Abstract
ObjectivesThe study aimed to investigate the prevalence and epidemiological characteristics of bla NDM-1 (encoding New Delhi metallo-β-lactamase 1) in Enterobacteriaceae and the Acinetobacter calcoaceticus-Acinetobacter baumannii complex (ABC) in China from July 2011 to June 2012.MethodsPCR was used to screen for the presence of bla NDM-1 in all organisms studied. For bla NDM-1-positive strains, 16S rRNA analysis and Analytical Profile Index (API) strips were used to identify the bacterial genus and species. The ABCs were reconfirmed by PCR detection of bla OXA-51-like. Antibiotic susceptibilities of the bacteria were assessed by determining minimum inhibitory concentration (MIC) of them using two-fold agar dilution test, as recommended by the Clinical and Laboratory Standards Institute (CLSI). Molecular typing was performed using pulsed-field gel electrophoresis (PFGE). S1 nuclease-pulsed-field gel electrophoresis (S1-PFGE) and Southern blot hybridization were conducted to ascertain the gene location of bla NDM-1. Conjugation experiments were conducted to determine the transmission of bla NDM-1-positive strains.ResultsAmong 2,170 Enterobacteriaceae and 600 ABCs, seven Enterobacteriaceae strains and two A. calcoaceticus isolates from five different cities carried the bla NDM-1 gene. The seven Enterobacteriaceae strains comprised four Klebsiella pneumoniae, one Enterobacter cloacae, one Enterobacter aerogen and one Citrobacter freundii. All seven were non-susceptible to imipenem, meropenem or ertapenem. Two A. calcoaceticus species were resistant to imipenem and meropenem. Three K. pneumoniae showed the same PFGE profiles. The bla NDM-1 genes of eight strains were localized on plasmids, while one was chromosomal.ConclusionsCompared with previous reports, the numbers and species containing the bla NDM-1 in Enterobacteriaceae have significantly increased in China. Most of them are able to disseminate the gene, which is cause for concern. Consecutive surveillance should be implemented and should also focus on the dissemination of bla NDM-1 among gram-negative clinical isolates.
Highlights
Carbapenems are the mainstream treatment for antibiotic-resistant bacterial infections, especially infections triggered by multi-drug resistant gram-negative bacteria [1]
New Delhi metallo-b-lactamase 1 (NDM-1), a new type of Ambler class B metallo-b-lactamases (MBLs), was first reported in K. pneumoniae and Escherichia coli derived from a Swedish patient of Indian origin who was admitted to hospital in New Delhi, India in 2009 [4]
Three of them were from Hunan Province, two from Shaanxi Province, two from Zhejiang Province, one from Xinjiang Province and one from Jiangsu Province (Table 1), located in the East and Northwest of China. 16S rRNA sequencing and biochemical Analytical Profile Index (API) strips revealed that four were K. pneumoniae (M186, M187, M194, U091), two were Acinetobacter baumannii complex (ABC) (G113, X231), one was Enterobacter cloacae (Q297), one was Enterobacter aerogenes (Q442) and one was Citrobacter freundii (X122), respectively. blaOXA-51-like detection in the two ABCs was negative, indicating that both G113 and X231 were A. calcoaceticus
Summary
Carbapenems are the mainstream treatment for antibiotic-resistant bacterial infections, especially infections triggered by multi-drug resistant gram-negative bacteria [1]. The blaNDM-1 gene has been detected in K. pneumoniae, E. coli, Klebsiella oxytoca, Enterobacter cloacae, Enterobacter aerogenes, Proteus spp., Citrobacter freundii, Morganella morganii, Providencia spp., Acinetobacter spp. and Raoultella ornithinolytica [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24] It is typically carried by plasmids, but can be chromosomal [25]. Plasmids carrying blaNDM-1 are mostly transferable and coexist with many other resistance determinants [12, 14, 18], further complicating the treatment of NDM1-producing bacteria infections
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