Emergence of multidrug-resistant Staphylococcus haemolyticus in neonatal intensive care unit in Southern France, a genomic study

An emergence of multidrug-resistant (MDR) Staphylococcus haemolyticus has been observed in the neonatal intensive care unit (NICU) of Nîmes University Hospital in southern France. A case-control analysis was conducted on 96 neonates, to identify risk factors associated with S. haemolyticus infection, focusing on clinical outcomes. Forty-eight MDR S. haemolyticus strains, isolated from neonates between October 2019 and July 2022, were investigated using routine in vitro procedures and whole-genome sequencing. Additionally, five S. haemolyticus isolates from adult patients were sequenced to identify clusters circulating within the hospital environment. The incidence of neonatal S. haemolyticus was significantly associated with low birth weight, lower gestational age, and central catheter use (p < 0.001). Sepsis was the most frequent clinical manifestation in this series (20/46, 43.5%) and was associated with five deaths. Based on whole-genome analysis, three S. haemolyticus genotypes were predicted: ST1 (6/53, 11%), ST25 (3/53, 5.7%), and ST29 (44/53, 83%), which included the subcluster II-A, predominantly emerging in the neonatal department. All strains were profiled in silico to be resistant to methicillin, erythromycin, aminoglycosides, and fluoroquinolones, consistent with in vitro antibiotic susceptibility tests. Moreover, in silico prediction of biofilm formation and virulence-encoding genes supported the association of ST29 with severe clinical outcomes, while the persistence in the NICU could be explained by the presence of antiseptic and heavy metal resistance-encoding genes. The clonality of S. haemolyticus ST29 subcluster II-A isolates confirms healthcare transmission causing severe infections. Based on these results, reinforced hygiene measures are necessary to eradicate the nosocomial transmission of MDR strains.

Upregulation of ica Operon Governs Biofilm Formation by a Coagulase-Negative Staphylococcus caprae

Staphylococcus caprae is a Gram-positive, coagulase-negative staphylococci (CoNS), which appears as commensal in the skin, as well as a prevalent mastitis pathogen of goats. Occasionally, it is also associated with infections in humans. Biofilm formation has been identified as a putative virulence factor in S. caprae. Biofilms are multicellular communities protected by a self-produced extracellular matrix (ECM), which facilitates the resistance of bacterial cells to antimicrobial treatments. The ECM is constructed by exopolysaccharides, including the major exopolysaccharide-polysaccharide intercellular adhesion (PIA), regulated by the ica operon in Staphylococcus species. The aim of this study was to characterize the expression of the ica operon in relation to biofilm formation in S. caprae. Results showed that within a few hours of growth, S. caprae could adhere to polystyrene surfaces, start to accumulate, and form biofilm. Peak biofilm biomass and maturation were reached after 48 h, followed by a reduction in biomass after 72 h. Confocal laser scanning microscopy showed the expression of matrix-associated proteins and polysaccharides at various time points. The expression dynamics of the ica operon were investigated using real-time reverse transcriptase PCR (RT)-qPCR, which showed elevated expression during the early stages of biofilm formation and subsequent downregulation throughout the biofilm aging process. In conclusion, our results show that the ica operon is essential in regulating biofilm formation in S. caprae, similar to other Staphylococcus species. Furthermore, the robustness of the observed biofilm phenotype could account for the successful intramammary colonization and may explain disease persistence caused by this pathogenic bacterium.

