Response of Group B Streptococcus to the Combination of Gold Nanoparticles-Erythromycin as a Nanoweapon

 Group B Streptococcus (GBS) causes a wide range of adverse effects in both mothers and infants during pregnancy and after delivery.

 This study aimed to evaluate the effects of erythromycin either alone or in combination with gold nanoparticles (AuNPs) on the clinical GBS isolated from pregnant women.

 This descriptive cross-sectional study was performed on 106 women aged 16 - 48 years. After identification of GBS strains by phenotypic and genotypic methods (PCR), erythromycin-resistant isolates were identified using the Kirby-Bauer test and broth microdilution method according to CLSI-2015 guidelines. The antibacterial properties and minimum inhibitory concentration (MIC) of erythromycin (either alone or combined with AuNPs) were assessed by the agar well-diffusion and broth microdilution methods, respectively.

 The frequency of GBS isolates was significantly high in the pregnant women aged less than 40 years (73.9%) (P = 0.0251), those with a history of abortion (60.9%) (P = 0.038), and residents of rural areas (60%) (P = 0.038). Moreover, 65.2% of the isolates were resistant to erythromycin. The MIC of AuNPs-erythromycin combination required to inhibit the growth of 50% of GBS isolates (MIC50 = 0.25 μg/mL) was significantly lower than the concentration of AuNP-erythromycin required to inhibit the growth of 90% of the isolates (MIC90 = 1 μg/mL) (P = 0.02), indicating a 16-fold lower dose than the values for erythromycin and AuNPs alone. In the agar well-diffusion method, the average diameter of the growth inhibition zone of AuNPs-erythromycin was 2.5-fold greater than that of free erythromycin (P = 0.037).

 The results showed that the combination of erythromycin with AuNPs increased the antibacterial effects of erythromycin against GBS isolates.