Environmental Streptococci Research Articles

Association between Mastitis Occurrence in Dairy Cows and Bedding Characteristics of Compost-Bedded Pack Barns.

Compost-bedded pack barns (CB) are receiving increasing attention as a housing system that can potentially improve the welfare of dairy cows. This study characterized the frequency and profile of pathogens isolated from clinical (CM) and subclinical (SCM) mastitis in dairy cows housed in CB. It evaluated the association between mastitis occurrence and bedding characteristics in CB systems. Over six months, seven dairy herds were visited monthly for milk and bedding sample collections. Milk samples from mastitis cases were submitted to microbiological identification by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF MS). Bedding samples were submitted to physical-chemical (pH, organic matter, moisture, and carbon to nitrogen ratio) and microbiological counting (total bacterial counts, coliforms, streptococci, and staphylococci) analyses. Regression analysis was used to determine the association between mastitis occurrence and CB characteristics. Our results showed that Escherichia coli and environmental streptococci were the most frequently isolated pathogens from CM cases, while Staphylococcus chromogenes and contagious pathogens (Staphylococcus aureus and Streptococcus agalactiae) were the most commonly isolated from SCM cases. Bedding moisture content was positively associated with the incidence of CM. The bedding carbon to nitrogen ratio was negatively associated with the incidence of SCM, and the bedding total bacteria counts tended to be associated with the incidence of SCM. Bedding counts of coliforms positively associated with the prevalence of SCM. Our results can support decision-makers in the dairy industry seeking strategies for bedding management and mastitis control.

Clinical field trial of parenteral amoxicillin for the treatment of clinical and subclinical mastitis in smallholder dairy farms in the upper region of Northern Thailand.

Mastitis, primarily caused by intramammary bacterial infection, is the most expensive disease in the global dairy industry due to its negative impact on milk composition and manufacturing properties. This study aimed to evaluate the efficacy of parenteral amoxicillin in the treatment of clinical and subclinical mastitis in smallholder dairy farms in Northern Thailand. A total of 51 cows with clinical and subclinical mastitis from dairy cooperatives in Lamphun and Chiang Mai provinces, Northern Thailand, were enrolled in this study. Conventional bacteriological procedures were applied to identify the causative bacteria in milk samples from these cows before and 7 days after treatment, and antibiotic susceptibility tests were conducted using the disk diffusion method for all bacteria isolated before treatment. All cows with mastitis were administered 15 mg/kg of amoxicillin (LONGAMOX®, Syva Laboratories SA, Spain) intramuscularly every other day for 3 days. Environmental streptococcal bacteria (Streptococcus uberis and Streptococcus spp.) were commonly isolated from infected quarters and were highly susceptible to amoxicillin (100%). The clinical efficacy of amoxicillin treatment for clinical mastitis cases was 80.43%, and the bacteriological efficacy was 47.82%, with opportunistic staphylococcal bacteria (coagulase-negative staphylococci) and contagious streptococcal bacteria (Streptococcus agalactiae) being the most sensitive microorganisms (100%). In subclinical mastitis cases, the bacteriological efficacy of parenteral amoxicillin was 70.45%, with environmental streptococcal bacteria (S. uberis) being the most (100%) sensitive microorganisms. Amoxicillin is highly efficacious and can be used to treat clinical and subclinical mastitis in dairy cows, particularly mastitis caused by environmental Streptococcus spp. These findings could be used to guide treatment regimens in veterinary practice in smallholder dairy farms in Thailand.

Mastite bovina por Mycobacteroides abscessus - relato de caso

ABSTRACT Mastitis is considered the main disease that affects dairy cattle worldwide, and it is caused mainly by Staphylococcus aureus and environmental Streptococcus spp. Eventually, nonconventional pathogens, as rapidly growing mycobacteria(RGM), may also cause chronic mastitis, which will not be responsive to antibiotic treatments. Diagnosis of mastitis caused by RGM is a difficult task, and most of time this agent may be misdiagnosed. Here we describe a case of clinical mastitis caused by the RGM Mycobacteroides abscessus in a cow from Southern Brazil, confirmed by microbiological and molecular characterization. Our results reinforce the necessity of a detailed laboratorial identification of the agent and to include this agent in differential diagnosis of chronical clinical mastitis nonresponsive to treatment.

