171 O Ags : > 100 K Ags (groups A, L and B) : 56 H Ags formula.
Mobile genetic elements :
Virulence factors gene expresssion :
=> colibacillosis
diarrhoeagenic Escherichia coli
enteropathogenic
Escherichia
coli (EPECs) : O55, O86, O111, O114, O119, O125, O127, O128, O142.
They produce a type IV fimbria known as the bundle-forming pilus (BFP),
through which is secreted Tir, the receptor for the plasmid-coded,
membrane-attached non fimbrial adhesin intimin / Escherichia
adhesion factor (EAF), present only in type I but not in type II) =>
"attaching
and effacing". They produce an enterotoxin similar to Stx,
causing an inflammatory response. They have localized adhesion (LA)
to HEp-2 cells. Serotype O86 is cross-reactive with human blood group Ag
B.
"typical" EPEC (tEPEC) have both chromosomal (the locus of enterocyte
effacement (LEE) island) and plasmid-borne (residing on the EPEC
adherence factor (EAF) plasmid) virulence factors, which are linked
by common gene regulatorsref
"atypical EPEC" (aEPEC) carry only the LEE island (Kaper JB. Defining
EPEC. Rev Microbiol Sao Paulo. 1996;27(Suppl1):130–3). Previously, these
investigators reported a high prevalence of aEPEC among pediatric diarrhea
patients in Melbourne, including both infants and older children (in contrast
to the strong tendency for infants to be infected with tEPEC)ref.
In contrast to patients infected with other pathogens, patients infected
with aEPEC are far more likely to experience diarrhea past 14 days, the
point long recognized as a clinical watershed that heralds increased risk
for illness and deathref.
aEPEC's prevalence among diarrhea patients, the pathogen's strong association
with diarrheal symptoms, and the infection's distinctively persistent nature
argue for a high disease burden in Melbourne. Although the authors define
aEPEC strictly on the basis of positivity for the LEE eae gene and failure
to amplify a bfpA pilin gene (not assessing additional plasmid loci), the
absence of tEPEC serotypes and the occurrence of disease in children older
than infants suggest that these are indeed aEPEC
=> endemic diarrhea
in babies (cholera nostras) (lethality : 16%)
Some types of EPEC are referred to as enteroadherent E. coli
(EAEC), based on specific patterns of adherence.
=> traveler's diarrhea
in Mexico and in North Africa.
Chemotherapy : doxycycline
enterohemorrhagic Escherichia
coli (EHECs) after 3-4 days incubation => abdominal
pain
and watery diarrhea
=> hemorrhagic colitis => bloody diarrhea
(often the patient is afebrile) => self-limiting in 6-7 days or evolving
to hemolytic
uremic syndrome (HUS) / Gasser syndrome
in 5-15% of patients aged < 10 years (those harbouring symbiont Escherichia
coli strains susceptible to lytic infection by the bacteriophage encoding
Stx2, as once infected they become toxin producing cells, too; lethality
3-5%; death or ESRD in 12%; 25% of survivors have long term kidney disease
as a sequel)
Prevention : probiotic therapy with phage-resistant
Escherichia
coli strains Therapy : hemodyalisis.
Antimicrobials are uneffective.
Epidemiology : in 1996 21 elderly
people died and another 500 were made ill after eating contaminated meat
supplied by a butcher's shop in Wishaw, Lanarkshire, UK.
Clinically, the O157 infections had a higher frequency of bloody stools,
fecal leukocytes, abdominal pain with shorter symptom duration and far
higher frequency of hemolytic-uremic syndrome (although a cluster of O121
HUS cases associated with a lake in Connecticut, USA, has been reported).
Since toxin assay did not identify all O157 strains found on sMAC plates,
the investigators did not advocate performing toxin assay alone.
Prevention : keeping animals off the fields
for the preceding 3 weeks prior to recreational use, mow the grass, keep
it short. Any visible animal dropping should also be removed at the beginning
of the 3-week period.
It is considered by CDC as a category B biological
weapon.
enterotoxigenic Escherichia
coli (ETECs) : O6, O16, O18, O25, O27, O78, O148, O159. The same
or separate plasmid has ToxA and ToxB genes coding respectively for
p83heat-labile (LT) AB5 toxin (~ cholera
toxin) binds to GM1 and cause ADP-ribosylation of Gas
subunits.
heat-stable (ST) toxins
p8STI / Sta (which can occur as either STaI or STaII) is coded
by the plasmid Tn1681 : they act as agonist for the membrane-bound guanylyl
cyclase C
=> increase in [cGMP]i. => activation of CNG channels => influx
of Ca2+ => inhibition of DNA synthesis and proliferation. As
part of the tumor-suppressive guanylin, uroguanylin=>guanylyl cyclase C
pathway is frequently lost during colorectal
cancer (CRC)
progression, there is an inverse correlation between CRC and ETEC infections.
p5STII / STb is coded by a R-Ent plasmid :
colonization factors (CFA) I-V are fimbrial Ags
=> diarrhea
without fever
in both babies and adults (80% of "traveller's diarrhoea")
enteroinvasive Escherichia
coli (EIECs) : O28, O112, O115, O124, O136, O143, O144, O147, O152.
They produce Shigellaadhesin (but not toxin !).
O157:H7
(70%; don't ferment sorbitol, and lactose-fermenting colonies shown to
be E. coli that are selected for being sorbitol-negative are tested
for the somatic O157 antigen by latex agglutination. Rarely, a O157:H7
strain is sorbitol-fermenting and, more commonly, other strains that produce
Shiga toxin, such as E. coli that contain an alternative somatic
antigen, will cause HUS. In Germany, non-O157 strains may cause more HUS
than O157 strainsref).
