Bacteriocins - exploring alternatives to antibiotics in mastitis treatment

Confronting the complexities of antimicrobial management for Staphyloccous aureus causing bovine mastitis: an innovative paradigm

Globally, Mastitis is a disease commonly affecting dairy cattle which leads to the use of antimicrobials. The majority of mastitis etiological agents are bacterial pathogens and Staphylococcus aureus is the predominant causative agent. Antimicrobial treatment is administered mainly via intramammary and intramuscular routes. Due to increasing antimicrobial resistance (AMR) often associated with antimicrobial misuse, the treatment of mastitis is becoming challenging with less alternative treatment options. Besides, biofilms formation and ability of mastitis-causing bacteria to enter and adhere within the cells of the mammary epithelium complicate the treatment of bovine mastitis. In this review article, we address the challenges in treating mastitis through conventional antibiotic treatment because of the rising AMR, biofilms formation, and the intracellular survival of bacteria. This review article describes different alternative treatments including phytochemical compounds, antimicrobial peptides (AMPs), phage therapy, and Graphene Nanomaterial-Based Therapy that can potentially be further developed to complement existing antimicrobial therapy and overcome the growing threat of AMR in etiologies of mastitis.

The Relationship between Mastitis and Antimicrobial Peptide S100A7 Expression in Dairy Goats

S100A7 is an inflammation-related protein and plays an essential role in host defenses, yet there is little research about the relationship between mastitis and S100A7 expression in dairy goats. Here, according to the clinical diagnosis of udders, SCC, and bacteriological culture (BC) of milk, 84 dairy goats were grouped into healthy goats (n = 25), subclinical mastitis goats (n = 36), and clinical mastitis goats (n = 23). The S100A7 concentration in subclinical mastitis goats was significantly upregulated than in healthy dairy goats (p = 0.0056) and had a limited change with clinical mastitis dairy goats (p = 0.8222). The relationship between log10 SCC and S100A7 concentration in milk was positive and R = 0.05249; the regression equation was Y = 0.1446 × X + 12.54. According to the three groups, the log10 SCC and S100A7 were analyzed using the receiver operating characteristics (ROC) curve; in subclinical mastitis goats, the area under the ROC curve (AUC) of log10 SCC was 0.9222 and p < 0.0001, and the AUC of S100A7 concentration was 0.7317 and p = 0.0022, respectively; in clinical mastitis goats, the AUC of log10 SCC was 0.9678 and p < 0.0001, and the AUC of S100A7 concentration was 0.5487 and p = 0.5634, respectively. In healthy goats, S100A7 was expressed weakly in the alveolus of the mammary gland of healthy goats while expressed densely in the collapsed alveolus of mastitis goats. Moreover, S100A7 expression increased significantly in mastitis goats than in healthy dairy goats. In this research, results showed the effects of mastitis on the S100A7 expression in the mammary gland and S100A7 concentration in milk and the limited relationship between SCC and mastitis, which provided a new insight into S100A7's role in the host defenses of dairy goats.

Antimicrobial Activity of Peptides Produced by Lactococcus lactis subsp. lactis on Swine Pathogens

Swine production is of great importance worldwide and has huge economic and commercial impact. Due to problems with bacterial infection, the use of antimicrobials has increased in the last decades, particularly in Latin America and Asia. This has led to concerns about antimicrobial resistance, which poses risks to human health and the environment. The use of probiotic organisms has been proposed as an alternative to this use, as these beneficial bacteria can produce antimicrobial peptides, such as bacteriocins, which allow the induction of inhibitory effects against pathogenic microorganisms. Among probiotics, some bacteria stand out with the inhibition of animal pathogens. The bacteriocin-like inhibitory substances (BLISs) of Lactococcus lactis subsp. lactis strain L2, present in its cell-free supernatant, were tested against pathogenic strains isolated from pig samples, such as Escherichia coli, Salmonella enterica, Streptococcus suis, Streptococcus dysgalactiae, Staphylococcus hyicus, and Enterococcus faecalis. Compounds secreted by L. lactis L2 have been shown to inhibit the growth of some pathogenic species, particularly Gram-positive bacteria, with S. suis being the most prominent. Antimicrobial peptides with a molecular size of 500-1160 Daltons were isolated from BLISs. The results highlight the potential of L. lactis BLISs and its peptides as natural antimicrobials for use in the food industry and to reduce the use of growth promoters in animal production.

Beneficial features of pediococcus: from starter cultures and inhibitory activities to probiotic benefits

Pediococci are lactic acid bacteria (LAB) which have been used for centuries in the production of traditional fermented foods. There fermentative abilities were explored by the modern food processing industry in use of pediococci as starter cultures, enabling the production of fermented foods with distinct characteristics. Furthermore, some pediococci strains can produce bacteriocins and other antimicrobial metabolites (AMM), such as pediocins, which are increasingly being explored as bio-preservatives in various food matrices. Due to their versatility and inhibitory spectrum, pediococci bacteriocins and AMM are being extensively researched not only in the food industry, but also in veterinary and human medicine. Some of the pediococci were evaluated as potential probiotics with different beneficial areas of application associated with human and other animals' health. The main taxonomic characteristics of pediococci species are presented here, as well as and their potential roles and applications as starter cultures, as bio-preservatives and as probiotic candidates.

