Augmentation of antibiotic resistance in Salmonella typhimurium DT104 following exposure to penicillin derivatives

Vet Microbiol. 2000 Apr 4;73(1):25-35. doi: 10.1016/s0378-1135(00)00154-1.


Antibiotic resistance in pathogenic bacteria has been a problem in both developed and developing countries. This problem is especially evident in Salmonella typhimurium, one of the most prevalent foodborne pathogens. While performing in vitro gentamicin protection-based invasion assays, we found that certain isolates of multiresistant S. typhimurium can be 'induced' to exhibit new resistance profiles. That is, bacteria become resistant to a wider range of antibiotics and they also exhibit quantitative increases in MIC values for antibiotics that were part of their pre-induction antibiograms. This 'induction' process involves growing the bacteria to stationary phase in the presence of antibiotics such as ampicillin, amoxicillin or ticarcillin. Since the isolates studied exhibited resistance to ampicillin, amoxicillin and ticarcillin prior to exposing the bacteria to these antibiotics, the observed phenomenon suggests that resistant Salmonella not only have a selective advantage over non-resistant Salmonella but their resistance phenotypes can be accentuated when an inappropriate antibiotic is used therapeutically.

MeSH terms

  • Ampicillin Resistance / genetics
  • Animals
  • Chloramphenicol Resistance / genetics
  • Cloning, Molecular
  • Drug Resistance, Microbial / genetics
  • Drug Resistance, Multiple / genetics*
  • Gentamicins / pharmacology
  • Kanamycin Resistance / genetics
  • Microbial Sensitivity Tests
  • Penicillins / pharmacology*
  • Salmonella Infections, Animal / drug therapy*
  • Salmonella typhimurium / drug effects*
  • Salmonella typhimurium / genetics


  • Gentamicins
  • Penicillins