Prevalence Of Macrolide Resistance

In a susceptibility surveillance study in Spain between 1996-1997 of patients with respiratory tract infection, among 1,113 S. pneumoniae isolates, 37% isolates were resistant to macrolides (40). The susceptibility of 302 S. pneumoniae central Italian isolates revealed that erythromycin resistance rates increased from 7.1 in 1993 to 32.8% in 1997. Erythromycin resistant isolates mostly carried ermAM determinant and a minority (5.8%) carried the mefA determinant (41). In a 1996-1997 winter US study, among 1276 S. pneumoniae clinical isolates, 23% were resistant to erythromycin, clarithromycin and azithromycin (42). In a Canada surveillance study on prevalence and mechanism of erythromycin-resistant S. pneumoniae involving 113 hospital and private laboratories, only 2.9 % of the isolates were erythromycin resistant, with 43.5% showing the MLSb phenotype (43). In Norway, the prevalence of erythromycin-resistant pneumococci is slightly higher than in Canada (44).

In Finland, 14.5% of S. pyogenes isolates were erythromycin-resistant. All of the M phenotype isolates had mefA gene which was found to be transferred by conjugation. The MLSB -resistant isolates had ermTR gene with one exception having the enriB gene (45). In Spain, 27% of the p-hemolytic group A streptococci isolates isolated in 11 hospital between May 1996 - April 1997 were found to be erythromycin resistant, displaying the M phenotype (46). However, in a Ontario, Canada surveillance study, 2.1% of the group A streptococci was found to erythromycin resistant, consistent with the finding with S. pneumoniae that, macrolide resistant streptococci is relatively low (47). The distribution of clinical isolates of erythromycin-resistant S. pyogenes in Italian laboratories from 1995 to 1998 was reported and 52.5% of the resistant strains were assigned to M phenotype, 31.0% to ¬°MLS phenotype and 16.5% to cMLS phenotype (48). 12% of group C streptococci clinical isolates in Spain were found to be erythromycin-resistant (46). The resistance mechanism in Lancefield group C and group G streptococci in Finland macrolide resistant isolates were found to be different. About 95% of the group C resistant streptococci had the mefE gene whereas 94% of the group G had the enriTR methylase gene (49). 55% of S. oralis isolates in Taiwan were found to be erythromycin-resistant (50). In France, the erythromycin resistance rate in viridans group streptococci was reported to around 40% (51). Azithromycin-resistant pneumococci obtained by subculturing have no ermB or mefE genes, contrary to those found in clinical resistant isolated (52). Antimicrobial susceptibility study from the SENTRY antimicrobial surveillance program conducted in United States and Canada found that macrolides are highly active against Moraxella catarrhalis isolates with less than 1% resistant, while for the H. influenzae isolates, less than 5% strains were found to resistant to macrolide (42,53). The distribution of genes en-coding resistance to MLS antibiotics among staphylococci was reported. Resistance was mainly due to the presence of ermA or ermC genes detected in 88% of the resistant isolates from 32 French hospitals in 1995. Macrolide resistance due to msrA was more prevalent in coagulase-negative staphylococci than in S. aureus (54).

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