γ-proteobacteria eject their polar flagella under nutrient depletion, retaining flagellar motor relic structures.

Bacteria switch only intermittently to motile planktonic lifestyles under favorable conditions. Under chronic nutrient deprivation, however, bacteria orchestrate a switch to stationary phase, conserving energy by altering metabolism and stopping motility. About two-thirds of bacteria use flagella to swim, but how bacteria deactivate this large molecular machine remains unclear. Here, we describe the previously unreported ejection of polar motors by γ-proteobacteria. We show that these bacteria eject their flagella at the base of the flagellar hook when nutrients are depleted, leaving a relic of a former flagellar motor in the outer membrane. Subtomogram averages of the full motor and relic reveal that this is an active process, as a plug protein appears in the relic, likely to prevent leakage across their outer membrane; furthermore, we show that ejection is triggered only under nutritional depletion and is independent of the filament as a possible mechanosensor. We show that filament ejection is a widespread phenomenon demonstrated by the appearance of relic structures in diverse γ-proteobacteria including Plesiomonas shigelloides, Vibrio cholerae, Vibrio fischeri, Shewanella putrefaciens, and Pseudomonas aeruginosa. While the molecular details remain to be determined, our results demonstrate a novel mechanism for bacteria to halt costly motility when nutrients become scarce.

Virulence, attachment and invasion of Caco-2 cells by multidrug-resistant bacteria isolated from wild animals.

Wild animals may be considered important reservoirs for bacterial pathogens and, consequently, possible sources of infection for humans. In this study, selected multidrug-resistant bacteria (Acinetobacter spp., Aeromonas salmonicida, Klebsiella pneumoniae, Pseudomonas fluorescens and Shewanella putrefaciens) isolated from wild animals were characterized on their ability to attach and invade/internalize human colonic carcinoma (Caco-2) cells. In addition, the viability of these bacteria to survive under simulated human gastrointestinal tract conditions as well as the production of virulence factors (homoserine lactones signal molecules, gelatinases, proteases, siderophores and biofilm formation) were studied. The results suggests that all the bacteria presented the capacity to attach and internalize into Caco-2 cells. A. salmonicida and P. fluorescens exhibited the highest ability to internalize. These bacteria were also found to be the highest proteases producers. A. salmonicida and K. pneumoniae survived under simulated human gastrointestinal conditions. These were the bacteria with the highest capacity to produce biofilms. K. pneumoniae was the only bacterium producing siderophores. Taken together, the present results reinforce the need for the "One Health" initiative, underscoring the environment and the animals as important reservoirs of infectious determinants.

Soft tissue infection and bacteremia caused by Shewanella putrefaciens.

Shewanella putrefaciens is as yet rarely responsible for clinical syndromes in humans. However, a case involving multiple organs in an elderly male under treatment with appropriate steroids confirms that attention should be devoted to unusual pathogens.

Diverse bacteria are pathogens of Caenorhabditis elegans.

Practically and ethically attractive as model systems, invertebrate organisms are increasingly recognized as relevant for the study of bacterial pathogenesis. We show here that the nematode Caenorhabditis elegans is susceptible to a surprisingly broad range of bacteria and may constitute a useful model for the study of both pathogens and symbionts.