Metabolites of bovine-associated non-aureus staphylococci influence expression of Staphylococcus aureus agr-related genes in vitro

Non-aureus staphylococci and mammaliicocci (NASM): their role in bovine mastitis and One Health

Non-aureus staphylococci (NAS) are gaining importance in mastitis and public health, and some NAS have been reclassified as mammaliicocci (NASM). Bovine milk production has a major influence on the world economy, being an essential source of income for small, medium and large producers, and bovine mastitis caused by NASM can cause an economic impact. Mastitis generates financial losses due to reduced revenue, increased veterinary costs and expenses associated with animal slaughter. However, it is also a public health issue involving animal health and welfare, human health and the ecosystem. Furthermore, it is an increasingly common infection caused by NASM, including antimicrobial-resistant strains. Despite all these adverse effects that NASM can cause, some studies also point to its protective role against mastitis. Therefore, this review article addresses the negative and positive aspects that NASM can cause in bovine mastitis, the virulence of the disease and resistance factors that make it difficult to treat and, through the One Health approach, presents a holistic view of how mastitis caused by NASM can affect both animal and human health at one and the same time.

Phenotypic and genotypic assessment of iron acquisition in diverse bovine-associated non-aureus staphylococcal strains

Although the role of iron in bacterial infections has been well described for Staphylococcus (S.) aureus, iron acquisition in (bovine-associated) non-aureus staphylococci and mammaliicocci (NASM) remains insufficiently mapped. This study aimed at elucidating differences between four diverse bovine NASM field strains from two species, namely S. chromogenes and S. equorum, in regards to iron uptake (with ferritin and lactoferrin as an iron source) and siderophore production (staphyloferrin A and staphyloferrin B) by investigating the relationship between the genetic basis of iron acquisition through whole genome sequencing (WGS) with their observed phenotypic behavior. The four field strains were isolated in a previous study from composite cow milk (CCM) and bulk tank milk (BTM) in a Flemish dairy herd. Additionally, two well-studied S. chromogenes isolates originating from a persistent intramammary infection and from a teat apex were included for comparative purpose in all assays. Significant differences between species and strains were identified. In our phenotypical iron acquisition assay, while lactoferrin had no effect on growth recovery for all strains in iron deficient media, we found that ferritin served as an effective source for growth recovery in iron-deficient media for S. chromogenes CCM and BTM strains. This finding was further corroborated by analyzing potential ferritin iron acquisition genes using whole-genome sequencing data, which showed that all S. chromogenes strains contained hits for all three proposed ferritin reductive pathway genes. Furthermore, a qualitative assay indicated siderophore production by all strains, except for S. equorum. This lack of siderophore production in S. equorum was supported by a quantitative assay, which revealed significantly lower or negligible siderophore amounts compared to S. aureus and S. chromogenes. The WGS analysis showed that all tested strains, except for S. equorum, possessed complete staphyloferrin A (SA)-synthesis and export operons, which likely explains the phenotypic absence of siderophore production in S. equorum strains. While analyzing the staphyloferrin A and staphyloferrin B operon landscapes for all strains, we noticed some differences in the proteins responsible for iron acquisition between different species. However, within strains of the same species, the siderophore-related proteins remained conserved. Our findings contribute valuable insights into the genetic elements associated with bovine NASM pathogenesis.

Comparison of non-aureus staphylococcal and mammaliicoccal species found in both composite milk and bulk-tank milk samples of dairy cows collected in tandem

Non-aureus staphylococci and the closely related mammaliicoccal species (NASM) are the most common causes of bovine subclinical mastitis on modern dairy farms and are highly prevalent in bulk-tank milk. The purpose of this study was to determine the distribution of NASM in both composite cow milk (CCM) and bulk-tank milk (BTM) samples collected in tandem in commercial Flemish dairy herds and to estimate the origin of the different (subgroups of) NASM species present in BTM by applying strain typing (random amplification of polymorphic DNA or random amplified DNA [RAPD]). A single cross-sectional sampling was performed over 5 herds that volunteered to participate in the study. Composite cow milk samples (n = 356) were collected from all lactating cows (except those with clinical mastitis) during a milking in tandem with 6 BTM samples per herd sequentially collected immediately post that milking (n = 30). In total, 421 and 80 NASM isolates were recovered and identified by MALDI-TOF mass spectrometry from the CCM and BTM samples, respectively and a total of 21 and 12 different NASM species were identified from CCM and BTM samples, respectively. Staphylococcus cohnii was the most prevalent NASM species found in BTM followed by Staphylococcus haemolyticus, Staphylococcus epidermidis, Mammaliicoccus lentus, and Staphylococcus equorum, whereas from CCM samples the most common species were S. hemolyticus, S. cohnii, S. equorum, S. epidermidis, and Staphylococcus chromogenes. The prevalent NASM species in both CCM and BTM samples was distinct for each herd, corroborating other studies observing a herd-specific NASM microbiota. Random amplified DNA analysis was performed on 9 NASM species (S. chromogenes, S. epidermidis, S. haemolyticus, S. equorum, Mammaliicoccus sciuri, Staphylococcus xylosus, S. cohnii, Staphylococcus debuckii, and M. lentus) because these species were isolated from both sample types in a herd. The same RAPD types were found in both sample types for all NASM species selected for strain typing in varying degrees. When assessing the distribution of NASM species, differences within NASM species should be examined meaning a closer look should be taken at the strain level rather than at the species level only.

