High Frequency of Isolation of Antibiotic-Resistant Oral Viridans Streptococci from Children in Kuwait

Abstract

Antimicrobial resistance among the Viridans group of streptococci (VGS) has emerged as a hindrance to effective antibiotic therapy. Our objective was to evaluate the prevalence of antibiotic-resistant VGS in healthy children.

Plaque samples were collected from tooth and tongue surfaces of 102 healthy subjects. Serially diluted samples were inoculated onto BHI agar plates and Mitis Salivarius Agar (MSA) plates and incubated as appropriate. Representative colonies were identified to species level by standard methods. Susceptibility of the VGS was performed by determining the minimum inhibitory concentrations (MICs) of 11 antibiotics using Etest.

Of the 540 VGS isolates from both sites, 58% were from the tooth surfaces and 42% from the tongue. The most prevalent were S. salivarius (21.5%) and S. sanguis (16.3%). Imipenem and vancomycin had excellent activities. Resistance rates to trimethoprim, amoxicillin, piperacillin, erythromycin, cefuroxime and cephalothin, were 60.7, 40.8, 34.7, 32.6, 27.5 and 25.3%, respectively. Resistance rates to penicillin and clindamycin were 15.9% and 15.4%, respectively. The majority of the erythromycin-resistant isolates were from the tongue; 41% versus 29%. At the species level, 26% and 23% of S. salivarius and 23% and 14% of S. mutans from the tooth and tongue, respectively were resistant to penicillin.

The data show species-related and site-related variations in the susceptibility pattern and an emerging high prevalence of antibiotic-resistant VGS. The difference in the susceptibilities between the species underscores the importance of accurate identification and the need for surveillance of antimicrobial resistance among clinical isolates in our hospitals.