In this study of bacteriostatic agents used in sheep dips, the results of earlier relevant work were first reviewed. The literature relating to the microbiology of fleece wool, the chemicals that have been used in the control of arthropod ectoparasites of sheep, and the micro-organisms of the fleece that cause problems with plunge sheep dipping, and the in vitro methods of testing the sensitivity of bacteria to chemicals was studied.
The seven bacteriostatic compounds selected for study were: lauryldimethylbenzylammonium chloride, a mixture of alkyl-, tolyl-, and methyl- trimethylammonium chlorides, 2-hydroxypropylmethanethiosulphonate, 4-chloro-2-cyclopentylphenol, 2,2'-dihydroxy-3,5,6, 3',5',6'-hexachlorodiphenylmethane, 3,4,4'-trichlorocarbanilide, and an arsenical preparation containing sodium arsenite. They were evaluated against the following indicator organisms; Escherichia coli (Migula) Castellani and Chalmers 1919, a sulphur reducing strain of E. coli Pseudomonas aeruginosa (Schroeter) Migula 1919, Erysipelothrix rhusiopathiae (Migula) Buchanan 1918, and Dermatophilus congolensis van Saceghem 1915, emend. 1916, 1934.
The laboratory methods used to assess the activity of the compounds were; a broth dilution turbidimetric and agar subculture technique, an agar diffusion technique, a manometric technique, and a gradient plate procedure. A field trial was undertaken to relate the laboratory results to the practical sheep dipping situation.
The quaternary ammonium compounds tested showed the greatest antibacterial activity, and their use as dip bacteriostats can be recommended. All the other compounds, except 3,4,4'-trichlorocarbanilide, have possible applications for the control of specific microbiological problems of sheep dipping or in fleece wool. Some observations are made concerning the phenomenon of hormesis as shown in agar diffusion plates. Comparisons have been drawn between the methods used in this study and assessment of their value has been made. An agar diffusion method is suggested as a standard test for sheep dip bacteriostatic agents. Finally some recommendations for further research work have been made
