Coagulase-negative Staphylococci Intramammary Infections Research Articles

Persistence of coagulase negative staphylococcal intramammary infections in dairy goats.

The objectives of the research described here were to describe the persistence of intramammary infections (IMI) caused by coagulase negative staphylococci (CNS) in goats using strain-typing, and to evaluate the relationship between species-specific CNS IMI and somatic cell score (SCS) at the udder-half level. Udder-half milk samples were collected from all 909 lactating goats (1817 halves; 1 blind half) in a single herd. Milk samples were cultured on Columbia blood agar, and 220 goats with at least one half yielding a single colony type CNS were enrolled for two additional half-level samplings at approximately 1-month intervals. Isolates were identified to the species level by matrix-assisted laser desorption-ionisation time-of-flight mass spectrometry or PCR amplification and partial sequencing of tuf or rpoB. An IMI was defined as persistent when ≥1 follow-up sample yielded the same species and strain as on Day 0 based on pulsed-field gel electrophoresis. A generalised mixed linear model was used to evaluate the odds of persistence as a function of CNS species. A mixed linear model was used to evaluate the relationship between IMI status on a given day and SCS. Among 192 IMI, 69.8% were persistent based on species and strain-type. Staphylococcus simulans IMI had higher odds of persistence than Staphylococcus arlettae IMI. In primiparous goats, Staphylococcus epidermidis IMI was associated with higher SCS than S. arlettae, Staphylococcus xylosus and 'other CNS' IMI. The differences detected in the present study between CNS species, with regard to persistence of IMI and association with SCS, highlight the need to study CNS at the species and strain level to understand the pathogenicity and epidemiology of CNS in goats.

Quarter- and cow-level risk factors for intramammary infection with coagulase-negative staphylococci species in Swiss dairy cows

Bacteriological status, evaluation of udder symmetry, udder hygiene, and teat end scores of 92 dairy cows were assessed on 3 Swiss dairy farms in a longitudinal 1-yr study to determine risk factors for intramammary infection (IMI) with coagulase-negative staphylococci (CNS) species. Farm visits were performed monthly including sterile quarter milk sampling and udder evaluation of all lactating cows. Milk samples were evaluated for the presence of staphylococci using selective agar plates. Species identification was performed using MALDI-TOF mass spectrometry. Intramammary infection was defined as milk samples having ≥100 cfu per mL of milk according to culture results. Overall, 3,151 quarter samples were included in the statistical analysis. Staphylococcus chromogenes, Staphylococcus haemolyticus, Staphylococcus xylosus, and a Staphylococcus warneri-like species were the 4 most prevalent CNS species found. Hierarchical multivariable logistic regression models were built to evaluate risk factors for species-specific CNS IMI. Risk factors for Staph. chromogenes IMI were presence in herd B, the period from June 2014 to August 2014 and December 2014 to February 2015, and presence of udder edema. For Staph. haemolyticus, the relevant risk factor included coinfection with Staph. xylosus coinfection with other than the above-mentioned CNS species ("others") and the period from June 2014 to November 2014. Coinfection with Staph. haemolyticus and "others," the periods from June 2014 to August 2014 and December 2014 to February 2015, early phase of lactation (1-60 d in milk), and belonging to herd B were significantly associated with Staph. xylosus IMI. Mid and late lactation, coinfection with Staph. xylosus, and the period September 2014 to May 2015 were identified as significant risk factors for Staph. warneri-like IMI. For Staph. chromogenes, 60.6 and 26% of the variance was observed at the quarter and cow level, respectively, whereas for the other investigated species the highest variance was observed at the sample level. The predominant species within herds differed and was most pronounced for the Staph. warneri-like species.

Intramammary infection with coagulase-negative staphylococci at parturition: Species-specific prevalence, risk factors, and effect on udder health

Coagulase-negative staphylococci (CNS) are the main cause of bovine intramammary infections (IMI) in many countries. Despite a high prevalence of CNS IMI at parturition, species-specific risk factor studies, relying on accurate identification methods, are lacking. Therefore, this observational study aimed at determining the prevalence and distribution of different CNS species causing IMI in fresh heifers and dairy cows in Flemish dairy herds and identifying associated species- and subgroup-specific risk factors at the herd, cow, and quarter level. The effect on udder health was investigated as well. Staphylococcus chromogenes, S. sciuri, and S. cohnii were the most frequently isolated species. The only CNS species causing IMI in fresh heifers and dairy cows in all herds was Staphylococcus chromogenes, whereas large between-herd differences in distribution were observed for the other species. Quarters from heifers and quarters with an inverted teat end had higher odds of being infected with S. chromogenes, S. simulans, or S. xylosus as well as with S. chromogenes solely. Prepartum teat apex colonization with S. chromogenes increased the likelihood of S. chromogenes IMI in the corresponding quarters at parturition. Quarters with dirty teat apices before calving were more likely to be infected with S. cohnii, S. equorum, S. saprophyticus, or S. sciuri, supporting the environmental nature of these CNS species. Three species (S. chromogenes, S. simulans, and S. xylosus) were associated with a higher quarter somatic cell count at parturition as compared with uninfected quarters.

