Generation of an inactivated vaccine for avian pathogenic Escherichia coli using microarrays: A more rational approach to inactivated vaccine design.

Background: Escherichia coli remains a major pathogen of poultry. Most vaccines are inactivated and produced empirically. Although inactivated Salmonella vaccines have been produced by culture under conditions of Fe deprivation, no vaccines have been produced which are likely to express all the proteins expressed during infection of antigen-presenting cells. Aim: The aim was to produce a more protective inactivated vaccine by culturing the avian E. coli in a synthetic medium that resembled the environment of the phagolysosome. Methods: Global gene expression in a pathogenic avian O78:K80 strain of E. coli, harvested from infected avian macrophage-like HD11 cells, was compared by microarray with bacteria cultured in a tissue culture medium. A liquid synthetic medium was produced based on the environmental conditions identified to which the bacteria were exposed intracellularly. A bacterin was produced from this strain and its protective ability was assessed in chickens. Results: The changes in E. coli gene expression observed included the use of different electron acceptors and carbon sources such as ethanolamine, ß-glucosides, galactonate, dicarboxylic acids, and amino acids, up-regulation of genes associated with Fe and Mn uptake, and up-regulation of type-1 and curli fimbriae, other adhesion genes and down-regulation of sialic acid synthesis genes. The bacterin produced in the synthetic medium was statistically more protective than a bacterin prepared from bacteria cultured in the nutrient broth when tested in vaccinated chickens challenged with a different virulent E. coli O78:K80 strain. Conclusion: The approach of using gene expression to produce synthetic media for the generation of more effective bacterins could be used for a number of intracellular bacteria pathogens including Enteroinvasive E. coli, Salmonella, and the Pasteurella/Riemerella/Mannheimia group of organisms.

The application of comprehensive two-dimensional gas chromatography to the analysis of wildfire debris for ignitable liquid residue.

Arsonous wildfires are complex investigations due to the high abundance of natural background compounds and subsequent pyrolysis by-products formed during combustion. These interfering compounds can be present in large concentrations and overwhelm the marker compounds used to identify ignitable liquid residue (ILR). Complex matrix effects often interfere with the identification of ILR, providing ambiguous results. The use of comprehensive two-dimensional gas chromatography with time of flight mass spectrometry (GC×GC-TOFMS) separates natural compounds from interfering with ILR compounds of interest. When compared to standard gas chromatography-mass spectrometry (GC-MS) analysis, GC×GC was able to reduce the number of tentative results by 20%. Certain compounds were determined to be unusable for the identification of ILR in wildfire debris samples, in particular the Three Musketeer Group (ethylbenzene, m,p-xylene, and o-xylene), which are ubiquitous in all samples, as well as long chain n-alkylbenzenes, which are formed in the pyrolysis of organic matter. Conversely, the presence of C1- and C2-alkylnaphthalenes were excellent indicators of the presence of gasoline-type ILR. A sizeable number of background samples were collected that helped to provide additional lines of evidence when classifying samples for ILR. Given the complicated matrices encountered in arsonous wildfires, it is evident that GC×GC provides better capabilities at identifying ILR than the standard GC-MS analytical technique.

Galacto-Oligosaccharides Modulate the Juvenile Gut Microbiome and Innate Immunity To Improve Broiler Chicken Performance.

Improvements in growth performance and health are key goals in broiler chicken production. Inclusion of prebiotic galacto-oligosaccharides (GOS) in broiler feed enhanced the growth rate and feed conversion of chickens relative to those obtained with a calorie-matched control diet. Comparison of the cecal microbiota identified key differences in abundances of Lactobacillus spp. Increased levels of Lactobacillus johnsonii in GOS-fed juvenile birds at the expense of Lactobacillus crispatus were linked to improved performance (growth rate and market weight). Investigation of the innate immune responses highlighted increases of ileal and cecal interleukin-17A (IL-17A) gene expression counterposed to a decrease in IL-10. Quantification of the autochthonous Lactobacillus spp. revealed a correlation between bird performance and L. johnsonii abundance. Shifts in the cecal populations of key Lactobacillus spp. of juvenile birds primed intestinal innate immunity without harmful pathogen challenge.IMPORTANCE Improvements in the growth rate of broiler chickens can be achieved through dietary manipulation of the naturally occurring bacterial populations while mitigating the withdrawal of antibiotic growth promoters. Prebiotic galacto-oligosaccharides (GOS) are manufactured as a by-product of dairy cheese production and can be incorporated into the diets of juvenile chickens to improve their health and performance. This study investigated the key mechanisms behind this progression and pinpointed L. johnsonii as a key species that facilitates the enhancements in growth rate and gut health. The study identified the relationships between the GOS diet, L. johnsonii intestinal populations, and cytokine immune effectors to improve growth.