QSAR, Docking, and Molecular Dynamics Simulation Studies of Sigmacidins as Antimicrobials against Streptococci.

Streptococci are a family of bacterial species significantly affecting human health. In addition, environmental Streptococci represent one of the major causes of diverse livestock diseases. Due to antimicrobial resistance, there is an urgent need for novel antimicrobial agent discovery against Streptococci. We discovered a class of benzoic acid derivatives named sigmacidins inhibiting the bacterial RNA polymerase-σ factor interaction and demonstrating excellent antimicrobial activity against Streptococci. In this work, a combinational computer approach was applied to gain insight into the structural basis and mechanism of action of sigmacidins as antimicrobials against Streptococcus pneumoniae. Both two- and three-dimensional quantitative structure-active relationships (2D and 3D QSAR) of sigmacidins displayed good predictive ability. Moreover, molecular docking and molecular dynamics simulation studies disclosed possible contacts between the inhibitors and the protein. The results obtained in this study provided understanding and new directions to the further optimizations of sigmacidins as novel antimicrobials.

Antimicrobial resistance studies in staphylococci and streptococci isolated from cows with mastitis in Argentina.

Staphylococcus aureus and Streptococcus agalactiae are the main cause of clinical mastitis in dairy cattle in Argentina, whereas coagulase-negative staphylococci (CNS) and environmental streptococci are the main cause of subclinical mastitis. Bacteria isolated from infected animals show increasing antimicrobial resistance. This study aims to determine the antimicrobial resistance of staphylococci and streptococci isolated from milk with mastitis, and to genotypically characterize the methicillin-resistant (MR) staphylococci. Isolation was performed on blood agar and identification was based on biochemical reactions. Antimicrobial susceptibility was according to the Clinical and Laboratory Standards Institute guidelines. The antimicrobial resistance genes, SCCmec type and spa type were detected by the polymerase chain reaction method. We isolated a total of 185 staphylococci and 28 streptococci from 148 milk samples. Among the staphylococcal isolates, 154 were identified as CNS and 31 as S. aureus. Among the 154 CNS, 24.6% (n = 38) were resistant to penicillin, 14.9% (n = 23) to erythromycin, 17.5% (n = 27) to clindamycin, 6.5% (n = 10) to cefoxitin and oxacillin. Among the S. aureus isolates, 16.1% (n = 5) were resistant to penicillin, 3.2% (n = 1) to cefoxitin and oxacillin (MRSA). Six MR isolates (5 CNS and 1 MRSA) were positive to the mecA gene, and presented the SCCmec IVa. The MRSA strain presented the sequence type 83 and the spa type 002. Among the 28 streptococcal isolates, 14.3% (n = 4) were resistant to penicillin, 10.7% (n = 3) to erythromycin and 14.3% (n = 4) to clindamycin. The present findings of this study indicate a development of antimicrobial resistance in main bacteria isolated from cows with mastitis in Argentina.

Characterisation of Clinical Mastitis Occurring in a Dairy Herd of Holstein Friesian Cows

The objective of the present study were to characterize clinical mastitis (CM) occurring in a dairy herd of Holstein Friesian cows located at Agricultural Research and Development Station (ARDS) Simnic-Craiova, Romania (182 m above sea level, 4°19’N and 23°48’E). The severity of CM was classified as grade 1 – when only the milk was abnormal, grade 2 – when abnormal milk was accompanied by swelling or redness of mammary gland and grade 3 – when the cow exhibited systemic signs of illness such as depression, anorexia, dehydration or fever. Only grade 1 and grade 2 of clinical mastitis were analysed in this study. Duplicate quarter milk samples from affected quarters when collected before treatment (Pre-treatment). After the collection, cows were treated using the form protocol. A second set of duplicate quarter milk sample were collected from enrolled quarters at 14 to 21 days after the end of treatment (Post-treatment). Cow level follow-up data was collected for 90 days after the enrolment. Microbiological diagnosis at enrolment included gram-negative, gram-positive and no growth. Data was collected between December 2016 and November 2020, of the 58 cases of CM only 52 cases of grade 1 (n=35) and grade 2 (n=17) were used in analysis. Six cases of CM were of grade 3 (not used in this study). Most causes of CM included in this study were caused by Gram-negative pathogens followed by gram positive pathogens. The common pathogens were E. coli, environmental streptococci Enterobacter spp. and coagulase-negative streptococci. Treatment cure was greater for Gram- negative pathogens. Identification of pathogens causing CM or severity is important in strategic treatment decisions.

