Relationship between antimicrobial susceptibility of clinical mastitis pathogens and treatment outcome in cows

OBJECTIVE: To determine whether there was any association between results of in vitro antimicrobial susceptibility testing of pathogens isolated from cows with mild or moderate clinical mastitis and outcome of treatment. DESIGN: Observational study. ANIMALS: 133 cows with mild or moderate mastitis in a single quarter. PROCEDURE: Cows were treated by means of intramammary infusion of pirlimycin (50 mg) in the affected quarter once daily for 2 days; additional intramammary treatments with the same product were administered if the milk continued to appear abnormal. Duration of treatment and days until clinical cure were recorded. Bacterial isolates were tested for antimicrobial susceptibility by means of a broth micro-dilution technique. RESULTS: Environmental streptococci, coliforms, and coagulase-negative Staphylococcus spp were the most commonly isolated pathogens. Duration of treatment and days until clinical cure were not significantly different for cows from which pathogens that were susceptible or resistant to pirlimycin were isolated. Bacteriologic cure rates 14 and 21 days after treatment were not significantly different for cows with mastitis caused by susceptible or resistant bacteria. Similar results were found when data only from cows with mastitis caused by gram-positive isolates were analyzed. CONCLUSIONS AND CLINICAL RELEVANCE: In the present study, differences in clinical outcome for cows with mild or moderate mastitis that could be attributed to differences in results of in vitro susceptibility testing were not identified. The use of in vitro susceptibility testing to guide intramammary mastitis treatment cannot be recommended on the basis of results of this study.     

奶牛乳腺炎主要病原菌的药物敏感性检测

为调查甘肃及周边地区奶牛乳腺炎主要病原菌的药物敏感性情况,对于从甘肃兰州市、宁夏吴忠市及青海民和县的382个临床型和隐性乳腺炎奶样中分离到的101株细菌,采用96孔板微量肉汤稀释法,以美国临床检验标准委员会(NCCLS)的临界浓度参数为标准,测定了这些分离菌株对11种抗生素的药物敏感性并计算其体外最小抑菌浓度(MIC)。结果表明,99株分离菌株(98.02%)对红霉素、青霉素G、万古霉素和四环素不敏感,不适宜作为奶牛乳腺炎的临床用药,96株分离菌株(95.05%)对喹诺酮类及氨基糖苷类抗生素仍具有较高的敏感性,其中环丙沙星、诺氟沙星、卡那霉素抑菌效果最好,可在临床实践中参考选用。     

Etiology and antimicrobial susceptibility of udder pathogens from cases of subclinical mastitis in dairy cows in Sweden

Background

A nationwide survey on the microbial etiology of cases of subclinical mastitis in dairy cows was carried out on dairy farms in Sweden. The aim was to investigate the microbial panorama and the occurrence of antimicrobial resistance. Moreover, differences between newly infected cows and chronically infected cows were investigated.

Methods

In total, 583 quarter milk samples were collected from 583 dairy cows at 226 dairy farms from February 2008 to February 2009. The quarter milk samples were bacteriological investigated and scored using the California Mastitis Test. Staphylococci were tested for betalactamase production and presence of resistance was evaluated in all specific udder pathogens. Differences between newly infected cows and chronically infected cows were statistically investigated using logistic regression analysis.

Results

The most common isolates of 590 bacteriological diagnoses were Staphylococcus (S) aureus (19%) and coagulase-negative staphylococci (CNS; 16%) followed by Streptococcus (Str) dysgalactiae (9%), Str. uberis (8%), Escherichia (E.) coli (2.9%), and Streptococcus spp. (1.9%). Samples with no growth or contamination constituted 22% and 18% of the diagnoses, respectively. The distribution of the most commonly isolated bacteria considering only bacteriological positive samples were: S. aureus - 31%, CNS - 27%, Str. dysgalactiae - 15%, Str. uberis - 14%, E. coli - 4.8%, and Streptococcus spp. - 3.1%. There was an increased risk of finding S. aureus, Str. uberis or Str. dysgalactiae in milk samples from chronically infected cows compared to findings in milk samples from newly infected cows. Four percent of the S. aureus isolates and 35% of the CNS isolates were resistant to penicillin G. Overall, resistance to other antimicrobials than penicillin G was uncommon.

