Characteristics of Lytic and Non-Lytic Derived Strains of Pseudomonas aeruginosa. ∗

Summary

Permanent auto-plaque negative (AP^-) colonies are rarely detectable in AP⁺ strains cultured on tryptone agar. However, two types of AP^- strains can be isolated from AP⁺ strains that are maintained for one to four weeks on refrigerated tryptose agar slants. One type appears to be permanently non-lytic and non-inducible with antibiotics, while the second type is inducible (AP_i ^-) with demethylchlortetracycline and may revert to the lytic state spontaneously. In addition, all AP^- strains exhibiting iridescent patches in the absence of visible lysis were found to be inducible auto-plaque producers. Comparative optical density measurements of AP⁺ cultures with their corresponding AP^- strains indicated no significant differences in their growth rate in aerated broth, nor was lysis detectable by this method. However, all AP⁺ strains exhibited auto-plaque formation in broth-containing petri plates when allowed to grow as a spreading thin pellicle under static conditions. Biochemical and antibiotic sensitivity comparisons of AP^- strains with their corresponding AP⁺ parent indicated no qualitative differences other than changes in pigmentation at 37°C. In addition, refrigeration of pigmented AP⁺ strains grown on tryptose agar lead to the appearance of pink pigmentation in many strains, whereas none of the stock AP^- cultures ever exhibited this property.