Chemical Composition, Antimicrobial Activity, and Withdrawal Period of Essential Oil-Based Pharmaceutical Formulation in Bovine Mastitis Treatment

Due to the emergence of antibiotic-resistant bacteria, the risk it represents to public health, and the possible consequences for animal health and welfare, there is an increasing focus on reducing antimicrobial usage (AMU) in animal husbandry. Therefore, a great interest in developing alternatives to AMU in livestock production is present worldwide. Recently, essential oils (EOs) have gained great attention as promising possibilities for the replacement of antibiotics. The current study aimed to test the potential of using a novel EO-based pharmaceutical formulation (Phyto-Bomat) in bovine mastitis treatment. The antibacterial activity was performed using the microdilution technique. Lactating dairy cows were treated with 15 mL of Phyto-Bomat in the inflamed quarter for 5 consecutive days in order to analyze blood and milk samples for thymol and carvacrol residues using gas chromatography and mass spectrometry (GC-MS). Antimicrobial activity expressed as the minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) indicates that this formulation has the highest activity against Gram-positive strains. The dominant compounds in Phyto-Bomat were thymol and carvacrol, at 12.58 ± 1.23 mg/mL and 23.11 ± 2.31 mg/mL, respectively. The quantification of these two compounds in evaluated biological samples showed that 24 h after administration the concentration of thymol and carvacrol in milk samples was at the same level as before application. On the other hand, thymol and carvacrol were detectable in plasma samples even after 24 h post-treatment, with values ranging from 0.15-0.38 and 0.21-0.66 µg/mL, respectively. The tested formulation showed encouraging results of antibacterial activity against bovine mastitis pathogens, as well as the withdrawal period of dominant compounds, which implies that further testing regarding the bacteriological and clinical cure rates in clinical settings is needed.

Microcins reveal natural mechanisms of bacterial manipulation to inform therapeutic development

Microcins are an understudied and poorly characterized class of antimicrobial peptides. Despite the existence of only 15 examples, all identified from the Enterobacteriaceae, microcins display diversity in sequence, structure, target cell uptake, cytotoxic mechanism of action and target specificity. Collectively, these features describe some of the unique means nature has contrived for molecules to cross the 'impermeable' barrier of the Gram-negative bacterial outer membrane and inflict cytotoxic effects. Microcins appear to be widely dispersed among different species and in different environments, where they function in regulating microbial communities in diverse ways, including through competition. Growing evidence suggests that microcins may be adapted for therapeutic uses such as antimicrobial drugs, microbiome modulators or facilitators of peptide uptake into cells. Advancing our biological, ecological and biochemical understanding of the roles of microcins in bacterial interactions, and learning how to regulate and modify microcin activity, is essential to enable such therapeutic applications.

Susceptibility to Nisin, Bactofencin, Pediocin and Reuterin of Multidrug Resistant Staphylococcus aureus, Streptococcus dysgalactiae and Streptococcus uberis Causing Bovine Mastitis

Antibiotics are the most effective strategy to prevent and treat intramammary infections. However, their misuse has led to the dissemination of multidrug resistant bacteria (MDR) for both animals and humans. Efforts to develop new alternative strategies to control bacterial infections related to MDR are continuously on the rise. The objective of this study was to evaluate the antimicrobial activity of different bacteriocins and reuterin against MDR Staphylococcus and Streptococcus clinical isolates involved in bovine mastitis. A bacterial collection including S. aureus (n = 19), S. dysgalactiae (n = 17) and S. uberis (n = 19) was assembled for this study. Antibiotic resistance profiles were determined by the disk diffusion method. In addition, sensitivity to bacteriocins and reuterin was evaluated by determining minimum inhibitory concentrations (MIC). A total of 21 strains (37.5%) were MDR. MICs ranged from ≤1.0 μg/mL to ≥100 μg/mL for nisin and 2.0 to ≥250 μg/mL for bactofencin. Reuterin was active against all tested bacteria, and MICs vary between 70 and 560 μg/mL. Interestingly, 20 MDR strains were inhibited by bactofencin at a concentration of ≤250 μg/mL, while 14 were inhibited by nisin at an MIC of ≤100 μg/mL. Pediocin did not show an inhibitory effect.

Effect on Intermediary Metabolism and Digestive Parameters of the High Substitution of Fishmeal with Insect Meal in Sparus aurata Feed

Hermetia illucens and Tenebrio molitor were tested on account of their potential to replace fish protein in feed. Two levels of replacement for H. illucens, 30% and 50% (H30 and H50), and one for T. molitor, 50% (T50), as well as an additional diet with a modified fatty acid fraction (H50M), were investigated in relation to juvenile Sparus aurata growth indices, enzyme activities and gut microbiome. A T50 diet showed similar results to a control (C) diet, with no significant differences regarding morphological indices and minor differences for nutritional indices. Regarding the gut microbiome, H50M was the diet which showed the more similar prokaryotic community to C, which suggests that fatty acid fractions might influence the composition of the gut microbiome. Nevertheless, differences appeared to be related to a redistribution of dominant species, while changes in species affiliation were limited to minoritary species. The positive correlation between some of these minoritary species (Peptostreptococcus russellii, Streptococcus dysgalactiae and Weisella confusa) and several fish growth parameters might explain differences between control and insect diets. Deciphering such uncertainty and revealing the potential role these unusual species may play on fish performance should be addressed in future investigations.

Genomic and proteomic comparisons of bacteriocins in probiotic species Lactobacillus and Bifidobacterium and inhibitory ability of Escherichia coli MG 1655

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The genomes and proteomes of 12 Bifidobacterium and 46 Lactobacillus were reviewed and then compared for bacteriocin identification.

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NCBI-Genome, UniProt-Proteome, Bactibase, and BAGL4 databases, as well as BLASTP, and Clustal Omega can be used for bacteriocin mining.

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Lactobacillus species have more diversity and abundance of bacteriocin compared to Bifidobacterium species.

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Notably, L. sakei, L. plamtarum, L. reuteri, L. fermentum, and L. casei had the highest pathogen inhibition (E. coli MG 1655); respectively.

