Environmental gram-positive mastitis treatment: in vitro sensitivity and bacteriologic cure

Synergistic streptococcal phage λSA2 and B30 endolysins kill streptococci in cow milk and in a mouse model of mastitis

Bovine mastitis results in billion dollar losses annually in the USA alone. Streptococci are among the most relevant causative agents of this disease. Conventional antibiotic therapy is often unsuccessful and contributes to development of antibiotic resistance. Bacteriophage endolysins represent a new class of antimicrobials against these bacteria. In this work, we characterized the endolysins (lysins) of the streptococcal phages λSA2 and B30 and evaluated their potential as anti-mastitis agents. When tested in vitro against live streptococci, both enzymes exhibited near-optimum lytic activities at ionic strengths, pH, and Ca(2+) concentrations consistent with cow milk. When tested in combination in a checkerboard assay, the lysins were found to exhibit strong synergy. The λSA2 lysin displayed high activity in milk against Streptococcus dysgalactiae (reduction of CFU/ml by 3.5 log units at 100 μg/ml), Streptococcus agalactiae (2 log), and Streptococcus uberis (4 log), whereas the B30 lysin was less effective. In a mouse model of bovine mastitis, both enzymes significantly reduced intramammary concentrations of all three streptococcal species (except for B30 vs. S. dysgalactiae), and the effects on mammary gland wet weights and TNFα concentrations were consistent with these findings. Unexpectedly, the synergistic effect determined for the two enzymes in vitro was not observed in the mouse model. Overall, our results illustrate the potential of endolysins for treatment of Streptococcus-induced bovine mastitis.

Staphylococcus haemolyticus prophage ΦSH2 endolysin relies on cysteine, histidine-dependent amidohydrolases/peptidases activity for lysis 'from without'

Staphylococcus aureus is an important pathogen, with methicillin-resistant (MRSA) and multi-drug resistant strains becoming increasingly prevalent in both human and veterinary clinics. S. aureus causing bovine mastitis yields high annual losses to the dairy industry. Conventional treatment of mastitis by broad range antibiotics is often not successful and may contribute to development of antibiotic resistance. Bacteriophage endolysins present a promising new source of antimicrobials. The endolysin of prophage ΦSH2 of Staphylococcus haemolyticus strain JCSC1435 (ΦSH2 lysin) is a peptidoglycan hydrolase consisting of two catalytic domains (CHAP and amidase) and an SH3b cell wall binding domain. In this work, we demonstrated its lytic activity against live staphylococcal cells and investigated the contribution of each functional module to bacterial lysis by testing a series of deletion constructs in zymograms and turbidity reduction assays. The CHAP domain exhibited three-fold higher activity than the full length protein and optimum activity in physiological saline. This activity was further enhanced by the presence of bivalent calcium ions. The SH3b domain was shown to be required for full activity of the complete ΦSH2 lysin. The full length enzyme and the CHAP domain showed activity against multiple staphylococcal strains, including MRSA strains, mastitis isolates, and CoNS.

Treatment of clinical mastitis

In summary, culture-based therapy and severity levels are key to management of clinical mastitis. Antibiotic therapy should be strongly considered for gram-positive clinical mastitis. Antibiotic therapy is not necessary for mild-to-moderate gram-negative clinical mastitis. Antibiotic therapy is warranted for practically all severe clinical mastitis as well as fluids and anti-inflammatory drugs. Clinical mastitis cases due to yeast and fungal pathogens or no growth isolates do not warrant antibiotic therapy.

