Macrolide Resistance Genes in Enterococcus spp

Abstract

Seventy-eight isolates of different Enterococcus species (E. faecalis, n ‫؍‬ 27; E. faecium, n ‫؍‬ 23; E. durans, n ‫؍‬ 8; E. avium, n ‫؍‬ 6; E. hirae, n ‫؍‬ 9; E. gallinarum, n ‫؍‬ 3; and E. casseliflavus, n ‫؍‬ 2) with a variety of erythromycin resistance phenotypes were examined for the presence of macrolide resistance genes (ermA, ermB, ermC, ermTR, mefA/E, and msrA). Positive PCR amplifications of ermB were obtained for 39 of 40 highly erythromycin-resistant Enterococcus isolates (MICs, >128 g/ml) of different species; the remaining highly resistant E. faecium isolate was positive for PCR amplification of ermA but was negative for PCR amplification of the ermB and ermC genes. For all enterococcal strains for which erythromycin MICs were <32 g/ml PCRs were negative for erm methylase genes. For all E. faecium isolates PCR amplified products of the expected size of 400 bp were obtained when msrA primers were used, with the results being independent of the erythromycin resistance phenotype. All the other enterococcal species gave negative results by msrA PCRs. Sequencing of the msrA PCR products from either erythromycin-susceptible, low-level-resistant, or highly resistant E. faecium strains showed that the amplicons did not correspond to the msrA gene described for Staphylococcus epidermidis but corresponded to a new putative efflux determinant, which showed 62% identity with the msrA gene at the DNA level and 72% similarity at the amino acid level. This new gene was named msrC.Over the last few years, Enterococcus has emerged as an important bacterial pathogen in nosocomial infections (13). The acquisition of specific mechanisms of resistance to different antibiotics, especially for the species Enterococcus faecium, has rendered infections with these microorganisms difficult to treat (8, 25); in just 10 years, antibiotic resistance has spread rapidly among enterococci and has become an important public health concern (11, 14). Macrolide-lincosamide-streptogramin (MLS) antibiotics constitute an alternative therapy for the treatment of insidious enterococcal infections. Three different mechanisms account for the acquired resistance to MLS antibiotics in gram-positive bacteria: modification of the drug target, inactivation of the drug, and active efflux of the antibiotic. In the first case, a single alteration of the 23S rRNA confers broad cross-resistance to macrolide-lincosamide-streptogramin B (MLS B ) antibiotics, whereas the inactivation mechanism confers resistance only to structurally related MLS antibiotics. Regarding the pump mechanisms, the mefA (4), mefE (34), msrA (29), and mreA (5) genes have been involved in the active efflux of macrolides in gram-positive bacteria. The mef and mreA genes have been associated with macrolide resistance, and the msrA gene has been associated with macrolide and streptogramin B resistance. Erythromycin resistance by erm methylases of the ermB-ermAM hybridization class has been described in Enterococcus isolates (3,15,19). However, even though some reports indicate the ...

Occurrence of Tylosin-Resistant Enterococci in Swine Manure and Tile Drainage Systems under No-Till Management

“…in different Enterococcus spieces have been described in recent studies (Jost et al, 2004;Luna et al, 1999;Portillo et al, 2000). As claimed by Portillo et al (2000), the most commonly erm class found in streptococci and enterococci is erm(B) class, followed by erm (TR), a subset of erm(A) class.…”

“…Enterococci are potential pathogens and they are becoming resistant and have acquired resistant genes to withstand the effects of antibiotics Butaye et al, 2001;Portillo et al, 2000;Thal et al, 1995;Yuri. et al, 2005).…”

“…Common antibiotic macrolides are known as erythromycin, Spiramycin and tylosin. Activity of macrolides is related to protein synthesis inhibition (Portillo et al, 2000).…”

The Evaluation of Hazards to Man and the Environment during the Composting of Sewage Sludge

“…It is noteworthy that resistance against these antibiotics has been connected with transferable genetic elements [34,65]. The appearance of resistant enterococci that might carry such elements (plasmids, transposons) gives rise to a very large discussion about the health risks posed by the dissemination of these genetic elements in the environment through the reuse of treated waste (manures and sewage sludge).…”

“…Over the last decade, enterococci have been implicated in nosocomial infections worldwide. Due to their ability to acquire high-level resistance to antimicrobial agents such as vancomycin and erythromycin, they have become a serious threat for public health [33,34].…”