Interrelationship of milk acute-phase proteins and casein percentage in cows and buffaloes subclinical mastitis.

A total number of 62 clinically healthy dairy animals of three farms located in Kafr El Sheikh governorate, Egypt, were subjected to field screening surveys of subclinical mastitis (SCM) using California mastitis test (CMT). The obtained results revealed that 38.80% of quarter milk samples were positive to CMT. The most frequently major causative agents isolated from the positive CMT samples were Escherichia coli, Staphylococcus aureus, and environmental streptococcus spp. Acute-phase proteins (APPs), as immunological biomarkers for SCM, including milk serum amyloid A (mSAA) and haptoglobin (Hp) were measured using ELISA. A significant positive correlation was found between the severity of the mammary infection of cow's quarter milk samples represented in somatic cell count (SCC) and each of APPs and pH values. The correlation coefficient (R) between SCC and mSAA, Hp and pH were 0.54, 0.38 and 0.73, respectively. On the other hand, there was a significant negative correlation between casein percentage in milk of SCM cases, and each of APPs, pH and the presence of bacterial pathogens in the milk samples. The obtained results threw light on the inter-relationship between SCC, mSAA, pH value and casein percentage in milk of cows and buffalo suffered from SCM. The percentage of casein in milk is considered a significant accurate tool for diagnosis of SCM and this finding offers the farmers a cheap and fast selection for diagnosis of such disease. These results presented a specific structured view on the efficacy of different diagnostic tools of SCM in dairy herds.

Bacterial pathogens associated with clinical and subclinical mastitis in a Mediterranean pasture-based dairy production system of Australia

Mastitis is an economically important production disease in the dairy industry worldwide. There is limited information on the aetiology of clinical mastitis (CM) and subclinical mastitis (SCM) in Australia's Mediterranean pasture-based production system. A prospective study was conducted in the south-west region of Western Australia to characterise the bacterial pathogens associated with CM and SCM cases and their associated antimicrobial susceptibility profiles. A total of 102 CM and 132 SCM milk samples were collected in twelve dairy farms between April 2020 and September 2020 recovering a total of 310 bacterial isolates. The isolates were evaluated for their antimicrobial susceptibility to twelve antibiotics using the agar disk diffusion (ADD) method. The most common pathogens associated with CM was Bacillus spp. (35.29%), followed by coagulase-negative staphylococci (CNS) (22.55%), Pseudomonas spp. (19.61%), Staphylococcus aureus (10.78%), Escherichia coli (5.88%) and Streptococcus uberis (2.94%). The most common pathogens associated with SCM was CNS (44.70%), followed by Bacillus spp. (30.30%), S. aureus (20.45%), Strep. uberis (15.91%), coliforms (Citrobacter spp., Cronobacter spp., Enterobacter spp., Klebsiella spp., Kosakonia spp., Morganella spp., Serratia spp.) (9.86%), environmental Streptococci (6.06%) and E. coli (6.06%). Beta-lactams resistance was the most common resistance observed in the Staphylococcal isolates and a high proportion of Streptococcal isolates exhibited resistance to enrofloxacin. Overall, the proportion of bacterial pathogens isolated in this study was comparable to the figures reported in other studies in Australia. Future research should focus on risk factors and the determination of resistant genetic components among the common isolates.

Environmental Streptococcus uberis Associated with Clinical Mastitis in Dairy Cows: Virulence Traits, Antimicrobial and Biocide Resistance, and Epidemiological Typing.

