Gut Microbes. 2022; 14(1): 2055943.

Tam metin için tıklayınız

Enterotoxigenic Escherichia coli (ETEC) is a major cause of diarrhea in children and travelers in developing countries. ETEC is characterized by the ability to produce major virulence factors including colonization factors (CFs) and enterotoxins, that bind to specific receptors on epithelial cells and induce diarrhea. The gut microbiota is a stable and sophisticated ecosystem that performs a range of beneficial functions for the host, including protection against pathogen colonization. Understanding the pathogenic mechanisms of ETEC and the interaction between the gut microbiota and ETEC represents not only a research need but also an opportunity and challenge to develop precautions for ETEC infection. Herein, this review focuses on recent discoveries about ETEC etiology, pathogenesis and clinical manifestation, and discusses the colonization resistances mediated by gut microbiota, as well as preventative strategies against ETEC with an aim to provide novel insights that can reduce the adverse effect on human health.

Tam metin için tıklayınız

ÖZET
İshalle ilişkili altı farklı Escherichia coli patotipi tanımlanmıştır. Barsak patojeni olmayan E.coli’lerle bir çok özelliklerinin ortak olması bu patotiplerin dışkıdan izolasyon ve identifikasyonunu güçleştirmektedir. Bugün, E.coli patotiplerinin her birini saptayan çeşitli tanı yöntemleri tarif edilmiş olmakla birlikte bir kısmı rutin laboratuvarlar için uygun de¤ildir. Son yıllarda virulans faktörlerinin saptanmasına yönelik moleküler tanı yöntemleri sıklıkla kullanılmaktadır. Bu yazıda E.coli ishallerinin tanısında kullanılan yöntemler ile bu yöntemlerin avantajları ve dezavantajları tartışılmıştır.

SUMMARY
Laboratory Diagnosis in Escherichia coli Diarrheae
Six different Escherichia coli pathotypes associated with diarrhea have been recognized. There are many properties shared with non-diarrheagenic E.coli, making their isolation and identification from fecal material difficult. Although various diagnostic methods detecting to each E.coli pathotype have been described now, some of them is not suitable for routine laboratories. In recent years, molecular diagnostic methods based on virulence factors have been frequently used. The diagnostic methods used in E.coli diarrhea and their advantages and disadvantages are discussed.

Almanya’daki araştırmacıların, biri İsveç’te çoğu Almanya’da olmak üzere bugüne dek 23 kişinin ölümüne yol açan E.Coli (EHEC) bakterisinin kaynağını araştırmaya devam ettikleri bildirildi.

AA

Berlin- Avrupa Hastalık ve Kontrol Merkezi (ECDC) yetkilileri yaptığı açıklamada, Almanya, Avusturya, Danimarka, Ispanya, Finlandya, Fransa, Lüksemburg, Norveç, Hollanda, Polonya, Çek Cumhuriyeti, İngiltere ve İsveç’te kanamalı ağır bağırsak enfeksiyonuna neden olan E.Coli bakterisine yakalanmış veya yakalandığından şüphe edilen kişiler tespit edildiğini belirtti. Amerikalı makamlar ise, ABD’de bazı kişilerin hastalığa yakalandığından şüphe ettiklerini ifade etti.

Dünya Sağlık Örgütü (DSÖ) yetkilileri, kadınların EHEC’ten daha fazla etkilendiğinin gözlemlendiğini belirterek, kadınların erkeklerden daha fazla tercih ettiği ve bakterinin bulaştığı bir gıda madesinin salgının yayılmasına neden olmuş olabileceğini kaydetti. Alman ulusal sağlık enstitüsü Robert Koch’tan (RKI) yapılan açıklamaya göre, salgında hayatını kaybedenlerin çoğu 22 ile 92 yaş arası kadınlar.

