Competition between plasmid-bearing and plasmid-free organisms in the host: population dynamics and antibiotic resistance.

OBJECTIVE To clarify the effects of antibiotic exposure on bacterial antibiotic resistance. MATERIALS AND METHODS A competitive population dynamics model for plasmid-bearing organisms and plasmid-free organisms in the host was established. The Poincaré-Bendixson theorem was used for analysis. RESULTS All possible results of the competition dependent on biologically meaningful parameters were obtained, which can be classified into eight categories. With the outcomes of the plasmid model, we discussed the sterilizing effect if an antibiotic was added to the host. CONCLUSION When antibiotic-resistant bacteria existed in a host, a higher dosage of antibiotics was needed with an increased risk of survival of plasmid-bearing organisms and greater danger of resistance to antibiotics.