MEDtube Science 2014 - The diversity of aminoglycoside-modifying enzymes among ESBL – positive Proteus mirabilis clinical strains

Background: Nowadays, the spreading of multi-drug resistant bacteria poses a serious threat, which significantly reduces therapeutic options. P. mirabilis is a common etiological factor of complicated urinary tract infections. Moreover, this species can acquire resistance genes through mobile genetic elements. The most prevalent resistance mechanism among P. mirabilis strains is the production of ESBL, which may occur along with other resistance determinants. Among them, AME creates the menace of aminoglycosides effectiveness. This study was designed to investigate the co-production of AME and ESBL in clinical isolates of P. mirabilis.
Material and Methods: A total of 228 P. mirabilis strains were tested for the production of ESBL by DDST. Then, PCR with specific primer pairs was used to detect genes encoding AME among 75 ESBL-positive P. mirabilis strains.
Results: The co-production of AME along with ESBL was reported in 88% of ESBL strains. The revealed AME genes were: ant(2″)-Ia (n=53), aph(3″)-Ib (n=14), aac(6’)-Ib (n=9), and aac(3)-Ia (n=1). Nine strains showed the presence of more than one AME gene. The most frequent combination was ant(2″)-Ia+aph(3″)-Ib (5 strains), followed by aac(6’)-Ib+aph(3″)-Ib (2 strains), and aac(6’)-Ib+ant(2″)-Ia+aph(3″)-Ib (2 strains). Isolates co-producing AME and ESBL showed high resistance rates to 3rd generation cephalosporins, aminoglycosides, and fluoroquinolones. Carbapenems were the only antibiotics active against all tested strains.
Conclusion: In this study we observed high prevalence of AME among P. mirabilis strains producing ESBL. The rapid dissemination of strains carrying genes for resistance to several groups of antibiotics creates the need for effective surveillance and appropriate antibiotic policy.