The effect of faecal loading of the colon on the healing of rat colonic anastomoses has been investigated in a prospective randomized and controlled study. Anastomotic dehiscence occurred significantly more often when the bowel was loaded with faeces at the time of operation than when it was empty. Suture line cultures bore no relationship to the outcome of the anastomosis. This result emphasizes the importance of an empty colon as a contributory factor in successful colonic healing in the rat.

The effect of surgical drainage materials on rat colonic healing has been investigated in a prospective randomized and controlled study. Latex, silicone rubber (Silastic), polyvinylchloride (PVC) and polytetrafluoroethylene (Teflon) tubes were implanted alongside a colonic anastomosis and compared with a 'no drain' group using mechanical and histological assessments. There was a significant increase in anastomotic leakage in the latex group in which there appears to be a local inhibition of healing. Silastic, PVC and Teflon were not found to interfere with healing. The continued use of latex drains in colonic surgery is therefore questioned.

Both the genetic and biochemical basis of tetracycline resistance in a number of staphylococcal strains was investigated. The strains examined could be classified into three groups: (i) those possessing a high basal level of resistance and in which resistance could be induced to higher levels (macro-inducible); (ii) those which had a high uninduced level of resistance, but which were virtually uninducible (macro-constitutive); (iii) one derivative which had a low basal level of resistance and was also uninducible (micro-constitutive). Resistance in macro-constitutive strains was plasmid mediated and typical of organisms possessing wild-type plasmids. The macro-constitutive pattern of resistance appeared to be correlated with a chromosomal location for the resistance genes, whereas the micro-constitutive pattern was correlated with loss of a region from the wild-type plasmid. Analysis of membrane proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis suggested that a number of membrane polypeptides became unstable in staphylococci possessing high-level tetracycline resistance. In particular, the absence of a polypeptide of 22,000 daltons was always associated with high-level resistance. There was no evidence that multiple gene copies are required for expression of tetracycline resistance in Staphylococcus aureus .

SUMMARY. The determinant responsible for the ability of Bacteroides spp. to inhibit polymorph phagocytic killing of aerobic organisms has not yet been identified. Therefore, the roles of lipopolysaccharide and capsular polysaccharide of B. fragilis were investigated. Serum-resistant and serum-sensitive strains of Proteus mirabilis were used to indicate inhibition of phagocytic killing and serum killing of aerobes. Whole organisms of B. fragilis, purified lipopolysaccharide and capsular polysaccharide were added to an in-vitro phagocytosis system. Results showed that > lo7 bacteroides/ml inhibited both serum and phagocytic killing. Concentrations below 1 07/ml had little effect on either process. Purified capsular polysaccharide (10 or 100 pg/ml), either alone in the system or in combination with sub-inhibitory concentrations of B. f r a g i h also markedly inhibited serum and phagocytic killing. Lipopolysaccharide (9 pg/ml) appeared relatively inert. B. ovatus, reputedly non-capsulated, produced identical results to those obtained with B. fragilis, but an encapsulated strain of Streptococcus pneumoniae did not inhibit serum or phagocytic killing.

The outer membranes of Escherichia coli K-12 cells carrying a derepressed F-like R factor contain about 7 times 10-4 molecules per cell of a protein similar to the subunit of the sex pili specified by the R factor. This protein pool is absent in cells carrying the repressed variant of the R factor. The size of the pool is about one-half of the amount of protein incorporated into mature sex pili at the peak of production and is independent of the phase of growth of the culture. The molecular weight of the protein in the pool and of the subunit of the sex pili specified by the cells is 12,500 plus or minus 600.