Conclusions

Staphylococcus aureus and CNS were the most frequently isolated pathogens and resistance to antimicrobials was rare.     

Effect of mastitis during the first lactation on production and reproduction performance of Holstein cows

The aim of this study was to evaluate the effect of postpartum mastitis between first calving and subsequent conception on production and reproduction performance as well as culling of Holstein cows. A data set of 9,183 first lactation cows was used. Results showed that the first cumulative 100?days' milk production and the milk yield standardized to 305?days were affected by the interval from calving to first mastitis (P??0.05). Calving year, calving difficulty score, and cumulative first 60?days milk production had significant impacts on mastitis risk (P?相似文献   

Rates of resistance of mastitis pathogens from cows in Switzerland

1215 strains of bacteria isolated from cows suffering from acute or chronic clinic mastitis were tested in the antibiogram according to the Kirby-Bauer method. The germ spectrum included: 304 DNase-positive strains of Staphylococci 304 DNase-negative strains of Staphylococci 304 CAMP-negative strains of Streptococci 303 Strains of Enterobacteriaceae The antibiotics selected were Penicillin, Cloxacillin, Neomycin und Gentamicin, then the combinations Penicillin/Neomycin, Cloxacillin/Gentamicin and Nafcillin/Penicillin/Dihydrostreptomycin. Gentamicin showed excellent action against Staphylococci and Enterobacteriaceae. Further on, the present investigations show, that the combination Cloxacillin/Gentamicin is fully effective in the gram-positive spectrum (against Streptococci and Staphylococci), as in the gram-negative spectrum (against E. coli).     

Antimicrobial drug susceptibility of Staphylococcus aureus isolated from bovine mastitis

Isolates of Staphylococcus aureus (106) from bovine mastitis were tested for susceptibility to antimicrobial agents. beta-lactamase was produced by 69.8 per cent of isolates and 7.5 per cent were resistant to streptomycin (minimum inhibitory concentration more than 32 micrograms/ml). Resistance to other agents was rare. Intrinsic resistance or tolerance to beta-lactam antibiotics was not found.     

Antimicrobial susceptibility patterns of respiratory tract pathogens from sheep and goats

OBJECTIVE: To determine the antimicrobial susceptibility of common respiratory tract pathogens from sheep and goats. DESIGN: Cross-sectional study. SAMPLE POPULATION: 41 respiratory tract isolates from sheep and 36 isolates from goats. PROCEDURES: Disk diffusion assay was used to determine antimicrobial susceptibility of isolates to amoxicillin-clavulanic acid, ceftiofur, ciprofloxacin, florfenicol, and tetracycline. Minimum inhibitory concentrations of florfenicol for these isolates were determined by use of the microbroth dilution technique. RESULTS: The most common isolates were Pasteurella multocida (n = 28) and Mannheimia haemolytica (39). All isolates were susceptible to amoxicillin-clavulanic acid, ceftiofur, ciprofloxacin, and florfenicol. Five percent (4/77) of isolates were resistant to tetracycline. CONCLUSIONS AND CLINICAL RELEVANCE: Susceptibility of respiratory tract pathogens isolated from sheep and goats to commonly used antimicrobial drugs in this study was high. Treatment of these species for bacterial respiratory tract disease is likely not complicated by antimicrobial resistance.     

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

Background 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.ObjectivesThis 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.MethodsIsolation 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.ResultsWe 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.ConclusionsThe present findings of this study indicate a development of antimicrobial resistance in main bacteria isolated from cows with mastitis in Argentina.     

