Biomedical subjects
Publications and source records attributed to D I Annear.
A strain of Enterobacter cloacae from a burn wound has displayed unstable resistance to silver nitrate and a linkage of this characteristic to that for rapid lactose fermentation and mucoidcolony structure. Attempts to demonstrate transferability of these unstable determinants gave negative results.
Methicillin-sensitive variants have been isolated from ageing broth cultures of the methicillin-resistant strain of Staphylococcus aureus NCTC 10442 and also from numerous other strains. There were wide variations and fluctuations in the incidence of sensitive variants from cultures incubated under uniform conditions.
Cold-sensitive (Cs) variants were obtained from ageing broth cultures of the Oxford strain of Staphylococcus aureus (NCTC 6571) and other penicillin-sensitive strains of this species. Growth of all strains was severely retarded on certain media at 30 degrees C but was stimulated by the addition of penicillins and cephalosporins. Revertants were derived which behaved as the parent cells did with respect to growth temperature requirements and response to these antibiotics.
Three strains of Pseudomonas aeruginosa have shown unstable resistance to gentamicin and a firm linkage between this property and the size of colonies produced on nutrient agar. The resistant parent cells yield distinctly smaller colonies than the sensitive variants. As a point of clinical interest, the smaller colonies may be obscured by the larger and the detection of gentamicin resistance compromised.
Sodium chloride and sucrose were shown to elevate the maximum temperature at which both coagulase positive and coagulase negative staphylococci would grow on the surface of nutrient agar. All of 200 isolates tested showed this effect.
The methicillin resistant strain of Staphylococcus aureus NCTC 10442 when aged in a broth culture at 42 degrees C yielded variants showing responses of sensitivity, dependence and indifference to the antibiotic. These responses and that of resistance in the parent cells were displayed in agar dilution and agar diffusion experiments at 30 degrees C. At 42 degrees C, all four organisms were sensitive to methicillin.
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Cultures of Staphylococcus aureus showing unstable resistance to kanamycin, streptomycin, lincomycin and penicillin have been preserved by drying. Particular attention has been paid to organisms showing linked resistance to pairs of these antibiotics. Recoveries of viable cells from the desiccates was high and the proportion of resistant and sensitive cells was maintained both during storage and during heating. The preservation of the organisms on ceramic beads stored in air over silica gel promises to be an effective and convenient method for maintaining staphylococcal desiccates during studies of unstable antibiotic resistance.
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