https://www.cdc.gov/coronavirus/mers/downloads/Isolation2007.pdf

2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Health Care Settings.

Various gram-negative animal and plant pathogens use a novel, sec-independent protein secretion system as a basic virulence mechanism. It is becoming increasingly clear that these so-called type III secretion systems inject (translocate) proteins into the cytosol of eukaryotic cells, where the translocated proteins facilitate bacterial pathogenesis by specifically interfering with host cell signal transduction and other cellular processes. Accordingly, some type III secretion systems are activated by bacterial contact with host cell surfaces. Individual type III secretion systems direct the secretion and translocation of a variety of unrelated proteins, which account for species-specific pathogenesis phenotypes. In contrast to the secreted virulence factors, most of the 15 to 20 membrane-associated proteins which constitute the type III secretion apparatus are conserved among different pathogens. Most of the inner membrane components of the type III secretion apparatus show additional homologies to flagellar biosynthetic proteins, while a conserved outer membrane factor is similar to secretins from type II and other secretion pathways. Structurally conserved chaperones which specifically bind to individual secreted proteins play an important role in type III protein secretion, apparently by preventing premature interactions of the secreted factors with other proteins. The genes encoding type III secretion systems are clustered, and various pieces of evidence suggest that these systems have been acquired by horizontal genetic transfer during evolution. Expression of type III secretion systems is coordinately regulated in response to host environmental stimuli by networks of transcription factors. This review comprises a comparison of the structure, function, regulation, and impact on host cells of the type III secretion systems in the animal pathogens Yersinia spp., Pseudomonas aeruginosa, Shigella flexneri, Salmonella typhimurium, enteropathogenic Escherichia coli, and Chlamydia spp. and the plant pathogens Pseudomonas syringae, Erwinia spp., Ralstonia solanacearum, Xanthomonas campestris, and Rhizobium spp.

/pdf/type-iii-protein-secretion-systems-in-bacterial-pathogens-of-4iowv8mqxc.pdf

Type III Protein Secretion Systems in Bacterial Pathogens of Animals and Plants

Major surgery is still associated with undesirable sequelae such as pain, cardiopulmonary, infective and thromboembolic complications, cerebral dysfunction, nausea and gastrointestinal paralysis, fatigue and prolonged convalescence. The key pathogenic factor in postoperative morbidity, excluding failures of surgical and anaesthetic technique, is the surgical stress response with subsequent increased demands on organ function. These changes in organ function are thought to be mediated by trauma-induced endocrine metabolic changes and activation of several biological cascade systems (cytokines, complement, arachidonic acid metabolites, nitric oxide, free oxygen radicals, etc). To understand postoperative morbidity it is therefore necessary to understand the pathophysiological role of the various components of the surgical stress response and to determine if modification of such responses may improve surgical outcome. While no single technique or drug regimen has been shown to eliminate postoperative morbidity and mortality, multimodal interventions may lead to a major reduction in the undesirable sequelae of surgical injury with improved recovery and reduction in postoperative morbidity and overall costs.

Multimodal approach to control postoperative pathophysiology and rehabilitation.

cagA, a gene that codes for an immunodominant antigen, is present only in Helicobacter pylori strains that are associated with severe forms of gastroduodenal disease (type I strains). We found that the genetic locus that contains cagA (cag) is part of a 40-kb DNA insertion that likely was acquired horizontally and integrated into the chromosomal glutamate racemase gene. This pathogenicity island is flanked by direct repeats of 31 bp. In some strains, cag is split into a right segment (cagI) and a left segment (cagII) by a novel insertion sequence (IS605). In a minority of H. pylori strains, cagI and cagII are separated by an intervening chromosomal sequence. Nucleotide sequencing of the 23,508 base pairs that form the cagI region and the extreme 3' end of the cagII region reveals the presence of 19 ORFs that code for proteins predicted to be mostly membrane associated with one gene (cagE), which is similar to the toxin-secretion gene of Bordetella pertussis, ptlC, and the transport systems required for plasmid transfer, including the virB4 gene of Agrobacterium tumefaciens. Transposon inactivation of several of the cagI genes abolishes induction of IL-8 expression in gastric epithelial cell lines. Thus, we believe the cag region may encode a novel H. pylori secretion system for the export of virulence determinants.

https://www.pnas.org/content/pnas/93/25/14648.full.pdf

cag, a pathogenicity island of Helicobacter pylori, encodes type I-specific and disease-associated virulence factors.

cagA, a gene that codes for an immunodom- inantantigen,ispresentonlyinHelicobacterpyloristrainsthat are associated with severe forms of gastroduodenal disease (type Is trains). We found that the genetic locus that contains cagA (cag) is part of a 40-kb DNA insertion that likely was acquired horizontally and integrated into the chromosomal glutamateracemasegene.Thispathogenicityislandisflanked by direct repeats of 31 bp. In some strains,cagis split into a right segment (cagI) and a left segment (cagII) by a novel insertion sequence (IS605). In a minority ofH. pyloristrains, cagI andcagII are separated by an intervening chromosomal sequence. Nucleotide sequencing of the 23,508 base pairs that formthecagIregionandtheextreme3*endofthecagIIregion reveals the presence of 19 ORFs that code for proteins predicted to be mostly membrane associated with one gene (cagE), which is similar to the toxin-secretion gene ofBorde- tella pertussis, ptlC, and the transport systems required for plasmid transfer, including the virB4 gene of Agrobacterium tumefaciens. Transposon inactivation of several of the cagI genes abolishes induction of IL-8 expression in gastric epi- thelial celllines. Thus, we believe thecagregion may encode a novel H. pylori secretion system for the export of virulence determinants.