Short communication: Species group-specific predictors at the cow and quarter level for intramammary infection with coagulase-negative staphylococci in dairy cattle throughout lactation

Coagulase-negative staphylococci (CNS) are frequently isolated from quarters with subclinical mastitis, teat apices, and the cows’ environment. Virulence, ecology, epidemiological behavior, and effect on udder health vary between different CNS species. Staphylococcus chromogenes, Staph. simulans, and Staph. xylosus are frequently present in milk and have a more substantial effect on quarter milk somatic cell count than other species. Therefore, these species are considered the “more relevant” CNS. As species-specific factors associated with CNS intramammary infection (IMI) have not yet been identified and susceptibility for IMI differs between cows and quarters, this study aimed to identify predictors for CNS IMI at the cow and quarter level (some of them changing over time) with a specific focus on the aforementioned more relevant CNS. Precise data were available from a longitudinal study (3,052 observations from 344 quarters from 86 dairy cows belonging to 3 commercial dairy herds). All CNS were molecularly identified to the species level, and multivariable, multilevel logistic regression models taking into account the longitudinal nature of the data, were fit to study the likelihood of infection. Staphylococcus chromogenes, Staph. xylosus, and Staph. cohnii were the most frequently isolated species from CNS IMI in older cows, whereas Staph. chromogenes, Staph. xylosus, and Staph. simulans were the main species found in IMI in heifers. Quarters from heifers (as opposed to multiparous cows), from heifers and multiparous cows in third or fourth month in lactation (as opposed to early lactation, <60 d in milk), and with an increasing quarter milk SCC were more likely to be infected with the more relevant CNS species. Quarter milk SCC was identified as the sole statistically significant predictor for IMI with other CNS species, although the size of the effect was lower [odds ratio of 1.6 (1.4–1.9) vs. 2.1 (1.8–2.5)] than the effect for IMI with the more relevant CNS. As a strong herd effect was present, studying herd-level predictors is warranted.

Pathogen group-specific risk factors for intramammary infection in treated and untreated dairy heifers participating in a prepartum antimicrobial treatment trial

Heifer mastitis is a well-known problem, with several pathogens being involved. Several generic risk factors associated with the likelihood of intramammary infections (IMI) in fresh dairy heifers have been identified before. Yet, a need exists to identify pathogen group-specific factors, as the effect of (groups of) pathogens on udder health and milk yield is different. The aim of the present study was to identify pathogen group-specific risk factors for IMI in heifers participating in a prepartum antimicrobial treatment trial, allowing us to test the hypothesis that different factors are of importance between treated and untreated control heifers as well. Data from a clinical trial in which end-term heifers were treated systemically (over 3 consecutive days) 2 wk before calving with penethamate hydriodide (n=76) or remained untreated (n=73), were available. Several potential risk factors at the herd, heifer, and quarter level were recorded in the first 3 d in milk. Quarters from untreated heifers supplemented with ≥4mg of selenium/d prepartum were significantly less likely to be infected with coagulase-negative staphylococci (CNS), whereas quarters were more likely to be infected with CNS when assistance during calving was needed. Udder edema before calving significantly decreased the odds of IMI with major pathogens. In treated heifers, no factors were detected that were associated with the likelihood of CNS IMI, whereas quarters from heifers were significantly more likely to be infected with major pathogens when they were housed in the calving pen more than 1 d and when they had been in contact with the lactating cows before calving. The risk factors for IMI that were identified in treated heifers were different than those in untreated heifers, independent of the pathogen group that was considered. It looks as if prepartum treatment not only changed the likelihood of infection, but also the factors that were associated with infection. However, except for treated heifers with an IMI with major pathogens, only a small proportion of the variation could be explained in the final models. Therefore, factors other than those that were studied could explain the likelihood of infection.