Metabolites of non-aureus staphylococci affect the ability of Staphylococcus aureus to adhere to and internalize into bovine mammary epithelial cells

This study investigated whether cell-free supernatants (SN) from four bovine non-aureus staphylococcal (NAS) isolates prevent Staphylococcus aureus adhesion to and internalization into bovine mammary epithelial cells (MAC-T cells) and if so, to determine whether such effects were potentially associated with the S. aureus accessory gene regulator (agr) system. Overall, we demonstrated that all SN obtained from the NAS isolates promoted adhesion of a S. aureus agr+ strain to, yet reduced the internalization into MAC-T cells, while similar effects were not observed for its agr- mutant strain. Our findings provide novel anti-virulence strategies for treating and controlling bovine S. aureus mastitis.

Exploring the distinct immunological reactions of bovine neutrophils towards major and minor pathogens responsible for mastitis

Bovine mastitis is primarily caused by a group of bacteria known as Staphylococcus and Streptococcus. However, additional types of bacteria, such as bovine non-aureus staphylococci and mammaliicocci (NASM) as well as lactic acid bacteria (LAB), are considered minor pathogens and have less impact on cows. Modulating bovine neutrophil activities and gene expressions in response to bacterial stimuli prompted the cells to execute effector functions to combat udder infections. Although neutrophils can manage major mastitis-causing bacteria, this strategy has not been tested against minor pathogens, i.e. NASM, Weissella spp. Our main objective was to investigate how neutrophils interacted with major and minor pathogens during in vitro bacterial stimulation. The results reveal that neutrophils performed offensive duties regardless of the type of bacteria encountered. Neutrophils generated high levels of reactive oxygen species, efficiently phagocytosed both types of bacteria, and facilitated extracellular killing by releasing NET structures against all bacteria. In addition, neutrophils migrated preferentially towards the majors rather than the minors, although myeloperoxidase (MPO) degranulation did not differ substantially across bacteria. Furthermore, the killing capacity of neutrophils was not dependent on any particular bacterium. The correlation of effector functions is intimately linked to the up-regulation of genes associated with the above functions, except for IL6, which was down-regulated. Furthermore, neutrophil apoptosis can be modulated by altering apoptosis-associated genes in response to harmful stimuli. These findings provide valuable information on how neutrophils react to major and minor mastitis-causing bacteria. However, future research should explore the interplay between minor pathogens and the host's responses.

Transcriptome Analysis revealed the Synergism of Novel Rhodethrin inhibition on Biofilm architecture, Antibiotic Resistance and Quorum sensing inEnterococcus faecalis

Enterococcus sp. emerged as an opportunistic nosocomial pathogen with the highest antibiotic resistance and mortality rate. Biofilm is problematic primarily since it is regulated by the global bacterial cell to cell communication mediated by the quorum sensing system. sing system. Thus, potential natural antagonists in a novel drug formulation against biofilm-forming Enterococcus faecalis is critical. We used RNA-Seq to evaluate the effects of the novel molecule rhodethrin with chloramphenicol induced on Enterococcus faecalis and DEGs were identified. In transcriptome sequence analysis, a total of 448 with control Vs rhodethrin, 1591 were in control Vs chloramphenicol, 379 genes were DEGs from control Vs synergies, in rhodethrin with chloramphenicol, 379 genes were differentially expressed, whereas 264 genes were significantly downregulated, indicating that 69.69% ofE. faecaliswas altered. The transcriptional sequence data further expression analysis qRT-PCR, and the results shed that the expression profiles of five significant biofilm formation responsible genes such as, Ace, AtpB, lepA, bopD, and typA, 3 genes involved in quorum sensing are sylA, fsrC and camE, and 4 genes involved in resistance were among including liaX, typA, EfrA, and lepA, were significantly suppressed expressions of the biofilm, quorum sensing, and resistance that are supported by transcriptome analysis.

