Antibiotics targeting bacterial protein synthesis reduce the lytic activity of bacteriophages.

Combination therapy of bacteriophages and antibiotics requires careful selection of specific antibiotics as it is crucial towards determining the success of phage therapy to treat multiple drug-resistant bacterial infections. So, we examined how different antibiotics can affect phage lytic activity when used in combination against targeted bacteria. Various antibiotics targeting bacterial protein synthesis pathways were tested for their bactericidal action in combination with bacteriophages of Acinetobacter baumannii (φAB145, φAB182), Staphylococcus aureus (φSA115, φSA116) and Salmonella Typhimurium (φST143, φST188). The phages displayed highly significant antagonism with most of the protein/ribosomal machinery targeting antibiotics: φSA115 (13/13); φSA116 (13/13); φST143 (11/13); φAB145 (11/13); φST188 (9/13); φAB182 (7/13). To validate this antagonistic effect, synergy assessment of these phages with gentamicin (GEN) and tetracycline (TE) was performed using time kill curve assays and counting the remaining viable bacterial cells at the end of the experiment. An increase in bacterial turbidity in phage-antibiotic combination groups was observed as compared to the treatment with phages individually. Also, GEN exhibited 4.22, 5.90, 2.02, 3.15, 2.68, and 2.60 log proliferation in viable cell count, respectively, for φSA115, φSA116, φST145, φAB182, φST143 and φAB188 in combination group in comparison to their individual actions. TE supplementation also led to 2.40, 4.90, 1.61, 2.73, 3.93, and 1.81 log increments in viable bacterial count when combined with φSA115, φSA116, φST145, φAB182, φST143 and φAB188, respectively. This study concludes that antibiotics targeting the bacterial protein biosynthetic machinery may lead to a reduction in the lytic activity of bacteriophages, thus lowering their therapeutic potential. Hence, such compounds must be carefully screened before their employment in combination treatment regimens.