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L K Fox

Publications and source records attributed to L K Fox.

At least 19 recordsLinked to original sources
PubMed1996

Evaluation of a coagulase-negative variant of Staphylococcus aureus as a cause of intramammary infections in a herd of dairy cattle.

A coagulase-negative variant of Staphylococcus aureus was identified in a herd of 250 lactating dairy cows. During testing of the entire herd, this strain of S aureus was isolated from aseptically collected milk samples of 25 cows. Cows with intramammary infections attributable to coagulase-negative S aureus had an increased somatic cell count in their milk, which was indicative of mastitis infection. Speciation of the Staphylococcus organisms was made, using a series of biochemical tests. A strain of a coagulase-positive S aureus also caused intramammary infections in the herd and shared identical biochemical characteristics with the coagulase-negative strain. Moreover, both strains could not be typed by the use of the International Set of Bovine Phages. Analysis of these findings indicated that a coagulase-negative variant of S aureus can cause intramammary infections in cattle, coagulase-negative variants of S aureus that cause mastitis can be more prevalent in herds than coagulase-positive variants, and clinicians should avoid misclassifying coagulase-negative S aureus as organisms that are clinically unimportant.

Animals↗
PubMed1996

Environmental reservoirs for Serratia marcescens intramammary infections in dairy cows.

Via special media, Serratia marcescens isolates were found in 3 bedding pack samples and in 2 milking parlor floor samples, and in milk samples from 19 cows during an episode of mastitis in a dairy cow herd. Chromosomal digest patterns of isolated S marcescens were indistinguishable for 18 of the milk samples and all bedding pack samples. Our findings provide strong evidence that the bedding pack was the reservoir of S marcescens associated with the outbreak of intramammary infections. Additionally, our ability to match digest patterns of isolates in the bedding pack and milk confirms the theory that S marcescens is an environmental pathogen capable of causing mastitis.

Animals↗
PubMed1996

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.

Animals↗
PubMed1996

Prevalence of coagulase-positive staphylococci, other than Staphylococcus aureus, in bovine mastitis.

OBJECTIVE: To determine prevalence and relevance of coagulase-positive Staphylococcus hyicus and S intermedius intramammary infections (IMI) in dairy cows and determine the ability of the 4-hour tube coagulase (TC) test to differentiate the coagulase-positive staphylococci (CPS). DESIGN: Prevalence of CPS was determined for primiparous cows (point prevalence and prevalence at first parturition) and multiparous cows (point prevalence) of 2 herd groups: < 6% CPS IMI prevalence = low prevalence (LP); > 10% CPS IMI prevalence = high prevalence (HP). SAMPLE POPULATION: For prevalence, cows of 22 dairy herds. For TC, 1,038 CPS strains isolated from cow milk. PROCEDURE: Speciation of CPS from aseptically collected composite milk samples was performed. Coagulase-positive isolates from 4 cow groups were tested for their ability to coagulate rabbit plasma by 4 hours: LP and HP primiparous cows at parturition, and LP and HP cows any time after first parturition. RESULTS: Of 487 CPS in the prevalence study, 82.1% were S aureus, 17.7% were coagulase-positive S hyicus, and 0.2% were S intermedius. Of all CPS IMI in LP herds, 34% were coagulase-positive S hyicus; of all CPS IMI in HP herds, 9% were coagulase-positive S hyicus. Coagulase-positive S hyicus appeared to persist to the end of lactation in 4 cows (mean linear somatic cell count = 3.7). The TC test was > or = 97% sensitive, < or = 33% specific, and had a predictive value positive range of 60 to 97% for S aureus isolates. CONCLUSION: Coagulase-positive S hyicus appears capable of inducing chronic, low-grade IMI. Staphylococcus intermedius does not appear to be an important mastitis pathogen. The TC test is not valid to use as the sole method to differentiate CPS species.

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PubMed1995

Sensitivity of bacteriologic culture for detection of Escherichia coli O157:H7 in bovine feces.

