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1.
The objective of this study was to determine the minimum inhibitory concentrations (MICs) and pharmacodynamic profiles of four ionophores (lasalocid, monensin, narasin and salinomycin) against staphylococcal isolates from clinical cases of human and veterinary staphylococcal infections, and to determine the effect of methicillin resistance on the antimicrobial activity of ionophores. Broth microdilution MIC testing was used to determine antimicrobial activity against 156 staphylococcal isolates of human and veterinary origin. Pharmacodynamic profiles were examined using time-kill kinetics profiles against an ATCC type strain of Staphylococcus aureus and a clinical isolate of methicillin-resistant Staphylococcus pseudintermedius. All tests were performed in accordance with CLSI guidelines. All four ionophores demonstrated antimicrobial activity against methicillin-resistant staphylococci at concentrations similar to those observed for methicillin-susceptible isolates of the same species. Testing of human and veterinary MRSA isolates also showed that MIC values were not influenced by the host origin of the isolates. Pharmacodynamic profiles were similar for both isolates tested across all four ionophores, with similar reductions in viable cell counts being observed over an 18- to 24-hr period. Lasalocid, monensin, narasin and salinomycin all demonstrated antimicrobial activity against staphylococcal isolates of human and veterinary origins, with activity being unaffected by methicillin resistance status, although some Staphylococcus species-specific effects were observed that require further investigation.  相似文献   

2.
Otitis externa (OE) is a frequently reported disorder in dogs associated with secondary infections by Staphylococcus, Pseudomonas and yeast pathogens. The presence of biofilms may play an important role in the resistance of otic pathogens to antimicrobial agents. Biofilm production of twenty Staphylococcus pseudintermedius and twenty Pseudomonas aeruginosa canine otic isolates was determined quantitatively using a microtiter plate assay, and each isolate was classified as a strong, moderate, weak or nonbiofilm producer. Minimum biofilm eradication concentration (MBEC) of two ionophores (narasin and monensin) and three adjuvants (N‐acetylcysteine (NAC), Tris‐EDTA and disodium EDTA) were investigated spectrophotometrically (OD570nm) and quantitatively (CFU/ml) against selected Staphylococcus and Pseudomonas biofilm cultures. Concurrently, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of planktonic cultures were assessed. 16/20 of the S. pseudintermedius clinical isolates were weak biofilm producers. 19/20 P. aeruginosa clinical isolates produced biofilms and were distributed almost equally as weak, moderate and strong biofilm producers. While significant antibiofilm activity was observed, no MBEC was achieved with narasin or monensin. The MBEC for NAC ranged from 5,000–10,000 µg/ml and from 20,000–80,000 µg/ml against S. pseudintermedius and P. aeruginosa, respectively. Tris‐EDTA eradicated P. aeruginosa biofilms at concentrations ranging from 6,000/1,900 to 12,000/3,800 µg/ml. The MBEC was up to 16‐fold and eightfold higher than the MIC/MBC of NAC and Tris‐EDTA, respectively. Disodium EDTA reduced biofilm growth of both strains at concentrations of 470 µg/ml and higher. It can be concluded that biofilm production is common in pathogens associated with canine OE. NAC and Tris‐EDTA are effective antibiofilm agents in vitro that could be considered for the treatment of biofilm‐associated OE in dogs.  相似文献   

3.
Mastitis is one of the most important diseases in dairy cattle of which Staphylococcus aureus is a major pathogen. Despite an apparently good antimicrobial susceptibility in vitro, the cure of diseased animals from this bacteriological infection is often disappointing, which results in cases of recurrent clinical- and chronic subclinical infections. It has been suggested that these recurrent and chronic Staphylococcus infections can be attributed to the growth of bacteria in biofilm. The objective of this study was to compare the susceptibility for antimicrobial agents of S. aureus isolates obtained from bovine mastitis growing under different conditions. These conditions include a conventional conventional microbroth dilution assay in which minimal inhibitory concentration values are determined, the MBEC assay which measures both the susceptibility in biofilm and the susceptibility of sequester cells released from the biofilm. A comparison of the susceptibility for antimicrobial agents of a number of representative S. aureus isolates grown in broth (representing in vitro growth conditions) or milk (representing in vivo growth conditions) is also made. The results indicate that S. aureus isolates obtained from bovine mastitis are highly resistant to antimicrobial agents when growing in biofilms.  相似文献   