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A set of Lactobacillus bacteria including L. sakei, L. reuteri, L. fermentum, and L. casei can be proposed as a biosecure and safe solution to control gastrointestinal pathogens.

Bacteriocins are a large family of bacterial peptides or proteins, ribosomally synthesized with antimicrobial activity against other bacteria. We investigated and compared the genomes and proteomes of 12 Bifidobacterium and 46 Lactobacillus species for bacteriocins using NCBI-Genome, UniProt-Proteome, Bactibase, and BAGL4 databases. Selected Lactobacillus species were examined for bile salt resistance, acid and pH resistance, pepsin and trypsin enzyme resistance, and antibiotic resistance. Also, the antimicrobial activity of selected Lactobacillus species was evaluated against E. coli MG 1655. Results showed that Lactobacillus species have more diversity and abundance of bacteriocin compared to Bifidobacterium species. Notably, L. sakei, L. plamtarum, L. reuteri, L. fermentum, and L. casei had the highest pathogen inhibition; respectively. Therefore, a combination of these Lactobacillus species can be suggested as a biochemical and safe solution to control gastrointestinal pathogens and suitable alternatives to antibiotics and chemicals in food technology.

Advances in therapeutic and managemental approaches of bovine mastitis: a comprehensive review

Mastitis (intramammary inflammation) caused by infectious pathogens is still considered a devastating condition of dairy animals affecting animal welfare as well as economically incurring huge losses to the dairy industry by means of decreased production performance and increased culling rates. Bovine mastitis is the inflammation of the mammary glands/udder of bovines, caused by bacterial pathogens, in most cases. Routine diagnosis is based on clinical and subclinical forms of the disease. This underlines the significance of early and rapid identification/detection of etiological agents at the farm level, for which several diagnostic techniques have been developed. Therapeutic regimens such as antibiotics, immunotherapy, bacteriocins, bacteriophages, antimicrobial peptides, probiotics, stem cell therapy, native secretory factors, nutritional, dry cow and lactation therapy, genetic selection, herbs, and nanoparticle technology-based therapy have been evaluated for their efficacy in the treatment of mastitis. Even though several strategies have been developed over the years for the purpose of managing both clinical and subclinical forms of mastitis, all of them lacked the efficacy to eliminate the associated etiological agent when used as a monotherapy. Further, research has to be directed towards the development of new therapeutic agents/techniques that can both replace conventional techniques and also solve the problem of emerging antibiotic resistance. The objective of the present review is to describe the etiological agents, pathogenesis, and diagnosis in brief along with an extensive discussion on the advances in the treatment and management of mastitis, which would help safeguard the health of dairy animals.

Pre-formulation and delivery strategies for the development of bacteriocins as next generation antibiotics

Bacteriocins, a class of antimicrobial peptide produced by bacteria, may offer a potential alternative to traditional antibiotics, an important step towards mitigating the ever-increasing antimicrobial resistance crisis. They are active against a range of clinically relevant Gram-positive and Gram-negative bacteria. Bacteriocins have been discussed in the literature for over a century. Although they are used as preservatives in food, no medicine based on their antimicrobial activity exists on the market today. In order to formulate them into clinical antibiotics, pre-formulation studies on their biophysical and physicochemical properties that will influence their activity in vivo and their stability during manufacture must be elucidated. Thermal, pH and enzymatic stability of bacteriocins are commonly studied and regularly reported in the literature. Solubility, permeability and aggregation properties on the other hand are less frequently reported for many bacteriocins, which may contribute to their poor clinical progression. Promising cytotoxicity studies report that bacteriocins exhibit few cytotoxic effects on a variety of mammalian cell lines, at active concentrations. This review highlights the lack of quantitative data and in many cases even qualitative data, on bacteriocins' solubility, stability, aggregation, permeability and cytotoxicity. The formulation strategies that have been explored to date, proposed routes of administration, trends in in vitro/in vivo behaviour and efforts in clinical development are discussed. The future promise of bacteriocins as a new generation of antibiotics may require tailored local delivery strategies to fulfil their potential as a force to combat antimicrobial-resistant bacterial infections.

Bovine mastitis prevention and control in the post-antibiotic era

Mastitis is the most important disease in the dairy industry. Antibiotics are considered to be the first choice in the treatment of the disease. However, the problem of antibiotic residue and antimicrobial resistance, in addition to the impact of antibiotic abuse on public health, leads to many restrictions on uncontrolled antibiotic therapy in the dairy sector worldwide. Researchers have investigated novel therapeutic approaches to replace the use of antibiotics in mastitis control. These efforts, supported by the revolutionary development of nanotechnology, stem cell assays, molecular biological tools, and genomics, enabled the development of new approaches for mastitis-treatment and control. The present review discusses recent concepts to control mastitis such as breeding of mastitis-resistant dairy cows, the development of novel diagnostic and therapeutic tools, the application of communication technology as an educational and epidemiological tool, application of modern mastitis vaccines, cow drying protocols, teat disinfection, housing, and nutrition. These include the application of nanotechnology, stem cell technology, photodynamic and laser therapy or the use of traditional herbal medical plants, nutraceuticals, antibacterial peptides, bacteriocins, antibodies therapy, bacteriophages, phage lysins, and probiotics as alternatives to antibiotics.