Öte yandan, merkezi İtalya’nın başkenti Roma’da bulunan Yüksek Sağlık Enstitünün (ISS) bünyesinde yer alan bir Avrupa referans laboratuvarından yayımlanan yazılı açıklama, laboratuvarda yapılan tahlilerin sonucunda, iddia edilenin aksine salatalıkların veya sebzelerin EHEC bakterisinin yayılmasına neden olduğu yönünde kanıt bulunmadığını ortaya koyduğunu belirtmişti.

Avrupalı sağlık makamları, bugüne dek yapılan gözlemlerin, Enterohemorajik Escherichia Coli (EHEC) bakterisinin bulaştığı et veya bazı sebzeler gibi çiğ veya az pişmiş gıdalardan insana geçtiğini ortaya koyduğunu ifade etti. Makamlar, yeterli hijyenin sağlanamadığı ortam ve durumlarda da bakterinin insandan insana geçebileceğini belirtti. Doktorlar, bakterinin özellikle bağırsaklarda ve dışkıda bulunduğunu kaydediyor.

Araştırmaların bakterinin kökeni hakkında ve nasıl geliştiği konusunda tam bir netice vermesine kadar, Alman makamlarının çiğ salata, domates, hıyar ve filizlenmiş tohum tüketimini yasakladığı belirtiliyor. Almanya’nın Hannover kentinde EHEC bakterisinin kaynağını araştıran bir uzman, Alman Haber Ajansı’na (DPA) yaptığı açıklamada, EHEC bakterisi salgınının filizlerden kaynaklanmış olabileceğini bildirmişti.

Uzman, bakterinin Uelzen kenti yakınlarındaki bir firmadan kaynaklandığının tahmin edildiğini, sözkonusu firmanın, daha önce Lübeck kentindeki bir restoranda yemek yiyen insanlarda ortaya çıkan rahatsızlıklarla ilgisi olduğunu ifade etmişti. Asya’da yıllar önce ortaya çıkan EHEC bakterisinin kaynağının da filizler olmuş olduğu hatırlatıldı. Öte yandan, Moskova, Almanya’da görülen E.coli salgınını takiben, AB üyesi ülkelerden tüm sebze ithalatını ve satışını yasaklamıştı.

