A new mutation, nalD, determining resistance of Escherichia coli to nalidixic acid (NAL) is reported. The nalD mutant described is resistant to NAL at 37 "C but sensitive at 30 "C. It is defective in penetration of NAL and glycerol through the outer membrane at 37 "C. The nalD mutation is located half-way between 89 and 89.5 min on the E. coli genetic map.
Plasmid pBCP 68 carrying the lamB gene of Escherichia coli was introduced and expressed in Yersinia enterocolitica cells. The presence of LamB protein in the outer membrane of the wild-type strain of Y. enterocolitica coincided with the loss of the OmpC and OmpF porins. Western blot analysis showed that LamB in Y. enterocolitica cells co-migrated with authentic monomeric LamB, indicating that its signal peptide was recognized and cleaved by Y. enterocolitica and properly integrated into the outer membrane. The expression of LamB made Y. enterocolitica sensitive to phage lambda.
Plasmid pBCP 68 carrying the lamB gene of Escherichia coli was introduced and expressed in Yersinia enterocolitica cells. The presence of LamB protein in the outer membrane of the wild-type strain of Y. enterocolitica coincided with the loss of the OmpC and OmpF porins. Western blot analysis showed that LamB in Y. enterocolitica cells co-migrated with authentic monomeric LamB, indicating that its signal peptide was recognized and cleaved by Y. enterocolitica and properly integrated into the outer membrane. The expression of LamB made Y. enterocolitica sensitive to phage lambda.
Two mutants of Escherichia coli resistant to beta-lactam antibiotics exhibited beta-lactamase activity slightly higher than the wild type strain. One showed disturbance in cephaloridine and penicillin penetration into cells. Neither differed from the wild strain in terms of the major outer membrane proteins or PBPs. It is suggested that the disturbance in penetration of beta-lactam antibiotics in one of the mutants concerns diffusion of the drug directly through the double-layer phospholipid membrane.
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