Campylobacter bacteriophages and bacteriophage therapy

Members of the genus Campylobacter are frequently responsible for human enteric disease with occasionally very serious outcomes. Much of this disease burden is thought to arise from consumption of contaminated poultry products. More than 80% of poultry in the UK harbour Campylobacter as a part of their intestinal flora. To address this unacceptably high prevalence, various interventions have been suggested and evaluated. Among these is the novel approach of using Campylobacter-specific bacteriophages, which are natural predators of the pathogen. To optimize their use as therapeutic agents, it is important to have a comprehensive understanding of the bacteriophages that infect Campylobacter, and how they can affect their host bacteria. This review will focus on many aspects of Campylobacter-specific bacteriophages including: their first isolation in the 1960s, their use in bacteriophage typing schemes, their isolation from the different biological sources and genomic characterization. As well as their use as therapeutic agents to reduce Campylobacter in poultry their future potential, including their use in bio-sanitization of food, will be explored. The evolutionary consequences of naturally occurring bacteriophage infection that have come to light through investigations of bacteriophages in the poultry ecosystem will also be discussed.

Effect of endogenous carotenoids on "adaptive" mutation in Escherichia coli FC40

The appearance over many days of Lac(+) frameshift mutations in Escherichia coli strain FC40 incubated on lactose selection plates is a classic example of apparent "adaptive" mutation in an episomal gene. We show that endogenously overproduced carotenoids reduce adaptive mutation under selective conditions by a factor of around two. Carotenoids are known to scavenge singlet oxygen suggesting that the accumulation of oxidative base damage may be an integral part of the adaptive mutation phenomenon. If so, the lesion cannot be 7,8-dihydro-8-oxoguanine since adaptive mutation in FC40 is unaffected by mutM and mutY mutations. If active oxygen species such as singlet oxygen are involved in adaptive mutation then they should also induce frameshift mutations in FC40 under non-selective conditions. We show that such mutations can be induced under non-selective conditions by protoporphyrin photosensitisation and that this photodynamic induction is reduced by a factor of just over two when endogenous carotenoids are present. We argue that the involvement of oxidative damage would in no way be inconsistent with current understanding of the mechanism of adaptive mutation and the role of DNA polymerases.

A UmuD,C-dependent pathway for spontaneous G:C to C:G transversions in stationary phase Escherichia coli mut Y

In Escherichia coli trpA23 bacteria lacking the MutY glycosylase and incubated on plates in the absence of tryptophan, tryptophan-independent mutants continue to arise during incubation over many days. Their appearance is enhanced in umuD+,C+ strains in comparison with strains carrying a deletion through the umu operon and the umuD,C-dependent mutants were greater in number in uvrA bacteria (lacking nucleotide excision repair) than in uvr+ bacteria. Sequencing of mutations occurring in uvrA bacteria revealed the presence of G:C to C:G transversions but only in umuD+,C+ strains. There is thus a pathway in starved bacteria that generates G:C to C:G transversions and requires the inducible UmuD,C proteins. The data are consistent with the occurrence of a lesion, probably 8-oxoguanine, against which guanine may be incorporated during DNA synthesis by "dNTP stabilised" misalignment against the downstream template base. Upon realignment the configuration is substrate for MutY glycosylase which can remove the unmodified guanine. It is hypothesised that UmuD,C proteins are required for primer extension from the mismatch once formed.

Ferritin mutants of Escherichia coli are iron deficient and growth impaired, and fur mutants are iron deficient

Escherichia coli contains at least two iron storage proteins, a ferritin (FtnA) and a bacterioferritin (Bfr). To investigate their specific functions, the corresponding genes (ftnA and bfr) were inactivated by replacing the chromosomal ftnA and bfr genes with disrupted derivatives containing antibiotic resistance cassettes in place of internal segments of the corresponding coding regions. Single mutants (ftnA::spc and bfr::kan) and a double mutant (ftnA::spc bfr::kan) were generated and confirmed by Western and Southern blot analyses. The iron contents of the parental strain (W3110) and the bfr mutant increased by 1.5- to 2-fold during the transition from logarithmic to stationary phase in iron-rich media, whereas the iron contents of the ftnA and ftnA bfr mutants remained unchanged. The ftnA and ftnA bfr mutants were growth impaired in iron-deficient media, but this was apparent only after the mutant and parental strains had been precultured in iron-rich media. Surprisingly, ferric iron uptake regulation (fur) mutants also had very low iron contents (2.5-fold less iron than Fur+ strains) despite constitutive expression of the iron acquisition systems. The iron deficiencies of the ftnA and fur mutants were confirmed by Mössbauer spectroscopy, which further showed that the low iron contents of ftnA mutants are due to a lack of magnetically ordered ferric iron clusters likely to correspond to FtnA iron cores. In combination with the fur mutation, ftnA and bfr mutations produced an enhanced sensitivity to hydroperoxides, presumably due to an increase in production of "reactive ferrous iron." It is concluded that FtnA acts as an iron store accommodating up to 50% of the cellular iron during postexponential growth in iron-rich media and providing a source of iron that partially compensates for iron deficiency during iron-restricted growth. In addition to repressing the iron acquisition systems, Fur appears to regulate the demand for iron, probably by controlling the expression of iron-containing proteins. The role of Bfr remains unclear.

