Large multidrug resistance plasmids of the A/C incompatibility complex (IncA/C) have been found in a diverse group of Gram-negative commensal and pathogenic bacteria. We present three completed sequences from IncA/C plasmids that originated from Escherichia coli (cattle) and Salmonella enterica serovar Newport (human) and that carry the cephamycinase gene bla CMY-2 . These large plasmids (148 to 166 kbp) share extensive sequence identity and synteny. The most divergent plasmid, peH4H, has lost several conjugationrelated genes and has gained a kanamycin resistance region. Two of the plasmids (pAM04528 and peH4H) harbor two copies of bla CMY-2 , while the third plasmid (pAR060302) harbors a single copy of the gene. The majority of single-nucleotide polymorphisms comprise nonsynonymous mutations in floR. A comparative analysis of these plasmids with five other published IncA/C plasmids showed that the bla CMY-2 plasmids from E. coli and S. enterica are genetically distinct from those originating from Yersinia pestis and Photobacterium damselae and distal to one originating from Yersinia ruckeri. While the overall similarity of these plasmids supports the likelihood of recent movements among E. coli and S. enterica hosts, their greater divergence from Y. pestis or Y. ruckeri suggests less recent plasmid transfer among these pathogen groups.

Salmonella enterica serovar Enteritidis (S. Enteritidis) is a major cause of food-borne gastroenteritis in humans worldwide. Poultry and poultry products are considered the major vehicles of transmission to humans. Using cell invasiveness as a surrogate marker for pathogenicity, we tested the invasiveness of 53 poultry-associated isolates of S. Enteritidis in a well-differentiated intestinal epithelial cell model (Caco-2). The method allowed classification of the isolates into low (n57), medium (n518) and high (n530) invasiveness categories. Cell invasiveness of the isolates did not correlate with the presence of the virulence-associated gene spvB or the ability of the isolates to form biofilms. Testing of representative isolates with high and low invasiveness in a mouse model revealed that the former were more invasive in vivo and caused more and earlier mortalities, whereas the latter were significantly less invasive in vivo, causing few or no mortalities. Further characterization of representative isolates with low and high invasiveness showed that most of the isolates with low invasiveness had impaired motility and impaired secretion of either flagella-associated proteins (FlgK, FljB and FlgL) or type III secretion system (TTSS)-secreted proteins (SipA and SipD) encoded on Salmonella pathogenicity island-1. In addition, isolates with low invasiveness had impaired ability to invade and/or survive within chicken macrophages. These data suggest that not all isolates of S. Enteritidis recovered from poultry may be equally pathogenic, and that the pathogenicity of S. Enteritidis isolates is associated, in part, with both motility and secretion of TTSS effector proteins. INTRODUCTIONSalmonella enterica serovar Enteritidis (S. Enteritidis) is the leading cause of food-borne salmonellosis (WHO, 2008). S. Enteritidis-induced salmonellosis in humans is characterized by diarrhoea, fever, headache, abdominal pain, nausea and vomiting (CDC, 2007). S. Enteritidis is also increasingly reported from cases of invasive and extra-intestinal infections such as septicaemia, arthritis, endocarditis, meningitis and urinary tract infections (Ghosh & Vogt, 2006; Gordon et al., 2008;Katsenos et al., 2008; Kobayashi et al., 2009;Morpeth et al., 2009;Mutlu et al., 2009;Tena et al., 2007). Between 1990 and 2001, the US state and territorial health departments reported 677 S. Enteritidis outbreaks, which accounted for 23 366 illnesses, 1988 hospitalizations and 33 deaths (CDC, 2003). In 2006, countries within the European Union reported 1729 outbreaks caused by S. Enteritidis leading to 13 853 illnesses, 2714 hospitalizations and 14 deaths (EFSA, 2007). The Health Protection Agency of the UK reported 4194 cases of foodborne S. Enteritidis infection in (HPA, 2008. Poultry is considered the single largest reservoir of S. Enteritidis and most risk attribution studies have identified poultry and poultry products as the major source of human infection. S. Enteritidis is passed to humans mainly via handling and consumption of contaminated po...

