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The chicken, which has no endogenous lactase, was assessed as a possible model for studies on lactose intolerance. The ability of yoghurt to reverse changes induced by lactose was examined. In the caecum lactose had little effect on the viable counts of three groups of organisms which utilize lactose and no effect on the water content. It suppressed body weight, induced gas formation in the caecum and slightly lowered caecum pH. None of these effects was reversed by yoghurt.

Twenty-eight isolates of coagulase negative staphylococci were obtained from nipple swabs provided by one non-lactating woman and five nursing mothers. All but two of these isolates were shown by scanning electron microscopy to adhere to the surface of human skin. Experiments with frozen sections of human skin confirmed and extended these results by showing that isolates exhibited one of three patterns of adhesion, suggesting that there are three different adhesion receptors on epidermal cells. It is proposed that adhesion of staphylococci to the nipple and areolar epidermis provides a mechanism whereby large numbers of bacteria, nourished by residues of milk and saliva, are maintained on the surface of the skin.

1. When Streptococcus faecium strain SY1 was established in the intestine of gnotobiotic chickens it depressed their growth. 2. Dietary penicillin relieved the growth depression and caused a significant reduction in the count of S. faecium in the intestinal contents and in the number of bacteria attached to the duodenum wall.

1. The influence of trace-nutrient-binding proteins on the growth of coliforms, streptococci and lactobacilli in the gastrointestinal tract was examined in neonatal rabbits delivered germ-free and dosed with an artificial flora (ESL), or born conventionally and dosed with ESL or rabbit faeces. 2. In the stomach and small intestine of both gnotobiotic and conventional animals the counts of coliforms were usually atypically high and those of streptococci were always low. In the colon the counts of coliforms and streptococci were high. Lactobacilli usually became established in the gut of the gnotobiotic animals but were not found in the conventional rabbits. 3. Sterilization (freeze-drying followed by gamma-irradiation) of the milk decreased its capacity to bind added iron by 45% and vitamin B12 by 30%. When compared with raw milk, feeding of radiation-sterilized milk did not affect the viable count of coliforms and streptococci in the gut of gnotobiotic animals. 4. Saturating the nutrient-feeding proteins in milk with Fe, folic acid and vitamin B12 had no effect on the numbers of coliforms, streptococci and lactobacilli recovered from the intestine.

1. Proteolytic and amylase activities were assayed in the gut contents of germ-free and conventional chickens aged 3 and 14 d. 2. The tendency was for the proteolytic activity to be increased and the amylase activity to be decreased in conventional chicks. These differences were statistically significant in the caecum. 3. All of the additional proteolytic activity detectable in the caecum of conventional chicks was inhibited by soybean trypsin inhibitor. However, the increased activity was not detectable in the small intestine and was, therefore, not due to pancreatic trypsin. 4. Attempts to demonstrate in vitro bacterial production of a trypsin-like enzyme were unsuccessful.

1. The gut microflora of chicks fed on a purified diet containing 300 g lactose plus 300 g starch/kg was compared with that of control birds receiving a diet containing 600 g starch/kg. 2. In 14-d-old conventional chicks, lactose in the diet decreased the incidence of lactobacilli and clostridia in the caecal contents, although when presenting lactose-fed chicks the counts of lactobacilli exceeded those of control chicks. 3. High counts of Proteus sp. were present in the caeca of control birds but they were completely suppressed in conventional birds fed on the lactose diet. In vitro tests showed that this inhibition was partially due to Escherichia coli and Streptococcus faecalis. 4. The growth of Lactobacillus acidophilus was inhibited by lactose when gnotobiotic chicks were monoassociated but not when polyassociated. The protective effect was shown in vitro to be due to L. salivarius. 5. The pH was markedly lowered in the caecum of conventional and polyassociated chicks receiving dietary lactose. Of the strains used in gnotobiotic experiments E. coli, S. faecalis and L. salivarius produced the lowest pH values in the caeca.

