Lp. Randall et Mj. Woodward, Multiple antibiotic resistance (mar) locus in Salmonella enterica serovar typhimurium DT104, APPL ENVIR, 67(3), 2001, pp. 1190-1197
In order to understand the role of the mar locus in Salmonella with regard
to multiple antibiotic resistance, cyclohexane resistance, and outer membra
ne protein F (OmpF) regulation, a marA::gfp reporter mutant was constructed
in an antibiotic-sensitive salmonella enterica serovar Typhimurium DT104 b
ackground. Salicylate induced marA, whereas a number of antibiotics, disinf
ect ants, and various growth conditions did not. Increased antibiotic resis
tance was observed upon salicylate induction, although this was shown to be
by both mar-dependent and mar-independent pathways. Cyclohexane resistance
, however, was induced by salicylate by a mar-dependent pathway. Complement
ation studies with a plasmid that constitutively expressed marA confirmed t
he involvement of map in Salmonella with low-level antibiotic resistance an
d cyclohexane resistance, although the involvement of mar in down regulatio
n of OmpF was unclear. However, marA overexpression did increase the expres
sion of a ca. 50-kDa protein, but its identity remains to be elucidated Pas
sage of the marA::gfp reporter mutant with increasing levels of tetracyclin
e, a method reported to select for mar mutants in Escherichia coli, led to
both multiple-antibiotic and cyclohexane resistance. Collectively, these da
ta indicate that low-level antibiotic resistance, cyclohexane resistance, a
nd modulation of OMPs in Salmonella, as in E. coli, can occur in both a mar
-dependent and mar-independent manner.