Biomedical subjects

R N Zadoks

Publications and source records attributed to R N Zadoks.

15 recordsLinked to original sources

PubMed2006

Invited Review: The role of cow, pathogen, and treatment regimen in the therapeutic success of bovine Staphylococcus aureus mastitis.

Staphylococcus aureus is an important cause of udder infections in dairy herds. Both lactational and dry cow therapy are part of Staph. aureus control programs. Reported cure rates for Staph. aureus mastitis vary considerably. The probability of cure depends on cow, pathogen, and treatment factors. Cure rates decrease with increasing age of the cow, increasing somatic cell count, increasing duration of infection, increasing bacterial colony counts in milk before treatment, and increasing number of quarters infected. Staphylococcus aureus mastitis in hind quarters has a low cure rate compared with front quarters. Antimicrobial treatment of intramammary infections with penicillin-resistant Staph. aureus strains results in a lower cure rate for treatment with either beta-lactam or non-beta-lactam antibiotics. Other strain-specific factors may affect the probability of cure but routine diagnostic methods for use in bacteriology laboratories or veterinary practices are not yet available. The most important treatment factor affecting cure is treatment duration. Increased duration of treatment is associated with increased chance of cure. Economically, extended treatment is not always justified, even when indirect effects of treatment such as prevention of contagious transmission are taken into consideration. Usefulness of treatment trials could be improved by standardization of case definitions, consideration of host and strain factors, and sufficient statistical power. Treatment of young animals with penicillin-sensitive Staph. aureus infections is often justified based on bacteriological cure and economic outcome, whereas treatment of older animals, chronic infections, or penicillin-resistant isolates should be discouraged.

Aging↗

PubMed2006

Fecal shedding of Klebsiella pneumoniae by dairy cows.

Klebsiella pneumoniae is a common cause of clinical mastitis in dairy cattle. Wood products are considered to be the main source of Klebsiella on dairy farms. Environmental hygiene and use of inorganic bedding materials such as sand are recommended to control Klebsiella mastitis. However, Klebsiella mastitis still occurs on well-managed dairy farms that use sand as bedding material. In a 5-mo study in a New York State dairy herd performed during the summer of 2005, all of 9 samples of unused sand bedding tested negative for Klebsiella, whereas 14 of 18 samples of used sand bedding contained Klebsiella at a median level of 10(4.6) cfu/g. We hypothesized that fecal shedding of Klebsiella by dairy cows contributes to the presence of Klebsiella in the environment. Using a cheap and simple method based on ampicillin-containing MacConkey agar for screening, and biochemical tests for confirmation of species identity, 595 fecal samples from healthy dairy cattle were screened for presence of Klebsiella. In a longitudinal study of 100 cows followed over 5 mo, more than 80% of fecal samples tested positive for K. pneumoniae. The average prevalence of K. pneumoniae-positive fecal samples was also above 80% in a cross-sectional study of 100 cows from 10 herds across New York and Massachusetts. Fecal shedding of K. pneumoniae by a large proportion of dairy cows may explain why Klebsiella mastitis occurs in herds that use inorganic bedding material or other bedding material that is free from Klebsiella upon introduction into the barn.

Animals↗

PubMed2005

Macrolide and lincosamide resistance genes of environmental streptococci from bovine milk.

Environmental streptococcus isolates from bovine milk were identified to the species and strain level and screened for resistance to macrolide and lincosamide antibiotics by phenotypic and genotypic methods. Isolates were tested for resistance to erythromycin and pirlimycin by broth microdilution assays. Presence of ribosomal methylase genes (ermA, ermB, ermC) and efflux pump genes (mefA/E, msrA/C) was detected by polymerase chain reaction (PCR). Resistance to pirlimycin (minimum inhibitory concentration (MIC) = 8microg/ml) was detected in 6 of 13 Enterococcus isolates that were identified as E. faecium by API20Strep typing. msrC was detected in 10 enterococcal isolates but the detection of msrC was not associated with phenotypic resistance. msrC negative isolates were reclassified as Enterococcus mundtii based on sequencing of housekeeping genes. Resistance to erythromycin and pirlimycin (MIC > 16microg/ml) was detected in 4 of 4 Streptococcus dysgalactiae and 12 of 20 Streptococcus uberis isolates and was encoded by ermB. All Streptococcus isolates tested negative for ermA, ermC, mefA/E and msrA/C. Among ermB positive streptococci, three alleles were identified based on a 527 bp gene fragment. Each allele was detected in at least two herds. The same alleles have also been detected in other bacterial species from bovine and non-bovine hosts and farm soil, suggesting a theoretical potential for horizontal transfer of macrolide resistance genes on dairy farms.

