Resistance of Pseudomonas aeruginosa PAO to nalidixic acid and low levels of beta-lactam antibiotics: mapping of chromosomal genes

Abstract

Resistance to high concentrations of nalidixic acid in Pseudomonas aeruginosa PAO was due to mutations in one locus designated nalA, which was mapped by transduction between hex-9001 and leu-10. The nalA mutants were cross-resistant to pipemidic acid, a nalidixic acid analog, at relatively low concentrations. Replicative DNA synthesis was resistant to both drugs in permeabilized cells of nalA mutants. A locus coding for low-level resistance to nalidixic acid, nalB, was cotransducible with pyrB, proC, and met-28. The nalB mutants were also resistant to low levels of pipemidic acid, novobiocin, and P-lactam antibiotics (e.g., carbenicillin, azlocillin, and cefsulodin), but not to other drugs, such as gentamicin, rifampin, kanamycin, or tetracycline. In nalB mutants, DNA replication showed wild-type sensitivity to nalidixic acid, whereas carbenicillin-induced filamentation required higher drug levels than in the wild-type strain. Thus, nalB mutations appear to decrease cell permeability to some antibiotics. The sensitivity of replicative DNA synthesis to nalidixic acid and novobiocin was very similar in P. aeruginosa and Escherichia coli; by contrast, the concentrations of these drugs needed to inhibit growth of P. aeruginosa were higher than those reported for E. coli by one or two orders of magnitude.

Mutations producing resistance to norfloxacin in Pseudomonas aeruginosa

“…We found previously that the outer membrane permeability to new quinolones such as norfloxacin in E. coli and Salmonella typhimurium differed from that to nalidixic acid (12). The incomplete cross-resistance among quinolones in E. coli is known (18,41), and this phenomenon was also observed in P. aeruginosa (32). The nfxB mutation resulted in a 4-to 16-fold increase in the MIC of new quinolones but only a slight (2-fold) increase in the MIC of nalidixic acid and pipemidic acid.…”

“…It has been reported that mechanisms of resistance to nalidixic acid in P. aeruginosa involve alterations in replicative DNA synthesis in permeabilized cells and alterations in cell permeability as a result of mutations in the nalA and nalB loci, respectively (32 (1,3,6,7,19,22,27,29,37). No (27).…”

“…However, resistance to nalidixic acid and other quinolones in bacteria is due to chromosomal mutations (10,13,(16)(17)(18)32). Plasmids or transposons that carry quinolone resistance genes have not been found in bacteria (4).…”

“…norA and nfxA were alleles of gyrA encoding the A subunit of DNA gyrase, while norB, norC, and nfxB determined outer membrane permeability resistance to norfloxacin, were associated with a decrease in OmpF porin protein, and were mapped at 34 min, near 8 min, and at 20 to 22 min, respectively (13,16). Two loci coding for resistance to nalidixic acid, nalA and nalB, have also been mapped on the P. aeruginosa PAO chromosome (32). It has been reported that DNA replication is resistant to nalidixic acid in permeabilized cells of nalA mutants and that nalB mutants cause a decrease of cell permeability to nalidixic acid and carbenicillin (32).…”

“…Two loci coding for resistance to nalidixic acid, nalA and nalB, have also been mapped on the P. aeruginosa PAO chromosome (32). It has been reported that DNA replication is resistant to nalidixic acid in permeabilized cells of nalA mutants and that nalB mutants cause a decrease of cell permeability to nalidixic acid and carbenicillin (32).…”