Relationship between postmilking standing duration and risk of intramammary infection in freestall-housed dairy cows milked 3 times per day

Recent evidence exists to suggest that the risk of subclinical mastitis, particularly those infections caused by environmental pathogens, in dairy cows is related to standing and lying patterns. The objective of this study was to determine the association between postmilking standing duration (PMSD) of dairy cows milked 3×/d and risk of intramammary infection (IMI). Four commercial freestall dairy herds in Eastern Ontario, milking 3×/d, were enrolled in a longitudinal study. Forty Holstein-Friesian cows per herd were randomly selected as focal animals from those cows in each herd that met our selection criteria of days in milk (<200 d) and somatic cell count (<100,000cells/mL). The study consisted of three 28-d periods. The study began following a regularly scheduled Dairy Herd Improvement test with the collection of quarter-level milk samples from all focal animals. Bacteriology was used to confirm infection status at the start of the study and for determination of incidence of IMI throughout the study. A new IMI was defined as having a culture-positive quarter-level sample when the previous sample (28 d prior) had been culture negative for the pathogen of interest. Four sets of quarter-level milk samples were obtained for each focal animal. Lying behavior was recorded for 5 d after each milk sampling using data loggers. For these 5 d, individual milking times, production, and feeding times were also recorded. Postmilking standing duration was analyzed by milking event, with increased PMSD being positively associated with provision of fresh feed or freshly pushed-up feed around the time of milking, greater feed bunk space per cow, and lower freestall stocking density. Over the study period, 456 new IMI were detected, resulting in a mean herd incidence rate of 3.22 IMI per quarter year. Coagulase-negative staphylococci (CNS) and Corynebacterium spp. IMI were statistically analyzed to determine relationship with PMSD; they were the 2 predominant pathogens representing 45 and 31% of IMI, respectively. Only CNS IMI was associated with PMSD. A nonlinear relationship between PMSD and incidence of CNS IMI was found; cows with a PMSD of 90 to 120min were at a reduced risk for CNS IMI. The risk of experiencing CNS IMI was also reduced with increased frequency of feed push-ups and provision of fresh feed 60min before to 90min after milking and >540min after milking. These results indicate that management practices that promote PMSD of 90 to 120min, such as the provision of fresh feed or freshly pushed-up feed around the time of milking, providing ample feed bunk space per cow, and keeping freestall stocking density low, should be encouraged to reduce the risk of CNS IMI in freestall-housed cows milked 3×/d.

The effect of intramammary infection with coagulase-negative staphylococci in early lactating heifers on milk yield throughout first lactation revisited

The objective of this study was to further scrutinize the previously found positive association between intramammary infection (IMI) caused by coagulase-negative staphylococci (CNS) in early lactating heifers and test-day daily milk yield (MY) throughout first lactation, with a specific focus on the effect of the heifers’ genetically determined milk production levels and the incidence of clinical mastitis. Two precise longitudinal data sets were analyzed using a series of statistical models including potential confounding and intermediate variables. The final database included the IMI status at calving, composite milk somatic cell count (SCC) and MY records at test day up to 285 d in milk (DIM), farmer-recorded clinical mastitis (CM) cases between 14 and 285 DIM, estimated new IMI incidence based on a SCC threshold of 100,000cells/mL between 14 and 285 DIM, DIM, average 305-d MY at the herd level, and the heifers’ genetic merit for MY from 240 dairy heifers from 29 dairy herds. Seventy-one (29.6%) early lactating heifers were noninfected, 108 heifers (45.0%) were CNS infected, and 61 heifers (25.4%) were infected with any major pathogen. The positive effect of CNS IMI in early lactation on test-day MY was estimated at 1.32kg/d using a first basic mixed regression model. Correcting for the confounder genetic merit for MY reduced this effect to 1.17kg. Interestingly, taking into account the confounding effect of herd resulted in an increase of the estimate from 1.32 to 2.2kg/d. The positive effect of CNS IMI in early lactation on MY after correcting the model for both confounders was estimated at 2.05kg/d. Heifers infected with CNS in the first DIM tended to have fewer CM cases throughout lactation compared with the noninfected herd mates. Including the intermediate variable CM in the model explained 0.16kg/d of the corrected effect of 2.05kg/d. Inclusion of test-day SCC, another intermediate variable, however, increased the estimate by 0.11kg/d. With an appropriate correction for several confounders and biologically understood intermediate variables such as CM, test-day SCC, and new IMI based on SCC threshold of 100,000cells/mL, an unexplained test-day MY difference between CNS-infected and noninfected heifers of 2.0kg/d remained.

