COMPARISON OF MUTATION AND INACTIVATION RATES INDUCED IN BACTERIOPHAGE AND TRANSFORMING DNA BY VARIOUS MUTAGENS

Therapeutics and prophylactic efficacy of novel lytic Escherichia phage vB_EcoS_PJ16 against multidrug-resistant avian pathogenic E. coli using in vivo study

Avian pathogenic Escherichia coli (APEC) is the causative agent of avian colibacillosis, which causes significant economic losses to the poultry industry. The growing resistance of bacteria to antibiotics is a major global public health concern. However, there is limited data on the efficacy of phage therapy in effectively controlling and treating APEC infections. In this study, a novel lytic Escherichia phage, vB_EcoS_PJ16, was isolated from poultry farm wastewater and characterized in both in vitro and in vivo conditions. Transmission electron microscopy analysis revealed the presence of an icosahedral head and a long non-contractile tail, classifying the phage under the Caudoviricetes class. Host range determination showed that Escherichia phage vB_EcoS_PJ16 exhibited lytic activity against multiple strains of pathogenic E. coli, while no significant signs of lysis for Klebsiella pneumoniae, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus. Biophysical characterization revealed that the isolated phage was sturdy, as it remained viable for up to 300 days at temperatures of 30 °C, 37 °C, and 42 °C and for up to 24 h at pH 5 to 11, with only minor changes in titer. Kinetic analysis at multiplicity of infection (MOI) 0.1 showed a latency period of about 20 min and a burst size of 26.5 phage particles per infected cell for phage vB_EcoS_PJ16. Whole genome sequencing unveiled that the phage vB_EcoS_PJ16 genome consists of a double-stranded linear DNA molecule with 57,756 bp and a GC content of 43.58%. The Escherichia phage vB_EcoS_PJ16 genome consisted of 98 predicted putative ORFs, with no transfer RNA identified in the genome. Among these 98 genes, 34 genes were predicted to have known functions. A significant reduction in APEC viability was observed at MOI 100 during in vitro bacterial challenge tests conducted at different MOIs (0.01, 1, and 100). In vivo oral evaluation of the isolated phage to limit E. coli infections in day-old chicks indicated a decrease in mortality within both the therapeutic (20%) and prophylactic (30%) groups, when compared to the control group. The findings of this study contribute to our current knowledge of Escherichia phages and suggest a potentially effective role of phages in the therapeutic and prophylactic control of antibiotic-resistant APEC strains.

Isolation and Physiomorphological Characterization of Escherichia coli O157:H7-Infecting Bacteriophages Recovered from Beef Cattle Operations

Bacteriophages, recovered from beef cattle environment and specifically targeting Escherichia coli O157:H7, were examined for their physiological and morphological characteristics. Degree of bacterial lysis and host range of isolated bacteriophages was determined against 55 isolates of E. coli O157:H7. Morphology of phages was examined under transmission electron microscope. Phage growth parameters, particularly rate of adsorption, rise period, latent period, and burst size were also determined. The stability of isolated phages was tested at acidic and alkaline pH, at high temperatures, and in cold storage. A total of 7 phages were isolated which showed lytic activity against 50 out of 55 isolates of E. coli O157:H7. Based on the morphology, phages were classified into Myoviridae or Siphoviridae family. Phages had a rise period between 19 and 40 min, a short latent period between 12 and 30 min, and a large burst size (89-631 virions per infected cell), indicating high lytic activity. Phages remained stable for 24 h at a wide pH (1-11) and temperature range (40-60°C) and for 90 d in cold storage. Characterization of bacteriophages, with a diverse host range of E. coli O157:H7, could aid in the development of effective biocontrol strategies for this pathogen in the food industry.