Simple SummaryMastitis remains one of dairy cattle’s most perplexing and expensive diseases. This study is the first to look into the virulence traits, antimicrobial and biocide resistance, and epidemiological typing of Streptococcus uberis (S. uberis) isolated from bovine clinical mastitis in dairy farms of diverse hygienic interventions in Egypt. The overall S. uberis infection rate was 20.59%; all were multidrug-resistant (MDR). The sua gene was the most frequent virulence gene (42.02%), followed by pauA (40.57%), cfu (21.73%), skc (20.28%), and opp (11.59%). The erm(B) gene serves as the predominant antimicrobial-resistant gene (75.36%), followed by fexA (52.63%) and tet(M), blaZ, and aac(6′)aph(2″) genes (46.38% each). Of note, 79.71% of S. uberis isolates carried qac genes; among them, 55 (79.71%), 54 (78.26%), and 13 (18.84%) harbored qacED1, qacC/D, and qacA/B genes, respectively. Restriction fragment length polymorphism–polymerase chain reaction (RFLP–PCR) indicated that all analyzed isolates were S. uberis type I by their unique RFLP pattern. This study shows a significant variation in the occurrence of virulent S. uberis in dairy cows with clinical mastitis regarding the prospective hygienic concerns. Furthermore, MDR coupled with the existence of biocide resistance genes indicates the importance of S. uberis surveillance and the prudent use of antimicrobials in veterinary clinical medicine to avoid the dissemination of antimicrobial resistance.Mastitis remains a serious problem for dairy animals. The misappropriation of antimicrobial agents helps accelerate resistance, which poses a serious challenge in controlling environmental S. uberis infection. Here, we study the virulence attributes, antimicrobial and biocide resistance, and epidemiological typing of S. uberis recovered from bovine clinical mastitis in dairy farms of diverse hygienic interventions in Egypt. The overall S. uberis infection rate was 20.59%; all were multidrug-resistant (MDR). The sua gene was the most frequent virulence gene (42.02%), followed by pauA (40.57%), cfu (21.73%), skc (20.28%), and opp (11.59%). The erm(B) gene served as the predominant antimicrobial-resistant gene (75.36%), followed by fexA (52.63%) and tet(M), blaZ, and aac(6′)aph(2″) genes (46.38% each). Of note, 79.71%, 78.26%, and 18.84% of S. uberis isolates harbored qacED1, qacC/D, and qacA/B genes, respectively. All analyzed isolates were S. uberis type I by their unique RFLP–PCR pattern. In conclusion, the sustained presence of pauA and sua genes throughout the investigated farms contributes to a better understanding of the bacterium’s pathogenicity. Furthermore, MDR coupled with the existence of biocide resistance genes indicates the importance of S. uberis surveillance and the prudent use of antimicrobials in veterinary clinical medicine to avoid the dissemination of antimicrobial resistance.

Pathogen effects on milk yield and composition in chronic subclinical mastitis in dairy cows

This study aimed to evaluate the effects of chronic subclinical mastitis (CSM) on milk production and component yields in dairy cows. A total of six herds located in the Midwest area of São Paulo State, Brazil were selected. Herds were visited once every 2 weeks to measure milk yield and to collect milk samples from lactating Holstein cows. Milk samples were collected at two stages (1 and 2), and each stage comprised three milk samplings. In stage 1, a total of 117 of 647 cows were diagnosed with CSM based on at least two of three repeated somatic cell counts (SCC) > 2000,000 cells/mL and positive bacterial milk culture results (BC). Cows with CSM were selected for the second stage. In stage 2, selected cows had quarter sampling aseptically collected for BC analyses prior to milking, and quarter milk yield was measured. Milk components (total protein, fat, lactose, and total solids) were measured using mid-infrared spectroscopy. Mammary quarters were considered healthy if all three repeated SCC results were ≤ 200,000 cells/mL and no bacterial growth was detected on BC. All quarters with positive bacterial growth were classified as having (non-chronic) subclinical mastitis when only one of three SCC results were > 200,000 cells/mL, and CSM when at least two of three SCC results were > 200,000 cells/mL. The effects of CSM by type of pathogen on milk and components yield were assessed using a linear mixed model.Mammary quarters with CSM caused by major pathogens had milk loss of 1.1 kg/quarter milking in comparison to healthy quarters. Milk losses were 0.8 and 1.3 kg/quarter milking when CSM was caused by Staphylococcus aureus or environmental streptococci, respectively. In addition, healthy quarters produced more milk components than quarters with CSM caused by major pathogens. Minor pathogens causing CSM (non-aureus staphylococci and Corynebacterium spp.) had no effect on milk yield. Quarters with CSM had lower milk and component yields when compared with healthy quarters. Milk losses varied according to the type of pathogen and were higher when associated with major pathogens such as S. aureus and environmental streptococci compared with healthy quarters.

