Browsing by Subject "Antimicrobial"

Now showing 1 - 3 of 3
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    Antibiotic resistance in the lower intestinal microbiota of dairy cattle: longitudinal analysis of phenotypic and genotypic resistance.
    (2012-02) Boyer, Timothy Charles
    This research focused on methods of measuring antibiotic resistance and analysis of antibiotic resistance data in dairy cattle that were sampled repeatedly over time. Specific objectives included: characterization and longitudinal analysis of phenotypic antibiotic resistance of commensal Escherichia coli, development of a statistical model for the analysis of low quantity resistance genes measured by quantitative real-time polymerase chain reaction (qPCR), measurement of antibiotic resistance genes in the lower intestinal bacterial communities of dairy cattle that received a short-term therapeutic dose of antibiotic and untreated cattle, and measurement and longitudinal analysis of the quantities of six antibiotic resistance genes in the lower intestinal bacterial communities of dairy cattle. Enteric E. coli collected from dairy cattle over 1.5 years were tested for phenotypic resistance to 17 antimicrobials. A total of 93 phenotypic patterns were observed among 3,402 isolates tested, with a majority (67%) susceptible to all 17 antimicrobials. The most prevalent resistances were to tetracycline, sulfamethoxazole, and streptomycin. Latent class and latent transition analyses were carried out to group the animals into classes according to their resistance phenotypes and to estimate the probabilities of transitioning into and out of classes over time. Probabilities of transitioning to a pan-susceptible class were high, as were the probabilities of remaining in the pan-susceptible class. Probabilities of transitioning form a pan-susceptible class to a resistant class were very low. Measurement of antibiotic resistance genes by qPCR presents challenges for genes that are present in very low quantities. A statistical model was developed to analyze qPCR data made up of a significant proportion of observations that fall below the limit of quantification of a qPCR assay. Computer simulations showed that the statistical model produced less biased estimates of regression parameters than common methods of handling low quantity qPCR data. qPCR was applied to a cohort of dairy cattle that received a five day course of ceftiofur and matched untreated cattle. Quantities of a gene (blaCMY-2) that confers resistance to ceftiofur were measured and analyzed using the statistical model developed for low quantity genes. Treated animals had significantly higher quantities of blaCMY-2 during treatment than untreated animals. By the first day post-treatment, gene quantities had returned to pre-treatment levels. The quantities of six different antibiotic resistance genes were measured by qPCR in the fecal community bacterial DNA of a cattle population that was sampled repeatedly over 2.5 years. Significantly increasing trends over time were observed for three of the six genes conferring resistance to tetracyclines, macrolides, and cephalosporins. Comparison of phenotypic resistance and qPCR data showed that qPCR performed on community DNA is a more sensitive method of detection that phenotypic testing of cultured isolates.
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    The effect of antibiotic treatment on Haemophilus parasuis colonization, disease and immunity
    (2015-07) Macedo, Nubia
    Glasser's disease is an important source of economic losses in commercial swine production systems. The success of controlled exposure in the field suggests that early exposure (colonization) with pathogenic H. parasuis protects pigs from Glasser's disease. However, little is known about the immune response that is generated during colonization and how antimicrobials can modulate the immune response to H. parasuis. The overall goal of this PhD dissertation was to investigate the influence of antimicrobial treatment on H. parasuis colonization and infection, and its effect on the development of immune responses against H. parasuis in swine. First, a species-specific ELISA assay and an experimental model of H. parasuis colonization were developed to study the immune response to H. parasuis colonization by a pathogenic strain in conventional pigs. Moreover, the effect of the antimicrobial enrofloxacin in reducing H. parasuis colonization in weaned pigs was assessed. It was demonstrated that enrofloxacin was able to affect H. parasuis colonization by temporarily reducing the bacterial load in the upper respiratory tract. However, enrofloxacin was unable to eradicate the organism. Then, it was demonstrated that the inoculation of pigs with a low dose of pathogenic H. parasuis protected pigs against secondary infection. Most importantly, the timing of enrofloxacin administration in relation to H. parasuis exposure was relevant to develop protection to a subsequent H. parasuis challenge. The protection observed after H. parasuis inoculation was not affected by enrofloxacin given 3 days before inoculation. In contrast, enrofloxacin given 3 days after inoculation with H. parasuis interfered with protection against challenge. Based on the lack of H. parasuis isolation after enrofloxacin treatment, it appeared that the antibiotic quickly inactivated and removed H. parasuis. For the given infectious dose of pathogenic H. parasuis used, more than 3 days of live bacteria exposure is necessary for pigs to seroconvert and be protected against reinfection. Enrofloxacin-induced abridgement of infection on day 3 post inoculation resulted in the absence of serum IgG response and protection.
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    Effects of chili pepper extracts on microbial viability and growth
    (2015-12) Omolo, Morrine
    Although there are hundreds of varieties of chili peppers, those of the Capsicum annuum are more readily available. However, the more promising varieties such as Capsicum Chinense have not been extensively investigated. This study, the capsaicin content of 29 chili peppers grown under the same conditions is determined. 24 of the samples belong to the Capsicum chinense species while the others belong to the C. annuum species. Several samples from similar pepper plants of the C. chinense species showed wide variation in capsaicin content. The methanol extracts of the 29 samples were then tested for antimicrobial effects against well-known foodborne pathogens and one commensal fungus. The resazurin assay tested for bactericidal properties while the growth inhibition assay tested for bacteriostatic properties. The samples high in capsaicin showed antimicrobial properties, while no effects of bacterial viability and growth was noted from the samples low in capsaicin, except for the Tobago Scotch Bonnet Red pepper.