Herd-level risk factors for Staphylococcus aureus and Streptococcus agalactiae intramammary infections

Herd-level risk factors for high herd prevalence of Staphylococcus aureus and Streptococcus agalactiae intramammary infection were studied using data from Holstein herds participating in the New York State Quality Milk Promotion Services Program during the period 1978–1983. Using information from initial surveys and bacteriologic sampling of all herds, a set of possible risk factors for each organism was examined. Comparisons between herds with high and zero prevalence of each infection were made. Failure to teat dip and use of common cloths or sponges for udder preparation increased the odds of high prevalence for both organisms. Selective or no dry cow therapy, having tie stall or stanchion housing and using dry massage or no udder preparation increased the risk for Str. agalactiae, but not for S. aureus infection. Milking machine function played a role in the risk of both infections.     

Epidemiology of Streptococcus uberis intramammary infections in a dairy herd.

From 1987 to 1991, almost 36,000 quarter samples of mammary secretion representing 1790 lactations of 510 dairy cows from a research herd were collected for bacteriological examination. The percentage of cows infected with Streptococcus uberis ranged from 12 to 16% of cows/year. S. uberis was isolated from 14.2% of lactations over the 5-year period. The prevalence of S. uberis intramammary infection (IMI) was significantly higher in cows with > or = 4 lactations than in cows with 3 or fewer lactations. Regardless of lactation number, the prevalence of S. uberis was highest before parturition, during early lactation and near drying off. The prevalence of S. uberis infected quarters ranged from 1.3 to 2.3% of quarters/year; the prevalence rate for the 5-year period was 2% of quarters. The quarter prevalence of S. uberis was lowest in cows with < or = 3 lactations, increased significantly with lactation number and was highest in cows with > or = 6 lactations. The percentage of quarters infected with S. uberis varied significantly by year. The majority (95%) of S. uberis IMI were subclinical. The ratio of subclinical IMI to clinical IMI was lowest during early lactation, and increased with days in milk, and with lactation age except for cows in their 5th and 6th lactations. Results of this epidemiological investigation suggest that opportunities exist where suitable control measures could be applied to reduce the impact of S. uberis infections in the dairy herd.     

An economic justification of "blitz" therapy to eradicate Streptococcus agalactiae from a dairy herd

Streptococcus agalactiae was identified as the cause of mastitis in a 240-cow dairy herd. Forty-five per cent of the herd had cell counts over 500,000/ml, and 28 per cent had cell counts over 1,000,000/ml. Dry cow therapy was used regularly but teat dipping had not been used for three years. The procedures at milking were modified, teat dipping was introduced, and the herd was divided into two according to cell count. The 120 cows with higher cell counts were treated with 300 mg erythromycin (Erythrocin intramammary; Sanofi Animal Health) preparation per quarter at two consecutive milkings. Towards the end of lactation, all the 90 lactating cows in the herd were again treated with erythromycin. Milk samples were collected from all the cows in the herd 12 months after the initial treatment, and S agalactiae was isolated from only one replacement heifer which had been purchased after the treatments with erythromycin. The butterfat and protein levels in the milk were compared with those of a similar, but untreated, herd for 12 months before and after therapy. The butterfat levels rose sharply after treatment, and financial assessment showed a 41 per cent return on investment in the 12 months following the treatment.     

High incidence of clinical mastitis due to Staphylococcus aureus in two dairy herds with low milk cell counts.

Five dairy herds with a high incidence of clinical mastitis were investigated. Two of these herds had a high incidence of mastitis caused by Staphylococcus aureus yet had a relatively low rolling mean cell count. The mean cell counts of samples from clinical cases submitted by the dairymen from these two farms were significantly lower than the counts of similar samples submitted from the other farms. It is suggested that a possible explanation of the low cell count on these two farms was the proficiency of the dairy-men in detecting clinical mastitis.     

