Gentamicin resistance in dairy and clinical enterococcal isolates and in reference strains

• Published in: Journal of antimicrobial chemotherapy Vol. 52; no. 2; pp. 214 - 219
• Main Authors: Lopes, Maria de Fátima Silva, Ribeiro, Tânia, Martins, Maria Paula, Tenreiro, Rogério, Crespo, Maria Teresa Barreto
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01-08-2003; Oxford Publishing Limited (England)
• Subjects: aminoglycosides; Animals; Antibacterial agents; antibiotic resistance; Antibiotics. Antiinfectious agents. Antiparasitic agents; Biological and medical sciences; Dairy Products - analysis; Dairy Products - microbiology; Drug Resistance, Bacterial - genetics; enterococci; Enterococcus - drug effects; Enterococcus - isolation & purification; Gentamicins - pharmacology; Hospitals - statistics & numerical data; Hospitals, Animal - statistics & numerical data; Humans; Medical sciences; Microbial Sensitivity Tests - statistics & numerical data; Pharmacology. Drug treatments; Enterococcus; Human; Gentamicin; Dairy product; In vitro; Resistance; Streptococcaceae; Antibiotic; Sensitivity resistance; Aminoglycoside; Animal; Minimum inhibitory concentration; Bacteria; Micrococcales; Antibacterial agent; Clinical isolate
• ISSN: 0305-7453; 1460-2091; 1460-2091
• DOI: 10.1093/jac/dkg304

Enterococci isolated from Portuguese dairy products (milk and cheese) and clinical settings (hospitals and veterinary clinics), together with reference strains from the genus Enterococcus, were screened for low- and high-level gentamicin resistance using the standard disc diffusion method (10 and 120 µg gentamicin discs). MICs were also determined using both the macrodilution method and the Etest. Four genes [aac(6′)-Ie-aph(2″)-Ia, aph(2″)-Ib, aph(2″)-Ic and aph(2″)-Id] responsible for high- and mid-level gentamicin resistance were sought using PCR. Although enterococci generally are regarded as being intrinsically resistant to low levels of gentamicin, results revealed that many dairy enterococci (around 30% of the isolates used) are not intrinsically resistant to gentamicin, showing MICs of £4 mg/L. High-level gentamicin resistance was not detected in any of the dairy isolates studied, except for aph(2″)-Ib, which was found in one. Therefore, gentamicin resistance should be monitored in dairy enterococci, although it does not seem to be a problem at present. In contrast, all clinical isolates studied were, as expected, intrinsically resistant to low levels of gentamicin, presenting MICs > 8 mg/L. Fifteen percent of these clinical isolates showed high-level gentamicin resistance (MICs > 512 mg/L), with the bifunctional gene aac(6′)-aph(2″) being detected in four of them. However, discs with gentamicin 120 µg failed to detect some isolates with high-level gentamicin resistance.