Muhammad Salman Rasool*, Fraz Siddiqui**, Sheikh Ajaz Rasool***, Saleem Hafiz**
*D.J. Sindh Govt. Science, College Karachi, **Sindh Institute of Urology and Transplantation SIUT,
*** University of Karachi,
Background: Antibiotic resistance is increasing steadily in pathogenic bacteria all over the world. The induction of bacterial resistance by sub-lethal concentrations of ampicillin may be due to mutations and adaptability to survive at sub-minimum inhibitory concentrations of ampicillin.
Objective: Demonstrate in-vitro model of acquisition of ampicillin resistance at sub-lethal concentrations.
Material and Methods: E.coli and Salmonella species were identified by conventional biochemical reactions, API 20 E kits and by anti sera. Antibiotic disc diffusion tests and Minimum inhibitory concentrations were performed according to CLSI (2012). 56 clinical isolates of E.coli and 47 strains of Salmonella species were step wise exposed to sub-lethal concentrations of ampicillin.
Results: Out of 56 isolates of E.coli, 9 strains developed permanent resistance to ampicillin and 17 adapted to intermediate resistant levels of ampicillin. Out of 47 isolates of Salmonella species, 8 strains developed permanent resistance to ampicillin and 16 got adapted to intermediate resistance concentrations. Few strains showed cross resistance to various antibiotics after exposure to ampicillin. Sub lethal concentrations of ampicillin leads to the development of resistance which may have therapeutic implications.
Conclusion: Sub lethal concentrations of ampicillin should be avoided because exposure to these concentrations may create the ability in bacteria to adapt higher concentrations of ampicillin and trigger the bacteria to develop the resistance not only against ampicillin but also other groups of antibiotics.
Keywords: Antibiotic resistance, E.coli, Salmonella, Typhoid, Ampicillin, Sub lethal dosage