Sensitivity and resistance of a blue-green alga Phormidium mucicola to streptomycin and penicillin

Summary The alga Phormidium mucicola was found quite sensitive to antibiotics. Several strains resistant to streptomycin and penicillin were isolated following single and several contacts of antibiotics respectively. The resistant character remained stable during subcultures in drug-free medium. However, to isolate a fully stable and resistant strain of a concentration of penicillin two additional exposures to the same dose were required, unless otherwise, resistance was gradually lost during subcultures in penicillin-free media. This observation has been attributed to the heterogeneous nature of the resistant clones. Neither streptomycin nor penicillin resistant strains revealed cross-resistance to ultraviolet (u.v.) or to themselves.