Bacteria irradiation

Irradiation. Although no irradiation systems for pasteurization have been approved by the U.S. Food and Dmg Administration, milk can be pasteurized or sterilized by P tays produced by an electron accelerator or y-rays produced by cobalt-60. Bacteria and enzymes in milk are more resistant to irradiation than higher life forms. For pasteurization, 5000—7500 Gy (500,000—750,000 tad) are requited, and for inactivating enzymes at least 20,000 Gy (2,000,000 rad). Much lower radiation, about 70 Gy (7000 tad), causes an off-flavor. A combination of heat treatment and irradiation may prove to be the most acceptable approach. 

Certain strains of Escherichia coli can be stimulated by irradiation with a moderate dose of ultraviolet (UV) light to stop normal growth and start producing bacteriophages that eventually lyse the bacterium. Bacteria of these so-called lysogenic strains carry the DNA of the phage integrated into their own... 

Viruses and bacteria may be eliminated by chemical methods or by irradiation, and organic poisons may also be controlled. Inorganic matter must be removed by other means. 

Ultraviolet (UV) irradiation at wavelengths between 280 and 240 nm (2800 and 2400 A) is used to reduce bacterial contamination of air, but is only active at a relatively short distance from source. Bacteria and mould spores, in particular those with heavily pigmented spore coats, are often resistant to such treatment... 

Different mechanisms to explain the disinfection ability of photocatalysts have been proposed [136]. One of the first studies of Escherichia coli inactivation by photocatalytic Ti02 action suggested the lipid peroxidation reaction as the mechanism of bacterial death [137]. A recent study indicated that both degradation of formaldehyde and inactivation of E. coli depended on the amount of reactive oxygen species formed under irradiation [138]. The action with which viruses and bacteria are inactivated by Ti02 photocatalysts seems to involve various species, namely free hydroxyl radicals in the bulk solution for the former and free and surface-bound hydroxyl radicals and other oxygen reactive species for the latter [139]. Different factors were taken into account in a study of E. coli inactivation in addition to the presence of the photocatalyst treatment with H202, which enhanced the inactivation... 

Some or all of the events of this sequence are readily thrown out of balance, or even completely inhibited. Thus bacteria, particularly the rod-shaped organisms, may be induced to elongate into filaments by various treatments which apparently inhibit cell division but which do not inhibit growth. Such an effect is produced by various chemical substances, by sub-bacteriostatic concentration of certain antibacterial agents, as, for example, methyl violet, sulfonamides, /w-cresol, penicillin, irradiation, and higher temperatures of incubation. 

These changes in morphology induced by chemical substances are usually temporary, since reversion to normal form occurs promptly when the filamentous bacteria are subcultured in the absence of the inhibitory agents. Irradiation, on the other band, may give rise to a temporary or permanent induction of filamentous cells. 

Mid-IR spectroscopy, alongside gravimetric and molecular weight determinations, has also been used to analyse the biodegradation by a thermophilic bacterium (isolated from soil) of an LDPE film [44], The mid-IR studies were undertaken using the ATR sampling technique on control samples, samples that had been UV irradiated, and samples that had been UV irradiated then incubated with bacteria. The study showed that the particular bacterial strain was capable of utilising standard and photo-oxidised polyethylene as the sole carbon source. 

De Duve (and other authors) consider the source to be iron, which as Fe2+ provides one electron per Fe atom when subject to solar UV irradiation. The Fe3+ generated can be precipitated from solution with Fe2+ as a mixed oxide (FeO Fe2C>3 = FesOzt). This is found today in the form of black-band ironstone, an ore which is between 1.5 and 3.5 billion years old and was produced by interaction of Fe2+ with oxygen produced by light-converting bacteria. (The figure of 3.5 billion years is, however, not accepted by some scientists see Sect. 10.1). 

By using an in vitro UV-crosslinking approach, bacteria-purified recombinant CPEB3 has been demonstrated to interact with the 2> UTR of GluR2 mRNA. To test whether this interaction occurs in vivo, hippocampal neuron cultures are ultraviolet (UV)-irradiated, homogenized, and immunoprecipitated with CPEB3 IgG or nonspecific IgG (Huang et al, 2006). Three plates of 2- to 3-week-old cultured neurons ( 6—8 million... 