Biofilm-Producing Ability of Staphylococcus aureus Obtained from Surfaces and Milk of Mastitic Cows

This study was conducted to evaluate the incidence of mastitis in 153 dairy cows and to evaluate the kinetics of adhesion of isolates obtained from surfaces and milk in comparison with the reference strain (RS), CCM 4223. The surfaces of the floor, teat cup, and cow restraints were aseptically swabbed in three replicates (n = 27). Of the total number of infected cows (n = 43), 11 samples were found to be positive for Staphylococcus aureus, 12 samples tested positive for non-aureus staphylococci, 6 samples tested positive for Streptococcus spp., and 11 samples tested positive for other bacteria (Escherichia coli, Pseudomonas spp.) or a mixed infection. The most represented pathogen in milk (11/43) and on surfaces (14/27) was S. aureus. The kinetics of adhesion of the reference strain and isolates of S. aureus on stainless steel surfaces were determined after 3, 6, 9, 12, 24, and 48 h, and 3, 6, 9, 12, and 15 days of incubation. All strains reached counts higher than 5 Log₁₀ CFU/cm² needed for biofilm formation, except RS (4.40 Log₁₀ CFU/cm²). The isolates of S. aureus revealed a higher capability to form biofilm in comparison with RS during the first 3 h (p < 0.001). Thus, there is a significant difference between the occurrence of S. aureus on monitored surfaces-floor, teat cup, and cow restraints-and the frequency with which mastitis is caused by S. aureus (p < 0.05). This finding raises the possibility that if various surfaces are contaminated by S. aureus, it can result in the formation of biofilm, which is a significant virulence factor.

Antimicrobial susceptibility and biofilm forming ability of staphylococci from subclinical buffalo mastitis

The starting objective of this research communication was to determine the prevalence of subclinical mastitis in buffalo in Turkey. We also seeked to isolate and identify staphylococci, determine their antimicrobial susceptibilities and biofilm-forming abilities as well as investigating the presence of biofilm-related genes and microbial surface components recognizing adhesive matrix molecules. A total of 107 (66.9%) staphylococci (28 S. aureus and 79 coagulase-negative staphylococci, CoNS) were isolated from 160 mastitic milk samples collected from 200 lactating water buffalos. The staphylococci were especially resistant to beta-lactams except for cefoxitin but were less resistant to the other antimicrobials that were tested. Based on the Congo red agar method, 92.9% of the S. aureus and 70.9% of the CoNS isolates were positive for biofilm-forming ability, while all S. aureus and 97.5% of CoNS isolates were positive by a microtiter plate analysis. The presence of icaA and icaD genes was not always correlated with biofilm synthesis, and even in the absence of these genes, the isolates were able to synthesize biofilm.

Detection of Some Virulence Factors in Staphylococci Isolated from Mastitic Cows and Ewes

About 150 million families around the world are engaged in milk production. However, inflammation of the mammary gland (mastitis) remains a major problem in dairy ruminants that affects the quality of milk worldwide. The aim of this study was the examination of udder health with detection of contagious and environmental pathogens causing mastitis in 960 and 940 dairy cows and ewes, respectively. The presence of selected virulence factors such as: the formation of haemolysis, gelatinase, biofilm, hydrolyse DNA, and resistance to antibiotics with detection of methicillin resistance gene (mecA), were determined in selected virulence factors associated with isolated staphylococci. These isolated staphylococci with selected virulence factors can have untoward effects on the severity of mastitis. The results of our study indicated that, in addition to the major udder pathogens (S. aureus, S. uberis, and S. agalactiae) causing mastitis, non-aureus staphylococci (NAS), is a major risk to dairy cows and ewes. NAS, such as S. chromogenes, S. warneri, and S. xylosus isolated from infected animals with clinical and chronic mastitis, had the highest representation of virulence factors in comparison to less virulent strains. In addition, the isolates of S. aureus and NAS demonstrated 77.0 % and 44.2 % resistance to one or more antimicrobial classes from mastitic milk samples obtained from dairy cows and ewes, respectively. Due to the high resistance to β-lactamantibiotics in two isolates of S. aureus and two species of NAS isolated from cows’ mastitic milk samples, the presence of a methicillin-resistant gene mecA poses serious complications for the treatment and a serious health risk to milk consumers.