Although Streptococcus faecium appeared rapidly in the gut of chicks reared in fumigated premises, the growth of the birds was not always depressed. Growth depression was often associated with the growth of Strep.faecium in the duodenum. The growth depression produced by mono‐association of germ‐free chicks with Strep. faecium grown aerobically was variable. A less variable response which was statistically significant was obtained by growing the inoculum anaerobically.

1. Chicks whose growth rate had been depressed either by a fully conventional flora or by association with a bile acid deconjugating strain of Streptococcus faecium and/or a filterable agent from chicken droppings showed no significant reduction in uptake of 3-0-methyl-alpha-D-glucopyranose compared with germ-free birds. 2. Association with a microflora increased the weight of the gut per unit length.

The counts of Streptococcus faecium SY1 in the duodenums of gnotobiotic chicks exceeded the counts in their crops, indicating that multiplication was occurring in the anterior small intestine. This growth was related to adhesion to the gut wall which could be demonstrated by viable counts of macerated washed duodenal tissue. Scanning electron microscopy demonstrated that adhesion occurred in restricted areas on the surface of the villus, and transmission studies showed the presence of a thick extracellular layer on the bacterium. Attachment of S. faecium SY1 was confirmed in vitro by using chicken duodenal brush borders. The washings, produced during the preparation of the brush borders, increased the number of S. faecium adhering to the brush borders. This enhancing effect was due to the presence of trypsin in the duodenal washings. However, the effect was not dependent on the enzymatic activity of the trypsin molecule. The initial adhesion was not prevented by pretreatment of the brush borders with soy bean trypsin inhibitor. There were, therefore, two adhesion systems operating, only one of which was dependent on trypsin. Pretreatment of brush borders with trypsin digested them, but they remained intact in the presence of S. faecium SY1, indicating that the enzymatic activity was being inhibited. This effect was specific for the adhering strain of S. faecium SY1; the nonadhering S. faecium strain CRS23 and an adhering strain of Lactobacillus sp. were inactive, as was strain SY1 when adhesion was prevented by including sodium periodate in the test system. The colonizations of the gut by strains of S. faecium of differing adhesive abilities were compared. The nonadhering strain CRS23 showed reduced ability to colonize the duodenum, but the penicillin-resistant mutant of S. faecium SY1, which had reduced adhesive ability but could still attach to a lesser degree, was able to colonize the duodenum as efficiently as the parent strain.

The interaction in the chick gut between Streptococcus faecium and its phage was examined. In conventional chicks, large numbers of S. faecium and phage were found in the cecum and smaller numbers were found in the anterior gut. In gnotobiotic chicks associated with S. faecium SY1 and its phage, there was no marked effect on bacterial numbers, but resistance to the phage rapidly developed. Depression of chick growth caused by S. faecium strain SY1 was partially reversed by its phage.

Some characteristics of the association between lactic acid bacteria and pig squamous epithelial cells were studied. Strains from several sources were tested for adhesion in vitro but only those from pigs and chickens attached. The adhesion rate of pig isolates was very variable and, of the isolates tested, strains of Lactobacillus fermentum and Streptococcus salivarius attached in largest numbers. These strains were selected for further study. They did not attach to columnar epithelial cells from the small and large intestine. Adhesion was reduced by sodium periodate or protease. Both strains had a microcapsule with fibrils which stained with ruthenium red. The adhesive bond between lactobacilli and squamous tissue was strong enough to resist washing 50 times but there was a persistent release of bacteria during the washing process. When the strains of both species or of L. fermentum alone were fed to artificially reared pigs there was a statistically significant reduction in the numbers of Escherichia coli in the stomach.

