LACTOFERRIN INTERACTION WITH SALMONELLAE POTENTIATES ANTIBIOTIC SUSCEPTIBILITY IN-VITRO

Interaction of lactoferrin (Lf) with the cell envelope (CE) and outer membrane (OM) of Salmonella typhimurium-type strain ATCC13311 was test ed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and We stern-blot analyses. The peroxidase-labeled bovine Lf (BLf) and human Lf both recognized a heat-modifiable protein with an estimated molecul ar mass of 38 kD in the OM. Simultaneous immunoblotting with an antipo rin monoclonal antibody specific for a conserved porin domain in membe rs of enterobacteriaceae confirmed that the Lf-binding protein is a po rin. Such Lf-binding porin proteins (37-39 kD range) were readily dete cted in nine other common Salmonella species: S. dublin, S. panama, S. restock, S. abony, S. hartford, S, kentucky, S. pullorum, S. thompson , and S. virchow. The latter six species also demonstrated one to thre e weak Lf-reactive bands of low molecular weight in their CE. The anti biotic susceptibility of Salmonena in the presence of Lf was examined. A mixture containing sub-minimum inhibitory concentration (MIC) level s of Lf (MIC/4) and cefuroxime (MIC/2) inhibited the bacterial growth. Lf strongly potentiated the action of erythromycin (eightfold), where as it increased the activity only by two-fold for ampicillin, ciproflo xacin, chloramphenicol, and rifampicin; similarly, these antibiotics a lso reduced the MIC of BLf by twofold in S. typhimurium. Such antimicr obial potentiation was not observed with BLf mixtures containing cefal exin, gentamycin, or polymyxin B against strain ATCC13311. BLf and cef uroxime also demonstrated potentiation of varying degrees (two to 16-f old) with nine other Salmonella species. These data established the bi nding of Lf to porins in salmonellae and a potentiation effect of Lf w ith certain antibiotics.