Identification, Genotypic Relation, and Clinical Features of Colistin-Resistant Isolates of Acinetobacter Genomic Species 13BJ/14TU from Bloodstreams of Patients in a University Hospital

Abstract

Colistin resistance remains rare among clinical isolates of Acinetobacter species. We noted the emergence of colistin-resistant bloodstream isolates of the Acinetobacter genomic species (GS) 13BJ/14TU from patients at a university hospital between 2003 and 2011. We report here, for the first time, the microbiological and molecular characteristics of these isolates, with clinical features of Acinetobacter GS 13BJ/14TU bacteremia. All 11 available patient isolates were correctly identified as Acinetobacter GS 13BJ/14TU using partial rpoB gene sequencing but were misidentified using the phenotypic methods Vitek 2 (mostly as Acinetobacter baumannii), MicroScan (mostly as A. baumannii/Acinetobacter haemolyticus), and the API 20 NE system (all as A. haemolyticus). Most isolates were susceptible to commonly used antibiotics, including carbapenems, but all were resistant to colistin, for which it is unknown whether the resistance is acquired or intrinsic. However, the fact that none of the patients had a history of colistin therapy strongly suggests that Acinetobacter GS 13BJ/14TU is innately resistant to colistin. The phylogenetic tree of multilocus sequence typing (MLST) showed that all 11 isolates formed a separate cluster from other Acinetobacter species and yielded five sequence types. However, pulsed-field gel electrophoresis (PFGE) revealed 11 distinct patterns, suggesting that the bacteremia had occurred sporadically. Four patients showed persistent bacteremia (6 to 17 days), and all 11 patients had excellent outcomes with cleared bacteremia, suggesting that patients with Acinetobacter GS 13BJ/14TU-associated bacteremia show a favorable outcome. These results emphasize the importance of precise species identification, especially regarding colistin resistance in Acinetobacter species. In addition, MLST offers another approach to the identification of Acinetobacter GS 13BJ/ 14TU, whereas PFGE is useful for genotyping for this species.

An Intrinsic Strain of Colistin-resistant <i>Acinetobacter</i> Isolated from a Japanese Patient

“…These strains were isolated from patients who had never received colistin treatment, suggesting that the strains were intrinsically resistant to colistin (18,19). These isolates were distinguished from the A. baumannii complex and are now classified as Acinetobacter GS 13BJ/14TU, based on partial nucleotide sequence homology.…”

“…A nucleotide sequence analysis is a reliable method for discriminating between minor species, but it is difficult to perform in a routine laboratory setting. Nonetheless, it should be considered in cases of isolates with atypical drug susceptibility patterns or in patients with specific clinical backgrounds (18,23).…”

Differentiation of Acinetobacter Genomic Species 13BJ/14TU from Acinetobacter haemolyticus by Use of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry (MALDI-TOF MS)

“…Previously, Acinetobacter genomic species 13BJ/14TU had not been correctly identified using some phenotypic identification systems and the VitekMS matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) microbial identification system, although correct identification was achieved using partial rpoB gene sequencing (4,8). In the present study, we showed that Acinetobacter genomic species 13BJ/14TU can be reliably differentiated from other Acinetobacter species using MALDI-TOF mass spectrometry (MS).…”

“…Later studies suggested that these two taxa were congruent with each other at the species level and represented a distinct phylogroup within the hemolytic-proteolytic clade of the genus Acinetobacter (3). Reports from different countries showed that strains of Acinetobacter genomic species 13BJ/14TU were found in clinical specimens at a frequency similar to or even higher than that of another hemolytic and proteolytic species, Acinetobacter haemolyticus (4)(5)(6). It has also been noted that strains of Acinetobacter genomic species 13BJ/14TU are intrinsically resistant to polymyxins (4,7), which further underpins the clinical relevance of this taxon.…”

Management of Infections with Drug-Resistant Organisms in Critical Care

“…34 Although colistin resistance has been reported, it remains an infrequent occurrence. 35 The most commonly used therapies for multidrug-resistant or XDR Acinetobacter spp include high-dose ampicillin/sulbactam, tigecycline, and colistin. It is unclear whether there is a benefit from combination therapy compared with monotherapy, but carbapenems, aminoglycosides, and rifampicins have been used as adjunctive therapy.…”