Priming of the murine mammary gland with Staphylococcus chromogenes IM reduces bacterial growth of Streptococcus uberis: a proof-of-concept study

Streptococcus uberis is a major causative agent of bovine mastitis, an inflammation of the mammary gland with substantial economic consequences. To reduce antibiotic use in animal agriculture, alternative strategies to treat or prevent mastitis are being investigated. Bovine-associated non-aureus staphylococci are proposed in that respect due to their capacity to inhibit the in vitro growth of S. uberis. We demonstrate that priming the murine mammary gland with Staphylococcus chromogenes IM reduces S. uberis growth in comparison with non-primed glands. The innate immune system is activated by increasing IL-8 and LCN2, which may explain this decreased growth.

Analysis of the Presence of the Virulence and Regulation Genes from Staphylococcus aureus (S. aureus) in Coagulase Negative Staphylococci and the Influence of the Staphylococcal Cross-Talk on Their Functions

Coagulase-negative staphylococci (CoNS) are increasingly becoming a public health issue worldwide due to their growing resistance to antibiotics and common involvement in complications related to invasive surgical procedures, and nosocomial and urinary tract infections. Their behavior either as a commensal or a pathogen is a result of strict regulation of colonization and virulence factors. Although functionality of virulence factors and processes involved in their regulation are quite well understood in S. aureus, little is known about them in CoNS species. Therefore, the aim of our studies was to check if clinical CoNS strains may contain virulence factors and genes involved in resistance to methicillin, that are homologous to S. aureus. Moreover, we checked the presence of elements responsible for regulation of genes that encode virulence factors typical for S. aureus in tested isolates. We also investigated whether the regulation factors produced by one CoNS isolate can affect virulence activity of other strains by co-incubation of tested isolates with supernatant from other isolates. Our studies confirmed the presence of virulence factor and regulatory genes attributed to S. aureus in CoNS isolates and indicated that one strain with an active agr gene is able to affect biofilm formation and δ-toxin activity of strains with inactive agr genes. The cognition of prevalence and regulation of virulence factors as well as antibiotic resistance of CoNS isolates is important for better control and treatment of CoNS infections.

Bovine-associated staphylococci and mammaliicocci trigger T-lymphocyte proliferative response and cytokine production differently

We examined whether distinct staphylococcal and mammaliicoccal species and strains trigger B- and T-lymphocyte proliferation and interleukin (IL)-17A and interferon (IFN)-γ production by peripheral blood mononuclear cells in nulliparous, primiparous, and multiparous dairy cows. Flow cytometry was used to measure lymphocyte proliferation with the Ki67 antibody, and specific monoclonal antibodies were used to identify CD3, CD4, and CD8 T lymphocyte and CD21 B lymphocyte populations. The supernatant of the peripheral blood mononuclear cell culture was used to measure IL-17A and IFN-γ production. Two distinct, inactivated strains of bovine-associated Staphylococcus aureus [one causing a persistent intramammary infection (IMI) and the other from the nose], 2 inactivated Staphylococcus chromogenes strains [one causing an IMI and the other from a teat apex), as well as an inactivated Mammaliicoccus fleurettii strain originating from sawdust from a dairy farm, and the mitogens concanavalin A and phytohemagglutinin M-form (both specifically to measure lymphocyte proliferation) were studied. In contrast to the "commensal" Staph. aureus strain originating from the nose, the Staph. aureus strain causing a persistent IMI triggered proliferation of CD4⁺ and CD8⁺ subpopulations of T lymphocytes. The M. fleurettii strain and the 2 Staph. chromogenes strains had no effect on T- or B-cell proliferation. Furthermore, both Staph. aureus and Staph. chromogenes strains causing persistent IMI significantly increased IL-17A and IFN-γ production by peripheral blood mononuclear cells. Overall, multiparous cows tended to have a higher B-lymphocyte and a lower T-lymphocyte proliferative response than primiparous and nulliparous cows. Peripheral blood mononuclear cells of multiparous cows also produced significantly more IL-17A and IFN-γ. In contrast to concanavalin A, phytohemagglutinin M-form selectively stimulated T-cell proliferation.