Bio-Engineered Nisin with Increased Anti-Staphylococcus and Selectively Reduced Anti-Lactococcus Activity for Treatment of Bovine Mastitis

Bovine mastitis is a significant economic burden for dairy enterprises, responsible for premature culling, prophylactic and therapeutic antibiotic use, reduced milk production and the withholding (and thus wastage) of milk. There is a desire to identify novel antimicrobials that are expressly directed to veterinary applications, do not require a lengthy milk withholding period and that will not have a negative impact on the growth of lactic acid bacteria involved in downstream dairy fermentations. Nisin is the prototypical lantibiotic, a family of highly modified antimicrobial peptides that exhibit potent antimicrobial activity against many Gram-positive microbes, including human and animal pathogens including species of Staphylococcus and Streptococcus. Although not yet utilized in the area of human medicine, nisin is currently applied as the active agent in products designed to prevent bovine mastitis. Over the last decade, we have harnessed bioengineering strategies to boost the specific activity and target spectrum of nisin against several problematic microorganisms. Here, we screen a large bank of engineered nisin derivatives to identify novel derivatives that exhibit improved specific activity against a selection of staphylococci, including mastitis-associated strains, but have unchanged or reduced activity against dairy lactococci. Three such peptides were identified; nisin A M17Q, nisin A T2L and nisin A HTK.

Old problems and new solutions: antibiotic alternatives in food animal production

The antimicrobial resistance crisis is a Global Health challenge that impacts humans, animals, and the environment alike. In response to increased demands for animal protein and by-products, there has been a substantial increase in the use of antimicrobial agents in the animal industry. Indeed, they are extensively used to prevent, control, and (or) treat disease in animals. In addition to infection control, in-feed supplementation with antimicrobials became common practice for growth promotion of livestock. Unfortunately, the global overuse of antimicrobials has contributed to the emergence and spread of resistance. As such, many countries have implemented policies and approaches to eliminate the use of antimicrobials as growth promoters in food animals, which necessitates the need for alternate and One Health strategies to maintain animal health and welfare. This review summarizes the antimicrobial resistance crisis from Global Health and One Health perspectives. In addition, we outline examples of potential alternate strategies to circumvent antimicrobial use in animal husbandry practices, including antivirulence agents, bacteriophages, and nutritional measures to control bacterial pathogens. Overall, these alternate strategies require further research and development efforts, including assessment of efficacy and the associated development, manufacturing, and labor costs.

Environmental Impact of Sulfate-Reducing Bacteria, Their Role in Intestinal Bowel Diseases, and Possible Control by Bacteriophages

Sulfate-reducing bacteria (SRB) represent a group of prokaryotic microorganisms that are widely spread in the anoxic environment (seabed, riverbed and lakebed sediments, mud, intestinal tract of humans and animals, metal surfaces). SRB species also have an impact on processes occurring in the intestinal tract of humans and animals, including the connections between their presence and inflammatory bowel disease (IBD). Since these SRB can develop antimicrobial resistance toward the drugs, including antibiotics and antimicrobial agents, bacteriophages could represent an additional potential effective treatment. The main objectives of the review were as follows: (a) to review SRB (both from intestinal and environmental sources) regarding their role in intestinal diseases as well as their influence in environmental processes; and (b) to review, according to literature data, the influence of bacteriophages on SRB and their possible applications. Since SRB can have a significant adverse influence on industry as well as on humans and animals health, phage treatment of SRB can be seen as a possible effective method of SRB inhibition. However, there are relatively few studies concerning the influence of phages on SRB strains. Siphoviridae and Myoviridae families represent the main sulfide-producing bacteria phages. The most recent studies induced, by UV light, bacteriophages from Desulfovibrio vulgaris NCIMB 8303 and Desulfovibrio desulfuricans ATCC 13541. Notwithstanding costly and medically significant negative impacts of phages on SRB, they have been the subject of relatively few studies. The current search for alternatives to chemical biocides and antibiotics has led to the renewed interest in phages as antibacterial biocontrol and therapeutic agents, including their use against SRB. Hence, phages might represent a promising treatment against SRB in the future.

Application of bacteriocins in food preservation and infectious disease treatment for humans and livestock: a review

Infectious diseases caused by bacteria that can be transmitted via food, livestock and humans are always a concern to the public, as majority of them may cause severe illnesses and death. Antibacterial agents have been investigated for the treatment of bacterial infections. Antibiotics are the most successful antibacterial agents that have been used widely for decades to ease human pain caused by bacterial infections. Nevertheless, the emergence of antibiotic-resistant bacteria has raised awareness amongst public about the downside of using antibiotics. The threat of antibiotic resistance to global health, food security and development has been emphasized by the World Health Organization (WHO), and research studies have been focused on alternative antimicrobial agents. Bacteriocin, a natural antimicrobial peptide, has been chosen to replace antibiotics for its application in food preservation and infectious disease treatment for livestock and humans, as it is less toxic.

Killing or inhibition actions of (a) antibiotics and (b) bacteriocin on gut microbiota.

Tackling Multidrug Resistance in Streptococci - From Novel Biotherapeutic Strategies to Nanomedicines

The pyogenic streptococci group includes pathogenic species for humans and other animals and has been associated with enduring morbidity and high mortality. The main reason for the treatment failure of streptococcal infections is the increased resistance to antibiotics. In recent years, infectious diseases caused by pyogenic streptococci resistant to multiple antibiotics have been raising with a significant impact to public health and veterinary industry. The rise of antibiotic-resistant streptococci has been associated to diverse mechanisms, such as efflux pumps and modifications of the antimicrobial target. Among streptococci, antibiotic resistance emerges from previously sensitive populations as result of horizontal gene transfer or chromosomal point mutations due to excessive use of antimicrobials. Streptococci strains are also recognized as biofilm producers. The increased resistance of biofilms to antibiotics among streptococci promote persistent infection, which comprise circa 80% of microbial infections in humans. Therefore, to overcome drug resistance, new strategies, including new antibacterial and antibiofilm agents, have been studied. Interestingly, the use of systems based on nanoparticles have been applied to tackle infection and reduce the emergence of drug resistance. Herein, we present a synopsis of mechanisms associated to drug resistance in (pyogenic) streptococci and discuss some innovative strategies as alternative to conventional antibiotics, such as bacteriocins, bacteriophage, and phage lysins, and metal nanoparticles. We shall provide focused discussion on the advantages and limitations of agents considering application, efficacy and safety in the context of impact to the host and evolution of bacterial resistance.

