The effect of a one-year vigorous physical activity intervention on fitness, cognitive performance and mental health in young adolescents: the Fit to Study cluster randomised controlled trial

Background

Physical activity (PA) may positively stimulate the brain, cognition and mental health during adolescence, a period of dynamic neurobiological development. High-intensity interval training (HIIT) or vigorous PA interventions are time-efficient, scalable and can be easily implemented in existing school curricula, yet their effects on cognitive, academic and mental health outcomes are unclear. The primary aim of the Fit to Study trial was to investigate whether a pragmatic and scalable HIIT-style VPA intervention delivered during school physical education (PE) could improve attainment in maths. The primary outcome has previously been reported and was null. Here, we report the effect of the intervention on prespecified secondary outcomes, including cardiorespiratory fitness, cognitive performance, and mental health in young adolescents.

Methods

The Fit to Study cluster randomised controlled trial included Year 8 pupils (n = 18,261, aged 12–13) from 104 secondary state schools in South/Mid-England. Schools were randomised into an intervention condition (n = 52), in which PE teachers delivered an additional 10 min of VPA per PE lesson for one academic year (2017–2018), or into a “PE as usual” control condition. Secondary outcomes included assessments of cardiorespiratory fitness (20-m shuttle run), cognitive performance (executive functions, relational memory and processing speed) and mental health (Strength and Difficulties Questionnaire and self-esteem measures). The primary intention-to-treat (ITT) analysis used linear models and structural equation models with cluster-robust standard errors to test for intervention effects. A complier-average causal effect (CACE) was estimated using a two-stage least squares procedure.

Results

The HIIT-style VPA intervention did not significantly improve cardiorespiratory fitness, cognitive performance (executive functions, relational memory or processed speed), or mental health (all p > 0.05). Subgroup analyses showed no significant moderation of intervention effects by sex, socioeconomic status or baseline fitness levels. Changes in cardiorespiratory fitness were not significantly related to changes in cognitive or mental health outcomes. The trial was marked by high drop-out and low intervention compliance. Findings from the CACE analysis were in line with those from the ITT analysis.

Conclusion

The one-academic year HIIT-style VPA intervention delivered during regular school PE did not significantly improve fitness, cognitive performance or mental health, but these findings should be interpreted with caution given low implementation fidelity and high drop-out. Well-controlled, large-scale, school-based trials that examine the effectiveness of HIIT-style interventions to enhance cognitive and mental health outcomes are warranted.

Trial registration

ISRCTN registry, 15,730,512. Trial protocol and analysis plan for primary outcome prospectively registered on 30th March 2017.

ClinicalTrials.gov, NCT03286725. Secondary measures (focus of current manuscript) retrospectively registered on 18 September 2017.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12966-021-01113-y.

BCG vaccination early in life does not improve COVID-19 outcome of elderly populations, based on nationally reported data

The reported numbers of Covid-19 cases and deaths were compared for 18 countries (14 in Western Europe, plus Australia, Brazil, Israel and the USA) to assess the effect of historic and current national BCG immunizations. In view of the high death rate for Covid-19 patients over 70 years of age, and given the fact that BCG vaccination is typically given early in life, we compared countries that had introduced BCG in the 1950s with those that had not. No effect on Covid-19 case fatality rate (CFR) or number of deaths per population could be demonstrated. Since some countries test for Covid-19 more than others, the effect of tests performed per million population on reported deaths per million was also assessed, but again did not demonstrate an effect of BCG vaccination in the 1950s. Whether countries had never used the vaccine, had historically used it but since ceased to do so, or were presently vaccinating with BCG did not correlate with national total number of deaths or CFR. We conclude that there is currently no evidence for a beneficial effect of BCG vaccination on Covid-19 reported cases or fatalities.

How industrial bacterial cultures can be kept stable over time

The tremendous variation that exists between bacterial species illustrates the power of evolution, which is the continuous process of mutation and selection over time. Even within a bacterial species, individual members can harbour an impressive degree of genetic variation, depending on the species. The question then arises how similar the offspring of a given bacterial cell over time is, and how long it takes before differences are noticeable? Here we show that on the one hand one can expect random mutations to arise, as a result of various mechanisms. On the other hand, there are forces at play that keep the offspring of a cell genetically relatively constant, unless there is selection for a particular characteristic. The most common mechanisms behind mutations that can appear in a bacterial population are briefly introduced. Next, it is explained why nevertheless such mutations are rarely observed, as long as single colonies are randomly selected, unless selective pressures apply. Since quality control of industrial bacterial cultures is likely to depend heavily on genome sequencing in the near future, the accuracy of whole‐genomic sequencing technologies is also discussed. It can be concluded that the bacteriologists who started picking single colonies from agar plates more than hundred years ago were unknowingly ingeneous, as their practice maintains a bacterial culture stable over time.

Significance and Impact of Study

The questions addressed here are relevant for industries that depend on live bacteria for (manufacturing of) their products, as they have to guard their bacterial cultures that remain unchanged over time. The explanation why randomly selection of single colonies keeps a population stable can be of use in bacteriology courses. The limitations of whole‐genome sequencing are relevant to legislators to avoid overinterpretation of those data.