Phage Biocontrol of Campylobacter jejuni in Chickens Does Not Produce Collateral Effects on the Gut Microbiota.

Bacteriophage biocontrol to reduce Campylobacter jejuni levels in chickens can reduce human exposure and disease acquired through the consumption of contaminated poultry products. Investigating changes in the chicken microbiota during phage treatment has not previously been undertaken but is crucial to understanding the system-wide effects of such treatments to establish a sustainable application. A phage cocktail containing two virulent Campylobacter phages was used to treat broiler chickens colonized with C. jejuni HPC5. Campylobacter counts from cecal contents were significantly reduced throughout the experimental period but were most effective 2 days post-treatment showing a reduction of 2.4 log10 CFU g-1 relative to mock-treated Campylobacter colonized controls. The administered phages replicated in vivo to establish stable populations. Bacteriophage predation of C. jejuni was not found to affect the microbiota structure but selectively reduced the relative abundance of C. jejuni without affecting other bacteria.

Polyanionic Ligand Platforms for Methyl- and Dimethylaluminum Arrays.

Trimethylaluminum finds widespread applications in chemical and materials synthesis, most prominently in its partially hydrolyzed form of methylalumoxane (MAO), which is used as a cocatalyst in the polymerization of olefins. This work investigates the sequential reactions of trimethylaluminum with hexaprotic phosphazenes (RNH)6P3N3 (=XH6) equipped with substituents R of varied steric bulk including tert-butyl (1H6), cyclohexyl (2H6), isopropyl (3H6), isobutyl (4H6), ethyl (5H6), propyl (6H6), methyl (7H6), and benzyl (8H6). Similar to MAO, the resulting complexes of polyanionic phosphazenates [XH n] n-6 accommodate multinuclear arrays of [AlMe2]+ and [AlMe]2+. Reactions were monitored by 31P NMR spectroscopy, and structures were determined by single-crystal X-ray diffraction. They included 1H4(AlMe2)2, 1H3(AlMe2)3, 2H3(AlMe2)3, 3(AlMe2)4AlMe, 4H(AlMe2)5, 4(AlMe2)6, {5H(AlMe2)4}2AlMe, 5(AlMe2)6, 6(AlMe2)6, {7(AlMe2)4AlMe}2, and 8(AlMe2)6. The study shows that subtle variations of the steric properties of the R groups influence the reaction pathways, levels of aggregation, and fluxional behavior. While [AlMe2]+ is the primary product of the metalation, [AlMe]2+ is utilized to alleviate overcrowding or to aid aggregation. At the later stages of metalation, [AlMe2]+ groups start to scramble around congested sites. The ligands proved to be very robust and extremely flexible, offering a unique platform to study complex multinuclear metal arrangements.

Prebiotic Driven Increases in IL-17A Do Not Prevent Campylobacter jejuni Colonization of Chickens.

Worldwide Campylobacter jejuni is a leading cause of foodborne disease. Contamination of chicken meat with digesta from C. jejuni-positive birds during slaughter and processing is a key route of transmission to humans through the food chain. Colonization of chickens with C. jejuni elicits host innate immune responses that may be modulated by dietary additives to provide a reduction in the number of campylobacters colonizing the gastrointestinal tract and thereby reduce the likelihood of human exposure to an infectious dose. Here we report the effects of prebiotic galacto-oligosaccharide (GOS) on broiler chickens colonized with C. jejuni when challenged at either an early stage in development at 6 days of age or 20 days old when campylobacters are frequently detected in commercial flocks. GOS-fed birds had increased growth performance, but the levels of C. jejuni colonizing the cecal pouches were unchanged irrespective of the age of challenge. Dietary GOS modulated the immune response to C. jejuni by increasing cytokine IL-17A expression at colonization. Correspondingly, reduced diversity of the cecal microbiota was associated with Campylobacter colonization in GOS-fed birds. In birds challenged at 6 days-old the reduction in microbial diversity was accompanied by an increase in the relative abundance of Escherichia spp. Whilst immuno-modulation of the Th17 pro-inflammatory response did not prevent C. jejuni colonization of the intestinal tract of broiler chickens, the study highlights the potential for combinations of prebiotics, and specific competitors (synbiotics) to engage with the host innate immunity to reduce pathogen burdens.

