The effect of discontinuation of postmilking teat disinfection in low somatic cell count herds. I. Incidence of clinical mastitis

Results are described of a split-udder trial on the effect of discontinuation of postmilking teat disinfection on the incidence of clinical mastitis in seven dairy herds with a low bulk milk somatic cell count and a high incidence of clinical mastitis. Overall incidence of clinical mastitis was non-significantly lower (18%), whereas the incidence of the most prevalent pathogen associated with clinical mastitis, Escherichia coli, was significantly lower in quarters for which postmilking teat disinfection was discontinued. We concluded that discontinuation of postmilking teat disinfection may decrease the incidence of clinical Escherichia coli mastitis in herds for which standard mastitis prevention measures are executed adequately, bulk milk somatic cell count is low, and incidence of clinical mastitis is high. However, because an increase in intramammary infections with contagious pathogens may occur, care is recommended when advising discontinuation of postmilking teat disinfection.     

Mathematical modeling to estimate efficacy of postmilking teat disinfection in split-udder trials of dairy cows

A mathematical model was used to estimate the efficacy of postmilking teat disinfection from observations in split-udder trials with natural exposure. Data were studied from an outbreak of Staphylococcus aureus IMI during a split-udder trial in a commercial herd with low SCC. The efficacy of postmilking teat disinfection was similar when calculated based on incidence density rates or on transmission rates of IMI in dipped and control quarters. If, however, first and subsequent S. aureus IMI in a cow were not assumed to be independent and were therefore treated separately in the models, the efficacy of post-milking teat disinfection was calculated as being higher with the modeling procedure. The analysis using mathematical modeling, which includes the effect of the number of existing IMI on the number of new IMI, is presented and discussed. This analysis also allows estimation of the basic reproduction ratio. The impact of postmilking teat disinfection on transmission of pathogens is quantified, and proposals for additional preventive measures can be generated. We concluded that efficacy estimations from split-udder trials, assuming quarters to be independent observations, might underestimate the effect of postmilking teat disinfectants on udder pathogens.     

Prevention of bovine mastitis by a premilking teat disinfectant containing chlorous acid and chlorine dioxide

The objective of this study was to evaluate the efficacy of a premilking teat disinfectant for the prevention of mastitis in dairy cows under natural exposure conditions. Predipping was compared with a negative control using a split udder experimental design. All teats were dipped after milking with the same teat dip. Percentage of quarters newly infected by major mastitis pathogens was 34% lower in quarters with teats predipped and postdipped than in quarters with teats postdipped only. New IMI by Streptococcus uberis and Staphylococcus aureus were significantly lower in quarters with teats predipped and postdipped than in quarters with teats postdipped only. Differences in incidence of clinical mastitis between treatment groups approached significance. Predipping and postdipping were no more effective against Gram-negative bacteria, coagulase-negative Staphylococcus species, and Corynebacterium bovis than postdipping only. No chapping or irritation of teats was observed, and no adverse effects were noted using the test product as a premilking and postmilking teat disinfectant. Results of this study suggest that predipping and then postdipping with the test product was a more effective procedure against major mastitis pathogens than postdipping only.     

Antigenic crossreactivity and lipopolysaccharide neutralization properties of bovine immunoglobulin G

We investigated a possible mechanism by which immunization against core and lipid A determinants of lipopolysaccharide reduced clinical cases of mastitis and symptoms commonly associated with heterologous Gram-negative IMI. The IgG fraction of sera from cows immunized with either Escherichia coli J5 bacterin, E. coli J5 lipopolysaccharide conjugate vaccine, or unimmunized controls was purified by precipitation with caprylic acid and ammonium sulfate. The degree of IgG crossreactivity with Gram-negative bacteria that were isolated from clinical quarters was greater than that with Gram-positive isolates of Staphylococcus aureus. The highest magnitude of crossreactivity was against smooth strain E. coli isolates, followed by heterologous species of Enterobacter, Serratia, and Klebsiella isolates. Serum IgG from cows immunized with conjugate was highly crossreactive to E. coli J5, E. coli O111:B4, Serratia marcescens, Klebsiella pneumoniae, and Salmonella typhimurium lipopolysaccharides. The magnitude of antibody crossreactivity with lipopolysaccharides coincided with the ability of IgG to suppress the mitogenic effect of lipopolysaccharides on bovine lymphocytes.     

