Cancer blues? A promising judgment bias task indicates pessimism in nude mice with tumors.

In humans, affective states can bias responses to ambiguous information: a phenomenon termed judgment bias (JB). Judgment biases have great potential for assessing affective states in animals, in both animal welfare and biomedical research. New animal JB tasks require construct validation, but for laboratory mice (Mus musculus), the most common research vertebrate, a valid JB task has proved elusive. Here (Experiment 1), we demonstrate construct validity for a novel mouse JB test: an olfactory Go/Go task in which subjects dig for high- or low-value food rewards. In C57BL/6 and Balb/c mice faced with ambiguous cues, latencies to dig were sensitive to high/low welfare housing: environmentally-enriched animals responded with relative 'optimism' through shorter latencies. Illustrating the versatility of this validated JB task across different fields of research, it further allowed us to test hypotheses about the mood-altering effects of cancer in male and female nude mice (Experiment 2). Males, although not females, treated ambiguous cues as intermediate; and males bearing subcutaneous lung adenocarcinomas also responded more pessimistically to these than did healthy controls. To our knowledge, this is the first evidence of a valid mouse JB task, and the first demonstration of pessimism in tumor-bearing animals. This task still needs to be refined to improve its sensitivity. However, it has great potential for investigating mouse welfare, the links between affective state and disease, depression-like states in animals, and hypotheses regarding the neurobiological mechanisms that underlie affect-mediated biases in judgment.

Maternal effects obscure condition-dependent sex allocation in changing environments.

Climate change increases environmental fluctuations which thereby impact population demography. Species with temperature-dependent sex determination may experience more extreme sex ratio skews, but this has not been considered in species with chromosomally determined sex. However, anticipatory maternal effects cause lifelong physiological changes impacting sex ratios. Here we show, in mice, that more sons were born to mothers in good condition when their breeding environment matched their gestational environment, consistent with theoretical predictions, but mothers in mismatched environments have no condition-sex ratio relationship. Thus, the predicted effect of condition on sex ratio was obscured by maternal effects when the environment changed. This may explain extreme sex ratio skews in reintroduced or translocated populations, and sex ratio skews may become more common and less predictable with accelerating environmental change.

Density-Driven Flows in Evaporating Binary Liquid Droplets.

In the evaporation of microlitre liquid droplets, the accepted view is that surface tension dominates and the effect of gravity is negligible. We report, through the first use of rotating optical coherence tomography, that a change in the flow pattern and speed occurs when evaporating binary liquid droplets are tilted, conclusively showing that gravitational effects dominate the flow. We use gas chromatography to show that these flows are solutal in nature, and we establish a flow phase diagram demonstrating the conditions under which different flow mechanisms occur.

An acoustic on-chip goniometer for room temperature macromolecular crystallography.

This paper describes the design, development and successful use of an on-chip goniometer for room-temperature macromolecular crystallography via acoustically induced rotations. We present for the first time a low cost, rate-tunable, acoustic actuator for gradual in-fluid sample reorientation about varying axes and its utilisation for protein structure determination on a synchrotron beamline. The device enables the efficient collection of diffraction data via a rotation method from a sample within a surface confined droplet. This method facilitates efficient macromolecular structural data acquisition in fluid environments for dynamical studies.

Time perception, pacing and exercise intensity: maximal exercise distorts the perception of time.

INTRODUCTION: Currently there are no data examining the impact of exercise on the perception of time, which is surprising as optimal competitive performance is dependent on accurate pacing using knowledge of time elapsed. METHODS: With institutional ethics approval, 12 recreationally active adult participants (f=7, m=5) undertook both 30s Wingate cycles and 20min (1200s) rowing ergometer bouts as short and long duration self-paced exercise trials, in each of three conditions on separate occasions: 1) light exertion: RPE 11, 2) heavy exertion: RPE 15, 3) maximal exertion: RPE 20. Participants were unaware of exercise duration and were required to verbally indicate when they perceived (subjective time) 1) 25%, 2) 50%, 3) 75% and 4) 100% of each bout's measured (chronological) time had elapsed. RESULTS: In response to the Wingate task, there was no difference between durations of subjective time at the 25%, nor at the 50% interval. However, at the 75% and 100% intervals, the estimate for the RPE 20 condition was shortest (P<0.01). In response to rowing, there were no differences at the 25% interval, but there was some evidence that the RPE 20 condition was perceived shorter at 50%. At 75% and 100%, the RPE 20 condition was perceived to be shorter than both RPE 15 (P=0.04) and RPE 11 (P=0.008) conditions. CONCLUSION: This study is the first to empirically demonstrate that exercise intensity distorts time perception, particularly during maximal exercise. Consequently external feedback of chronological time may be an important factor for athletes undertaking maximal effort tasks or competitions.

