Resistance-guided isolation and characterization of antibiotic-producing bacteria from river sediments

Antibiotic-resistant bacteria in hospital wastewater treatment plant effluent and the possible consequences of its reuse in agricultural irrigation

Wastewater from hospitals should be monitored precisely and treated properly before discharge and reuse to avoid epidemic and pandemic complications, as it contains hazardous pollutants for the ecosystem. Antibiotic residues in treated hospital wastewater effluents constitute a major environmental concern since they resist various wastewater treatment processes. The emergence and spread of multi-drug-resistant bacteria, that cause public health problems, are therefore always a major concern. The aims and objectives of this study were mainly to characterize the chemical and microbial properties of the hospital effluent of wastewater treatment plant (WWTP) before discharge to the environment. Special attention was paid to the presence of multiple resistant bacteria and the effects of hospital effluent reuse in irrigation on zucchini as an economically important plant. The risk of cell-free DNA carrying antibiotic resistance genes contained in the hospital effluent as a long-lasting hazard had been discussed. In this study, 21 bacterial strains were isolated from the effluent of a hospital WWTP. Isolated bacteria were evaluated for multi-drug resistance ability against 5 antibiotics (Tetracycline, Ampicillin, Amoxicillin, Chloramphenicol, and Erythromycin) at a concentration of 25 ppm. Out of them, three isolates (AH-03, AH-07, and AH-13) were selected because they recorded the highest growth in presence of tested antibiotics. Selected isolates were identified using 16S rRNA gene sequence homology as Staphylococcus haemolyticus (AH-03), Enterococcus faecalis (AH-07), and Escherichia coli (AH-13). Their susceptibility to ascending concentrations of tested antibiotics indicated that they were all susceptible at a concentration above 50 ppm. Results of the greenhouse experiment regarding the effect of hospital WWTP effluent reuse on zucchini plant fresh weights compared to that irrigated with fresh water indicated that the former recorded a limited increase in total fresh weights (6.2 g and 5.3 g/plant, respectively). Our results demonstrated the low impact of the reuse of Hospital WWTP effluent in agriculture irrigation compared to its greater risk in transferring multiple antibiotic bacteria and antibiotic resistance genes to soil bacteria through natural transformation.

Characterization of Streptomyces Species and Validation of Antimicrobial Activity of Their Metabolites through Molecular Docking

Finding new antibacterial agents from natural products is urgently necessary to address the growing cases of antibiotic-resistant pathogens. Actinomycetes are regarded as an excellent source of therapeutically important secondary metabolites including antibiotics. However, they have not yet been characterized and explored in great detail for their utility in developing countries such as Nepal. In silico molecular docking in addition to antimicrobial assays have been used to examine the efficacy of chemical scaffolds biosynthesized by actinomycetes. This paper depicts the characterization of actinomycetes based on their morphology, biochemical tests, and partial molecular sequencing. Furthermore, antimicrobial assays and mass spectrometry-based metabolic profiling of isolates were studied. Seventeen actinomycete-like colonies were isolated from ten soil samples, of which three isolates showed significant antimicrobial activities. Those isolates were subsequently identified to be Streptomyces species by partial 16S rRNA gene sequencing. The most potent Streptomyces species_SB10 has exhibited an MIC and MBC of 1.22 μg/mL and 2.44 μg/mL, respectively, against each Staphylococcus aureus and Shigella sonnei. The extract of S. species_SB10 showed the presence of important metabolites such as albumycin. Ten annotated bioactive metabolites (essramycin, maculosin, brevianamide F, cyclo (L-Phe-L-Ala), cyclo (L-Val-L-Phe), cyclo (L-Leu-L-Pro), cyclo (D-Ala-L-Pro), N6, N6-dimethyladenosine, albumycin, and cyclo (L-Tyr-L-Leu)) were molecularly docked against seven antimicrobial target proteins. Studies on binding energy, docking viability, and protein-ligand molecular interactions showed that those metabolites are responsible for conferring antimicrobial properties. These findings indicate that continuous research on the isolation of the Streptomyces species from Nepal could lead to the discovery of novel and therapeutically relevant antimicrobial agents in the future.

The Production of Streptomyces W-5B Extract for Antibiofilm against Methicillin-resistant Staphylococcus aureus

The ability of Methicillin-resistant Staphylococcus aureus (MRSA) to form biofilms is one of the triggering factors for the emergence of MRSA resistance to antibiotics. Streptomyces W-5B has shown potency as an antibacterial producer against MRSA. However, the production of microbial bioactive compounds is strongly affected by the source of nutrients in the fermentation medium. Therefore, the objective of this study was to determine the optimal sources of carbon and nitrogen for the production of bioactive compounds with antibiofilm activities. The research method included cultivating Streptomyces W-5B, extract production, and variation of carbon (glucose, sucrose, starch) and nitrogen (casein, peptone, urea) sources for fermentation medium. Antibiofilm activities were measured based on inhibition of biofilm formation and biofilm degradation tests using the microtiter plate method with a crystal violet stain. The results showed that the highest inhibition of biofilm formation was 68.206 ± 1.750% after 12 days of incubation in a fermentation medium containing sucrose and urea. Meanwhile, the highest biofilm degradation was 73.023 ± 1.972% after nine days of incubation on a fermentation medium containing starch and urea. These findings indicated that Streptomyces W-5B has the potency to produce antibiofilm extract against MRSA.