Vibrio parahaemolyticus is an emerging food-and waterborne pathogen that encodes two type III secretion systems (T3SSs). Previous studies have linked type III secretion system 1 (T3SS1) to cytotoxicity and T3SS2 to intestinal fluid accumulation, but animal challenge models needed to study these phenomena are limited. In this study we evaluated the roles of the T3SSs during infection using two novel animal models: a model in which piglets were inoculated orogastrically and a model in which mice were inoculated in their lungs (intrapulmonarily). The bacterial strains employed in this study had equivalent growth rates and beta-hemolytic activity based on in vitro assays. Inoculation of 48-h-old conventional piglets with 10 11 CFU of the wild-type strain (NY-4) or T3SS1 deletion mutant strains resulted in acute, self-limiting diarrhea, whereas inoculation with a T3SS2 deletion mutant strain failed to produce any clinical symptoms. Intrapulmonary inoculation of C57BL/6 mice with the wild-type strain and T3SS2 deletion mutant strains (5 ؋ 10 5 CFU) induced mortality or a moribund state within 12 h (80 to 100% mortality), whereas inoculation with a T3SS1 deletion mutant or a T3SS1 T3SS2 double deletion mutant produced no mortality. Bacteria were recovered from multiple organs regardless of the strain used in the mouse model, indicating that the mice were capable of clearing the lung infection in the absence of a functional T3SS1. Because all strains had a similar beta-hemolysin phenotype, we surmise that thermostable direct hemolysin (TDH) plays a limited role in these models. The two models introduced herein produce robust results and provide a means to determine how different T3SS1 and T3SS2 effector proteins contribute to pathogenesis of V. parahaemolyticus infection.Vibrio parahaemolyticus is a Gram-negative food-and waterborne pathogen that is recognized worldwide as a causative agent of gastroenteritis associated with the consumption of undercooked seafood (22). Gastrointestinal infection is characterized by acute self-limiting diarrhea, abdominal cramps, nausea, and vomiting. In approximately 5% of cases, V. parahaemolyticus gastrointestinal infection can progress to septicemia and may be fatal for immunocompromised patients, including those with leukemia, liver disease, and patients infected by human immunodeficiency virus (14, 28).The thermostable direct hemolysin (TDH) is a widely recognized virulence factor of V. parahaemolyticus. This hemolysin is associated with the Kanagawa phenomenon, which is a beta-hemolysis reaction on a defined blood agar (10). TDH is encoded by 1 or 2 genes (tdhA and tdhS), and the protein increases permeability in human erythrocytes (19), increases chloride secretion in an intestinal cell line (29), and is also thought to be responsible for enterotoxigenicity in a rabbit small intestine model (5, 23). Early studies demonstrated that deletion of tdhS and tdhA will significantly reduce fluid accumulation in a rabbit ileal-loop model, but the phenotype is not completely abrogated, sug...

The aim of this work was to elucidate the mechanism of mediated microbial electrosynthesis via neutral red from an electrode to fermenting Escherichia coli cultures in a bioelectrochemical system. Chemical reduction of NAD+ by reduced neutral red did not occur as predicted. Instead, neutral red was shown to reduce the menaquinone pool in the inner bacterial membrane. The reduced menaquinone pool altered fermentative metabolite production via the arcB redoxsensing cascade in the absence of terminal electron acceptors. When the acceptors DMSO, fumarate, or nitrate were provided, as many as 19% of the electrons trapped in the reduced acceptors were derived from the electrode. These results demonstrate the mechanism of neutral red-mediated microbial electrosynthesis during fermentation as well as how neutral red enables microbial electrosynthesis of reduced terminal electron acceptors.

Bovine-origin Escherichia coli isolates were tested for resistance phenotypes using a disk diffusion assay and for resistance genotypes using a DNA microarray. An isolate with gentamicin and amikacin resistance but with no corresponding genes detected yielded a 1,056-bp DNA sequence with the closest homologues for its inferred protein sequence among a family of 16S rRNA methyltransferase enzymes. These enzymes confer high-level aminoglycoside resistance and have only recently been described in Gram-negative bacteria.