Molecular and epidemiological characterization of carbapenem-resistant Acinetobacter baumannii in non-tertiary Korean hospitals

Antibiotic-resistant clones in Gram-negative pathogens: presence of global clones in Korea

Antibiotic resistance is a global concern in public health. Antibiotic-resistant clones can spread nationally, internationally, and globally. This review considers representative antibiotic-resistant Gram-negative bacterial clones-CTX-M- 15-producing ST131 in Escherichia coli, extended-spectrum ß-lactamase-producing ST11 and KPC-producing ST258 in Klebsiella pneumoniae, IMP-6-producing, carbapenem-resistant ST235 in Pseudomonas aeruginosa, and OXA-23-producing global clone 2 in Acinetobacter baumannii-that have disseminated worldwide, including in Korea. The findings highlight the urgency for systematic monitoring and international cooperation to suppress the emergence and propagation of antibiotic resistance.

Epidemiological characterizations of class 1 integrons from multidrug-resistant acinetobacter isolates in Daejeon, Korea

Background

Multidrug-resistant (MDR) Acinetobacter spp. acquire antimicrobial agent-resistance genes via class 1 integrons. In this study, integrons were characterized to investigate the antimicrobial resistance mechanisms of MDR Acinetobacter isolates. In addition, the relationship between the integron type and integron-harboring bacterial species was analyzed by using epidemiological typing methods.

Methods

Fifty-six MDR Acinetobacter spp.-A. baumannii (N=30), A. bereziniae (N=4), A. nosocomialis (N=5), and A. pittii (N=17)-were isolated. The minimum inhibitory concentrations (MICs) were determined on the basis of the results of the Epsilometer test (Etest). PCR and DNA sequencing was performed to characterize the gene cassette arrays of class 1 integrons. Multilocus sequence typing (MLST) and repetitive extragenic palindromic sequence (REP)-PCR were performed for epidemiological typing.

Results

Class 1 integrons were detected in 50 (89.3%) of the 56 isolates, but no class 2 or 3 integron was found within the cohorts. The class 1 integrons were classified into 4 types: 2.3-kb type A (aacA4-catB8-aadA1), 3.0-kb type B (aacA4-blaI_MP-1-bla_OXA-2), 3.0-kb type C (bla_VIM-2-aacA7-aadA1), and 1.8-kb type D (aac3-1-bla_OXA-2-orfD). Type A was most prevalent and was detected only in A. baumannii isolates, except for one A. bereziniae isolate; however, type B was amplified in all Acinetobacter isolates except for A. baumannii isolates, regardless of clone and separation time of the bacteria.

Conclusions

Although class 1 integron can be transferred horizontally between unrelated isolates belonging to different species, certain types of class 1 integrons tend to transfer horizontally and vertically among A. baumannii or non-baumannii Acinetobacter isolates.

Molecular Characterization of Carbapenem Resistant Isolates of Acinetobacter baumannii in An Intensive Care Unit of A Tertiary Care Centre at Central India

OBJECTIVE

To detect genes encoding carbapenem resistance in Acinetobacter baumannii in an intensive care unit.

METHODS

A. baumannii isolates were recovered from various clinical specimens of hospitalized patients admitted to the Medical and Surgical intensive care units of a tertiary care centre in Pune. Bacterial identification was performed by routine conventional microbial culture and biochemical tests using standard recommended techniques. Antibiotic sensitivity test was performed by standard Kirby Bauer disc diffusion technique. PCR amplification and automated sequencing was carried out.

RESULTS

A total of 155 /368 (42.11%) isolates A. baumannii were found to have reduced susceptibility to imipenem (diameter of zones of inhibition ≤13mm) by disc diffusion method. Among these 155 isolates tested 130 (83.87%) isolates showed MIC values for imipenem and meropenem ranging from16-64 mg/L as per CLSI breakpoints. Among these 155 isolates, Carbapenemase production was confirmed by Modified Hodge test for 93 (60%) isolates. Out of 155 isolates, DDST was positive for 89 (57.41%), CDST was positive for 73(47.09%) and MBL (IP/IPI) E-test was positive for 105 (67.74%). blaOXA-51 gene was detected in 47/105 (44.76%), blaOXA-23 gene in 55/105 (52.38%) and blaOXA-58 like gene in 15/105 (14.28%).

CONCLUSION

MBL production along with co- production of OXA enzymes are considered to be the important reason for resistance to imipenem in Acinetobacter in our health care settings. Hence, early detection of these drug resistant genes by molecular methods is essential in limiting the spread of infection due to these organisms.

Phenotypic and genotypic characteristics of tetracycline resistant Acinetobacter baumannii isolates from nosocomial infections at Tehran hospitals

OBJECTIVE(S)

To date, the most important genes responsible for tetracycline resistance among Acinetobacter baumannii isolates have been identified as tet A and tet B. This study was carried out to determine the rate of resistance to tetracycline and related antibiotics, and mechanisms of resistance.

MATERIALS AND METHODS

During the years 2010 and 2011, a total of 100 A. baumannii isolates were recovered from patients in different hospitals of Tehran, Iran. Antimicrobial susceptibility to tetracycline, minocycline, doxicycline and tigecycline was evaluated by E-test. Polymerase chain reaction (PCR) of the tet A and tet B genes was performed using specific primers, after which the isolates were subjected to Repetitive Extragenic Palindromic-PCR (PCR) to identify the major genotypes.

RESULTS

Of all isolates, 89% were resistant to tetracycline (MIC50 = 32 µg/ml, MIC90 = 512 µg/ml). Minocycline with the resistant rate of 35% (MIC50 = 16 µg/ml, MIC90 =32 µg/ml) and doxicycline with the resistant rate of 25% (MIC50 = 16 µg/ml, MIC90= 32 µg/ml) have a good activity against A. baumannii isolates. All isolates were sensitive to tigecycline. Frequencies of tet B and tet A genes and coexistence of tet A and tet B among the isolates resistant to tetracycline, were 87.6%, 2.2% and 1.1%, respectively. Distribution of REP-types among A. baumannii isolates was types A (40%), B (30%), C (10%), D (5%) and E (5%).

CONCLUSION

It seems that tet A and tet B genes play an important role in the induction of resistance towards tetracyclines used in this study. It is suggested that further studies focus on other antimicrobial drugs and combinations in order to achieve a successful therapy against multi drug resistance (MDR) A. baumannii strains in Iran.