Brucella abortus and its closest phylogenetic relative, Ochrobactrum spp., differ in outer membrane permeability and cationic peptide resistance - PubMed (original) (raw)

Comparative Study

Brucella abortus and its closest phylogenetic relative, Ochrobactrum spp., differ in outer membrane permeability and cationic peptide resistance

J Velasco et al. Infect Immun. 2000 Jun.

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.

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Figures

FIG. 1

Permeability to NPN and effect of OM-disturbing agents on normal bacteria (A to C) and O. intermedium heterologous S-LPS chimeric bacteria (D). Arrows mark the time at which the bacteria were exposed to NPN (black arrow), EDTA (10 mM; empty arrow), or polymyxin B (12.5 units; grey arrow). Experimental conditions: (A and C) bacterial suspensions at OD600 of 0.5; slit width, 2.5 nm; (B and D) bacterial suspensions at OD600 0.3; slit width, 4 nm.

FIG. 2

Maximum of the peak position of the symmetric stretching vibration νs(CH2) versus temperature for the S-LPSs of B. abortus, O. anthropi, and E. coli O:8 K27.

FIG. 3

Effect of polymyxin B (160 U, 15 min) on B. abortus, O. intermedium, and E. coli.

FIG. 4

Interaction of polymyxin B with O. anthropi S-LPS (○), O. intermedium R-LPS (●), B. abortus S-LPS (□), and E. coli S-LPS (▵). (A) Polymyxin B absorbed by increasing amounts of S-LPSs; (B) zeta potential (ζsm) of LPS aggregates on dependence of polymyxin B concentration (each point corresponds to six measurements, and the standard deviations are included in the size of the symbol).

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Brucella abortus and its closest phylogenetic relative, Ochrobactrum spp., differ in outer membrane permeability and cationic peptide resistance - PubMed (original) (raw)