Emergence of OXA-72-producing Acinetobacter pittii clinical isolates.

The genus Acinetobacter comprises 47 characterised genomic species, among which species belonging to the Acinetobacter calcoaceticus–Acinetobacter baumannii complex are the most clinically relevant. Within this complex, A. baumannii, Acinetobacter nosocomialis (formerly genomic species 13TU) and Acinetobacter pittii (formerly genomic species 3) are frequently associated with hospital-acquired infections [1]. Carbapenem resistance is being increasingly reported in Acinetobacter spp. isolates and this resistance trait is often related to the production of acquired carbapenem-hydrolysing class D -lactamases (CHDLs) that are disseminating worldwide [2]. Five groups of acquired CHDLs have been identified to date in A. baumannii, namely OXA-23, OXA24/-40, OXA-58, OXA-143 and OXA-235 [2]. OXA-72 is a point mutant of OXA-40 that was first described in carbapenem-resistant A. baumannii clinical isolates in China [2]. It was then reported in Colombia from a clinical isolate (A. pittii 2688), which has been used here as a reference strain [3]. This study was initiated by the isolation of three imipenemnon-susceptible Acinetobacter spp. isolates recovered in three hospitals in France in 2011–2013. Isolate RA1 was from the sputum of a patient hospitalised in November 2011, isolate RA2 was from pus of an 84-year-old patient in December 2011, and isolate RA3 was recovered after rectal screening of a 56-year-old patient in May 2013. These isolates were resistant to penicillins and penicillin–inhibitor combinations and were of intermediate susceptibility to carbapenems according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints (http://www.eucast.org/clinical breakpoints/). By contrast, they remained susceptible to ceftazidime and cefepime as well as to amikacin, rifampicin, colistin, fluoroquinolones, tetracycline and tigecycline according to the EUCAST guidelines. The isolates were identified using the API32GN system (bioMérieux, Marcy l’Étoile, France), partial sequencing of their 16S rDNA genes and matrix-assisted laser desorption/ionisation time-of-flight mass (MALDI-TOF) analysis. Identification results showed that the three Acinetobacter spp. strains belonged to the A. pittii species. Since the resistance phenotype to -lactams suggested the production of a CHDL, corresponding genes were searched by PCR as described previously [2]. Interestingly, PCR followed by sequencing analysis identified the blaOXA-72 gene in the three isolates. To determine the genetic location of the blaOXA-72 gene, transfer of the ticarcillin resistance marker into A. baumannii BM4547 was attempted by liquid mating-out assays at 37 ◦C and by electrotransformation of a plasmid DNA suspension extracted from the three clinical isolates and the reference strain (A. pittii 2688). Conjugation remained unsuccessful; nevertheless, transformants were obtained for the three clinical isolates and the reference strain, revealing Fig. 1. Results of DiversiLab (bioMérieux, La Balme-les-Grottes, France) analysis. The horizontal similarity line showed the cut-off to separate different clones.