A comparison between multivariate Slash, Student's t and probit threshold models for analysis of clinical mastitis in first lactation cows

Robust threshold models with multivariate Student's t or multivariate Slash link functions were employed to infer genetic parameters of clinical mastitis at different stages of lactation, with each cow defining a cluster of records. The robust fits were compared with that from a multivariate probit model via a pseudo‐Bayes factor and an analysis of residuals. Clinical mastitis records on 36 178 first‐lactation Norwegian Red cows from 5286 herds, daughters of 245 sires, were analysed. The opportunity for infection interval, going from 30 days pre‐calving to 300 days postpartum, was divided into four periods: (i) ?30 to 0 days pre‐calving; (ii) 1–30 days; (iii) 31–120 days; and (iv) 121–300 days of lactation. Within each period, absence or presence of clinical mastitis was scored as 0 or 1 respectively. Markov chain Monte Carlo methods were used to draw samples from posterior distributions of interest. Pseudo‐Bayes factors strongly favoured the multivariate Slash and Student's t models over the probit model. The posterior mean of the degrees of freedom parameter for the Slash model was 2.2, indicating heavy tails of the liability distribution. The posterior mean of the degrees of freedom for the Student's t model was 8.5, also pointing away from a normal liability for clinical mastitis. A residual was the observed phenotype (0 or 1) minus the posterior mean of the probability of mastitis. The Slash and Student's t models tended to have smaller residuals than the probit model in cows that contracted mastitis. Heritability of liability to clinical mastitis was 0.13–0.14 before calving, and ranged from 0.05 to 0.08 after calving in the robust models. Genetic correlations were between 0.50 and 0.73, suggesting that clinical mastitis resistance is not the same trait across periods, corroborating earlier findings with probit models.     

Effects of oral selenium supplementation on mastitis markers and pathogens in Estonian cows

The effects of selenium supplementation on mastitis parameters in milk and on glutathione peroxidase (GPx) levels in blood were evaluated. Fifty-five Estonian dairy cows were allocated to selenium-supplemented (n=39) and nonsupplemented (n=16) groups. The supplemented group received 0.2 ppm organic selenium in the form of selenium yeast in their diet daily for 8 weeks. The nonsupplemented cows received their standard diet with no selenium supplementation. Mastitis parameters (i.e., bacteriologic findings and somatic cell count, N-acetyl-beta-D-glucosaminidase, and bovine serum albumin concentration) and GPx levels were monitored. The increase in the activity of GPx was significantly (P<.001) greater in selenium-supplemented cows than in nonsupplemented ones. Milk samples from each quarter were examined before and 8 weeks after initiation of the study. The proportion of quarters still pathogen-free after 8 weeks was significantly (P<.01; odds ratio [OR]=9.7) higher in selenium-supplemented cows than in nonsupplemented cows. However, when quarters milk-tested as pathogen-infected at the start of the study were reexamined after 8 weeks, there was no significant (P=.14; OR 3.6) difference in the proportion of pathogen-free quarters between selenium-supplemented cows and nonsupplemented cows. Differential positive rate (Youden's index) revealed that individual quarters were more prone to be infected by pathogens when the blood GPx activities in cows were below the cutoff value of 3.3 microkat/g hemoglobin than when GPx activity was above this value. It was concluded that selenium supplementation in cows with low GPx activity seems to support udder defense mechanisms that favor reduction of the incidence of new mastitis cases.     

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.     

Genetic factors affecting susceptibility of dairy cows to udder pathogens

Bovine mastitis remains the most costly disease in dairy cattle. Breeding for resistance to udder pathogens has been proposed as a complementary tool to therapeutic and prophylactic measures not totally effective against the disease. This paper reviews factors affecting cows' susceptibility to pathogens at the animal, cellular/hormonal and DNA levels. Such factors will be useful in achieving genetic improvement for resistance only if they have desirable properties at the genetic and immunological levels. Because such properties are not always of significant magnitude, further research is necessary to identify characteristics of resistance in cows, considering the constant and complex interactions that occur between hosts and pathogens.     