2019_nCoV/SARS-CoV-2: rapid classification of betacoronaviruses and identification of Traditional Chinese Medicine as potential origin of zoonotic coronaviruses

The current outbreak of a novel severe acute respiratory syndrome‐like coronavirus, 2019_nCoV (now named SARS‐CoV‐2), illustrated difficulties in identifying a novel coronavirus and its natural host, as the coding sequences of various Betacoronavirus species can be highly diverse. By means of whole‐genome sequence comparisons, we demonstrate that the noncoding flanks of the viral genome can be used to correctly separate the recognized four betacoronavirus subspecies. The conservation would be sufficient to define target sequences that could, in theory, classify novel virus species into their subspecies. Only 253 upstream noncoding sequences of Sarbecovirus are sufficient to identify genetic similarities between species of this subgenus. Furthermore, it was investigated which bat species have commercial value in China, and would thus likely be handled for trading purposes. A number of coronavirus genomes have been published that were obtained from such bat species. These bats are used in Traditional Chinese Medicine, and their handling poses a potential risk to cause zoonotic coronavirus epidemics.

Significance and Impact of the Study

The noncoding upstream and downstream flanks of coronavirus genomes allow for rapid classification of novel Betacoronavirus species and correct identification of genetic relationships. Although bats are the likely natural host of 2019_nCoV, the exact bat species that serves as the natural host of the virus remains as yet unknown. Chinese bat species with commercial value were identified as natural reservoirs of coronaviruses and are used in Traditional Chinese Medicine. Since their trading provides a potential risk for spreading zoonoses, a change in these practices is highly recommended.

Anti-genotoxic and anti-mutagenic activity of Escherichia coli Nissle 1917 as assessed by in vitro tests

Anti-genotoxic or anti-mutagenic activity has been described for a number of Gram-positive probiotic bacterial species. Here we present evidence that Gram-negative Escherichia coli Nissle 1917 (EcN) also displays anti-genotoxic/anti-mutagenic activity, as assessed in vitro by the Comet Assay and the Ames Test, respectively. This activity was demonstrated by use of the mutagens 4-nitroquinoline-1-oxide (NQO), hydrogen peroxide (H₂O₂) and benzo(a) pyrene (B[a]P). For both assays and all three test agents the anti-genotoxic/anti-mutagenic activity of EcN was shown to be concentration dependent. By the use of extracts of bacteria that were inactivated by various procedures (heat treatment, ultrasound sonication or ultraviolet light irradiation), mechanistic explanations could be put forward. The proposed mechanisms were enforced by treating the bacterial material with proteinase K prior to testing. The mutagen H₂O₂ is most likely inactivated by enzymic activity, with catalase a likely candidate, while several explanations can be put forward for inactivation of B[a]P. NQO is most likely inactivated by metabolising enzymes, since the formation of the metabolite 4-aminoquinoline could be demonstrated. In conclusion, the in vitro results presented here make a strong case for antimutagenic properties of EcN.

Effects of a programme of vigorous physical activity during secondary school physical education on academic performance, fitness, cognition, mental health and the brain of adolescents (Fit to Study): study protocol for a cluster-randomised trial

BACKGROUND

Early adolescence is a period of dynamic neurobiological change. Converging lines of research suggest that regular physical activity (PA) and improved aerobic fitness have the potential to stimulate positive brain changes, improve cognitive function and boost academic attainment in this age group, but high-quality studies are needed to substantiate these findings. The primary aim of the Fit to Study trial is to investigate whether short infusions of vigorous PA (VPA) delivered during secondary school physical education (PE) can improve attainment in maths, as described in a protocol published by NatCen Social Research. The present protocol concerns the trial's secondary outcome measures, which are variables thought to moderate or mediate the relationship between PA and attainment, including the effect of the intervention on cardiorespiratory fitness, cognitive performance, mental health and brain structure and function.

METHOD

The Fit to Study project is a cluster-randomised controlled trial that includes Year 8 pupils (aged 12-13) from secondary state schools in South/Mid-England. Schools were randomised into an intervention condition in which PE teachers delivered an additional 10 min of VPA per PE lesson for one academic year, or a 'PE as usual' control condition. Intervention and control groups were stratified according to whether schools were single-sex or co-educational. Assessments take place at baseline (end of Year 7, aged 11-12) and after 12 months (Year 8). Secondary outcomes are cardiorespiratory fitness, objective PA during PE, cognitive performance and mental health. The study also includes exploratory measures of daytime sleepiness, attitudes towards daily PA and PE enjoyment. A sub-set of pupils from a sub-set of schools will also take part in a brain imaging sub-study, which is embedded in the trial.

DISCUSSION

The Fit to Study trial could advance our understanding of the complex relationships between PA and aerobic fitness, the brain, cognitive performance, mental health and academic attainment during adolescence. Further, it will add to our understanding of whether school PE is an effective setting to increase VPA and fitness, which could inform future PA interventions and education policy.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03286725 . Retrospectively registered on 18 September 2017. ClinicalTrials.gov, NCT03593863 . Retrospectively registered on 19 July 2018.

