BRUCELLA-SALMONELLA LIPOPOLYSACCHARIDE CHIMERAS ARE LESS PERMEABLE TOHYDROPHOBIC PROBES AND MORE SENSITIVE TO CATIONIC PEPTIDES AND EDTA THAN ARE THEIR NATIVE BRUCELLA SP COUNTERPARTS

A rough (R) Brucella abortus 45/20 mutant was more sensitive to the ba ctericidal activity of polymyxin B and lactoferricin B than was its sm ooth (S) counterpart but considerably more resistant than Salmonella m ontevideo, The outer membrane (OR;I) and isolated lipopolysaccharide ( LPS) of S. montevideo showed a higher affinity for these cationic pept ides than did the corresponding B. abortus OR I and LPS, We took advan tage of the moderate sensitivity of R B, abortus to cationic peptides to construct live R B. abortus-S-LPS chimeras to test the activities o f polymyxin B, lactoferricin B, and EDTA, Homogeneous and abundant per ipheral distribution of the heterologous S-LPS was observed on the sur face 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 t he more sensitive bacterium S. montevideo, the chimeras were more susc eptible to the action of peptides and EDTA, A direct correlation betwe en the amount of heterologous S-LPS on the surface of chimeric Brucell a cells and peptide sensitivity was observed, Whereas the damage produ ced by polymyxin B in S. montevideo and B, abortus-S. montevideo S-LPS chimeras was manifested mainly as OM blebbing and inner membrane roll ing, 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 pr obe 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 NP N uptake similar to that observed for S. montevideo was detected for t he B. abortus-S. montevideo LPS chimeras, The partition of NPN into na tive or EDTA-, polymyxin B-, or lactoferricin B-treated LPS micelles o f S, montevideo or B. abortus mimicked the effects observed with intac t 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-d isturbing 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 phagocy tes.