6 Haziran 2011

Clinical Microbiology Reviews, January 1998, p. 142-201, Vol. 11, No. 1

Classic mechanisms of action of ETEC toxins (see the text for details and additional proposed mechanisms). (A) LT-I. The LT holotoxin, consisting of one A subunit and five B subunits, is internalized by epithelial cells of the small bowel mucosa via endocytosis. The A1, or catalytic, subunit translocates through the vacuolar membrane and passes through the Golgi apparatus by retrograde transport. In the figure, the A subunit is shown passing through the B subunit ring, but this may not be the case in vivo. A1 catalyzes the ADP-ribosylation of arginine 201 of the α subunit of Gs-protein (which may be apically located); the ADP-ribosylated G-protein activates adenylate cyclase, which elicits supranormal levels of intracellular cAMP. cAMP is an intracellular messenger which regulates several intestinal epithelial cell membrane transporters and other host cell enzymes, as well as having effects on the cytoskeleton. The activation of the cAMP-dependent A kinase results in phosphorylation of apical membrane transporters (especially the cystic fibrosis transmembrane conductance regulator), resulting in secretion of anions (predominantly Cl− by a direct effect, and HCO3 −indirectly) by crypt cells and a decrease in absorption of Na+ and Cl− by absorptive cells. cAMP may also have important effects on basolateral transporters and on intracellular calcium levels, both of which may increase the magnitude of the effects on fluid and ion transport. (B) STa. Less is known about the action of ST than of LT. ST is thought to act by binding the ST membrane receptor, GC-C. Activation of GC-C results in increased levels of intracellular cGMP. cGMP exerts its effects in increasing chloride secretion and decreasing NaCl absorption by activating the cGMP-dependent kinase (G-kinase) and/or the cAMP dependent kinase (A-kinase). Other effects of STa in inducing fluid secretion have also been postulated
SUMMARY
INTRODUCTION
ISOLATION AND IDENTIFICATION
Biochemicals
Serotyping
Phenotypic Assays Based on Virulence Characteristics
Molecular Detection Methods
Nucleic acid probes.
PCR.
COMMON THEMES IN E. COLI VIRULENCE
ENTEROTOXIGENIC E. COLI
Pathogenesis
Heat-labile toxins.
(i) LT-I.
(ii) LT-II.
Heat-stable toxins.
(i) STa.
(ii) STb.
Colonization factors.
Epidemiology
Clinical Considerations
Detection and Diagnosis
ENTEROPATHOGENIC E. COLI
Pathogenesis
Attaching-and-effacing histopathology.
Three-stage model of EPEC pathogenesis.
(i) Localized adherence.
(ii) Signal transduction.
(iii) Intimate adherence.
Secreted proteins.
Locus of enterocyte effacement.
EAF plasmids.
Regulation.
Other potential virulence factors.
(i) Other fimbriae.
(ii) EAST1.
(iii) Invasion.
Mechanism of diarrhea.
Epidemiology
Age distribution.
Transmission and reservoirs.
EPEC in developed countries.
EPEC in developing countries.
Clinical Considerations
Detection and Diagnosis
Definition of EPEC.
Diagnostic tests.
(i) Phenotypic tests.
(ii) Genotypic tests.
(a) eae gene.
(b) EAF plasmid.
ENTEROHEMORRHAGIC E. COLI
Origins
Pathogenesis
Histopathology.
Shiga toxins.
(i) Structure and genetics.
(ii) Stx in intestinal disease.
(iii) Stx in HUS.
EAST1.
Enterohemolysin.
Intestinal adherence factors.
pO157 plasmid.
Iron transport.
Other potential virulence factors.
Epidemiology
Incidence.
Animal reservoir.
Transmission.
Non-O157:H7 serotypes.
Clinical Considerations
Clinical disease.
Treatment.
Vaccines.
Diagnosis and Detection
General considerations.
(i) Why and when to culture.
(ii) Biosafety issues.
(iii) Diagnostic methods.
Culture techniques.
Immunoassays.
(i) O and H antigens.
(ii) Shiga toxins.
(iii) Other antigens.
(iv) Immunomagnetic separation.
(v) Free fecal cytotoxic activity.
DNA probes and PCR.
(i) Detection of stx genes.
(ii) Detection of eae genes.
(iii) Detection of the pO157 plasmid/hemolysin gene.
(iv) Detection of other genes.
Strain subtyping.
Serodiagnosis.
ENTEROAGGREGATIVE E. COLI
Pathogenesis
Histopathology.
Adherence.
EAST1.
Invasiveness.
Cytotoxins.
Model of EAEC pathogenesis.
Epidemiology
Clinical Features
Detection and Diagnosis
HEp-2 assay.
DNA probe.
Other tests for EAEC.
ENTEROINVASIVE E. COLI
Pathogenesis
Invasiveness.
Enterotoxin production.
Epidemiology
Clinical Considerations
Detection and Diagnosis
DIFFUSELY ADHERENT E. COLI
Pathogenesis
Epidemiology
Clinical Features
Detection and Diagnosis
OTHER CATEGORIES OF E. COLI WHICH ARE POTENTIALLY DIARRHEAGENIC
CONCLUSIONS
ACKNOWLEDGMENTS
REFERENCES

ETEC
Characteristics:
Distinguished from other E. coli pathotypes their by production of enterotoxins LT (heat-labile enterotoxin) and ST (heat-stable enterotoxin). ETEC strains might express only an LT, only an ST, or both LTs and STs
Pruducing one or more colonization factors (CFs) that mediate attachment to intestinal mucosal surfaces, a central step in ETEC virulence
Figures:

Pathogenic schema of ETEC

Major virulence factors in ETEC:
Adherence
Adhesive fimbriae
Toxin
Heat-labile toxin (LT)
Heat-stable toxin (ST)

Diğer E.coli virulansları için tıklayınız

E. coli is one of the most common bacteria found in the gut of animals. This includes humans. There are other animal species that contain this organism in the gut including reptiles and fish. E. coli colonizes the gut within a few hours or days of birth depending on the species involved. In humans the intestines can be colonized within 40 hours of birth. E. coli adheres to the mucus overlaying the large intestine. Other bacteria that are growing in the gut may be intestinal pathogens including Salmonella,
Shigella, Yersinia, Enterobacter, Enterobacter, and Klebsiella all of these may be associated with human illness.
Physiologically, E. coli can grow in the presence or absence of oxygen (O2), this is referred to as being facultatively anaerobic. E. coli can respond to environmental signals such as chemicals, pH, temperature, osmolarity, etc., and can swim toward or away from them. In response to changes in the environment E. coli can change the size of the outer membrane pores to accommodate larger molecular nutrients or exclude inhibitory substances. Treatment of water with chlorine, bromine or ozone interferes with the membranes ability to transport nutrients.
“E. coli is the predominant facultative organism in the human intestinal tract, however, it makes up a very small proportion the total bacterial count. Other bacteria such as Bacterioides out number E. coli by 20: 1. It is the regular presence of E. coli in the intestine that leads to its use as an indicator of fecal contamination of water and wastewater.
Over 700 serotypes of pathogenic E. coli, have been recognized based on O(body antigen), H (flagellar antigen), and K (capsular antigen) antigens. Serotyping is important in distinguishing the small number of strains that cause disease. E. coli can cause infection in the urinary tract and brain stem (meningitis) as well as intestinal diseases referred to as gastroenteritis.
There are five classes of E. coli that produce disease. They are classified by the method of pathogenesis: 1) toxins (enterotoxigenic), 2) invasive (enteroinvasive), 3) hemorrhagic (enterohemorrhagic), 4) pathogenic (enteropathogenic), and 5) aggregative (clumping or enteroaggregative). The pathogenesis may be described as:
Enterotoxigenic;
These are important in causing diarrhea in infants and travelers especially in regions of poor sanitation. The disease may vary from minor discomfort to a severe cholera like disease. Disease requires colonization and excretion of one or more toxins. These toxins lead to secretion of fluid and resulting diarrhea.
Enteroinvasive;
This type closely resembles shigellosis in its mechanism. These organisms penetrate the cell wall of the colon causing cell destruction and extreme diarrhea. They do not produce shiga toxin.
Enteropathogenic;
The E. coli induces a watery diarrhea. The organisms to adhere to the intestinal mucosa and are “moderately-invasive” which causes an inflammatory response. The diarrhea and other symptoms are probably caused by invasion of the host cells and interference with cellular process rather that by production of toxins.
Enteroaggregative;
The distinguishing feature is the ability of the organism to attach to tissue culture cells in an aggregative manner. These strains are associated with persistent diarrhea in young children. They adhere to the intestinal mucosa and cause non-bloody diarrhea and inflamation. This may be related to toxin production.
Enterohemorrhagic (EHEC);
This syndrome is represented by a single strain (serotype O157:H7) which causes diarrhea distinct from some others (including Shigella)in that there is copious bloody discharge and no fever. The life threatening situation is its toxic effects on the kidneys (hemolytic uremia). The E. coli does not invade the intestinal mucosa as readily as Shigella but does produce two toxins that are virtually identical to shiga toxin. The toxins play a role in the intense inflammatory response and are enhanced by iron deficiency2 .
At this time E. coli O157:H7 is a difficult organism for which to screen. It does not grow well at 44.5°C ( defines fecal coliforms from total coliforms) and therefore is not indicated as a fecal coliform. It does not cleave(split) MUG and therefore does not show as E. coli in Colilert. It does show as a presumptive positive in P/A broth and as a Total Coliform in Colilert. We should take the Total Coliform and presumptive positives a little more serious than we have in the past.
At this time we sub-culture all presumptive positives in P/A media onto Sorbitol MacConkey’s medium which will give us a presumptive positive for E. coli O157:H7. The colonies are clear rather than red for the normal E. coli organism. It so happens that Pseudomonas also gives clear colonies and is everywhere in water and makes it difficult to differentiate the organisms. So far, we have been using this procedure for about 2 years on drinking water and have not had an O157:H7 positive verified.
If we did find an isolate of O157:H7 the Diagnostic Lab is able to supply us with anti-sera for serotype identification and Pulse Field gel electrophoresis to determine its exact type.
We are now considering a new medium called CHROMagar O157 but have not put it into production. It is an expensive medium, as all new defined substrate media are, but we will try to move ahead and see if we can obtain some for experimentation.
One more difficulty is, that by the time we finish the analysis, we would not be able to stop an epidemic. That must be done by the vigilance of the Public Health Offices, City, County Health Departments and especially the physicians and nurses that are attending those individuals reporting with bloody diarrhea.