Baicalin acts as an adjuvant to potentiate the activity of azithromycin against Staphylococcus saprophyticus biofilm: an in vitro, in vivo, and molecular study

Staphylococcus saprophyticus is frequently involved in various difficult-to-treat infections due to the formation of biofilms. To identify useful antibiofilm strategies, this study explored the efficacy and mechanism of baicalin in enhancing the ability of azithromycin against multidrug-resistant Staphylococcus saprophyticus-Liu-2016-Liyang, China-francolin (MDRSS) biofilms in vitro and in vivo. When azithromycin was used in combination with baicalin, the minimum inhibitory concentration in biofilm (MICB) for azithromycin decreased 4- to 512-fold. Compared with the azithromycin and baicalin groups, the combination of azithromycin and baicalin could not reduce the biofilm biomass, but the dispersion rates of biofilm were decreased and the bactericidal ability was increased. Furthermore, the relative transcript levels of WalK/R system-related genes were upregulated by the addition of baicalin or azithromycin plus baicalin compared with that of the azithromycin and blank control groups. The strong correlation relationship between the WalK/R system and the bactericidal index demonstrated that baicalin enhanced the bactericidal effect of azithromycin on MDRSS biofilms by modulating the WalK/R system. In the mouse cutaneous infection model, the combination of azithromycin and baicalin succeeded in eradicating MDRSS and decreasing pathological injuries. This study indicated that baicalin has the potential to be an adjuvant to enhance the antimicrobial activity of azithromycin against MDRSS in the biofilm form by modulating the WalK/R system.

Biofilm production by Staphylococcus spp. isolated from bovine mastitis in dairy herds in state of Acre, Brazil and its implications

ABSTRACT This study aimed to identify the Staphylococcus species responsible for bovine mastitis in dairy herds in northern Brazil, to investigate the capacity of biofilm production, and to analyze the association of biofilm production with multiresistance and intensity of California Mastitis Tests (CMT) reactions that can make treatment more difficult and cause misdiagnoses, respectively. Milk samples were collected from 23 dairy farms located in five municipalities in the state of Acre. A total of 339 crossbred cows were tested by CMT, with 109 animals (229 udder ceilings) reacting to the test. After bacterial isolation in blood agar, the catalase-positive and gram-positive cocci were submitted for identification by MALDI-TOF MS. Of 103 strains identified as staphylococci, Staphylococcus chromogenes (58.3%) and Staphylococcus aureus (19.4%) were the most prevalent species. Biofilm production was quantitatively evaluated using a microplate adherence test. Among the Staphylococcus strains, 71.8% were biofilm producers. Most strains of S. chromogenes (68.3%) had the capacity to produce biofilms, ranging from weak (43.3%), moderate (13.3%), and strong (11.7%) producers. Among S. aureus strains, 50% were non-biofilm producers, and none were strong producers. Our data showed an association between biofilm production capacity and multidrug resistance. In addition, there was a reduction in the response to the CMT test, which can mask the diagnosis.

Dairy Cows’ Udder Pathogens and Occurrence of Virulence Factors in Staphylococci

Simple Summary

Dairy farmers and those involved in primary milk production face the challenge of maintaining the health of their animals. Although the level of technological support during milking has increased and appropriate veterinary measures are available, mastitis remains a major health problem in dairy cows as well as a major threat to dairy farm profitability. The results of this study indicate that, in addition to the major udder pathogens (S. aureus, S. uberis and S. agalactiae) causing dairy mastitis, non-aureus staphylococci (NAS) are a major risk to dairy cows during early lactation. NAS, such as S. chromogenes, S. warneri and S. xylosus, which were isolated from animals with clinical mastitis characterized by mild, moderate, or severe symptoms and persistent infections, had the highest representation of virulence factors (production of hemolysis, gelatinase and biofilm; the ability to hydrolyze DNA; resistance to antibiotics) in comparison to less virulent strains. In addition, isolates S. aureus and NAS showed resistance to one or more antimicrobials in 77.2%, and in 16 (11.7%) isolates, multi-drug resistance to three or more antimicrobial classes was confirmed. Due to the high resistance to β-lactam-antibiotics in two isolates of S. aureus and two species of NAS, the presence of a methicillin-resistant gene, mecA, was confirmed, which potentially poses serious complications for the treatment of dairy cows and a serious health risk to milk consumers.