The mobile dso-gene-sso element in rolling-circle plasmids of staphylococci reflects the evolutionary history of its resistance gene

The qacC and lnuA genes of Staphylococcus species were recently proposed to comprise a mobile element when residing on rolling-circle plasmids. Here we present other examples of resistance genes on staphylococcal rolling-circle plasmids, including fosB producing resistance to fosfomycin, cat resulting in resistance to chloramphenicol and cadB for resistance to the toxic heavy metal cadmium. For three of these genes (qacC, lnuA and fosB), evidence was obtained that the genes have spread between different plasmid backgrounds. The lack of mutations in qacC suggests that the spread occurred relatively recently, while the build up of mutations in lnuA and fosB suggests their mobilization occurred in the more distant past. These observations can be explained by the use of the respective antibiotics over time. However, the cat and cadB genes sequences analysed had not collected any mutations, an observation that is not completely understood but possible explanations are discussed.

SIGNIFICANCE AND IMPACT OF THE STUDY

We have analysed five resistance genes in Staphylococcus aureus that are positioned between the replication elements of rolling-circle plasmids. For three of these genes, evidence was obtained indicative of recent mobilization. The historical use of the antibiotics to which the genes produce resistance could be related to the number of mutations collected in these genes. However, two other resistance genes have not collected any mutations over time, and the reasons for this are discussed. The analyses presented provide insights into the spread and evolution of antibiotic resistance genes.

Is a foetus developing in a sterile environment?

Novel findings in microbiology question the long-standing paradigm that a healthy pregnancy implies a sterile uterus. It now seems that the placenta is frequently colonized with bacteria, and a placental microbiome has been identified. Recent literature findings are summarized here, and an attempt is made to separate pathological bacterial presence from a naturally occurring microbiome.

The effect of different isolation protocols on detection and molecular characterization of Campylobacter from poultry

We determined whether different methods to isolate Campylobacter (including the ISO standard 10272:2006-1) affected the genotypes detectable from poultry, at three points during slaughter: caecal content, neck skin and meat. Carcasses from 28 independent flocks were thus sampled (subset A). In addition, ten neck skin samples from four flocks, ten caecal samples from ten different flocks and ten unrelated meat samples obtained from local supermarkets were collected (subset B). Campylobacter was isolated using eight different protocols: with and without enrichment using Bolton broth, Preston broth or Campyfood broth (CFB), followed by culture on either modified Charcoal Cefoperazone Deoxycholate Agar (mCCDA) or Campyfood agar (CFA). All obtained isolates were genotyped for flaA-SVR, and over half of the isolates were also typed by MLST. The strain richness, as a measure of number of detected fla-genotypes, obtained from subset A neck skin and caecal samples was higher than that of meat samples. In half of the cases, within a flock, at least one identical fla-genotype was obtained at all three slaughter stages, suggestive of autologous contamination of carcasses. Enrichment reduced the observed richness of isolates, while CFA plates increased richness compared to mCCDA plates, irrespective of inclusion of an enrichment step. Because the isolation protocol used influences both the yield and the fla-genotype richness obtained from poultry, this variable should be taken into account when different studies are being compared.

Detection of methicillin-resistant Staphylococcus aureus in Iberian pigs

AIMS

Iberian pigs are bred in Spain for the production of high-value dry-cured products, whose export volumes are increasing. Animals are typically reared outdoors, although indoor farming is becoming popular. We compared carriage of methicillin-resistant Staphylococcus aureus (MRSA) in Iberian pigs, raised indoors and outdoors, with intensively farmed Standard White pigs.

METHODS AND RESULTS

From June 2007 to February 2008, 106 skin swabs were taken from Iberian pigs and 157 samples from SWP at slaughterhouses in Spain. We found that Iberian pigs carried MRSA, although with a significantly lower prevalence (30/106; 28%) than SWP (130/157; 83%). A higher prevalence of indoor Iberian pigs compared with animals reared under outdoor conditions was not significant; however, all but one positive indoor Iberian pig samples were detected from one slaughterhouse. Overall, 16 different spa types were identified, with t011 predominating in all three animal populations. A subset of isolates was characterized by MLST. Most of these belonged to ST398. MRSA isolates from Iberian pigs presented a higher susceptibility to antibiotics than those isolated from SWP.

CONCLUSIONS

Despite limited contact with humans, pigs raised outdoors are colonized by an MRSA population that genetically overlaps with that of intensively farmed pigs, although antimicrobial resistance is lower.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, this is the first detection of MRSA in food animals raised in free-range conditions.

Following an imaginary Campylobacter population from farm to fork and beyond: a bacterial perspective

It has been known for decades that poultry meat is the most common single source for campylobacteriosis, yet the problem has not been solved. This review identifies some of the reasons why our attempts to reduce the incidence of this pathogen have largely failed. Based on the literature, the events a virtual population of Campylobacter may encounter, from growing in the gut of a broiler to eventually infecting humans and causing disease, are reviewed. Most steps in the farm-to-fork process are well studied, though there are gaps in our knowledge about survival and spread of Campylobacter populations before they enter the farm. Key events in the farm-to-fork chain that are suitable targets for prevention and control, to reduce food-borne campylobacteriosis, are indicated. Novel insights into the pathogenic mechanism responsible for disease in humans are summarized, which hypothesize that an overactive immune response is the reason for the typical inflammatory diarrhoea. A role of genetic microheterogeneity within a clonal population in this chain of events is being proposed here. The human host is not necessary for the survival of the bacterial species, nor have these bacteria specifically evolved to cause disease in that host. More likely, the species evolved for a commensal life in birds, and human disease can be considered as collateral damage owing to an unfortunate host-microbe interaction. The indirect environmental burden that results from poultry production should not be ignored as it may pose a diffuse, but possibly significant risk factor for disease.

