Title

Investigating the antimicrobial effect of caprylic acid and its derivatives on Dermatophilus congolensis and developing a species specific PCR to detect Dermatophilus congolensis

Date of Completion

January 2011

Keywords

Biology, Molecular|Agriculture, Animal Culture and Nutrition|Biology, Veterinary Science

Degree

Ph.D.

Abstract

Dermatophilus congolensis is a gram positive bacterium which causes a skin disease in a wide range of animals including man. This disease is called dermatophilosis, commonly known as rain rot. Dermatophilosis causes extensive damage within the animal industry, including loss of days at work, reduction in milk yield, and deterioriation of hide and meat quality. This disease requires quick diagnostic tools and sustainable treatment to avoid economic losses. ^ The 1029 bp DNA segment of the alkaline ceramidase gene of D. congolensis was targeted to develop a species-specific PCR to speed up the diagnostic and treatment process to minimize economic losses. The PCR is sensitive, specific and detects as low as 50 × 10-3µg of D. congolensis DNA within 4 hours. This PCR has potential clinical application for rapid diagnosis of dermatophilosis. ^ Caprylic acid is a medium chain fatty acid that contains 8 carbons in its structure. Caprylic acid and its derivatives, namely monocaprylin and sodium caprylate, are naturally occurring and proven to be potential alternatives for traditional antimicrobials. This research indicated that minimum inhibitory concentrations of caprylic acid, monocaprylin and sodium caprylate on D. congolensis were 7.5 mM, 2.5 mM, 15 mM respectively. The minimum bactericidal concentrations of caprylic acid, monocaprylin and sodium caprylate on D. congolensis were 15 mM, 5 mM and 70 mM respectively. Electron microscopy experiments indicated that caprylic acid disrupts the plasma membrane of the bacteria. These compounds could potentially be used to treat D. congolensis infection. ^ NMR experiments were conducted to study the interaction of the D. congolensis membrane with caprylic acid. These NMR experiments indicated that caprylic acid binds to aromatic amino acids on the surface membrane proteins of D. congolensis. However it was not clear how these compounds exert their antibacterial action on D. congolensis . Elucidation of the antimicrobial mechanisms was attempted through a proteomic approach. It was found that caprylic acid down-regulates RNA polymerase B, superoxide dismutase and heat shock proteins. Down regulation of RNA polymerase B disrupts the transcriptional mechanism, and down regulation of superoxide dismutase renders the cell vulnerable to oxidative damage. ^ Species specific PCR to detect D. congolensis is very sensitive, specific and could be potentially used to detect D. congolensis , however further research is needed to ascertain the sensitivity and specificity of this PCR with clinical samples from the infected animals. Caprylic acid exerts its antimicrobial action on D. congolensis by disrupting the plasma membrane and inhibiting various cellular pathway by inhibiting the production RNA polymerase B, super oxide dismutase and heat shock proteins. Results of this research indicate that caprylic acid and its derivatives have the potential as alternatives to antibiotics currently in use. In vivo efficacy of Caprylic acid and its derivatives needs to be studied in order to use these compounds to their full potential. ^