4.
Mycoplasma spp. are highly contagious pathogens and intramammary Mycoplasma infection is a serious issue for the dairy industry. As there is no effective vaccine for Mycoplasma infection, control depends on good husbandry and chemo‐antibiotic therapy. In this study, antimicrobial susceptibility of Mycoplasma strains recently isolated from cases of bovine mastitis in Japan was evaluated by minimum inhibitory concentration (MIC). All Mycoplasma bovis strains were sensitive to pirlimycin, danofloxacin and enrofloxacin, but not kanamycin, oxytetracycline, tilmicosin or tylosin. M. californicum and M. bovigenitalium strains were sensitive to pirlimycin, danofloxacin, enrofloxacin, oxytetracycline, tilmicosin and tylosin, but not to kanamycin. This is the first report to describe the MIC of major antimicrobial agents for Mycoplasma species isolated from bovine mastitis in Japan.  相似文献   

5.
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.  相似文献   

6.
Biofilm formation and antimicrobial resistance of Staphylococcus aureus are important virulence factors in cases of mastitis in dairy cows. However, few studies have investigated mastitis strains isolated from heifers. Within this context, the objective of the present study was to investigate biofilm formation on Congo red agar, the presence of the icaA and icaD genes by polymerase chain reaction (PCR), and the percentage of in vitro antimicrobial resistance of 110 S. aureus isolates from mammary gland secretions of heifers and cows with mastitis. PCR detected the icaA and icaD genes in 98% and 100% of isolates, respectively. However, only 55.5% of all isolates produced a biofilm on Congo red agar. Antimicrobial susceptibility testing revealed that 47.0% of isolates from heifers and 70.4% of isolates from cows were resistant to at least one of the antimicrobial agents tested. Resistance to penicillin and/or ampicillin was the most frequent (44.5%). These results indicate the need to implement prophylactic and control measures of mastitis for heifers. Heifers and cows can carry resistant strains with the capacity of biofilm production, a fact representing a threat to public health and animal well‐being and generating losses to dairy farmers.  相似文献   

7.
Maduramicin ammonium was given at 2.5-8 ppm in the feed to broilers experimentally infected with coccidia recently isolated from broiler farms where ionophores had been used for several years. Infection pressure varied from mild to severe in five trials: mortality in unmedicated controls ranged from 0 to 59%, intestinal lesion scores were high, and weight gain was depressed by the infections. The cultures of Eimeria were partly resistant to ionophores: birds medicated with monensin at 100-121 ppm had only modest reductions in lesion scores and incomplete protection against weight loss or mortality. Control of infections by maduramicin was significant at 4 ppm but best at 5-7 ppm. Maduramicin was more effective than monensin or narasin, but about the same as salinomycin, in reducing lesions and mortality and in protecting performance. Maduramicin was well tolerated within the dose range of 5-7 ppm.  相似文献   

8.
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.  相似文献   

9.
Antimicrobial therapy is a useful tool to control bovine mastitis caused by Staphylococcus aureus, as consequence an increase in staphylococci resistant cases has been registered. Alternative strategies are desirable and bacteriocins represent attractive control agents to prevent bovine mastitis. The aim of this work was to evaluate the activity of five bacteriocins synthesized by Bacillus thuringiensis against S. aureus isolates associated to bovine mastitis. Fifty S. aureus isolates were recovered from milk composite samples of 26 Holstein lactating cows from one herd during September 2007 to February 2008 in México and susceptibility of those isolates to 12 antibiotics and 5 bacteriocins from B. thuringiensis was evaluated. S. aureus isolates were mainly resistant to penicillin (92%), dicloxacillin (86%), ampicillin (74%) and erythromycin (74%); whereas susceptibility to gentamicin, trimethoprim and tetracycline was detected at, respectively, 92%, 88%, and 72%. All S. aureus isolates showed susceptibility to the five bacteriocins synthesized by B. thuringiensis, mainly to morricin 269 and kurstacin 287 followed by kenyacin 404, entomocin 420 and tolworthcin 524. Our results showed that S. aureus isolates had differences in the antimicrobial resistance patterns and were susceptible to bacteriocins produced by B. thuringiensis, which could be useful as an alternative method to control bovine mastitis.  相似文献   