Enterotoxin genes in coagulase-negative and coagulase-positive staphylococci isolated from bovine milk

The objective of this study was to isolate and identify the main staphylococcal species causing bovine mastitis in 10 Brazilian dairy herds and study their capability to produce enterotoxins. Herds were selected based on size and use of milking technology, and farms were visited once during the study. All mammary glands of all lactating cows were screened using the California Mastitis Test (CMT) and a strip cup. A single aseptic milk sample (20mL) was collected from all CMT-positive quarters. Identification of Staphylococcus spp. was performed using conventional microbiology, and PCR was used to determine the presence of enterotoxin-encoding genes (sea, seb, sec, and sed). Of the 1,318 CMT-positive milk samples, Staphylococcus spp. were isolated from 263 (19.9%). Of these isolates, 135 (51%) were coagulase-positive staphylococci (CPS) and 128 (49%) were coagulase-negative staphylococci (CNS). Eighteen different species of CNS were isolated, among which S. warneri, S. epidermidis and S. hyicus were the most frequent. The distribution of Staphylococcus species was different among herds: S. epidermidis was found in 8 herds, S. warneri was found in 7 herds, and S. hyicus in 6 herds. Some of the CNS species (S. saprophyticus ssp. saprophyticus, S. auricularis, S. capitis, and S. chromogenes) were isolated in only one of the farms. Genes related to production of enterotoxins were found in 66% (n=85) of all CNS and in 35% of the CPS isolates. For both CNS and CPS isolates, the most frequently identified enterotoxin genes were sea, seb, and sec; the prevalence of sea differed between CPS (9.5%) and CNS (35.1%) isolates. Staphylococcus warneri isolates showed a greater percentage of sea than seb, sec, or sed, whereas S. hyicus isolates showed a greater percentage of sea than sec. Over 60% of CNS belonged to 3 major species, which carried 62.2 to 81.3% of the enterotoxin genes. The high prevalence highlights the potential for food poisoning caused by these species. For possible high-risk situations for food poisoning, such as milk produced with total bacterial counts greater than regulatory levels and stored under inappropriate temperatures, monitoring contamination with CNS could be important to protect human health. Because the prevalence of CNS intramammary infections in dairy herds is usually high, and these species can be found in great numbers in bulk milk, identification of risk factors for production of staphylococcal enterotoxins should be considered in future studies.

Transmission dynamics of intramammary infections with coagulase-negative staphylococci

A field trial was conducted on 2 US dairy herds to evaluate the transmission dynamics of coagulase-negative staphylococci (CNS) during the lactation period. Quarter milk cultures positive for CNS were classified as intramammary infection (IMI) or incidental isolation (transient colonization). The average proportion of quarters with CNS IMI was 0.114 in farm 1 and 0.09 in farm 2, and corresponding estimates for quarters with transient colonization of CNS were 0.122 and 0.088 throughout the 13-mo study period. Transmission parameters were obtained both for IMI caused by CNS and for CNS-positive quarters classified as the combination of transient colonization and IMI. Transmission between cows and between quarters in the same cow was assessed. The transmission parameters (β) for IMI caused by CNS were 0.0066 (farm 1) and 0.0111 (farm 2). Corresponding estimates of β when IMI and transient colonization of CNS were assessed jointly were 0.0256 (farm 1) and 0.0253 (farm 2). On farm 1, risk of transmission for CNS IMI between quarters in the same cow was 2 times greater than that between quarters from cow to cow. Transmission of CNS was considered contagious in one farm but no distinction between contagious and environmental transmission could be made in the other. We hypothesize that between-farm variation may be related to diversity between prevailing CNS species or by differences in management. In the current study, estimates of the basic reproduction number (R0) at the farm level for CNS IMI were 0.59 and 0.84 in farms 1 and 2, respectively. This shows that the transmission of CNS from IMI during the lactation period would to be too low to maintain the observed herd prevalence of CNS IMI. The R0 values for the combination of transient colonization and IMI by CNS were 1.13 and 1.17 in farms 1 and 2, respectively. This indicates potential for sustained endemic infection of CNS throughout lactation. However, prevailing CNS species may also differ between transient colonization and IMI. Therefore, not only CNS originating from IMI or incidental isolation events, but also CNS IMI occurring from the period outside the lactation pen are essential for maintenance of the observed herd prevalence of CNS IMI throughout lactation in this study. The effect of IMI originating outside the lactation pen was verified in simulations with reduced entry of infectious quarters to the lactation pens. Measures against CNS IMI would probably increase in efficiency if prevention of infection during the dry period and early lactation were further emphasized in herd health programs.

