Reproducibility of staphylococcal bacteriophage types by use of different concentrations of bacteriophage.

A comparative investigation was carried out on the reproducibility of staphylococcal bacteriophage types at 100 routine test dilution (RTD) and at the conventional concentrations, RTD and 1,000 RTD. The comparison includes multiple typing of laboratory strains and duplicate isolates from hospital patients. No significant difference was found in the reproducibility of the types at the different concentrations. A single concentration corresponding to 100 RTD is recommended for routine use in phage typing as a possible substitute for typing with two different concentrations.