Environmental and genetic factors affecting mutability to aminoglycoside antibiotics among Escherichia coli K12 strains

Environmental and genetic factors affecting the in vitro spontaneous mutation frequencies to aminoglycoside resistance in Escherichia coli K12 were investigated. Spontaneous mutation frequencies to kanamycin resistance were at least 100 fold higher on modified Luria agar (L2) plates, when compared to results obtained in experiments carried out with Nutrient agar (NA) plates. In contrast to rifampincin, the increased mutability to kanamycin resistance could not be attributed to a mutator phenotype expressed by DNA repair defective strains. Kanamycin mutant selection windows and mutant preventive concentrations on L2 plates were at least fourfold higher than on NA plates, further demonstrating the role of growth medium composition on the mutability to aminoglycosides. Mutability to kanamycin resistance was increased following addition of sorbitol, suggesting that osmolarity is involved on the spontaneous mutability of E. coli K12 strains to aminoglycosides. The spontaneous mutation rates to kanamycin resistance on both L2 and NA plates were strictly associated with the selective antibiotic concentrations. Moreover, mutants selected at different antibiotic concentrations expressed heterogeneous resistance levels to kanamycin and most of them expressing multiple resistance to all tested aminoglycoside antibiotics (gentamicin, neomycin, amykacin and tobramycin). These results will contribute to a better understanding of the complex nature of aminoglycoside resistance and the emergence of spontaneous resistant mutants among E. coli K12 strains

Sensibilidade de linhagens de Proteus mirabilis portadores do plasmidio R ao desoxicolato de sodio. / Sensitivity of Proteus mirabilis strains carrying plasmid R to sodium deoxycholate

A presenca de plasmidio R, em clones excretores e nao excretores da protease, de uma linhagem de Proteus mirabilis, confere maior sensibilidade ao desoxicolato de sodio

Acao de alguns agentes curagenicos na perda da excrecao de protase em Proteus mirabilis. / Effects of some cu excretion of Proteus mirabilis

Drogas curagenicas, como brometo de etidio acriflavina e mitomicina C, aumentam grandemente, a conversao de celulas excretoras de protease instaveis de Proteus mirabilis em celulas nao excretoras. Esse efeito nao ocorre sobre celulas excretoras estaveis de protease. A rifampicina apenas seleciona celulas protease-negativas, por eliminacao preferencial de celulas excretoras.Temperaturas superiores a fisiologica nao sao efetivas na perda de excrecao de protease em linhagens de P. mirabilis que excretam protease de maneira instavel

Behavior of protease (gelatinase)-excreting and non-excreting cells from a single Proteus mirabilis strain when inoculated into mice.

Celulas excretoras e nao excretoras de protease (gelatinase), que tiveram origem na mesma populacao de Proteus mirabilis, comportam-se diferentemente quando inoculadas intraperitonealmente em camundongos.As celulas excretoras de protease diminuem a sobrevivencia de camundongos inoculados, quando comparadas com as nao excretoras