The genus burkholderia: analysis of 56 genomic sequences

The genus Burkholderia consists of a number of very diverse species, both in terms of lifestyle (which varies from category B pathogens to apathogenic soil bacteria and plant colonizers) and their genetic contents. We have used 56 publicly available genomes to explore the genomic diversity within this genus, including genome sequences that are not completely finished, but are available from the NCBI database. Defining the pan- and core genomes of species results in insights in the conserved and variable fraction of genomes, and can verify (or question) historic, taxonomic groupings. We find only several hundred genes that are conserved across all Burkholderia genomes, whilst there are more than 40,000 gene families in the Burkholderia pan-genome. A BLAST matrix visualizes the fraction of conserved genes in pairwise comparisons. A BLAST atlas shows which genes are actually conserved in a number of genomes, located and visualized with reference to a chosen genome. Genomic islands are common in many Burkholderia genomes, and most of these can be readily visualized by DNA structural properties of the chromosome. Trees that are based on relatedness of gene family content yield different results depending on what genes are analyzed. Some of the differences can be explained by errors in incomplete genome sequences, but, as our data illustrate, the outcome of phylogenetic trees depends on the type of genes that are analyzed.

Genome comparison of bacterial pathogens

Bacterial pathogens are being sequenced at an increasing rate. To many microbiologists, it appears that there simply is not enough time to digest all the information suddenly available. In this chapter we present several tools for comparison of sequenced pathogenic genomes, and discuss differences between pathogens and non-pathogens. The presented tools allow comparison of large numbers of genomes in a hypothesis-driven manner. Visualization of the results is very important for clear presentation of the results and various ways of graphical representation are introduced.

Genetic instability is associated with changes in the colonization potential of Campylobacter jejuni in the avian intestine

AIMS

A panel of pulsed field gel electrophoresis (PFGE) type variants of Campylobacter jejuni, previously identified as of clonal origin, were investigated to determine whether genomic instability could be observed during competitive growth.

METHODS AND RESULTS

Upon recovery from frozen storage, some variants had undergone alterations in PFGE profiles, but subsequent culture produced constant genotypes. Individual variants did not display differences in colonization potential when tested in orally challenged 1-day-old chickens. However, competitive colonization using mixtures of two or three PFGE types generally resulted, by 4 weeks postchallenge, in one predominant PFGE type in all birds. For some variant mixtures, a minor population of novel PFGE types was detected in individual birds. The creation of new variants appeared to be dependent on the extent of competition and of the individual host. Genomic rearrangements most likely explain this increase in genetic diversity, apparently without the involvement of natural transformation or plasmid acquisition. In vitro cultivation of mixed inoculations were again selected for particular variants; but genetic diversity was not generated, suggesting that the selection pressures in vitro differed from those active in vivo.

CONCLUSION

These observations support the hypothesis that by generating genetic diversity, C. jejuni can improve its phenotypic fitness to survive and colonize subsequent hosts.

SIGNIFICANCE AND IMPACT OF THE STUDY

The consequences of such observations for the development of campylobacter control strategies for poultry may be substantial.

Phenon cluster analysis as a method to investigate epidemiological relatedness between sources of Campylobacter jejuni

AIMS

To develop a method for assessing the relative epidemiological significance of possible infection sources for human campylobacteriosis.

METHODS AND RESULTS

Using fluorescent amplified fragment length polymorphism (AFLP), 243 apparently epidemiologically unrelated Campylobacter jejuni isolates were genotyped (77 human, 46 cattle, 49 pet and 71 poultry isolates). In total 136 different phena were identified, of which 48 were clusters grouping at least two isolates. Isolates from different sources were frequently clustered together, underlining the high degree of source mixing and the lack of host specificity of C. jejuni. The phena were classified into different phenon types according to the sources of the isolates they contained. The occurrence of these phenon types was analysed using an area-proportional Euler diagram to describe epidemiological relatedness among C. jejuni isolates. Group separation statistics revealed that 43% of analysed human isolates expressed maximum similarity to other human isolates, 9% to cattle isolates, 21% to pet isolates and 27% to poultry isolates; these results were in accordance with the pattern observed in the phenon cluster analysis.

CONCLUSIONS

Based on the grouping of strains into molecular similarity clusters, ecological patterns between sources can be investigated.

SIGNIFICANCE AND IMPACT OF THE STUDY

This approach is a new methodological contribution to establish the relative epidemiological significance of concurrent infection sources.

Genetic diversity and antibiotic resistance patterns in a campylobacter population isolated from poultry farms in Switzerland

The diversity and genetic interrelation of Campylobacter jejuni and C. coli isolated from Swiss poultry were assessed by three independent typing methods. Samples were derived prior to slaughter from 100 randomly selected flocks (five birds per flock) raised on three different farm types. The observed flock prevalence was 54% in total, with 50% for conventional and 69% for free-range farms. Birds held on farms with a confined roaming area had the lowest prevalence of 37%. Campylobacter isolates were characterized by amplified fragment length polymorphism (AFLP), restriction fragment length polymorphism of flaA PCR fragments (flaA-RFLP), and disk diffusion testing for eight antimicrobial agents that are commonly used in veterinary or human medicine in Switzerland. Analysis of the genotypic results indicates that the Campylobacter population in Swiss poultry is genetically highly diverse. Nevertheless, occasionally, isolates with identical or nearly identical characteristics were isolated from different farms or farm types in different locations. Genetic typing by AFLP and flaA-RFLP was found to be complementary. The majority of isolates (67%) were susceptible to all tested antibiotics; however, single, double, and triple resistances were observed in 7%, 23%, and 2% of the strains, respectively. There was no correlation between genotype and antibiotic resistance. Surprisingly, sulfonamide resistance was frequently found together with streptomycin resistance. Our findings illustrate the results of common genetic exchange in the studied bacterial population.

