Occurrence of IMP-1 in non-baumannii Acinetobacter clinical isolates from Brazil

Bacteria belonging to the genus Acinetobacter are ubiquitous in soil and water. Only a few species, including Acinetobacter baumannii, and the unnamed Acinetobacter genomic species (gen. sp.) 3 and 13TU, which together with the soil organism Acinetobacter calcoaceticus are combined in the A. calcoaceticus-A. baumannii (Acb) complex, have been recognized as important nosocomial infectious agents. The ecology, epidemiology and pathology of most species are not yet well established. Lack of practical and accurate methods limits routine identification of clinical isolates and thus hampers precise identification of those of the Acb complex and other Acinetobacter species of possible clinical significance. We previously identified a 350 bp highly variable zone on the rpoB gene which appeared to be a promising target for rapid molecular identification. In the present study, we validated this method for accuracy on a collection of reference strains belonging to A. calcoaceticus (5 strains), Acinetobacter gen. sp. 3 (29 strains), A. gen. sp. 13TU (18 strains), A. baumannii (30 strains) and one strain each of A. radioresistens, A. gen. sp. 15TU, A. gen. sp. 10, A. gen. sp. 11, A. gen. sp. 'between 1 and 3' and A. gen. sp. 14TU=13BJ. This represents the largest analysis to date that compares a large number of well-identified strains of the Acb complex to assess the intra- and interspecies variation within this complex. All were correctly identified with 98.9-100 % intraspecies relatedness based on partial rpoB sequence analysis. We then applied this tool to identify 99 Acinetobacter clinical isolates from four public hospitals in Marseille, France. All isolates could easily be identified to species as they were separated into 13 species sequence types with a sequence variance of 0-2.6% from their respective type strains. Of these 99 isolates, 10 were A. haemolyticus, 52 were A. baumannii, 27 were A. gen. sp. 3, 5 were A. schindleri, 1 was A. lwoffii, and 1 was A. gen. sp. 13TU. Three were provisionally identified as A. gen. sp. 9. This is the first work to identify all specimens of a set of clinical Acinetobacter isolates at species level using rpoB sequence analysis. Our data emphasize the recognition of A. schindleri as an emerging cause of Acinetobacter-related infection and confirm that A. gen. sp. 3 is the second most commonly isolated Acinetobacter species after A. baumannii in patients.

Acinetobacter species isolates from a range of environments, including soil, were investigated. We determined 16S rRNA and rpoB gene sequences for species identification and performed tests of antimicrobial resistance susceptibility. Twenty-nine of the isolates (8 from soil and 21 from life environment) belonged to the genus Acinetobacter. Fourteen Acinetobacter species were identified among 29 isolates: 4 A. baumannii, 3 A. calcoaceticus, 1 A. nosocomialis, 2 A. pittii, and 2 Acinetobacter gen. sp. 'close to 13TU' as A. calcoaceticus-baumannii complex. Three Acinetobacter species isolates were identified as novel species candidates. Three Acinetobacter species isolates were resistant to imipenem: 1 A. parvus and 2 novel species candidates of Acinetobacter. Eight isolates showed resistance to colistin: all Acinetobacter gen. sp. 'close to 13TU' (2 isolates) and A. parvus isolates (3 isolates) were resistant to colistin. Although the genotypes of A. baumannii isolates from various natural environments were different from those of clinical isolates, the presence of clinically important and antimicrobial resistant Acinetobacter species in the natural environment may represent a threat to public health. Copyright © 2012 Elsevier Inc. All rights reserved.

Although many studies have been performed on carbapenem-resistant Acinetobacter baumannii, only a few studies have addressed carbapenem resistance in Acinetobacter spp. other than A. baumannii (non-baumannii Acinetobacter). Amongst 287 Acinetobacter spp. isolates from patients with bacteraemia in a South Korean hospital collected between 2003 and 2010, 160 (55.7%) were non-baumannii Acinetobacter spp. Antimicrobial susceptibility testing was performed and the effect of efflux pump inhibitors was examined. Antimicrobial resistance genes were identified and pulsed-field gel electrophoresis (PFGE) analysis was performed. OprD expression was also evaluated by quantitative real-time polymerase chain reaction (qRT-PCR), and CarO disruption was investigated by PCR. Seventeen non-baumannii Acinetobacter isolates (10.6%) were resistant to imipenem or meropenem, comprising eight Acinetobacter pittii (or Acinetobacter genomospecies 3), four Acinetobacter nosocomialis (or Acinetobacter genomospecies 13TU), two Acinetobacter genomospecies 'close to 13TU', two Acinetobacter bereziniae (or Acinetobacter genomospecies 10) and one Acinetobacter genomospecies 16. bla(IMP-1) genes were detected in seven and two carbapenem-resistant A. pittii and A. bereziniae isolates, respectively. PFGE showed that A. pittii isolates carrying bla(IMP-1) belonged to the same clone. In addition, bla(SIM-1) and bla(PER-1) genes were simultaneously identified in two A. nosocomialis isolates. In four isolates (one each of A. pittii, A. nosocomialis, Acinetobacter genomospecies 'close to 13TU' and Acinetobacter genomospecies 16), efflux pumps were implicated in the increase in carbapenem minimum inhibitory concentrations. No decreased expression of OprD was identified in any carbapenem-resistant non-baumannii Acinetobacter isolates, and disruption of carO was also not detected. Clonal spread of carbapenem-resistant A. pittii carrying bla(IMP-1), which contributes to a high resistance rate in this species, was identified. The bla(IMP-1) and bla(SIM-1) genes were first identified in A. bereziniae and A. nosocomialis, respectively. Since no carbapenem resistance mechanisms could be identified, further efforts to find the resistance mechanism should be made.