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United States Department of Agriculture

Agricultural Research Service

Title: Augmentation of Antibiotic Resistance in Salmonella Typhimurium Dt104 Following Exposure to Penicillin Derivatives

Authors
item Carlson, Steven
item Ferris, K - USDA-APHIS-NVSL

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 23, 1999
Publication Date: N/A

Interpretive Summary: Antibiotic resistance in disease-causing 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 evaluating the disease-causing ability of multiresistant Salmonella typhimurium, we found that certain isolates can be induced to become even more resistant. That is, bacteria not only become resistant to a wider range of antibiotics, but they also exhibit quantitative increases in resistance values for antibiotics to which they are intrinsically resistant. The induction process involves growing the bacteria in the presence of a specific group of penicillin-related antibiotics including ampicillin, amoxicillin, or ticarcillin. Since the isolates studied are resistant to ampicillin, amoxicillin and ticarcillin, this phenomenon suggests that resistant Salmonella not only have a selective advantage over nonresistant Salmonella, but their resistance abilities can be potentiated when an inappropriate antibiotic is used therapeutically.

Technical Abstract: 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 antibiograms. That is, bacteria not only become resistant to a wider range of antibiotics, but they also exhibit quantitative increases in MIC values for antibiotics that were part of their intrinsic antibiograms. The "induction" process involves growing the bacteria to stationary phase in the presence of beta-lactam antibiotics, such as ampicillin, amoxicillin, or ticarcillin. This phenomenon suggests that resistant Salmonella not only have a selective advantage over nonresistant Salmonella, but their resistance phenotypes can be potentiated when an inappropriate antibiotic is used therapeutically.

Last Modified: 12/20/2014
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