Selected Bibliography
1. Manual of Water Supply Practices: M48, First Edition,1999;
Waterborne Pathogens:1999;American Water Works
Association; Denver, CO.
2. Sonnenwirth, A.C., The Enteric Bacilli and Similar Gram-
Negative Bacteria, p 788 – 789 In, Microbiology, Second
Edition, 1973, Davis, B. et. al., Harper and Row, Hagerstown,
MD.
3. Todar, K.; University of Wisconsin Department of
Bacteriology; 1997; Bacteriology 330 Lecture: Pathogenic E.
coli; Cholera; Cryptosporidium.
www.bact.wsc.edu/bact303/bact303mainpage.

—-
http://www.kdheks.gov/envmicro/download/E_coli_Pathogenesis.pdf

Clinical Microbiology Reviews, January 2008, p. 26-59, Vol. 21, No. 1

Pathogenesis of biofilm formation on urinary catheters during CAUTIs. The inset (reprinted from reference 393) shows a scanning electron micrograph of a urinary catheter encrusted with P. aeruginosa.

Turkiye Klinikleri J Med Sci 2007, 27:768-773

“Enterotoksijenik Escherichia coli (ETEC), gelismekte olan ülkelerde turistler ve infantlarda ishalin önemli bir nedenidir. Kontamine yiyecek ve suların alınması ile geçer. Isıya duyarlı ve ısıya dirençli toksinler üretir. Bu toksinlerin genleri plazmidler tarafından kodlanır. Hastalık bakterinin kolonizasyonunu ve bir ya da daha fazla toksinin salınmasını gerektirir. Bakteri gastrointestinal sisteme, bir fimbrial adezin aracılığı ile kolonize olur, kolonizasyon faktör I ve II gibi. ETEC invaziv değildir. Isı labil toksin (LT) konak hücrede “cyclic adenosine monophosphate” (cAMP) artmasına neden olur. Isı stabil toksin (ST) konak hücre sitoplazmasında “cyclic guanosine monophosphate” (cGMP) seviyelerini artırır. Hücresel cAMP ve cGMP, sıvı ve elektrolitlerin salınımının artmasına yol açar. Bu, atessiz ishalle sonuçlanır. ETEC enfeksiyonu tanısı, gayta örneklerinden bakteri toksinleri saptandığı zaman konur. Oral rehidratasyon sıvısı çocuklarda hayat kurtarıcıdır. Çoğu hasta uygun destekleyici tedavi ile iyilesir. ETEC enfeksiyonundan bakteri ile kontamine yiyecek ve içeceklerden kaçınarak korunulabilir. Endemik alanda yetiskinlerde bağısıklık gelisir. Toksin ve “colonization-factor antigens” (CFA) temeline dayanan asılar, bagısıklamada en genis yeri tutar.”