Phenotypic and Molecular Characterization of Acinetobacter Clinical Isolates Obtained from Inmates of California Correctional Facilities

Abstract

Acinetobacter spp. increasingly have been wreaking havoc in hospitals and communities worldwide. Although much has been reported regarding Acinetobacter isolates responsible for nosocomial infections, little is known about these organisms in correctional facilities. In this study, we performed species identification, examined the antibiotic resistance profiles, and determined the mechanisms of resistance and clonal relationships of 123 Acinetobacter isolates obtained from inmates of 20 California correctional facilities (CCFs). We found that 57.7% of the isolates belong to A. baumannii, followed by isolates of Acinetobacter genomic species 3 (gen. sp. 3; 23.6%) and of Acinetobacter gen. sp. 13TU (10.6%). Multidrug-resistant (MDR) CCF isolates were found in only six CCFs. Additionally, DNA sequences of gyrA and parC genes were consistent with fluoroquinolone (FQ) susceptibility phenotypes. Furthermore, the presence of class 1 integrons was detected in 15 CCF isolates, all of which are MDR. Integron-associated gene cassettes encode several aminoglycoside modification enzymes, which correlate with most of the aminoglycoside-resistant phenotypes. Antimicrobial susceptibility testing in the presence of Phe-Arg-␤-naphthylamide dihydrochloride and 1-(1-naphthylmethyl)-piperazine indicated the involvement of efflux pumps in the FQ resistance of only a few CCF isolates. Finally, genetic profiling showed that there was no evidence of A. baumannii outbreaks in CCFs. Instead, our analyses revealed only limited clonal dissemination of mostly non-MDR A. baumannii strains in a few facilities. This study represents the first report to characterize phenotypic and molecular features of Acinetobacter isolates in correctional facilities, which provides a baseline for monitoring the antimicrobial resistance changes and dissemination patterns of these organisms in such specialized institutions.

The Challenge of Efflux-Mediated Antibiotic Resistance in Gram-Negative Bacteria

“…In other studies, PA␤N at 10 g/ml decreased the MIC values of chloramphenicol, clindamycin, and trimethoprim against clinical isolates regardless of the adeFGH expression status mostly 2-to 4-fold (552), while PA␤N at 20 g/ml reduced the nalidixic acid MIC up to 16-fold but displayed little effect on ciprofloxacin susceptibility (553). PA␤N and NMP, each at 100 g/ ml, restored susceptibility to fluoroquinolone (2-to 16-fold reduction of MICs) and tigecycline (mostly by a 2-fold MIC decrease) (554). Apparently, these EPIs have a stronger effect on resistance reversal with agents that have relatively high MIC values, such as chloramphenicol, clarithromycin, clindamycin, linezolid, rifampin, and trimethoprim (552,553,555), agents whose OM penetration is likely to be slow.…”

Genotyping methods for monitoring the epidemic evolution of A. baumannii strains

“…It was found that 16S-23S rRNA intergenic spacer sequences have a low degree of intra-species variation and high degrees of inter-species divergence. In another study [7], 28 types of strains, including 11 reference strains, were used; amplification and restriction of sequences was followed by DNA sequencing, revealing low-level similarity within the ACB complex. This study also demonstrated that internal transcribed spacer (ITS) sequences have better discriminatory power than a 16S rRNA gene.…”

“…Associated with the A. baumannii strain is a group of phenotypically and genetically closely related Gramnegative bacteria. These are non-motile, aerobic, rodshaped bacteria with polar fimbriae, which can have oxidase-negative and catalase-positive biochemical reactions [7,8]. These particular species have been named Acinetobacter calcoaceticus, Acinetobacter pittii (formerly referred to as the Acinetobacter genomic species 3), and Acinetobacter nosocomialis (formerly referred to as the Acinetobacter genomic species 13TU).…”

“…These particular species have been named Acinetobacter calcoaceticus, Acinetobacter pittii (formerly referred to as the Acinetobacter genomic species 3), and Acinetobacter nosocomialis (formerly referred to as the Acinetobacter genomic species 13TU). Collectively, they are now referred to as the ACB complex, having a 16S rRNA sequence identity value of between 97% and 99.9% and inter-species values of between 65% and 75% [7]. Although the ACB complex is considered to be an important nosocomial infectious agent, the clustering of A. nosocomialis and A. pittii together in an ACB complex is unsatisfactory because of the ambiguity in biological and pathological differences within the species.…”

“…Only few phenotypic techniques have been validated to identify clinically important Acinetobacter species, with large numbers of strains already having been identified by DNA-DNA hybridization [7]. A different and largely adopted 19 biochemical test pattern developed by Bouvet and Grimont [11] identified 12 different Acinetobacter species.…”