Cryptic male choice: experimental evidence of sperm sex ratio and seminal fluid adjustment in relation to coital rate.

The differential allocation hypothesis suggests that a mother should adjust the sex of offspring in relation to her mate's attractiveness, thereby increasing future reproductive fitness when her sons inherit the attractive traits. More attractive males have been shown to sire more sons, but it is possible that the sex ratio skew could be a result of paternal rather than maternal manipulation, which would be a more parsimonious explanation. We manipulated coital rate (an indicator of attractiveness) in laboratory mice and showed that males that mate more often have higher levels of glucose in their semen despite lower blood glucose levels. Since peri-conceptual glucose levels in utero increase male conceptus survival, this could result in male-biased sex ratios. The males that mated most also had more remaining X-chromosome-bearing-spermatozoa, suggesting depletion of Y-chromosome-bearing-spermatozoa during mating. We hypothesise that males may alter both seminal fluids and X:Y ratios in an ejaculate to influence subsequent sex ratios. Our results further support a paternal role in sex allocation.

Efficacy of inspiratory muscle training as a practical and minimally intrusive technique to aid functional fitness among adults with obesity.

OBJECTIVE: To examine the efficacy of inspiratory muscle training (IMT) as a non-intrusive and practical intervention to stimulate improved functional fitness in adults with obesity. As excess adiposity of the chest impedes the mechanics of breathing, targeted re-training of the inspiratory muscles may ameliorate sensations of breathlessness, improve physical performance and lead to greater engagement in physical activity. METHODS: Sixty seven adults (BMI=36±6.5) were randomized into either an experimental (EXP: n=35) or placebo (PLA: n=32) group with both groups undertaking a 4-week IMT intervention, comprising daily use of a inspiratory resistance device set to 55% (EXP), or 10% (PLA) of maximum inspiratory effort. RESULTS: Inspiratory muscle strength was significantly improved in EXP (19.1 cmH20 gain; P<0.01) but did not change in PLA. Additionally, the post training walking distance covered was significantly extended for EXP (P<0.01), but not for PLA. Bivariate analysis demonstrated a positive association between the change (%) of performance in the walking test and BMI (r=0.78; P<0.01) for EXP. CONCLUSION: The findings from this study suggest IMT provides a practical, self-administered intervention for use in a home setting. This could be a useful strategy to improve the functional fitness of obese adults and perhaps lead to better preparedness for engagement in physical activity initiatives.

Gestational experience alters sex allocation in the subsequent generation.

Empirical tests of adaptive maternal sex allocation hypotheses have presented inconsistent results in mammals. The possibility that mothers are constrained in their ability to adjust sex ratios could explain some of the remaining variation. Maternal effects, the influence of the maternal phenotype or genotype on her developing offspring, may constrain sex allocation through physiological changes in response to the gestational environment. We tested if maternal effects constrain future parental sex allocation through a lowered gestational stress environment in laboratory mice. Females that experienced lowered stress as embryos in utero gave birth to female-biased litters as adults, with no change to litter size. Changes in offspring sex ratio was linked to peri-conceptual glucose, as those females that had increasing blood glucose peri-conceptionally gave birth to litters with a higher male to female sex ratio. There was, however, no effect of the lowered prenatal stress for developing male embryos and their sperm sex ratio when adult. We discuss the implications of maternal effects and maternal stress environment on the lifelong physiology of the offspring, particularly as a constraint on later maternal sex allocation.

Brain and Cardiorespiratory Responses to Exercise in Hot and Thermoneutral Conditions.