The effect of the timing of exposure to Campylobacter jejuni on the gut microbiome and inflammatory responses of broiler chickens.

BACKGROUND: Campylobacters are an unwelcome member of the poultry gut microbiota in terms of food safety. The objective of this study was to compare the microbiota, inflammatory responses, and zootechnical parameters of broiler chickens not exposed to Campylobacter jejuni with those exposed either early at 6 days old or at the age commercial broiler chicken flocks are frequently observed to become colonized at 20 days old. RESULTS: Birds infected with Campylobacter at 20 days became cecal colonized within 2 days of exposure, whereas birds infected at 6 days of age did not show complete colonization of the sample cohort until 9 days post-infection. All birds sampled thereafter were colonized until the end of the study at 35 days (mean 6.1 log10 CFU per g of cecal contents). The cecal microbiota of birds infected with Campylobacter were significantly different to age-matched non-infected controls at 2 days post-infection, but generally, the composition of the cecal microbiota were more affected by bird age as the time post infection increased. The effects of Campylobacter colonization on the cecal microbiota were associated with reductions in the relative abundance of OTUs within the taxonomic family Lactobacillaceae and the Clostridium cluster XIVa. Specific members of the Lachnospiraceae and Ruminococcaceae families exhibit transient shifts in microbial community populations dependent upon the age at which the birds become colonized by C. jejuni. Analysis of ileal and cecal chemokine/cytokine gene expression revealed increases in IL-6, IL-17A, and Il-17F consistent with a Th17 response, but the persistence of the response was dependent on the stage/time of C. jejuni colonization that coincide with significant reductions in the abundance of Clostridium cluster XIVa. CONCLUSIONS: This study combines microbiome data, cytokine/chemokine gene expression with intestinal villus, and crypt measurements to compare chickens colonized early or late in the rearing cycle to provide insights into the process and outcomes of Campylobacter colonization. Early colonization results in a transient growth rate reduction and pro-inflammatory response but persistent modification of the cecal microbiota. Late colonization produces pro-inflammatory responses with changes in the cecal microbiota that will endure in market-ready chickens.

Forensic source attribution for toluene in environmental samples.

The formation of toluene by microbiological processes can confound environmental investigations relating to petroleum releases. This is because toluene is a constituent of petroleum and can move readily within wetland environments, and analysis for toluene in relation to a petroleum release can lead to incorrect assignment of detected biogenic toluene as related to the release. No legally defensible method of distinguishing biogenic and petrogenic origins of detectible concentrations of toluene have been demonstrated to date. Using example petrogenic samples and samples of peat from 2 wetland environments, a poor bog and a poor fen, the present study demonstrates the use of an established ASTM International analytical methodology that was originally designed for arson analysis for the determination of the origin of toluene. Environmental forensic data-interpretation methods such as chromatogram inspection and diagnostic ratios are shown to be capable of readily distinguishing biogenic and petrogenic origins of toluene. Environ Toxicol Chem 2018;37:729-737. © 2017 SETAC.

Dental Hygiene Students' Perceptions of Importance and Confidence in Applying Motivational Interviewing During Patient Care.

Purpose: Motivational Interviewing (MI) is an evidence-based, patient-centered counseling approach for eliciting behavior change. In 2012, the University of Michigan (U-M) Dental Hygiene Program significantly enhanced their behavior change curriculum by reinforcing and building upon the Motivational Interviewing segment. The purpose of this study was to examine students' perceptions of the importance of MI and their confidence in applying it during patient care.Methods: A convenience sample of 22 U-M Class of 2015 dental hygiene students who had received an enhanced curriculum participated in this study, utilizing a retrospective, pre-test/post-test design.Results: A Wilcoxon signed rank test was used to compare the differences in average ranks between T1 (Retrospective Pre-Test) and T4 (Post-Test 3) for the importance and confidence questions at each time point for the Class of 2015. Students' perceptions of importance increased with statistical significance in five out of eight MI strategies. Perceptions in confidence increased in seven out of eight strategies. Effect size ranged from .00 to .55. Assessment of qualitative data provided additional insight on student experiences.Conclusion: Student perceptions of importance of using MI and their confidence in applying MI increased in a majority of the strategy categories. Successes with patient health behavior change and challenges with time to integrate this in practice were noted. Research on the longitudinal impact and faculty feedback calibration is recommended.

