Resuscitation and quantification of stressed Escherichia coli K12 NCTC8797 in water samples

The aim of this study was to investigate the impact on numbers of using different media for the enumeration of Escherichia coli subjected to stress, and to evaluate the use of different resuscitation methods on bacterial numbers. E. coli was subjected to heat stress by exposure to 55 °C for 1 h or to light-induced oxidative stress by exposure to artificial light for up to 8 h in the presence of methylene blue. In both cases, the bacterial counts on selective media were below the limits of detection whereas on non-selective media colonies were still produced. After resuscitation in non-selective media, using a multi-well MPN resuscitation method or resuscitation on membrane filters, the bacterial counts on selective media matched those on non-selective media. Heat and light stress can affect the ability of E. coli to grow on selective media essential for the enumeration as indicator bacteria. A resuscitation method is essential for the recovery of these stressed bacteria in order to avoid underestimation of indicator bacteria numbers in water. There was no difference in resuscitation efficiency using the membrane filter and multi-well MPN methods. This study emphasises the need to use a resuscitation method if the numbers of indicator bacteria in water samples are not to be underestimated. False-negative results in the analysis of drinking water or natural bathing waters could have profound health effects

E. coli Nissle 1917 Affects Salmonella Adhesion to Porcine Intestinal Epithelial Cells

BACKGROUND: The probiotic Escherichia coli strain Nissle 1917 (EcN) has been shown to interfere in a human in vitro model with the invasion of several bacterial pathogens into epithelial cells, but the underlying molecular mechanisms are not known. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we investigated the inhibitory effects of EcN on Salmonella Typhimurium invasion of porcine intestinal epithelial cells, focusing on EcN effects on the various stages of Salmonella infection including intracellular and extracellular Salmonella growth rates, virulence gene regulation, and adhesion. We show that EcN affects the initial Salmonella invasion steps by modulating Salmonella virulence gene regulation and Salmonella SiiE-mediated adhesion, but not extra- and intracellular Salmonella growth. However, the inhibitory activity of EcN against Salmonella invasion always correlated with EcN adhesion capacities. EcN mutants defective in the expression of F1C fimbriae and flagellae were less adherent and less inhibitory toward Salmonella invasion. Another E. coli strain expressing F1C fimbriae was also adherent to IPEC-J2 cells, and was similarly inhibitory against Salmonella invasion like EcN. CONCLUSIONS: We propose that EcN affects Salmonella adhesion through secretory components. This mechanism appears to be common to many E. coli strains, with strong adherence being a prerequisite for an effective reduction of SiiE-mediated Salmonella adhesion

Effect of norepinephrine on growth of <i>Salmonella </i>and its enterotoxin production

285-286Salmonella typhimurium was cultured in presence or absence of norepinephrine in conditioned media. Two conditioned media containing bovine and pig serum were prepared. Supplementation of fresh cultures with norepinephrine (5 × 10-5 M per mL of medium) resulted in ten-fold increase in growth as compared to controls. No significant difference in growth of organisms in media containing bovine and pig serum was observed. Growth was more in culture incubated under shaking condition than in non-shaking condition. Enterotoxin production increased by two to eight-folds in the medium supplemented with norepinephrine

Siderophores in marine coastal waters and their relevance for iron uptake by phytoplankton: experiments with the diatom Phaeodactylum tricornutum

Natural marine bacteria populations collected from nearshore waters produce different types of siderophores depending on the degree of iron limitation. These siderophores can facilitate iron uptake in the marine diatom Phaeodactylum tricornutum. Water samples from 15 stations along the Italian coast of the northwest Adriatic Sea were collected and filter fractionated (3.0, 0.8 and 0.2 µm). Siderophore production in the fractions was determined using cross-feeding experiments with siderophore-auxotrophic bacteria. At most stations sampled, bacteria collected in the 3.0 and 0.8 µm filters produced siderophores which stimulated growth in Morganella morganii, the indicator strain for α-keto/ α-hydroxy acids. The results suggest that MGF (ŒMorganella-Growth Factor¹) production is common among filamentous and appendaged bacteria or strains associated with particles. Natural bacteria populations grown in iron-deficient media stimulated growth of all the indicator strains in the cross-feeding tests. Examples of known MGF which supply iron to M. morganii were tested for their ability to act as iron source for the marine diatom P. tricornutum. Iron uptake from 55Fe-MGFs was measured in P. tricornutum cells grown in Fe-sufficient and Fe-deficient media. Unchelated iron (55FeCl3 ) and 55FeEDTA were used as controls. The uptake of iron from the 55Fe-MGF and 55FeCl3 by Fe-deficient cells was higher (109 to 150 pgFe mg-1) than from 55FeEDTA (34 pgFe mg-1). Similarly, Fe-sufficient P. tricornutum took up iron from the 55Fe-MGF and 55FeCl3 to the same extent (~50 pgFe mg-1) while minimal uptake (8 pgFe mg-1) was measured from FeEDTA. In growth experiments where iron-deficient diatom cells were incubated in media containing different sources of iron, e.g. FeCl3, Fe-MGF and FeEDTA, a greater increase in number was observed in cells supplied with Fe-MGF. Further experiments also show that the uptake of Fe from MGF was enhanced by light and that a reduction step was involved in the uptake process. MGF also promoted the uptake of colloidal ferrihydrites. This study gives further evidence that siderophores produced by bacteria can be utilized by phytoplankton as an iron source. We therefore suggest that these substances play an important role in increasing the availability of iron to phytoplankton in coastal waters and thus are major factors defining the chemistry of iron in the marine environment

Enterobacterial Autoinducer of Growth Enhances Shiga Toxin Production by Enterohemorrhagic Escherichia coli

The addition of the enterobacterial autoinducer of growth to nutrient-poor minimal medium markedly accelerated the exponential growth rates of strains of enterohemorrhagic Escherichia coli but had little or no effect on maximal cell densities in stationary phase. Growth in the presence of the autoinducer resulted in an approximately twofold enhancement in Shiga toxin production