Epidemiology of coagulase-negative staphylococci intramammary infection in dairy cattle and the effect of bacteriological culture misclassification

Objectives of this study were to identify the manageable risk factors associated with the lactational incidence, elimination, and prevalence of coagulase-negative staphylococci (CNS) intramammary infections (IMI) while taking into account the difficulties inherent to their diagnosis. A second objective was to evaluate the effect of CNS IMI misclassification in mastitis research. A cohort of 90 Canadian dairy herds was followed throughout 2007 to 2008. In each herd, series of quarter milk samples were collected from a subsample of cows and bacteriological culture was performed to identify prevalent, incident, and eliminated CNS IMI. Practices used on farms were captured using direct observations and a validated questionnaire. The relationships between herd CNS IMI prevalence and herd incidence and elimination rates were explored using linear regression. Manageable risk factors associated with the prevalence, incidence, or elimination of CNS IMI were identified via Bayesian analyses using a latent class model approach, allowing adjustment of the estimates for the imperfect sensitivity and specificity of bacteriological culture. After adjustment for the diagnostic test limitations, a mean CNS IMI quarter prevalence of 42.7% [95% confidence interval (CI): 34.7, 50.1] and incidence and elimination rates of 0.29 new IMI/quarter-month (95% CI: 0.21, 0.37) and 0.79 eliminated IMI/quarter-month (95% CI: 0.66, 0.91), respectively, were observed. Considerable biases of the estimates were observed when CNS IMI misclassification was ignored. These biases were important for measures of association with risk factors, were almost always toward the null value, and led to both type I and type II errors. Coagulase-negative staphylococci IMI incidence appeared to be a stronger determinant of herd IMI prevalence than IMI elimination rate. The majority of herds followed were already using blanket dry cow treatment and postmilking teat disinfection. A holistic approach considering associations with all 3 outcomes was used to interpret associations between manageable risk factors and CNS IMI. Sand and wood-based product bedding showed desirable associations with CNS IMI compared with straw bedding. Quarters of cows that had access to pasture during the sampling period had lower odds of acquiring a new CNS IMI and of having a prevalent CNS IMI. Many practices showed an association with only one of the CNS outcomes and should, therefore, be considered with caution.

Intramammary infections and teat canal colonization with coagulase-negative staphylococci after postmilking teat disinfection: Species-specific responses

Coagulase-negative staphylococci (CNS) are the most common pathogens associated with intramammary infections (IMI) in dairy cows. We hypothesized that postmilking teat disinfection would reduce microbial colonization of the teat canal and thus reduce the prevalence of IMI caused by certain CNS species. The efficacy of iodine postmilking teat dip was tested against CNS colonization of the teat canal, and incidence of IMI was measured. Using an udder-half model, 43 Holstein cows at the Washington State University Dairy were enrolled in the trial; postmilking teat dip was applied to one udder-half, treatment (TX), and the remaining half was an undipped control (CX). Teat canal swabbing and mammary quarter milk samples were taken in duplicate once a week for 16 wk for microbial culture. Isolates from agar cultures were presumptively identified as CNS and then speciated using PCR-RFLP and agarose gel electrophoresis. Colonization of the teat canal and IMI by CNS were assessed. Thirty CNS IMI were diagnosed and the number of new IMI in CX quarters (21) was significantly greater than that in TX mammary quarters (9). The majority of CNS IMI were caused by Staphylococcus chromogenes (30%) and Staphylococcus xylosus (40%), and the latter were appreciably reduced by teat dip. Except for S. xylosus, an association was observed between teat canal colonization and IMI by all CNS species in this study, in which the majority of IMI were preceded by teat canal colonization. The total number of CNS IMI was greater for CX group cows compared with TX group cows. However, the effect of disinfection on IMI did not appear to be the same for all CNS species.

Effect of nonclinical Staphylococcus aureus or coagulase-negative staphylococci intramammary infection during the first month of lactation on somatic cell count and milk yield in heifers

Coagulase-negative staphylococci (CNS) are the most prevalent cause of intramammary infections in heifers around calving, but Staphylococcus aureus should not be ignored because it is also prevalent, contagious, and more likely to persist into lactation. The objective of this study was to determine the effect of a subclinical infection caused by S. aureus or CNS diagnosed during the first month of lactation in heifers on SCC, milk production, and culling risk during the entire first lactation. Data were obtained from a cohort of 50 farms following a mastitis monitoring and control program and subscribing to the animal health record system (DS@HR) through the ambulatory clinic of the Faculté de médecine vétérinaire of the Université de Montréal (St-Hyacinthe, Québec, Canada). This program included routinely collecting a composite milk sample at each farm visit from all recently freshened heifers. A total of 2,273 Holstein heifers were examined. Among the 1,691 heifers meeting the full selection criteria, 90 (5%) were diagnosed with S. aureus, 168 (10%) were diagnosed with CNS, and 153 (9%) were negative (no pathogen isolated). Test-day natural logarithm somatic cell count (lnSCC) was modeled in a repeated measures linear regression model with herd as random effect. The model-adjusted mean lnSCC in S. aureus and CNS groups were significantly higher than in the culture-negative group from 40 to 300 d in milk. At the test-day level, lnSCC in S. aureus and CNS groups were on average 1.2 and 0.6 higher, respectively, than the culture-negative group. A similar model for milk yield showed that mean milk yield was not statistically different between culture groups from 40 to 300 d in milk. The presence of a S. aureus or CNS intramammary infections in the first month of lactation in heifers correlates with future increased SCC over the entire first lactation.

