The interaction between Bacteroides fragilis and Escherichia coli was investigated by following their growth kinetics in an in vitro mixed culture system. In Bacto-peptone or in a semisynthetic medium (SSM-M) Bacteroides fragilis could initiate growth only when a small number of viable Escherichia coli initially coexisted for a short period of time. Both Bacto-peptone and SSM-M previously spent by Escherichia coli also allowed Bacteroides fragilis growth to occur but the supplementation of heat killed Escherichia coli cells or viable cell homogenates to fresh media failed to stimulate Bacteroides fragilis growth. The in vitro stimulation of Bacteroides fragilis growth by Escherichia coli observed in this study may be best explained by the combination of (a) removal of oxygen and other toxic substances and (b) de novo production of Bacteroides fragilis growth stimulating factor(s) by coexistent Escherichia coli.

An improved animal model of intraperitoneal abscess formation was developed in order to study the role of Bacteroides fragilis and Escherichia coli. Both microorganisms were found to independently cause abscesses, although Bacteroides fragilis-induced abscesses were invariably minute. The combined inoculation of these microorganisms resulted in the induction of intraabdominal abscesses larger than those formed by Bacteroides fragilis or Escherichia coli alone. However, the size difference between abscesses produced by Escherichia coli alone and by the combination of both organisms was not statistically significant. The animal model defined in this study differed from earlier models in that use of the complex sterile cecal contents can be avoided. This allows for a more precise evaluation of the contribution of each organism to the pathogenic process of intraabdominal abscess formation.

Tumor metastasis to the posterior pituitary-hypothalamic area rarely is expressed by either clinical or radiographic evidence. A case is reported of widespread metastic ACTH secreting bronchogenic carcinoma presenting to the clinician as diabetes insipidus. This type of tumor associated with diabetes insipidus is apparently rare, as is antemortem radiographic documentation of metastasis to the pituitary--hypothalamic region. A review of the ten-year experience of Loyola University Medical Center and Hines VA Hospital with the association of bronchogenic carcinoma and diabetes insipidus is presented with a brief review of metastic disease to the pituitary.