Consistent with earlier reports [12, 51], the combined effect of antibiotics with AgNPs was additive. Interestingly, the action of six different antibiotics (ampicillin, chloramphenicol, erythromycin, gentamicin, and tetracycline) showed better enhanced activity PF-02341066 nmr against Gram-negative than against Gram-positive bacteria in the presence of AgNPs. There was a significant enhancement seen with ampicillin in P. aeruginosa and S. flexneri (Figure 9). In contrast, the maximum increase in activity against S. aureus and S. pneumoniae was observed with vancomycin. These data are consistent with earlier reports [12, 51, 52]. The differential CX-4945 susceptibility of Gram-negative and Gram-positive

bacteria toward antibacterial agents may depend on differences in their cell wall structure [53]. Enhanced antibacterial effects of antibiotics and AgNPs In vitro killing studies were performed to explore the possibility of using AgNPs as an antibiotic adjuvant, increasing the effect of both AgNPs and antibiotics were analysed using sublethal concentrations. In order to analyze, the bacterial test strains were treated with sublethal concentrations of ampicillin and vancomycin. The addition of sublethal concentrations of AgNPs to these antibiotics treatments resulted in significantly enhanced antimicrobial activity

(p < 0.05). Interestingly, both of these antibiotics showed an enhanced effect with specific bacteria, compared to control or AgNPs alone. The most significant effects were observed MM-102 manufacturer with ampicillin toward Gram-negative

bacteria (Figure 10A) and with vancomycin toward Gram-positive bacteria (Figure 10B). Overall, ampicillin displayed significant effects in both Gram-negative and Gram-positive bacteria [18]. A similar inhibitory effect was observed on biofilm activity when these agents were combined. The possibility of using AgNPs as an antibiotic adjuvant [21] was explored by assessing their additive or synergistic effects on bacterial antibiotic susceptibility. The capacity of silver ions to potentiate the bactericidal effect of antibiotics was hypothesized to share a common mechanism of action involving Dichloromethane dehalogenase the overproduction of ROS [21, 54]. The greatest enhancement by AgNPs was observed with ampicillin against Gram-negative and vancomycin against Gram-positive bacteria. These two antibiotics were, therefore, selected to test the antibacterial and anti-biofilm activity of combined treatments in Gram-negative and Gram-positive bacteria. In this experiment, bacteria were incubated with sublethal concentrations of antibiotics or AgNPs, or combinations of AgNPs and antibiotics, during exponential bacterial growth. CFUs were determined at 24 h after harvesting bacteria at different time points. Figure 10 Enhanced antibacterial effect of antibiotics in the presence of AgNPs.