Tetracycline efflux pump in different Salmonella enterica isolated from diarrhea patients in two rural health centers in Western Kenya

Background: Tetracyclines (TCs) are a type of broad-spectrum bacteriostatic antibiotics used for treatment of a wide variety of infections. These antibiotics eventually reach terrestrial and aquatic environments via application of manure or slurry to areas used agriculturally, or by other methods. Bacteria resistance to tetracycline is due to efflux pump among others. This study discerned the existence of tetracycline efflux pump in Salmonella enterica belonging to different serovars isolated from diarrhea patients in two rural health centers in Western Kenya. Patients and method: Forty-five unrelated tetracycline-resistant Salmonella isolates from diarrheal patients were cultured and phenotypically identified using conventional methods. Phenotypic tetracycline resistance profile was determined by using Agar Disc Dilution. Tetracycline growth curve for resistant isolates were determined by incubating 106 cfu in 10 ml nutrient broth having 30?g/ml tetracycline and incubated at 37°C in a rotary incubator. Generation rate was spectrophotometrically assayed at 600nm. Tetracycline resistant isolates DNA were extracted using QIAMP Qiagen protocol and amplified using specific tetracycline primers. Results: Tetracycline resistance genes were isolated in 62.2% (n=28/45) Salmonella isolates. Out of these, 64.3% (n =18/28) were S. typhi, 17.8% (n =5/28) S. typhimurium, and 14.3% (n=4/28) S. enteritidis. S. typhi expressed resistance to tetA 3.6% (n=1/28), tetB 10.7% (n=3/28), tetD 10.7% (n=3/28), tetG 10.7% (n=3/28), tetE, H, J, 10.7% (n=3/28) and tet AC 17.8% (n=5/28) in isolation or in combination. All the 5 S. typhimurium expressed tetA resistance. Totally, S. enteritidis displayed tetA, tetB and tetC resistance in 7.1%, 3.6%, and 3.6%, respectively. Conclusion: These data show that the identified gene encoded tet resistance gene as MFS–type multi-substrate efflux transporter, which contributes to intrinsic resistance on range of structurally unrelated compounds in Salmonella species.