| Congresso Brasileiro de Microbiologia 2023 | Resumo: 52-1 | ||||
Resumo:Belonging to the normal microbiota, it is estimated that Staphylococcus aureus asymptomatically colonizes one-third of the human population. As an opportunistic pathogen, staphylococcal infections range from mild to life-threatening diseases, such as skin infections, pneumonia and bacteremia. This microorganism counts with a set of virulence factors that aid to establish infections and confers protection against the host immune response, frequently associated with foodborne poisoning events caused by staphylococcal enterotoxins. The notorious ability to become resistant to antibiotics is a global concern, with outbreaks of methicillin-resistant S. aureus (MRSA) emerging as worldwide cause of community-associated infections, rising interest in the research for new antibiotics. In this work, we investigated the antimicrobial activity of Rhamnolipid and Oxacillin (OXA) against susceptible and resistant S. aureus strains under different pHs and the synergic effect between them. RL is an amphipathic biosurfactant produced by Pseudomonas aeruginosa , composed by a hydrophobic lipid and one or two rhamnose molecule in the hydrophilic moiety. First, we determined the Minimal Inhibitory Concentration (MIC) of RL and OXA by serial dilution in 96 wells microplate at pH 5.0, 6.0 and 7.5, and Minimal Bactericidal Concentration (MBC) using Tetrazolium Bromide (MTT) for methicillin susceptible S. aureus (MSSA) and MRSA. A growth curve was constructed incubating S. aureus ATCC 25923 and ATCC 33591 in the presence of RL at 2.500, 1.250, 625 and 312,5 µg/mL at pH 5.0, 7.5 and 9.0. For the next step, we used the Checkerboard Method to determine if there is any synergic effect between RL and OXA at pH 5.0 and 7.5 against S. aureus ATCC 25923 and ATCC 33591. We found that, in agreement with the literature, RL and OXA showed stronger antimicrobial activity against MSSA and MRSA at lower pH. Analyzing the growth curve, we found that at pH 5.0 rhamnolipid completely inhibited S. aureus ATCC 25923 and ATCC 33591 at 2.500 µg/mL, but at pH 7.5 it had a partial bacteriostatic effect extending the lag phase to 8 and 10 hours, respectively, reaching up to 50% growth compared to the control in the stationary phase. However, at pH 9.0 rhamnolipid showed no effect even in the highest concentration tested (2.500 µg/mL). The Checkerboard assay revealed a synergic effect between RL and OXA in both pH, 5.0 and 7.5, against MSSA ATCC 25923 (∑FIC = 0.5), but was indifferent against MRSA ATCC 33591 (∑FIC = 0.75). Palavras-chave: Antimicrobial resistance, OXACILLIN, RHAMNOLIPID , Staphylococcus aureus Agência de fomento:Universidade do Oeste Paulista - Unoeste | |||||