Therapeutic and prophylactic effect of prepartum antibiotic infusion in heifers

Prepartum bacteriologic examination of secretions from 42 dairy heifers 12-14 weeks prepartum revealed a total of 24 Staphylococcus aureus infected quarters, 53 Staphylococcus species infected quarters, and 20 Streptococcus species infected quarters. Prepartum intramammary therapy of primigravid dairy heifers with two commercially available dry cow antibiotics (penicillin-novobiocin or cephapirin) resulted in cure rates of 94%, 97%, and 100% for S. aureus, Staphylococcus species, and Streptococcus species intramammary infections (IMI), respectively. No protective effect was observed for dry cow treatment of uninfected quarters of heifers for any of the antibiotic preparations. No antibiotic was detectable in heifer secretions collected at parturition indicating that antibiotic concentrations may have fallen below protective levels prior to parturition.     

A comparison of two methods of evaluation of teat skin pathology

A split-plot design with repeated measures was used to test the relationship between visual teat skin condition score, the degree of transepidermal water loss from the skin, and the colonization by Staphylococcus aureus on experimentally chapped and inoculated teats of 20 lactating Holstein cows. Visual teat skin chapping score and the number of S. aureus colonies obtained from a teat skin swab were correlated (r = 0.53). Transepidermal water loss and S. aureus count were not correlated (r = 0.02). Results indicated that visual teat skin evaluation is superior to measurements of transepidermal water loss in the prediction of the susceptibility of teat skin to colonization by S. aureus.     

Management practices associated with low, medium, and high somatic cell counts in bulk milk

Management practices associated with bulk milk somatic cell counts (SCC) were studied for 201 dairy herds grouped into three categories according to bulk milk SCC. The cumulative production of fat-corrected milk over 305 d of lactation and category for bulk milk SCC were highly correlated; herds within the low category had the highest milk production. Differences in bulk milk SCC among the categories were well explained by the management practices studied. This correlation was not only true for the difference between the high (250,000 to 400,000) and low (< or = 150,000) categories for bulk milk SCC but also for the difference between the medium (150,000 to 250,000) and low categories and the high and medium categories. Management practices that are known to be important for herds in the high category for bulk milk SCC, such as dry cow treatment, milking technique, postmilking teat disinfection, and antibiotic treatment of clinical mastitis, were also found to be important in the explanation of the difference between herds in the medium and low categories for bulk milk SCC. More attention was paid to hygiene for herds in the low category than for herds in the medium or high category. Supplementation of the diet with minerals occurred more frequently for cows in the low category for bulk milk SCC than for cows in the medium and high categories.     

Relationship between thickness, chapping and Staphylococcus aureus colonization of bovine teat tissue

Post-milking measurements of teat skin chapping score, teat thickness and colonization by Staphylococcus aureus were determined for 11.5 d. Three teats on each of twelve Holstein cows, free from Staph. aureus intramammary infections, were immersed in 1 M-NaOH solution to induce teat chapping; the fourth teat served as a control. To achieve different degrees of chapping, one teat per cow received one immersion after each milking for three consecutive milking periods, a second teat received two immersions, and the third teat received one immersion which coincided with the last immersion of the other two teats. All teats were challenged twice with a skim milk broth culture of Staph. aureus (5 x 10(6) cfu) after the first and second milking following NaOH treatment. Measures were initiated with the milking following the last Staph. aureus challenges. Tissue thickness of the lateral side of the teat (barrel) and colonization by Staph. aureus declined with time. Thickness of the teat end varied more erratically. Teat skin chapping score was positively correlated (P < 0.001) with tissue thickness of the barrel and Staph. aureus colonization. Thickness of the barrel was not significantly correlated with Staph. aureus colonization. Barrel thickness as a covariate had a significant effect (P < 0.05) on teat skin colonization of Staph. aureus, whereas teat skin score and teat end thickness had no significant effect. Thus, thickness of the lateral side of the teat explained the greatest variation in Staph. aureus teat skin colonization in the model tested.     

Relationship of somatic cell count and cell volume analysis of goat's milk to intramammary infection with coagulase-negative staphylococci

