An Increase in Antimicrobial Effects of Standard Antibiotics in Combination with the Active Metabolites Isolated from Marine Streptomyces: A Laboratory Study

Combination therapy has been considered as a potential approach to overcome antimicrobial resistance. In this study the antimicrobial effects of active compounds produced by some marine Streptomyces spp. in combination with some standard antibiotics against multidrug-resistant pathogens was investigated.

In this laboratory study, the bacteria isolated from Caspian Sea were tested for their ability to produce antimicrobial compounds active against some drug-resistant pathogens using disc diffusion methods. Then, the producer strains were cultivated in suitable liquid media. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the ethyl acetate extracts were measured against some drug-resistant species including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) using microbroth dilution technique. Data was analysed using paired t-test.

In the first screening, strains MN2, MN39, MN40 and MN41 showed a broad antimicrobial activity against MRSA, VRE, Salmonella typhi and pseudomonas aeruginosa, among which, the best MIC against MRSA was obtained from strain MN39 at 280 (µg/ml). These extracts in combination with some standard antibiotics resulted in a noticeable improved antimicrobial activity against multidrug-resistant pathogens, while in some cases the activity was decreased.

The bioactive compounds produced by actinomyces possess remarkable antimicrobial properties against drug-resistant pathogens when used in a combination therapy with standard antibiotics which requires further research in the future.