Phenotypic and Genotypic Evaluation of Aminoglycoside Resistance in Clinical Isolates of Staphylococci in Tehran, Iran

Abstract

Aminoglycosides play an important role in the treatment of staphylococcal infections, despite the emerging widespread resistance among Staphylococcus. To determine the prevalence of aminoglycoside resistance and aminoglycoside modifying enzyme (AME) genes among infected patients at a teaching hospital in Tehran, Iran, we tested 585 Staphylococcus isolates, of which 322 were Staphylococcus aureus and 263 were coagulase-negative staphylococci, as determined by the disk diffusion method and multiplex PCR. The minimum inhibitory concentration of gentamicin for each isolate was determined by microbroth dilution. All methicillin-resistant staphylococci were mecA-positive by PCR. Of the 585 isolates, 27.6% were susceptible to gentamicin and kanamicin, 27.1% to tobramicin and amikacin, and 21.3% to netilmicin. The most prevalent AME genes included aac(6')-Ie-aph(2'') (93.7%) followed by aph(3')-IIIa (84.3%) and ant (4')-Ia (28.1%). More than 90% of aminoglycoside-resistant staphylococci contained at least one AME gene. The coexistence of two or three AME genes was detected in most gentamicin-resistant isolates. These results suggest an alarming rate of aminoglycoside resistance in this test location in Tehran, Iran. Continued surveillance at the genotypic and phenotypic levels, and adherence to well-designed antibiotic and infection-control policies are necessary to limit the spread of antimicrobial resistance.

Aminoglycoside-resistant staphylococci in Greece: prevalence and resistance mechanisms

“…Compared these results with our current data an inversion of the resistant phenotypes is observed, with a decrease of gentamicin and tobramycin-resistance (6.3% and 12.9% respectively) followed by a significant increase of kanamycin and amikacin resistance (48.2% for both agents versus 29.2% in 2000), partially due to the predominance of ST80 MRSA clone in the country [14,15]. In addition, in contrast to other studies, the aph(3')-IIIa was the most prevalent AMEs gene (73.3%) in our strains [2,12,13]. The significant differences on the resistance rate and AME gene distribution of S. aureus among Greek regions may be due to the predominance of specific clones and to aminoglycoside usage in each clinical setting combined with a possible horizontal AME gene transfer, as reflected in the results of participating hospitals.…”

“…The rate of staphylococcal resistance to aminoglycosides varies from country to country and from year to year [2,11,12,13]. In a European multicenter study during 1999, Schmitz et al reported that 23%, 29% and 31% of S. aureus were resistant to gentamicin, tobramycin and kanamycin, whereas, Hope et al reported that 9% of MRSA and 2.5% of MSSA, collected from bacteraemia cases in UK and Ireland 11 during 2001-2006, were resistant to gentamicin [2,11].…”

“…In a European multicenter study during 1999, Schmitz et al reported that 23%, 29% and 31% of S. aureus were resistant to gentamicin, tobramycin and kanamycin, whereas, Hope et al reported that 9% of MRSA and 2.5% of MSSA, collected from bacteraemia cases in UK and Ireland 11 during 2001-2006, were resistant to gentamicin [2,11]. On the other hand, recent studies from Middle East showed a high incidence of aminoglycoside-resistant S. aureus [12,13]. In Greece, until now there was little information about the rates of aminoglycoside-resistant S. aureus.…”

Molecular characterization of Staphylococcus aureus isolated from children with adenoid hypertrophy: Emergence of new spa types t7685 and t7692

“…The adenoids might act as a reservoir of potentially pathogenic bacteria [4]. Staphylococcus aureus is a facultative anaerobic, Gram-positive coccus that is an important cause of serious infections in both hospitals and the community and can be isolated from the adenoid of patients with adenoid hypertrophy [5,6]. Because of the importance of S. aureus to health care facilities, many molecular typing methods including the Pulsed-Field Gel Electrophoresis (PFGE), Multi-Locus Sequence Typing (MLST) and protein A gene (spa) typing have been developed to determine the common type and to differentiate between the multiresistant strains of S. aureus.…”

Activity of ACHN-490 against meticillin-resistant Staphylococcus aureus (MRSA) isolates from patients in US hospitals

“…Similarly, the low percentage of strains containing aph(2 )-Ia/aac6 -Ie may explain the low level of gentamicin resistance amongst this sample of MRSA isolates. A 2009 survey of aminoglycoside resistance genes amongst gentamicin-resistant isolates of staphylococci from Tehran, Iran, indicated that the ant(4 )-Ia determinant was present in 28.1% of isolates whilst the aph(2 )-Ia/aac6 -Ie determinant was identified in 93.7% of aminoglycoside-resistant isolates [16]. In contrast, a recent survey of 90 MRSA isolates from 21 hospitals in Spain showed that 61% carried ant(4 )-Ia whilst only 20% carried aph(2 )-Ia/aac6 -Ie.…”