Reversion of the tyrosine ochre strain Escherichia coli WU3610 under starvation conditions depends on a new gene tas

When 3 x 10(8) bacteria of the Escherichia coli tyrA14(oc) leu308(am) strain WU3610 are plated on glucose salts agar supplemented with leucine only, colonies of slow-growing Tyr+ suppressor mutants begin to appear after about a week and increase in numbers roughly linearly with time thereafter (stationary phase or starvation-associated mutation). From a library constructed from two of these mutants, a clone was obtained that suppressed the tyrosine requirement of WU3610 when present on a multicopy plasmid. The activity was identified to an open reading frame we call tas, the sequence for which has homology with a variety of known genes with aldo-keto reductase activity. The activity of tas complements the prephenate dehydrogenase dysfunction of tyrA14 (the chorismate mutase activity of tyrA possibly being still functional). A strain deleted for tas showed no spontaneous mutation under starvation conditions. Whereas neither tas+ nor tas bacteria showed any increase in viable or total count when plated under conditions of tyrosine starvation at 3 x 10(8) cells per plate, at lower density (approximately 10(7) per plate) tas+ but not tas bacteria showed considerable residual growth. We suggest that the single copy of tas present in WU3610 allows cryptic cell or DNA turnover under conditions of tyrosine starvation and that this is an essential prerequisite for starvation-associated mutation in this system. The target gene for mutation is not tas, although an increase in the expression of this gene, for example, resulting from a suppressor mutation affecting supercoiling, could be responsible for the slow-growing Tyr+ phenotype.

Mutation in Escherichia coli under starvation conditions: a new pathway leading to small deletions in strains defective in mismatch correction

Strains of Escherichia coli carrying the mutY mutation lack a mismatch correction glycosylase that removes adenines from various mismatch situations. In growing bacteria, 8-oxoguanine-adenine mispairs persist and can give rise to G-->T transversions during subsequent replication cycles. We now show that when trpA23 mutY bacteria are held under tryptophan starvation conditions the tryptophan-independent mutants that arise include small in-frame deletions in addition to transversions. The trpA23 reversion system appears to be unusual in that small in-frame deletions occurring in a particular region of the gene can lead to the production of a functional protein. We suggest that this is a consequence of the deletion causing the polar group on the arginine at the trpA23 site to be pulled away from the active site of the enzyme. Such deletions are also found with starved bacteria defective in methyl-directed mismatch correction activity (mutH, mutL or mutS), and deletion mutations are also found among the much lower number of mutants that arise in bacteria wild-type for mismatch correction. There is thus a pathway, hitherto undetected, leading to deletions probably from mismatches under conditions of growth restraint. RecA, UmuC, UvrA, MutH,L,S, SbcC and SbcD proteins are not required for the operation of the deletion pathway. A possible explanation is that the deletion pathway is not dependent upon further replication and that it fails to be discernible in growing cells because it is relatively slow acting and mismatches are likely to encounter a DNA replication fork before the initial step of the deletion pathway.

The tyrT locus of Escherichia coli B

The tyrT (tRNA(1TYr)) locus of Escherichia coli B differs structurally from that of K-12 strains by the absence of 2 of 3.14 terminal repeat sequences.

Growth rate effects of mutations conferring streptomycin-dependence and of ancillary mutations in the rpsL gene of Escherichia coli: implications for the clustering (hypermutation) hypothesis for spontaneous mutation

Colonies of newly arising streptomycin-dependent (SmD) mutants frequently contain a high proportion of cells with additional mutations (ancillary mutations) in the same gene (rpsL). The ancillary mutations appear to have arisen at a rate greatly above expectation. To better estimate this rate it is necessary to allow for any selective advantage conferred by the ancillary mutations. We have previously measured their effect on growth rate of established SmD strains in the presence of streptomycin. In the present work a pair of single and double mutant alleles (rpsL832 and rpsL852 respectively) has been employed together with the wild-type allele to model the situation soon after such mutations first arise, i.e. when the cell still contains wild-type S12 protein (the rpsL gene product). When these alleles, under the control of an IPTG-inducible promoter and carried on a plasmid, were expressed in the presence of a chromosomal wild-type allele, the double mutant allele permitted much faster cell growth than the single mutant allele. In the presence of streptomycin, and with rpsL+ on a plasmid, bacteria with a double mutant chromosomal gene grew faster than those with a single mutant chromosomal gene. If these results can be extrapolated to a bacterial cell in which an SmD mutation has just occurred, the ancillary mutation should be able to confer a selective advantage during a limited period when wild-type S12 protein is still present, both in the absence and in the presence of streptomycin.(ABSTRACT TRUNCATED AT 250 WORDS)

Double, independent mutational events in the rpsL gene of Escherichia coli: an example of hypermutability?