Effect of Faculty Development Activities on Dental Hygiene Faculty Perceptions of and Teaching About Motivational Interviewing: A Pilot Study.

The aims of this pilot study were to assess dental hygiene faculty members' perceptions of the importance of motivational interviewing (MI) and their confidence in teaching students about MI and to determine the effect of MI training sessions on those perceptions. Participants were a convenience sample of all 16 dental hygiene faculty members who teach in the clinic at the University of Michigan School of Dentistry. Participants' perceptions were assessed prior to a workshop in MI (pretest), immediately after the workshop (posttest 1), and eight months after the workshop, at the end of the academic year (posttest 2). During the same period, some of the workshop participants took part in team grading sessions of audio recordings of student-patient MI interactions. The results showed that the majority of the faculty members perceived it was important to personally embrace the overall spirit of MI during patient care, and they were confident supporting students as well. Their ratings for embracing the spirit of MI increased from pretest to posttest 1, but slightly decreased at posttest 2. This trend was also seen in their assessment of the importance of and their confidence in teaching the eight MI strategies over time. Among the workshop participants, 56% were part of team grading; they reported the most helpful professional development activities overall were team grading (58%) and the workshop (25%). These results suggest the importance of making use of a variety of faculty development activities and of introducing appropriate follow-up to training sessions over time to ensure long-lasting effects. Future research using carefully designed, multi-institution, longitudinal studies is needed to determine the most effective ways to prepare dental hygiene faculty members to educate their students about MI.

Reduction in self-monitoring of blood glucose in type 2 diabetes: an observational controlled study in east London.

BACKGROUND: Self-monitoring of blood glucose (SMBG) confers no benefit for many people with type 2 diabetes not being treated with insulin. It accounts for 21% of diabetes prescribing costs. AIM: To improve care quality at reduced cost for type 2 diabetes by reducing unnecessary SMBG. DESIGN AND SETTING: Non-randomised, observational controlled study in two intervention clinical commissioning groups (CCGs) and one control CCG in east London. METHOD: In total, 19,602 people with type 2 diabetes not being treated with insulin were recruited from two intervention CCGs; 16,033 were recruited from a control CCG. The intervention (from 2010 to 2013) comprised implementation of a locally developed guideline, including IT support and peer feedback of performance. Data on practice prescribing SMBG testing strips were gathered using GP electronic health records. Information on costs were obtained via the ePACT electronic database. RESULTS: Over 4 years, in all non-insulin type 2 diabetes treatment groups, use of SMBG was reduced in the two intervention CCGs from 42.8% to 16.5%, and in the control CCG from 56.4% to 47.2%. In people on metformin alone or no treatment, intervention CCGs reduced SMBG use from 29.6% to 6.0%, and in the control CCG use dropped from 47.1% to 38.7% (P<0.001). From 2009 to 2012 the total cost of all SMBG prescribing (type 1 and type 2 diabetes, including users of insulin) was reduced by 4.9% (£62,476) in the two intervention CCGs and increased in the control CCG by 5.0% (£42,607); in England, the total cost increased by 13.5% (£19.4 million). In total, 20% (3865 of 19 602) fewer patients used SMBG in the intervention CCGs. CONCLUSION: This low-cost programme demonstrated a major reduction in unnecessary prescribing of SMBG, along with cost savings. If replicated nationally, this would avoid unnecessary testing in 340 000 people and prescribing costs that total £21.8 million.

Structure-activity studies on the anti-proliferation activity of ajoene analogues in WHCO1 oesophageal cancer cells.