Outcome prediction from the first examination in clinical mastitis using ultrasonography in dairy cows

The aim of this study was to examine whether ultrasonography can be used to predict the outcome of clinical mastitis in dairy cows. Forty‐seven mastitic quarters of Holstein‐Friesian cows were examined using ultrasonography at the time of the first examination. In mastitic mammary tissue, three sonographic signs indicating tissue abnormality were found: a hyperechoic spot in the parenchyma area, structural changes to the milk duct, and non‐homogeneous parenchyma. Logistic regression was used to evaluate whether the abnormal findings in the sonographic images can be used to predict the outcome of clinical mastitis. The outcomes of clinical mastitis were defined by the return, or failure to return, to marketable milk production. The sonogram finding of non‐homogeneous parenchyma in the first examination did predict the outcome of clinical mastitis, whereas the type of systemic symptoms (severe or moderate) was not a predictor in this regression model. Therefore, ultrasound examinations of mammary glands in the first examination could be a useful method for predicting outcome of clinical mastitis. There is an economic benefit if ultrasound examination in first examination helps in the decision of whether or not to treat the mastitic cows.     

Use of antimicrobial susceptibility testing of bacterial pathogens isolated from the milk of dairy cows with clinical mastitis to predict response to treatment with cephapirin and oxytetracycline

OBJECTIVE: To determine whether results of antimicrobial susceptibility testing of bacterial pathogens isolated from the milk of dairy cows with clinical mastitis were associated with duration of clinical signs or bacteriologic cure rate following treatment with cephapirin and oxytetracycline. DESIGN: Observational study on a convenience sample. ANIMALS: 58 dairy cows with 121 episodes of clinical mastitis. PROCEDURE: Cows that only had abnormal glandular secretions were treated with cephapirin alone. Cows with an inflamed gland and abnormal glandular secretions were treated with oxytetracycline and cephapirin. Cows with systemic signs of illness, an inflamed gland, and abnormal glandular secretions were treated with oxytetracycline and flunixin meglumine and frequent stripping of the affected glands. The Kirby-Bauer method was used for antimicrobial susceptibility testing, and current guidelines were used to categorize causative bacteria as susceptible or resistant to the treatment regimen. RESULTS: Median durations of episodes of clinical mastitis caused by susceptible (n = 97) and resistant (24) bacteria were not significantly different. Bacteriologic cure rates at 14 and 28 days were similar for episodes caused by susceptible and resistant bacteria; however, for 56 episodes of clinical mastitis caused by gram-positive bacteria and treated with cephapirin alone, bacteriologic cure rate at 28 days was significantly higher for susceptible than for resistant bacteria. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that antimicrobial susceptibility testing was of no value in predicting duration of clinical signs or bacteriologic cure rate in dairy cows with mastitis, except for episodes caused by gram-positive organisms treated with intramammary administration of cephapirin alone.     

Prevalence of subclinical mastitis and isolated udder pathogens in dairy cows in Southern Vietnam

Dairy production is not traditional in Vietnam. The farmers have little practical knowledge and udder health control is generally lacking. In order to give the farmers appropriate advice, knowledge about the distribution of udder pathogens is crucial. The aim of the study was to investigate the prevalence of sub-clinical mastitis and to identify udder pathogens isolated from smallholder dairy herds in Southern Vietnam. Twenty farms with a herd somatic cell count (SCC) ranging from low (≤400?×?10³?cells/mL) to high (>400?×?10³?cells/mL) were randomly selected. Milk samples were collected from 458 quarters of 115 clinically healthy cows. SCC was analyzed on farm by a portable cell counter. Bacteriological samples were taken using Mastistrip^© cassettes and sent to Sweden for examination. For all herds the mean herd SCC was 632?×?10³/mL milk. The prevalence of subclinical mastitis at quarter SCC basis was 63.2 % and at cow basis 88.6 %. Only 40 % of all cows were bacteriologically negative in all quarters. Streptococcus agalactiae was the most commonly found bacteria species, isolated from 96 of the 458 quarter samples, in 13 of the 20 farms. The results indicate pronounced subclinical mastitis problems among the dairy cows in this region mainly due to infections with S. agalactiae. The high prevalence of this highly contagious pathogen is probably attributable to the generally poor milking hygiene and low awareness of proper measures to prevent occurrence and spread of udder infections. A strict, targeted action program for the herds in this area is required in order to lower the prevalence of subclinical mastitis.     

