Group A streptococcus (GAS) or Streptococcus pyogenes is an important human pathogen responsible for a myriad of infections such as pharyngo-tonsillitis, pyoderma, scarlet fever, necrotizing fasciitis, toxic shock syndrome and septicemia. Molecular mimicry between streptococcal and host antigens results in generation of cross-reactive antibodies which target host tissues leading to non-suppurative sequelae such as rheumatic fever (RF), rheumatic heart disease (RHD), post streptococcal glomerulonephritis (PSGN), reactive arthritis, chorea and other brain disorders.

Penicillin is the drug of choice for GAS. However, in patients allergic to penicillin, alternative antibiotics such as macrolides and quinolones are prescribed. In view of the increasing number of reports on drug resistance among beta hemolytic streptococci (?? HS), we wanted to assess the burden of antibiotic resistance among strains isolated from Chennai city. Studies on antibiotic resistance among isolates from pharyngeal carriers are rarely done. Screening of carrier strains could provide important data on resistance profiles of strains circulating in the community.

» Materials and Methods

We studied 117 GAS isolates (61 carrier, 32 tonsillitis and 24 pyoderma strains), sixty GGS isolates (40 carrier, 13 tonsillitis and 7 pyoderma) and 20 GCS isolates (10 carrier, 8 tonsillitis and 2 pyoderma strains). All strains were isolated from school children. They were screened for susceptibility to penicillin (10U), amoxycillin (10??g), cephalexin (30??g), cefotaxime (30 ??g), ceftriaxone (30 ??g), erythromycin (15 ??g), roxithromycin (15 ??g), clarithromycin (15 ??g), clindamycin (2 ??g), tetracycline (30 ??g), ciprofloxacin (5 ??g) ofloxacin (5 ??g), levofloxacin (5 ??g), chloramphenicol (30 ??g) and linezolid (30 ??g) by the Kirby Bauer disc diffusion method on Mueller-Hinton agar supplemented with 5% sheep blood.

» Results

Among the GAS strains tested, 35% (41/117) were sensitive to all 15 antibiotics. Erythromycin resistance was encountered among 16.2% (19/117) of GAS strains (10 carrier strains, 5 tonsillitis strains and 4 pyoderma strains). Tetracycline resistance was observed in 27.4% (32/117) of the strains (15 carrier strains, 8 tonsillitis strains and 9 pyoderma strains). A total of 8 strains (6.8%, 8/117) were resistant to clindamycin and 5 strains (4.3%, 5/117) to chloramphenicol. Three GAS strains (2.5%, 3/117) were non-susceptible to ciprofloxacin. Reduced susceptibility to ofloxacin and levofloxacin was observed in 1.7% (2/117) of the GAS strains tested. No resistance was observed to penicillin, amoxycillin, the cephalosporins and linezolid.

Among the GGS, 28.3% (17/60) of strains tested were sensitive to all antibiotics. Resistance to erythromycin (28.3%, 17/60) and tetracycline (26.7%, 16/60) was observed. Some strains were found to be resistant to clindamycin (8.3%, 5/60), ciprofloxacin (8.3%, 5/60), ofloxacin (1.6%, 1/60) and levofloxacin (1.6%, 1/60). Forty-five percent of GCS strains (9/20) were sensitive to all antibiotics tested. Among the 20 GCS strains tested, 6 showed resistance to tetracycline, 5 to erythromycin, 2 to ciprofloxacin and 3 to chloramphenicol.