A proportion (up to 20%) of newly arising streptomycin-dependent (SmD) colonies of Escherichia coli WP2 contain bacteria where, in addition to a known SmD-determining (primary) mutation in the rpsL gene, there is a further ancillary mutation in the same gene. These ancillary mutations occur at 10 sites between 11 and 201bp away from the primary mutation. Ancillary mutations have been found in mutant colonies arising both spontaneously and after treatment with ultraviolet light and some have been found repeatedly. Ancillary mutations were frequently found to occur in mixed clones with an excess of bacteria carrying only the primary SmD mutation. No ancillary mutations were found in an adjacent non-coding region and there were no coding sequence changes that did not alter the amino acid specified. Although a selective advantage for bacteria containing ancillary mutations could not be demonstrated directly in every case, some small advantage must be presumed to have occurred to explain the absence of mutations at the other sites and particularly at third (wobble) codon positions. Ancillary mutations appear to occur fairly early in the life of a newly arisen SmD mutant clone in some sort of hypermutable process. Whether they are noticed appears to depend on their conferment of some selective advantage on the bacteria carrying them. While the ancillary mutations within rpsL lie close to, and may be consequent upon the formation of a primary SmD mutation, their mechanism of formation appears to be at least to some extent independent and does not involve the recA or umuC genes.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutant sequences in the rpsL gene of Escherichia coli B/r: mechanistic implications for spontaneous and ultraviolet light mutagenesis

Mutants able to grow in the presence of 1.2 mg/ml streptomycin were isolated from Escherichia coli WP2 after exposure to ultraviolet light (UV) or in the absence of any treatment (spontaneous), and from a umuC derivative after exposure to UV and delayed photoreversal. These mutants, characterized as streptomycin resistant (Smr) or dependent (Smd), carry mutations in the rpsL gene. This gene was amplified using the polymerase chain reaction and sequenced. Mutations induced by UV were largely (76%) of the Smr phenotype, all of which were changes at an A:T base pair at codons 42 or 87. Mutations induced by UV plus delayed photoreversal in the non-UV-mutable umuC122 derivative of WP2 were exclusively of the Smd phenotype and all occurred at G:C base pairs at codons 41, 90 or 91. These results are consistent with current understanding of the mechanism of mutagenesis by UV and delayed photoreversal. A broader spectrum of mutations was seen in the spontaneous series including three-base deletions leading to amino acid loss (2 of codon 93, 1 of codon 87). Of particular note was the number of intragenic second site mutations in the spontaneous series, most if not all of which appeared to be silent with respect to streptomycin phenotype. It is necessary to postulate a high rate of formation of such mutations at some stage during the experiment. One possibility is that spontaneous mutation may often occur in bursts when an error correction mechanism (eg., proofreading, mismatch correction) is temporarily inactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of glucose absorption by 3-phenylpropylaminoguanidine-HCl (SaH 43-522) in laboratory animals

The present studies were undertaken to define the effects of 3-phenylpropylaminoguanidine-HCl (SaH 43-522 or 43-522) on glucose active transport in the gastrointestinal tract. A comparison with phenformin (DBI) was made in certain studies. SaH 43-522 is 2 to 3 times more potent than DBI with regard to its inhibitory effect on glucose active transport in the gastrointestinal tract of rats. The activity lasts for 5 hr after oral administration. SaH 43-522 also inhibits intestinal glucose absorption in the hamster, guinea-pig, dog, and monkey in either in vitro or in vivo systems. SaH 43-522 differs from DBI in that when glucose active transport is studied in vitro by adding drug into the incubation fluid, DBI is active only when the drug is present in the incubation fluids on both the mucosal and serosal sides, whereas SaH 43-522 is active in inhibiting intestinal glucose active transport when the drug is present in mucosal fluid only.

Modification of Lofland's colorimetric semiautomated serum triglyceride determination, assessed by an enzymatic glycerol determination

Erroneously high values for serum triglyceride levels obtained with the semiautomated method of Lofland were found to be due to contamination of the isopropanol extracts with glucose or other carbohydrate. Treatment of the isopropanol extracts with a mixture of copper sulfate and calcium hydroxide removed the contaminating glucose. Analysis of the glucose-free extracts by either the semiautomated or manual colorimetric method gave values in good agreement with each other and with those obtained by a new specific enzymatic method. The simple modification described in this paper obviates the necessity for the more expensive automated fluorometric apparatus.