Antimicrobial peptides are evolving as novel therapeutic options against the increasing problem of multidrug-resistant microorganisms, and nisin is one such avenue. However, some bacteria possess a specific nisin resistance system (NSR) which cleaves the peptide reducing its bactericidal efficacy. NSR-based resistance was identified in strains of
Streptococcus uberis
, a ubiquitous pathogen that causes mastitis in dairy cattle. Previous studies have demonstrated that a nisin A derivative termed nisin PV, featuring S29P and I30V, exhibits enhanced resistance to proteolytic cleavage by NSR. Our objective was to investigate the ability of this nisin derivative to eradicate and inhibit biofilms of
S. uberis
DPC 5344 and
S. uberis
ATCC 700407 (
nsr+
) using crystal violet (biomass), XTT (viability) assays and confocal microscopy (viability and architecture). When pre-established biofilms were assessed, over 60% of the biofilm biomass was reduced by both peptides compared to the untreated controls. However, a 42% higher reduction in viability was observed following treatment with nisin PV compared to nisin A. Accordingly, confocal microscopy analysis revealed significantly more dead cells on the biofilm upper surface and a reduced thickness following treatment with nisin PV. When biofilm inhibition was assessed, nisin PV inhibited biofilm formation and decrease viability up to 56% and 85% more than nisin A, respectively. Confocal microscopy analysis revealed a lack of biofilm for
S. uberis
ATCC 700407 and only dead cells for
S. uberis
DPC 5344. These results suggest that nisin PV is a promising alternative to effectively reduce the biofilm formation of
S. uberis
strains carrying NSR.
IMPORTANCE.
One of the four most prevalent species of bovine mastitis-causing pathogens is
S. uberis.
Its ability to form biofilms confers on the bacteria greater resistance to antibiotics requiring higher doses to be more effective. In a bid to limit antibiotic resistance development, the need for alternative antimicrobials is paramount. Bacteriocins such as nisin represent one such alternative that could alleviate the impact of mastitis caused by
S. uberis.
However, many strains of
S. uberis
have been shown to possess nisin resistance determinants such as the nisin resistance protein (NSR). In this study, we demonstrate the ability of nisin and a nisin derivative termed PV that is insensitive to NSR to prevent and remove biofilms of NSR-producing
S. uberis
strains. These findings will add new information to the antimicrobial, bacteriocins and control of
S. uberis
research fields specifically in relation to biofilms and
nsr
+ mastitis-associated strains.
A Streptococcus uberis
transposon mutant screen reveals a negative role for LiaR homologue in biofilm formation
