O antigen restricts lysogenization of non-O157 Escherichia coli strains by Stx-converting bacteriophage phi24B.

Acquisition of new prophages that are able to increase the bacterial fitness by the lysogenic conversion is believed to be an important strategy of bacterial adaptation to the changing environment. However, in contrast to the factors determining the range of bacteriophage lytic activity, little is known about the factors that define the lysogenization host range. Bacteriophage phi24B is the paradigmal model of Stx-converting phages, encoding the toxins of the Shiga-toxigenic E. coli (STEC). This virus has been shown to lysogenize a wide range of E. coli strains that is much broader than the range of the strains supporting its lytic growth. Therefore, phages produced by the STEC population colonizing the small or large intestine are potentially able to lysogenize symbiotic E. coli in the hindgut, and these secondary lysogens may contribute to the overall patient toxic load and to lead to the emergence of new pathogenic STEC strains. We demonstrate, however, that O antigen effectively limit the lysogenization of the wild E. coli strains by phi24B phage. The lysogens are formed from the spontaneous rough mutants and therefore have increased sensitivity to other bacteriophages and to the bactericidal activity of the serum if compared to their respective parental strains.

The O-polysaccharide of Escherichia coli F5, which is structurally related to that of E. coli O28ab, provides cells only weak protection against bacteriophage attack.

Several types of Escherichia coli O-antigens form highly effective shields protecting the bacterial cell surface and preventing bacteriophages from interacting directly with their secondary (terminal) receptors. However, it is not clear if O-antigens of various types (O-serotypes) differ in their anti-phage protection efficacy. Here, we describe a new E. coli strain, F5, which has an E. coli O28ab-related O-antigen. Although the amount of O-antigen produced by this strain is comparable to that produced by other E. coli strains we tested, it appears to give the cells significantly lower protection against phage attack than other O-antigen types, such as the O-polysaccharide of E. coli F17, which we studied earlier.

O-Antigens of Escherichia coli Strains O81 and HS3-104 Are Structurally and Genetically Related, Except O-Antigen Glucosylation in E. coli HS3-104.

Glycerophosphate-containing O-specific polysaccharides (OPSs) were obtained by mild acidic degradation of lipopolysaccharides isolated from Escherichia coli type strain O81 and E. coli strain HS3-104 from horse feces. The structures of both OPSs and of the oligosaccharide derived from the strain O81 OPS by treatment with 48% HF were studied by monosaccharide analysis and one- and two-dimensional 1H- and 13C-NMR spectroscopy. Both OPSs had similar structures and differed only in the presence of a side-chain glucose residue in the strain HS3-104 OPS. The genes and the organization of the O-antigen biosynthesis gene cluster in both strains are almost identical with the exception of the gtr gene cluster responsible for glucosylations in the strain HS3-104, which is located elsewhere in the genome.

[Characteristic of the rats' immune status during vitamin and mineral deficiency].

The article presents the results of rats' immune status evaluation in conditions of different levels of B vitamins (B1, B2, B3, B6) and minerals (Fe3+ and Mg2+) supplying. Male Wistar rats (with initial body weight 90-110 g) within 65 days received model diets with 75, 30 and 19% content of the essential substances, females (with initial body weight 56-76 g) received diets with 75, 28 and 18% content. Some indicators of humoral and cellular immunity, including leukocyte count, lysozyme serum activity, IgG and IgE level, cytokine profile of blood serum and of the masses of the immune system internal organs have been examined. It has been shown that the decrease in the content of B vitamins, iron and magnesium in the diet didn't cause complex changes of the rats' immune status, therefore, the proposed model of adaptive potential change is not optimal for studying of immune system condtion. The extensive research of the immune status of rats (18 studied indicators, a sample of 90 males and 90 females) allows to set the range of physiological fluctuations of these indexes in Wistar rats of the corresponding gender and age.

Ecological basis for rational phage therapy.

Understanding the mutual interactions of bacterial and phage populations in the environment of a human or animal body is essential in any attempt to influence these complex processes, particularly for rational phage therapy. Current knowledge on the impact of naturally occurring bacteriophages on the populations of their host bacteria, and their role in the homeostasis maintenance of a macro host, is still sketchy. The existing data suggest that different mechanisms stabilize phage-bacteria coexistence in different animal species or different body sites. The defining set of parameters governing phage infection includes specific physical, chemical, and biological conditions, such as pH, nutrient densities, host prevalence, relation to mucosa and other surfaces, the presence of phage inhibiting substances, etc. Phage therapy is also an ecological process that always implies three components that form a complex pattern of interactions: populations of the pathogen, the bacteriophages used as antibacterial agents, and the macroorganism. We present a review of contemporary data on natural bacteriophages occuring in human- and animal-body associated microbial communities, and analyze ecological and physiological considerations that determine the success of phage therapy in mammals.