First Report of bla_NDM and bla_OXA-58 Coexistence in Acinetobacter junii

LETTER

Acinetobacter species are a major cause of hospital-acquired infections, especially in intensive care units (ICUs) (1). This, in part, is due to the bacteria's ability to survive long-term on hospital environment surfaces and their ability to acquire antibiotic resistance genes (2). One of the Acinetobacter species most often associated with high morbidity and mortality is A. baumannii (1). However, other Acinetobacter species have also been associated with acquiring broad-spectrum antibiotic resistance genes and causing severe disease (3–6). Here we report the isolation of an A. junii strain that was resistant to all β-lactam antibiotics, including the carbapenems, and the aminoglycosides. This isolate's carbapenem resistance mechanism was a result of acquiring two carbapenem resistance genes, bla_NDM-1 and bla_OXA-58. To our knowledge, this is the first report of the coexistence of bla_NDM-1 and bla_OXA-58 in A. junii.

The A. junii strain was isolated from surveillance swabs collected from a 5-day-old baby girl who was referred to Caritas Baby Hospital (CBH) on 9 October 2012 from another hospital located in the northern part of Palestine. Upon admission to CBH's pediatric ward, surveillance (nose, rectal, and umbilical) swabs were collected from the patient on Copan Transystem swabs (Copan Diagnostics, Corona, CA) and transferred to the clinical laboratory within 30 min. This is part of the infection control policies that were followed at CBH to evaluate the presence of bacteria resistant to broad-spectrum antibiotics in high-risk patients referred from other medical institutions. The Caritas Baby Hospital Medical Research Committee approved the study (MRC-14).

The specimens were inoculated on a selective agar medium (MacConkey-cefotaxime [10 μg/ml] and MacConkey-meropenem [0.5 μg/ml]) and incubated for 24 h at 37°C as previously described (7, 8). A weakly lactose-fermenting, oxidase-negative, Gram-negative coccobacillus was isolated on both selective media and was presumptively identified as Acinetobacter species. The identification of the isolate as A. junii was obtained after sequencing the first 500 bp of the amplified 16S rRNA gene as previously described (9). Antimicrobial susceptibility testing was performed by disk diffusion (Oxoid, United Kingdom) according to the standards of the Clinical and Laboratory Standards Institute (10). For the antimicrobial agent colistin, we used the Etest (AB Biodisk; bioMérieux, France) to determine its MIC. The antibiogram showed a total resistance to all β-lactam antibiotics and the aminoglycosides (Table 1). On the other hand, the isolate was susceptible to the fluoroquinolones, tetracyclines, trimethoprim-sulfamethoxazole, and colistin (Table 1).

TABLE 1.

Susceptibility patterns of the bla_NDM- and bla_OXA-58-positive A. junii isolate^a

Antibiotic(s) (concn [μg])	Susceptibility
Mezlocillin (75)	R
Piperacillin-tazobactam (100, 10)	R
Ceftazidime (30)	R
Cefepime (30)	R
Cefotaxime (30)	R
Ceftriaxone (30)	R
Imipenem (10)	R
Meropenem (10)	R
Amikacin (30)	R
Gentamicin (10)	R
Ciprofloxacin (5)	S
Levofloxacin (5)	S
Trimethoprim-sulfamethoxazole (1.25, 23.75)	S
Tetracycline (30)	S

^aThe isolate identification number is 132390. The colistin MIC was 0.125 μg/ml. R, resistant; S, susceptible.

In order to identify the carbapenem resistance mechanism that mediated A. junii's resistance, PCR using primers for the class A carbapenemases (bla_NCM, bla_SME, bla_IMI, bla_GES, and bla_KPC), the class D oxacillinases (bla_OXA-58-like, bla_OXA-23-like, bla_OXA-24-like, bla_OXA-51-like, bla_OXA-23, bla_OXA-24, bla_OXA-69, bla_OXA-48, bla_OXA-50, and bla_OXA-60), and the class B metalloenzymes (bla_IMP-1, bla_IMP-2, bla_VIM-1, bla_VIM-2, bla_SPM-1, bla_GIM-1, bla_NDM, and bla_SIM-1) was performed on the isolate's nucleic acid as previously reported (8, 11, 12). PCR amplification from the A. junii isolate nucleic acid gave the appropriate PCR product for bla_NDM and bla_OXA-58. The bla_NDM and bla_OXA-58 PCR products were sequenced using the BigDye Terminator v3.1 cycle sequencing kit (Life Technology, USA) to confirm the identities of both genes. This represents the first report of A. junii positive for both the bla_OXA-58 and the bla_NDM carbapenem resistance genes.

Carbapenem resistance mediated by either the bla_NDM or the bla_OXA-58 gene has been reported before in A. junii (6, 13). The bla_NDM gene was detected in an A. junii isolate from China. This isolate was resistant to the β-lactam antibiotics but sensitive to the aminoglycosides and the fluoroquinolones (13). On the other hand, bla_OXA-58-positive A. junii isolates were detected in Romania and Australia (6, 14). The characterized isolate from Australia has an antibiotic resistance profile similar to the one detected in Palestine. It was resistant to all β-lactam antibiotics and gentamicin but sensitive to the fluoroquinolones, amikacin, tetracycline, and polymyxin B (6).

The isolation of carbapenem-resistant A. junii with combined antibiotic resistance mechanisms suggests that surveillance swabs collected from high-risk patients play an important role in controlling the spread of drug-resistant bacteria.

Nucleotide sequence accession numbers.

The first 500 bp of the amplified 16S rRNA gene of our isolate was deposited in GenBank under accession number KJ024808. Its bla_OXA-58 and the bla_NDM sequences were deposited under accession numbers KJ024809 and KJ024810.