The aim of this study was to test whether or not concurrent evaluations of brain (electroencephalography [EEG]) and cardiorespiratory responses to exercise are influenced by environmental conditions. 10 adult male participants performed a standardized incremental exercise test to exhaustion on a cycle ergometer in an environment controlled laboratory on 2 separate occasions, in a randomized order; one in a hot condition (34.5°C) and one in a thermoneutral condition (20°C). EEG, heart rate and expired air were collected throughout. EEG data were decontaminated for artefacts, log-transformed and expressed as aggregated alpha and beta power responses across electrodes reflecting the frontal cortex of the brain. Performance outcomes showed there was no difference in V˙O2 peak across hot (42.5 ml/kg/min) and neutral (42.8 ml/kg/min) conditions, although ventilatory threshold (VT) occurred at a lower threshold (68%) in hot compared to neutral condition (74%) (p<0.05). EEG alpha and beta wave responses both demonstrated significant increases from baseline to VT (p<0.01). EEG beta-band activity was significantly elevated in the heat compared to the neutral condition. In conclusion, elevated EEG beta-band activity in response to incremental exercise in the heat suggests that beta-band activation and cortical awareness increases as exercise becomes increasingly intense.

Utility of field-based techniques to assess Indigenous Australians' functional fitness and sedentary time.

OBJECTIVE: To examine the utility of field-based techniques to assess functional exercise capacity and sedentary time in Indigenous and non-Indigenous regional Australian adults. STUDY DESIGN: Observational, analytic cohort study. METHODS: Ninety six adults residing in regional and remote Australian communities participated in this study (Indigenous n = 61 and non-Indigenous Australians n = 35). Participants undertook a field-based test of functional exercise capacity (6 min walk test; 6 MWT) and wore an accelerometer during waking hours for seven days, provided self-report data on physical activity and sedentary time and rated experiences in regard to the ease of complying with study protocols. RESULTS: There were high levels of compliance in this study (Indigenous: 91% and non-Indigenous: 97%). Functional exercise capacity was lower in Indigenous Australians (P < 0.001), and independently associated with advancing age, higher BMI, and indigeneity, with 45% of variability in the 6 MWT distance explained by these factors. The relationship between accelerometer and self-report measures of sedentary behaviour was significant (P < 0.001) but only explained 17% of the total variation. CONCLUSIONS: This study demonstrated very good compliance for the methods utilised and is the first to report reduced functional exercise capacity in Indigenous people. IMPLICATIONS: The field-based techniques from this study demonstrate good utility for larger scale implementation in regional Indigenous populations.

Utilization of a high-throughput shoot imaging system to examine the dynamic phenotypic responses of a C4 cereal crop plant to nitrogen and water deficiency over time.

The use of high-throughput phenotyping systems and non-destructive imaging is widely regarded as a key technology allowing scientists and breeders to develop crops with the ability to perform well under diverse environmental conditions. However, many of these phenotyping studies have been optimized using the model plant Arabidopsis thaliana. In this study, The Plant Accelerator(®) at The University of Adelaide, Australia, was used to investigate the growth and phenotypic response of the important cereal crop, Sorghum bicolor L. Moench and related hybrids to water-limited conditions and different levels of fertilizer. Imaging in different spectral ranges was used to monitor plant composition, chlorophyll, and moisture content. Phenotypic image analysis accurately measured plant biomass. The data set obtained enabled the responses of the different sorghum varieties to the experimental treatments to be differentiated and modelled. Plant architectural instead of architecture elements were determined using imaging and found to correlate with an improved tolerance to stress, for example diurnal leaf curling and leaf area index. Analysis of colour images revealed that leaf 'greenness' correlated with foliar nitrogen and chlorophyll, while near infrared reflectance (NIR) analysis was a good predictor of water content and leaf thickness, and correlated with plant moisture content. It is shown that imaging sorghum using a high-throughput system can accurately identify and differentiate between growth and specific phenotypic traits. R scripts for robust, parsimonious models are provided to allow other users of phenomic imaging systems to extract useful data readily, and thus relieve a bottleneck in phenotypic screening of multiple genotypes of key crop plants.

Effect of enhanced whole-milk feeding in calves on subsequent first-lactation performance.

The objective of this study was to determine the effect of enhanced whole-milk (WM) feeding systems in calves from birth to 8wk of age on subsequent first-lactation performance. The experiment was conducted as a completely randomized design consisting of 2 treatment groups. At birth, 152 Holstein heifer calves were randomly assigned to 1 of 2 treatments: (i) 4L of WM/d or (ii) 8L of WM/d. The calves were bucket fed 2 or 4L of WM twice daily at 0700 and 1600h. Each calf was housed individually in temperature-controlled nurseries and had ad libitum access to water and textured calf starter daily. Calves consumed greater volumes of textured calf starter when fed 4 versus 8L of WM/d. Water intakes mirrored starter intakes, leading to greater water consumption at weaning. Calves reared on 8L of WM/d were heavier at d 56 than calves reared on 4L of WM/d. The average daily gain of the calves offered 8L of WM/d from d 0 to 56 was greater than that of calves offered 4L of WM/d. Structural measurements were significantly greater for calves that consumed 8L of WM/d. The differences observed in withers height and live BW due to WM feeding level were not apparent by 3 and 12mo of age, respectively. Rumen pH was higher in calves that consumed 8L of WM/d than in calves that consumed 4L of WM/d. Whole-milk feeding level did not affect age at first calving or milk-production parameters. These results suggest that enhanced WM feeding improved growth performance until 3mo of age. However, first-lactation results indicated no lactation-performance benefits of increased nutrition and growth performance during the milk-fed period in dairy calves.

