Implications of free Shiga toxin-converting bacteriophages occurring outside bacteria for the evolution and the detection of Shiga toxin-producing Escherichia coli

In this review we highlight recent work that has increased our understanding of the distribution of Shiga toxin-converting phages that can be detected as free phage particles, independently of Shiga toxin-producing bacteria (STEC). Stx phages are a quite diverse group of temperate phages that can be found in their prophage state inserted within the STEC chromosome, but can also be found as phages released from the cell after activation of their lytic cycle. They have been detected in extraintestinal environments such as water polluted with feces from humans or animals, food samples or even in stool samples of healthy individuals. The high persistence of phages to several inactivation conditions makes them suitable candidates for the successful mobilization of stx genes, possibly resulting in the genes reaching a new bacterial genomic background by means of transduction, where ultimately they may be expressed, leading to Stx production. Besides the obvious fact that Stx phages circulating between bacteria can be, and probably are, involved in the emergence of new STEC strains, we review here other possible ways in which free Stx phages could interfere with the detection of STEC in a given sample by current laboratory methods and how to avoid such interference.

Local perception and use of the multifunctionality of water tanks in two villages of Tamil Nadu, South India

Using data from free listings and a survey in two villages of Tamil Nadu, India, we discuss local perceptions and uses of water tanks, a traditional irrigation infrastructure. We hypothesize that both farmers and nonfarmers perceive and use water tanks for purposes other than irrigation. We found that informants recognized the importance of water tanks for irrigation, but also acknowledged other socioeconomic uses and ecological functions. Marginal sectors (i.e., Scheduled Castes) use tank resources in more diverse ways than other sectors of the population. Findings are relevant for development. International organizations working on the revival of water tanks aim to transfer water management to farmers for the purpose of irrigation. By recognizing that tanks benefit people other than farmers and in ways other than providing irrigation water, organizations working on tank rejuvenation could achieve a more equitable management of tank resources.