Mutations in either recA or lexA can abolish the SOS-response and eliminate both W-reactivation and W-mutagenesis. These mutations also eliminate the mutability of the bacteria by UV-irradiation (16) The observation that UV mutagenesis depended on the SOS-response established that mutations were not inevitable outcomes of DNA damage and that DNA damage required processing by cellular mechanisms in order for mutations to be recovered. What specific processes regulated by the SOS-response are responsible for mutagenesis ... 

The observations that mutation frequencies are elevated severalfold above normal levels in mutants which constitutively express their SOS-functions (32) and that the mutation frequency of unirradiated phage is elevated by growing them on irradiated (i.e. SOS-induced) bacteria (33), have been invoked to argue for the notion that mutagenesis via SOS-processing may be indirect. 

It would be interesting to know if the mutational consequences of DNA lesions in mammalian cells were the same as those which obtain in bacteria. Methods for retrieving and sequencing mutations in mammalian cells and their viruses are now being developed (81-83) If yeast, a eukaryotic microorganism, can be considered representative of higher eukaryotes, then judging from the observations that the mutational spectra for UV-irradiation and 4-nitroquinoline-l-oxide treatment are identical for yeast (84) and bacteria (85), the spectrum of mutations induced by BPDE in mammalian cells could well resemble those induced in E. coli. 

The objective of irradiation of food with y-rays is elimination of parasitizing insects, fungi, and bacteria to prevent premature spoiling of the food and the outbreak of diseases. In addition, retardation of aging and ripening of fruits and vegetables can be achieved. In the Federal Republic of Germany, irradiation of food with the exception of spices is not permissible. 

Another unique example was observed for the recently isolated marine natural product, alteramide A (209), isolated from a symbiotic bacteria (Alteromonas sp.) found on the sponge Halichondria okaclai96. It was found that the tetraene core of this compound underwent intramolecular [4 + 4]-photocycloaddition upon exposure to sunlight (equation 9). Deliberate irradiation led to a quantitative conversion to cyclooctadiene 210. 

Yet just as all people are not alike, neither are all food crises alike. They can vary in their familiarity, severity, proximity, consequence, and the extent to which they can be avoided. This review covers a wide range of crises from bacteria contamination, to product tampering, to fears related to irradiation and biotechnology. Different types of crises will be evaluated differently by different groups of consumers. What has been done in this review is to focus on worst-case scenarios involving initial responses to food safety issues. These will provide the most clear and illustrative profiles of consumer response. Less extreme scenarios will elicit less extreme responses. 

Considering that severe health hazards and diseases that can be induced by the adhesion and proliferation of bacteria on the surface of numerous materials, bioactive materials incorporated in the surfaces will be required. The cellulose-functionalised with porphyrin 69-71 and 80 were shown to kill gram positive and gram negative bacteria upon irradiation with visible light. Such materials could be used in industrial, household and medical environments, and more generaly in areas that would benefit from permanent and efficient surface disinfection.62 64... 

Another possibility is described by Chapman et al. (27). Bacteria cells can incorporate diacetylene carbonic acids into their membrane, if they are grown on these lipids. Brief irradiation of the cells causes visible spectral changes similar to those observed when synthetic lipid liposomes are irradiated. 

The introduction of techniques for mutagenesis by UV irradiation or by the use of chemicals considerably extended the applications of microbial studies to nutrition (Davis, 1954-1955). Auxotrophic mutants were produced with nutrient dependencies not shown in the untreated parental strains (Beadle and Tatum, 1940). The fortuitous discovery of penicillin by Fleming and its successful use in the treatment of infections (Florey) promoted exhaustive research into its mode of action. Eventually it was established that penicillin prevented the proliferation of gram-positive bacteria by blocking the synthesis of their cell walls... 

An irradiation dose of 1.0 kGy treatment decreased mesophilic bacteria in Mexican salads (Erickson, 2008). However, irradiation can cause changes in pectin structure leading to texture loss and hence shelf life. Also, viruses seem to be relatively resistant to irradiation treatment and relative to vegetative cells, suggesting that doses delivered to inactive... 

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