The prevalence of intramammary infection in 4 commercial goat herds was studied in conjunction with electronic somatic cell count and volume analysis determined using a Coutler Counter and volume analyser. Neither streptococci nor mycoplasma were isolated from any half and the prevalence of intramammary infection with Staphylococcus aureus ranged from 0 to 3% between herds. For coagulase-negative staphylococci the range from infected halves was 36-71%. There was no significant difference between the mean total microscopic somatic cell count for halves infected with coagulase-negative staphylococci and those free from infection. A similar trend was observed for electronic somatic cell counts although the mean electronic cell count was greater than the mean total microscopic count on the 2 occasions that they were compared. The correlation coefficients between the 2 cell counting methods were 0.86 and 0.94. Between herds there were significant differences in mean electronic somatic cell count, with herd means ranging from 438 x 103 to 1684 x 103 cells/ml. In 2 of the 4 herds studied, milk samples from halves infected with coagulase-negative staphylococci had a significantly higher prevalence of cell volume distributions with a modal cell volume between 65 mu 3 and 100 mu 3. This was attributed to a higher proportion of polymorphonuclear neutrophils. Use of electronic somatic cell count and cell volume analysis were considered of little value in predicting infection caused by coagulase-negative staphylococci as there was a high proportion of false negative and false positive predictions.     

Accuracy of methods using somatic cell count and N-acetyl-beta-D-glucosaminidase activity in milk to assess the bacteriological cure of bovine clinical mastitis

This study examined the capability of milk somatic cell count (SCC) and NAGase activity to discriminate between quarters that had been cured versus those that had not been cured at 4 wk after antimicrobial therapy for clinical mastitis. The distribution of microorganisms that were isolated before therapy from 630 quarters with mastitis was as follows: 225 strains of Staphylococcus aureus, 96 strains of coagulase-negative staphylococci, 152 strains of streptococci (Streptococcus dysgalactiae and Streptococcus uberis), and 157 strains of coliform bacteria. Bacteriological cure rates were 35% for mastitis caused by Staph. aureus, 75% for mastitis caused by coagulase-negative staphylococci, 66% for mastitis caused by streptococci, and 72% for mastitis caused by coliforms. Diagnostic accuracy of milk SCC and NAGase and their interquarter ratios for predicting bacteriological status of the control samples was assessed by calculating sensitivity, specificity, and accuracy and by means of receiver operating characteristic analysis. The efficiency of milk SCC and NAGase for predicting bacteriological cure was greatest for cows that had been infected with Staph. aureus. The main problem in detecting coagulase-negative staphylococci was low sensitivity, and the main problem in detecting streptococci and coliforms was low specificity. Receiver operating characteristic analysis is not completely suitable for the detection of mastitis because reference method bacteriology and indirect tests can never fully agree. To assess the recovery of cows from mastitis caused by Staph. aureus, bacteriology should be supplemented with an examination of milk SCC or NAGase activity at threshold values such as those presented here.     

Subclinical and clinical mastitis on dairy farms in The Netherlands: epidemiological developments

In this review a number of the main epidemiological developments in the field of udder health in the Netherlands are summarized. The changes considering the bulk milk somatic cell count are described, as are the population dynamics of subclinical mastitis. Additionally, clinical mastitis caused by Escherichia coli and Staphylococcus aureus and their risk factors are reviewed. Finally, some future developments and the possible applications of these developments are discussed.     

Inhibitory activities of gatifloxacin (AM-1155), a newly developed fluoroquinolone, against bacterial and mammalian type II topoisomerases

We determined the inhibitory activities of gatifloxacin against Staphylococcus aureus topoisomerase IV, Escherichia coli DNA gyrase, and HeLa cell topoisomerase II and compared them with those of several quinolones. The inhibitory activities of quinolones against these type II topoisomerases significantly correlated with their antibacterial activities or cytotoxicities (correlation coefficient [r] = 0.926 for S. aureus, r = 0.972 for E. coli, and r = 0.648 for HeLa cells). Gatifloxacin possessed potent inhibitory activities against bacterial type II topoisomerases (50% inhibitory concentration [IC50] = 13.8 microg/ml for S. aureus topoisomerase IV; IC50 = 0.109 microg/ml for E. coli DNA gyrase) but the lowest activity against HeLa cell topoisomerase II (IC50 = 265 microg/ml) among the quinolones tested. There was also a significant correlation between the inhibitory activities of quinolones against S. aureus topoisomerase IV and those against E. coli DNA gyrase (r = 0.969). However, the inhibitory activity against HeLa cell topoisomerase II did not correlate with that against either bacterial enzyme. The IC50 of gatifloxacin for HeLa cell topoisomerase II was 19 and was more than 2,400 times higher than that for S. aureus topoisomerase IV and that for E. coli DNA gyrase. These ratios were higher than those for other quinolones, indicating that gatifloxacin possesses a higher selectivity for bacterial type II topoisomerases.     

