This study showed that the dissemination of TNAN isolates in Taiwan is attributable mainly to the spread of ST410. The AdeABC efflux pump appeared to play an important role in the tigecycline resistance of A. nosocomialis.

The over-expression of AdeABC efflux pumps was directly activated by the AdeRS two-component system and simultaneously reduced the susceptibilities of tigecycline, eravacycline, and omadacycline. Omadacycline and eravacycline MICs were correlated closely with those of eravacycline.

Letter to the Editor Emergence of carbapenem-resistant Acinetobacter nosocomialis strain ST410 harbouring plasmid-borne bla OXA-72 gene in Taiwan Acinetobacter nosocomialis is increasingly identified as a causative agent of nosocomial infections in recent years [1]. Carbapenems, especially imipenem, is often used as the drug of choice for treating multidrug-resistant Gram-negative bacterial infection, but the carbapenem-nonsusceptible rate of the Acinetobacter species is increasing worldwide. The Ambler class B-metallo-b-lactamases and carbapenem-hydrolyzing class D b-lactamases (CHDLs) are two common mechanisms for the imipenem nonsusceptibility of Acinetobacter species [2]. CHDLs are most strongly associated with imipenem nonsusceptibility of Acinetobacter species. Acinetobacter baumannii and A. nosocomialis, the two most common species, together account for >80% of all Acinetobacter infections in Taiwan. The imipenem-nonsusceptible rate of A. nosocomialis in bloodstream infections increased in recent years. However, the mechanism of imipenem-nonsusceptible A. nosocomialis is rarely reported [1]. The aim of this study was to investigate the mechanism and molecular epidemiology of imipenem-nonsusceptible A. nosocomialis isolated from bloodstream infections in Taiwan. In this retrospectively study, we analysed a total collection of 111 nonduplicate A. nosocomialis of bloodstream infections in Tri-Service General Hospital, National Defense Medical Center, Taiwan, from 2012 April to 2016 June. All isolates were identified using the VITEK 2 system (bioM erieux, Marcy l' Etoile, France) and were confirmed by sequencing of the 16Se23S rRNA intergenic transcribed spacer region and rpoB gene. Antimicrobial susceptibility tests were performed by the VITEK 2 system. The MIC values (mg/L) of imipenem were determined by both the agar dilution method and the Etest (AB Biodisk, Solna, Sweden). All isolates were nonsusceptible to ampicillin, cefazolin and ceftriaxone. Their nonsusceptible rates of piperacillin/tazobactam, imipenem, ciprofloxacin, cefepime, gentamicin and tigecycline ranged 27% to 40.5%. In contrast, more than 92.8% of the isolates were susceptible to amikacin. Comparison of the susceptibility patterns between isolates from the intensive care unit (ICU) and the non-ICU, A. nosocomialis strains isolated from ICU showed significantly higher resistance rates to piperacillin/tazobactam, imipenem, ciprofloxacin, cefepime, gentamicin and tigecycline than those isolated from general wards (Fisher's exact test, p <0.05). Using the Clinical and Laboratory Standards Institute breakpoints for Acinetobacter species (susceptible, 2 mg/L; intermediate, 4 mg/L; resistant, 8 mg/L), 41 isolates were nonsusceptible to imipenem, including 37 isolates with MIC >16 mg/L, three isolates with MIC of 8 mg/L and one isolate with MIC of 4 mg/L. The remaining 70 (63.1%) of 111 isolates were imipenem susceptible. Contents lists available at ScienceDirect Clinical Microbiology and Infection j o u r n a l h o m e p a g e : w w w. c l i n i ...

Infections caused by extensively drug-resistant (XDR) Acinetobacter nosocomialis have become a challenging problem. The frequent use of colistin as the last resort drug for XDR bacteria has led to the emergence of colistin-resistant A. nosocomialis (ColRAN) in hospitals. The mechanism of colistin resistance in A. nosocomialis remains unclear. This study aimed to investigate the mechanisms underlying colistin resistance in clinical ColRAN isolates. We collected 36 A. nosocomialis isolates from clinical blood cultures, including 24 ColRAN and 12 colistin-susceptible A. nosocomialis (ColSAN). The 24 ColRAN isolates clustered with ST1272 (13), ST433 (eight), ST1275 (two), and ST410 (one) by multilocus sequence typing. There was a positive relationship between pmrCAB operon expression and colistin resistance. Further analysis showed that colistin resistance was related to an amino acid substitution, Ser253Leu in PmrB. By introducing a series of recombinant PmrB constructs into a PmrB knockout strain and protein structural model analyses, we demonstrated that the association between Ser253Leu and Leu244 in PmrB was coupled with colistin resistance in ColRAN. To the best of our knowledge, this is the first study 3 demonstrating that the key amino acid Ser253Leu in PmrB is associated with overexpression of the pmrCAB operon and hence colistin resistance. This study provides insight into the mechanism of colistin resistance in A. nosocomialis.

Introduction. Outbreaks of carbapenem-resistant A. baumannii and A. nosocomialis have occurred worldwide in healthcare settings. Rapid and reliable molecular typing of bacterial isolates is vital for the effective surveillance of institutional outbreaks. The Pan-PCR and OXA-PCR assays are two multiplex PCR-based assays for the molecular typing of Acinetobacter species. Gap statement. However, few studies have investigated the discriminatory power of two multiplex PCR assays in in the genotyping of Acinetobacter species. Aim. We aimed to evaluate the efficacies of the Pan-PCR and OXA-PCR assays for molecular typing of A. baumannii and A. nosocomialis . Methodology. A total of 105 carbapenem-resistant A. baumannii isolates (CRABs) and 93 carbapenem-resistant A. nosocomialis isolates (CRANs) obtained from blood cultures were used for molecular typing by the Pan-PCR and OXA-PCR assays and two multilocus sequence typing (MLST) schemes. Results. The isolates were individually divided into 12 and 21 different sequence types via the Pasteur and Oxford MLST schemes, respectively. Additionally, these isolates were distinguished into 18 different types by the Pan-PCR and OXA-PCR assays. The results of the Pan-PCR and OXA-PCR assays distinguished CRABs and CRANs with a sensitivity of 98.13 % and a specificity of 100 %. Conclusion. The Pan-PCR and OXA-PCR assays are promising alternative methods for rapid molecular typing of CRABs and CRANs in a routine laboratory setting.