Possible association of mucous blanket integrity with postirradiation colonization resistance.

Radiation-induced infections can be associated with changes in colonization potential of the intestine. Since the mucous blanket, which overlays the epithelium, is a major mucosal structure and is heavily colonized by microorganisms, we examined the status of the mucus after radiation and evaluated susceptibility to intestinal challenge with bacteria. A downward shift (2.5 X 10(8) cells/g to 5.3 X 10(5)) of total facultatively anaerobic bacteria of the ileum of C3HeB/FeJ mice was detected by 3 days post exposure to 10 Gy 60Co. Numbers of flora returned to normal by 11 days after radiation. Scanning electron microscopy was used to show that the loss of bacteria could be associated with major disruptions of the continuity of the mucous blanket. The pathogen Pseudomonas aeruginosa adhered to mouse mucous films used in in vitro assays. When irradiated mice were challenged orally with 1 X 10(5) P. aeruginosa on days 1, 2, or 3 after irradiation, a progressive increase in susceptibility was seen, but no animals died before Day 4 postirradiation. Sensitivity to subcutaneous (sc) challenge with Pseudomonas also increased by Day 3 and was probably due largely to the profound neutropenia observed. Immunoglobulin G (Gamimmune), which protected burned mice infected with Pseudomonas, was ineffectual in treatment of 7 or 10 Gy irradiated mice challenged either orally or sc with the organism. The ileal mucosal barrier was compromised after radiation in ways which could facilitate epithelial colonization, an event which combined with other immunological and physiological decrements in this model can compromise the effectiveness of therapeutic modalities.

Poly(A)+ RNA from Tetrahymena: stimulation of protein synthesis in vitro.

Cell-free synthesis of high molecular weight polypeptides, programmed by RNA from Tetrahymena pyriformis strain W is reported, and methods for preparation of the RNA are described. The RNA was extracted by the SDS-phenol-chloroform-isoamyl alcohol technic. The bulk of extracted RNA was ribosomal and on sucrose gradients peaked at approximately 17S and 25S. After heat denaturation all the 25S RNA was converted to 17S, indicating the presence of hidden breaks, possibly the result of nuclease activity during extraction. Nevertheless, when poly(A) +/- RNA was collected using oligo-(dT)-cellulose column chromatography, it promoted a 15-fold increase in incorporation of [35S] methionine into TCA-precipitable material. Slab-gel electrophoresis and autoradiography of the product revealed 12 different major polypeptides, varying in weight from 28,000 to 65,000 Daltons. A method for preparation of translatable RNA from Tetrahymena will make possible the comparison of messenger RNAs associated with specific cell structures and with different developmental events.

Adherence of Bacteroides fragilis group species.

The ability of piliated and capsulated Bacteroides fragilis and Bacteroides ovatus to adhere to intestinal cells and mucus was investigated. The adherence of piliated and capsulated strains was at least five times greater than the adherence of their nonpiliated and noncapsulated or capsulated only counterparts. These data illustrate the importance of pili as promoters of adherence of B. fragilis group species to the gastrointestinal mucosa.

Altered colonizing ability for mouse large intestine of a surface mutant of a human faecal isolate of Escherichia coli.

Escherichia coli F-17 Sr a human faecal isolate, is resistant to the T-series of bacteriophages (i.e. T2 to T7). A T2-sensitive mutant of E. coli F-17 Sr was isolated following acriflavin treatment. This mutant, E. coli F-17 Sr Ts was found to be sensitive to the entire T-series of phages. E. coli F-17 Sr and E. coli F-17 Sr Ts did not differ quantitatively in total LPS content. However, analysis of LPS revealed that a large fraction of E. coli F-17 Sr Ts was devoid of O-side-chains. This accounted for the sensitivity of this strain to bacteriophages T3, T4, and T7. In addition, E. coli F-17 Sr Ts contained only about half the amount of capsular material contained by E. coli F-17 Sr accounting for the sensitivity of the mutant to bacteriophages T2, T5, and T6. Although the two strains colonized equally well when fed individually to streptomycin-treated mice, when fed simultaneously to streptomycin-treated mice, E. coli F-17 Sr Ts colonized at a level of about 1 x 10(8) cells (g faeces)-1, whereas E. coli F-17 Sr colonized at only 1 x 10(4) cells (g faeces)-1. These studies suggest that bacterial cell surface components modulate the large intestine colonizing ability of E. coli F-17 Sr in the mouse large intestine.

Relative colonizing abilities of human fecal and K 12 strains of Escherichia coli in the large intestines of streptomycin-treated mice.

Male CD-1 mice, fed streptomycin in their drinking water, were used to study colonization of the mouse intestine by both fecal Escherichia coli strains isolated from healthy humans and Escherichia coli K12 strains which are routinely used as hosts for recombinant DNA. Prior to use in mice, all the strains were made resistant to streptomycin. Several facts emerged from these studies: (a) Strains isolated from different healthy humans colonized the mouse intestine with equal ability (approximately 10(8) cells/g feces), but may have colonized biochemically distinct sites. (b) K12 strains tested had, at most, one hundredth the colonizing ability of human fecal strains. (c) Rifampicin-resistant mutants of strains which contain one or no plasmids were poor colonizers relative to their parents. (d) Rifampicin-resistant mutants of strains which contain six or more plasmids retained the colonizing abilities of their parents. (e) Introduction of the F-amp or pJBK5 plasmid into HS-4, a human fecal strain which does not normally carry these plasmids, reduced its colonizing ability 1000-fold. (f) Strains used in this study colonized the mouse caecum and colon exclusively. The system presented here offers a simple, rapid test to determine whether a specific genetic alteration in a bacterium (e.g. antibiotic resistance) results in enhanced, reduced, or unchanged colonizing ability. Such a test might prove to be of value as a part of the clinical testing of antibiotics.