Abstract

This study investigated 960 Slovak and Czech spotted cattle from four different conventional (non-organic) dairy herds located in Eastern Slovakia and Czechia during early lactation (14–100 days after calving). Dairy cows were examined clinically; milk from fore-stripping of each udder quarter was subjected to sensory examination and assessed by the California mastitis test (CMT), and laboratory analyses of bacterial pathogens in milk, including virulence factors, were conducted. Positive CMT scores (1–3) for one or more quarters were detected in 271 (28.2%) of the examined animals. Out of 230 infected milk samples, representing 24.0% of all dairy cows, staphylococci (59.1% of positive findings) were the most commonly isolated organisms, followed by E. coli (11.3%), streptococci Str. uberis (9.1%) and Str. agalactiae (3.4%), and enterococci (6.1%). From 136 isolates of S. aureus (38 isolates) and non-aureus staphylococci (NAS; 98 isolates), virulence factors and their resistance to 14 antimicrobials were detected using the disk diffusion method, with PCR detection of the methicillin resistance gene, mecA. An increased incidence of clinical and chronic forms of mastitis has been reported in mastitic cows in which staphylococci, especially S. aureus and NAS (S. chromogenes, S. warneri, and S. xylosus), have been detected and compared to other isolated udder pathogens. From those species, S. aureus and isolates of NAS mentioned above showed multiple virulence factors that are more likely to hydrolyze DNA, hemolysis, produce gelatinase and biofilm, and have multi-drug resistance as compared to other less virulent staphylococci. Generally, the isolated staphylococci showed 77.2% resistance to one or more antimicrobials, in particular to aminoglycosides, β-lactams, macrolides, or cephalosporins. Isolates that showed the ability to form a biofilm were more resistant to more than one antimicrobial than isolates without biofilm production. Multi-drug resistance to three or more antimicrobial classes was recorded in 16 isolates (11.7%), and the presence of the mecA gene was also confirmed in two isolates of S. aureus and two species of NAS.

Whole Genome Sequencing of Staphylococci Isolated From Bovine Milk Samples

Staphylococci are among the commonly isolated bacteria from intramammary infections in bovines, where Staphylococcus aureus is the most studied species. This species carries a variety of virulence genes, contributing to bacterial survival and spread. Less is known about non-aureus staphylococci (NAS) and their range of virulence genes and mechanisms, but they are the most frequently isolated bacteria from bovine milk. Staphylococci can also carry a range of antimicrobial resistance genes, complicating treatment of the infections they cause. We used Illumina sequencing to whole genome sequence 93 staphylococcal isolates selected from a collection of staphylococcal isolates; 45 S. aureus isolates and 48 NAS isolates from 16 different species, determining their content of antimicrobial resistance genes and virulence genes. Antimicrobial resistance genes were frequently observed in the NAS species as a group compared to S. aureus. However, the lincosamide resistance gene lnuA and penicillin resistance gene blaZ were frequently identified in NAS, as well as a small number of S. aureus. The erm genes conferring macrolide resistance were also identified in several NAS isolates and in a small number of S. aureus isolates. In most S. aureus isolates, no antimicrobial resistance genes were detected, but in five S. aureus isolates three to six resistance genes were identified and all five of these carried the mecA gene. Virulence genes were more frequently identified in S. aureus, which contained on average five times more virulence genes compared to NAS. Among the NAS species there were also differences in content of virulence genes, such as S. chromogenes with a higher average number of virulence genes. By determining the content of a large selection of virulence genes and antimicrobial resistance genes in S. aureus and 16 different NAS species our results contribute with knowledge regarding the genetic basis for virulence and antimicrobial resistance in bovine staphylococci, especially the less studied NAS. The results can create a broader basis for further research into the virulence mechanisms of this important group of bacteria in bovine intramammary infections.

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.

