Antibiotic Resistance and Its Mechanism of Group A Streptococci in School Children of Jinju

Park, Soo Jin; Kim, Sunjoo

Abstract

BACKGROUND: Group A streptococci (GAS) is the most common cause of bacterial pharyngitis. Recently, a high frequency of resistance to erythromycin (EM), the drug of choice for penicillin-allergic patients, has been reported, especially in countries where antibiotics are overused. Resistance is classified as constitutive, inducible, or M according to the sensitivity results with EM and clindamycin (CC). These EM resistance phenotype is attributable to the erm , ermTR, and mefA genes, respectively. Although EM resistance of GAS is a serious problem in our country, there are very few reports regarding to its mechanism.
METHODS
GAS were isolated from elementary school children of Jinju in 2002. Antibiotic sensitivity testing by disk diffusion was performed against tetracycline (TC), ofloxacin, EM and CC, and the results were compared to the previous one in 1995 at the same area. The phenotypes of EM resistance were evaluated, and the frequency of ermB and mefA genes was determined by PCR. The resistance pattern was analyzed by each emm genotype.
RESULTS
The resistance rate to EM and CC was 51% and 34%, respectively, which is significantly higher than the rate of 25% and 9% recorded in 1995. Constitutive resistance was seen in 64% of the EM-resistant strains, the M phenotype in 34%, and inducible resistance in only 2%, compared to 38% of constitutive resistance and 62% of M phenotype in 1995. The ermB and mefA genes were present in 64% and 34% of strains, respectively. Most (88%) of the emm12 strains showed constitutive resistance, while emm18 and emm75 showed M phenotype. The organisms with most of the other emm genotypes were susceptible to EM.
CONCLUSION
The EM and CC resistance rate had increased more than twofold. Constitutive resistance was twice as common as the M phenotype, whereas the mefA gene was more common in 1995. The resistance pattern was variable according to emm type, which suggests an association between the emm and resistance genes. Continuous microbiologic and epidemiological surveillance should be conducted and the seriousness of antibiotic resistance should be underscored in our community.