Dietary vitamin E and selenium affect mastitis and milk quality

Vitamin E and selenium (SE) are essential nutrients that are integral components of the antioxidant defense of tissues and cells. Soils in many of the important dairy regions of the world are Se-deficient, and feedstuffs grown on these soils will not provide adequate dietary Se. Cattle consuming stored forages are likely to be low in vitamin E unless supplemented, and vitamin E deficiencies are frequently observed in peripartum dairy cows. Many new intramammary infections (IMI) occur in the 2 wk before and after calving. Deficiencies of either vitamin E or Se have been associated with increased incidence and severity of IMI, increased clinical mastitis cases, and higher somatic cell counts (SCC) in individual cows and bulk tank milk. Somatic cell counts are a primary indicator of mastitis and milk quality in dairy herds. The polymorphonuclear neutrophil (PMN) is a major defensive mechanism against infection in the bovine mammary gland. A know consequence of vitamin E and Se deficiency is impaired PMN activity and postpartum vitamin E deficiencies are frequently observed in dairy cows. Dietary supplementation of cows with Se and vitamin E results in a more rapid PMN influx into milk following intramammary bacterial challenge and increased intracellular kill of ingested bacteria by PMN. Subcutaneous injections of vitamin E approximately 10 and 5 d before calving successfully elevated PMN alpha-tocopherol concentrations during the periparturient period and negated the suppressed intracellular kill of bacteria by PMN that commonly is observed around calving.     

Discontinuation of prophylaxis for Pneumocystis carinii pneumonia in HIV-1-infected patients treated with highly active antiretroviral therapy

BACKGROUND: Prophylactic drugs for Pneumocystis carinii pneumonia (PCP) are strongly recommended for HIV-1-infected patients with CD4 cell counts of less than 200 cells/microL. Because of the highly active antiretroviral therapy (HAART) currently available, we speculated that prophylaxis can be discontinued in patients with CD4 cell counts of more than 200 cells/microL. METHODS: In this prospective observational study, PCP prophylaxis (primary or secondary) was discontinued in HIV-1-infected patients whose CD4 cell count had increased above 200 cells/microL (documented twice with an interval of at least 1 month) as a result of HAART. Patients and their CD4 cell counts were monitored every 3 months. The primary endpoint of the study was the occurrence or reoccurrence of PCP. FINDINGS: 78 patients were enrolled: 62 patients were receiving prophylaxis for primary prevention of PCP and 16 patients for secondary prevention of PCP. At the time of discontinuation of prophylaxis, the mean CD4 cell count was 347 cells/microL, and HIV-1-RNA was not detectable in 61 patients. The lowest mean CD4 cell count during prophylaxis was 79 cells/microL. Patients stopped prophylaxis 9.8 (SD 6.4) months after they started HAART. The mean follow-up after discontinuation of prophylaxis was 12.7 (SD 7.6) months, and none of the patients developed PCP (97.5% one-sided CI 0-4.4%). INTERPRETATION: The preliminary results of this study indicate that PCP prophylaxis can be stopped safely in HIV-1-infected patients whose CD4 cell counts have increased above 200 cells/microL after treatment with HAART.     

Effect of coliform challenge at milking time on new udder infections

This project was designed to study rates of infection in udders of cows exposed to an Escherichia coli broth culture at milking time. Forty Holstein cows of varied stages of lactation were divided randomly into three treatment and one control group of ten cows each. The treatment groups were exposed for 3 wk to an Escherichia coli broth of 10(9) colony forming units per ml at milking time by either 1) dipping teat ends in broth before milking, 2) spraying the udder and leaving it dripping wet during milking, or 3) dipping teat ends in broth after milking. Eleven of 30 treated cows became infected in one or more quarters; all control cows remained uninfected. The infection rate of the three Escherichia coli-treated groups was higher than the controls. However, there was no difference among treated groups. Exposure to the broth culture of Escherichia coli increased the infection rate, but the time at which the udder was exposed to the organisms was unimportant. All infections were of the same type with the same O and H group antigens as the Escherichia coli broth.     

Rapid, automated separation of specific bacteria from lake water and sewage by flow cytometry and cell sorting

The use of fluorescence-activated flow cytometric cell sorting to obtain highly enriched populations of viable target bacteria was investigated. Preliminary studies employed mixtures of Staphylococcus aureus and Escherichia coli. Cells of S. aureus, when mixed in different proportions with E. coli, could be selectively recovered at a purity in excess of 90%. This was possible even when S. aureus composed only approximately 0.4% of the total cells. Cell sorting was also tested for the ability to recover E. coli from natural lake water populations and sewage. The environmental samples were challenged with fluorescently labelled antibodies specific for E. coli prior to cell sorting. Final sample purities of greater than 70% were routinely achieved, as determined by CFU. Populations of E. coli released into environmental samples were recovered at greater than 90% purity. The use of flow cytometry and cell sorting to detect and recover viable target bacteria present at levels of less than 1% within an indigenous microflora was also demonstrated.     

