High Prevalence of OXA-23 group Carbapenemase and Widespread
of ISAba1 in Carbapenem-Resistant Acinetobacter baumannii |
High Prevalence of OXA-23 group Carbapenemase and Widespread of ISAba1 in Carbapenem-Resistant Acinetobacter baumannii |
Seong Il Suh; Won Ki Baek; Min Ho Suh |
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Abstract |
Carbapenem-resistant Acinetobacter baumannii (CRAB) cause infections that are difficult to
treat and have high mortality rates due to their acquisition of multidrug-resistant (MDR)
phenotypes. A total of 172 strains of CRAB isolated from various clinical specimens in Daegu
area were tested to provide an information on the current status of the molecular epidemiology of
carbapenemase genes in CRAB and the genetic platforms participating in their expression. All the
CRAB isolates harboured OXA (oxacillinase)-51-like carbapnenemase gene and 90.7% of them
contained OXA-23-like gene in addition to OXA-51-like gene. We did not detect any genes
encoding the carbapenemases OXA-24-like and OXA-58-like; and none of the genes encoding
metallo-ß-lactamases (IMP: imipenemase; VIM: Verona-imipenemase; GIM: Germanimipenemase;
SPM: Sao-Paulo-imipenemase; SIM: Seoul-imipenemase) were detected in this
study. ISAba1 gene was upstream of bla OXA-23-like in 90.1% of CRAB isolates and 8.7% of
isolates contained an ISAba1 -bla OXA-51-like structure. The presence of ISAba1 upstream of
bla OXA-23 gene in CRAB was highly correlated with resistance to imipenem and meropenem. High
level (minimal inhibitory concentration; MIC=64 mg/L) of resistance to imipenem and meropenem
was observed in isolates containing an ISAba1 -bla OXA-23-like structure. One isolate with bla OXA-
23-like gene lacking ISAba1 upstream also showed high level (MIC=64 mg/L) of resistance to
carbapenems. Some unidentified IS elements may contribute to the carbapeneme resistances of
CRAB isolates lacking ISAba1 upstream. Repetitive extragenic palindromic sequence-based PCR
(REP-PCR) was chosen as the molecular epidemiologic typing method to monitor and control the
spread of CRAB in the hospital environment. More than 98% of isolates containing ISAba1 -
bla OXA-23-like structure were clustered into one molecular type group 1a; suggesting that they
originated from common bacteria and clonally spread in the study hospital. And 86.7% of isolates
containing ISAba1 -bla OXA-51-like structure were clustered into group 2a; also suggesting that
they originated from another common bacteria and clonally spread. Given that clonal spread is likely responsible for the majority of CRABs presented in this study; CRAB infections may
indicate a serious infection control problem and represents a serious challenge to public health. In
conclusion; continuous monitoring of CRAB and discovery of mechanisms of the acquisition of
resistances by concerted multidisciplinary efforts and rigorous infection control measures are
essential to help develop effective therapy regimens and to prevent the further spread of CRAB
infections. |
Key Words:
Acinetobacter baumannii, bla OXA-23, bla OXA-51, Carbapenem resistance, ISAba1,
OXA-carbapenemase genes, REP-PCR. |