Prevalence of intramammary infection in Dutch dairy herds

A survey was carried out in 2003 in 49 dairy herds to determine the overall and pathogen-specific prevalence of intramammary infection (IMI) in Dutch dairy herds, and to compare the distribution with four studies performed from 1973 to 1985 in The Netherlands. Herds were randomly selected stratified over the 12 Dutch provinces, had at least 40 lactating cows and participated in the Dutch milk recording system. Quarter milk samples were collected from all 408 cows with a somatic cell count (SCC) >or=250,000 cells/ml and 145 heifers with SCC >or=150,000 cells/ml at the last milk test before the farm visit. Additionally, samples were collected from 519 (approximately 25%) of the remaining low-SCC cows and heifers with a SCC at the last milk test before the farm visit of <250 000 and <150 000 cells/ml, respectively. Bacterial growth occurred in 37.3% of milk samples of high-SCC cows and in 21.1% of low-SCC cows. Coagulase-negative staphylococci (CNS) were the most frequently isolated group of bacteria (10.8% of quarters) and were found in all herds. Prevalence of Staphylococcus aureus IMI was lower in 2003 than in 1973, respectively 1.8% and 6.2% of quarters. Prevalence of Streptococcus uberis and Str. dysgalactiae IMI was almost the same in the five samplings during the 30-year period, at 1.1-1.7 and 0.9-1.5%, respectively. Str. agalactiae was not found in this study. Prevalence of CNS IMI was higher in lactating heifers, while prevalence of Str. uberis, Str. dysgalactiae and penicillin-resistant Staph. aureus IMI was higher in older cows. Because distribution of pathogens changes over time, herd-level samples for bacteriological culturing must be taken regularly to monitor udder health. Additionally, national mastitis prevalence studies give important information through monitoring the national udder health status.

Effect of bovine lactoferrin on the internalization of coagulase-negative staphylococci into bovine mammary epithelial cells under in-vitro conditions

Coagulase-negative staphylococci (CNS) have emerged as bovine mastitis pathogens in many countries. CNS mastitis is generally mild but can persist in the udder for long periods. Pathogenesis of CNS intramammary infection is not well understood. In the present study, adhesion, invasion and intracellular replication of twenty-two CNS strains isolated from bovine mastitis and the effect of bovine lactoferrin (bLf) on the internalization were studied in vitro in a bovine mammary epithelial (BME) cell model. The CNS strains were of Staphylococcus chromogenes, Staph. simulans, Staph. epidermidis, Staph. haemolyticus and Staph. cohnii urealyticus; two strains of Staph. aureus were used as controls. Seven of the CNS strains originated from persistent and five from transient mastitis infections. The in-vitro susceptibility of the strains to bLf was also investigated. All CNS species examined had an adhesive ability equal to that of Staph. aureus, but internalization varied among staphylococcal strains. The antagonistic effect of bLf on the adhesion and invasion of CNS strains was weak, but bLf significantly decreased intracellular replication and replication rates of CNS. No correlation between the in-vitro susceptibility of the strain to bLf or internalization among clinical signs of mastitis was established. No difference between the persistent and transient CNS strains in adhesion, invasion or replication rate was recorded. This in-vitro BME cell model can be used to study the virulence potential of mastitis pathogens, although the severity and persistence of eventual infections shall be further investigated in vivo. The role of bLf in intramammary infection caused by CNS may be limited.

