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2017 ; 2
(5
): ä Nephropedia Template TP
gab.com Text
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English Wikipedia
The Biofilm Inhibitor Carolacton Enters Gram-Negative Cells: Studies Using a
TolC-Deficient Strain of Escherichia coli
#MMPMID28959742
Donner J
; Reck M
; Bunk B
; Jarek M
; App CB
; Meier-Kolthoff JP
; Overmann J
; Müller R
; Kirschning A
; Wagner-Döbler I
mSphere
2017[Sep]; 2
(5
): ä PMID28959742
show ga
The myxobacterial secondary metabolite carolacton inhibits growth of
Streptococcus pneumoniae and kills biofilm cells of the caries- and
endocarditis-associated pathogen Streptococcus mutans at nanomolar
concentrations. Here, we studied the response to carolacton of an Escherichia
coli strain that lacked the outer membrane protein TolC. Whole-genome sequencing
of the laboratory E. coli strain TolC revealed the integration of an insertion
element, IS5, at the tolC locus and a close phylogenetic relationship to the
ancient E. coli K-12. We demonstrated via transcriptome sequencing (RNA-seq) and
determination of MIC values that carolacton penetrates the phospholipid bilayer
of the Gram-negative cell envelope and inhibits growth of E. coli TolC at similar
concentrations as for streptococci. This inhibition is completely lost for a C-9
(R) epimer of carolacton, a derivative with an inverted stereocenter at carbon
atom 9 [(S) ? (R)] as the sole difference from the native molecule, which is also
inactive in S. pneumoniae and S. mutans, suggesting a specific interaction of
native carolacton with a conserved cellular target present in bacterial phyla as
distantly related as Firmicutes and Proteobacteria. The efflux pump inhibitor
(EPI) phenylalanine arginine ?-naphthylamide (PA?N), which specifically inhibits
AcrAB-TolC, renders E. coli susceptible to carolacton. Our data indicate that
carolacton has potential for use in antimicrobial chemotherapy against
Gram-negative bacteria, as a single drug or in combination with EPIs. Strain
E. coli TolC has been deposited at the DSMZ; together with the associated RNA-seq
data and MIC values, it can be used as a reference during future screenings for
novel bioactive compounds. IMPORTANCE The emergence of pathogens resistant
against most or all of the antibiotics currently used in human therapy is a
global threat, and therefore the search for antimicrobials with novel targets and
modes of action is of utmost importance. The myxobacterial secondary metabolite
carolacton had previously been shown to inhibit biofilm formation and growth of
streptococci. Here, we investigated if carolacton could act against Gram-negative
bacteria, which are difficult targets because of their double-layered cytoplasmic
envelope. We found that the model organism Escherichia coli is susceptible to
carolacton, similar to the Gram-positive Streptococcus pneumoniae, if its
multidrug efflux system AcrAB-TolC is either inactivated genetically, by
disruption of the tolC gene, or physiologically by coadministering an efflux pump
inhibitor. A carolacton epimer that has a different steric configuration at
carbon atom 9 is completely inactive, suggesting that carolacton may interact
with the same molecular target in both Gram-positive and Gram-negative bacteria.