Drug-resistant genes carried by Acinetobacter baumanii isolated from patients with lower respiratory tract infection

Background Acinetobacter baumanii （A. baumanii ） remains an important microbial pathogen resulting in nosocomialacquired infections with significant morbidity and mortality. The mechanism by which nosocomial bacteria, like A. baumanii, attain multidrug resistance to antibiotics is of considerable interest. The aim in this study was to investigate the spread status of antibiotic resistance genes, such as multiple 13-1actamase genes and aminoglycoside-modifying enzyme genes, from A. baumanii strains isolated from patients with lower respiratory tract infections （LRTIs）. Methods Two thousand six hundred and ninety-eight sputum or the bronchoalveolar lavage samples from inpatients with LRTIs were collected in 21 hospitals in the mainland of China from November 2007 to February 2009. All samples were routinely inoculated. The isolated bacterial strains and their susceptibility were analyzed via VITEK-2 expert system. Several kinds of antibiotic resistant genes were further differentiated via polymerase chain reaction and sequencing methods. Results Totally, 39 A. baumanii strains were isolated from 2698 sputum or bronchoalveolar lavage samples. There was not only a high resistant rate of the isolated A. baumanfi strains to ampicillin and first- and second-generation cephalosporins （94.87%, 100% and 97.44%, respectively）, but also to the third-generation cephalosporins （ceftriaxone at 92.31%, ceftazidine at 51.28%） and imipenem （43.59%） as well. The lowest antibiotic resistance rate of 20.51% was found to amikacin. The OXA-23 gene was identified in 17 strains of A. baumanii, and the AmpC gene in 23 strains. The TEM-1 gene was carried in 15 strains. PER-1 and SHV-2 genes were detected in two different strains. Aminoglycoside-modifying enzyme gene aac-3-1a was found in 23 strains, and the aac-6＂lb gene in 19 strains, aac-3-1a and aac-6＂lb genes hibernated in three A. baumanfi strains that showed no drug-resistant phenotype. Conclusions A. baumanii can carry multiple drug-resistant genes at the same time and result in multi-drug resistance. Aminoglycoside-modifying enzyme genes could be hibernating in aminoglycoside sensitive strains without expressing their phenotype.

Detection of the Relationship between Imipenem Susceptible and Non-Susceptible Clinical Isolates of Acinetobacter Baumannii by Repetitive Element PCR-Mediated DNA Fingerprinting in an Egyptian Hospital

In this work, the authors aimed to detect the clonal relatedness of the isolated imipenem-susceptible and non-susceptible Acenitobacter baumanii. This study was conducted from September 2008 through August 2009 in Aboelreech-Elmounira paediatric-Cairo University-teaching hospital in Egypt. All the isolated acenitobacter species were identified by standard laboratory procedures. The clonal relationship of the A. baumanii （the most common detected clinical type） was studied by biotyping and AST and then confirmed using rep-PCR with primers aimed at repetitive extragenic palindromic sequences and enterobacterial repetitive intergenic consensus sequences. A total of 100 A. baumanii isolates out of 104 acenitobacter species were recovered from different clinical samples. Sixty two percent of the isolates were resistant to imipenem. The resulting rep-PCR patterns oftheA, baumanii strains revealed 8 clones, 3 clones found in the imipenem resistant group, and 5 clones in imipenem sensitive group with statistically significant clonal distribution in both groups （P-value 0.00）. Clonality was proved in imipenem resistant group with an alarming predominance of clone 1 representing 80.6% of IMP-R isolates. In accordance the prevalence of resistant acenitobacter strains seems to be correlated with inappropriate antibiotic use. These results call for strict compliance of coordinated strategy of infection control measures and judicious use of antimicrobials which is likely to effectively deal with this serious public health issue.