Influence of pathogens causing clinical mastitis on reproductive variables of dairy cows

In dairy cattle, mastitis is a disease of the mammary gland caused by pathogens such as bacteria, viruses, fungi, and algae. Mastitis causes economic losses to dairy farms as well as public health concerns. The reproductive efficiency of commercial dairy herds has important implications for the economic success of dairy operations and is strongly associated with the health status of cows. Mastitis has previously been linked with decreased fertility of dairy cows, but the effect of specific pathogens on the severity of fertility reduction is still unclear. In this study, cows diagnosed with mastitis caused by major pathogens (Staphylococcus aureus, Streptococcus agalactiae, Escherichia coli, Klebsiella spp., Mycoplasma spp., and environmental Streptococcus) needed more artificial inseminations (AI) than did cows with mastitis caused by minor pathogens (coagulase-negative Staphylococcus and Corynebacterium spp.) and healthy cows. Cows diagnosed with mastitis, independent of what pathogen was causing mastitis, had more days open compared with nonmastitic cows. The percentage of cows that successfully established pregnancy at first AI was greater for the control group than for the major pathogens group but not significantly different from the minor pathogens group. Pregnancy loss was lower in the control group than in the major pathogens group; however, there was no difference compared with the minor pathogen group. Mastitis caused by gram-negative bacteria decreased the percentage of pregnancy per first AI and increased days open and pregnancy loss compared with the control group. Cows with mastitis caused by gram-positive bacteria also had increased days open compared with control cows. This study shows that different mastitis-causing bacteria can affect the fertility of cows differently. Mastitis events caused by major pathogens and gram-negative bacteria were associated with the greatest decrease in reproductive efficiency.

Effects of intramammary infusion of Bifidobacterium breve on mastitis pathogens and somatic cell response in quarters from dairy cows with chronic subclinical mastitis.

The present study assessed the effects of intramammary infusion of Bifidobacterium breve (B. breve) on mastitis-causing pathogens and on the somatic cell counts (SCC) in lactating cows with chronic subclinical mastitis. The bacteriological cure rates of 42 quarters from 42 cows infected with Staphylococcus aureus, Corynebacterium bovis, coagulase-negative staphylococci, and environmental streptococci were 18.2% (2/11), 14.3% (1/7), 58.8% (10/17), and 28.6% (2/7), respectively, on day 14 after B. breve infusion. In a second trial, B. breve was infused into 18 quarters from 18 cows with chronic subclinical mastitis from which pathogens had not been isolated; the rates of quarters showing SCC>50×104 cells/ml prior to B. breve infusion that decreased to<30×104 cells/ml after infusion were significantly (p <.01) increased to 61.1% (11/18) on day 14 compared to that prior to infusion (0/18). The intramammary infusion of B. breve appears to be a non-antibiotic approach for elimination of minor pathogens and decreasing SCC in quarters with chronic subclinical mastitis in dairy cows.

Frequency of microorganisms isolated at different stages of lactation and milk production loss associated with somatic cell count and to mastitis-causing pathogens

ABSTRACT The aim of this study was to evaluate the frequency of isolation of agents causing subclinical mastitis in a herd and to estimate production losses associated with SCC&gt; 200,000cells/mL. Three 7-day interval microbiological cultures were performed in all lactating animals from the same farm that was evaluated from June to July. To evaluate the negative and positive isolation frequencies between the lactation phases, a Chi-square test was performed. Simple linear regressions were performed to evaluate the lactation curve of animals grouped by pathogens isolated from negative cows in the microbiological culture and with SCC &lt;200,000cells/mL. To estimate the production losses between the groups, regression coefficients were used. Results found in this experiment were: Culture-negative cows with SCC ≥ 200,000cells/mL, cows testing positive in milk culture, with SCC &lt;200,000cells/mL and cows testing positive in milk culture, with SCC ≥ 200,000cells/mL. Milk production was -3.5; -0.5 and -4.27kg, respectively, when compared to culture-negative cows with SCC &lt;200,000cells/mL. Cows infected with yeast cells, Coagulase-negative staphylococci (CNS), Staphylococcus aureus and environmental streptococci produced -3.42; -0.5; -0.168 and -2.5kg of milk when compared to culture-negative cows with SCC &lt;200,000cells/mL. SCC indicates an inflammatory reaction in the mammary gland and it is directly associated with milk production losses and with presence of microorganisms in the mammary gland.