Phenotypic and Molecular Detection of Biofilm Formation in Staphylococcus aureus Isolated from Different Sources in Algeria

Staphylococcus aureus is an opportunistic bacterium causing a wide variety of diseases. Biofilm formation of Staphylococcus aureus is of primary public and animal health concern. The purposes of the present study were to investigate the ability of Staphylococcus aureus isolated from animals, humans, and food samples to form biofilms and to screen for the presence of biofilm-associated and regulatory genes. In total, 55 Staphylococcus aureus isolated from sheep mastitis cases (n = 28), humans (n = 19), and from food matrices (n = 8) were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The ability of Staphylococcus aureus for slime production and biofilm formation was determined quantitatively. A DNA microarray examination was performed to detect adhesion genes (icaACD and biofilm-associated protein gene (bap)), genes encoding microbial surface components recognizing adhesive matrix molecules (MSCRAMMs), regulatory genes (accessory gene regulator (agr) and staphylococcal accessory regulator (sarA)), and the staphylococcal cassette chromosome mec elements (SCCmec). Out of 55 Staphylococcus aureus isolates, 39 (71.0%) and 23 (41.8%) were producing slime and biofilm, respectively. All Staphylococcus aureus strains isolated from food showed biofilm formation ability. 52.6% of the Staphylococcus aureus strains isolated from sheep with mastitis, and 17.9% of isolates from humans, were able to form a biofilm. Microarray analysis typed the Staphylococcus aureus into 15 clonal complexes. Among all Staphylococcus aureus isolates, four of the human isolates (21.1%) harbored the mecA gene (SCCmec type IV) typed into 2 clonal complexes (CC22-MRSA-IV and CC80-MRSA-IV) and were considered as methicillin-resistant, while two of them were slime-producing. None of the isolates from sheep with mastitis harbored the cna gene which is associated with biofilm production. The fnbB gene was found in 100%, 60% and 40% of biofilm-producing Staphylococcus aureus isolated from food, humans, and sheep with mastitis, respectively. Three agr groups were present and agr group III was predominant with 43.6%, followed by agr group I (38.2%), and agr group II (18.2%). This study revealed the capacity of Staphylococcus aureus isolates to form biofilms and highlighted the genetic background displayed by Staphylococcus aureus isolates from different sources in Algeria.

Capacity of two Staphylococcus aureus strains with different adaptation genotypes to persist and induce damage in bovine mammary epithelial cells and to activate macrophages

The aim of this study was to evaluate and compare the ability to adhere/internalize, persist, and induce damage in mammary epithelial cells (MAC-T) of two Staphylococcus aureus strains with different adaptation genotypes (low and high) to the bovine mammary gland (MG). Also, the phagocytic and bactericidal capacity induced after the interaction between macrophages, isolated from mammary secretion, of both S. aureus strains was evaluated. Two isolates (designated 806 and 5011) from bovine intramammary infection (IMI) harboring genes involved in adherence and biofilm production, belonging to different capsular polysaccharide (CP) type, accessory gene regulator (agr) group, pulsotype (PT) and sequence type/clonal complex (ST/CC). Strains 806 and 5011 were associated with low (nonpersistent-NP) and high (persistent-P) adaptation to the MG, respectively. Strain 5011 (P), agr group I, cap8 positive and strong biofilm producer showed higher capacity to adhere/internalize in MAC-T compared with strain 806 (NP), characterized as agr group II, cap5 positive and weak biofilm producer. Strain 5011(P) could be recovered from MAC-T lysates up to 72 h pi; while strain 806 (NP) could be recovered only at 4 h pi. Strain 5011 (P) showed greater capacity to induce apoptosis compared with strain 806 (NP) at 4, 24 and 48 h pi. Macrophages infected with strain 5011 (P) showed a greater phagocytic capacity and higher percentage of intracellular reactive oxygen species (ROS) production than strain 806 (NP). No viable bacteria were isolated from macrophages lysates stimulated with any of the S. aureus strains at 2, 4, 8 and 24 h pi. The knowledge of the molecular profile of the S. aureus strains causing bovine mastitis in a herd could become a tool to expose the most prevalent virulence gene patterns and advance in the elucidation of the pathogenesis of chronic mastitis.

