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Plasmid-associated transfer of tetracycline resistance in Bacteroides ruminicola
H J Flint1, A M Thomson, J Bisset
1Nutrition Division, Rowett Research Institute, Bucksburn, Aberdeen, United Kingdom.
Abstract:
Tetracycline resistance was transferred at frequencies between 10(-7) and 10(-6) per recipient cell in anaerobic matings between two strains of the strictly anaerobic rumen bacterium Bacteroides ruminicola. The donor strain, 223/M2/7, was a multiple-plasmid-bearing tetracycline-resistant strain from the ovine rumen, and the recipient, F101, was a rifampin-resistant mutant of B14, a bovine strain belonging to B. ruminicola subsp. brevis. Resistance transfer could occur in the presence of DNase, but not in dummy mating mixtures in which filtrate from a donor culture replaced donor cells. Acquisition of tetracycline resistance by the recipient was accompanied by the appearance of a 19.5-kilobase pair plasmid (designated pRRI4) which was homologous with a plasmid of similar size and restriction pattern present in the donor strain. A transconjugant (F115) carrying pRRI4 was also able to act as a donor of tetracycline resistance and plasmid DNA in matings with another recipient. Derivatives of F115 that had spontaneously lost tetracycline resistance lacked detectable plasmid DNA. It is concluded that pRRI4 mediated the transfer of tetracycline resistance. Transfer of resistance was not detectably enhanced by pregrowth of the donor in medium containing tetracycline. Transfer of tetracycline resistance was not detected from 223/M2/7 to a strain, 23 belonging to B. ruminicola subsp. ruminicola.
Insights
Tetracycline resistance transfer in Bacteroides ruminicola was mediated by a specific plasmid (pRRI4). This plasmid facilitated the spread of antibiotic resistance between rumen bacteria, highlighting potential mechanisms of resistance dissemination.
Area of Science:
- Microbiology
- Bacterial genetics
- Antibiotic resistance
Background:
- The rumen bacterium Bacteroides ruminicola is a key component of herbivore digestive systems.
- Understanding the mechanisms of antibiotic resistance transfer in anaerobic bacteria is crucial for animal and human health.
- Plasmids are known vectors for antibiotic resistance genes in bacteria.
Purpose of the Study:
- To investigate the mechanism of tetracycline resistance transfer in Bacteroides ruminicola.
- To identify the genetic element responsible for mediating tetracycline resistance dissemination.
- To characterize the plasmid involved in resistance transfer.
Main Methods:
- Anaerobic bacterial matings were performed between tetracycline-resistant donor and rifampin-resistant recipient strains of Bacteroides ruminicola.
- Plasmid DNA was isolated and analyzed in donor, recipient, and transconjugant strains.
- DNase was used to confirm cell-to-cell contact was necessary for transfer.
- Molecular techniques were employed to characterize the plasmid mediating resistance.
Main Results:
- Tetracycline resistance was transferred at frequencies of 10(-7) to 10(-6) per recipient cell.
- Acquisition of tetracycline resistance was associated with the presence of a 19.5-kilobase pair plasmid, pRRI4.
- The transconjugant strain carrying pRRI4 could act as a donor, confirming its role in resistance transfer.
- Loss of tetracycline resistance correlated with the absence of detectable plasmid DNA.
Conclusions:
- The plasmid pRRI4 is responsible for mediating the transfer of tetracycline resistance in Bacteroides ruminicola.
- Plasmid-mediated transfer is a significant mechanism for the dissemination of antibiotic resistance in this rumen bacterium.
- Further research is needed to understand the prevalence and implications of such resistance transfer in the rumen ecosystem.