The sensitivities of several plating and broth enrichment methods for the detection of Escherichia coli O157:H7 in (i) bovine fecal samples directly inoculated with E. coli O157:H7, (ii) fecal samples from cattle in herds previously positive for E. coli O157:H7, and (iii) fecal samples from calves shedding E. coli O157:H7 after experimental oral inoculation were compared. Three enrichment protocols and three plating protocols were evaluated with directly inoculated fecal samples. All broth enrichment methods were superior to direct plating when they were combined with subsequent plating on sorbitol-MacConkey with cefixime and tellurite (SMACct). SMACct was the most sensitive plating medium, and the three alternative broth enrichment methods gave similar improvements in sensitivity. Of 351 fecal samples from known positive herds, 24 samples (6.8%) were positive by one or more methods. By the most sensitive plating method, cultures of 10-g samples were slightly more sensitive (19 of 351 [5.4%]) than cotton-tipped swab fecal samples (14 of 351 [4.0%]); however, this difference was not significant. For samples from calves orally inoculated with E. coli O157:H7, separation by immunomagnetic beads was slightly more sensitive (79%) than broth enrichment followed by plating at two dilutions (10(-3) and 10(-4)) (71%); however, this difference was not significant. The combination of overnight enrichment of swab fecal samples (0.1 g) and plating on SMACct at two dilutions (10(-3) and 10(-4)) appears to be a sensitive method for detection in large-scale studies involving hundreds of samples per week.

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PubMed1995

Survey of intramammary infections in dairy heifers at breeding age and first parturition.

A survey was conducted to determine and contrast prevalence of IMI in nulligravid and primigravid dairy heifers pre- and postpartum. Contrasts were made to evaluate the risk factors of location of dairy, trimester of gestation, and season of sampling on IMI. Twenty-eight dairies in California, Louisiana, Vermont, and Washington were studied. Lacteal secretions were collected aseptically from heifers at breeding age (8 to 19 mo) from one side of the gland and again at 4 d postpartum from all quarters. Of the quarters sampled, 65.6% prepartum and 64.0% postpartum were free of IMI. The percentages of quarters with IMI from coagulase-negative staphylococci or Staphylococcus aureus IMI were 27.1 and 9% prepartum and 21.8 and 2.9% postpartum. Staphylococcus aureus IMI were most prevalent in Louisiana during the months other than summer. Location, herd, and season significantly influenced prevalence of IMI. The prevalence of IMI was greatest during the last trimester of pregnancy, ranging from 49.2% in the winter to 36.8% in the summer. The significant effects of herd location and season suggest that management variables influence prevalence of heifer IMI. Because prevalence of IMI was greatest during the last trimester of pregnancy compared with prevalence during earlier stages of pregnancy, the heifer may be most susceptible to this disease during this period of first gestation.

Aging↗
PubMed1995

The visual appearance and somatic cell count of mammary secretions collected from primigravid heifers during gestation and early postpartum.

Mammary secretions, obtained before and after calving, were examined for visual appearance, SCC, and bacteriology as part of a larger study determining the prevalence of IMI in 1588 primigravid heifers. Appearance of secretions was categorized into five groups: thin and watery, honey-like, serumy, milky, or thickened colostrum. Precalving secretions were further characterized as low viscosity (thin and watery, serumy, or milky) or high viscosity (honey-like and thickened colostrum). Postcalving secretions were further characterized as normal (milky, thickened colostrum) or abnormal (thin and watery, serumy, or honey-like). Infected precalving quarters (81%) had low viscosity secretions. Quarters that were uninfected precalving (75%) had high viscosity secretions. Greater than 90% of all postcalving milk samples appeared to be normal, regardless of geographic location, season, or bacterial infection status. Only 77% of the samples from quarters infected with contagious and noncontagious mastitis pathogens had normal appearance. Precalving SCC from bacteriologically negative quarters were lower than SCC from infected quarters. Similarly, postcalving SCC were lower from the bacteriologically negative quarters than from the infected quarters. Infected quarters had higher mean SCC than the uninfected quarters during both pre- and postcalving periods.

Animals↗
PubMed1995

Antimicrobial susceptibility of microorganisms isolated from the mammary glands of dairy heifers.

