Could Acinetobacter pittii act as an NDM-1 reservoir for Enterobacteriaceae?

Sir, Carbapenemases are the most common mechanism of carbapenem resistance and include b-lactamases of Ambler classes A, B (metallo-b-lactamases) and D. Among the carbapenemases, the New Delhi metallo-b-lactamase-1 (NDM-1) has been recovered worldwide in Gram-negative bacteria, especially in Enterobacteriaceae, but also in Pseudomonas aeruginosa and in several Acinetobacter species, including Acinetobacter baumannii and other Acinetobacter species isolated from clinical samples, environmental samples and food animals. – 4 Several reports showed that blaNDM-1 is frequently located on mobile genetic elements inserted into the chromosome or on plasmids that often carry several additional resistance genes. Here, we report a case of infection due to an NDM-1-producing Acinetobacter pittii recovered in Belgium from an immunocompromised patient who had previously travelled to Egypt and to north-west India (Rajasthan). In 2012, a patient was admitted to hospital for an episode of acute alcoholic pancreatitis. This patient had received successive courses of treatment with various antimicrobial broad-spectrum antibiotics, including amoxicillin/clavulanate and amikacin, piperacillin/tazobactam and meropenem. A rectal swab obtained upon admission for the screening of asymptomatic carriage of carbapenemase producers was cultured on a selective Brilliance CRE agar plate (Oxoid, Cambridge, UK), but yielded no growth after 24 h. A few days later, the patient developed severe abdominal pain and high-grade fever with elevated serum amylase and lipase levels. An abdominal CT scan image showed the presence of multiple pancreatic pseudocysts, which led to surgical drainage of the intra-abdominal collections. Perioperative abdominal fluid and liquid from pancreatic cyst punctures grew an A. pittii isolate, 2012276, identified by matrix-assisted laser desorption/ ionization–time of flight mass spectrometry (MALDI-TOF MS; Bruker Daltonik, Bremen, Germany), which displayed resistance to piperacillin/tazobactam (MIC .64/4 mg/L), ceftazidime (MIC .256 mg/L), cefepime (MIC .256 mg/L), meropenem, doripenem and imipenem (MIC .32 mg/L) and susceptibility to ciprofloxacin (MIC 0.5 mg/L), gentamicin (MIC 2 mg/L), tobramycin (MIC ≤1 mg/L), amikacin (MIC 16 mg/L) and colistin (MIC 0.5 mg/L) by the broth microdilution method using CLSI interpretative criteria. The production of a metallo-b-lactamase was confirmed by the Neo-SensitabsTM combined disc test (Rosco Diagnostica, Taastrup, Denmark) using meropenem and dipicolinic acid as an inhibitor of metallo-b-lactamases (results not shown). The presence of blaNDM-1 was detected using a Check-Points array (CT102, Wageningen, the Netherlands) and further analysis of the presence of b-lactamase-coding genes by endpoint multiplex PCRs targeting minor extended-spectrum b-lactamases (blaBEL, blaVEB, blaGES and blaPER), carbapenemases (blaOXA-48, blaKPC, blaVIM, blaIMP and blaNDM) and OXA carbapenemases (blaOXA-23, blaOXA-24 and blaOXA-58) 6 confirmed that A. pittii was positive for blaNDM-1 only. Plasmid extraction revealed the presence of a 47 kb plasmid, which was easily transferred by conjugation to azide-resistant Escherichia coli J53, conferring on the recipient strain nonsusceptibility to ertapenem (MIC 16 mg/L), imipenem (MIC 4 mg/L), meropenem (MIC 2 mg/L) and doripenem (MIC 2 mg/L) (results not shown). PCR mapping and sequencing of the genetic context of blaNDM-1 revealed a Tn125 composite transposon bracketed by two copies of ISAba125 as previously reported in A. baumannii Ab11314 reported in Belgium (Figure 1). This structure is also identical to the sequence described in non-baumannii Acinetobacter spp. recovered in China. In particular, this transposon includes an ISCR27, which could be at the origin of the acquisition of the blaNDM-1 gene by a rolling-circle mechanism from its progenitor. The genetic context of the transposon was determined by PCR mapping and partial sequencing using a set of 12 primer pairs described by Hu et al. and showed a plasmid scaffold identical to the type IV secretion system (T4SS) plasmid pNDM-BJ01 recovered from Acinetobacter lwoffii in China (results not shown). T4SS is an extremely versatile secretion system involved in conjugation, in translocation of protein effectors, such as virulence proteins, and in DNA uptake. A combined therapy, including 400 mg of ciprofloxacin intravenously twice daily and 3 IU of colistin intravenously four-times daily, was administered for 21 days. The patient was eventually discharged following a control abdominal CT scan that showed a significant decrease in the collections. Non-baumannii Acinetobacter spp. expressing NDM-1 have mostly been reported in China and have not yet been described in European countries. In the present case the patient had a history