ANTIBACTERIAL EVALUATION OF EXTRACTS PRODUCED BY Streptomyces sp. MG13: AN ENDOPHYTE FROM Mikania glomerata (SPRENG.)

Studies with natural products to remedy human infectious diseases has been increase, once bacteria have become increasingly resistant to known antibiotics. Endophytic microorganisms are promising source of these, because inhabit the interior of plant hosts without causing damage, could contribute with several activities as secondary metabolites production with antimicrobial activities, among others. The aims of these work was qualitatively analyze the antimicrobial activity against Staphylococcus aureus ATCC 25923 of secondary metabolites produced by Streptomyces sp. Mg13, an Actinobacteria isolated from medicinal plant Mikania glomerata (Spreng.). The strains was inoculated in six 1L Erlenmeyers with 600mL of Luria-Bertani broth (LB) and incubated in a shaker (150 rpm) at 28 °C for 7 days. After, the fermented broth was centrifuged in 50mL tubes at 3600 ×g and filtrated. Half the volume (1.8L) has your pH adjusted to 3.5, being 200mL frozen at -80 °C and freeze-dried (=extract Aq3). The remainder was partitioned with ethyl acetate (EtOAc) and concentrated in rotary evaporator (=extract AE3). 200mL of aqueous phase from these EtOAc partition was rotary evaporated to remove traces of EtOAc, frozen at -80 °C and freeze-dried (=extract AqAE3). The same process was made with the other half of the fermented broth, but without adjustment of pH (pH= 8.5). Then, was obtained 6 extracts. For antibiogram test, S. aureus strain was grown on Muller-Hinton agar (MHA) and adjusted the inoculum concentration with McFarland 0.5 scale, by diluting the cells in salt solution (0.85% NaCl). The bacteria were inoculated with a swab in Petri dishes with MHA and filter paper discs embedded with 10 µL of extracts (50 mg/mL) was distributed in the dishes. The EtOAc extracts was diluted in methanol (MeOH) and the aqueous extracts in ultra-pure water. So, the controls were MeOH, ultra-pure water and tetracycline (1 mg/mL). The Petri dishes was incubated at 37 °C by 24 hours, being evaluated the halos formation and measured the diameter. All extracts and controls were tested in triplicate. Was not observed halos in aqueous extracts and in the MeOH and ultra-pure water controls. The extracts of AE3 and AE8 showed positive results with 13.4mm and 11.3mm of diameter halos, respectively. In tetracycline control, halos with 33.93mm on average was observed. The results showed potential to isolation and chemical characterization of bioactive compounds presents in crude extracts of EtOAc produced by Streptomyces sp. Mg13.