Bovine subclinical mastitis reduces milk yield and economic return

The effect of different pathogens was studied by evaluating the contralateral (healthy and infected) mammary quarters of 146 lactating cows. The impact of SM on economic return (quarter milk yield × milk price) was determined by applying milk payment estimates on milk collected from healthy vs. infected glands. Cows were considered infected when they had at least 2 out of 3 weekly composite SCC results > 200 × 103 cells/mL and a microbiological culture (MC) positive result from composite foremilk samples, collected in the third week of sampling. Infected cows were evaluated a second time within 15 days and had milk yield measured at the quarter level and foremilk samples collected by aseptic technique for analysis of MC, milk composition and SCC. Of the 611-composite milk samples, 397 (65%) were culture-negative, and 214 (35%) were culture-positive and the most frequent isolated bacteria were Corynebacterium spp. (7.9%), coagulase negative staphylococci (5.8%), Staphylococcus aureus (5.3%), Streptococcus uberis (4.6%), Streptococcus agalactiae (3.9%), other environmental streptococci (2.4%), Gram-negative isolates (2.4%), Enterococcus spp. (1.4%) and Streptococcus dysgalactiae (0.7%). A total of 55 pairs of healthy contralateral quarters (control) were compared, and no difference was observed between them when evaluating SCC, milk yield, fat and protein concentration and economic return. A total of 124 pairs of healthy had lower SCC (274.9 × 103 cells/mL) than infected contralateral quarters (SCC of 1038.5 × 103 cells/mL). At the quarter level, IMI caused by minor pathogens had no effect on SCC, milk yield and economic return. Subclinical mastitis caused by contagious and environmental pathogens increased SCC and decreased milk yield when compared with healthy contralateral quarters. Moreover, quarters infected by contagious pathogens had increased concentrations of milk protein and fat when compared with healthy contralateral quarters. Therefore, the milk economic return was lower in quarters with SM caused by environmental pathogens (US$ 0.18/quarter.milking) and contagious (US$ 0.22/quarter.milking) when compared with healthy contralateral quarters. The milk losses ranged from 0.07 kg/quarter.milking to 1.4 kg/quarter.milking and the economic losses ranged from US$ 0.02–0.4/quarter.milking according to the pathogen causing SM.

An investigation of risk factors for two successive cases of clinical mastitis in the same lactation

The objective of this study was to identify risk factors for the occurrence of two successive cases of clinical mastitis (CM). Two farms were visited monthly during 10 months. Milk samples were collected from all cases of CM that occurred during the study. Cows were observed prospectively from the beginning of the study and a case cow was defined when she experienced the second case of CM within the same lactation. For each case cow, 3 control cows matched by days in milk (DIM) were randomly selected from the cohort of cows who did not experience CM. On each visit day, a series of udder and teat characteristics were recorded during milking time: teat-end hyperkeratosis scoring, milking ease scoring, teat length and diameter, teat-to-ground distance, and udder position in relation to the hock. A total of 113 case cows and 324 control cows were used for analyses. The median time to occurrence of the first case of CM was 84 DIM and the median interval between the first and second cases of CM was 39 days. Of all second cases, 49.6% (N=55) occurred in the same mammary gland. Of these 55 cases, 29.1% had identical milk culture results from both first and second cases. Most cases of CM were caused by coliforms and environmental streptococci. Teat-to-ground distance, teat-end hyperkeratosis, udder position in relation to the hock, milking ease, parity, and milk production at the first test of lactation were individually associated with the occurrence of two successive cases of CM. Of all explanatory variables, 3 remained in the final multivariable model. The odds of two successive cases of CM were 3.7 times greater for cows who were “very easy to milk”, as compared with cows who were “difficult to milk”. Cows who had their udders below the hock, and those of parity >2 were 3.6 and 2.5 times more likely to experience two successive cases of CM, as compared with cows whose udder was positioned above the hock, and cows of parity 1, respectively. Findings of this study highlight the importance of teat and udder characteristics as risk factors for two successive cases of CM. Further investigations are needed to elucidate the role of the teat canal in preventing mastitis for modern cows that have been selected for increased milk production, shorter teats, and greater milk flow rates.

