Evaluation of <i>in-vitro</i> interactions of <i>streptomyces</i> antibiotic substances and standard antibiotics against sensitive and resistant bacteria by activity index profile

Abstract

Evaluation of the combined in-vitro antibacterial activities of Streptomyces antibiotic substances (UY1 – UY9) produced by Streptomyces species isolated from soil and standard antibiotics: ampicillin (AMP), tetracycline (TET) and chloramphenicol (CHL) against bacterial isolates: Staphylococcus aureus (SA), coagulase-negative Staphylococcus aureus (CONSA), methicillin–resistant Staphylococcus aureus (MRSA), Bacillus subtilis (BS), Streptococcus pnueumoniae (SP), Escherichia coli (EC), Pseudomonas aeruginosa (PA), Salmonella typhimurium (ST), Shigella dysentariae (SD) and Vibrio cholerae (VC) was carried out at 1 x MIC by the modified agar – well diffusion technique. The inhibitory zones of the interactions were assessed by the activity index profile (AIP), to evaluate the nature of the interactions. The combination of the agents at 1 x MIC against the test organisms showed qualitative inhibitory activity within the range (10.0 – 25.0 mm). The comparative assessment of the inhibitory activities by AIP, indicated synergism, additivity, indifferent and antagonism interactions. The standard definitions of synergy, additivity, indifference and antagonism were utilized in the assay. All the antimicrobial combinations demonstrated some degrees of synergism against the test organisms mostly the Gram-positives for ampicillin, and both Gram-positives and Gram–negatives for chloramphenicol; and lessly, tetracycline with infrequent antagonism. Conversely, antagonism was predominantly demonstrated in the combinations with tetracycline, while synergism was infrequent.

Keywords: In-vitro interactions, Streptomyces Antibiotic Substances, Sensitive and Resistant Bacteria, Activity Index Profile