Bohumil S. Drasar

Response of toxigenic Vibrio cholerae 01 to physico-chemical stresses in aquatic environments.

The survival and growth of toxigenic Vibrio cholerae 01 in water under various conditions of salinity, pH, temperature and cation composition and concentration were studied in an extensive series of laboratory experiments. Inter- and intra-strain variation in stress response (of 01 and non-01 strains) and the ability of V. cholerae to adapt to stressful environments were also studied. Toxigenic V. cholerae 01 were able to survive for at least 70 days at 25 degrees C in solutions of sea salt. The optimal salt concentration was 2.0% though all solutions in the range 0.25-3.0% gave good support. Substrains with enhanced capacity to persist at sub-optimal salinity (0.1%) were demonstrated. A great degree of inter-strain variation in stress response at low salinity (0.05%) was found among 59 strains, and this variation was unrelated to serogroup (01 or non-01), source (clinical or environmental) or country of origin (Tanzania or Bangladesh). At optimal salinity, inter-strain variation was less and 18 out of 20 strains remained viable at high concentrations for at least 40 months at 25 degrees C. V. cholerae 01 could not survive beyond 45 days at 4 degrees C and optimal salinity, either with or without nutrients. The optimal pH range for survival at 25 degrees C was 7.0-8.5 at optimal salinity, and 7.5-9.0 at low salinity. V. cholerae 01 require Na+ for survival in the absence of nutrients, and for enhanced growth in their presence. The presence of Ca2+ or Mg2+, in addition to Na+, further enhanced survival. These, and other results reported in this paper, suggest that toxigenic V. cholerae 01 are able to survive for extended periods in warm water containing no nutrients but having a salinity of 0.25-3.0% and a pH of around 8.0. With added nutrients and under the same conditions, rapid growth is possible. The implications of these findings for the identification of putative aquatic reservoirs of V. cholerae 01, and for the epidemiology of cholera, are considerable.

Cholera epidemiology in developed and developing countries: new thoughts on transmission seasonality and control.

It is hypothesized that geographical regions where cholera is endemic, V. cholerae 01 may be maintained in estuarine environments. Endemic cholera, unlike epedemic cholera, occurs regularly, and sometimes seasonally, in certain geographical areas without evidence of importation. Measures used to control epedemic cholera are not very effective in preventing endemic cholera. Areas of endemic cholera include southeastern US and several African and Asian countries, including Bangladesh. It has previously been suggested that V. cholerae 01 is maintained in these areas between outbreaks by 1) living in nonhuman animals; 2) residing in chronic human carriers, who may not excrete the organism; 3) by continous transmission to individuals who manifest only mild symptoms of the disease; and 4) by living in aquatic environments. The 1st 3 explanations are to supported by available evidence. The 4th explanation, previously thought to be impossible, is now engendering new interest. Recent studies reveal that V. cholerae 01 can survive in warm water with a salinity of 0.25-3.0% and a ph of 8.0 for a considerable length of time. Estuarine environments may be suitable for the organisms survival. It is hypothesized further that outbreaks of primary cases in estuarine environments may be precipatated by eating certain types of raw or inadequately cooked estuarian plants or animals, perhaps on a seasonal basis. In areas where sanitation is poor, the disease will be transmitted to secondary cases, and in areas where sanitation is good, secondary cases will be rare. Primary cases may also develop in areas some distance from the estuarian environment by the importation of estuarian products. Outbreaks of secondary cases in nonestuarian environments may be due to the seasonal movement of estuarian inhabitants through the area. This explanation fits the epidemiological evidence available for the southeastern US and Bangladesh. If this hypothesis is correct, appropriate control measures will include educating people to refrain from eating raw and improperly cooked seafood.

Effect of fermentation of Ghanaian maize dough on the survival and proliferation of 4 strains of Shigella flexneri

Fermented and non-fermented Ghanaian maize dough was seeded with approximately 10(7) colony forming units of 4 strains of Shigella flexneri which had been isolated from patients with dysentery. In the non-fermented maize dough (pH 6.2) the shigellae were detectable in large numbers for up to 24 h after exposure. In the maize dough that had been fermented for 3 d (pH 3.2) 3 strains were detectable in small numbers for up to 6 h after inoculation. Thereafter none was isolated. The fourth strain, though detectable for up to 24 h after inoculation, had its numbers reduced considerably. This suggests that traditional methods of food preparation using fermentation have important anti-diarrhoeal functions and the current decline in popularity of such food technologies in certain developing countries may increase the risk of childhood diarrhoea.