Campylobacter spp. in Dogs and Cats in Switzerland: Risk Factor Analysis and Molecular Characterization with AFLP

A 1-year cross-sectional study was carried out to determine the prevalence, risk factors for carriage, and genetic diversity of Campylobacter spp. in healthy dogs and cats in Switzerland. Veterinary practitioners collected samples from 1268 animals (all ages) presented for vaccination. The prevalence of Campylobacter spp. in 634 dogs and 596 cats that were eligible for the study was 41.2% (confidence interval 95%: 37.3-45.1%) and 41.9% (CI 95%: 37.9-46%), respectively. Risk factors identified for carriage of Campylobacter jejuni were found to be different from risk factors for C. upsaliensis/C. helveticus. Young animals (< or =3 years) had significantly higher odds of carrying C. upsaliensis/C. helveticus than older animals (OR 1.8-3.3), whereas for C. jejuni carriage, the age was not a risk factor. Amplified fragment length polymorphism (AFLP) genotyping revealed heterogeneity among C. jejuni strains and was found to clearly separate C. helveticus from C. upsaliensis. It was shown that cats more often carry C. helveticus with an estimated prevalence of 28.2%, whereas dogs mainly are carrying C. upsaliensis.

PCR detection of virulence genes in Yersinia enterocolitica and Yersinia pseudotuberculosis and investigation of virulence gene distribution

PCR-based assays were developed for the detection of plasmid- and chromosome-borne virulence genes in Yersinia enterocolitica and Yersinia pseudotuberculosis, to investigate the distribution of these genes in isolates from various sources. The results of PCR genotyping, based on 5 virulence-associated genes of 140 strains of Y. enterocolitica, were compared to phenotypic tests, such as biotyping and serotyping, and to virulence plasmid-associated properties such as calcium-dependent growth at 37 degrees C and Congo red uptake. The specificity of the PCR results was validated by hybridization. Genotyping data correlated well with biotype data, and most biotypes resulted in (nearly) homogeneous genotypes for the chromosomal virulence genes (ystA, ystB, and ail); however, plasmid-borne genes (yadA and virF) were detected with variable efficiency, due to heterogeneity within the bacterial population for the presence of the virulence plasmid. Of the virulence genes, only ystB was present in biotype 1A; however, within this biotype, pathogenic and apathogenic isolates could not be distinguished based on the detection of virulence genes. Forty Y. pseudotuberculosis isolates were tested by PCR for the presence of inv, yadA, and lcrF. All isolates were inv positive, and 88% of the isolates contained the virulence plasmid genes yadA and lcrF. In conclusion, this study shows that genotyping of Yersinia spp., based on both chromosome- and plasmid-borne virulence genes, is feasible and informative and can provide a rapid and reliable genotypic characterization of field isolates.

Evolutionary history of hrgA, which replaces the restriction gene hpyIIIR in the hpyIII locus of Helicobacter pylori

A recently identified Helicobacter pylori gene, hrgA, was previously reported to be present in 70 (33%) of 208 strains examined (T. Ando, T. M. Wassenaar, R. M. Peek, R. A. Aras, A. I. Tschumi, L.-J. Van Doorn, K. Kusugami, and M. J. Blaser, Cancer Res. 62:2385-2389, 2002). Sequence analysis of nine such strains indicated that in each strain hrgA replaced hpyIIIR, which encodes a restriction endonuclease and which, together with the gene for its cognate methyltransferase, constitutes the hpyIII locus. As a consequence of either the hrgA insertion or independent mutations, hpyIIIM function was lost in 11 (5%) of the 208 strains examined, rendering chromosomal DNA sensitive to MboI digestion. The evolutionary history of the locus containing either hpyIII or hrgA was reconstructed. By homologous recombination involving flanking sequences, hrgA and hpyIIIR can replace one another in the hpyIII locus, and there is simultaneous replacement of several flanking genes. These findings, combined with the hpyIM/iceA2 locus discovered previously, suggest that the two most strongly conserved methylase genes of H. pylori, hpyIIIM and hpyIM, are both preceded by alternative genes that compete for presence at their loci.

Bacterial virulence: can we draw the line?

The molecular approach to microbial pathogenesis has resulted in an impressive amount of data on bacterial virulence genes. Bacterial genome sequences rapidly add candidate virulence genes to electronic databases. The interpretation of this overwhelming information is obscured because every gene involved in pathogenicity is called a virulence gene, regardless of its function in the complex process of virulence. This review summarizes the changing concept of bacterial virulence and the detection and identification strategies followed to recognize virulence genes. A refined definition of virulence genes is proposed in which the function of the gene in the virulence process is incorporated. We propose to include the life-style of bacteria in the assessment of their putative virulence genes. A universal nomenclature in analogy to the EC enzyme numbering system is proposed. These recommendations would lead to a better insight into bacterial virulence and a more precise annotation of (putative) virulence genes, which would enable more efficient use of electronic databases.

