Ionic Modulation of Bacterial Virulence and Its Role in Surgical Infection

Background: Bacterial virulence is a dynamic property of pathogens that is expressed in a context-dependent manner. For a bacterial pathogen, the expression of virulence is a tradeoff, as there is an energy cost that can disturb other functions. As a result, virulence is activated only when bacteria sense the need for it. Methods: Recent work from our laboratory has identified many of the local cues in the environmental context that activate bacterial virulence during surgical injury, resulting in bacterial invasion, tissue inflammation, and, in some cases, lethal sepsis. Results: After surgical injury, cytokines, opioids, and end-products of ischemia can activate bacterial virulence circuits, such as the quorum-sensing signaling system, directly. However, when key ions are present, such as phosphate and iron, certain pathogenic bacteria become insensitive to these incoming host cues. Conclusion: In this review, we provide molecular insight into the process by which certain surgical infections may be prevented by ionic modulation of the local microenvironment.

High Iron Stores in the Low Malaria Season Increase Malaria Risk in the High Transmission Season in a Prospective Cohort of Rural Zambian Children

Background: Higher iron stores, defined by serum ferritin (SF) concentration, may increase malaria risk.Objective: We evaluated the association between SF assessed during low malaria season and the risk of malaria during high malaria season, controlling for inflammation.Methods: Data for this prospective study were collected from children aged 4-8 y (n = 745) participating in a biofortified maize efficacy trial in rural Zambia. All malaria cases were treated at baseline (September 2012). We used baseline SF and malaria status indicated by positive microscopy at endline (March 2013) to define exposure and outcome, respectively. Iron status was defined as deficient (corrected or uncorrected SF <12 or <15 μg/L, depending on age <5 or ≥5 y, respectively), moderate (<75 μg/L, excluding deficient), or high (≥75 μg/L). We used a modified Poisson regression to model the risk of malaria in the high transmission seasons (endline) as a function of iron status assessed in the low malaria seasons (baseline).Results: We observed an age-dependent, positive dose-response association between ferritin in the low malaria season and malaria incidence during the high malaria season in younger children. In children aged <6 y (but not older children), we observed a relative increase in malaria risk in the moderate iron status [incidence rate ratio (IRR) with SF: 1.56; 95% CI: 0.64, 3.86; IRR with inflammation-corrected SF: 1.92; 95% CI: 0.75, 4.93] and high iron status (IRR with SF: 2.66; 95% CI: 1.10, 6.43; or IRR with corrected SF: 2.93; 95% CI: 1.17, 7.33) categories compared with the deficient iron status category. The relative increase in malaria risk for children with high iron status was statistically significant only among those with a concurrently normal serum soluble transferrin receptor concentration (<8.3 mg/L; IRR: 1.97; 95% CI: 1.20, 7.37).Conclusions: Iron adequacy in 4- to 8-y-old children in rural Zambia was associated with increased malaria risk. Our findings underscore the need to integrate iron interventions with malaria control programs. This trial was registered at clinicaltrials.gov as NCT01695148.

Iron and infection: narrative review of a major iron supplementation study in Papua New Guinea undertaken by the Department of Tropical Paediatrics, Liverpool School of Tropical Medicine, 1979-1983, its aftermath and the continuing relevance of its results

In 1978, I returned from a 2-year government posting as provincial paediatrician to East and West Sepik provinces of Papua New Guinea (PNG), having already enrolled on the Diploma of Tropical Medicine and Hygiene (DTM&H) course at the Liverpool School of Tropical Medicine. I had been too late to enrol for the more relevant Diploma in Tropical Paediatrics course, but, whilst on the DTM&H course, made up for lost time by presenting myself to Professor Ralph Hendrickse in his office. I outlined my proposal for a double-blind, controlled, randomised trial of iron intervention with the aim of improving iron nutrition and decreasing susceptibility to and morbidity from infections in a cohort of infants in PNG. My reason for suggesting such a study was the high rate of anaemia in infants there and my perception from the literature of the time that the balance of studies favoured a beneficial effect of iron supplementation on infectious susceptibility, and that iron deficiency was associated with reversible abnormalities of immune function (although it had and has since been difficult to demonstrate the severity and relevance of these in observational in-vivo studies in humans).1,2 Ralph made an on-the-spot decision, immediately offering me the opportunity to join his department on 1 January 1979 on temporary funding while I applied for (and secured) a major grant from the Wellcome Trust for this work.

Use of laboratory studies for the design, explanation, and validation of human micronutrient intervention studies

Many micronutrient supplementation trials have led to important new findings relevant to public health, but some outcomes have been unclear or concerning. Can and should laboratory studies and animal models be used more extensively to pretest the proposed designs of human studies? This paper illustrates, as examples, the contributions that animal models have made to several major advances in understanding the biology of the micronutrients vitamin A and carotenoids, and it proposes that animal studies can play a more integrated role in public health nutrition by serving as a first line of interrogation for study designs and thereby as a means of refining the designs of human studies so that large, expensive, and logistically difficult human trials will yield the best possible information.

Dangers, and benefits of the cytokine mediated response to injury and infection

The inflammatory response is essential for survival in an environment where continuous exposure to noxious events threaten the integrity of the organism. However, the beneficial effects of the response are influenced by factors, which disadvantage individuals within a population. These factors include malnutrition, infection, genotype, gender, pre-existing inflammation, and chronic intoxication. Although the inflammatory response is generally successful in dealing with noxious events, life-long exposure to these events takes its toll on the integrity of the body and becomes apparent as chronic disease, atherosclerosis, organ failure, and frailty. Progress in ameliorating the consequences of lifetime exposure to inflammatory events can only occur if a fuller understanding can be obtained of the factors, which influence the persistence and outcome of the inflammatory response at an individual level. A multitude of studies has shown that specific nutrients, diets, and dietary restriction are able to modulate the inflammatory response in the population as a whole. To advance in this area, precise knowledge is needed of how the disadvantageous factors, mentioned above, affect the individual's response to anti-inflammatory nutrients.