Biofilm formation: A possible mechanism for penicillin treatment failure in strains of group A Streptococcus

Up to one-third of patients treated for Group A Streptococcal (GAS) pharyngitis fail to respond to antibiotic therapy. The object of this cohort study was to evaluate GAS biofilm formation as a mechanism for penicillin treatment failure. The MBEC Assay Device was used to determine biofilm forming capability, efficiency and antibiotic susceptibility. The Minimum Biofilm Eradication Concentration (MBEC) and Minimum Inhibitor Concentration (MIC) of GAS were determined for several antibiotics. All 99 GAS isolates evaluated formed biofilms with varying efficiency. Antibiotic MBECs were higher than MICs for each GAS isolate. MBEC values demonstrated the first report of in vitro GAS penicillin insensitivity. Using MBECs to predict penicillin treatment failure had low sensitivity (56%) and positive predictive value (PPV) (50%). However, this was an improvement when compared to the sensitivity and PPV of MICs (0%). More studies are needed to understand the role of biofilms and the MBEC assay in predicting treatment failure.