When pigs are weaned at two days of age large numbers of Excherichia coli appear in the anterior gut and the incidence of diarrhoea rises. The two phenomena do not appear to be directly related because the strains of E coli isolated are not serotypes previously found to be associated with neonatal pig scouring. Representative strains of the non-enteropathogenic serotypes did not produce enterotoxin and did not adhere to small intestine brush borders. Moreover when antibiotics were fed to eliminate E coli from the gut, the pigs still scoured. Rotavirus was detected in the gut contents and gut epithelium of scouring pigs and a bacteria-free filtrate of gut contents produced diarrhoea when administered to germ-free pigs. It is suggested that rotavirus may be one of the causes of the scouring seen shortly after weaning pigs at two days of age.

Growth depression was induced in chicks and a collection of aerobic and anaerobic bacteria was isolated from the crop and caecum. The collection of bacteria was tested in gnotobiotic chickens for its ability to depress growth with and without a bacteria‐free faecal filtrate. None of the anaerobic bacteria depressed growth. Aerobic bacteria always depressed growth but only in the case of Streptococcus faecium was this statistically significant. The faecal filtrate also depressed growth. A statistically significant effect was obtained when faecal filtrate was combined with any of the following treatments: (a) the total collection of bacteria, (b) the aerobic group, (c) the anaerobic group, (d) Strep. faecalis var. liquefaciens, (e) Strep, faecium, (f) the unclassified streptococci, and (g) a group containing the lactobacilli and coliform organisms. The largest growth depression was obtained in chickens dosed with Strep, faecium and faecal filtrate.

Light and electron microscopy showed lactobacilli and, to a lesser degree, streptococci to be closely associated with the squamous area of the pig stomach known as the pars esophagea. Several different types of extracellular layers were seen on bacteria attached to the epithelial surface. The total number of bacteria per square centimeter did not change with age up to 10 days, and there was no effect of weaning at 2 days. Lactobacillus fermentum, L. salivarius, and Streptococcus salivarius were isolated more frequently from sucking pigs than from those that were early weaned, whereas the reverse was true of L. acidophilus and S. bovis. All isolates recovered from washed macerated pars esophagea adhered to pig esophageal epithelial cells when tested in vitro.

Four strains of lactobacilli with different abilities to adhere to chicken crop epithelial cells in vitro were administered to germfree chickens and their colonization of the intestine compared. Ability to colonize the gut effectively was related to adhesion index and, in the absence of adhesive ability, to growth rate. Tolerance of low pH was also a factor in determining good colonization of the small intestine. With only one strain did diet appear to affect colonization.

The gastrointestinal microflora and gastric physiology of piglets weaned at 2 days was compared with that of piglets allowed to continue sucking the sow. Although there was a significantly higher count of Escherichia coli in the stomach, duodenum, and jejunum of the early-weaned compared with sow-reared pigs, these differences were not detectable in samples from the ileum. There were no quantitative differences in lactobacilli and in streptococci between the two treatments. Lactobacillus fermentum, L. acidophilus, Streptococcus salivarius, S. bovis, and related biotypes were isolated from both groups of pigs. L. fermentum and S. salivarius were isolated more frequently from sow-reared piglets. The weight of digesta in the stomach was greater in weaned than in sucking pigs and was even greater in scouring weaned pigs, suggesting that in scouring pigs there may be gastric stasis. The gastric pH was higher in the weaned pigs at 4 days of age, but gradually decreased up to 10 days, during which time the lactic acid concentration rose. In weaned pigs there was a highly significant negative correlation between pH and lactic acid concentration in the stomach digesta, and also a positive correlation between pH and number of E. coli. These correlations suggest that lactic acid, from bacterial fermentation, is the major component in the regulation of gastric pH in weaned pigs. Three of twenty sucking pigs, but none of the weaned pigs, were secreting HCl (chloride concentration > 3 mg/g, pH < 3.5). In sucking pigs there was an inverse relationship between the chloride and lactic acid concentrations in the digesta. In weaned scouring pigs there was a nonsignificant increase in pepsin concentration in the stomach tissue. There was a threefold increase in the total proteolytic activity of the stomach tissue.