Resistotyping, phenotyping and genotyping of New Delhi metallo-β-lactamase (NDM) among Gram-negative bacilli from Iranian patients.
OBJECTIVE
The purpose of this study was to investigate New Delhi metallo-β-lactamase (NDM) production among Gram-negative bacilli.


METHODS
Antibiogram-resistotyping and detection of New Delhi metallo-β-lactamase (NDM) in clinical isolates of Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa and comparative evaluation of the diagnostic performance of three phenotypic methods for NDM detection, with PCR considered as the gold standard, were performed. Minimum inhibitory concentration (MIC) of antibiotics against NDM-positive strains using E-tests and clonal relationship analysis using enterobacterial repetitive intergenic consensus (ERIC)-PCR in these strains were determined.


RESULTS
The most effective antibiotics against strains of the species K. pneumoniae were Colistin, Chloramphenicol and Tigecycline; against P. aeruginosa were Fosfomycin and Polymyxins, and against A. baumannii were Polymyxins, Ampicillin/Sulbactam and Minocycline. Overall, 66, 31 and 40 different resistotypes were observed among K. pneumoniae, A. baumannii and P. aeruginosa strains, respectively. The blaNDM-1 gene was detected in 28 (8.5 %) strains of the bacteria investigated. The sensitivities and specificities of the Meropenem-EDTA combined disk test, the meropenem-dipicolinic acid combined disk test and the modified Hodge test methods for NDM detection were 96.43, 55.15; 96.43, 54.85; and 89.29, 35.15, respectively. Additionally, in spite of the low positive predictive values of these tests, their negative predictive values were high. ERIC-PCR results revealed two main clusters in NDM-positive strains of each of the species P. aeruginosa and A. baumannii, and ten main clusters in K. pneumoniae. In all the NDM-positive strains maximum MIC rates (>256) were observed for all beta-lactam antibiotics.


CONCLUSIONS
There were high levels of antibiotic resistance and a high frequency of multi-drug resistance and extensive-drug resistance profiles, as well as highly prevalent blaNDM-1 genes in the bacteria investigated.
Nosocomial Infection Research Center, Isfahan University of Medical Sciences, Isfahan, Iran.
Dariush
D
Shokri
Department of Biology, School of Sciences, University of Isfahan, Isfahan, Iran.
Mohammad
M
Rabbani Khorasgani
Department of Microbiology, Islamic Azad University, Faculty of Basic Sciences, Shahrekord Branch, Shahrekord, Iran.
Seyed Masih
SM
Fatemi
Department of Biology, School of Sciences, University of Isfahan, Isfahan, Iran.
Abbas
A
Soleimani-Delfan
D040981:Acinetobacter baumannii / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D015780:Carbapenems / Q000494:pharmacology; D016000:Cluster Analysis; D024881:Drug Resistance, Bacterial; D005838:Genotype; D006801:Humans; D007492:Iran; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D000077731:Meropenem; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D013845:Thienamycins / Q000494:pharmacology; D001618:beta-Lactamases / Q000235:genetics*
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015780:Carbapenems; D013845:Thienamycins; D001618:beta-Lactamases; C552864:beta-lactamase NDM-1; D000077731:Meropenem
Acinetobacter baumannii; Carbapenemase; New Delhi metallo-beta-lactamase (NDM); Klebsiella pneumoniae; Meropenem-EDTA/Meropenem-Dipicolinic acid combined disk test; Pseudomonas aeruginosa; antibiogram-resistotyping; blaNDMgene; modified Hodge test; polymerase chain reaction