The organosulfur compound ajoene derived from the rearrangement of allicin found in crushed garlic can inhibit the proliferation of tumour cells by inducing G(2)/M cell cycle arrest and apoptosis. We report on the application of a concise four-step synthesis (Hunter et al., 2008 [1]) that allows access to ajoene analogues with the end allyl groups substituted. A library of twelve such derivatives tested for their anti-proliferation activity against WHCO1 oesophageal cancer cells has identified a derivative containing p-methoxybenzyl (PMB)-substituted end groups that is twelve times more active than Z-ajoene, with an IC(50) of 2.1µM (Kaschula et al., 2011 [2]). Structure-activity studies involving modification of the sulfoxide and vinyl disulfide groups of this lead have revealed that the disulfide is the ajoene pharmacophore responsible for inhibiting WHCO1 cell growth, inducing G(2)/M cell cycle arrest and apoptosis by caspase-3 activation, and that the vinyl group serves to enhance the anti-proliferation activity a further eightfold. Reaction of the lead with cysteine in refluxing THF as a model reaction for ajoene's mechanism of action based on a thiol/disulfide exchange reveals that the allylic sulfur of the vinyl disulfide is the site of thiol attack in the exchange.

General dentists and periodontal referrals.

Questionnaire data were collected from 160 MDA members. The data showed that 16 percent of the respondents had not made a periodontal referral during the last month, 67 percent had made one to five referrals, 7 percent between six and 10 referrals, and 10 percent referred more than 10 patients. The number of referrals did not differ as a function of patients' disease characteristics or dentists' periodontal treatment patterns. They were affected by considerations of practice characteristics and patient's oral hygiene efforts. In conclusion, general dentists differ greatly in the number of periodontal referrals they make. Referral frequencies were not affected by diagnostic considerations or treatment patterns.

Providing care for underserved patients: periodontists' and periodontal residents' educational experiences, attitudes, and behaviors.

BACKGROUND: Patients with special health care needs (SHCNs) and patients from underrepresented minority and/or low socioeconomic backgrounds are more likely to have problems accessing oral health care services. The objectives of this study are: 1) to explore how well the dental education of periodontists prepared them to treat these underserved patients, 2) to assess related professional attitudes and confidence when treating these patients as well as professional behaviors, and 3) whether educational experiences are related with attitudes, confidence, and behaviors in this context. METHODS: Survey data were collected from a randomly selected sample of 291 members of the American Academy of Periodontology (AAP) and 64 periodontal residents. RESULTS: Overall, large percentages of residents agreed that their predoctoral and graduate dental educations had prepared them well to treat patients with special needs (predoctoral education: 58%; clinical graduate education: 45%; and classroom-based graduate education: 37%), from different ethnic/racial backgrounds (predoctoral education: 74%; clinical graduate education: 74%; and classroom-based graduate education: 60%), and on Medicaid (predoctoral education: 60%; clinical graduate education: 61%; and classroom-based graduate education: 42%). Practicing clinicians were least positive about their educations. Students were more positive about treating patients on Medicaid and pro bono cases than practicing clinicians. However, the two groups did not differ in their confidence when treating underserved patients. The quality of predoctoral and graduate educations regarding underserved patients correlates with the attitudes, confidence, and behaviors of providers concerning providing care for these patients. CONCLUSIONS: The findings of this study stress the importance of preparing future periodontists in their predoctoral and graduate programs for providing care for underserved patients such as patients with SHCNs. The better that dental education prepares future periodontists to provide care for underserved patients, the more confident periodontists will be when encountering these patients in their own practices and the more likely they will be to contribute to reducing disparities in oral health care access in the United States by treating these patients.

Periodontal referral patterns of general dentists: lessons for dental education.

The objectives of this study were to investigate periodontal treatment and referral patterns and the considerations used in the process of dentists who make no periodontal referrals, relatively few referrals, or more referrals. Specifically, the role of disease characteristics, patient- and provider-related factors, attitudes towards periodontal referrals, and perceptions of dental education were explored. The relationships between the perceived quality of dental education concerning periodontal diagnosis and treatment and the considerations used in this process were evaluated as well. Data were collected from 160 members of the Michigan Dental Association using a mailed questionnaire. The respondents were predominantly male (77 percent) and white (96 percent) and had practiced for an average of twenty-three years (SD=10.7). While 13 percent of the respondents had not made any periodontal referrals during the past month, 69 percent had referred between one and five patients, and 18 percent more than five patients. Dentists who referred more than three patients per month considered the patients' oral hygiene as more important, had fewer patients from lower socioeconomic backgrounds and more patients with private insurance, and felt less well prepared by their dental education compared to general dentists who referred fewer than three patients per month to a periodontist. The more positively dentists evaluated their dental education in periodontics, the more conservative they were when considering percentage of bone loss as a basis for referral (r=.228; p=.014), the more frequently they used systemic antibiotics in their treatment of periodontal disease (r=.180; p=.036), and the more they considered whether their patients would return after the periodontal treatment (r=.185; p=.028) as a factor in their referral decisions. General dentists' perceptions of the quality of their dental school education in periodontics decreased their willingness to refer patients and increased their desire to treat these patients in their own practices. Future research should analyze the ways in which dental school curricula could prepare students to make timely and necessary periodontal referrals.

