Genetic Control In Methicillin-Resistant Strains Of Staphylococcus Aureus

Effect of Plasmid Carriage on the Virulence of Staphylococcus Aureus

“…13136-wild is a methicillin-resistant strain of S. aureus (Jevons, 1960) and no. 13136 met-s is a spontaneously occurring methicillin-sensitive variant of it (Lacey, 19726).…”

Genetic Variation of Streptomycin Resistance in Clinical Strains of Staphylococcus Aureus

“…Strains isolated from clinical material usually exhibit low-level resistance; the genes coding for this are carried on R factors and specify inactivating enzymes . Low-level resistance to streptomycin in E. coli may be accompanied by resistance to spectinomycin because of the production of a single enzyme that inactivates both drugs (Davies, Brzezinska and Benveniste, 1971).Some strains of Staphylococcus aureus isolated from clinical material are resistant to high levels of streptomycin, a character determined by chromosomal genes (Lacey, 1972;Lacey and Chopra, 1972); in our experience, lowlevel resistance to the drug also occurs in clinical strains of s. aureus. We have examined the frequency of high-and low-level resistance in streptomycinresistant strains of s. aureus isolated from clinical material.…”

“…Some strains of Staphylococcus aureus isolated from clinical material are resistant to high levels of streptomycin, a character determined by chromosomal genes (Lacey, 1972;Lacey and Chopra, 1972); in our experience, lowlevel resistance to the drug also occurs in clinical strains of s. aureus. We have examined the frequency of high-and low-level resistance in streptomycinresistant strains of s. aureus isolated from clinical material.…”

“…Media, and methods for the determination of antibiotic sensitivity and delta-haemolysin production, bacteriophage typing, and for attempts at transduction were as described previously (Lacey, 1972). Treatment with nitrosoguanidine was by the method of Lacey (1971~); the cultures were treated with nitrosoguanidine (100 pg per ml) for sufficient time to give about 10 per cent.…”

“…The strains were isolated initially on antibiotic-free medium, then checked by disk-testing for antibiotic sensitivity. Single colonies were used to inoculate nutrient agar slopes, which were then stored at room temperature without subculture.Media, and methods for the determination of antibiotic sensitivity and delta-haemolysin production, bacteriophage typing, and for attempts at transduction were as described previously (Lacey, 1972). Treatment with nitrosoguanidine was by the method of Lacey (1971~); the cultures were treated with nitrosoguanidine (100 pg per ml) for sufficient time to give about 10 per cent.…”