To understand the regulation of the MexAB OprM efflux system in a clinical strain of Pseudomonas aeruginosa presenting a decreased susceptibility to ticarcillin and aztreonam, the mexR repressor gene was amplified by polymerase chain reaction (PCR) and was shown to be disrupted by an insertion sequence of more than 2 kb, with characteristic direct and inverted repeat sequences. Sequencing revealed a 2131-bp IS21 insertion sequence. A reverse transcription PCR method was used to quantify mexA transcripts and showed an increased transcription rate of mexA in this strain, compared with a PAO1 control strain. The nalB phenotype in P. aeruginosa may be due to point mutations, but also to the presence of an insertion sequence in the mexR regulator gene. © 2003 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.
Boutoille, D., Corvec, S., Caroff, N., Giraudeau, C., Espaze, E., Caillon, J., … Reynaud, A. (2004). Detection of an IS21 insertion sequence in the mexR gene of Pseudomonas aeruginosa increasing β-lactam resistance. FEMS Microbiology Letters, 230(1), 143–146. https://doi.org/10.1016/S0378-1097(03)00882-6