Novel Quantitative Assay to Describe In Vitro Bovine Mastitis Bacterial Pathogen Inhibition by Non-aureus Staphylococci

In this paper, we describe a new quantitative method to evaluate and quantify in vitro growth inhibition of mastitis-related bacteria. Colony-forming units of Staphylococcus (S.) aureus (n = 10), Escherichia (E.) coli (n = 10), and Streptococcus (S.) uberis (n = 10) were quantified after their growth on top of layers of trypticase soy agar (TSA) containing six different concentrations (varying from 10² to 10⁷ CFU/mL) of bovine non-aureus staphylococci (NAS), i.e., S. chromogenes (n = 3) and S. simulans (n = 3) isolates. Growth inhibition of the mastitis-related major bacterial pathogens, including E. coli, was confirmed by all NAS, an effect that varied highly among NAS isolates and was not evident from the semiquantitative method with which the new method was compared. By subsequent application of the new method on a larger set of 14 bovine NAS isolates, we observed that S. simulans and NAS originating from teat apices (especially S. epidermidis) required lower concentrations to inhibit both methicillin-sensitive (MSSA) (n = 5) and methicillin-resistant S. aureus (MRSA) isolates (n = 5) originating from milk. Therefore, the new assay is a promising tool to precisely quantify the intra- and inter-species differences in growth inhibition between NAS.

Colonization and local host response following intramammary Staphylococcus chromogenes challenge in dry cows

Although extensive research has been performed on bovine non-aureus staphylococci (NAS), several aspects such as bacteria-host interaction remain largely unstudied. Moreover, only a few mastitis pathogen challenge studies in cows have been conducted in the dry period, an important period that allows intramammary infection (IMI) to cure and new IMI to occur. We challenged 16 quarters of 4 Holstein Friesian cows at dry off with 100; 100 000 or 10 000 000 CFU of the udder-adapted S. chromogenes IM strain. Four quarters from one cow served as negative controls. Internally sealed quarters remained untouched, whereas non-sealed quarters were sampled 3 times during the dry period. After parturition, colostrum and daily milk samples were taken during the first week of lactation of all quarters. In total, 8 quarters appeared to be colonized, since S. chromogenes IM was recovered at least once during the experiment, as substantiated using Multilocus Sequence Typing. S. chromogenes IM shedding was highest in dry quarters inoculated with 10 000 000 CFU. Colonized quarters had the highest quarter somatic cell count (qSCC) in early lactation. Inoculated quarters (both colonized and non-colonized) had lower IL-6 and IL-10 concentrations in the dry period, whilst IFN-γ levels tended to be higher in colonized quarters compared to non-inoculated quarters. Also, IgG2 levels were higher in inoculated compared to non-inoculated quarters and the IgG2/IgG1 ratio was on average above 1. To conclude, we showed that dry quarters can be colonized with S. chromogenes IM, resulting in a shift towards a Th1 response in late gestation and early lactation characterised by an increased IgG2 concentration. However, further research is needed to confirm our findings.

Bovine-associated non-aureus staphylococci suppress Staphylococcus aureus biofilm dispersal in vitro yet not through agr regulation

Biofilm formation is a significant virulence factor in Staphylococcus (S.) aureus strains causing subclinical mastitis in dairy cows. A role of environmental signals and communication systems in biofilm development, such as the agr system in S. aureus, is suggested. In the context of multispecies biofilm communities, the presence of non-aureus staphylococci (NAS) might influence S. aureus colonization of the bovine mammary gland, yet, such interspecies interactions have been poorly studied. We determined whether 34 S. chromogenes, 11 S. epidermidis, and 14 S. simulans isolates originating from bovine milk samples and teat apices (TA) were able to affect biofilm formation and dispersion of S. aureus, and if so, how isolate traits such as the capacity to regulate the S. aureus agr quorum sensing system are determinants in this process. The capacity of an agr-positive S. aureus strain to form biofilm was increased more in the presence of S. chromogenes than in the presence of S. simulans and S. epidermidis isolates and in the presence of NAS isolates that do not harbor biofilm related genes. On the other hand, biofilm dispersion of this particular S. aureus strain was suppressed by NAS as a group, an effect that was more pronounced by isolates from TA. Furthermore, the observed effects on biofilm formation and dispersion of the agr-positive S. aureus strain as well as of an agr-negative S. aureus strain did not depend on the capacity of NAS to repress the agr system.