Distribution of SCCmec types, tetracycline and aminoglycoside resistance genes in hospital-associated methicillin-resistant Staphylococcus aureus strains

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common bacterial diseases in hospitals around the world. Treatment of MRSA infections is complicated by acquire and rapid development of multiple resistance to a wide range of antibiotics including tetracyclines and aminoglycosides. We sought to evaluate the rate of tetracycline and aminoglycoside resistance genes and the distribution of staphylococcal cassette chromosome mec (SCCmec) types among MRSA strains recovered from nosocomial infections in Tehran, Iran. A total of 95 MRSA isolates were collected from various clinical samples and were subjected to culture, standard biochemical tests and the presence of the nuc gene. Cefoxitin disk diffusion method was applied to screen the MRSA strains with subsequent molecular confirmation for the presence of the mecA gene by polymerase chain reaction (PCR) assay. The phenotypic antimicrobial susceptibility of MRSA isolates against tetracycline and aminoglycoside antibiotics was determined by agar disk diffusion method. Genotypic determinants of resistance to tetracycline and aminoglycosides were detected by PCR assay. Isolates were genotyped using multiplex-PCR for SCCmec typing. The mecA gene was present in all MRSA isolates. Resistance to gentamicin, kanamycin, amikacin, tobramycin, netilmicin, tetracycline, doxycycline, and minocycline was found in 75.8, 70.5, 64.2, 37.9, 30.5, 53.7, 18.9, and 6.3% of the isolates, respectively. The frequency of aac(6′)-Ie/aph(2″)-I, ant (4′)-Ia, aph(3′)-IIIa, aph(2′)-Ib and aph(2′)-Ic genes among MRSA strains, were 71.6, 52.6, 46.3, 2.1, and 2.1%, respectively. The most prevalent tet genes were tet(M) (45.3%) followed by tet(K) (41.1%), tet(L) (2.1%) and tet(O) (2.1%). Totally five distinct SCCmec patterns, numbered MRSA-I to MRSA-V, with the majority of SCCmec type III (42.1%) were observed. Our results illustrated a decreased sensitivity of MRSA to the antibiotics used which is a great concern in human infections supporting the view that treatment strategies must be changed in Iran.