Molecular epidemiology of carbapenem-resistant
Acinetobacter baumannii
group in Taiwan
Authors: Quyen Tran Lam Tu , Hsieh Yu-Chia , Li Shiao-Wen , Wu Lii-Tzu , Liu Ya-Zhu , Pan Yi-Jiun 
Published: December 2024

Acinetobacter,
particularly the
Acinetobacter baumannii
group, is a major cause of nosocomial infections, and carbapenem-resistant
Acinetobacter
spp. are important human pathogens. We collected 492
Acinetobacter
spp. strains from two hospitals in Taiwan and classified them using MALDI-TOF MS and
bla
OXA-51-like
PCR; 94.5% were
A. baumannii,
and 5.5% were non-
A
.
baumannii
(NAB). We confirmed their identity by
rpo
B gene sequencing of 239 randomly selected
A. baumannii
strains and all 27 NAB strains. Our analysis revealed that the
rpo
B alleles of OXA51-like-negative strains matched those of two NAB species,
A. seifertii
and
A. nosocomialis
, while all OXA51-like-positive strains matched
A. baumannii
, as per the Pasteur MLST scheme database. Among the 492 strains, 240 exhibited carbapenem resistance, including 237 carbapenem-resistant
A. baumannii
(CRAB) strains and three CR-NAB strains. All CRAB strains were positive for
bla
OXA-51-like
; 72.6% also carried
bla
OXA-23-like
, 22.8% carried
bla
OXA-24-like
, 3.4% co-carried
bla
OXA-23-like
+
bla
OXA-24-like
, and 1.27% carried
bla
OXA-51-like
alone. Among the three CR-NAB strains, one carried
bla
NDM-1
, and two co-carried
bla
OXA-58-like
+
bla
IMP
. We also established a new multiplex PCR method for rapid screening of common capsular types (KL), which showed a difference between CRAB and carbapenem-susceptible
A. baumannii
(CSAB). KL2, KL10, KL22, and KL52 accounted for 76.6% of CRAB strains, whereas about half of the CSAB strains were other KL types. Of the remaining CSAB strains, KL14 was the most predominant type at 10.3%. We further conducted MLST Pasteur typing for 262 isolates and found that the carbapenemase genes were correlated with either ST or KL types. Additionally, KL types showed correlations with ST types, carbapenem resistance, and certain clinical records. Whole-genome sequencing of a
bla
NDM-1
-carrying
A. seifertii
strain revealed a plasmid transferable via
in vitro
conjugation, suggesting
A. seifertii
may be a reservoir for NDM-1 plasmids.

IMPORTANCE

Carbapenem-resistant
Acinetobacter
spp. have been identified by the World Health Organization as a top priority for new antibiotic development. We established a rapid KL-typing method for efficient screening of
Acinetobacter baumannii
strains to enable epidemiological surveillance and provide a foundation for effective infection control. Our investigation of the molecular epidemiology of the
A. baumannii
group isolates revealed the prevalence of carbapenemase genes and major KL types among CR and CS strains of
A. baumannii
and NAB. We identified an
A. seifertii
strain carrying a Ti-type conjugative operon on a small plasmid that harbored genes encoding the NDM-1 carbapenemase alongside genes conferring resistance to aminoglycosides and bleomycin and closely resembled sequences detected in
A. soli
and
A. pittii
in Taiwan and China, respectively, suggesting its potential for transmitting multidrug resistance and contributing to the spread of antimicrobial resistance.