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R Freter

Publications and source records attributed to R Freter.

At least 19 recordsLinked to original sources
PubMed1991

Role of gram-negative and gram-positive gastrointestinal flora in temperature regulation of mice.

An earlier study showed that the presence of gut flora elevates body temperature of mice and rats. In these experiments, we questioned whether the signal coming from the gut was endotoxin from gram-negative (Gm-) bacteria or some signal derived from gram-positive (Gm+) microorganisms. To test the idea that endotoxin is responsible for the effects of flora, we compared the temperature of the endotoxin-resistant mouse (C3H/HeJ) with that of endotoxin-sensitive strains of mice (C3H/SnJ and C3H/HeN). Temperature of C3H/HeJ was not different from that of C3H/SnJ or C3H/HeN during the light period but was significantly lower during the later hours of the dark period. We speculated that, if endotoxin leaking across the gut wall were responsible for elevating temperature, then reduction of gut flora with nonabsorbable antibiotics would depress the temperature of the endotoxin-sensitive mice more than that of the endotoxin-resistant mice. Because antibiotics lowered the temperature of both strains of mice to the same extent, the signal coming from the gut is unlikely to be endotoxin. To test whether Gm+ flora can be responsible for elevating temperature, we inoculated one group of germfree mice with Gm+ organisms. Their mean temperature was significantly higher than that of mice that remained germfree. Cecectomy had no effect on temperature, indicating that the special properties of the germfree cecum were not involved in lowering the temperature of germfree mice. These data support the hypotheses that Gm+ organisms are a major source of the stimulatory effect of flora on normal body temperature and that the presence of Gm- organisms is unnecessary.

Animals↗
PubMed1990

Effect of gastrointestinal flora on body temperature of rats and mice.

The purpose of these experiments was to test the hypothesis that gut flora influences the body temperature of rodents. Rats and mice were implanted with biotelemetry transmitters that enabled us to record both abdominal temperature and activity for long periods of time. Rats given nonabsorbable antibiotics in their drinking water, which reduced their gut flora, had a marked decrease in both their daytime and nighttime temperatures. Similar results were found with germfree mice. The circadian rhythms in body temperature of germfree and conventionalized mice were not different. However, the body temperatures of the germfree mice were lower than those of the conventionalized mice during both the daytime and nighttime. The decrease in body temperature in the germfree mice was not related to changes in activity. These results support the hypothesis that gut flora has a tonic stimulatory effect on both the daytime and nighttime body temperature of rodents.

Abdomen↗
PubMed1989

Control of Escherichia coli populations by a combination of indigenous clostridia and lactobacilli in gnotobiotic mice and continuous-flow cultures.

The function of indigenous lactobacilli in the control of other intestinal microbial species is not clear. Still more controversial is the effect of dietary bacterial supplements containing lactobacilli or other species. This situation is unlikely to change unless the mechanisms that control the colonization of ingested bacteria are better understood, and until more detailed information becomes available on the mechanisms by which certain populations of indigenous bacteria can affect the population sizes of other species. We used gnotobiotic mice and a continuous-flow culture system to study the interactions between Escherichia coli and (i) clostridia (in chloroform-treated cecal suspensions from conventional mice) and (ii) three strains of lactobacilli isolated from conventional mice. In gnotobiotic mice, the lactobacilli suppressed E. coli multiplication in the stomach and the small intestine, but had no demonstrable effect on E. coli multiplication in the large intestine. In contrast, clostridia were most effective in controlling E. coli multiplication in the large intestine. In the presence of both lactobacilli and clostridia, E. coli populations in the various regions of the gastrointestinal tract resembled those found in conventionalized control animals. The control of E. coli populations was not related to changes in pH or intestinal motility. In vitro stimulation of the above-described in vivo interactions required a two-stage continuous-flow culture in which the effluent from the first stage represented the influx to the second. The first stage was inoculated with lactobacilli, and the second stage was inoculated with either a pure culture of E. coli or E. coli and clostridia. In these instances, the E. coli populations in the second stage of the culture resembled in size those found in the large intestine of gnotobiotic mice harboring a similar flora. Although there are some current shortcomings of this in vitro model, we expect that a multistage continuous-flow culture can be developed to satisfactorily model the interactions among bacterial populations along the entire gastrointestinal tract.

Animals↗
PubMed1986

Gnotobiotic models for study of the microbial ecology of Clostridium difficile and Escherichia coli.