Genetic characterization of Campylobacter jejuni O:41 isolates in relation with Guillain-Barré syndrome

Campylobacter jejuni O:41 strains are found in association with Guillain-Barré syndrome in South Africa. Strains of this serotype collected over 17 years were characterized by amplified fragment length polymorphism and flagellin typing to determine their clonal nature. Despite minor variation in GM1 expression, all of the strains were genetically indistinguishable, indicating that they are representative of a genetically stable clone.

Pathophysiology of Campylobacter jejuni infections of humans

Campylobacter jejuni and closely related organisms are major causes of human bacterial enteritis. These infections can lead to extraintestinal disease and severe long-term complications. Of these, neurological damage, apparently due to the immune response of the host, is the most striking. This review examines current knowledge of the pathophysiology of the organism. Diversity of C. jejuni isolates in genotypic and phenotypic characteristics now is recognized and clinically relevant examples are presented. Expected future directions are outlined.

High-resolution genotyping of Campylobacter strains isolated from poultry and humans with amplified fragment length polymorphism fingerprinting

For epidemiological studies of Campylobacter infections, molecular typing methods that can differentiate campylobacters at the strain level are needed. In this study we used a recently developed genotyping method, amplified fragment length polymorphism (AFLP), which is based on selective amplification of restriction fragments of chromosomal DNA, for genetic typing of Campylobacter jejuni and Campylobacter coli strains derived from humans and poultry. We developed an automated AFLP fingerprinting method in which restriction endonucleases HindIII and HhaI were used in combination with one set of selective PCR primers. This method resulted in evenly distributed band patterns for amplified fragments ranging from 50 to 500 bp long. The discriminatory power of AFLP was assessed with a C. jejuni strain, an isogenic flagellin mutant, and distinct C. jejuni strains having known pulsed-field gel electrophoresis and fla PCR-restriction fragment length polymorphism genotypes. Unrelated C. jejuni strains produced heterogeneous patterns, whereas genetically related strains produced similar AFLP patterns. Twenty-five Campylobacter strains obtained from poultry farms in The Netherlands grouped in three C. jejuni clusters that were separate from a C. coli cluster. The band patterns of 10 C. jejuni strains isolated from humans were heterogeneous, and most of these strains grouped with poultry strains. Our results show that AFLP analysis can distinguish genetically unrelated strains from genetically related strains of Campylobacter species. However, desirable genetically related strains can be differentiated by using other genotyping methods. We concluded that automated AFLP analysis is an attractive tool which can be used as a primary method for subtyping large numbers of Campylobacter strains and is extremely useful for epidemiological investigations.

Evidence of genomic instability in Campylobacter jejuni isolated from poultry

Poultry isolates of Campylobacter jejuni derived from a survey of meat processing batches were genotyped by pulsed-field gel electrophoresis (PFGE) of chromosomal DNA to establish the clonal relationships between single-colony isolates. In the majority of batches studied, one or two genotype patterns predominated. However, in one batch (batch A), 21 single-colony isolates gave 14 different PFGE genotypes. The banding patterns obtained with SmaI were sufficiently different to distinguish between genotypes, although the patterns also produced many common bands. The question of whether these isolates represented different clones or had a common clonal ancestry was addressed by additional genotypic and phenotypic methods. Restriction length polymorphism of PCR products obtained from the flagellin genes showed an identical flagellin genotype for all of these isolates. In contrast, unrelated control isolates resulted in different flagellin genotypes. Moreover, all 14 different PFGE genotypes of batch A had identical Penner serotypes and identical or similar biotypes and phage types. It was concluded that the isolates were of clonal origin and that the diversity in the PFGE banding patterns had most likely originated from genomic rearrangements. However, the PFGE genotypes were shown to be stable upon subculturing in vitro and after in vivo passage in chickens, and natural transformation between isogenic mutants carrying antibiotic markers did not occur in vivo in a chick colonization model. The possible mechanisms for the hypothesized genomic recombinations and the conditions that allow, induce, or select for such events are discussed.

Differential uptake and killing potential of Campylobacter jejuni by human peripheral monocytes/macrophages

The ability of Campylobacter jejuni to survive in monocytes after phagocytic uptake was tested in a new in vitro model using adherent macrophages derived from human peripheral monocytes. The cells were stimulated with cytokines before use to ensure full phagocytic and killing activity. The kinetics of uptake and killing of bacteria was followed for 72 h with 16 strains, including stool and blood isolates and laboratory adapted strains. Significant bacterial strain differences were not observed, but the viability of phagocytosed bacteria was dependent on the individual donating the macrophages. The majority of blood donors carried macrophages that killed phagocytosed Campylobacter within 24 or 48 h. There was no correlation between the source of isolation of the strains and relative intracellular survival. Bacterial mutants of superoxide dismutase, catalase or polyphosphate kinase were all as sensitive to macrophage killing as their isogenic wild-type strain. In contrast, about 10% of the voluntary blood donors carried monocytes which were incapable of killing phagocytosed bacteria. Such macrophages displayed normal uptake, but killing was insufficient and bacterial growth was observed with all strains and mutants tested. We conclude that (1) since in most cases activated human macrophages kill C. jejuni efficiently after phagocytosis, intra-phagocytic survival is not a common phenomenon during Campylobacter infection; and (2) those individuals carrying macrophages that are unable to destroy phagocytosed bacteria are at risk to develop a bacteremia during Campylobacter infection.