Self-reported health behaviour change in adults: analysis of the Canadian Community Health Survey 4.1.

INTRODUCTION: Knowledge of Canadians' experiences in making health behaviour changes (HBCs) in general, and among those at risk due to body mass index (BMI), would help inform health promotion / disease prevention programs. Selected self reported HBCs in the past 12 months by BMI category were examined in this secondary analysis of the Canadian Community Health Survey 4.1. These HBCs included increased sports/exercise, weight loss and improved eating habits. Barriers to HBC were also examined. METHODS: Descriptive analyses and forward stepwise logistic regression were completed on data from respondents 18 years and older. Self-reported BMI was corrected by the method of Connor Gorber et al. (2008). RESULTS: Our final sample was n = 111 449. Overall, 58% of respondents had made an HBC, with increased sports/exercise as the most important HBC in 29% of the sample, followed by improved eating habits (10%) and weight loss (7%). Half (51%) experienced barriers to HBC; lack of will power was most commonly cited, followed by work and family responsibilities. Obese respondents reported HBC more frequently than normal-weight respondents (60% vs. 55%), but the prevalence of increased sports/ exercise and improved eating habits was similar across BMI categories. Regression models accounted for only 6%-10% of the total variance. CONCLUSION: That a majority of respondents had made at least one HBC bodes well for positively shifting population health. Additional work to further characterize the population, and to improve on population indicators, is needed to assess the impact of health promotion/disease prevention efforts. These findings provide important first population benchmarks for future work.

TITRE: Changements de comportement en matière de santé autodéclarés chez les adultes : une analyse de l'Enquête sur la santé dans les collectivités canadiennes, cycle 4.1. INTRODUCTION: Connaître l'expérience des Canadiens ayant trait aux changements de comportement en matière de santé (CCS), que ce soit en général ou celle des personnes à risque en raison de leur indice de masse corporelle (IMC), serait utile à l'élaboration de programmes de promotion de la santé et de prévention des maladies. Nous avons ainsi examiné, dans le cadre d'une analyse secondaire du cycle 4.1 de l'Enquête sur la santé dans les collectivités canadiennes, une sélection de CCS autodéclarés au cours des douze derniers mois, par catégorie d'IMC : faire plus d'exercice ou de sport, perdre du poids et améliorer ses habitudes alimentaires. Nous nous sommes aussi penchés sur les obstacles aux CCS. MÉTHODOLOGIE: Nous avons analysé les données provenant des répondants de 18 ans et plus à l'aide d'une méthode de régression logistique progressive ascendante. Les IMC autodéclarés ont été corrigés à l'aide de la méthode de Connor Gorber et ses collaborateurs (2008). RÉSULTATS: Notre échantillon final était de 111 449 répondants. Sur l'ensemble des répondants, 58 % avait fait un CCS, l'augmentation de la pratique sportive ou d'exercice étant le plus important (29 % des répondants), suivi par l'amélioration des habitudes alimentaires (10 %) et la perte de poids (7 %). La moitié (51 %) des répondants avaient rencontré des obstacles, le manque de volonté étant l'obstacle le plus souvent mentionné, suivi par l'emploi du temps professionnel et les responsabilités familiales. Les répondants obèses ont fait état de CCS plus souvent que les répondants dont le poids était normal (60 % contre 55 %), mais la fréquence de l'augmentation de la pratique sportive ou d'exercice et de l'amélioration des habitudes alimentaires était similaire selon toutes les catégories d'IMC. Les modèles de régression ne représentaient que de 6 % à 10 % de la variance totale. CONCLUSION: Le fait que la majorité des répondants ait tenté d'apporter au moins un CCS est de bon augure pour une évolution positive de la santé de la population. D'autres travaux sont nécessaires pour mieux caractériser la population et pour améliorer les indicateurs qui lui sont associés, et ainsi évaluer l'incidence des efforts de promotion de la santé et de prévention des maladies. Nos résultats fournissent des données de référence pouvant servir de base à ces travaux.

