A novel bioengineered derivative of nisin displays enhanced antimicrobial activity against clinical Streptococcus agalactiae isolates

Guarding the walls: the multifaceted roles of Bce modules in cell envelope stress sensing and antimicrobial resistance

Bacteria have developed diverse strategies for defending their cell envelopes from external threats. In Firmicutes, one widespread strategy is to use Bce modules-membrane protein complexes that unite a peptide-detoxifying ABC transporter with a stress response coordinating two-component system. These modules provide specific, front-line defense for a wide variety of antimicrobial peptides and small molecule antibiotics as well as coordinate responses for heat, acid, and oxidative stress. Because of these abilities, Bce modules play important roles in virulence and the development of antibiotic resistance in a variety of pathogens, including Staphylococcus, Streptococcus, and Enterococcus species. Despite their importance, Bce modules are still poorly understood, with scattered functional data in only a small number of species. In this review, we will discuss Bce module structure in light of recent cryo-electron microscopy structures of the B. subtilis BceABRS module and explore the common threads and variations-on-a-theme in Bce module mechanisms across species. We also highlight the many remaining questions about Bce module function. Understanding these multifunctional membrane complexes will enhance our understanding of bacterial stress sensing and may point toward new therapeutic targets for highly resistant pathogens.

Nisin variants: What makes them different and unique?

Nisin A is a lantibiotic bacteriocin typically produced by strains of Lactococcus lactis. This bacteriocin has been approved as a natural food preservative since the late 1980 s and shows antimicrobial activity against a range of food-borne spoilage and pathogenic microorganisms. The therapeutic potential of nisin A has also been explored increasingly both in human and veterinary medicine. Nisin has been shown to be effective in treating bovine mastitis, dental caries, cancer, and skin infections. Recently, it was demonstrated that nisin has an affinity for the same receptor used by SARS-CoV-2 to enter human cells and was proposed as a blocker of the viral infection. Several nisin variants produced by distinct bacterial strains or modified by bioengineering have been described since the discovery of nisin A. These variants present modifications in the peptide structure, biosynthesis, mode of action, and spectrum of activity. Given the importance of nisin for industrial and therapeutic applications, the objective of this study was to describe the characteristics of the nisin variants, highlighting the main differences between these molecules and their potential applications. This review will be useful to researchers interested in studying the specifics of nisin A and its variants.

Multiple potential strategies for the application of nisin and derivatives

Nisin is a naturally occurring bioactive small peptide produced by Lactococcus lactis subsp. lactis and belongs to the Type A (I) lantibiotics. Due to its potent antimicrobial activity, it has been broadly employed to preserve various food materials as well as to combat a variety of microbial pathogens. The present review discusses the antimicrobial properties of nisin and different types of their derivatives employed to treat microbial pathogens with a detailed underlying mechanism of action. Several alternative strategies such as combination, conjugation, and nanoformulations have been discussed in order to address several issues such as rapid degradation, instability, and reduced activity due to the various environmental factors that arise in the applications of nisin. Furthermore, the evolutionary relationship of many nisin genes from different nisin-producing bacterial species has been investigated. A detailed description of the natural and bioengineered nisin variants, as well as the underlying action mechanisms, has also been provided. The chemistry used to apply nisin in conjugation with natural or synthetic compounds as a synergetic mode of antimicrobial action has also been thoroughly discussed. The current review will be useful in learning about recent and past research that has been performed on nisin and its derivatives as antimicrobial agents.

Bioengineered Nisin A Derivatives Display Enhanced Activity against Clinical Neonatal Pathogens

Neonatal infection is a significant cause of mortality and morbidity in infants. The global incidence of multi-drug resistance continues to rise among neonatal pathogens, indicating a need for alternative treatment strategies. Nisin is an antimicrobial peptide that exhibits broad-spectrum activity against a wide variety of clinical pathogens and can be used in combination with antibiotics to improve their effectiveness. This study examined the activity of nisin and bioengineered derivatives against multi-drug resistant Streptococcus agalactiae and Staphylococcus capitis isolates and investigated the potential synergy between nisin peptides and selected antibiotics. Whole genome sequence analysis of the strains revealed the presence of multi-drug resistant determinants, e.g., macrolide, tetracycline, β-lactam, aminoglycoside, while the S. agalactiae strains all possessed both nsr and nsrFP genes and the S. capitis strains were found to encode the nsr gene alone. Deferred antagonism assays demonstrated that nisin PV had improved antimicrobial activity against all strains tested (n = 10). The enhanced specific activity of this peptide was confirmed using minimum inhibitory concentrations (MIC) (0-4-fold lower MIC for nisin PV) and broth-based survival assays. Combinations of nisin peptides with antibiotics were assessed for enhanced antimicrobial activity using growth and time-kill assays and revealed a more effective nisin PV/ampicillin combination against one S. capitis strain while a nisin A/erythromycin combination displayed a synergistic effect against one S. agalactiae strain. The findings of this study suggest that nisin derivatives alone and in combination with antibiotics have potential as alternative antimicrobial strategies to target neonatal pathogens.

A Bioengineered Nisin Derivative To Control Streptococcus uberis Biofilms

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), 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) (viability) assays, and confocal microscopy (viability and architecture). When preestablished biofilms were assessed, both peptides reduced biofilm biomass by over 60% compared to that of the untreated controls. However, a 42% higher reduction in viability was observed following treatment with nisin PV compared to that of 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 decreased 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.

