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Journal of Clinical Microbiology, August 2008, p. 2499-2507, Vol. 46, No. 8
0095-1137/08/$08.00+0     doi:10.1128/JCM.00367-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Phenotypic and Molecular Characterization of Acinetobacter baumannii Clinical Isolates from Nosocomial Outbreaks in Los Angeles County, California{triangledown}

Sonya C. Valentine,1 Deisy Contreras,1 Stephanie Tan,1 Lilian J. Real,1 Sheena Chu,2 and H. Howard Xu1*

California State University,1 Los Angeles County Public Health Laboratory, Los Angeles, California2

Received 23 February 2008/ Returned for modification 17 April 2008/ Accepted 24 May 2008

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.

* Corresponding author. Mailing address: Department of Biological Sciences, California State University, Los Angeles, 5151 State University Dr., Los Angeles, CA 90032. Phone: (323) 343-2188. Fax: (323) 343-6451. E-mail: hxu3{at}calstatela.edu

{triangledown} Published ahead of print on 4 June 2008.

Journal of Clinical Microbiology, August 2008, p. 2499-2507, Vol. 46, No. 8
0095-1137/08/$08.00+0     doi:10.1128/JCM.00367-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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