Occurrence of resistance to antibiotics therapy in coagulase-positive and coagulase-negative Staphylococci isolated from sheep´s milk in holding in Slovakia

The occurrence of bacteria Staphylococcus spp. was examined in a total of 3466 individuals and in 12 pool milk samples from 2017 to 2019. The experiment was carried out in two herds of the breed of sheep, Improved Valaska, in the Slovakia region. Eleven species of the genus Staphylococcus spp. (n = 431) were isolated and taxonomically identified. From the coagulase-positive staphylococci (CPS), S. aureus was isolated during the reporting period, however, most often in the third year (50). The incidence of S. intermedius and S. hyicus were irregular. The incidence of S. schleiferi was highest at the end of the follow-up duration. From the coagulase-negative staphylococci (CNS) (n = 158), were isolated S. epidermidis present in 20.4% (88) and S. chromogenes 11.4 % (49), S. caprae, S. xylosus, and other species rarely occurred. S. aureus (n = 133) showed maximum resistance to erythromycin 12.0%, novobiocin 10.5%, and neomycin 9.0%. The incidence of intermedial susceptibility was observed predominantly to a penicillin (16 strains), novobiocin (11 strains), erythromycin (14 strains), oxacillin, and cloxacillin (12 strains), neomycin (11 strains), and lincomycin (9 strains). Observantly, S. schleiferi (n = 101) showed the highest resistance to novobiocin (5.9%) and erythromycin (5.0%), however, a high incidence of intermediate susceptibility to erythromycin (9), amoxicillin, novobiocin (8), ampicillin, lincomycin (7), penicillin, methicilin and cefoperazone (5 strains) can be identified as adverse. The incidence of resistant and intermediate sensitive test strains S. aureus and S. schleiferi, especially for erythromycin, novobiocin, and neomycin, which are often used to treat udder inflammation in sheep, is relatively adverse.

Microcin J25 Exhibits Inhibitory Activity Against Salmonella Newport in Continuous Fermentation Model Mimicking Swine Colonic Conditions

Microcin J25 (MccJ25), a 21-amino acid bacteriocin produced by Escherichia coli (E. coli), is a potent inhibitor of Enterobacteriaceae, including pathogenic E. coli, Salmonella, and Shigella. Its lasso structure makes it highly stable and therefore of interest as a possible antimicrobial agent in foods or as an alternative to antibiotics in livestock production. In the present study, we aimed to evaluate in vitro the inhibitory activity of MccJ25 against Salmonella enterica subsp. enterica serovar Newport ATCC 6962 (Salmonella Newport) used as a model pathogen under conditions simulating those of the swine proximal colon. The growth inhibition activity of MccJ25 against Salmonella Newport was examined in lysogeny broth (LB) and in modified MacFarlane medium that allows miming the swine colonic conditions. The MccJ25 activity was further determined using the Polyfermentor intestinal model (PolyFermS), an in vitro continuous fermentation model that permits deciphering the activity of any antimicrobial molecule in real colon fermentation conditions using selected microbiota. It was set up here to simulate the porcine proximal colon fermentation. In these conditions, the inhibition activity of MccJ25 was compared to those of two antimicrobial agents, reuterin and rifampicin. The minimal inhibitory concentration (MIC) of MccJ25 was determined at 0.03 μM in LB medium, compared to 1,079 and 38 μM for reuterin and rifampicin, respectively, showing a significantly higher potency of MccJ25. Total inhibition of Salmonella Newport was observed in LB medium over 24 h of incubation at concentrations starting from the MIC. In the PolyFermS model, MccJ25 induced a significantly stronger inhibition of Salmonella Newport growth than reuterin or rifampicin. A specific and sensitive LC-MS method allowed to detect and quantify MccJ25 in the PolyFermS fermentation system, showing that MccJ25 remains stable and active against Salmonella in conditions mimicking those found in swine colon. This study paves the way for further exploring the potential of this bacteriocin as an alternative to antibiotics in livestock.

Staphylococcus aureus persistence properties associated with bovine mastitis and alternative therapeutic modalities

Staphylococcus aureus is an important agent of contagious bovine intramammary infections in dairy cattle. Its ability to persist inside the udder is based on the presence of important mechanisms such as its ability to form biofilms, polysaccharide capsules small colony variants, and their ability to invade professional and nonprofessional cells, which will protect S. aureus from the innate and adaptive immune response of the cow, and from antibiotics that are no longer considered to be sufficient against S. aureus bovine mastitis. In this review, we present the recent research outlining S. aureus persistence properties inside the mammary gland, including its regulation mechanisms, and we highlight alternative therapeutic strategies that were tested against S. aureus isolated from bovine mastitis such as the use of probiotic bacteria, bacteriocins and bacteriophages. Overall, the persistence of S. aureus inside the mammary gland remains a pressing veterinary problem. A thorough understanding of staphylococcal persistence mechanisms will elucidate novel ways that can help in the identification of novel treatments.

Antimicrobial resistance patterns and biofilm formation of coagulase-negative Staphylococcus species isolated from subclinical mastitis cow milk samples submitted to the Onderstepoort Milk Laboratory

Background

Increased prevalence of antimicrobial resistance, treatment failure, and financial losses have been reported in dairy cows with coagulase-negative Staphylococcus (CoNS) clinical mastitis, however, studies on CoNS infections are limited in South Africa. Therefore, the objectives of this study were to investigate the antimicrobial resistance patterns and biofilm formation in CoNS isolated from cow milk samples submitted to the Onderstepoort Milk Laboratory.