Substituted ajoenes as novel anti-cancer agents.

A new synthesis of the ajoene pharmacophore core is presented involving the regioselective radical addition of a thiyl radical to a terminal alkyne as the key step. The synthesis allows structural variation of the two end groups on sulfur, and a range of novel derivatives varying the R(1) group (sulfoxide end) has been prepared and tested against CT-1 transformed fibroblast cells for anti-cancer activity. The results indicate comparable or even improved activity compared to the parent natural product ajoene isomers. This opens up the way to systematically studying the biology of the ajoene core.

In situ recrystallisation of a coordination polymer with hemilabile linkers.

The variable coordination pattern of a hemilabile phosphazene ligand equipped with six pendent olefin groups facilitates the in situ recrystallisation of a silver(I) complex from an amorphous precipitate into a 1D coordination polymer and its subsequent isomerisation to a 3D coordination network.

Periodontal health, quality of life, and smiling patterns--an exploration.

BACKGROUND: This study explored whether periodontal health/disease affects psychosocial outcomes in smiling patterns of particular subjects and their smile-related quality of life. METHODS: We collected data from 21 regularly scheduled patients in a periodontal graduate student clinic (four males and 17 females; average age: 50.38 years; age range: 24 to 82 years). The subjects were videotaped while watching a funny television (TV) program. Two independent raters rated each videotape at 31 predetermined time points to assess four aspects of the objective smiling patterns of the subjects. In addition, the subjects responded to a questionnaire to assess their smile-related quality of life. Provider ratings and chart review data were used to assess the clinically assessed oral health status of the subjects. RESULTS: The smile-related quality of life of the subjects correlated significantly with indicators of the periodontal health of the subjects, such as the number of mobile teeth (r = 0.681; P =0.000), missing teeth (r = 0.784; P = 0.001), and gingival recession in the esthetic zone (r = 0.718; P = 0.001). Periodontal health and smiling patterns also were correlated. The more teeth with probing depths between 4 and 6 mm the subjects had, the less widely they opened their mouths when they smiled (r = -0.468; P = 0.032); the more hypermobile teeth the subjects had, the less open their smiles were (r = -0.442; P = 0.045) and the more likely they were to cover their mouths when they smiled (r = 0.517; P = 0.017); and the more sites of gingival recession in the esthetic zone the subjects had, the fewer teeth they showed when they smiled (r = -0.491; P = 0.028). CONCLUSIONS: The periodontal health of the subjects affects their smiling patterns and their smile-related quality of life. Poor periodontal health may prevent adults from expressing positive emotions which, in turn, can impact their self-concept as well as their social interactions.

Suicide through stress: a bacterial response to sub-lethal injury in the food environment.

The response of bacteria to sub-lethal injury is an important aspect of food microbiology as many inimical processes to which bacteria are subjected during processing are non-lethal. For pathogens like Salmonella and Escherichia coli, the difference in injury levels of exponential phase cells compared to their stationary phase counterparts in this regard is well recognised and evident for a variety of inimical processes. The expression of a range of stress resistance genes under the control of the sigma factor RpoS provides some explanation for the greater resistance of stationary phase cells. However in 1997 the suicide response hypothesis was put forward as an explanation for the observed response of Salmonella and E. coli to sub-lethal stresses. This hypothesis arose as an explanation for the observed protection of Salmonella and E. coli strains to heat and freeze-thaw injury by the presence of a high level of competitor organisms, a protection that had been shown to be RpoS independent. The central tenet of this theory was that under sub-lethal stress bacteria produce a burst of intracellular free radicals and it is these that lead to sub-lethal injury and/or death. Exponential phase cells because of their more active metabolism are more susceptible to this effect and suffer greater damage. This paper reviews the origins of this theory, the evidence for a free radical response and explores the potential mechanisms by which competitor cells produce a protective effect.