In vitro antibiotic susceptibility and biofilm production of Staphylococcus aureus isolates recovered from bovine intramammary infections that persisted or not following extended therapies with cephapirin, pirlimycin or ceftiofur

Staphylococcus aureus intramammary infections (IMIs) have low cure rates using standard antibiotic treatment and increasing the duration of treatment usually improves therapeutic success. Chronic IMIs are thought to be caused by bacteria presenting a specific virulence phenotype that includes the capacity to produce greater amounts of biofilm. In this study, antibiotic susceptibility and biofilm production by S. aureus isolates recovered from IMIs that were cured or not following an extended therapy with cephapirin, pirlimycin or ceftiofur for 5, 8 and 8 days, respectively, were compared. An isolate was confirmed as from a persistent case (not cured) if the same S. aureus strain was isolated before and after treatment as revealed by the same VNTR profile (variable number of tandem repeats detected by multiplex PCR). The antibiotic minimal inhibitory concentrations (MICs) were determined for these isolates as well as the capacity of the isolates to produce biofilm. Isolates from persistent cases after extended therapy with cephapirin or ceftiofur had higher MICs for these drugs compared to isolates from non-persistent cases (p < 0.05) even though the antibiotic susceptibility breakpoints were not exceeded. Isolates of the ceftiofur study significantly increased their biofilm production in presence of a sub-MIC of ceftiofur (p < 0.05), whereas isolates from the pirlimycin group produced significantly less biofilm in presence of a sub-MIC of pirlimycin (p < 0.001). Relative antibiotic susceptibility of the isolates as well as biofilm production may play a role in the failure of extended therapies. On the other hand, some antibiotics may counteract biofilm formation and improve cure rates.

Preconditioning with Lipopolysaccharide or Lipoteichoic Acid Protects against Staphylococcus aureus Mammary Infection in Mice

Staphylococcus aureus is one of the most causative agents of mastitis and is associated with chronic udder infections. The persistency of the pathogen is believed to be the result of an insufficient triggering of local inflammatory signaling. In this study, the preclinical mastitis model was used, aiming to evaluate if lipopolysaccharide (LPS) or lipoteichoic acid (LTA) preconditioning could aid the host in more effectively clearing or at least limiting a subsequent S. aureus infection. A prototypic Gram-negative virulence factor, i.e., LPS and Gram-positive virulence factor, i.e., LTA were screened whether they were able to boost the local immune compartment. Compared to S. aureus-induced inflammation, both toxins had a remarkable high potency to efficiently induce two novel selected innate immunity biomarkers i.e., lipocalin 2 (LCN2) and chitinase 3-like 1 (CHI3L1). When combining mammary inoculation of LPS or LTA prior to a local S. aureus infection, we were able to modulate the innate immune response, reduce local bacterial loads, and induce either LCN2 or CHI3L1 at 24 h post-infection. Clodronate depletion of mammary macrophages also identified that macrophages contribute only to a limited extend to the LPS/LTA-induced immunomodulation upon S. aureus infection. Based on histological neutrophil influx evaluation, concomitant local cytokine profiles and LCN2/CHI3L1 patterns, the macrophage-independent signaling plays a major role in the LPS- or LTA-pretreated S. aureus-infected mouse mammary gland. Our results highlight the importance of a vigilant microenvironment during the innate immune response of the mammary gland and offer novel insights for new approaches concerning effective immunomodulation against a local bacterial infection.