Alleles↗

PubMed2005

Biofilm production by Staphylococcus aureus associated with intramammary infection.

Biofilm production by 221 Staphylococcus aureus isolates from 45 dairy herds was evaluated. Isolates were from composite milk of 117 cows, from teat skin of 70 cows, and from 34 milking machine unit liners. Of S. aureus from milk samples, 41.4% were biofilm producers, as compared to 24.7 and 14.7% of the isolates collected from skin and liners. Pulsed field gel electrophoresis (PFGE) best categorized S. aureus biofilm producers as compared to phage typing and binary typing. PFGE types that were significantly associated with isolation from milk as opposed to teat skin or liners, had isolates that were more likely to produce biofilm than PFGE types that were isolated from milk, skin and liners at similar frequencies. By contrast, PFGE type A was significantly associated with isolation from teat skin and had few biofilm producers. PFGE type Q, which is exclusively a milk, isolate produced more biofilm as evidenced by absorbance values. Given S. aureus that are associated with milk are more likely to produce biofilm as compared to extramammary sources (teat skin and milking unit liners), suggests that biofilm production is a risk factor for infection.

Animals↗

PubMed2005

Multilocus sequence typing of intercontinental bovine Staphylococcus aureus isolates.

A total of 258 bovine-associated Staphylococcus aureus isolates from the United States, Chile, and the United Kingdom, plus the reference isolate S. aureus Newbould 305 (NCIMB 702892), were analyzed by multilocus sequence typing (MLST). A collection of previously characterized United Kingdom isolates were also included in the analysis. The results demonstrated that MLST is suitable for the differentiation of bovine S. aureus isolates from various sites (milk, teat skin, milking machine unit liners, hands, and bedding) and countries. The theory of the host specificity of S. aureus is supported by the detection of a previously undescribed clonal complex that comprised 87.4% of the isolates studied, with representatives from all geographic locations investigated. This suggests that a single clonal group has achieved a widespread distribution and is responsible for the majority of infections. Some sequence types (STs; ST25, ST115, ST124, and ST126) demonstrated site specificity, as they were significantly (P < 0.05) associated with milk or teat skin.

Animals↗

PubMed2005

Cross-infection between cats and cows: origin and control of Streptococcus canis mastitis in a dairy herd.

Group G streptococci in animals usually belong to the species Streptococcus canis and are most commonly found in dogs and cats. Occasionally, Strep. canis is detected in milk from dairy cows. An outbreak of Strep. canis mastitis in a dairy herd is described. Based on results from bacterial culture and ribotyping, a cat with chronic sinusitis was the most likely source of the outbreak. Subsequent cow-to-cow transmission of Strep. canis was facilitated by poor udder health management, including use of a common udder cloth and failure to use postmilking teat disinfection. Infected cows had macroscopically normal udders and milk, but significantly higher somatic cell counts than Strep. canis-negative herd mates. The outbreak was controlled through antibiotic treatment of lactating cows, early dry-off with dry cow therapy, culling of infected animals, and implementation of standard mastitis prevention measures. Cure was significantly more likely in dry-treated cows (87.5%) and cows treated during lactation (67%) than in untreated cows (9%). Whereas mastitis due to group G streptococci or Strep. canis in dairy cows is usually limited to sporadic cases of environmental (canine or feline) origin, this case study shows that crossing of the host species barrier by Strep. canis may result in an outbreak of mastitis if management conditions are conducive to contagious transmission. In such a situation, measures that are successful in control of Strep. agalactiae can also be used to control Strep. canis mastitis.

