Version 3: Characterization of Group A streptococci causing invasive diseases in Sri Lanka

Group A, β haemolytic streptococci (GAS) or Streptococcus pyogenes is a human pathogen that causes an array of infections including pharyngitis, cellulitis, impetigo, scarlet fever, toxic shock syndrome, and necrotizing fasciitis. The present study characterizes 51 GAS isolates from invasive infections in Sri Lanka, focusing on resistance profiles, genetic determinants of resistance, and virulence markers.

Isolates were tested for sensitivity to penicillin, erythromycin, clindamycin and tetracycline. The presence of erm(A), erm(B), mef(A) was detected in erythromycin-resistant isolates while tet(M) was detected in the tetracycline-resistant isolates. PCR was used to identify SpeA, SpeB, SpeC, SpeF, SpeG, smez and ssa as virulence markers.  Selected GAS isolates were emm-typed using the updated CDC protocol.

All 51 isolates were susceptible to penicillin. The number of isolates non-susceptible to erythromycin was 16. The commonest resistant determinant identified was erm(B) (11/16).  Tetracycline nonsusceptibility was found in 36 (70.6%) isolates and 26 of them contained the tet(M) gene. Thirteen (25.5%) isolates were resistant to both tetracycline and erythromycin while 12 (23.5%) isolates were sensitive to both antibiotics. The commonest virulence markers detected among the isolates was SpeB (44, 86.3%), SpeG (36, 70.6%), SpeF (35, 68.6%) while SpeJ (15, 29.4%), SpeA (10, 19.6%) and ssa (5,9.8%) were less common.

In conclusion, GAS isolates studied showed resistance to erythromycin and tetracycline, while retaining universal susceptibility to penicillin. Additionally, these isolates exhibited diverse genetic backgrounds, displaying varying patterns of virulence genes and emm types.