Inflammation in the bovine teat cistern induced by Staphylococcus aureus

The inflammatory response, characterized by the accumulation of leukocytes, bovine serum albumin and the lysosomal enzyme N-acetyl-beta-D-glucosaminidase, was studied after inoculation of either 5 x 10(5) colony-forming units (CFU) or 2 x 10(2) CFU of the Staphylococcus aureus strain SA 14391 into teat cisterns of dry cows after surgical closure of the passage between the teat and udder cisterns. Teat cistern samples were taken before, and twice daily for 7 days after, inoculation of the bacteria. Infusion of sterile saline constituted a control. Persistent infections occurred in all teats inoculated with the higher dose (5 x 10(5) CFU) of bacteria, and a prominent inflammatory response was elicited. Marked differences were observed in leukocyte migration patterns between different cows, and a cyclic influx of leukocytes was evident. Inoculation of the lower dose (2 x 10(2) CFU) of bacteria did not result in a persistent infection, and only a slight inflammatory response was observed. The results indicate that the bovine teat tissues are capable of mounting a strong local inflammatory response to S. aureus infection. A large number of leukocytes invaded the teat, but, despite their numbers, they were unable to subdue the infection, except when the bacterial count was low.     

Upregulation of urokinase-type plasminogen activator by endogenous and exogenous HIV-1 Tat protein in tumour cell lines derived from BK virus/tat-transgenic mice

A universal protocol for PCR detection of 13 species of foodborne pathogens in foods was developed. The protocol used a universal culture medium and the same PCR conditions with 13 sets of specific primers. The 13 species of foodborne pathogens examined were Escherichia coli, E. coli-ETEC, E. coli-O157:H7, Shigella spp., Salmonella spp., Yersinia enterocolitica, Y. pseudotuberculosis, Vibrio cholerae, V. parahaemolyticus, V. vulnificus, Listeria monocytogenes, Staphylococcus aureus and Bacillus cereus. No interference was observed using the PCR assay when food sample was artificially inoculated with each individual bacterial species. Twelve different seafood samples and two soft cheese samples without artificial inoculation were examined by this protocol. Vibrio vulnificus, Salmonella spp., E. coli, Listeria monocytogenes and Bacillus cereus were detected in some foods. Internal probe hybridization and nested PCR procedures were used to confirm the above findings.     

Environmental streptococcal intramammary infections of the bovine mammary gland

Characteristics of environmental streptococcal IMI were investigated over a 7-yr period for a herd in total confinement. A total of 374 new environmental streptococcal IMI was detected. Approximately 50.5% of IMI were new in the dry period, and 49.5% were new in lactation. The rate of new IMI was .00312 IMI/cow day during the dry period and .00054 IMI/cow day during lactation. The percentages of cows and quarters with an environmental streptococcal IMI present at calving were 10.6 and 3.2%, respectively. The percentage of heifers with an environmental streptococcal IMI at calving was similar to that for cows. The rate of new environmental streptococcal IMI was greater during the 1st mo of lactation than during the remainder of lactation. The rate of IMI during late lactation was higher for older cows than for either heifers or cows in second lactation. The rate of environmental streptococcal IMI during the dry period and during lactation was greatest during summer. The mean days of lactation that cows were infected for all IMI was 12.3 d. Approximately 41% of IMI had a duration of < 8 d. Stage of lactation, season of the year, and parity influenced the rate of new IMI.     

Gram-negative enteric bacteremia in children in the Negev (1989-1994)

During 1989-1994, there were 322 episodes of Gram-negative enteric bacteremia in 308 children. The incidence increased from 31/100,000 in children younger than 15 years of age during 1989-1991, to 50/100,000 during 1992-1994. The most common pathogens were Klebsiella, E. Coli, Salmonella and Enterobacter. 39% of episodes were nosocomial and a significant increase was recorded for each species during the last 3 years of the study. Klebsiella represented the most common pathogen causing nosocomial bacteremia, while E. coli and Salmonella were the main pathogens causing community-acquired bacteremia. In this study in southern Israel, the incidence of Gram-negative enteric bacteremia was significantly higher in Bedouin children, with the exception of bacteremia due to Salmonella, which occurred mainly in Jewish children.