Identification of factors influencing teat dip efficacy trial results by meta-analysis.

Two meta-analyses were conducted using data from peer-reviewed natural exposure (NE) and experimental challenge (EC) teat dip efficacy trials to identify factors influencing the new intramammary infection (IMI) rate. A NE data set containing 16 studies and an EC data set containing 21 studies were created. New IMI rate was calculated based on the percentage of new quarter infections per month (PNQI/mo) for each observation, in both data sets, and used as the dependent variable for model derivation. A linear, mixed-effects model with a random study effect, weighted by number of quarters eligible for infection, was derived for each data set. The final NE model included the effects of experimental design (split herd or split udder), mastitis pathogen group (Staphylococcus aureus, Streptococcus agalactiae, environmental streptococci, gram-negative species, Corynebacterium spp., or coagulase-negative staphylococci), postmilking treatment (iodine, chlorhexidine, linear dodecyl benzene sulfonic acid, chlorine compounds, phenol compounds, or undipped negative controls), and the interaction between mastitis pathogen group and postmilking treatment. Overall, Corynebacterium spp. had the highest new IMI rate (0.0139±0.0018 PNQI/mo), and environmental streptococci and gram-negative species had the lowest (0.0023±0.0022 PNQI/mo). Additionally, trials utilizing a split herd experimental design had a 2-fold higher new IMI rate than trials using a split udder design. The final EC model included the effects of mastitis pathogen (Staph. aureus and Strep. agalactiae), postmilking treatment (iodine, chlorine compounds, "other" active ingredients, or undipped negative controls), geographic region of study (Eastern, Southern, and Pacific Northwest), and the 2-way interactions of region and pathogen group and postmilking treatment and pathogen group. Overall, Staph. aureus and Strep. agalactiae had similar new IMI rates. Quarters dipped postmilking in either iodine (0.0127±0.0099 PNQI/mo), chlorine compounds (0.0258±0.0095 PNQI/mo), or "other" active ingredient teat dips (0.0263±0.0106 PNQI/mo) had lower new IMI rates than undipped quarters (0.0859±0.0087 PNQI/mo). These results indicate that experimental design influences the new IMI rate of teat dip efficacy trials and that using an effective postmilking teat dip has a greater effect on controlling the new Staph. aureus and Strep. agalactiae IMI rate than the teat dip's active ingredient.

0155 The treatment of only environmental Streptococci clinical mastitis cases reduced antibiotic use, days out of the tank, recurrence of clinical mastitis and a tendency to reduce culling

The objective was to compare antibiotic use and clinical and bacteriological outcomes for selective treatment of only clinical cases where environmental streptococci were isolated vs blanket therapy.

The treatment of only environmental streptococci clinical mastitis cases reduced antibiotic use, days out of the tank, recurrence of clinical mastitis and a tendency to reduce culling

The objective was to compare antibiotic use and clinical and bacteriological outcomes for selective treatment of only clinical cases where environmental streptococci were isolated vs blanket therapy.

Antimicrobial Susceptibility Patterns of Environmental Streptococci Recovered from Bovine Milk Samples in the Maritime Provinces of Canada.

