread of NDM-positive strains.

DOI: 10.7754/Clin.Lab.2021.201214