Coexistence of blaNDM-1 with the Prevalent blaOXA23 and blaIMP in Pan-drug Resistant Acinetobacter baumannii Isolates in China

Abstract

To the Editor—The emergence of New Delhi metallo-beta-lactamase–1 (NDM1) in India, Pakistan, and the UK has sparked great fear of the threat posed by resistant microbial strains and by the use of antibiotics worldwide [1]. Thus far, NDM-1 carbapenemase has been detected in several countries in a diverse group of bacteria. Acinetobacter baumannii has emerged as one of the most troublesome pathogens for health care institutions globally. Its clinical significance has been propelled by its remarkable capability to upregulate or acquire resistance determinants, making it one of the most important organisms threatening the current antibiotic era. In Chinese hospitals, A. baumannii is the most common genus of carbapenemresistant bacteria [2]. We screened carbapenem-resistant A. baumannii for the presence of blaNDM-1 and successfully detected a blaNDM-1–positive strain, to our knowledge the first such strain of A. baumannii isolated in China. In addition to carbapenem, this isolate is resistant to various types of antibiotics—consistent with what has been observed in other countries [1]. Resistance to carbapenem is mainly mediated by 4 classes of carbapenemases among different bacterial species [3]. The carbapenemases found in A. baumannii thus far belong to either the OXA class D family of serine b-lactamases or to the IMP/VIM class B family of metallo-b-lactamases [4]. Polymerase chain reaction screening was performed to identify OXA type (OXA-23, OXA-24, and OXA-58–like) and the IMP/VIM genes. Of the 122 A. baumannii isolates from Chinese patients, 115 (94.2%) were positive for OXA-23 and 66 (54.0%) were positive for IMP. No other carbapenemase genes were detected. Sequencing of blaOXA-23 and blaIMP genes showed 100% identity with previously reported genes. All the IMP-positive isolates were also positive for OXA-23. The isolates positive for both OXA-23 and IMP showed increased resistance to most antibiotics (Table 1). Interestingly, the NDM1–positive isolate was also positive for both OXA-23 and IMP. The blaNDM-1– positive strain was more resistant to antibiotics than were strains that harbor both OXA-23 and IMP. However, we also found that the NDM-1–positive strain was susceptible to several fluoroquinolone antibiotics and to polymyxin B. Hospital-acquired infections with A. baumannii have been reported worldwide [5]. The success of the organism has been attributed to its ability for long-term survival in a hospital environment and its ability to rapidly acquire resistance to antibiotics. Although the exact mechanisms remain to be further defined, the emergence of blaNDM-1 in A. baumannii, and its coexistence with other carbapenemase genes, will seriously limit future therapeutic options.