Determination of antimicrobial susceptibility of bovine mastitis pathogens is important for guiding antimicrobial treatment decisions and for the detection of emerging resistance. Environmental streptococci are ubiquitous in the farm environment and are a frequent cause of mastitis in dairy cows. The aim of the study was to determine patterns of antimicrobial susceptibility among species of environmental streptococci isolated from dairy cows in the Maritime Provinces of Canada. The collection consisted of 192 isolates identified in milk samples collected from 177 cows originating from 18 dairy herds. Results were aggregated into: (1) Streptococcus uberis (n = 70), (2) Streptococcus dysgalactiae (n = 28), (3) other Streptococci spp. (n = 35), (4), Lactococcus spp. (n = 32), and (5) Enterococcus spp. (n = 27). Minimum inhibitory concentrations (MICs) were determined using the Sensititre microdilution system and mastitis plate format. Multilevel logistic regression models were used to analyze the data, with antimicrobial susceptibility as the outcome. The proportion of susceptible S. uberis ranged from 23% (for penicillin) to 99% (for penicillin/novobiocin), with a median of 82%. All S. dysgalactiae were susceptible to all antimicrobials except for penicillin (93% susceptible) and tetracycline (18% susceptible). The range of susceptibility for other Streptococcus spp. was 43% (for tetracycline) to 100%, with a median percent susceptibility of 92%. Lactococcus spp. isolates displayed percent susceptibilities ranging from 0% (for penicillin) to 97% (for erythromycin), median 75%. For the antimicrobials tested, the minimum inhibitory concentrations were higher for Enterococcus spp. than for the other species. According to the multilevel models, there was a significant interaction between antimicrobial and bacterial species, indicating that susceptibility against a particular antimicrobial varied among the species of environmental streptococci and vice versa. Generally, susceptibility decreased with increasing within-herd average somatic cell count, isolates recovered in mid-lactation were more susceptible than isolates recovered in early lactation, and isolates recovered in samples collected post-clinical mastitis were more susceptible than isolates recovered from non-clinical lactating quarters. The results of this research support continued susceptibility of environmental streptococci to beta-lactam antimicrobials. A departure from the expected susceptibility to beta-lactams was the apparent reduced susceptibility of S. uberis to penicillin.

Factors associated with mastitis epidemiologic indexes, animal hygiene, and bulk milk bacterial concentrations in dairy herds housed on compost bedding

The primary objective of this study was to identify compost bedding characteristics associated with mastitis epidemiologic indexes, cow cleanliness, and concentration of selected bacterial populations found in bulk tank milk. Secondary objectives were to monitor the occurrence of environmental mastitis outbreaks, and to describe the profile of pathogens isolated from mastitis cases of cows housed in the CBP system. Three dairies were visited monthly during 1 year. On each visit day, milk samples were collected from the bulk tank and from a sample of mammary quarters for microbiological examination. Milk samples were collected from all cases of clinical mastitis. Flank, leg, udder, and teat cleanliness were assessed using a score chart based on a 4-point scale (1=clean to 4=very dirty). Bedding samples were collected to estimate concentrations of total bacteria, streptococci, and coliforms, moisture, organic matter, carbon–nitrogen ratio, pH, and density. Mixed models were used to identify factors associated with incidence and prevalence of mastitis, and cow cleanliness. Except for farm A, on which contagious pathogens caused most cases, Escherichia coli, coagulase-negative staphylococci, and environmental streptococci were the most frequent pathogens isolated from clinical mastitis cases. Corynebacterium bovis was the most frequent pathogen isolated from subclinical cases of farms B (17.6) and C (26.0%). Environmental pathogens were isolated from 17.2%, 10.1%, and 14.8% of all subclinical cases of farms, A, B, and C, respectively. No outbreaks of environmental mastitis were observed during the course of the study. Bedding moisture, carbon–nitrogen ratio, pH, and dry density were unconditionally associated with the incidence of environmental clinical mastitis. Nonetheless, bedding moisture remained as a sole predictor in the final model. The odds of a case of environmental clinical mastitis increased 5.7% for each one-unit increase in bedding moisture. The odds of a new case of subclinical mastitis, and of a cow having SCC ≥200,000cells/mL increased 32% and 16% for each one-unit increase in leg cleanliness score, respectively. Overall means for udder, teat, flank, and leg hygiene scores were less than 2.1 for all farms and did not vary among seasons of the year. Bedding wet density was positively associated with all cleanliness scores and bulk milk concentration of total bacteria. Results suggest that managing bedding to remain dry and loose will result in cleaner animals with decreased risk of mastitis.