Antimicrobial susceptibility of Staphylococcus spp. isolated from mammary parenchymas of slaughtered dairy cows

The high prevalence of the great resistance to antimicrobials shown by the aetiological agents of infectious bovine mastitis, often leads to chronic recurrent mastitis, one of the main causes of early culling of dairy cows. The purpose of this study was to determine the in vitro susceptibility pattern of Staphylococcus spp. isolated from mammary parenchymas of slaughtered dairy cows, to different anti-microbials. A total of 45 Staphylococcus spp. strains [33 coagulase-negative Staphylococcus (CNS) and 12 Staphylococcus aureus (SA)] were used. These strains were tested with 12 different antimicrobials by the Kirby and Bauer standardized disc diffusion method; 84.44% and 86.66% of the 45 strains were resistant to ampicillin and penicillin, respectively. The highest sensitivity was to cephalothin (84.44%), gentamicin (80%) and to sulphazotrin (77.77%). CNS showed higher resistance (P < 0.05) than SA. The in vitro susceptibility pattern of Staphylococcus spp. strains isolated from mammary parenchymas studied in the present investigation was similar to that observed in recent studies of in vitro and in vivo susceptibility patterns of Staphylococcus spp. isolated from cases of bovine mastitis.     

An immunogenomics approach to understanding periparturient immunosuppression and mastitis susceptibility in dairy cows

Studies comparing in vivo and in vitro functional capacities of leukocytes from non-parturient and periparturient dairy cows have provided substantial evidence that systemic and local mammary immune defenses are deficient around parturition. This evidence has lead to the reasonable hypothesis that immune deficiency underlies the heightened mastitis susceptibility of periparturient cows. Nutrition and vaccine studies substantiate this hypothesis, showing that dietary antioxidant supplementation and rigorous immunization regimes can bolster innate and humoral immunity to the point that mastitis severity and time for return to normal milk production are reduced. However, completely effective resolution of this significant production disease has not been achieved because so little is understood about its complex etiology. In particular, we possess almost no knowledge of how or why immune cells responding to parturient physiology end up with deficient functional capacities. Fluctuations in reproductive steroid hormones and chronic shifts in neuroendocrine hormones with roles in nutrient partitioning and appetite control may affect the expression of critical leukocyte genes in periparturient dairy cows. A thorough understanding of leukocyte biology during periparturition would seem a critical goal for future development of effective mastitis prevention strategies. Recently, our group has begun to use cDNA microarray technology to explore bovine leukocyte RNA for global gene expression changes occurring around parturition. We are working within the context of a hypothesis that the physiology of parturition negatively affects expression of critical genes in blood leukocytes. In the current study we initiated hypothesis testing using leukocyte RNA from a high producing Holstein cow collected at 14 days prepartum and 6 hours postpartum to interrogate a cDNA microarray spotted with > 700 cDNAs representing unique bovine leukocyte genes. This analysis revealed 18 genes with > or = 1.2-fold higher expression 14 days prepartum than 6 hours postpartum. BLASTN analysis of these genes revealed only one that can be considered a classical immune response gene. All other repressed genes were either unknown or putatively identified as encoding key proteins involved in normal growth and metabolism of cells. Given the critical roles of these repressed genes in normal cell functions, we may have identified good candidates to pursue with respect to periparturient immunosuppression and mastitis susceptibility.