Animals↗

PubMed2005

A partial budget model to estimate economic benefits of lactational treatment of subclinical Staphylococcus aureus mastitis.

Subclinical Staphylococcus aureus mastitis is rarely treated during lactation because it is widely believed to be uneconomical, although there are no economic studies that support this view. Partial budgeting was used to develop a deterministic simulation model to estimate the net cost or benefit of antibiotic treatment of subclinical S. aureus mastitis during lactation. Direct and indirect effects of treatment were taken into account, including prevention of clinical flare-ups and contagious transmission. Input variables were based on literature and on 2003-2004 prices in the Netherlands. When contagious transmission of S. aureus was likely (reproductive ratio R = 5.3), 3- and 8-d treatments resulted in an average net profit of 95.62 euros and 142.42 euros, respectively, compared with no treatment. When the probability of S. aureus transmission was low (R = 0.32), the average economic benefit of 3- or 8-d treatment was -21.12 euros and -57.70 euros, respectively. On low-transmission farms, 3-d treatment was profitable when the appropriate cows were selected for treatment using known risk factors for cure. Sensitivity analysis showed that the 6 most influential input variables in the model were chance of bacteriological cure, R, probability of culling, retention pay-off, and cost of antibiotics and bacterial culture. Although the economic outcome of lactational treatment of subclinical S. aureus mastitis is highly herd-, cow-, and strain-dependent, treatment is economically justified in many situations.

Animals↗

PubMed2004

Mastitis-causing streptococci are important contributors to bacterial counts in raw bulk tank milk.

The objective of this study was to probe the contribution of streptococci to the microbial quality of raw milk. Over a 5-month period, bulk tank milk samples from 48 New York State dairy farms were analyzed qualitatively for bacterial ecology and quantitatively for total bacterial, streptococcal, staphylococcal, and gram-negative bacterial counts. Linear regression analysis was used to determine the contribution of differential counts to total bacterial counts. Streptococci, staphylococci, and gram-negative bacteria accounted for 69, 3, and 3% of total bacterial count variability, respectively. Randomly selected Streptococcus isolates from each bulk tank milk sample were identified to species by means of the API 20 STREP identification system. The most commonly identified streptococcal species were Streptococcus uberis, Aerococcus viridans, and Streptococcus agalactiae, which were detected in 81, 50, and 31% of 48 bulk tank samples, respectively. For five herds, S. uberis isolates from bulk tank milk and individual cows were characterized by PvuII ribotyping. A farm-specific dominant ribotype was found in each bulk tank sample, and that ribotype was isolated from at least one cow within each herd of origin. Bacteriological and strain typing data indicate that control of streptococci, specifically mastitis-causing species, is important for improvement of the microbial quality of raw milk in New York State.

Animals↗

PubMed2003

Clinical, epidemiological and molecular characteristics of Streptococcus uberis infections in dairy herds.

A longitudinal observational study (18 months) was carried out in two Dutch dairy herds to explore clinical, epidemiological and molecular characteristics of Streptococcus uberis mastitis. Infections (n = 84) were detected in 70 quarters of 46 cows. Bacterial isolates were characterized at strain level by random amplified polymorphic DNA (RAPD) fingerprinting. Persistent infections were usually attributable to one strain, while recurrent infections could be caused by different strains. When multiple quarters of a cow were infected, infections were mostly caused by one strain. In each herd, multiple strains were identified yet one strain predominated. The majority of all infections were subclinical, and infections attributed to predominant strains were more chronic than infections attributed to other strains. Epidemiological and molecular data suggest infection from environmental sources with a variety of S. uberis strains as well as within-cow and between-cow transmission of a limited number of S. uberis strains, with possible transfer of bacteria via the milking machine.

Animals↗

PubMed2002

A mathematical model of Staphylococcus aureus control in dairy herds.

