Prevalence of the tetA and tetB genes as mechanisms of resistance to tetracycline and minocycline in Acinetobacter baumannii clinical isolates

INTRODUCTION. Two hundred twenty-one Acinetobacter baumannii clinical strains were collected from 25 hospitals in Spain. The aim of this study was to analyze the prevalence of the tetA and tetB genes in a collection of A. baumannii strains that were not epidemiologically related. METHODS. The strains were distributed in 79 clones by genomic DNA analysis with low frequency restriction enzymes and pulsed-field gel electrophoresis. The MICs for tetracycline and minocycline were determined by the E-test. One strain representing each of the tetracycline-resistant clones was analyzed by polymerase chain reaction (PCR) with specific primers for the tetA and tetB genes. RESULTS. Fifty-nine (74.7%) out of the 79 clones were tetracycline-resistant (MIC >= 16 mg/l) and 40 (50.6% of the total) were also minocycline-resistant (MIC > 1 mg/l). One strain representative of each tetra cycline-resistant clone was taken to study the prevalence of the tetA and tetB genes. The PCR analysis showed that 39 strains representing the same number of clones (66%) had the tetB gene, while only 8 (13.6%) were positive for the tetA gene. Twelve strains did not have any of these genes. None of the analyzed strains had both genes. CONCLUSION. Although resistance to tetracycline in Acinetobacter baumannii clinical isolates is greater than that to minocycline, the tetB gene, which affects both antimicrobial agents, has a higher prevalence than the tetA gene, which affects only tetracycline.