Hamster flora introduced into germfree mice reduced the cecum to conventional size, suppressed populations of Escherichia coli and Clostridium difficile to the same degree that mouse flora did, and corrected the hypocellularity that is characteristic of the small bowel of germfree mice. A highly toxigenic strain of C. difficile readily induced cecitis in germfree and antibiotic-treated conventional mice, and histological examination frequently revealed pseudomembranes. Toxins A and B were both detected in ceca of animals with colitis. Gnotobiotic mice provide a model in which to study the role of the indigenous microflora in protecting against antibiotic-associated colitis.

Animals↗
PubMed1986

Interaction of Clostridium difficile and Escherichia coli with microfloras in continuous-flow cultures and gnotobiotic mice.

We studied the interactions between the entire cecal flora of hamsters and the pathogens Clostridium difficile and Escherichia coli in gnotobiotic mice and in a continuous-flow (CF) culture system in which the growth medium consisted of an extract of fecal pellets from germfree mice. CF cultures and germfree mice were colonized first with C. difficile and E. coli and then with the cecal flora of hamsters. Both in vivo and in vitro hamster flora markedly suppressed the potential pathogens. Contents of CF cultures inoculated with hamster flora were introduced into gnotobiotic mice previously colonized with C. difficile and E. coli. These mice were compared with mice given homogenates of hamster ceca. In both groups, the C. difficile population decreased by a factor of more than 10(6) and the E. coli population decreased by a factor of 10(4) to 10(5). CF culture contents also reduced the size of the dilated germfree mouse cecum to normal. When veal infusion broth was used as a medium, contents of CF cultures colonized with hamster flora failed to eliminate C. difficile from mice. Thus, the extract of fecal pellets appeared to contain a substance important for sustained colonization by important components of the cecal flora. We also studied the ability of collections of isolates to suppress the potential pathogens in both gnotobiotic mice and CF cultures. A total of 150 isolates obtained from predominant hamster flora at the ecologic climax stage (C flora) suppressed C. difficile and E. coli to 10 and 1 to 3%, respectively, of the population sizes attained in monoassociated mice. A total of 67 isolates obtained during ecologic succession combined with a C flora consisting of 100 isolates suppressed the potential pathogens to 0.3 and 0.03% of their original levels, respectively. Similar degrees of suppression occurred in CF cultures, further indicating that anaerobic CF cultures are promising models for investigation of the microbial ecology of C. difficile.

Animals↗
PubMed1985

Population dynamics of ingested Clostridium difficile in the gastrointestinal tract of the Syrian hamster.

The population dynamics of Clostridium difficile in the hamster gastrointestinal tract were studied after intragastric inoculation with organisms and a 51Cr tracer. Seventy-eight percent of spores germinated within the small intestine within 1 hr. Germinated spores and vegetative cells both showed two phases of elimination from the hamster cecum--an initial phase of rapid death that was not affected by antibiotic treatment followed by a phase of complete inhibition of multiplication. The latter phase of inhibition was not seen in antibiotic-treated animals and was thus attributable to the indigenous flora. The 51Cr tracer mixed well with cecal contents and was eliminated exponentially with a dilution rate constant ranging from -0.46/hr to -0.31/hr in normal hamsters. The hamster cecum was therefore dynamically analogous to a continuous flow system, a finding supporting the concept that anaerobic continuous flow cultures are useful in vitro models of the cecal ecosystem.

Animals↗
PubMed1983

Experimental and mathematical models of Escherichia coli plasmid transfer in vitro and in vivo.

