In-vitro Evaluation of Antimicrobial Activity of Nargenicin-A1 against Gram Positive Clinical Isolates and its Comparison with Various Antibiotics

Introduction: The development of Multidrug Resistance (MDR) is a serious health problem, which demands the quest and development of many antibacterial agents. The class Actinomycetes represents best source for many antimicrobial agents. The present focus on Actinomycetes has yielded many antimicrobial agents including Nargenicin-A1. The Nargenicin-A1 belonging to class macrolides was found to have strong antibacterial activity against Staphylococcus and Streptococcus.

Aim: To determine the Minimum Inhibitory Concentration (MIC) of Nargenicin-A1 against clinically isolated aerobic gram positive bacteria and comparing its antimicrobial activities with various antibiotics.

Materials and Methods: A prospective, hospital-based, observational study was conducted at the Department of Microbiology, Raichur Institute of Medical Sciences, Raichur, Karnataka, India, from August 2015 to July 2016. All the clinical samples like pus, sputum, urine, ear swabs, wound swabs and body fluids received for culture and sensitivity testing at the Department of Microbiology during the study period was included. The antimicrobial activity was determined by measuring the MIC of Nargenicin-A1 by broth dilution method following standard procedure and the mean MIC was calculated. Pearson’s coefficient of correlation was calculated to find out correlation between MIC of Nargenicin-A1 and MIC of various antibiotics effective against gram positive bacteria.

Results: The most common isolate was Staphylococcus followed by Enterococcus and Streptococcus. The least mean MIC of Nargenicin-A1 was observed for Streptococcus (0.017 μg/mL) followed by S. aureus (3.97 μg/mL), and the highest mean MIC value was recorded for Enterococcus (27.34 μg/mL). Among Staphylococcus aureus, the mean MIC value of Nargenicin-A1 for Methicillin Sensitive Staphylococcus aureus (MSSA), Methicillin Resistant Staphylococcus aureus (MRSA) and Vancomycin Resistant Staphylococcus aureus (VRSA) was 0.06 μg/mL, 0.12 μg/mL
and 25 μg/mL, respectively. When compared Nargenicin-A1 with various antibiotics in terms of their MICs, the activity of Nargenicin-A1 was in close proximity to that of vancomycin and linezolid against MSSA, MRSA, and Enterococci and marginally with linezolid against VRSA.

Conclusion: Nargenicin-A1 exhibits strong antibacterial property against a broad spectrum of aerobic gram positive bacteria, including VRSA. The study revealed that Nargenicin-A1 can be considered as a potential alternative against MDR gram positive bacteria.