Mastitis therapy and antimicrobial susceptibility: a multispecies review with a focus on antibiotic treatment of mastitis in dairy cattle

Mastitis occurs in numerous species. Antimicrobial agents are used for treatment of infectious mastitis in dairy cattle, other livestock, companion animals, and humans. Mastitis is an economically important disease of dairy cattle and most mastitis research has focused on epidemiology and control of bovine mastitis. Antibiotic treatment of clinical and subclinical mastitis in dairy cattle is an established component of mastitis control programs. Research on the treatment of clinical and subclinical mastitis in other dairy species such as sheep and goats has been less frequent, although the general principles of mastitis therapy in small ruminants are similar to those of dairy cattle. Research on treatment of clinical mastitis in humans is limited and as for other species empirical treatment of mastitis appears to be common. While antimicrobial susceptibility testing is recommended to direct treatment decisions in many clinical settings, the use of susceptibility testing for antibiotic selection for mastitis treatments of dairy cattle has been challenged in a number of publications. The principle objective of this review is to summarize the literature evaluating the question, "Does antimicrobial susceptibility predict treatment outcome for intramammary infections caused by common bacterial pathogens?" This review also addresses current issues related to antimicrobial use and treatment decisions for mastitis in dairy cattle. Information on treatment of mastitis in other species, including humans, is included although research appears to be limited. Issues related to study design, gaps in current knowledge and opportunities for future research are identified for bovine mastitis therapy.

Elimination of erythromycin in milk after intramammary administration in cows with specific mastitis: relation to dose, milking frequency and udder health

Elimination of erythromycin in milk following intramammary therapy of specific mastitis in cows was studied. Five cows received therapy in one quarter (G1), and eight in two quarters with five milked twice (G2) and three thrice a day (G3). Dose infused was 300 mg/quarter 12 h × 5 times. The drug concentrations in milk were determined using microbial assay technique with Micrococcus luteus as the test organism. Considerable variations occurred in the excretion of drug; levels for treated quarters being 8.25 to 37.61 μg/ml at first milking that declined rapidly at 24 h and no drug activity was observed beyond 36 h post treatment. In total, about 6-25% of the last infused dose appeared in the milk. Drug crossed to 1/15 quarter (G1), 6/10 quarters (G2) and all the six untreated quarters (G3). Crossover levels were significantly higher in mastitic quarters and for G3 cows, but duration of excretion remained same in all cases. It seems that crossover of erythromycin to untreated quarters is related to the udder health and dose infused.

Short communication: In vitro antimicrobial susceptibility of Prototheca wickerhamii and Prototheca zopfii isolated from bovine mastitis

Bovine mastitis caused by Prototheca spp. can assume high significance because of economic losses and the potential risk to public health. Studies on the susceptibility of Prototheca spp. to antimicrobials have demonstrated its high level of resistance. We report the susceptibility of bovine isolates of Prototheca wickerhamii and Prototheca zopfii to amphotericin B and nystatin, 2 antifungal agents commonly used in the control of protothecosis, and discuss the results. After subculture, minimum inhibitory concentrations of both antifungal drugs were determined using macrodilution and agar diffusion methods. The inoculum concentration was standardized by determination of colony-forming units per milliliter. Nystatin showed more efficacy than amphotericin B in inhibiting P. wickerhamii growth. In contrast, growth inhibition of P. zopfii was similar for both antifungal agents. This study demonstrates different in vitro susceptibility patterns of P. wickerhamii and P. zopfii, reinforcing the necessity for more investigation into drugs that can be used with clinical efficacy.

Pharmacokinetic Profile of Erythromycin after Intramammary Administration in Lactating Dairy Cows with Specific Mastitis