10.
OBJECTIVE: To determine whether antimicrobial resistance patterns of major mastitis pathogens isolated from milk samples from dairy cows have changed over time. DESIGN: Retrospective study. SAMPLE POPULATION: 8905 bacterial isolates obtained from milk samples submitted to the Wisconsin Veterinary Diagnostic Laboratory between January 1994 and June 2001. PROCEDURE: Antimicrobial susceptibility was determined by means of the Kirby-Bauer disk diffusion method. Logistic regression was used to determine whether percentages of isolates resistant to various antimicrobials changed over time. RESULTS: For the gram-positive mastitis pathogens, percentages of isolates resistant to various flactam antimicrobials did not increase over the course of the study. Percentage of Staphylococcus aureus isolates resistant to penicillin decreased from 49 to 30%; percentage of Streptococcus isolates resistant to penicillin decreased from 6 to 1%. Percentage of isolates resistant to erythromycin increased for S aureus, Escherichia coli, Enterobacter spp, Enterococcus spp, and Pasteurella spp. Percentage of isolates resistant to lincomycin increased for S aureus and Staphylococcus spp. Percentage of coagulase-negative Staphylococcus isolates resistant to pirlimycin increased from 6 to 19%. For several pathogens, percentages of isolates resistant to sulfisoxazole and to trimethoprim-sulfamethoxazole decreased. No pathogens had a significant increase in the percentage of isolates resistant to novobiocin-penicillin. CONCLUSIONS AND CLINICAL RELEVANCE: Results did not indicate a trend toward increased antimicrobial resistance among mastitis pathogens isolated from milk samples from dairy cows between 1994 and 2001. Reduced resistance to flactam antimicrobials was identified for several gram-positive mastitis pathogens.  相似文献   

11.
Henri, J., Maurice, R., Postollec, G., Dubreil‐Cheneau, E., Roudaut, B., Laurentie, M., Sanders, P. Comparison of the oral bioavailability and tissue disposition of monensin and salinomycin in chickens and turkeys. J. Vet. Pharmacol. Therap.  35 , 73–81. The current study describes the pharmacokinetic parameters of two carboxylic polyether ionophores: monensin in turkeys and salinomycin in chickens. These data can be used to understand and predict the occurrence of undesirable residues of coccidiostats in edible tissues of these animal species. Special attention is paid to the distribution of residues between the different edible tissues during and at the end of the treatment period. For the bioavailability studies, monensin was administered to turkeys intravenously, in the left wing vein, at a dose of 0.4 mg /kg and orally at a dose of 20 mg /kg. Salinomycin was administered to chickens intravenously, in the left wing vein, at a dose of 0.25 mg /kg and orally at a dose of 2.5 mg /kg. Residue studies were carried out with supplemented feed at the rate of 100 mg /kg of feed for monensin in turkeys and 70 mg /kg for salinomycin in chickens, respectively. Coccidiostats had a low bioavailability in poultry (around 30% for monensin in chickens, around 1% for monensin in turkeys and around 15% for salinomycin in chickens). Monensin in chickens had a longer terminal half‐life (between 3.07 and 5.55 h) than both monensin in turkeys (between 1.36 and 1.55 h) and salinomycin in chickens (between 1.33 and 1.79 h). The tissue /plasma partition coefficients showed a higher affinity of both monensin and salinomycin for fat, followed by liver and muscle tissue. The depletion data showed a fairly rapid elimination of coccidiostats in all the tissues after cessation of treatment. According to the results of depletion studies, a withdrawal period of 1 day seems sufficient to avoid undesirable exposure of consumers.  相似文献   