Evaluation of the biofilm forming ability and its associated genes in Staphylococcus species isolates from bovine mastitis in Argentinean dairy farms

Staphylococcus aureus and coagulase-negative staphylococci (CNS) are important causes of intramammary infection in dairy cattle, and their ability to produce biofilm is considered an important virulence property in the pathogenesis of mastitis. However, the published date on mechanisms and factors involved in infection persistence in the mammary gland remains unclear. The aim of this study was to investigate whether the main Staphylococcus species involved in bovine intramammary infections possess specific characteristics that promote colonization of the udder. We evaluated the biofilm-forming ability and distribution of adhesion- and biofilm-associated genes of Staphylococcus spp. isolated from bovine mastitis infected animals in Argentinean dairy farms. For this purpose, the phenotypic biofilm formation ability of 209 Staphylococcus spp. from bovine mastitis was investigated. All isolates produced biofilm in vitro, being 35,0% and 45,0% of the 127 S. aureus or 51,0% and 29,0% of the 82 CNS strong and moderate biofilm producers respectively. All S. aureus samples were PCR-positive for icaA, icaD, clfA, clfB and fnbpA genes, 76.3% were positive for fnbpB gene and 11.0% were positive for bap gene. In CNS isolates, the positive rates for icaA and icaD were 73.2%, while for clfA, clfB, fnbpA fnbpB and bap genes the percentage were lower. The results demonstrate that in Staphylococcus spp. biofilm formation, the polysaccharide and the adhesion- and biofilm-associated genes are of overall importance on bovine mastitis in Argentina. Therefore, future works should focus on these pathogenic specific factors for the development of more effective therapies of control, being essential to consider the ability of isolates to produce biofilm.

Factors responsible for subclinical mastitis in cows caused by Staphylococcus chromogenes and its susceptibility to antibiotics based on bap, fnbA, eno, mecA, tetK, and ermA genes

The aim of this study was to recognize selected factors of virulence determining the adhesion of Staphylococcus chromogenes to cows' udder tissues in subclinical mastitis and to evaluate the susceptibility of this pathogen to antibiotics. The subjects of the study were 38 isolates of Staph. chromogenes from 335 samples of milk from cows with subclinical coagulase-negative staphylococci mastitis. Somatic cell count ranged between 216,000 and 568,000/mL of milk (average 356,000/mL of milk). We confirmed the ability to produce slime in 24 isolates (63.2%), and the ability to produce protease in 29 isolates (76.3%). In each slime-producing isolate, the bap gene was not found, and the fnbA and eno genes were not detected. In vitro tests showed that ceftiofur had the highest effectiveness against Staph. chromogenes (89.5% of susceptible isolates). Minimum inhibitory concentrations ranged from 0.06 to 2µg/mL for susceptible isolates. The minimum concentrations required to inhibit growth of 90 and 50% of the isolates for ceftiofur were at or below the cutoffs recommended by the Clinical and Laboratory Standards Institute (2 and 0.06µg/mL, respectively). A significant percentage of the isolates were susceptible to other β-lactam antibiotics: amoxicillin with clavulanic acid (84.2%) and ampicillin (81.6%). The lowest effectiveness among β-lactams was for penicillin (73.7% of susceptible isolates), and the minimum inhibitory concentration for penicillin ranged from <0.06 to 8µg/mL. None of the examined isolates had the mecA gene, but β-lactamase was detected in 4 isolates (10.5%). Erythromycin and oxytetracycline exhibited the lowest activity against Staph. chromogenes (71.1 and 63.2% of susceptible isolates, respectively). The genes tetK (6 isolates) and ermA (1 isolate) were also detected.

Existence of two groups of Staphylococcus aureus strains isolated from bovine mastitis based on biofilm formation, intracellular survival, capsular profile and agr-typing

Staphylococcus (S.) aureus is recognised worldwide as an important pathogen causing contagious acute and chronic bovine mastitis. Chronic mastitis account for a significant part of all bovine cases and represent an important economic problem for dairy producers. Several properties (biofilm formation, intracellular survival, capsular expression and group agr) are thought to be associated with this chronic status. In a previous study, we found the existence of two groups of strains based on the association of these features. The aim of the present work was to confirm on a large international and non-related collection of strains the existence of these clusters and to associate them with case history records. In addition, the genomes of eight strains were sequenced to study the genomic differences between strains of each cluster. The results confirmed the existence of both groups based on capsular typing, intracellular survival and agr-typing: strains cap8-positive, belonging to agr group II, showing a low invasion rate and strains cap5-positive, belonging to agr group I, showing a high invasion rate. None of the two clusters were associated with the chronic status of the cow. When comparing the genomes of strains belonging to both clusters, the genes specific to the group "cap5-agrI" would suggest that these strains are better adapted to live in hostile environment. The existence of these two groups is highly important as they may represent two clusters that are adapted differently to the host and/or the surrounding environment.

