Different CprABC amino acid sequences affect nisin A susceptibility in Clostridioides difficile isolates

Area of Science:

• Microbiology
• Genetics
• Antimicrobial Resistance

Background:

• Clinical isolates of Clostridioides difficile (C. difficile) often display multidrug resistance, necessitating alternative treatments beyond metronidazole and vancomycin.
• Nisin A, a bacteriocin from Lactococcus lactis, has shown promise as an alternative antimicrobial agent against C. difficile infections.
• Understanding the mechanisms of nisin A susceptibility in C. difficile is crucial for developing effective therapies.

Purpose of the Study:

• To investigate the susceptibility of clinical C. difficile isolates to nisin A.
• To explore the correlation between nisin A susceptibility and the expression of genes involved in nisin A efflux (CprABC) and cell surface charge (DltDABC).
• To identify genetic factors, particularly variations in CprABC, that contribute to differential susceptibility to nisin A and related bacteriocins.

Main Methods:

• Evaluated nisin A susceptibility in 11 clinical C. difficile isolates, categorizing them into high and low susceptibility groups.
• Assessed the expression levels of cprA and dltA genes in response to nisin A exposure.
• Performed cytochrome C binding assays to determine cell surface charge.
• Conducted whole-genome sequencing and phylogenetic analysis of the isolates.
• Analyzed amino acid sequences of CprABC proteins between susceptible and resistant groups.
• Tested susceptibility to structurally similar bacteriocins, epidermin and mutacin III.

Main Results:

• C. difficile isolates exhibited varied susceptibility to nisin A, dividing into high and low susceptibility groups.
• Nisin A induced cprA expression in all strains, but dltA expression was unaffected and neither correlated with susceptibility.
• Cell surface charge did not correlate with nisin A susceptibility.
• Phylogenetic analysis revealed two major clusters consistent with nisin A susceptibility differences.
• Distinct amino acid variations were identified in CprA, CprB, and CprC proteins between the two clusters.
• Susceptibility patterns to epidermin and mutacin III mirrored those of nisin A.

Conclusions:

• Genotypic variations within C. difficile strains, specifically in the CprABC efflux pump system, are associated with differential susceptibility to nisin A.
• These findings suggest that variations in bacteriocin susceptibility are linked to specific genetic differences in C. difficile.
• The study highlights the potential of bacteriocins as alternatives to conventional antibiotics for treating C. difficile infections, with susceptibility influenced by strain-specific genetic makeup.