Little is known about the factors that govern plasmid transfers in natural ecosystems such as the gut. The consistent finding by earlier workers that plasmid transfer in the normal gut can be detected only at very low rates, if at all, has given rise to numerous speculations concerning the presence in vivo of various inhibitors of plasmid transfer. Plasmids R1, R1drd-19, and pBR322 were studied in Escherichia coli K-12 and wild-type E. coli hosts in two experimental systems: (i) gnotobiotic mice carrying a synthetic indigenous microflora (F-strains) which resemble in their function the normal indigenous microflora of the mouse large intestine, and (ii) anaerobic continuous-flow cultures of indigenous large intestinal microflora of the mouse, which can simulate bacterial interactions observed in the mouse gut. Mathematical models were developed to estimate plasmid transfer rates as a measure of the "fertility," i.e., of the intrinsic ability to transfer the plasmid under the environmental conditions of the gut. The models also evaluate the effects of plasmid segregation, reduction of the growth rates of plasmid-bearing bacterial hosts, repression of transfer functions, competition for nutrients, and bacterial attachment to the wall of the gut or culture vessel. Some confidence in the validity of these mathematical models was gained because they were able to reproduce a number of known phenomena such as the repression of fertility of the R1 plasmid, as well as known differences in the transmission and mobilization of the plasmids studied. Interpretation of the data obtained permitted a number of conclusions, some of which were rather unexpected. (i) Fertility of plasmid-bearing E. coli in the normal intestine was not impaired. The observed low rates of plasmid transfer in the normal gut can be explained on quantitative grounds alone and do not require hypothetical inhibitory mechanisms. (ii) Conditions for long-term spread and maintenance throughout human or animal populations of a diversity of conjugative and nonconjugative plasmids may be optimal among E. coli strains of low fertility, as are found among wild-type strains. (iii) E. coli strains carrying plasmid pBR322 plus R1drd-19 were impaired in their ability to transfer R1drd-19, but strains carrying pBR322 were significantly better recipients of R1drd-19 than a plasmid-free recipient E. coli. (iv) Long-term coexistence of plasmid-bearing and plasmid-free E. coli, in spite of undiminished fertility, appeared to be due to a detrimental effect of the plasmid on the growth rate of its host bacterium, rather than due to high rates of plasmid segregation. (v) Mathematical analysis of experimental data published by earlier investigators is consistent with the conclusion that plasmid transfer occurs consistently in the human gut, but that the resulting transconjugant E. coli populations are too small to be detected regularly with the culture methods used by earlier investigators. It is concluded that the long-term interactions observed were often the consequences of minor differences in parameters such as growth rates, fertility, rates of segregation, etc., which were too small to be detected except by precise mathematical analysis of long-term experiments, but which were nevertheless decisive determinants of the ultimate fates of the plasmids and their hosts.

Animals↗
PubMed1983

Continuous-flow cultures as in vitro models of the ecology of large intestinal flora.

An anaerobic continuous-flow (CF) culture method has been developed which reproduces a number of bacterial interactions that occur in the large intestine of mice. These were determined in the following ways. (i) Bacterial counts in smears stained with 37 specific fluorescent antisera showed that the numeric balance between 37 strict anaerobes isolated from conventional mice was maintained in CF culture of conventional mouse flora in the same manner as in conventional mice. (ii) Mixed populations of various complexity of bacteria isolated from conventional mice were able to suppress Escherichia coli populations to similar levels in gnotobiotic mice and in CF cultures. (iii) Contents of CF cultures when fed to germfree mice were found to redress the germfree abnormalities studied, namely, cecal size and size of the E. coli population. Furthermore, dense layers of bacterial growth formed on the wall of CF cultures of mouse cecal flora, in a manner analogous to the colonization of mouse large intestinal mucosa. In the absence of such bacterial layers, the culture no longer exhibited these interactions. Because of the complexity and diversity of the interactions studied it is highly probable that at least the major underlying ecological control mechanisms operating in the culture model resemble those of the mouse intestine. We speculate that the somewhat surprising similarity between the ecology of the mouse large intestine and that of a CF culture in a glass vessel is due to the fact that both are dominated by thick layers of complex bacterial flora, the composition of which is controlled by their metabolic activities and by their relative ability to adhere to each other.

Anaerobiosis↗
PubMed1983

Mechanisms that control bacterial populations in continuous-flow culture models of mouse large intestinal flora.

A previous study had established that anaerobic continuous-flow (CF) cultures of conventional mouse cecal flora were able to maintain the in vivo ecological balance among the indigenous bacterial species tested. This paper describes experiments designed to determine the mechanisms which control the population sizes of these species in such CF cultures. One strain each of Escherichia coli, Fusobacterium sp., and Eubacterium sp. were studied. Growth of these strains in filtrates of CF cultures was considerably more rapid than in the CF cultures themselves, indicating that the inhibitory activity had been lost in the process of filtration. Growth rates to match those in CF cultures could be obtained, however, by restoring the original levels of H(2)S in the culture filtrates. The inhibitory effect of H(2)S in filtrates and in dialysates of CF cultures could be abolished by adding glucose or pyruvate, but not formate or lactate. The fatty acids present in CF cultures matched those in the cecum of conventional mice in both quality and concentration. These acids could not account for the slow rates of growth of the tested strains in CF cultures, but they did cause a marked increase in the initial lag phase of E. coli growth. The results obtained are compatible with the hypothesis that the populations of most indigenous intestinal bacteria are controlled by one or a few nutritional substrates which a given strain can utilize most efficiently in the presence of H(2)S and at the prevailing conditions of pH and anaerobiosis. This hypothesis consequently implies that the populations of enterobacteria, such as the E. coli strain tested, and those of the predominant anaerobes are controlled by analogous mechanisms.

