Phenotypic and Molecular Characterization ofAcinetobacter baumanniiClinical Isolates from Nosocomial Outbreaks in Los Angeles County, California

Abstract

Multidrug-resistant Acinetobacter baumannii strains have increasingly resulted in nosocomial outbreaks worldwide, leaving limited options for treatment. To date, little has been reported on the antimicrobial susceptibilities and genomic profiles of A. baumannii strains from hospital outbreaks in the Greater Los Angeles area. In this study, we examined the susceptibilities and genetic profiles of 20 nonduplicate isolates of A. baumannii from nosocomial outbreaks in Los Angeles County (LAC) and determined their mechanisms of fluoroquinolone resistance. Antibiotic susceptibility testing indicated that the majority of these LAC isolates were not susceptible to 14 of the 17 antibiotics tested, with the exception of doxycycline, minocycline, and tigecycline. In particular, all isolates were found to be resistant to ciprofloxacin. Genomic DNA analysis revealed eight epidemiologically distinct groups among these 20 A. baumannii isolates, consistent with antibiotic susceptibility profiles. Sequencing analysis confirmed that concurrent GyrA and ParC amino acid substitutions in the "hot spots" of their respective quinolone resistance-determining regions were primarily responsible for the high-level ciprofloxacin resistance of these isolates. Antibiotic susceptibility testing using two efflux pump inhibitors suggested that the presence of efflux pumps was only a secondary contributor to ciprofloxacin resistance for some of the isolates. In summary, the present study has revealed good correlation between the antibiotic susceptibility profiles and genetic fingerprints of 20 clinical isolates from nosocomial outbreaks in Los Angeles County and has determined their mechanisms of fluoroquinolone resistance, providing an important foundation for continued surveillance and epidemiological analyses of emerging A. baumannii isolates in Los Angeles County hospitals.

Determination of Different Fluoroquinolone Mechanisms Among Clinical Isolates of Acinetobacter baumannii in Tehran, Iran

“…In this study, the antibiotic resistance rates of 103 Acinetobacter isolates to ciprofloxacin and levofloxacin were 74.7% and 33%, respectively. In contrast to ciprofloxacin, most of the isolates were susceptible to levofloxacin; this was also confirmed by the results (18). In contrast to the above-mentioned studies, Ribera et al observed that PAβN had no effect on MIC of ciprofloxacin (31); however, in general, in many studies such as the present one, the inhibitory effect of both compounds on the performance of efflux pumps has been observed (32).…”

“…The size of the culture medium was reduced and an inhibitor of the same amount was added, so that in each microplate, there were 48 µL of the adjusted Mueller-Hinton medium (Merck, Germany) and 2 µL of PAβN. After dilution of the antibiotic, the bacterial suspension was added by the same amount, ie, 50 µL (final volume of 100 µL), and all the remaining steps were conducted as MIC (18). As for the NMP inhibitor, based on the protocol, first 100 mg of the inhibitor was solved in 2 mL of DMSO, and then 2 mL of 0.25 molar HCL was added to it.…”

Multi-drug resistance profiles and the genetic features of Acinetobacter baumannii isolates from Bolivia

“…PCR assays as described by Valentine and colleagues [3] were used for the amplification of the QRDRs of the gyrA and parC genes. The gene fragments were sequenced and checked for specific amino acid changes.…”

“…Acinetobacter baumannii has been considered the paradigm of multiresistant bacteria because of emerging multi-drug resistance to various antimicrobial agents [2], notably mutations in gyrA and parC genes that confer fluoroquinolone resistance and activation of the aminoglycoside inactivating enzymes [2,3,4]. Betalactam antibiotics (mainly carbapenems) are now the first drug of choice to treat these microorganisms; however, in the last decade, resistance to carbapenems has appeared in hospitals worldwide owing to the production of beta-lactamases, changes in permeability, increase in efflux, and modification of the affinity of penicillin-binding proteins (PBPs) in these bacteria [2,3]. Transposable elements also play a major role in gene expression.…”

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“…Another contains bile salts, ampicillin, cefsulodin, and vancomycin. In the Leeds medium formulation, ampicillin was removed and the concentrations of the other antibiotics were adjusted to optimise performance [5]. CHROMagar Acinetobacter® (CHROMagar, Paris, France) was recently developed as a selective agar for the rapid identification of A. baumannii.…”