Toxin production by Campylobacter spp

Of all the virulence factors that were proposed for Campylobacter jejuni and related species to cause disease in humans, the discovery of toxin production was the most promising but led to a rather confusing and even disappointing stream of data. The discussion of whether proteinaceous exotoxins are relevant in disease remains open. One important reason for this lack of consensus is the anecdotal nature of the literature reports. To provide a basis for an unbiased opinion, this review compiles all described exotoxins, compares their reported properties, and provides a summary of animal model studies and clinical data. The toxins are divided into enterotoxins and cytotoxins and are sorted according to their biochemical properties. Since many Campylobacter toxins have been compared with toxins of other species, some key examples of the latter are also discussed. Future directions of toxin research that appear promising are defined.

Potent membrane-permeabilizing and cytocidal action of Vibrio cholerae cytolysin on human intestinal cells

Many strains of Vibrio cholerae non-O1 and O1 El Tor that cause diarrhea do not harbor genes for a known secretogenic toxin. However, these strains usually elaborate a pore-forming toxin, hitherto characterized as a hemolysin and here designated V. cholerae cytolysin, whose action on intestinal cells has not yet been described. We report that V. cholerae cytolysin binds as a monomer to Intestine 407 cells and then assembles into detergent-stable oligomers that probably represent tetra- or pentamers. Oligomer formation is accompanied by generation of small transmembrane pores that allow rapid flux of K+ but not influx of Ca2+ or propidium iodide. Pore formation is followed by irreversible ATP depletion and cell death. Binding of fewer than 10(4) toxin molecules per cell in vitro is lethal. The possibility is raised that production of this toxin by bacteria that are in close contact with intestinal cells is rapidly cytocidal in vivo, and death of intestinal cells may be a cause of diarrhea.

Increased colonization potential of Campylobacter jejuni strain 81116 after passage through chickens and its implication on the rate of transmission within flocks

The mechanisms by which Campylobacter jejuni rapidly spreads through large broiler flocks are unknown. Recent evidence suggests that the minimum infective oral dose for 100% caecal colonization is about 10(4) cfu, which, with such a 'fragile' organism, may limit transmissibility. However, the colonization potential of laboratory-adapted strains may be anomalous compared with fresh isolates or those passaged in vivo. The colonization potential of two chicken and one human C. jejuni isolates, which were minimally passaged, have been investigated using a quantitative model of chicken colonization. There was no detectable difference between these strains but all were more efficient colonizers than a laboratory-adapted strain 81116. In addition, the colonization potential of C. jejuni strain 81116 following a passage in vivo was also determined. The results indicated this increased c. 10000 fold following a single passage in vivo, such that a dose of only 40 cfu caused maximal colonization. Enhanced colonization potential may, therefore, account for the rapid rate of transmission within large flocks.

Variation of the flagellin gene locus of Campylobacter jejuni by recombination and horizontal gene transfer

The capacity of Campylobacter jejuni to generate genetic diversity was determined for its flagellar region. Recombination within a genome, as well as recombination after the uptake of exogenous DNA, could be demonstrated. The subunit of the flagellar filament of C. jejuni is encoded by two tandem genes, flaA and flaB, which are highly similar and therefore subject to recombination. A spontaneous recombination within this locus was demonstrated in a bacterial clone containing an antibiotic-resistance gene inserted in flaA. A recombinant was isolated in which the antibiotic-resistance gene had been repositioned into flaB, indicating that genetic information can be exchanged between the two flagellin genes of C. jejuni. The occurrence of recombinational events after the uptake of exogenous DNA by naturally competent bacteria was demonstrated with two mutants containing different antibiotic-resistance markers in their flagellin genes. Double-resistant transformants were formed when purified chromosomal donor DNA was added to a recipient strain, when the two bacterial cultures were mixed under conditions that induce natural competence, or when the two strains were cocultured. Both mechanisms of recombination may be used by the pathogenic organism to escape the immunological responses of the host or otherwise adapt to the environment.

Differential flagellin expression in a flaA flaB+ mutant of Campylobacter jejuni

Campylobacter jejuni 81116 has two genes coding for flagellin, flaA and flaB. Fully motile wild-type C. jejuni bacteria express the flaA gene, with no flaB message being detected. A nonmotile flaA flaB+ mutant, R1, produced detectable levels of flagellin B which was incorporated into truncated flagella. After R1 had invaded INT-407 cells, a variant with increased motility, R1-V2, was isolated. R1-V2 produced full-length flagella and an increased amount of flagellin B. Transcriptional analysis showed that R1-V2 contained more flaB mRNA than its parental strain, R1. The flaB gene promoter sequence and primer extension experiments confirmed that transcription of the flaB gene is initiated from a sigma 54 promoter. Neither the promoter sequence nor the coding sequence of flaB had changed in R1-V2. In contrast to R1, R1-V2 no longer produced (truncated) flaA mRNA. The sigma 28 flaA promoter sequence was not changed in R1-V2. We propose that expression of the two flagellin genes in C. jejuni 81116 is regulated at the transcriptional level, in such a way that predominantly one gene at a time is transcribed. We compared the levels of invasiveness of the wild-type strain, R1, and R1-V2 for INT-407 cells. The shift in expression from flaA to flaB occurred not only during invasion assays but also under different conditions in the absence of eukaryotic cells.