An ordinary differential equation model was developed to simulate dynamics of Staphylococcus aureus mastitis. Data to estimate model parameters were obtained from an 18-month observational study in three commercial dairy herds. A deterministic simulation model was constructed to estimate values of the basic (R0) and effective (Rt) reproductive number in each herd, and to examine the effect of management on mastitis control. In all herds R0 was below the threshold value 1, indicating control of contagious transmission. Rt was higher than R0 because recovered individuals were more susceptible to infection than individuals without prior infection history. Disease dynamics in two herds were well described by the model. Treatment of subclinical mastitis and prevention of influx of infected individuals contributed to decrease of S. aureus prevalence. For one herd, the model failed to mimic field observations. Explanations for the discrepancy are given in a discussion of current knowledge and model assumptions.

Animal Husbandry↗

PubMed2002

Comparison of Staphylococcus aureus isolates from bovine and human skin, milking equipment, and bovine milk by phage typing, pulsed-field gel electrophoresis, and binary typing.

Staphylococcus aureus isolates (n = 225) from bovine teat skin, human skin, milking equipment, and bovine milk were fingerprinted by pulsed-field gel electrophoresis (PFGE). Strains were compared to assess the role of skin and milking equipment as sources of S. aureus mastitis. PFGE of SmaI-digested genomic DNA identified 24 main types and 17 subtypes among isolates from 43 herds and discriminated between isolates from bovine teat skin and milk. Earlier, phage typing (L. K. Fox, M. Gershmann, D. D. Hancock, and C. T. Hutton, Cornell Vet. 81:183-193, 1991) had failed to discriminate between isolates from skin and milk. Skin isolates from humans belonged to the same pulsotypes as skin isolates from cows. Milking equipment harbored strains from skin as well as strains from milk. We conclude that S. aureus strains from skin and from milk can both be transmitted via the milking machine, but that skin strains are not an important source of intramammary S. aureus infections in dairy cows. A subset of 142 isolates was characterized by binary typing with DNA probes developed for typing of human S. aureus. Typeability and overall concordance with epidemiological data were lower for binary typing than for PFGE while discriminatory powers were similar. Within several PFGE types, binary typing discriminated between main types and subtypes and between isolates from different herds or sources. Thus, binary typing is not suitable as replacement for PFGE but may be useful in combination with PFGE to refine strain differentiation.

Animals↗

PubMed2001

[Serum gammaglobulin titer in goat kids after colostrum administration: effect of commercial colostrum replacers].

Seven commercially available colostrum replacers were tested for their ability to substitute for goat colostrum as a source of gammaglobulin for goat kids. One hundred kids were fed with goat colostrum or colostrum replacer after separation from their mothers at birth. Blood samples were taken from ten kids at birth, and from all kids at 48 hours after birth. Samples were used to measure the total protein content and gammaglobulin concentration of serum. Kids fed with goat colostrum had higher gammaglobulin concentrations than newborn kids or kids fed with replacer. For three replacers, the gammaglobulin concentrations were the same as those of newborn kids. For three other replacers, the gammablobulin concentrations were similar but higher than those of newborn kids. For one replacer, the levels of gammaglobulin were higher than those of in newborn kids and higher than those measured after feeding of the other replacers. None of the replacers was an adequate substitute for goat colostrum as a source of gammaglobulins.

Animal Feed↗

PubMed2001

Analysis of an outbreak of Streptococcus uberis mastitis.