cag, a pathogenicity island of Helicobacter pylori, encodes type I-specific and disease-associated virulence factors (secretionyinsertion sequenceyinflammationyevolution)

Members of the endogenous flora have become recognized as major pathogens in nosocomial infections, and the intestinal tract has become recognized as a major portal of entry for these pathogens. The English-language literature on this topic has been summarized and a working hypothesis devised describing a mechanism whereby intestinal bacteria can escape and cause systemic disease. It is postulated that the motile phagocyte ingests intestinal bacteria, transports them to extraintestinal sites, fails to accomplish intracellular killing, and then liberates the bacteria in the extraintestinal site. This hypothesis is consistent with many observations found in the literature: (1) The intestinal bacteria that most readily translocate out of the intestinal tract are classified as facultative intracellular pathogens. (2) Intestinal particles with no intrinsic motility (e.g., yeast, ferritin, starch) can translocate out of the intestinal lumen within hours after their ingestion. (3) The rate of translocation of intestinal bacteria can be altered with agents that modulate immune (including phagocytic) function. In the context of the mechanisms involved in intestinal immune responses, bacterial translocation appears to be a part of the normal antigen-sampling process of gut-associated lymphoid tissue. Systemic disease caused by translocating intestinal bacteria could be due to a maladaptation of the antigen-sampling process that has been designed to regulate the immune response to intestinal antigens.

Proposed mechanisms for the translocation of intestinal bacteria.

Contact with epithelial cells induces the formation of surface appendages on Salmonella typhimurium.

The pathogenesis of Enterococcus (Streptococcus) faecalis was studied in mice with E. faecalis intestinal overgrowth (10(9) - 10(10) per gram of cecum) induced by metronidazol and streptomycin treatment coupled with oral inoculation of E. faecalis. E. faecalis was recovered from the mesenteric lymph nodes, liver, and spleen; mortality was noted in 8 (13%) of 62 mice after 14 days of E. faecalis intestinal overgrowth. Light, immunofluorescent, and electron (scanning and transmission) microscopy of ileal tissue was used in an attempt to localize E. faecalis translocating across intestinal tissue. Dense coccal bacteria were observed in the intestinal lumen, and the epithelium appeared intact. Coccal bacteria were observed adherent to the microvillus border of the entire villous epithelium, including the deeper regions of the intestinal crypts. Immunofluorescence localized E. faecalis within columnar epithelial cells, lamina propria, submucosa, and muscularis externa (including the lumen of small vessels). Transmission electron microscopy localized coccal bacteria within vacuoles in the cytoplasm of intact epithelial cells. These results indicated that E. faecalis could translocate across an intact intestinal tract and cause systemic infection and death. In this model, the intestinal epithelial cell appeared to be a portal of entry in the pathogenesis of systemic E. faecalis infection.

https://www.jstor.org/stable/pdfplus/30127845.pdf

Evidence for the translocation of Enterococcus faecalis across the mouse intestinal tract.

During a nosocomial outbreak of infection due to vancomycin-resistant enterococci (VRE), rectal swabs that were collected weekly were used to identify and isolate VRE carriers. Over 6 months, 1,458 stool specimens from 724 high-risk patients were cultured, and 187 VRE isolates were recovered from 61 patients; 96% of the isolates were Enterococcus faecium. VRE tended to be isolated from clinical specimens from patients identified as VRE carriers by stool surveillance (P < .01). However, isolation of VRE from surveillance cultures preceded clinical isolation for only approximately 50% of the patients from whom a clinical VRE isolate was recovered. Mortality was greater (P < .05) among patients from whom a clinical VRE isolate was recovered than among patients from whom VRE was isolated only by stool surveillance. The mortality (1[17%] of 6) among patients for whom VRE was isolated from blood was similar to that (10 [27%] of 37) among patients for whom vancomycin-susceptible enterococcus was isolated from blood (P = .97). Despite prompt initiation of contact precautions for VRE carriers, the incidence of fecal carriage of VRE remained approximately 8% among this patient population for the 6-month period of the study.

Stool carriage, clinical isolation, and mortality during an outbreak of vancomycin-resistant enterococci in hospitalized medical and/or surgical patients.

The microbial glycocalyx is composed of a variety of polyanionic exopolysaccharides and plays important roles in microbial attachment to different substrata and to other cells. Here we report the successful use of low-voltage scanning electron microscopy (LVSEM) to visualize the glycocalyx in two microbial models (Klebsiella pneumoniae and Enterococcus faecalis biofilms) at high resolution, and also the dependence on fixation containing polycationic dyes for its visualization. Fixation in a paraformaldehyde-glutaraldehyde cocktail without cationic dyes was inadequate for visualizing the glycocalyx, whereas addition of various dyes (alcian blue, safranin, and ruthenium red) to the aldehyde cocktail appeared necessary for stabilization. The cationic dyes varied in size, shape, and charge density, and these factors appeared responsible for different phenotypic appearances of the glycocalyx with each dye. These results suggest that aldehyde fixation with cationic dyes for high-resolution LVSEM will be a useful tool for investigation of microbial biofilms as well as investigation of the extent and role of the glycocalyx in microbial attachment to surfaces.

https://journals.sagepub.com/doi/pdf/10.1369/jhc.4A6428.2004

Carol L. Wells

Papers

Proposed mechanisms for the translocation of intestinal bacteria.

Contact with epithelial cells induces the formation of surface appendages on Salmonella typhimurium.

Evidence for the translocation of Enterococcus faecalis across the mouse intestinal tract.

Stool carriage, clinical isolation, and mortality during an outbreak of vancomycin-resistant enterococci in hospitalized medical and/or surgical patients.

High-resolution visualization of the microbial glycocalyx with low-voltage scanning electron microscopy: dependence on cationic dyes.