Combination Of Phages And Antibiotic Therapy To Control And Revert Antimicrobial Resistance Of Salmonella Enteritidis Isolated From Poultry Farms In Kiambu And Nairobi Counties, Kenya

Abstract

Multi-drug resistant (MDR) Salmonella enterica Enteritidis (S. Enteritidis) is an important cause of food-related illness globally. MDR Salmonella infections have complicated the current chemotherapeutic options. Bacteriophages (phages) can be used as an alternative to control Antimicrobial resistant (AMR) infections. Furthermore, phage-antibiotic combination therapy has been suggested as a strategy to revert antibiotic resistance while also decreasing the occurrence of bacteriophage-insensitive mutants (BIMs). This study tested the ability of two newly isolated S. Enteritidis-specific phages to reverse antibiotic resistance in six Kenyan field strains of S. Enteritidis. We isolated 44 BIMs using six AMR S. Enteritidis strains exposed to two broad host range phages. First, we observed that most BIMs demonstrated lowered phage adsorption. Their antibiotic susceptibility profile was then assessed using 23 antibiotics. Comparing the relative antibiotic sensitivities of the BIMs to the parental host, we observed a higher proportion of BIMs becoming susceptible to the antibiotics to which the parent was previously resistant (25/44), whereas 12/44 had maintained their relative sensitivities to the antibiotics. A small number of the BIMs (4/44) became resistant to antibiotics the parent had been susceptible to. Remarkably, one BIM from isolate Sal 572 had drastic increases in nalidixic acid, gentamicin, and tetracycline susceptibilities. We further tested whether a panel of AMR genes known to be present in the parental strains could still be detected in the BIMs. Interestingly, the BIMs isolated from Sal 572 had lost tetA, tetB, strA, and strB genes. Finally, after carrying out kill curves with antibiotics and phages used in combination, we observed a more significant bacterial load reduction than phages or antibiotics used alone in four isolates. In conclusion, our study demonstrates the potential use of a combination of antibiotics and phages for therapy against MDR Salmonella from Kenya. Keywords: Salmonella Enteritidis; AMR; MDR; BIMs; Combination therapy; phages; antibiotics