MORPHOLOGICAL RESPONSE OF BILOPHILA-WADSWORTHIA TO IMIPENEM - CORRELATION WITH PROPERTIES OF PENICILLIN-BINDING PROTEINS

The penicillin-binding protein (PBP) patterns of six strains of Biloph ila wadsworthia were investigated by sodium dodecyl sulfate-polyacryla mide gel electrophoresis analysis and subsequent fluorography of membr ane preparations labelled with [H-3] benzylpenicillin. The PBP profile s among the strains were similar; generally, seven to nine PBP-reactiv e bands could be visualized; their molecular weights ranged from 31 to 137 kDa. The relative affinities of the PBPs of four strains of B. wa dsworthia for imipenem were examined and correlated with the morpholog ical responses of the cells to imipenem. Morphological changes were ex amined by light and electron microscopies. Light microscopy revealed t hat at low concentrations (less than the MIC), imipenem induced the fo rmation of rounded and bulging cells; rarely, elongation without filam entation was observed. In the presence of imipenem at the MIC, spherop last formation was observed. Scanning and transmission electron micros copies revealed round forms together with larger, multilobate cells in the presence of subinhibitory concentrations of imipenem, suggesting that new growth sites were initiated while cell division was inhibited . Peeling of the outer membrane was also seen. Spheroplasts were very large (up to 30 mu m in diameter) and stable in aqueous solution. Inhi bition of the PBPs could be seen in the presence of low imipenem conce ntrations.