Recovery of Streptococcus agalactiae and Staphylococcus aureus from fresh and frozen bovine milk

Three hundred seventy-three milk samples were screened for Streptococcus agalactiae and Staphylococcus aureus. After sample storage at -20 C for 23 days, the frequency of Str agalactiae isolation increased 2.50 times. The frequency of S aureus isolation increased 1.48 times in the same interval. Increases in the proportion of these isolates were highly significant (P = 0.000006 and 0.0001, respectively). Results of the study indicate that optimal procedures for microbiological testing for these mastitis pathogens may include preculture freezing. The magnitude of the increase in the proportion of isolates indicates the existence of an important population of infected cattle shedding bacteria at concentrations not detected by use of standard microbiological techniques.     

Annual incidence, prevalence and transmission characteristics of Streptococcus agalactiae in Danish dairy herds

Contagious mastitis pathogens continue to pose an economic threat to the dairy industry. An understanding of their frequency and transmission dynamics is central to evaluating the effectiveness of control programmes. The objectives of this study were twofold: (1) to estimate the annual herd-level incidence rates and apparent prevalences of Streptococcus agalactiae (S. agalactiae) in the population of Danish dairy cattle herds over a 10-year period from 2000 to 2009 inclusive and (2) to estimate the herd-level entry and exit rates (demographic parameters), the transmission parameter, β, and recovery rate for S. agalactiae infection. Data covering the specified period, on bacteriological culture of all bulk tank milk samples collected annually as part of the mandatory Danish S. agalactiae surveillance scheme, were extracted from the Danish Cattle Database and subsequently analysed. There was an increasing trend in both the incidence and prevalence of S. agalactiae over the study period. Per 100 herd-years the value of β was 54.1 (95% confidence interval [CI] 46.0-63.7); entry rate 0.3 (95% CI 0.2-0.4); infection-related exit rate 7.1 (95% CI 5.6-8.9); non-infection related exit rate 9.2 (95% CI 7.4-11.5) and recovery rate 40.0 (95% CI 36.8-43.5). This study demonstrates a need to tighten the current controls against S. agalactiae in order to lower its incidence.     

Staphylococcus aureus variety hominis in a cattle herd

A site-linked hominis variety of Staphylococcus aureus was isolated from a cattle herd. The find coincided with accumulated occurrence of clinical mastitis in cows and the affliction of one milker with a nose furuncle. The origin of the strain was not elucidated. The same strain had been isolated throughout three years of observation from clinical and subclinical mastitis as well as from chronic udder affection of cows, but no extraordinary accumulation of clinically manifest mastitis had been observed. The hominis site variety was quite rare among Staphylococcus aureus strains isolated from other cow herds. Enterotoxin formation was recorded from strains of the hominis site variety and from strains which could not be coordinated with any other of the known site varieties and fell under crystal-violet Type A. No enterotoxin formation was recordable from the strains of the bovis variety. The same applied to the group of staphylococci of crystal-violet Type C which could not be coordinated either with any known site variety and which is assumed to have originated from the hominis site variety. The above findings do not support any conclusion as to whether the cows had been infected by the milker or vice versa.     

牛乳中金黄色葡萄球菌和无乳链球菌的PCR检测应用研究

采集92份患隐性乳房炎牛的乳汁,分别用PCR法和常规法进行致病菌检测,常规细菌鉴定法检测出金黄色葡萄球菌感染样18份,无乳链球菌感染样30份;双重PCR检测出金黄色葡萄球菌感染样22份、无乳链球菌感染样27份。本试验从基因水平对致病性乳汁进行检测,具有操作简便、快速、敏感性高、特异性强等特点。     

Application of the California mastitis test in intramammary Streptococcus agalactiae and Staphylococcus aureus infections of camels (Camelus dromedarius) in Kenya

A study was conducted on 207 lactating camels in six herds in Kenya to evaluate the California mastitis test (CMT) for the detection of intramammary infections (IMIs) caused by Streptococcus agalactiae and Staphylococcus aureus and to investigate the prevalence of both the pathogens in the camel udder. IMI with S. agalactiae was found in 12% of all camels sampled. IMI with S. aureus was present in 11% of all camels sampled. The herd-level prevalence of IMI varied between 0 and 50% for S. agalactiae and between 0 and 13% for S. aureus. Longitudinal observations over 10–12 months confirmed persistent infections for both pathogens. Observations in one herd suggested that camel pox was a contributing factor in spreading and exacerbating S. agalactiae udder infections.