12.
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.  相似文献   

13.
The aims of this study were to investigate the antibacterial activity of lemongrass oil (LG) and its major components which were citral, geraniol and myrcene, against four strains of clinically isolated bovine mastitis pathogens, including Staphylococcus aureus, Streptococcus agalactiae, Bacillus cereus and Escherichia coli by the broth microdilution method, as well as their activity on S. aureus biofilm formation. Attempts to clarify their mechanisms of action by investigation of the effects on intracellular material leakage and morphological changes of S. aureus DMST 4745 were also made. The results demonstrate that S. agalactiae and B. cereus are more susceptible to LG, citral and geraniol than S. aureus and E. coli. Moreover, they also inhibit S. aureus biofilm formation and exhibit effective killing activities on preformed biofilms. The LG appears to have multiple targets in the bacterial cell, depending on concentration used as well as the amount of its components.  相似文献   

14.
Staphylococcus aureus is one of the most prevalent causes of bovine mastitis. The antimicrobial treatment of this disease is currently based on antimicrobial susceptibility tests according to CLSI standards. However, various studies have shown that there is a discrepancy between the results of this standard susceptibility test and the actual cure rate of the applied antimicrobial treatment. Increasing evidence suggests that biofilm formation by S. aureus is associated with this problem. The currently available antimicrobial susceptibility assays for bacteria growing in biofilms, are not considered reliable enough for routine application. Therefore, the objective of this study was to further develop a susceptibility test for bacteria growing in biofilm, suitable for routine testing of the antimicrobial susceptibility of S. aureus. With the expansion of the available MBEC assay to an extended biofilm susceptibility test, that comprises 2 and 4 consecutive days of antimicrobial challenge, the antimicrobial susceptibility for S. aureus growing in biofilm was further analysed. The results showed clear differences between strains and various antimicrobial agents with respect to the effect of longer duration of the antimicrobial challenge on the eradication of S. aureus growing in biofilm. The extended biofilm susceptibility test also indicates that each bacterial strain requires a specific duration of antimicrobial therapy, which cannot be derived from a standard susceptibility test or from a 24-h biofilm susceptibility test.  相似文献   

15.
Batch culture fermentations were used to determine the effects of avoparcin, lasalocid, monensin, narasin, salinomycin, thiopeptin, tylosin, virginiamycin, monensin + tylosin combination, and two new ionophore compounds (RO22-6924/004 and RO21-6447/009) on lactic acid and volatile fatty acid (VFA) production. Ruminal fluid from cattle fed a high alfalfa hay diet was incubated with glucose for 12 h in a buffered medium to determine the effect of antimicrobial compounds on lactic acid concentration. Fermentations treated with antimicrobial compounds had higher final pH and lower L(+) lactic acid concentration. Narasin and salinomycin were more inhibitory than other ionophore compounds. Monensin and tylosin in combination was more effective than monensin alone. Among the nonionophore compounds, avoparcin was the least effective and thiopeptin, tylosin and virginiamycin were extremely effective in reducing lactic acid concentration. Ruminal fluid from cattle fed a diet of alfalfa hay and grain (50:50) was incubated with a mixture of sugars, casein and urea for 12 h in a buffered medium to determine the effect of antimicrobial compounds on VFA production. Generally, total VFA concentration was not affected by antimicrobial compounds except RO22-6924/004, tylosin and virginiamycin, which caused a reduction at high concentrations. Tylosin, monensin and tylosin mixture, thiopeptin and virginiamycin at high concentrations (greater than 6.0 micrograms/ml) increased the acetate proportion. All compounds increased the molar proportion of propionate. Tylosin and virginiamycin at high concentrations (greater than 6.0 micrograms/ml) decreased the proportion of propionate. Monensin and tylosin in combination had no effect on propionate proportion. Among the compounds tested, narasin and salinomycin were the most effective in enhancing propionate proportion. Ionophore compounds were more inhibitory to butyrate production than the nonionophore compounds. Batch culture fermentations may be used to quantitate the relative efficacy of antimicrobial compounds to alter ruminal fermentation characteristics.  相似文献   

