Biomedical subjects
Publications and source records attributed to G K Scott.
The serum killing of Escherichia coli ML308 225 and PB94 was inhibited by lipopolysaccharide extracted from either organism, but not by lipopolysaccharide from three pathogenic Enterobacteriaceae.
Escherichia coli ML308 225 was killed and lysed by human serum. Bacterial sensitivity to serum was maximal for organisms in the early-exponential phase of batch culture and declined as growth proceeded. Bacterial killing was dependent upon the complete complement sequence and the subsequent action of serum lysozyme caused bacteriolysis. Purified lipopolysaccharide from this organism bound to serum-sensitive bacteria and inhibited the bactericidal reaction.
Escherichia coli ML308 225 in the early exponential phase of batch cultures was killed by human serum in a complement-dependent reaction. Under the same conditions, a mutant derived from this strain by multiple subcultures in human serum was resistant to killing by serum. The components of the outer membrane of both the parent and mutant strains were analyzed. The protein and phospholipid analyses were identical, but the mutant strain produced twice as much lipopolysaccharide as the parent strain. These results suggest that the extent of bacterial surface coverage by lipopolysaccharide determines the degree of sensitivity to serum.
Isolated outer membranes and outer-membrane extracts from Escherichia coli ML308-225 in the early-exponential growth phase contain more protein than do corresponding preparations from late-exponential- or stationary-phase bacteria. Isotope-dilution experiments show that this is due to a loss of protein from the membrane during the exponential growth phase. Inhibition of bacterial growth and protein synthesis stabilizes the outer-membrane-protein concentration. Protein synthesis in the absence of bacterial growth results in higher concentrations of protein in the outer membrane.
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Direct studies of the amino acid sequence of an Escherichia coli plasmid-coded penicillinase (penicillin amido-beta-lactamhydrolase, EC 3.5.2.6) are in complete agreement with results derived from the translation of the DNA sequence of a related plasmid, apart from a single amino acid substitution. This penicillinase from a Gram-negative bacterium shows 30-35% identity with functionally similar enzymes from Gram-positive bacteria. This paper should be read in conjunction with the report of the DNA sequence of the gene.
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Purified penicillinase, in gram quantities, has been prepared from Escherichia coli strain W3310 by using methods developed to handle large amounts of material. The final product had a specific enzyme activity of 3.08 units/mug of protein, which was over twice as high as that reported previously (Datta & Richmond, 1966). The purified enzyme was similar to that from E. coli strain TEM, but different in molecular weight and some other respects. The differences observed may be a result of the greater purity obtained.