Minimum inhibitory concentrations were determined with 1494 microorganisms isolated from the mammary glands of dairy heifers. The antimicrobial agents tested were penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enrofloxacin, erythromycin, and pirlimycin. All minimum inhibitory concentrations were expressed as micrograms per milliliter. The isolates tested included 135 Staphylococcus aureus, 1222 Staphylococcus sp., 42 Streptococcus sp., 15 Enterococcus sp., 60 enteric species, and 20 miscellaneous organisms. The minimum inhibitory concentrations for 90% of isolates for the various antimicrobial agents with Staph. aureus were as follows: penicillin, .13; cloxacillin, .5; cephapirin, .5; ceftiofur, 1; novobiocin, .5; enrofloxacin, .5; erythromycin, .5, and pirlimycin, .5. In comparison, the minimum inhibitory concentrations for 90% of isolates for the Staphylococcus sp. were 1, 1, .5, 1, .5, .5, 1, and .5 for penicillin, cloxacillin, cephapirin, ceftiofur, novobiocin, enrofloxacin, erythromycin, and pirlimycin, respectively. The minimum inhibitory concentrations for 90% of isolates for the Streptococcus sp. were 2, 32, 2, 2, 8, 1, 64, and 32 for the respective antimicrobial agents; the minimum inhibitory concentrations for 90% of isolates were 4, 64, 32, 64, 4, 1, 4, and 4 for the enterococci. Against the Gram-negative enteric bacilli, only ceftiofur and enrofloxacin were active; minimum inhibitory concentrations for 90% of isolates were 1 microgram/ml for ceftiofur and .25 microgram/ml for enrofloxacin. Results indicated that the majority of staphylococcal strains were susceptible to the antimicrobial agents tested but that antimicrobial susceptibility varied for Streptococcus sp. Compounds currently available in intramammary infusion products demonstrated poor activity against the enteric organisms.

Animals↗
PubMed1995

Survey of dairy managers in the Pacific Northwest identifying factors associated with teat chapping.

Telephone interviews were conducted to evaluate the association of teat chapping with combinations of premilking and postmilking teat disinfectants (predip and postdip), other management practices, and climatic conditions. Holstein dairies (n = 100) in the DHIA SCC program were randomly selected from three northwest regions. During nonwinter seasons, herd managers using an iodophor dip without skin conditioner both premilking and postmilking were 9.7 times more likely to report chapping than were those using iodophor with conditioner. The herd managers least likely to report chapping problems were those using conditioner in both the predip and postdip. Use of conditioner in postdip only was associated with intermediate frequency of reported chapping. No conditioner in either predip or postdip was associated with the greatest frequency of reported chapping. Herd managers using a different germicide in the predip and postdip reported more chapping than herd managers using the same germicide. The frequency of chapping was highest during winter in all regions, and the percentage of herd managers reporting chapping within a region was associated with the temperature extremes of the region. For seasons other than winter, characteristics of predip and postdip combinations and parlor exit or barn design were the management factors that best described an association with reported chapping.

Animals↗
PubMed1995

Mastitis of periparturient Holstein cattle: a phenotypic and genetic study.

Environmental and genetic factors affecting somatic cell scores, clinical mastitis, and IMI by minor and major pathogens were studied on 137 periparturient Holstein cows selected for milk production. Environmental effects were obtained by generalized least squares and logistic regression. Genetic parameters were from BLUP and threshold animal models. Lactation number affected the number of quarters with clinical mastitis and the number of quarters infected with minor pathogens. The DIM affected somatic cell score and number of quarters infected with major pathogens. Heritabilities for all mastitis indicators averaged 10%, but differences occurred among the indicators. Correlations between breeding values of the number of quarters infected with minor pathogens and the number infected with major pathogens were antagonistic and statistically significant.

Animals↗
PubMed1994

Genomic fingerprints of Staphylococcus aureus of bovine origin by polymerase chain reaction-based DNA fingerprinting.

Staphylococcus aureus (n = 75) isolated from mammary secretions of cows with subclinical and clinical mastitis from several geographic locations in the USA were examined using polymerase chain reaction-based DNA fingerprinting. DNA fingerprints were produced using a synthetic oligonucleotide primer (5'GTAACGCC3') to produce a distinct spectrum of amplified DNA fragments facilitating a high degree of resolution for differentiating S. aureus strains. PCR-based DNA fingerprinting grouped the 75 S. aureus isolates into 19 distinct profiles. The technique differentiated closely related strains within and between geographic locations. Findings suggest that certain types are found across geographic regions suggesting a common clonal type. Within herd data suggest heterogeneity among subclinical and clinical isolates of S. aureus strains. Compared to existing typing methods, PCR-based DNA fingerprinting is easy to perform and interpret. Use of PCR-based DNA fingerprinting may allow for a more detailed investigation of the epidemiology of S. aureus mastitis in dairy cows.

