INHIBITION OF PENICILLIN-BINDING PROTEIN-3 OF ESCHERICHIA-COLI K-12 - EFFECTS UPON GROWTH, VIABILITY AND OUTER-MEMBRANE BARRIER FUNCTION

A temperature-conditional, cell division mutant of Escherichia coli K-12 possessing a thermolabile penicillin-binding protein (PBP) 3 was isolated. The mutant phenotype was due to a lesion in the pbpB gene. This mutant, and leu+ pbpB co-transductants of E. coli C600 grew as rods at 30.degree. C but were converted to filaments at 42.degree. C upon denaturation of PBP 3 and concomitant cessation of cell division. These strains have been used to study the consequences of the specific inhibition of PBP3 of E. coli K-12 upon growth, viability and outer membrane integrity. Our results indicate that the singular inhibition of PBP3 is bactericidal in E. coli K-12, even though the turbidimetric response of the bacteria in broth culture suggests bacteriostasis. Furthermore, filament formation is accompanied by disruption of outer membrane barrier function, as witnessed by the rapid leakage of periplasmic .beta.-lactamase. This latter finding was confirmed by observing the lytic effect of a sub-inhibitory concentration of cefsulodin on filaments of E. coli K-12 induced by PBP3-specific .beta.-lactams. The impact of these results upon the testing of .beta.-lactam sensitivity of E. coli K-12 is discussed.