Broadly reactive human CD4+ T cells against Enterobacteriaceae are found in the naïve repertoire and are clonally expanded in the memory repertoire.

Enterobacteriaceae are a large family of Gram-negative bacteria that includes both commensals and opportunistic pathogens. The latter can cause severe nosocomial infections, with outbreaks of multi-antibiotics resistant strains, thus being a major public health threat. In this study, we report that Enterobacteriaceae-reactive memory Th cells were highly enriched in a CCR6+ CXCR3+ Th1*/17 cell subset and produced IFN-γ, IL-17A, and IL-22. This T cell subset was severely reduced in septic patients with K. pneumoniae bloodstream infection who also selectively lacked circulating K. pneumonie-reactive T cells. By combining heterologous antigenic stimulation, single cell cloning and TCR Vß sequencing, we demonstrate that a large fraction of memory Th cell clones was broadly cross-reactive to several Enterobacteriaceae species. These cross-reactive Th cell clones were expanded in vivo and a large fraction of them recognized the conserved outer membrane protein A antigen. Interestingly, Enterobacteriaceae broadly cross-reactive T cells were also prominent among in vitro primed naïve T cells. Collectively, these data point to the existence of immunodominant T cell epitopes shared among different Enterobacteriaceae species and targeted by cross-reactive T cells that are readily found in the pre-immune repertoire and are clonally expanded in the memory repertoire.

Chromobacterium violaceum bacteraemia: a new entity in Switzerland.

We report the uncommon clinical case of our patient, an 83-year-old woman with Alzheimer disease, who acquired a potentially fatal tropical infection in an open-air swimming pool in the Alps. Chromobacterium violaceum is a rare gram-negative anaerobe bacillus, generally associated with serious waterborne infections in tropical and subtropical regions. The patient presented to our emergency department with a 2-day history of fever and a small non-necrotic wound on the right leg after a minor injury 9 days before. It turned out to be the first infection in Switzerland due to C. violaceum, a deadly bacterium typical of tropical regions. C. violaceum appeared for the first time in Europe in the 2011. This is now the third documented case in less than a year and the second autochthonous infection ever in our continent. A delay in adequate treatment of this emerging pathogen may be associated with high fatality rates.