Intact pap2 downstream of mcr-1 appears to be required for colistin resistance

Area of Science:

• Microbiology
• Genetics
• Antimicrobial Resistance

Background:

• Colistin is a critical antibiotic for treating multidrug-resistant Gram-negative infections.
• The emergence of colistin resistance, often mediated by plasmid-borne genes like mcr-1, poses a significant public health threat.
• The role of other genetic elements, such as pap2, in modulating antibiotic resistance is not fully understood.

Purpose of the Study:

• To investigate the contribution of the pap2 gene to colistin susceptibility.
• To determine whether an intact or truncated pap2 gene influences colistin resistance in the presence of mcr-1.
• To elucidate the genetic mechanisms underlying plasmid-mediated colistin resistance.

Main Methods:

• Plasmid construction and conjugation to introduce pap2 and mcr-1 genes into bacterial hosts.
• Antibiotic susceptibility testing (e.g., determining Minimum Inhibitory Concentrations) to assess bacterial response to colistin.
• Time-killing assays to evaluate the bactericidal activity of colistin over time.

Main Results:

• Conjugation experiments confirmed the presence of intact and truncated pap2 genes on plasmids also carrying mcr-1.
• Antibiotic susceptibility testing revealed that reduced colistin susceptibility was observed only when an intact pap2 gene was present alongside mcr-1.
• Time-killing assays demonstrated that bacteria harboring both intact pap2 and mcr-1 were significantly less susceptible to colistin compared to those with only mcr-1 or truncated pap2.

Conclusions:

• An intact pap2 gene, in conjunction with mcr-1, is essential for the observed reduction in colistin susceptibility.
• Truncated pap2 (pap2∆351) does not contribute to reduced colistin susceptibility when co-located with mcr-1.
• These findings highlight the importance of understanding the interplay between different genes on mobile genetic elements in the development of antibiotic resistance.