Animals↗
PubMed1994

Coagulase-positive Staphylococcus intramammary infections in primiparous dairy cows.

Objectives were to determine the prevalence of coagulase-positive staphylococcal IMI in primiparous cows at first parturition, to contrast the differences in coagulase-positive staphylococcal IMI in primiparous cows at parturition in herds with high and low prevalences of coagulase-positive staphylococcal IMI in the lactating herd, and to determine the percentage of primiparous cows having persistent coagulase-positive staphylococcal IMI. Milk samples were collected aseptically from cows at the start and end of the study, at dry-off, and at parturition. Herds (n = 18) were split evenly into two categories: high (> 10%) or low (< 5%) prevalence of coagulase-positive staphylococcal IMI. At the start, the mean prevalence of coagulase-positive staphylococcal IMI in high prevalence herds was 30%, ranging from 13 to 65%, and in low prevalence herds was 2%, ranging from 0 to 5%. Overall the prevalence of coagulase-positive staphylococcal IMI in primiparous cows at parturition was 8.1% (67 of 828), ranging from 0 to 27%. Although primiparous cows from high prevalence herds had a higher prevalence of coagulase-positive staphylococcal IMI (9.2%; 40 of 436) at parturition than did primiparous cows from low herds (6.9%; 27 of 392), the difference was not significant. Of primiparous cows with coagulase-positive staphylococcal IMI at parturition, 43% had coagulase-positive staphylococcal IMI at least 2 mo after parturition. Primiparous cows with coagulase-positive staphylococcal IMI at parturition may represent significant reservoirs of infection to uninfected herdmates.

Animals↗
PubMed1994

Staphylococcus aureus colonization of teat skin as affected by postmilking teat treatment when exposed to cold and windy conditions.

Study 1 was conducted to determine whether postmilking teat treatment with ointment before exposure to cold and wind resulted in better skin health than standard teat treatment. Teat treatments tested were 1% I2 and 10% glycerin, ointment with 1% chloroxylenol, ointment with .3% 8-hydroxyquinoline sulfate, and no treatment (control). Teats were treated 7 d prior to chapping. A broth culture of Staphylococcus aureus was applied once to teats after chapping was established. Treatments were applied after milking and before sample collection for 11 d following S. aureus application. Milk samples were collected aseptically, teat skin swabbing solutions were collected, and teat condition was scored. Cows were exposed to ambient winter conditions, and a wind velocity of 152.4 m/min was applied to the mammary gland surface for 15 min immediately postmilking. Ointment and control teats had significantly better skin condition than teats treated with I2 solution. Colonization of S. aureus was greatest on ointment treated teats. Study 2 was conducted to determine whether teat condition of cows receiving postmilking I2 solution treatments would be improved if teats were blotted dry before exposure to wind and cold ambient conditions. Two mammary quarters of each cow received I2 solution treatment of study 1, but teats were blotted dry prior to exit from the milking parlor. No treatment was applied to the other teats. Teat condition scores were similar between treatments, but S. aureus colonization was significantly greater on control teats. Results indicate a possible disadvantage to treating teats with ointments after milking, as evidenced by increased S. aureus colonization.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Ecology of Staphylococcus aureus isolated from various sites on dairy farms.