16.
Staphylococcus aureus is one of the most common pathogens responsible for contagious mastitis in ruminants. The ability of S. aureus to form biofilm in vivo is considered to be a major virulence factor influencing its pathogenesis in mastitis. The objectives of the study were to examine in vitro slime production, biofilm formation, and the presence of the ica gene locus and icaA and icaD genes in S. aureus isolates from bovine mastitis. Thirty-two of the 35 isolates tested produced slime on Congo red agar, whereas only 24 of the isolates were found to produce biofilm in vitro. However, all the 35 isolates possessed the ica locus, icaA and icaD genes. This study indicates a high prevalence of the ica genes among S. aureus mastitis isolates, and their presence is not always associated with in vitro formation of slime or biofilm. A combination of phenotypic and genotypic tests is recommended for investigating biofilm formation in S. aureus.  相似文献   

17.
A bovine myeloid antimicrobial peptide (BMAP‐28) is a member of the cathelicidin family which is included in the innate immune system of mammals. Recently, there have been many studies about antimicrobial peptides. This study aims to clarify whether BMAP‐28 has bactericidal activity against methicillin‐resistant Staphylococcus aureus (MRSA) and compares its activity against methicillin‐susceptible S. aureus (MSSA) and MRSA. We found that the peptide was effective in killing MRSA (minimal inhibitory concentration (MIC) range; 5–20 µg/mL). It was also revealed that MSSA (MIC range; 1.25–20 µg/mL) had two levels of susceptibility to BMAP‐28. We also examined the effect of BMAP‐28 on bacterial shape to visually show its activity. After exposure to the peptide, both MSSA and MRSA cells showed the morphological changes on their surfaces. Our results indicate that BMAP‐28 is a promising candidate for medicine against drug‐resistant bacteria.  相似文献   

18.
A bovine myeloid antimicrobial peptide antimicrobial peptide (BMAP‐28) is a member of the cathelicidin family and acts as a component of innate immunity. There are few reports of susceptibility difference of methicillin‐resistant Staphylococcus aureus (MRSA) and susceptible strains (MSSA) against BMAP‐28. This study aims to clarify how a few amino acid substitutions of BMAP‐28 are related to its antimicrobial activity using four analog peptides of BMAP‐28. We also compared cellular fatty acid components of MSSA and MRSA using gas chromatography. We found that a few amino acid substitutions of BMAP‐28 do not change antimicrobial activity. It was also revealed that the percentage of cis‐11‐eicosenoic acid in total detected fatty acids of MRSA was significantly higher than that of MSSA. In addition, the percentage of palmitic acid in total detected fatty acids of MRSA tended to be lower than that of MSSA. Our results will provide new information to deal with the question of differences in bacterial susceptibility against BMAP‐28.  相似文献   

19.
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20.
Coagulase-negative staphylococci-emerging mastitis pathogens   总被引：3，自引：0，他引：3  
Coagulase-negative staphylococci (CNS) have become the most common bovine mastitis isolate in many countries and could therefore be described as emerging mastitis pathogens. The prevalence of CNS mastitis is higher in primiparous cows than in older cows. CNS are not as pathogenic as the other principal mastitis pathogens and infection mostly remains subclinical. However, CNS can cause persistent infections, which result in increased milk somatic cell count (SCC) and decreased milk quality. CNS infection can damage udder tissue and lead to decreased milk production. Staphylococcus simulans and Staphylococcus chromogenes are currently the predominant CNS species in bovine mastitis. S. chromogenes is the major CNS species affecting nulliparous and primiparous cows whereas S. simulans has been isolated more frequently from older cows. Multiparous cows generally become infected with CNS during later lactation whereas primiparous cows develop infection before or shortly after calving. CNS mastitis is not a therapeutic problem as cure rates after antimicrobial treatment are usually high. Based on current knowledge, it is difficult to determine whether CNS species behave as contagious or environmental pathogens. Control measures against contagious mastitis pathogens, such as post-milking teat disinfection, reduce CNS infections in the herd. Phenotypic methods for identification of CNS are not sufficiently reliable, and molecular methods may soon replace them. Knowledge of the CNS species involved in bovine mastitis is limited. The dairy industry would benefit from more research on the epidemiology of CNS mastitis and more reliable methods for species identification.  相似文献   

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