Antibacterial and antibiotic-modulating activities of Rhinella jimi and three other animal extracts against multidrug-resistant Gram-negative phenotypes

Background: The antibiotic resistance of pathogenic bacteria is one of the major health problems worldwide. The development of novel antimicrobial therapies based on natural products that greatly reduce this resistance is urgent. The present study aimed at evaluating the antimicrobial potential of four animal methanol extracts, Gryllus campestris, Testudo hermanni, Cardisoma guanhumi, and Rhinella jimi as well as their synergistic effects with antibiotics against twenty Gram-negative bacteria. Methods: Zoochemical analysis of extracts was performed using qualitative reference methods for the detection of secondary metabolites and the ninhydrin reaction for the detection of protein constituents. The antibacterial activity of animal extracts alone and in combination with antibiotics was carried out using broth microdilution methods. Results: Amino acids, peptides, or proteins were present in all extracts. Alkaloids were detected in extracts of C. guanhumi and R. jimi and were absent in other extracts. Flavonoids, tannins, and steroids were evidenced only in dried and fresh extracts of R. jimi. Polyphenols, anthocyanins, anthraquinones, and saponins were not detected in all extracts. Dried extract from R. jimi was most active. It had antibacterial potential against 85% of the tested bacterial strains with significant activity (100≤MIC≤512 µg/mL) against 35% of bacteria; this included three E. coli (ATCC8739, AG100ATet and MC4100), one E. aerogenes (ATCC13048), one K. pneumoniae (ATCC11296) and two P. aeruginosa (PA01 and PA124). Dried and fresh extracts from C. guanhumi displayed an antibacterial activity against 40% and 20% of the bacteria tested, respectively, whereas dried extracts from G. campestris and fresh extracts from T. hermanni inhibited the growth of 15% and 10% of bacteria, respectively (MIC range of 512 to 2048 µg/mL). The dried and fresh extracts of R. jimi, at MIC/2 and MIC/4, potentialized the activities of more than 70% of the antibiotics respectively against more than 70% of studied bacteria. Both extracts highly improved the activity of oxacillin, gentamicin, erythromycin, and ciprofloxacin with improved activity factors (IAFs) ranging from 16 to 256. Conclusion: This work demonstrated that R. jimi extracts had a broad spectrum of antibacterial activities. The overall data provided evidence that animals investigated in this study might be potential sources of natural antimicrobial agents; They can be combined with clinically used antibiotics to overcome bacterial resistance. Keywords: Animal extract, antibiotics; Gram-negative bacteria; efflux pumps; multidrug resistance; Rhinella jimi.