Results

A total of 142 confirmed CoNS isolates were used for this study. Biofilm formation was identified in 18% of CoNS tested. Staphylococcus chromogenes (11%) had the highest proportion of biofilm formation followed by S. haemolyticus (4.0%), S. epidermidis, S. hominis, S. xylosus, and S. simulans with 1% respectively. Ninety percent (90%) of CoNS were resistant to at least one antimicrobial (AMR) and 51% were multidrug-resistant (MDR). Resistance among CoNS was the highest to ampicillin (90%) and penicillin (89%), few isolates resistant to cefoxitin and vancomycin, 9% respectively. Similarly, MDR-S. haemolyticus (44%), MDR-S. epidermidis (65%), and MDR-S. chromogenes (52%) were mainly resistant to penicillins. The most common resistance patterns observed were resistance to penicillin-ampicillin (16%) and penicillin-ampicillin-erythromycin (10%). Only 42% of biofilm positive CoNS were MDR.

Conclusion

The majority of CoNS in this study were resistance to penicillins. In addition, most isolates were β-lactam resistant and MDR. Biofilm formation among the CoNS in this study was uncommon and there was no significant difference in the proportion of MDR-CoNS based on the ability to form a biofilm.

Alternative Sigma Factor B in Bovine Mastitis-Causing Staphylococcus aureus: Characterization of Its Role in Biofilm Formation, Resistance to Hydrogen Peroxide Stress, Regulon Members

This study examines treatments of the bacterial pathogen Staphylococcus aureus, namely, in the context of its being a major cause of subclinical bovine mastitis. Such infections caused by S. aureus among dairy cows are difficult to detect and can easily become chronic, leading to reduced productivity and large losses for dairy manufacturers. In this study, the role of alternative sigma factor B (σ^B), which has been shown to be a global regulator for S. aureus infections, was explored in a mastitis-causing S. aureus strain, RF122. For comparison with the wild-type strain, a sigB null (ΔsigB) mutant was constructed and analyzed for its phenotypes and transcriptome. Our study found that σ^B is essential for biofilm formation as the ΔsigB mutant strain produced significantly less biofilm than did the wild-type strain at 48 h. σ^B is involved in response to H₂O₂ stress. However, σ^B plays a minor or no role in resistance to antiseptics (e.g., povidone-iodine and chlorhexidine), resistance to tested antibiotics, hemolysin activity, and invasion ability. RNA sequencing identified 225 σ^B-dependent genes, of which 171 are positively regulated and 54 are negatively regulated. The identified genes are involved in stress response, pathogenesis, and metabolic mechanisms. Quantitative TaqMan RT-PCR was performed to verify the RNA sequencing results; i.e., σ^B is a positive regulator for asp23, sarA, katA, yabJ, sodA, SAB2006c, and nrdD expressions. In the RF122 strain, σ^B plays a role in biofilm formation, general stress response (e.g., H₂O₂), and regulation of virulence factors and virulence-associated genes.

Screening of bacteriocin associated genes of Streptococcus uberis strains

A wide variety of contagious and environmental bacteria can cause bovine mastitis worldwide. Antibiotic therapy is currently used for the treatment of the disease, although its intensive use leads to the emergence of resistant strains. Bacteriocins arise as potential antibacterial option for mastitis treatment. The aim of this work was to analyze bacteriocin associated genes as Streptococcus uberis ubericin A (ubaA), ubericin A immunity protein (ubaI), uberolysin A (ublA), Lantibiotic nisin-U (nsuA and nsuB) in 68 S uberis strains. Furthermore, the ability of the strains to inhibit important mastitis pathogens was assayed. Results showed that genes were present in combination and all the strains carried at least one gene. Seven bacteriocion associated gene patterns were identified. S. uberis strains were able to inhibit different mastitis pathogens and the greatest inhibition was observed in CNS strains. The results obtained provide new insights on antibacterial activity produced by S. uberis strains against different mastitis pathogens and could contribute to the development of strategies to treat intramammary infections.

Prevalence, Risk Factors, and Antibiogram of Bacteria Isolated from Milk of Goats with Subclinical Mastitis in Thika East Subcounty, Kenya

A cross-sectional study was carried out to determine the prevalence and risk factors of subclinical mastitis in dairy goats in Thika East Subcounty, Kenya. Further the bacterial pathogens and their antibiogram were investigated. Farm level data on risk factors were obtained from 41 farmers using questionnaires. Milk was obtained from 110 lactating dairy goats and tested for submastitis using California Mastitis Test (CMT). The prevalence of subclinical mastitis at goat level was estimated to be at 50.9% using CMT, out of which 86.5% yielded bacteria on culture. The significant risk factors associated with the occurrence of subclinical mastitis were cleaning schedule (p=0.022, OD=1.047) and parity of the goat (p=0048, OD=1.37). Higher prevalence of subclinical mastitis was observed for goats residing in houses cleaned at least once a fortnight. Does in the first parity were least affected. 169 bacterial isolates were obtained from culture, of which 52 isolates from major classes of isolated bacteria were tested for antibiotic sensitivity to six antibiotics. Fourteen different bacteria were isolated and identified from the milk samples. Coagulase-negative Staphylococci (20.7%), Serratia spp. (19.5%), Citrobacter spp. (16%), Klebsiella spp. (11%), Staphylococcus aureus (10.7%), Enterobacter spp. (6.5%), Escherichia coli (5.9%), Proteus spp. (3%), Corynebacterium spp. (1.8%), Morganella spp. (1.8%), Streptococcus spp. (1.2%), Providencia spp. (0.6%), Micrococcus spp. (0.6%), and Staphylococcus intermedius (0.6%) were isolated and identified from the samples. All the isolates were resistant to Penicillin G, while 98% of the isolates were sensitive to Streptomycin. In conclusion, the study showed that a large proportion of goats were affected by subclinical mastitis, with the main bacteria being Staphylococci spp. and coliforms, and that most of the tested antibiotics can be used in the treatment of mastitis. Farmers need to be trained on improved control of mastitis through adoption of good dairy husbandry and milking practices.