Pacing and awareness: brain regulation of physical activity.

The aim of this current opinion article is to provide a contemporary perspective on the role of brain regulatory control of paced performances in response to exercise challenges. There has been considerable recent conjecture as to the role of the brain during exercise, and it is now broadly accepted that fatigue does not occur without brain involvement and that all voluntary activity is likely to be paced at some level by the brain according to individualised priorities and knowledge of personal capabilities. This article examines the role of pacing in managing and distributing effort to successfully accomplish physical tasks, while extending existing theories on the role of the brain as a central controller of performance. The opinion proposed in this article is that a central regulator operates to control exercise performance but achieves this without the requirement of an intelligent central governor located in the subconscious brain. It seems likely that brain regulation operates at different levels of awareness, such that minor homeostatic challenges are addressed automatically without conscious awareness, while larger metabolic disturbances attract conscious awareness and evoke a behavioural response. This supports the view that the brain regulates exercise performance but that the interpretation of the mechanisms underlying this effect have not yet been fully elucidated.

Respiratory muscle training extends exercise tolerance without concomitant change to peak oxygen uptake: physiological, performance and perceptual responses derived from the same incremental exercise test.

BACKGROUND AND OBJECTIVE: There is conjecture over the efficacy of respiratory muscle training (RMT). The aim of this study was to establish whether or not exercise tolerance, physical performance and effort perceptions are influenced by RMT. METHODS: Thirty-six healthy males (age 24 ± 4) agreed to participate (experimental group (EXP) n = 18, control (CON) n = 18). RMT was performed using an inspiratory pressure-threshold training device at either 55% (EXP) or 10% (CON) of maximal inspiratory effort. Measurements of spirometry and maximal static inspiratory mouth pressure were taken before and after 4 weeks of RMT in addition to an incremental test to volitional exhaustion for the determination of: (i) V˙O(2) peak; (ii) maximal velocity at volitional exhaustion (vV˙O(2) peak)); (iii) time to volitional exhaustion; and (iv) effort perceptions. RESULTS: There were no differences in spirometry, but mean maximal static inspiratory mouth pressure increased significantly in EXP (P < 0.01). V˙O(2) peak was unchanged following the 4-week intervention for both EXP and CON, although the proportion of EXP attaining the criteria for a V˙O(2) plateau significantly increased (P < 0.05). Both time to volitional exhaustion (P < 0.05) and vV˙O(2) peak were significantly improved for EXP (P < 0.05), while effort perceptions were reduced (P < 0.05). CONCLUSIONS: EXP tolerated higher running velocities during incremental exercise and demonstrated a significant flattening (plateau) of V˙O(2) after training. This suggests that RMT may promote an improved performance outcome vV˙O(2) peak probably as a result of blunted afferent sensations reducing the perceived discomfort of exercise at high ventilatory loads.

Physiological responses to self-paced exercise: effort-matched comparisons across running and rowing modalities.

AIM: The purpose of this study was to examine whether or not physiological responses to self-pacing are similar across different exercise modalities where the rating of perceived exertion (RPE) is matched. METHODS: Ten recreationally active adult male subjects completed baseline tests of peak oxygen uptake (.VO2) and subsequently on two separate occasions performed 20-min exercise bouts at RPE 15 (Hard) on both a motorized treadmill and a rowing ergometer. RESULTS: Mean relative work intensity (% of baseline peak (.VO2) for treadmill running was significantly higher than for rowing (86.1% vs. 83.7%) (P<0.05). Mean heart rates (174.7±5.9 vs. 165.5±6.6 b∙min-1) and pre- to post-bout changes in blood lactate concentration (4.0±0.8 vs. 3.3±1.2 mmol/L) were also greater in the running trial than rowing (P<0.05). Baseline peak (.VO2 was positively correlated between modalities (r=0.63; P<0.05) as were the main trial mean (.VO2 (r=0.73; P<0.05) and heart rate (r=0.67; P<0.05) from the 20-min bouts. CONCLUSION: The elevated relative exercise intensity and physiological responses to motorized treadmill running suggests greater work outputs can be accomplished in this modality for the same perceived effort compared to rowing among recreationally active participants.