The CMT had quarter-level sensitivities of 77 and 68% for S. agalactiae and S. aureus in camels, respectively. The CMT specificities were 91% for both the pathogens.     

Immunogenic properties of Staphylococcus aureus and Streptococcus agalactiae administered separately and in combination to lactating cows

Composite bacterins of Staphylococcus aureus and Streptococcus agalactiae, or either bacterin alone, were administered systemically to groups of lactating cows. The response to each bacterin was unaffected by the simultaneous administration of the antigens when assessed by comparing the antibody levels in milk by enzyme-linked immunosorbent assay. There was no evidence of cross reactivity of the antigens studied, nor immunopotentiation by either bacteria.     

Bacteriological survey of mammary secretions from prepartum heifers in a dairy herd with a high prevalence of Staphylococcus aureus infection

This study was performed to examine the bacteriological findings in 58 mammary secretions from 15 heifers at 4-5 weeks before parturition, and to evaluate whether a high prevalence of S. aureus infection in lactating cows affects the occurrence of S. aureus infection in prepartum heifers in the dairy herd. A total of 86.7%(13/15) of the heifers and 60.3%(35/58) of quarter milk samples from the heifers were bacteriologically positive. No S. aureus isolate was detected in mammary secretions from the heifers. Coagulase-negative staphylococcus (CNS) species were predominantly detected in 54.3%(19/35) and Streptococci other than Streptococcus agalactiae were isolated from 22.9%(8/35) of the quarters. A high S. aureus prevalence in the herd may not necessarily be a decisive factor for S. aureus infection in heifers.     

In vitro antimicrobial activity of Combretum molle (Combretaceae) against Staphylococcus aureus and Streptococcus agalactiae isolated from crossbred dairy cows with clinical mastitis

Following the rapidly expanding dairy enterprise, mastitis has remained the most economically damaging disease. The objective of this study was mainly to investigate the in vitro antibacterial activities of ethanol extracts of Combretum molle (R.Br.Ex.G.Don) Engl & Diels (Combretaceae) against antibiotic-resistant and susceptible Staphylococcus aureus and Streptococcus agalactiae isolated from clinical cases of bovine mastitis using agar disc diffusion method. The leaf and bark extracts showed antibacterial activity against S. aureus at concentrations of 3 mg/ml while the stem and seed extract did not show any bioactivity. Although both leaf and bark extracts were handled in the same manner, the antibacterial activity of the bark extract against the bacterial strains had declined gradually to a lower level as time advanced after extraction. The leaf extract had sustained bioactivity for longer duration. The susceptibility of the bacteria to the leaf extract is not obviously different between S. aureus and S. agalactiae. Also, there was no difference in susceptibility to the leaf extract between the antibiotic-resistant and antibiotic-sensitive bacteria. Further phytochemical and in vivo efficacy and safety studies are required to evaluate the therapeutic value of the plant against bovine mastitis.     

The susceptibility of bovine udder quarters colonized with Corynebacterium bovis to experimental infection with Staphylococcus aureus or Streptococcus agalactiae.

Twenty bovine udder quarters colonized with Corynebacterium bovis SR6 and 20 uncolonized quarters were challenged by inoculation of Staphylococcus aureus Newbould 305 (ATCC 29740) into the teat cistern. The percentage of infection in quarters colonized with C. bovis (50%) was significantly lower than that in controls (100%). By similar challenge no significant difference was observed between the percentage of infection with Streptococcus agalactiae ATCC 27956 in 33 quarters colonized with C. bovis (70%) compared to 33 controls (87.9%). A total of 37 quarters colonized with C. bovis and 37 control quarters were challenged with Staph. aureus Newbould 305 (ATCC 29740) and Maxi (ATCC 27543) and Strep. agalactiae (ATCC 27956) by exposure of the teat orifice. The percentage of teat ducts colonized with C. bovis which became infected with either pathogen was not different from that for controls.