Anaerobiosis↗
PubMed1983

Survival and implantation of Escherichia coli in the intestinal tract.

Preliminary experiments established that a 0.5-ml inoculum that is introduced directly into the stomach of mice was cleared rapidly into the small intestine. Bicarbonate buffer, but not skim milk, protected such an inoculum from stomach acid until at least 90% of it had entered the small intestine. Passage and survival of various Escherichia coli strains through the mouse gut were tested by introducing a buffered bacterial inoculum directly into the stomach, together with the following two intestinal tracers: Cr(51)Cl(3) and spores of a thermophilic Bacillus sp. Quantitative recovery of excreted bacteria was accomplished by collecting the feces overnight in a refrigerated cage pan. The data show that wild-type E. coli strains and E. coli K-12 are excreted rapidly (98 to 100% within 18 h) in the feces without overall multiplication or death. E. coli varkappa1776 and DP50supF, i.e., strains certified for recombinant DNA experiments underwent rapid death in vivo, such that their excretion in the feces was reduced to approximately 1.1 and 4.7% of the inoculum, respectively. The acidity of the stomach had little bactericidal effect on the E. coli K-12 strain tested, but significantly reduced the survival of more acidsensitive bacteria (Vibrio cholerae) under these conditions. Long-term implantation of E. coli strains into continuous-flow cultures of mouse cecal flora or into conventional mice was difficult to accomplish. In contrast, when the E. coli strain was first inoculated into sterile continuous-flow cultures or into germfree mice, which were subsequently associated with conventional mouse cecal flora, the E. coli strains persisted in a large proportion of the animals at levels resembling E. coli populations in conventional mice. Metabolic adaptation contributed only partially to the success of an E. coli inoculum that was introduced first. A mathematical model is described which explains this phenomenon on the basis of competition for adhesion sites in which an advantage accrues to the bacterium which occupies those sites first. The mathematical model predicts that two or more bacterial strains that compete in the gut for the same limiting nutrient can coexist, if the metabolically less efficient strains have specific adhesion sites available. The specific rate constant of E. coli growth in monoassociated gnotobiotic mice was 2.0 h(-1), whereas the excretion rate in conventional animals was -0.23 h(-1). Consequently, limitation of growth must be regarded as the primary mechanism controlling bacterial populations in the large intestine. The beginnings of a general hypothesis of the ecology of the large intestine are proposed, in which the effects of the competitive metabolic interactions described earlier are modified by the effects of bacterial association with the intestinal wall.

Adaptation, Physiological↗
PubMed1983

Contribution of adhesion to bacterial persistence in the mouse urinary tract.

The affinity of uropathogenic Escherichia coli to kidneys and bladders of experimentally infected mice was shown to be determined in part by the adhesive properties of the infecting bacteria. Mice were infected with various pairwise combinations of two homogeneic sets of bacteria: (i) mutants derived from a human pyelonephritis E. coli isolate which were selected to express either or both adhesins specific for globoseries glycolipid receptors or for "mannosides"; and (ii) transformants of a normal fecal isolate which harbored recombinant plasmids encoding the genes for one or the other adhesin or which harbored only the vector plasmid. The relative efficiency of survival of the strains to be compared was evaluated in each animal by plating on selective media of samples of homogenized kidneys and bladders taken 24 h after intravesical inoculation. The presence of adhesins specific for globoseries glycolipid receptors, which mediate the in vitro mannose-resistant attachment to human and mouse uroepithelial cells, enhanced bacterial recovery from both kidneys and bladders of infected animals. The addition to the infecting strain of adhesins binding mannoside residues further improved bacterial recovery from the bladder, but not from the kidney. The mutants and transformants with adhesins binding only mannosides were recovered in higher numbers from the bladder than those expressing adhesins specific for the globoseries glycolipids only. There was apparent selection in vivo decreasing expression of mannoside binding adhesins in the kidneys, but not in the bladders, of animals infected with the mutant expressing both types of adhesins. Regardless of adhesive properties, the mutants of the pyelonephritis isolate were recovered in significantly higher numbers than the fecal isolate with adhesins encoded on recombinant plasmids. We conclude that the adhesive properties in part determine the localization and retention of bacteria in the mouse urinary tract. However, the addition of adhesins to a commensal E. coli strain was not sufficient to confer colonization capacity comparable to that of a pyelonephritis strain.

