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J. Bacteriol., 07 1996, 3683-3688, Vol 178, No. 13
GI McLeod and MP Spector
A common stress encountered by Salmonella serovars involves exposure to
membrane-permeabilizing antimicrobial peptides and proteins such as
defensins, cationic antibacterial proteins, and polymyxins. We wanted to
determine if starvation induces cross-resistance to the membrane-
permeabilizing antimicrobial peptide polymyxin B (PmB). We report here that
starved and stationary-phase (Luria-Bertani [LB] medium) cells exhibited
ca. 200- to 1,500-fold-higher (cross-)resistance to a 60-min PmB challenge
than log-phase cells. Genetic analysis indicates that this PmB resistance
involves both phoP-dependent and -independent pathways. Furthermore, both
pathways were sigma(S) independent, indicating that they are different from
other known sigma(S) -dependent cross-resistance mechanisms. Additionally,
both pathways were important for PmB resistance early during C starvation
and for cells in stationary phase in LB medium. However, only the
phoP-independent pathway was important for P-starvation-induced PmB
resistance and the sustained PmB resistance seen in 24-h-C-starved (and
N-starved) or stationary-phase cells in LB medium. The results indicate the
presence of an rpoS- and phoP-independent pathway important to starvation-
and stationary-phase-induced resistance to membrane-permeabilizing
antimicrobial agents.
Copyright © 1996, American Society for Microbiology
Starvation- and Stationary-phase-induced resistance to the antimicrobial peptide polymyxin B in Salmonella typhimurium is RpoS (sigma(S)) independent and occurs through both phoP-dependent and - independent pathways
Department of Biomedical Sciences, University of South Alabama, Mobile, Alabama 36688-0002, USA.
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