Standard Reference Strains Research Articles

Facilitating quality control of the antimicrobial susceptibility test.

Standard reference strains of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were suspended in sterile deionized water and tested daily via disk agar diffusion for their antimicrobial susceptibilities. Inocula of E. coli and P. aeruginosa yielded acceptable results for up to 32 days; however, results on S. aureus were unacceptable due to loss of viability of the organism in water. E. coli and P. aeruginosa inocula, in water, can be used daily for quality control of the disk gear diffusion test.

Resistance to synthetic pyrethroids in a DDT‐resistant strain of Boophilus microplus

AbstractThe susceptibility of a standard reference strain of the cattle tick Boophilus microplus, to a group of synthetic pyrethroids, has been compared with that of a DDT‐resistant strain. Cross resistance has been demonstrated in laboratory and field tests.

A possible rôle for microsomal oxidases in metamorphosis and reproduction in the housefly

Housefly larvae and adults of the Isolan-B strain, insecticide resistant because of high microsomal oxidase activity, and the susceptible WHO Standard Reference (SR) strain, were reared on diets containing phenobarbital or piperonyl butoxide. Periodically throughout the treatments groups of insects were assayed for microsomal aldrin epoxidase activity. This activity was compared with such growth and development parameters as pupation, adult emergence, and reproduction in similar groups of insects. At diet levels of 0·01 to 0·50 per cent both chemicals caused large increases, as much as elevenfold in microsomal oxidase activity in third instar larvae and 15 to 100 per cent inhibition of pupation and emergence. In the adult diet at 1 per cent, both compounds caused at least 50 per cent decrease in egg production. Phenobarbital enhanced the enzyme system in both larval and adult stages of both strains but piperonyl butoxide, while enhancing enzyme activity in larvae of the Isolan-B strain, was an inhibitor in the adult stage. The results are interpreted as an indication of a direct connexion between microsomal oxidase activity and the action of hormones in the housefly, probably through regulation of hormone titre by these enzymes.

Antigenic variation in strains of avian infectious bronchitis virus.

SummaryFifteen british field strains of IBV were compared using cross serum neutralization tests in embryonated eggs with seven standard reference strains of IBV. While the British field strains were considered to form a relatively homogeneous group considerable antigenic variation did occur. It was considered that it was not feasible at this time to describe accurately a serotype classification for IBV, similar to that described for other virus groups.

Identification of L forms by polyacrylamide-gel electrophoresis.

Crude membranes were obtained from L forms by allowing the cells to lyse in distilled water. The crude membranes were washed several times in distilled water, lyophilized, and extracted with phenol-acetic acid-water. The membrane proteins were separated electrophoretically in polyacrylamide gels run at pH 4.5. Electrophoretic patterns and densitometric tracings of the gels showed distinct, reproducible intergeneric differences among L forms of Proteus, Streptobacillus, Staphylococcus, and Streptococcus. Differences within a genus could not be detected except between the group A streptococcal L forms and the one group D F-24 L form. This electrophoretic method offers possibilities for ready identification of L forms through the use of standard reference strains.

Brain Cholinesterase Activity and Its Inheritance in Cattle Tick (Boophilus Microplus) Strains Resistant and Susceptible to Organophosphorus Acaricides

Brain acetylcholinesterase (AChE) activities of individual cattle ticks, B. microplus, of an organophosphorus-resistant strain were compared with those of a standard reference strain. When measured by a histochemical-densitometric method on photographic transparencies and by a biochemical method, brains from homozygous resistant adult female ticks had about 12% of the AChE activity of brains from homozygous susceptible ticks_ Brains of hybrid adult females had about 78%, histochemically and biochemically, of the AChE activity of their susceptible parents, indicating that low AChE activity was incompletely recessive although the associated resistance to organophosphorus compounds had been shown previously to be incompletely dominant_