Bacteriocins: perspective for the development of novel anticancer drugs

Antimicrobial peptides (AMPs) from prokaryotic source also known as bacteriocins are ribosomally synthesized by bacteria belonging to different eubacterial taxonomic branches. Most of these AMPs are low molecular weight cationic membrane active peptides that disrupt membrane by forming pores in target cell membranes resulting in cell death. While these peptides known to exhibit broad-spectrum antimicrobial activity, including antibacterial and antifungal, they displayed minimal cytotoxicity to the host cells. Their antimicrobial efficacy has been demonstrated in vivo using diverse animal infection models. Therefore, we have discussed some of the promising peptides for their ability towards potential therapeutic applications. Further, some of these bacteriocins have also been reported to exhibit significant biological activity against various types of cancer cells in different experimental studies. In fact, differential cytotoxicity towards cancer cells as compared to normal cells by certain bacteriocins directs for a much focused research to utilize these compounds as novel therapeutic agents. In this review, bacteriocins that demonstrated antitumor activity against diverse cancer cell lines have been discussed emphasizing their biochemical features, selectivity against extra targets and molecular mechanisms of action.

Integration of machine learning and meta-analysis identifies the transcriptomic bio-signature of mastitis disease in cattle

Gram-negative bacteria such as Escherichia coli (E. coli) are assumed to be among the main agents that cause severe mastitis disease with clinical signs in dairy cattle. Rapid detection of this disease is so important in order to prevent transmission to other cows and helps to reduce inappropriate use of antibiotics. With the rapid progress in high-throughput technologies, and accumulation of various kinds of '-omics' data in public repositories, there is an opportunity to retrieve, integrate, and reanalyze these resources to improve the diagnosis and treatment of different diseases and to provide mechanistic insights into host resistance in an efficient way. Meta-analysis is a relatively inexpensive option with good potential to increase the statistical power and generalizability of single-study analysis. In the current meta-analysis research, six microarray-based studies that investigate the transcriptome profile of mammary gland tissue after induced mastitis by E. coli infection were used. This meta-analysis not only reinforced the findings in individual studies, but also several novel terms including responses to hypoxia, response to drug, anti-apoptosis and positive regulation of transcription from RNA polymerase II promoter enriched by up-regulated genes. Finally, in order to identify the small sets of genes that are sufficiently informative in E. coli mastitis, the differentially expressed gene introduced by meta-analysis were prioritized by using ten different attribute weighting algorithms. Twelve meta-genes were detected by the majority of attribute weighting algorithms (with weight above 0.7) as most informative genes including CXCL8 (IL8), NFKBIZ, HP, ZC3H12A, PDE4B, CASP4, CXCL2, CCL20, GRO1(CXCL1), CFB, S100A9, and S100A8. Interestingly, the results have been demonstrated that all of these genes are the key genes in the immune response, inflammation or mastitis. The Decision tree models efficiently discovered the best combination of the meta-genes as bio-signature and confirmed that some of the top-ranked genes -ZC3H12A, CXCL2, GRO, CFB- as biomarkers for E. coli mastitis (with the accuracy 83% in average). This research properly indicated that by combination of two novel data mining tools, meta-analysis and machine learning, increased power to detect most informative genes that can help to improve the diagnosis and treatment strategies for E. coli associated with mastitis in cattle.

Biofilm production and other virulence factors in Streptococcus spp. isolated from clinical cases of bovine mastitis in Poland

Background

Mastitis is a common disease in dairy cattle throughout the world and causes considerable economic losses each year. An important aetiological agent of this disease is bacteria of the genus Streptococcus; hence, exploring the mechanisms of virulence in these bacteria is an extremely important step for the development of effective prevention programmes. The purpose of our study was to determine the ability to produce biofilm and the occurrence of selected invasiveness factors among bacteria of the genus Streptococcus isolated from cattle with the clinical form of mastitis in northeastern Poland.

Results

Most of the isolates analysed demonstrated an ability to produce biofilm (over 70%). Virulence genes were searched for in the three most common streptococci in our experiment: S. agalactiae, S. uberis and S. dysgalactiae. For S. agalactiae, only four genes were confirmed: rib (33%), cylE (78%), bca (37%), and cfb (100%). The genes pavA, scpB, bac and lmb were not present in any of the tested strains. The dominant serotypes of the species were Ia (n = 8) and II (n = 8), in addition to some strains that were not classified in any of the groups (n = 6). Out of the eight selected genes for S. uberis (sua, pauA/skc, gapC, cfu, lbp, hasA, hasB, hasC), only one was not found (lbp). Finally, two genes were chosen for S. dysgalactiae (eno and napr), and their presence was confirmed in 76% and 86% of the strains, respectively.

Conclusions

The experiment showed that strains of Streptococcus spp. isolated from dairy cattle with clinical cases of mastitis in the northeastern part of Poland possess several invasiveness factors that can substantially affect the course of the disease, and this should be considered when developing targeted prevention programmes.