LINKAGE RELATIONSHIPS OF GENES CONTROLLING ISOLEUCINE, VALINE, AND LEUCINE BIOSYNTHESIS IN BACILLUS SUBTILIS

Barat, M. (Centre National de la Recherche Scientifique, Gif-sur-Yvette, Seine et Oise, France), C. Anagnostopoulos, and A.-M. Schneider. Linkage relationships of genes controlling isoleucine, valine, and leucine biosynthesis in Bacillus subtilis. J. Bacteriol.90:357-369. 1965.-In Bacillus subtilis, the genetic loci controlling isoleucine and valine biosynthesis are not all clustered. Some of them were located on two distinct transforming deoxyribonucleic acid "molecules." One of these molecules (the "ileilva(2-4)-met segment") carries the threonine deaminase and the dihydroxy acid dehydrase loci linked to methionine markers. The other (the "ilva(1-3)-leu segment") bears the reductoisomerase locus and one or more loci involved in leucine synthesis. A phenylalanine marker was also shown to be weakly linked to this latter group. In transduction mediated by phage PBS-1, these groups are transferred jointly with other gene clusters. The phage appears to convey chromosome fragments considerably longer than the transforming "molecules." The genetic maps of both the above segments were extended by transduction. Some groups previously studied by transformation can be placed in the following linear order: the ile-ilva(2-4)-met segment, the cluster of loci involved in aromatic amino acid synthesis (try segment), and a lysine locus. An arginine locus is cotransduced with the phe-ilva(1-2)-leu segment. Recombination frequencies between linked markers are much lower in transduction by this phage than in transformation.

Nitrates, nitrites and N-nitrosocompounds: a review of the occurrence in food and diet and the toxicological implications

Data on occurrence of nitrate, nitrite and N-nitrosocompounds in food and drinking water, and on total dietary intakes are reviewed. Metabolic, toxicological and epidemiological studies are surveyed and the implications with respect to safety evaluation are addressed. It is concluded that, on the basis of recent long-term animal studies and of clinical experience in man, the current Acceptable Daily Intake (ADI) allocated to nitrate by the Joint FAO/WHO Expert Committee on Food Additives of 0-5 mg/kg body weight/day (expressed as sodium nitrate) might be increased to 0-25 mg/kg body weight/day. Based on similar criteria, the ADI for nitrite would be 0-0.1 mg/kg body weight/day (expressed as sodium nitrite). In view of the known carcinogenicity of N-nitrosocompounds, exposure to these compounds in food should be minimized by appropriate technological means, such as lowering the nitrite concentration in preserved foods to the minimum required to ensure microbiological safety and use of inhibitors of nitrosation like alpha-tocopherol or ascorbic acid. Further work is needed to define the minimal levels of nitrite in foods needed to inhibit outgrowth of Clostridium botulinum and toxin production.

Epidemiologic and toxicologic evidence for chronic health effects and the underlying biologic mechanisms involved in sub-lethal exposures to acidic pollutants

Since the 1880s, a disparate and extensive literature has evolved examining the biologic effects of acidification on cells. More recently, effects on the health of human and other species of acidic agents contained, for example, in pollutants have been suggested, particularly relating to long-term exposures. This paper provides a review of the epidemiologic and toxicologic evidence concerning health effects--particularly carcinogenicity--attributable to sub-lethal acid exposure. Underlying biologic mechanisms that explain adverse health outcomes include pH modulation of toxicity for a number of xenobiotics (including carcinogens, genotoxins, and teratogens), and low-pH-induced changes of cells involving, for example, alterations in mitotic and enzyme regulation. More focused research is recommended to test the relationship between long-term exposures to acidic agents (with a consequent lowered cellular pH) and various health effects.

Nitrite promotes lymphoma incidence in rats

Rats were exposed to sodium nitrite in food or water at concentrations of 0, 250, 1000, and 2000 parts per million. Lymphoma was increased in all groups fed nitrite; the overall combined incidence was 5.4 percent in 573 control rats and 10.2 percent in 1383 treated rats. The mechanism of cancer induction did not appear to be through the formation of nitrosamines but through a more direct effect of nitrite on the lymphocyte.

Transformation in Bacillus subtilis with nitrogen mustard crosslinked DNA. Effect on cotransformation and mutation frequencies

Bacillus subtilis DNA was treated in vitro with nitrogen mustard and the crosslinked molecules were purified, after alkali denaturation, by hydroxyapatite chromatography. When tested for the ability to transform the trpC2-hisB2 segment, these molecules exhibited a decrease in the cotransformation index (r) as compared to native or renatured DNA. The decrease in r was not accompanied by an increase in mutagenicity.