Efficacy of vaccination against staphylococcal mastitis: A review and new data

Infection of the heifer mammary gland with common mastitis pathogens, particularly staphylococci, prior to calving is well documented. Efforts to eliminate pre-partum intramammary infections (IMI) in heifers have focused primarily on intramammary antibiotic therapy shortly before or at the time of calving. Few studies have evaluated vaccination of heifers against staphylococcal mastitis. The objectives of the present study were to evaluate the efficacy of a commercially available Staphylococcus aureus bacterin in protecting against staphylococcal IMI ( S. aureus and coagulase-negative staphylococci (CNS)), to study the effect of vaccination on milk SCC, and to evaluate the milk antibody isotype response to vaccination using a lactating cow model. Ninety Holstein–Friesian lactating dairy cows of various parities were systematically assigned to a vaccinated ( n = 44) or control ( n = 46) group. Vaccinates received two 5 ml doses of the bacterin 14 days apart starting on day 0. Quarter milk samples for bacterial culture were collected prior to each vaccination and approximately monthly thereafter for 6 months. Composite milk samples were collected on days 0, 14, 28, 49 and 70 for IgA, IgG 1, IgG 2, and IgM determinations and somatic cell count. No animals in either group developed a new S. aureus IMI after vaccination. The numbers of mammary quarters that developed a new CNS IMI, time to new CNS IMI, milk somatic cell count, and milk antibody isotype sample-to-positive ratio did not significantly differ between groups ( P > 0.05). In a herd with a 3% prevalence of S. aureus IMI and a 30% prevalence of CNS IMI, the vaccine did not reduce the new staphylococcal IMI rate. There may be insufficient vaccine-induced opsonizing antibody in milk to facilitate phagocytosis and clearance of staphylococci from the mammary gland.

CNS mastitis: Nothing to worry about?

In this paper, we analyzed a very large field data set on intramammary infections (IMI) and the associated somatic cell count (SCC) in dairy cows. The objective of the study was to analyze the impact of coagulase-negative staphylococci (CNS) IMI on cow SCC, both mean and variability, and on the potential of these infections to have a major impact on the bulk milk SCC (BMSCC). Data and milk samples for bacterial culture were collected by Quality Milk Production Services (QMPS) between 1992 and March of 2007. The QMPS program services dairy farms in New York State and other states in the Northeastern USA and operates in conjunction with Cornell University. Only records from cows where SCC and milk production data were available, and where only one organism was isolated from bacterial cultures of milk samples (or where culture was negative) were used for this analysis. A total of 352,614 records from 4200 whole herd mastitis screening sampling qualified for this study. Within herds an average of 15% (S.D. 12%) of cows sampled were infected with CNS, ranging between 0 and 100%. Average within herd prevalence of cows with a CNS IMI and an SCC over 200,000 cells/ml was 2% (S.D. 4%) with a minimum of 0% and a maximum of 50%. Results of linear mixed models showed three distinct populations of IMI statuses: negative cultures with the lowest SCC; CNS and Corynebacterium bovis with a moderate increase in SCC, and Streptococcus agalactiae, Streptococcus spp. and Staphylococcus aureus showing an important increase in SCC. Surprisingly, milk production was slightly but significantly higher in CNS infected cows compared to culture-negative cows, whereas it was strongly reduced in cows with a major pathogen IMI. The percentage contribution of CNS infections to the BMSCC was 17.9% in herds with a BMSCC less than 200,000 cells/ml. This value decreased to 11.9 and 7.9% in herds with bulk milk SCC between 200,000 and 400,000 and over 400,000 cells/ml, respectively. We concluded that very few herds with milk quality problems would have an important increase in BMSCC that could be mostly attributed to CNS infections. On the other hand, in herds with low BMSCC, CNS infections may be an important contributor to the total number of somatic cells in the bulk milk.

Prevalence and herd-level risk factors for intramammary infection with coagulase-negative staphylococci in Dutch dairy herds

In this study, the prevalence of intramammary infection (IMI) with coagulase-negative staphylococci (CNS) in The Netherlands was estimated on 49 randomly selected herds with at least 40 lactating cows. In total, 4220 quarter milk samples were collected. The prevalence of CNS IMI in The Netherlands was estimated at 10.8% at quarter level and 34.4% at cow level, making it the most frequently isolated group of pathogens. Fourteen species of CNS were identified; the most frequently isolated species was Staphylococcus chromogenes (30.3%) followed by Staphylococcus epidermidis (12.9%) and Staphylococcus capitis (11.0%). Prevalence of CNS IMI was higher in heifers compared to older cows. Geometric mean quarter SCC of CNS-positive quarters was 109,000 cells/ml, which was approximately twice as high as culture-negative quarters. Quarters infected with S. chromogenes, S. capitis and Staphylococcus xylosus had a higher SCC ( P < 0.05) than culture-negative quarters, while quarters that were culture-positive for S. epidermidis and Staphylococcus hyicus tended to have a higher SCC than culture-negative quarters. An increased prevalence of CNS IMI was associated with the herd-level variables source of drinking water not being tap water, housing of dry cows in one group instead of multiple groups, measurement of cow SCC every month, udder health monitoring by the veterinarian, pasturing during outdoor season, percentage of stalls contaminated with milk, and BMSCC > 250,000 cells/ml. Although a causal relation between these factors and prevalence of CNS is not proven and for some factors not even likely, knowledge of the associations found may be helpful when approaching CNS problems on dairy farms.