The impact of physico-chemical stress on the toxigenicity of Vibrio cholerae.

The expression of toxigenicity by Vibrio cholerae, before and after exposure to various conditions of salinity, pH and cation composition and concentration, has been measured. Exposure to these conditions did not select for hyper- or hypo-toxigenic strains. This suggests that toxigenic V. cholerae O1 are unlikely to lose their toxigenicity when exposed to environmental stress and that V. cholerae toxin production is not a response to the stresses included in this study. These results are consistent with an aquatic reservoir for toxigenic V. cholerae O1.

Dysentery in World War 1: Shigella a century on

www.thelancet.com Vol 384 November 8, 2014 1651 induction and the subsequent combination with a proliferation signal inhibitor could potentially generate protolerogenic immunological eff ects (like so-called prope, or near, tolerance and upregulated T regulatory cells). Prevention of cumulative alloimmunological injury to the graft from subclinical rejection and acute and chronic (donor-specifi c) antibody-mediated rejection could potentially translate into measurably better graft function and survival after 5 years. Alemtuzumab with sirolimus could reduce nephrotoxicity and cardiovascular and metabolic adverse eff ects through avoidance of calcineurin inhibitors. However, given the complexity of cardiovascular morbidity and mortality after renal transplantation, improvement in a few laboratory results in a clinical trial is a long way from achievement of improvements in the disease course over 5 years. Ideally, these goals would all be achieved without excess malignancies and opportunistic infections. Irrespective of the current and anticipated long-term results of the 3C Study, investigators will question the cause of the results. This will be a diffi cult question to answer because the 3C investigators changed all parts of the standard of care immunosuppressive regimen (the type of induction drug, the dose of calcineurin inhibitor and mycophenolate, and even the use of corticosteroids) rather than one element only. 6 months later, they changed the regimen again. Therefore, the 3C Study will not only address its own predefi ned hypotheses, but will also represent a test case for what type of trials in clinical transplantation are needed to regain some of the academic vigour and pharmaceutical impetus towards development of new pipelines for novel immunosuppressive drugs. Dirk R J Kuypers Department of Nephrology and Renal Transplantation, University Hospitals Leuven, Leuven B-3000, Belgium dirk.kuypers@uzleuven.be

6 – Microbial flora of the gut

The bacterial microflora of humans is the friendliest portion of their biological environment and mediates many of their interactions with the chemical environment. The intestinal physiology and host defence mechanisms play an important role in preventing the microflora from overrunning the host and in determining the distribution of the microflora within the intestine. The environmental factors, such as diet, also influence the microflora. The ecological interactions between the bacterial species are significant in the large intestine. The flow rate of the gut contents contributes to control of the bacterial colonization, being greatest at the top of the small intestine—where the microbial multiplication does not exceed the rate at which the organisms are removed. The anatomically normal small intestine can only be colonized by adhesion to the epithelium. Water is absorbed in the ileum, which reduces the flow rate and allows bacterial multiplication. The lower small intestine—the distal and terminal ileum—contain many more cultivable bacteria than the proximal ileum. Although lactobacilli and streptococci are still prominent, bacteroides and enterobacteria occur more constantly. In the terminal ileum, the viable bacterial counts of 10 5 -10 7 per ml are common, and the flora here qualitatively begins to resemble that of feces.

International law and infectious diseases.

International law and infectious diseases. David P Fidler. (Pp 364; price not stated). Oxford: Oxford University Press, 1999. ISBN 0-19-826851-3 Infectious diseases are usually considered from the view point of the human populations affected, the diseases that are caused, and the biology of the micro-organisms. Microbiologists and epidemiologists seldom consider the political dimensions of their activities. This book outlines the ways in which international law has attempted to deal with the spread of microbial diseases. Consideration is not only in terms of international …