Affiliation:
1. Departamento de Microbiologı́a, Universidad de Navarra, Pamplona, Spain1;
2. Forschungszentrum Borstel, Borstel, Germany2; and
3. Escuela de Medicina Veterinaria, Universidad Nacional, Heredia, Costa Rica3
Abstract
ABSTRACT
The outer membrane (OM) of the intracellular parasite
Brucella abortus
is permeable to hydrophobic probes and resistant to destabilization by polycationic peptides and EDTA. The significance of these unusual properties was investigated in a comparative study with the opportunistic pathogens of the genus
Ochrobactrum
, the closest known
Brucella
relative.
Ochrobactrum
spp. OMs were impermeable to hydrophobic probes and sensitive to polymyxin B but resistant to EDTA. These properties were traced to lipopolysaccharide (LPS) because (i) insertion of
B. abortus
LPS, but not of
Escherichia coli
LPS, into
Ochrobactrum
OM increased its permeability; (ii) permeability and polymyxin B binding measured with LPS aggregates paralleled the results with live bacteria; and (iii) the predicted intermediate results were obtained with
B. abortus-Ochrobactrum anthropi
and
E. coli-O. anthropi
LPS hybrid aggregates. Although
Ochrobactrum
was sensitive to polymyxin, self-promoted uptake and bacterial lysis occurred without OM morphological changes, suggesting an unusual OM structural rigidity.
Ochrobactrum
and
B. abortus
LPSs showed no differences in phosphate, qualitative fatty acid composition, or acyl chain fluidity. However,
Ochrobactrum
LPS, but not
B. abortus
LPS, contained galacturonic acid.
B. abortus
and
Ochrobactrum
smooth LPS aggregates had similar size and zeta potential (−12 to −15 mV). Upon saturation with polymyxin, zeta potential became positive (1 mV) for
Ochrobactrum
smooth LPS while remaining negative (−5 mV) for
B. abortus
smooth LPS, suggesting hindered access to inner targets. These results show that although
Ochrobactrum
and
Brucella
share a basic OM pattern, subtle modifications in LPS core cause markedly different OM properties, possibly reflecting the adaptive evolution of
B. abortus
to pathogenicity.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
83 articles.
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