The pharmacokinetics of erythromycin was studied in five lactating dairy cows following single intramammary infusion of 300 mg erythromycin in each of two quarters per cow with specific mastitis. Levels of erythromycin in plasma and quarter milk samples were measured by agar plate diffusion assay using Micrococcus luteus (ATCC 9341) as the test organism. Erythromycin level in plasma reached a peak concentration value (C(max)) of 0.07 +/- 0.01 microg/ml at 30 min; thereafter, levels declined gradually to reach 0.05 +/- 0.00 microg/ml 12 h post drug administration. The pharmacokinetic profile of the drug revealed mean absorption half life (t(1/2 ka)) as 0.26 +/- 0.05 h. The drug was eliminated slowly with elimination half-life (t(1/2 beta)) of 13.75 +/- 0.35 h and elimination rate constant (k(el)) of 0.04 +/- 0.00 h(-1). The volume of distribution based on the zero-time plasma concentration intercept of the least-squares regression line of the elimination phase (V(d(B))) was 0.032 L/kg. The drug crossed to untreated quarters also; mean drug levels of 0.20 +/- 0.07, 0.23 +/- 0.07, 0.17 +/- 0.04, and 0.17 +/- 0.04 microg/ml were found at 3, 6, 8 and 12 h, respectively. The mean drug concentration for treated quarters was measured as 22.97 +/- 2.31 microg/ml milk at first milking (12 h) following drug infusion. No apparent adverse reaction was seen in cows administered erythromycin. It is concluded that following intramammary infusion erythromycin diffuses readily and extensively in various body fluids and tissues and adequate concentration is maintained in udder tissues for at least 12 h post intramammary administration. Thus, erythromycin may be recommended for local therapy of acute mastitis caused by Gram-positive bacteria in lactating dairy cows.

Evaluation of the use of an on-farm system for bacteriologic culture of milk from cows with low-grade mastitis

OBJECTIVE

To determine factors associated with implementation and use of an on-farm system for bacteriologic culture of milk from cows with lowgrade mastitis, including information on how producers used the on-farm bacteriologic culture system to guide antimicrobial selection practices and the resulting impact on patterns of antimicrobial use.

DESIGN

Retrospective cohort study.

SAMPLE POPULATION

Producers of 81 dairy farms.

PROCEDURE

Farms that used an on-farm system for bacteriologic culture of milk from January 2001 to July 2003 were surveyed.

RESULTS

Over half of those producers continuing to use the on-farm culture delayed antimicrobial treatment pending results of bacteriologic culture. Most other producers initiated empirical antimicrobial treatment while bacteriologic culture results were pending. Several barriers to the use of an on-farm system were identified. Significant reductions in rates of antimicrobial use were detected when comparing antimicrobial use rates before and during use of the on-farm system. Most producers chose to treat cows with mastitis caused by gram-positive pathogens with antimicrobials, whereas treatment choices for cows with mastitis caused by gram-negative bacteria and in cases in which no growth was detected varied.

CONCLUSIONS AND CLINICAL RELEVANCE

Readily available results permit antimicrobial selections to be made on the basis of the causative agent of mastitis. Adoption of an on-farm system for bacteriologic culture of milk may result in significant reductions in the percentage of cows treated with antimicrobials. Decreasing antimicrobial use may have several benefits including preventing unnecessary discarding of milk, decreasing the potential for drug residues in milk, and improving treatment outcomes as a result of targeted treatments.

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.

Treatment of clinical mastitis. Using antimicrobial susceptibility profiles for treatment decisions

Antibiotic susceptibility of clinical mastitis pathogens has traditionally been determined using the agar diffusion method that was designed to reflect the antibiotic concentration in serum and interstitial fluid of human patients after receiving oral or intravenous administration. The validity of applying agar diffusion susceptibility breakpoints derived from humans to the treatment of bovine mastitis has not been established and is extremely questionable because (1) bovine milk pH and electrolyte, fat, protein, and leukocyte concentrations, growth factor composition, and pharmacokinetic profiles are different than those for human plasma and (2) human bacterial pathogens are often different from bovine mastitis pathogens. Also, antibiotics are distributed unevenly in an inflamed gland, and high antibiotic concentrations can alter neutrophil morphology or function in vitro and thereby inhibit bacterial clearance in vivo. The current cost of antibiotic susceptibility testing is $12 to $20 per test. Because the dairy industry is economically driven, any diagnostic test should be validated, have appropriate sensitivity and specificity, and have an acceptable economic return on the cost of testing before it can be routinely recommended. In the authors' opinion, antimicrobial susceptibility testing of mastitis pathogens has not been adequately validated for most mastitis pathogens and antibiotics; therefore, the authors do not currently recommend the use of susceptibility testing to guide treatment decisions for individual cows. Additional research is needed to further define the role, if any, that antimicrobial susceptibility testing should play in the treatment of clinical mastitis.

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.