The purposes of this study were to identify sources of Staphylococcus aureus on dairies and to determine whether S. aureus colonization of heifer body sites increases the risk of S. aureus IMI at parturition. In herds with high (> 10%) or low (< 3%) prevalence of S. aureus IMI, S. aureus was isolated from heifer teat skin, heifer external orifices, housing, feedstuffs, humans, nonbovine animals, air, and equipment. Additionally, in herds with high prevalence, S. aureus was isolated from bedding, insects, and water. The predominant sources of S. aureus for both groups were other IMI and heifer body sites. Heifers with prepartum lacteal secretions with S. aureus were at greater risk of S. aureus IMI at parturition than were prepartum heifers with lacteal secretions that were negative for S. aureus. Heifers with teat skin colonized by S. aureus were 3.34 times more likely to have S. aureus IMI at parturition than were noncolonized heifers. Overall, 35% of 700 heifers were colonized with S. aureus on a body site at least once. Although colonizations of most body sites appeared to be transient, a few heifers were colonized on the same site for 1 yr. Persistently colonized heifers may represent the primary reservoirs of S. aureus for other heifers.

Animals↗
PubMed1993

Suppression of proliferative response of BoCD4+ T lymphocytes by activated BoCD8+ T lymphocytes in the mammary gland of cows with Staphylococcus aureus mastitis.

Investigations were conducted to determine the mechanisms that account for differences in the responses of BoCD4+ lymphocytes from mammary gland secretions (MGS) in healthy cows and in cows with Staphylococcus aureus infection. The proliferative response to lectins and S. aureus antigens of mammary gland lymphocytes from healthy, S. aureus immunized cows was less than the response of peripheral blood lymphocytes. The lower responses of mammary gland lymphocytes were attributable both to less efficient antigen presentation by mammary gland antigen-presenting cells (APC) than by peripheral blood APC, and to lower responsiveness of mammary gland lymphocytes to lectins and antigen. In addition, the proliferative response of infected mammary gland lymphocytes was less than the response of uninfected mammary gland lymphocytes. This difference resulted from decreased proliferation of BoCD4+ lymphocytes in infected MGS. Flow cytometric analysis revealed that infected MGS contained increased numbers of BoCD8+ cells which coexpressed an activation molecule, ACT2, relative to BoCD8+ cells from uninfected MGS. Removal of BoCD8+, ACT2+ lymphocytes resulted in increased antigen responsiveness by lymphocytes from infected mammary glands. Also, when purified BoCD4+ lymphocytes were stimulated with antigen in the presence of varying numbers of ACT2+, BoCD8+ lymphocytes, antigen responsiveness was decreased in a dose-related manner. These data demonstrate that hyporesponsiveness of mammary gland lymphocytes to lectins and S. aureus antigen is, in part, mediated by activated BoCD8+ lymphocytes and suggest that this population enhances persistent intramammary infection by S. aureus.

Animals↗
PubMed1993

Contagious mastitis.

Contagious mastitis is defined. The major mastitis pathogens are Streptococcus agalactiae, Staphylococcus aureus, Corynebacterium bovis, Mycoplasma sp, and Streptococcus dysgalactiae. These pathogens are discussed relative to prevalence, virulence factors, pathology, and control. These control measures include milking time hygiene, segregation, culling, vaccination, and treatment.

Animals↗
PubMed1992

Evaluation of methods for differentiation of coagulase-positive staphylococci.

The purpose of this study was to determine the minimum number of tests that could be used to differentiate between the coagulase-positive strains of staphylococcus: Staphylococcus aureus, Staphylococcus hyicus, and Staphylococcus intermedius. Eighty coagulase-positive strains of each of the three species were examined. The five tests conducted were growth on modified Baird-Parker agar, growth on P agar supplemented with acriflavin, production of acetoin, anaerobic fermentation of mannitol, and presence of beta-galactosidase. Positive test percentages for S. aureus were 100% for growth on modified Baird-Parker agar, 100% for growth on P agar supplemented with acriflavin, 94% for production of acetoin, 99% for anaerobic fermentation of mannitol, and 0% for presence of beta-galactosidase. Positive test percentages for S. intermedius were 0% for growth on modified Baird-Parker agar, 0% for growth on P agar supplemented with acriflavin, 1% for production of acetoin, 0% for anaerobic fermentation of mannitol, and 100% for presence of beta-galactosidase. S. hyicus isolates were negative in all five tests. Results from the 240 coagulase-positive staphylococcus strains tested would suggest correct identification of coagulase-positive staphylococci with P agar supplemented with acriflavin and the beta-galactosidase test. These two tests are simple to conduct and result in quick and easy differentiation of the three coagulase-positive staphylococcal species.

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