The resistance of Micrococcus radiodurans to killing and mutation by agents which damage DNA

The resistance of Micrococcus radiodurans to the lethal and mutagenic action of ultraviolet (UV) light, ionising (gamma) radiation, mitomycin C (MTC), nitrous acid (NA), hydroxylamine (HA), N-methyl-N'-nitro-N-nitrosoguanidine (NG), ethylmethanesulphonate (EMS) and beta-propiolactone (betaPL) has been compared with that of Escherichia coli B/r. M. radiodurans was much more resistant than E. coli B/r to the lethal effects of UV light (by a factor of 33), gamma-radiation (55), NG (15) and NA (62), showed intermediate resistance to MTC (4) and HA (7), but was sensitive to EMS (1) and betaPL (2). M. radiodurans was very resistant to mutagens producing damage which can be repaired by a recombination system, indicating that it possesses an extremely efficient recombination repair mechanism. Both species were equally sensitive to mutation to trimethoprim resistance by NG, but M. radiodurans was more resistant than E. coli B/R to the other mutagens tests, being non-mutable by UV light, gamma-radiation, MTC and HA, and only slightly sensitive to mutation by NA, EMS and betaPL. The resistance of M. radiodurans to mutation by UV-light, gamma-radiation and MTC is consistent with an hypothesis that recombination repair in M. radiodurans is accurate since these mutagens may depend on an "error-prone" recombination system for their mutagenic effect in E. coli B/r. However, because M. radiodurans is also resistant to mutagens such as HA and EMS, which are mutagenic in E. coli in the absence of an "error-prone" system, we propose that all the mutagens tested may have a common mode of action in E. coli B/r, but that this mutagenic pathway is missing in M. radiodurans.

Localized mutagenesis of the aroE-strA section of the Escherichia coli chromosome coding for ribosomal proteins

In order to obtain E. coli strains altered in ribosomal proteins the following isolation technique was used: Phage P1 grown in a streptomycin resistant E. coli strain, was mutagenized by hydroxylamine or nitrous acid, and was used to transduce into a strain auxotrophic for aroE. Transductants with streptomycin resistance and aroE prototrophy were selected and tested for their growth at various temperatures (20 degrees, 30 degrees and 42 degrees) and their response to different antibiotics. Ribosomes from seventeen transductants with an altered response to temperature or antibiotics were isolated. They were tested for alterations in their ribosomal subunit profiles by sucrose centrifugation and for altered ribosomal proteins by two dimensional gel electrophoresis. Two strains showed accumulation of 50S ribosomal precursors and three strains had an altered 50S protein L18. This protein belongs to the 5S RNA-protein complex having GTPase and ATPase activity.

Absence of mutation following ultrasonic treatment of Bacillus subtilis cells and transforming deoxyribonucleic acid

Possible mutagenic effects of ultrasound at medical dosages have been assessed using genetic systems of Bacillus subtilis. The induction of mutations, after treatment of cells and of extracted transforming DNA with ultrasound has been tested. High-frequency (2 MHz diagnostic regime and higher intensities) ultrasound was unable to increase significantly the spontaneous frequency of back-mutation of an auxotrophic strain. Moreover, high-frequency treatments (1.5 MHz diagnostic and therapeutic regimes) were incapable of producing detectable levels of mutagenic lesions after in vitro irradiation of transforming DNA. Slight decreases in transforming activity of the treated DNA were apparent while the degree of linkage between two contiguous markers was unaffected. It is concluded that the ultrasound treatments employed under the conditions pertaining do not result in production of detectable mutagenic effects in cells or in vitro treated DNA. Before extrapolating such results to the human hazard situation, it is suggested that tests using genetic systems of higher organisms should be carried out.

Recognition of altered deoxyribonucleic acid in recombination

Kinetics of inactivation of transduction by phage P1bt which had been treated with ultraviolet light (UV) or nitrous acid (NA) was examined. With Escherichia coli B/r (radiation-resistant), low doses of UV increased transduction frequency, but the frequency was exponentially inactivated by higher doses. Little initial stimulus was observed in strain B(s-1) (radiation-sensitive). The final rate of decay was the same as in B/r. The initial stimulus of transduction in B/r was probably a consequence of increased recombination resulting from dark repair. It was estimated that another nucleotide within 1000 nucleotide pairs had to be damaged by UV to prevent a given nucleotide from successful transduction. The NA dose response was the same for the two strains. An initial stimulus of transduction was followed by exponential decline. The UV-repair enzymes missing in B(s-1) were not required for repair of NA-induced damage to transducing or lytic phage DNA. Low recovery of new mutations in the transductants showed that mutagen-induced damage to transducing DNA was excluded from recombinant chromosomes. The few recovered mutants may have resulted from "normal" error in recombination.