Adhesins, Escherichia coli↗
PubMed1983

Ascending, unobstructed urinary tract infection in mice caused by pyelonephritogenic Escherichia coli of human origin.

A model for ascending unobstructed urinary tract infection was developed in mice to study the pathogenesis of urinary tract infection induced by Escherichia coli associated with urinary tract infection in humans. Specifically, the model was designed to monitor the initial stages of the infectious process, e.g., bacterial adhesion. Mice were selected since the specificity and intensity of bacterial attachment of pyelonephritogenic E. coli strains to human and mouse uroepithelial cells were similar. Female mice were infected by urethral catheterization and installation of bacteria in the urinary bladder. To maximize clearance of unattached bacteria, no obstructive manipulations were performed. After sacrifice, the persistence of bacteria in kidneys and bladder was determined by viable counts on homogenized tissues. The experimental infection was standardized by using one pyelonephritis (HU734) and one normal fecal (414) E. coli isolate. With both strains all of the bladders became infected, but E. coli 414 was eliminated more rapidly than HU734. The percentage of positive kidney cultures increased with the bacterial inoculum concentration and volume. An inoculum of 0.05 ml containing 10(10) bacteria per ml was selected, giving the highest percentage of positive kidney cultures without detectable bacterial spread to the blood stream. The variation in the percentage of positive kidney cultures possibly depended on the degree of vesicoureteric reflux in the individual animals. Both in the kidneys and in the urinary bladders, strain HU734 yielded higher numbers of bacteria at 24 h and persisted longer than did strain 414. Several E. coli pyelonephritis isolates with properties associated with virulence in the human urinary tract consistently were recovered from mouse kidneys and bladders in higher numbers than E. coli strains of human fecal origin lacking those properties. The role of bacterial adhesion per se is the topic of the accompanying paper.

Adhesiveness↗
PubMed1982

Inhibition of experimental ascending urinary tract infection by an epithelial cell-surface receptor analogue.

It has been shown that the establishment of urinary tract infection by Escherichia coli is dependent on attachment of the bacteria to epithelial cells. The attachment involves specific epithelial cell receptors, which have been characterized as glycolipids. Reversible binding to cell-surface mannosides may also be important. This suggests an approach to the treatment of infections--that of blocking bacterial attachment with cell membrane receptor analogues. Using E. coli mutants lacking one or other of the two binding specificities (glycolipid and mannose), we show here that glycolipid analogues can block in vitro adhesion and in vivo urinary tract infection.

Animals↗
PubMed1981

Mechanisms of association of bacteria with mucosal surfaces.

Bacterial association with host mucosal surfaces involves a large number of steps. Successful negotiation of each of these requires -- or is at least facilitated by -- the development of a distinct set of characteristics (virulence factors) by the bacterium. The major steps include: (a) chemotactic attraction of motile bacteria to the surface of the mucus gel, (b) penetration of and trapping within the mucus gel (which may be passive or can be promoted actively by bacterial motility and chemotaxis), (c) adhesion to receptors in the mucus gel or to mucosa-associated layers of the indigenous microflora, (d) adhesion to epithelial cell surfaces, and (e) multiplication of the mucosa-associated bacteria. Each reaction is further modified -- or reversed entirely -- by substances such as taxins, inhibitors of adhesion, and substrates for bacterial growth that are present in the mucosal microenvironment. Association with the mucosa is often important for bacterial colonization but can also lead to more effective elimination of the bacterium by the host. Bacteria lacking one or several of these virulence factors may still be successful colonizers if they show exceptionally high competence in relation to others. Examples are the strong adhesion to epithelial cells by Escherichia coli strains bearing the K88 antigen (such strains need not be motile in order to be pathogenic) or the active chemotactic association with mucus gel by cholera vibrios (some of which do not appear to adhere strongly to epithelial cells). Consequently a single in vitro assay for "adhesion" can be expected to correlate with bacterial pathogenicity only when the assay is based on the same specific mechanism(s) which the bacterium under study actually uses for mucosal association in vivo.

Adhesiveness↗
PubMed1981

Role of chemotaxis in the association of motile bacteria with intestinal mucosa: chemotactic responses of Vibrio cholerae and description of motile nonchemotactic mutants.