Nisin resistance in Gram-positive bacteria and approaches to circumvent resistance for successful therapeutic use

Antibiotic resistance among bacterial pathogens is one of the most worrying problems in health systems today. To solve this problem, bacteriocins from lactic acid bacteria, especially nisin, have been proposed as an alternative for controlling multidrug-resistant bacteria. Bacteriocins are antimicrobial peptides that have activity mainly against Gram-positive strains. Nisin is one of the most studied bacteriocins and is already approved for use in food preservation. Nisin is still not approved for human clinical use, but many in vitro studies have shown its therapeutic effectiveness, especially for the control of antibiotic-resistant strains. Results from in vitro studies show the emergence of nisin-resistant bacteria after exposure to nisin. Considering that nisin has shown promising results for clinical use, studies to elucidate nisin-resistant mechanisms and the development of approaches to circumvent nisin-resistance are important. Thus, the objectives of this review are to identify the Gram-positive bacterial strains that have shown resistance to nisin, describe their resistance mechanisms and propose ways to overcome the development of nisin-resistance for its successful clinical application.

Resistance Mechanisms to Antimicrobial Peptides in Gram-Positive Bacteria

With the alarming increase of infections caused by pathogenic multidrug-resistant bacteria over the last decades, antimicrobial peptides (AMPs) have been investigated as a potential treatment for those infections, directly through their lytic effect or indirectly, due to their ability to modulate the immune system. There are still concerns regarding the use of such molecules in the treatment of infections, such as cell toxicity and host factors that lead to peptide inhibition. To overcome these limitations, different approaches like peptide modification to reduce toxicity and peptide combinations to improve therapeutic efficacy are being tested. Human defense peptides consist of an important part of the innate immune system, against a myriad of potential aggressors, which have in turn developed different ways to overcome the AMPs microbicidal activities. Since the antimicrobial activity of AMPs vary between Gram-positive and Gram-negative species, so do the bacterial resistance arsenal. This review discusses the mechanisms exploited by Gram-positive bacteria to circumvent killing by antimicrobial peptides. Specifically, the most clinically relevant genera, Streptococcus spp., Staphylococcus spp., Enterococcus spp. and Gram-positive bacilli, have been explored.

A review of antibiotic resistance in Group B Streptococcus: the story so far

Group B Streptococcus (GBS) is the leading cause of neonatal disease worldwide, and invasive disease in adults is becoming more prevalent. Currently, some countries adopt an intrapartum antibiotic prophylaxis regime to help prevent the transmission of GBS from mother to neonate during delivery. This precaution has reduced the incidence of GBS-associated early-onset disease; however, rates of late-onset disease and stillbirths associated with GBS infections remain unchanged. GBS is still recognized as being universally susceptible to beta-lactam antibiotics; however, there have been reports of reduced susceptibility to beta-lactams, including penicillin, in some countries. Resistance to second-line antibiotics, such as erythromycin and clindamycin, remains high amongst GBS, with several countries noting increased resistance rates in recent years. Moreover, resistance to other antibiotic classes, such as fluoroquinolones and aminoglycosides, also continues to rise. In instances where patients are allergic to penicillin and second-line antibiotics are ineffective, vancomycin is administered. While vancomycin, a last resort antibiotic, still remains largely effective, there have been two documented cases of vancomycin resistance in GBS. This review provides a comprehensive analysis of the prevalence of antibiotic resistance in GBS and outlines the specific resistance mechanisms identified in GBS isolates to date.

Invited review: Advances in nisin use for preservation of dairy products

Dairy product safety is a global public health issue that demands new approaches and technologies to control foodborne pathogenic microorganisms. Natural antimicrobial agents such as nisin can be added to control the growth of pathogens of concern in dairy foods, namely Listeria monocytogenes and Staphylococcus aureus. However, several factors affect the antimicrobial efficacy of nisin when directly added into the food matrix such as lack of stability at neutral pH, interaction with fat globules, casein, and divalent cations. To overcome these limitations, new and advanced strategies are discussed including nisin encapsulation technology, addition to active packaging, bioengineering, and combination with other antimicrobials. This review highlights advanced technologies with potential to expand and improve the use of nisin as a dairy preservative.

In vitro synergistic activity of erythromycin and nisin against clinical Group B Streptococcus isolates

AIMS

This study investigated the potential synergy between erythromycin and nisin against clinical Group B Streptococcus (GBS) strains.

METHODS AND RESULTS

The combination of erythromycin and nisin was examined for synergistic activity using checkerboard and time-kill assays against invasive and colonizing GBS strains. Additionally, the immunological effect of the antibiotic combination was investigated in vitro using human U937 cells and ELISA analysis. Checkerboard assays confirmed an additive effect when the antimicrobials were combined, while time-kill assays demonstrated a synergistic effect when antimicrobials were combined for invasive GBS isolates. Furthermore, a significantly lower TNF-alpha response (P < 0·05) was observed in U937 cells challenged with GBS when erythromycin and nisin were used in combination.

CONCLUSIONS

The results suggest that erythromycin and nisin can act synergistically to inhibit the growth of GBS.

SIGNIFICANCE AND IMPACT OF THE STUDY

Group B Streptococcus is the leading cause of invasive neonatal disease worldwide and is becoming increasingly more prevalent in adults. Resistance to some conventionally used antibiotics, such as erythromycin and clindamycin, continue to rise among GBS, indicating a need for alternative treatments. This study demonstrates the potential of an erythromycin-nisin combination for treatment of GBS infections and encourages further investigation of this treatment option.