Species identification of coagulase-negative staphylococci: Genotyping is superior to phenotyping

Coagulase-negative staphylococci (CNS) are isolated commonly from bovine milk and skin. Their impact on udder health and milk quality is debated. It has been suggested that sources and consequences of infection may differ between CNS species. Species-specific knowledge of the impact and epidemiology of CNS intramammary infections is necessary to evaluate whether species-specific infection control measures are feasible and economically justified. Accurate measurement of impact, sources, and transmission mechanisms requires accurate species level identification of CNS. Several phenotypic and genotypic methods for identification of CNS species are available. Many methods were developed for use in human medicine, and their ability to identify bovine CNS isolates varies. Typeability and accuracy of typing methods are affected by the distribution of CNS species and strains in different host species, and by the ability of test systems to incorporate information on new CNS species into their experimental design and reference database. Generally, typeability and accuracy of bovine CNS identification are higher for genotypic methods than for phenotypic methods. As reviewed in this paper, DNA sequence-based species identification of CNS is currently the most accurate species identification method available because it has the largest reference database, and because a universally meaningful quantitative measure of homology with known species is determined. Once sources, transmission mechanisms, and impact of different CNS species on cow health, productivity and milk quality have been identified through use of epidemiological data and accurate species identification methods, appropriate methods for routine use in research and diagnostic laboratories can be proposed.

Coagulase-negative staphylococcal intramammary infections in cows and heifers during the nonlactating and periparturient periods.

Coagulase-negative staphylococci (CNS) are isolated frequently from unbred and primigravid heifers and from lactating and nonlactating dairy cows. The importance of CNS intramammary infections that occur during the nonlactating period has not been adequately delineated. Mammary secretions from udders infected with CNS during early lactation and the nonlactating period have increased somatic cell counts, CNS have been isolated in mammary secretions from cows with clinical mastitis, and a few studies have indicated that CNS infected mammary glands produced significantly less milk during lactation than uninfected mammary glands. In addition, mammary glands of postpubertal heifers infected with CNS were not as well developed as uninfected mammary glands. Consequently, CNS intramammary infections in heifers and cows during the nonlactating period could impair mammary gland growth and development and ultimately influence mammary function during lactation resulting in decreased lactational performance. Some CNS IMI detected in heifers and multiparous cows at calving do not persist into early lactation. Postmilking teat disinfection with an effective germicide and antibiotic therapy during the nonlactating period markedly reduces the prevalence of CNS in dairy herds. Methods of controlling CNS infections in primigravid heifers based on prepartum intramammary antibiotic therapy have been developed, and results have shown that prepartum antibiotic therapy is very effective against CNS and other mastitis pathogens as well. Additional research is required to determine the influence of CNS infections that occur during the nonlactating period on milk yield in the subsequent lactation.

Mastitis in a flock of milking sheep

Milk samples were aseptically collected from 62 ewes at lambing from a flock of about 400 machine-milked Dorset and Polypay sheep. Of these, 24 ewes were sampled again at weaning upon entry into the milking group. An additional 18 ewes with clinical mastitis were sampled during lactation. Somatic cell counting was done on the milk from 59 ewes in the milking group. At lambing, milk from 29% of the ewes tested was culture-positive. Unilateral infections predominated. Coagulase-negative staphylococci (CNS) were found in 88% of the samples. Of the ewes sampled at both lambing and weaning, 33% were free of intramammary infections (IMI), 38% developed IMI during this period, 21% had spontaneous cures, and 8% had CNS IMI at lambing but were infected with coagulase-positive staphylococci (CPS) at weaning. Of the milking ewes with clinical mastitis, CPS were isolated in 66% of the milk samples while 22% had no growth. Nearly 90% of the milk samples had somatic cell counts of under 200 000 cells ml −1. The reason for the high incidence of CPS clinical mastitis in the milking group was not determined. Somatic cell counts in this milking flock of sheep were similar in magnitude to those found in non-mastitic dairy cows but lower than those for milking goats. This suggests that somatic cell count standards for cow milk could probably be applied to sheep milk. The somatic cell counts indicated a low level of IMI in this milking flock, reflective of the preventive mastitis measures used.