Production of slime by coagulase-negative staphylococci (CNS) isolated from clinical and subclinical mastitis in cows

The aim of the study was to evaluate the slime-producing ability of coagulase-negative staphylococci (CNS) isolated from clinical and subclinical mastitis in cows. The study was carried out on 100 isolates of CNS obtained from milk of 86 cows from farms located in the Lublin region (Poland). Slime-producing ability was observed in over half of coagulase-negative staphylococci (54.0% of isolated CNS), including 19 isolates of methicillin-resistant staphylococci (95.5% of all MRCNS). Of 22 isolates of CNS responsible for the clinical form of mastitis, 20 isolates (90.9%) produced slime: S. xylosus (7 isolates), S. haemolyticus (6 isolates), S. chromogenes (4 isolates), and S. sciuri (3 isolates), including 9 isolates of MRCNS (45.0%). The remaining 34 isolates of CNS (43.6%) with the ability to produce this exopolysaccharide were isolated from the milk of cows with subclinical form of mastitis: S. xylosus (12 isolates), S. sciuri (9 isolates), S. chromogenes (6 isolates), S. haemolyticus (3 isolates), S. warneri (3 isolates) and S. saprophyticus (1 isolate), including 10 isolates of MRCNS (12.8%).

Virulence factors and ability of staphylococci from bovine milk and the cowshed environment to biofilm formation

The aim of this study was to examine virulence factors and the ability of S. aureus and CNS species isolated from milk of cows with mastitis to form biofilm, and to compare them with virulence factors of staphylococci from milk of cows without mastitis and cowshed environment. Most of S. aureus strains from cows with mastitis showed haemolytic activity (93.9%), among them 72.7% and 21.2% produced alpha- and beta-haemolysin, respectively. S. aureus from cows with mastitis symptoms produced proteases (above 48%) and esterase (42.4%). The highly significant relationship between the number of S. xylosus strains producing haemolysins (62%) and the origin of these strains from milk of cows with mastitis was observed. The ability to produce proteases was significantly associated with S. sciuri from milk of cows with mastitis. The ability of biofilm formation by staphylococcal strains from milk of cows with mastitis was greater than in strains from milk of cows without mastitis and the difference was significant (p < or = 0.05). The highest percentage of strains from milk of cows with mastitis were weak biofilm formers (48.6%), while 40% and 11.4% of strains were moderate and strong biofilm producers, respectively. S. xylosus showed the highest ability to form biofilm, while the lowest ability to form biofilm was observed in S. aureus and S. epidermidis. In conclusion, production of exotoxins and enzymes, and ability of biofilm formation shown by many CNS isolated from milk of cows with mastitis symptoms indicates that these features are important in pathogenesis of this disease.

Staphylococcus aureus in veterinary medicine

Staphylococcus aureus is a major opportunistic pathogen in humans and one of the most important pathogenic Staphylococcus species in veterinary medicine. S. aureus is dangerous because of its deleterious effects on animal health and its potential for transmission from animals to humans and vice-versa. It thus has a huge impact on animal health and welfare and causes major economic losses in livestock production. Increasing attention is therefore being paid to both livestock and companion animals in terms of this pathogen. In this review, we summarise the current knowledge on the animal host adaptation of S. aureus. Different types of S. aureus infections in animals are also presented, with particular emphasis on mastitis in dairy herds, which is probably the costliest and therefore the best documented S. aureus infection seen in animals.