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J. Bacteriol., 10 1996, 5867-5876, Vol 178, No. 20
E Freer, E Moreno, I Moriyon, J Pizarro-Cerda, A Weintraub and JP Gorvel
A rough (R) Brucella abortus 45/20 mutant was more sensitive to the
bactericidal activity of polymyxin B and lactoferricin B than was its
smooth (S) counterpart but considerably more resistant than Salmonella
montevideo. The outer membrane (OM) and isolated lipopolysaccharide (LPS)
of S. montevideo showed a higher affinity for these cationic peptides than
did the corresponding B. abortus OM and LPS. We took advantage of the
moderate sensitivity of R B. abortus to cationic peptides to construct live
R B. abortus-S-LPS chimeras to test the activities of polymyxin B,
lactoferricin B, and EDTA. Homogeneous and abundant peripheral distribution
of the heterologous S-LPS was observed on the surface of the chimeras, and
this coating had no effect on the viability or morphology of the cells.
When the heterologous LPS corresponded to the less sensitive bacterium S B.
abortus S19, the chimeras were more resistant to cationic peptides; in
contrast, when the S-LPS was from the more sensitive bacterium S.
montevideo, the chimeras were more susceptible to the action of peptides
and EDTA. A direct correlation between the amount of heterologous S-LPS on
the surface of chimeric Brucella cells and peptide sensitivity was
observed. Whereas the damage produced by polymyxin B in S. montevideo and
B. abortus-S. montevideo S-LPS chimeras was manifested mainly as OM
blebbing and inner membrane rolling, lactoferricin B caused inner membrane
detachment, vacuolization, and the formation of internal electron-dense
granules in these cells. Native S and R B. abortus strains were permeable
to the hydrophobic probe N-phenyl-1- naphthylamine (NPN). In contrast, only
reduced amounts of NPN partitioned into the OMs of the S. montevideo and B.
abortus-S. montevideo S-LPS chimeras. Following peptide exposure,
accelerated NPN uptake similar to that observed for S. montevideo was
detected for the B. abortus-S. montevideo LPS chimeras. The partition of
NPN into native or EDTA-, polymyxin B-, or lactoferricin B-treated LPS
micelles of S. montevideo or B. abortus mimicked the effects observed with
intact cells, and this was confirmed by using micelle hybrids of B. abortus
and S. montevideo LPSs. The results showed that LPS is the main cause of B.
abortus' resistance to bactericidal cationic peptides, the OM- disturbing
action of divalent cationic chelants, and OM permeability to hydrophobic
substances. It is proposed that these three features are related to the
ability of Brucella bacteria to multiply within phagocytes.
Copyright © 1996, American Society for Microbiology
Brucella-Salmonella lipopolysaccharide chimeras are less permeable to hydrophobic probes and more sensitive to cationic peptides and EDTA than are their native Brucella sp. counterparts
Departamento de Fisiologia, Facultad de Medicina, Universidad de CostaRica, San Jose.
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