Four weeks of inspiratory muscle training improves self-paced walking performance in overweight and obese adults: a randomised controlled trial.

Objective. To examine whether a programme of inspiratory muscle training (IMT) improves accumulative distance of self-paced walking in overweight and obese adults. Methods. A total of 15 overweight and obese adults were randomized into experimental (EXP: n = 8) and placebo (PLA: n = 7) groups. Lung function, inspiratory muscle performance, 6-minute walking test, and predicted [Formula: see text]O(2) max were assessed prior to and following the 4-week IMT intervention. Both groups performed 30 inspiratory breaths, twice daily using a proprietary inspiratory resistance device set to 55% of baseline maximal effort (EXP), or performing the same inspiratory training procedure at the minimum resistive setting (PLA). Results. Lung function was unchanged in both groups after-training; however inspiratory muscle strength was significantly improved in EXP (19 ± 25.2 cm H(2)O gain; P < 0.01) but did not significantly change in PLA. Additionally, the posttraining distance covered in the 6-minute walking test was significantly extended for EXP (62.5 ± 37.7 m gain; P < 0.01), but not for PLA. A positive association was observed between the change (%) of performance gain in the 6-minute walking test and body mass index (r = 0.736; P < 0.05) for EXP. Conclusion. The present study suggests that IMT provides a practical, minimally intrusive intervention to significantly augment both inspiratory muscle performance and walking distance covered by overweight and obese adults in a clinically relevant 6-minute walk test. This indicates that IMT may provide a useful priming (preparatory) strategy prior to entry in a physical training programme for overweight and obese adults.

Sport-specific fitness testing differentiates professional from amateur soccer players where VO2max and VO2 kinetics do not.

AIM: The purpose of this study was to identify if sport-specific and cardiopulmonary exercise testing differentiated professional from amateur soccer players. METHODS: Thirty six men comprising 18 professional (mean±s: age 23.2±2.4 years) and 18 amateur (mean±SD: age 21.1±1.6 years) soccer players participated and performed four tests on separate occasions: 1) a graded exercise test to determine VO2max; 2) four exercise transients from walking to 80%Δ for the determination of VO2 kinetics; 3) the Yo-Yo Intermittent Recovery Test level 2 (Yo-Yo IR2) and 4) a repeated sprint test (RST). RESULTS: The players did not differ in VO2max (professional 56.5±2.9 mL.kg-1.min-1; amateur 55.7±3.5 mL.kg-1.min-1: P=0.484) or VO2 kinetic fundamental measures (τ1 onset, professional 24.5±3.2 s; amateur 24.0±1.8 s: τ1 cessation, professional 28.7±2.8 s; amateur 29.3±3.5 s: P=0.923). However, the amateurs were outperformed in the Yo-Yo IR2 (Professional 966±153 m; Amateur 840±156 m) (P=0.034) and RST (best time, professional 6.46±0.27 s; amateur 6.84±0.24 s, P=0.012). CONCLUSION: Performance indices derived from field-based sport-specific performance tests identified significant differences between professional and amateur players (P<0.05). However, neither tests of VO2 kinetics nor VO2max differentiated between groups, suggesting laboratory tests of cardiorespiratory parameters are probably less consequential to soccer than sport-specific field-based observations.

Molecular mechanisms of Staphylococcus aureus nasopharyngeal colonization.

Staphylococcus aureus is responsible for a wide range of different infections ranging in severity from mild to fatal. However, it primarily exists as a commensal organism in a number of different anatomical sites including the nasopharynx. Although colonization itself is a harmless state, colonized individuals are at risk of endogenous infection when S. aureus enters otherwise sterile sites via wounds or indwelling medical devices. As such, studies of colonization may identify important targets for vaccines or other prophylactic approaches. Colonization is a dynamic process; S. aureus must attach to host surfaces, overcome immune components and compete with other commensal microbes. This occurs via a number of surface-attached and secreted proteins and other factors such as wall teichoic acid. In addition, colonizing S. aureus must constantly replicate to maintain its niche and exclude other strains. These myriad interactions provide a strong selective pressure for the maintenance or enhancement of mechanisms of adhesion, invasion and immune evasion. The evolutionary implications of this may explain why S. aureus is such a capable pathogen because many of the proteins involved in colonization have also been identified as virulence factors. This review describes the diverse molecular mechanisms used by S. aureus to colonize the host and discusses how the pressures that have selected for these may have led to its virulence.