A motile, chemotactic, Ogawa strain of Vibrio cholerae was attracted by all 20 L-amino acids tested, in contrast to Escherichia coli AW 405, which did not react to several of these. The maximum number of vibrios entering a capillary was much lower when the capillary contained carbohydrates rather than amino acids, but the minimum effective concentrations of the carbohydrates and amino acids tested were of the same order of magnitude. L-Fucose, a sugar known to inhibit the adhesion of this vibrio strain to brush border membranes, had no attraction (taxin activity) for it. A pepsin digest of rabbit mucosal scrapings or tryptone attracted vibrios as strongly as the most active amino acids. Several nonchemotactic and one nonmotile mutant were selected from the parent vibrio. The nonchemotactic mutants were indistinguishable from the parent in their ability to attach in vitro to isolated intestinal brush border membranes, whereas the nonmotile mutant had lost this ability. Parent and nonchemotactic mutants had equal growth rates in stirred and still continuous flow cultures that were maintained in an anaerobic environment.

Amino Acids↗
PubMed1981

Role of chemotaxis in the association of motile bacteria with intestinal mucosa: fitness and virulence of nonchemotactic Vibrio cholerae mutants in infant mice.

Contrary to earlier findings with all other in vivo and in vitro models of cholera studied, nonchemotactic vibrio mutants showed a relatively greater fitness in 5-day-old infant mice as compared with chemotactic parent or chemotactic revertant strains. This trend was manifest in the relatively greater number of nonchemotactic mutants recovered from the upper small intestine at 4 and 18 h after intragastric infection. The same trend was also revealed in the significantly greater virulence (in terms of time to death) of nonchemotactic mutants as compared with the chemotactic parent or revertant strains. Histological studies in infant mice of the penetration of chemotactic and nonchemotactic vibrios into the mucus gel of the small intestine yielded the same findings as in all other models studied, i.e., significantly greater penetration by chemotactic vibrios. There was no correlation between the relative fitness of nonchemotactic vibrios in the small intestine of infant mice and the rate of recovery of viable nonchemotactic vibrios from that site. In contrast, excellent correlation was found between the relative fitness of nonchemotactic vibrios and a decrease in the recovery of viable cells of the chemotactic strain from the small intestine. This indicates that the relatively greater fitness of the nonchemotactic vibrios in infant mice was only apparent and that the observed phenomenon was actually due to an antibacterial mechanism which prevented the accumulation of the chemotactic strains in the small intestine rather than to any stimulating effect on the nonchemotactic mutant itself. To study the in vivo fate of the inoculum in infant mice, vibrios were labeled with either 32P, 35S, or [3H]thymidine. Specific activity determinations of the 32P label were compatible with the assumption of an accelerated rate of death of the chemotactic parent strain in the small intestine. Results with the other isotopes, however, were significantly different. Indeed, the amount of radioactivity retained in the small intestine after feeding labeled bacteria correlated more closely with the isotope used than with the strain of vibrio under study. Consequently, considerable doubt must be cast on the general validity of this not uncommon technique for determining the in vivo location and the death or survival of radioactively labeled bacteria.

Animals↗
PubMed1981

Role of chemotaxis in the association of motile bacteria with intestinal mucosa: in vivo studies.

In vivo loops were prepared in the small intestine of rabbits and injected with mixtures of Vibrio cholerae and polystyrene spheres (1.1-micrometers diameter). The loops were removed and frozen after 15 min and then sectioned in a cryostat. The locations of particles and vibrios were determined microscopically. The vibrio/particle ratio was unity in the lumen of the loops, but increased 10-fold in the deep intervillous spaces, indicating active invasion of the mucus gel by the chemotactic parent strain. Motile nonchemotactic mutants and nonmotile mutants of this strain invaded the mucus at the same rate as inert particles. Similar results were obtained with intestinal loops prepared in germfree mice. When germfree mice were disassociated with mixtures of chemotactic (parent or revertant) and nonchemotactic mutant vibrios in equal proportions, the chemotactic strain rapidly outgrew its nonchemotactic counterpart in the intestine. Nonchemotactic mutants introduced as monoassociates into germfree mice were rapidly overgrown by nonmotile mutants which apparently arose spontaneously in the gut. Motility was therefore beneficial to survival only when it was directed by chemotactic stimuli, whereas it was a liability in the absence of such stimuli. Growth of chemotactic vibrios in small intestinal loops of rabbits paralleled that of nonchemotactic mutants for the first 4 to 6 h. Thereafter, the growth rate of the chemotactic vibrios was significantly faster. This was correlated with a significantly higher degree of association with the mucosa on the part of the chemotactic vibrios.

Animals↗