An outbreak of Streptococcus uberis mastitis was described to gain insight into the dynamics of Strep. uberis infections at a herd level. Data were obtained from a longitudinal observational study on a commercial Dutch dairy farm with good udder health management. Quarter milk samples for bacteriological culture were routinely collected at 3-wk intervals from all lactating animals (n = 95 +/- 5). Additional samples were collected at calving, clinical mastitis, dry-off, and culling. During the 78-wk observation period, 54 Strep. uberis infections were observed. The majority of infections occurred during a 21-wk period that constituted the disease outbreak. The incidence rate was higher in quarters that had recovered from prior Strep. uberis infection than in quarters that had not experienced Strep. uberis infection before. The incidence rate of Strep. uberis infection did not differ between quarters that were infected with other pathogens compared with quarters that were not infected with other pathogens. The expected number of new Strep. uberis infections per 3-wk interval was described by means of a Poisson logistic regression model. Significant predictor variables in the model were the number of existing Strep. uberis infections in the preceding time interval (shedders), phase of the study (early phase vs. postoutbreak phase), and prior infection status of quarters with respect to Strep. uberis, but not infection status with respect to other pathogens. Results suggest that contagious transmission may have played a role in this outbreak of Strep. uberis mastitis.

Animals↗

PubMed2001

Cow- and quarter-level risk factors for Streptococcus uberis and Staphylococcus aureus mastitis.

This study was designed to identify risk factors for intramammary infections with Streptococcus uberis and Staphylococcus aureus under field conditions. An 18-mo survey with sampling of all quarters of all lactating cows at 3-wk intervals was carried out in three Dutch dairy herds with medium bulk milk somatic cell count (200,000 to 300,000 cells/ml). Quarter milk samples were used for bacteriology and somatic cell counting. Data on parity, lactation stage, and bovine herpesvirus 4-serology were recorded for each animal. During the last year of the study, body condition score, and teat-end callosity scores were recorded at 3-wk intervals. A total of 93 new infections with Strep. uberis were detected in 22,665 observations on quarters at risk for Strep. uberis infection, and 100 new infections with Staph. aureus were detected in 22,593 observations on quarters at risk for Staph. aureus infection. Multivariable Poisson regression analysis with clustering at herd and cow level was used to identify risk factors for infection. Rate of infection with Strep. uberis was lower in first- and second-parity cows than in older cows, and depended on stage of lactation in one herd. Quarters that were infected with Arcanobacterium pyogenes or enterococci, quarters that had recovered from Strep. uberis- or Staph. aureus-infection in the past, and quarters that were exposed to another Strep. uberis infected quarter in the same cow had a higher rate of Strep. uberis infection. Teat-end callosity and infection with coagulase-negative staphylococci or corynebacteria were not significant as risk factors. Rate of Staph. aureus infection was higher in bovine herpesvirus 4-seropositive cows, in right quarters, in quarters that had recovered from Staph. aureus or Strep. uberis infection, in quarters exposed to other Staph. aureus infected quarters in the same cow, and in quarters with extremely callused teat ends. Infection with coagulase-negative staphylococci was not significant as a risk factor. The effect of infection with corynebacteria on rate of infection with Staph. aureus depended on herd, stage of lactation, and teat-end roughness. Herd level prevalence of Strep. uberis or Staph. aureus, and low quarter milk somatic cell count were not associated with an increased rate of infection for Strep. uberis or Staph. aureus.

Animals↗

PubMed2000

[Serum gamma globulin concentration in goat kids after colostrum administration: effect of time of administration, volume and type of colostrum].

In this study, which was performed on a Dutch dairy goat farm, several aspects of the administration of colostrum to new-born goat kids were examined. Time of colostrum administration and amount and type of colostrum administered were compared. Effectiveness was measured as total serum protein content and gamma globulin fraction. No significant differences in serum gamma globulin titre were observed between kids that received colostrum at 30 or 60-90 minutes post partum, respectively. Titres were significantly lower in kids that received 100 ml of colostrum instead of 150-200 ml. The effect of sheep colostrum replacer or cow colostrum was also examined. Gamma globulin titres were significantly high with goat colostrum than with cow colostrum or sheep colostrum replacer, and titres were higher with cow colostrum than with sheep colostrum replacer. Based on the results of this experiment, the following protocol is suggested for colostrum administration to goat kids: single administration of 150-200 ml of goat colostrum within 90 minutes of birth. Use of cow colostrum is not advised because it may lead to transmission of paratuberculosis. Use of sheep colostrum replacer as a source of passive immunity is not recommended.

Animals↗