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Transfer of penicillin resistance between Neisseriae in microcosm
Abstract:
Horizontal gene transfer between commensal and pathogenic Neisseriae is the mechanism proposed to explain how pathogenic species acquire altered portions of the penA gene, which encodes penicillin binding protein 2. These changes resulted in a moderately penicillin-resistant phenotype in the meningococci, whose frequency of isolation in Spain increased at the end of the 1980s. Little has been published about the possibility of this gene transfer in nature or about its simulation in the laboratory. We designed a simple microcosm, formed by solid and liquid media, that partially mimics the upper human respiratory tract. In this microcosm, penicillin-resistant commensal strains and the fully susceptible meningococcus were co-cultivated. The efficiency of gene transfer between the strains depended on the phase of bacterial growth and the conditions of culture. Resistance of penicillin was acquired in different steps irrespective of the source of the DNA. The presence of DNase in the medium had no effect on gene transfer, but it was near zero when nicked DNA was used. Cell-to-cell contact or membrane blebs could explain these results. The analysis of sequences of the transpeptidase domain of PBP2 from transformants, and from donor and recipient strains demonstrated that the emergence of moderately resistant transformants was due to genetic exchange between the co-cultivated strains. Finally, mechanisms other than penA modification could be invoked to explain decreased susceptibility.
Insights
Horizontal gene transfer enables pathogenic Neisseria to acquire penicillin resistance by altering the penA gene. This study simulated gene transfer in a lab model, confirming its occurrence and mechanisms.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Horizontal gene transfer (HGT) is proposed for pathogenic Neisseria acquiring altered penA genes, conferring penicillin resistance.
- Increased isolation of penicillin-resistant meningococci in Spain during the late 1980s highlights the clinical relevance of this phenomenon.
- Limited research exists on the natural occurrence and laboratory simulation of HGT in Neisseria species.
Purpose of the Study:
- To investigate the feasibility and mechanisms of horizontal gene transfer between commensal and pathogenic Neisseria species in a controlled laboratory setting.
- To simulate conditions mimicking the human respiratory tract to study Neisseria gene exchange.
- To analyze the genetic basis of penicillin resistance acquisition in Neisseria.
Main Methods:
- Co-cultivation of penicillin-resistant commensal Neisseria strains with fully susceptible pathogenic Neisseria in a dual-phase microcosm simulating the upper respiratory tract.
- Assessment of gene transfer efficiency based on bacterial growth phases and culture conditions.
- DNA sequence analysis of the transpeptidase domain of penicillin-binding protein 2 (PBP2) in donor, recipient, and transformant strains.
Main Results:
- Penicillin resistance was acquired by susceptible Neisseria through gene transfer from resistant commensals, occurring in distinct steps.
- Gene transfer efficiency was dependent on bacterial growth phase and culture conditions, suggesting cell-to-cell contact or membrane blebs as mechanisms.
- DNase had no impact, while nicked DNA significantly reduced gene transfer, indicating a requirement for intact DNA and direct interaction.
- Sequence analysis confirmed genetic exchange within the PBP2 transpeptidase domain as the cause of moderate penicillin resistance in transformants.
Conclusions:
- Horizontal gene transfer is a viable mechanism for the acquisition of penicillin resistance in Neisseria, mediated by genetic exchange of the penA gene.
- The study successfully simulated Neisseria gene transfer in a microcosm, providing insights into the process and influencing factors.
- Alternative mechanisms beyond penA modification may also contribute to decreased penicillin susceptibility in pathogenic Neisseria.