[Pathogenicity factors of enteric Salmonellae]

The number of cases of salmonellosis has steadily increased during the last decade. Until the end of the 70s, the serotype Salmonella typhimurium was most commonly isolated, but since 1986 the serotype S. enteritidis has become more common. Recent research has shown that the colon is more frequently infected than was earlier recognized, but most common is still an acute enterocolitis during an infection with salmonella. In severe cases, salmonella can spread from the gut, the site of infection, to cause a systemic disease. As in vitro studies have shown, gastroenteritic salmonellae seem to possess a number of so-called virulence factors that help them to evade the host's defenses against bacterial infection. Colonisation in the gut seems to be dependent on a 66 kD heat shock protein (HSP), which binds to a 15 kD glycoprotein present in gut mucus. For penetration into the mucosa, by invasion of the epithelial cells, bacterial invasions are newly synthesized. These proteins distort the epithelial membrane and induce a port of entrance. Macrophages will attack and engulf the bacteria, but salmonella can withstand these professional killers, and even grow intracellularly in them. In order to do so, not only LPS is required, but also specific outer membrane proteins (OMP), porins. Moreover, during their intracellular survival the bacteria need to adapt to the new microenvironment, and in reaction to stress, new HSPs are expressed. Finally, the O-specific sugar chains prevent the otherwise lytic action of complement in blood serum.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic manipulation of Campylobacter: evaluation of natural transformation and electro-transformation

Two methods, natural transformation and electro-transformation, for the introduction of DNA into nine strains of Campylobacter jejuni were compared. Both methods were successful with a limited number of strains. Natural transformation was efficient only for the introduction of C. jejuni chromosomal DNA, while electro-transformation was also applicable for the introduction of Escherichia coli-derived vector DNA into at least one C. jejuni strain. The efficiency of DNA recombination after entry was determined using C. jejuni chromosomal DNA containing disrupted flagellin genes of C. jejuni or suicide vectors containing a portion of these genes. In the latter case, DNA recombination occurred with as little as 200-bp homology present, indicating that only short homologous DNA segments are required.

Colonization of chicks by motility mutants of Campylobacter jejuni demonstrates the importance of flagellin A expression

Campylobacter jejuni strain 81116 contains two flagellin genes, flaA and flaB. Wild-type (WT) bacteria express flaA only, but flaB can be expressed under certain conditions. We have determined the importance of flagella for colonization of the avian caecum, which appears to be the natural environment for these bacteria. Mutants in which flaA or flaB, or both had been inactivated, and motility variants, were investigated. Flagella are not a requisite for colonization, but mutants lacking both flagellin genes colonized less efficiently than WT. Inactivation of the flaB gene, which had no effect on bacterial motility, enhanced chicken caecal colonization 1000-fold compared to WT. A variant (SF-1) with flagella composed of flagellin A, but with poor motility, also colonized better than WT. Conversely, mutants with an inactivated flaA gene colonized 100- to 1000-fold less efficiently than WT, regardless of their motility conferred by truncated or full-length flagellin B flagella. These results suggest that the presence of flagellin A, rather than motility, is essential for optimal bacterial colonization of chicken caeca.

Inactivation of Campylobacter jejuni flagellin genes by homologous recombination demonstrates that flaA but not flaB is required for invasion

The role of the Campylobacter jejuni flagella in adhesion to, and penetration into, eukaryotic cells was investigated. We used homologous recombination to inactivate the two flagellin genes flaA and flaB of C. jejuni, respectively. Mutants in which flaB but not flaA is inactivated remain motile. In contrast a defective flaA gene leads to immotile bacteria. Invasion studies showed that mutants without motile flagella have lost their potential to adhere to, and penetrate into, human intestinal cells in vitro. Invasive properties could be partially restored by centrifugation of the mutants onto the tissue culture cells, indicating that motility is a major, but not the only, factor involved in invasion.

The extended promoter of the gene encoding ribosomal protein S33 in yeast consists of multiple protein binding elements

At least 4 different, protein binding cis-acting elements are present in the upstream region of the S33-gene. The major protein binding site is situated between positions -148 and -163 relative to the ATG start codon. It binds a trans-acting factor designated SUF (S33 Upstream Factor). When yeast cells are growing on glucose, deletion of this site results in a decrease of transcription of 50%. Using ethanol as a carbon-source, deletion of the SUF-responsive site lowers the transcription as much as 80%. A second protein binding site is found between positions -85 and -105. Only extracts from glucose-grown cells contain a factor that is able to bind to this site in vitro. A third protein binding site was found using a protein extract from ethanol-grown cells. This site, which is located quite close to the transcriptional start site, is probably responsible for the 20% residual transcription when the SUF binding site is removed. Finally, a site far upstream was found, which binds a protein from both glucose-grown and ethanol-grown cells. This site may function as an upstream repression site which is only functional when a non-fermentable carbon-source is used. Taking these findings into account, we present a model for the carbon-source dependent transcription activation of the gene encoding S33.