Induction of Ampicillin Resistance in E.coli and Salmonella species by Sub-lethal Doses

Abstract

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.