Determination of the optimum concentration of decontaminants for the primary isolation of Mycobacterium bovis.

The majority of tissue specimens submitted for the isolation of Mycobacterium bovis contain contaminating microorganisms and therefore require selective decontamination before bacteriological examination. The purpose of this study was to identify the preferred decontaminant amongst four commonly used reagents. The four decontaminants used in the study were 1-hexadecylpyridinium chloride, sodium hydroxide, benzalkonium chloride and oxalic acid. A comparison was made of the toxicity of the four decontaminants for M. bovis and their ability to control contamination. Used at the recommended concentrations, all reagents showed a significant degree of toxicity. The toxicity of the decontaminants for three field strains and one laboratory strain of M. bovis were similar, but a second laboratory strain, AN5, was more susceptible. It was also observed that as the concentration of each reagent decreased an abrupt change from control to lack of control of contaminating micro-organisms occurred. Hexadecylpyridinium chloride was found to be the best all-round reagent because at concentrations that effectively controlled contamination this reagent was the least toxic to M. bovis. A protocol for handling specimens based on an assessment of the risk of contamination is recommended.

An evaluation of 1-hexadecylpyridinium chloride as a decontaminant in the primary isolation of Mycobacterium bovis from bovine lesions.

For the primary isolation of Mycobacterium bovis from bovine lesions, 1-hexadecylpyridinium chloride (HPC) at a concentration of 0.75% was as effective as 2% NaOH in controlling the growth of contamination. The advantages of using HPC over NaOH are that it is a rapid one-step procedure not requiring neutralisation with acid, it is less toxic to M. bovis thus increasing isolation rates, and it promotes the earlier appearance of colonies.

A rapid technique for the recovery of strongyloid infective larvae from pasture and soil samples.

A technique is described for the recovery of infective larvae of strongyloid nematodes from sediment resulting from the washing of pasture and soil samples. The process of recovery and counting of larvae is described by a model based on the binomial distribution. Tests of the technique have shown that it will recover approximately 50% of the larvae present in samples of pasture sediment of either 7.5 or 12.5 ml in volume after centrifugation. The efficiency of the technique was independent of the number of larvae present in samples of pasture sediment. The technique was shown to be less efficient and more variable in recovery of larvae from samples of soil sediment. Estimations in efficiency of recovery from soil sediment ranged from 64 to 110.2% and a significant effect of volume of sediment on recovery was detected.