Phenotypic and genotypic antimicrobial susceptibility pattern of Streptococcus spp. isolated from cases of clinical mastitis in dairy cattle in Poland

Mastitis of dairy cattle is one of the most frequently diagnosed diseases worldwide. The main etiological agents of mastitis are bacteria of the genus Streptococcus spp., in which several antibiotic resistance mechanisms have been identified. However, detailed studies addressing this problem have not been conducted in northeastern Poland. Therefore, the aim of our study was to analyze, on phenotypic and genotypic levels, the antibiotic resistance pattern of Streptococcus spp. isolated from clinical cases of mastitis from dairy cattle in this region of Poland. The research was conducted using 135 strains of Streptococcus (Streptococcus uberis, n = 53; Streptococcus dysgalactiae, n = 41; Streptococcus agalactiae, n = 27; other streptococci, n = 14). The investigation of the antimicrobial susceptibility to 8 active substances applied in therapy in the analyzed region, as well as a selected bacteriocin (nisin), was performed using the minimum inhibitory concentration method. The presence of selected resistance genes (n = 14) was determined via PCR. We also investigated the correlation between the presence of resistance genes and the antimicrobial susceptibility of the examined strains in vitro. The highest observed resistance of Streptococcus spp. was toward gentamicin, kanamycin, and tetracycline, whereas the highest susceptibility occurred toward penicillin, enrofloxacin, and marbofloxacin. Additionally, the tested bacteriocin showed high efficacy. The presence of 13 analyzed resistance genes was observed in the examined strains [gene mef(A) was not detected]. In most strains, at least one resistance gene, mainly responsible for resistance to tetracyclines [tet(M), tet(K), tet(L)], was observed. However, a relationship between the presence of a given resistance gene and antimicrobial susceptibility on the phenotypic level was not always observed.

Isolation, Biochemical and Molecular Identification, and In-Vitro Antimicrobial Resistance Patterns of Bacteria Isolated from Bubaline Subclinical Mastitis in South India

Buffaloes are the second largest source of milk. Mastitis is a major impediment for milk production, but not much information is available about bubaline mastitis, especially subclinical mastitis. The aim of this study was to (a) investigate the application of various tests for the diagnosis of bubaline subclinical mastitis, (b) identify the major bacteria associated with it, and (c) evaluate the antibiotic resistance pattern of the bacteria. To this end, 190 quarter milk samples were collected from 57 domesticated dairy buffaloes from organized (64 samples) and unorganized (126 samples) sectors. Of these, 48.4%, 40.0%, 45.8%, 61.1%, and 61.6% were positive for subclinical mastitis by somatic cell count, electrical conductivity, California mastitis test, bromothymol blue test, and N-acetyl glucosaminidase test, respectively. As compared to the gold standard of somatic cell count, California mastitis test performed the best. However, a combination of the two methods was found to be the best option. Microbiological evaluation, both by biochemical methods as well as by monoplex and multiplex polymerase chain reaction, revealed that coagulase-negative staphylococci were the most predominant (64.8%) bacteria, followed by streptococci (18.1%), Escherichia coli (9.8%) and Staphylococcus aureus (7.3%). Most of the pathogens were resistant to multiple antibiotics, especially to β-lactam antibiotics. We propose that California mastitis test be combined with somatic cell count for diagnosis of subclinical mastitis in domestic dairy buffaloes. Further, our results reveal high resistance of the associated bacteria to the β-lactam class of antibiotics, and a possible major role of coagulase-negative staphylococci in causing the disease in India.

Physicochemical factors differentially affect the biomass and bacteriocin production by bovine Enterococcus mundtii CRL1656

Bovine Enterococcus mundtii CRL1656 (Centro de Referencia para Lactobacilos Culture Collection) produces an anti-Listeria and anti-Streptococcus dysgalactiae bacteriocin identified as mundticin CRL1656. The strain and its bacteriocin are candidates to be included in a beneficial product to prevent bovine mastitis as an alternative to antimicrobial agents. To optimize the production of biomass and mundticin CRL1656 by E. mundtii CRL1656, a complete 3 × 2(4) factorial design was applied. The effect of culture medium, initial pH, inoculum size, incubation temperature, and agitation conditions on biomass and bacteriocin production was evaluated simultaneously. Growth parameters were determined using the modified Gompertz model. A nonlinear model was used to estimate the effects of the variables on growth parameters. Bacteriocin production was analyzed using a linear mixed model. Optimal biomass and mundticin CRL1656 production by E. mundtii CRL1656 were obtained in different conditions. Maximal growth was recorded in autolyzed yeast, peptone, tryptone, Tween 80, and glucose or M17 broths, pH 6.5, 5.0% inoculum, 30 °C, with agitation. However, bacteriocin titers were higher in autolyzed yeast, peptone, tryptone, Tween 80, and glucose or de Man-Rogosa-Sharpe (MRS) broths, pH 6.5, 30°C, both with or without agitation. Knowledge of the optimum conditions for growth and bacteriocin production of E. mundtii CRL1656 will allow the obtainment of high levels of biomass and mundticin CRL1656 as bioingredients of potential products to prevent bovine mastitis.

Anti-infective properties of bacteriocins: an update

Bacteriocin production is a widespread phenomenon among bacteria. Bacteriocins hold great promise for the treatment of diseases caused by pathogenic bacteria and could be used in the future as alternatives to existing antibiotics. The anti-infective potential of bacteriocins for inhibiting pathogens has been shown in various food matrices including cheese, meat, and vegetables. However, their inhibition of pathogens in vivo remains unclear and needs more investigation, due mainly to difficulties associated with demonstrating their health benefits. Many bacteriocins produced by established or potential probiotic organisms have been evaluated as potential therapeutic agents and interesting findings have been documented in vitro as well as in a few in vivo studies. Some recent in vivo studies point to the efficacy of bacteriocin-based treatments of human and animal infections. While further investigation remains necessary before the possibilities for bacteriocins in clinical practice can be described more fully, this review provides an overview of their potential applications to human and veterinary health.