Toxin production can be detected by immunoblot, and O157 antigen can be
detected by ELISA. Not only do these isolates ferment sorbitol, but they
also are tellurite-susceptibleref
and will not be isolated on cefixime-tellurite Sorbitol-MacConkey agar
(CT-SMAC), a selective medium for the usual E. coli O157. Sorbitol-fermenting
VTEC O157 grow as pink colonies on SMAC agar and some may grow relatively
poorly on CT-SMAC, although this property appears variable. If clinical
symptoms are suggestive of VTEC infection (particularly in children aged
under 15 years and adults aged over 65 years), and presumptive sorbitol
non-fermenting E. coli O157 colonies are not observed on SMAC or
CT-MAC agar, then sorbitol-fermenting colonies should be tested for agglutination
with E. coli O157 antiserum. Colonies giving agglutination should
be identified as E. coli and sent for confirmation, phage typing,
and detection of VT genes. Fecal samples from appropriate clinical cases
from whom VTEC O157 has not been isolated may be submitted for detection
of non-O157 VTEC. Lactose-fermenting
Salmonella species represent
a similar diagnostic problemref.
Although first recognized in Germany in 1988 during an outbreak of HUSref,
sorbitol-fermenting, verotoxigenic E. coli O157 was thought to be
restricted to continental Europeref
until an isolation in Australia in 2002. The first isolation in the UK
was reported in 2002 (1 case in Scotland), then in 2003 (1 case in Scotland),
2004 (1 case in England)ref,
and 2006 (4 cases in England)ref.
All isolates possessed genes for verocytotoxin (VT) 2, and pulsed field
gel electrophoresis of DNA fragments gave indistinguishable profilesref.
>> O26:H1 (motile), O103, O104:H21 (motile), O111:H2, O111:NM (or
H-) (nonmotile), O113, O121, O127, O128, O142, O145, O153, O163 (30%: don't
ferment sorbitol). O145 infections make up only 224 of 9358 reports (2.4%)
in the Enter-net VTEC database between the years 2000-2004. When data from
the United Kingdom and Ireland (where O157 infections predominate) are
excluded, O145 is the 4th most common serogroup reported in mainland Europe,
making up 224 of 5123 cases (4.4%). Underascertainment of non-O157 VTECs
is thought to be common, as stool samples are not routinely tested for
VTEC strains other than serogroup O157. Such non-O157 isolates can be obtained
from sheep and cattle and, although causing as much as 30% of outbreaks
of VTECref,
appear to be somewhat less virulent -- or at least more variable in virulence
-- in a variety of in vivo and in vitro assaysref1,
ref2,
ref3.
In analyzing the genetic and phenotypic profiles of non-O157 groups, it
has been found that they belong to their own lineages and have unique profiles
of virulence traits different from O157ref.
The serogroups appearing to be most prominent are O26, O111, O128, and
O103ref.
If a laboratory is using sorbitol-MacConkey (sMAC) plates to identify VTEC
by virtue of O157's ability to ferment sorbitol, the non-O157 strains will
be missed. In a 3-year pediatric study from the University of Washington,
USAref,
1851 stool samples were processed for sorbitol fermentation as well as
toxin production by EIA, and 28 strains of O157 were found along with O103
(4 strains), O118 (2 strains), O111 (2 strains), and 3 other strains. Clinically,
the O157 infections had a higher frequency of bloody stools, fecal leukocytes,
and abdominal pain with shorter symptom duration. 5 (18%) of O157 infections
developed hemolytic-uremic syndrome; none of the non-O157 strains did.
Since toxin assay did not identify all O157 strains found on sMAC plates,
the investigators did not advocate performing toxin assay alone. Non-O157
can produce hemolytic-uremic syndrome, as demonstrated by a cluster of
O121 cases associated with a lake in Connecticut, USAref.
Since toxin assays are not uniformly performed in many areas, and most
cases do not produce HUS, it is likely that cases due to non-O157 strains
are being missed. How frequent this phenomenon will become over time
is unclear
They arose from E.coli O55 + Shigella Stx gene => verotoxins
(i.e. toxic for Vero cell
line) :
verotoxin 1 (VT-1) / Shiga toxin 1
(Stx1) / Shiga-like toxin I (SLT-I), very similar to Shiga
toxin (Stx) produced by Shigella dysenteriae type I.
verotoxin 2 (VT-2) / Shiga toxin (Stx2) / Shiga-like toxin II (SLT-II),
dissimilar from Shiga toxin (Stx)
They are AB5 toxins : B subunits bind to CD77
/ Pk blood group antigen / globotriaosylceramide (Gb3), while A
subunit is an N-glycosylase that cleaves an A residue in rRNA 28S.
As for Stx, the operator region of Stx1 (but not Stx2) contains a consensus
fur box that is responsible for iron-regulated production. Neither iron
nor any other environmental factors examined affect the expression of Stx2.
However, intestinal mucus enhances the activity of some Stx2 variants.
The Stxs, which carry typical N-terminal leader sequences, are not
actively secreted from the bacterial cell and are thought to be released
into the milieu during cell lysis. Other virulence factors are eae,
intimin
(responsible for attachment of the organism and mucosal effacing lesions),
E-hly,
espA,
etp
and katP.
Epidemiology : those in rural environments,
with continuous exposure to cattle, have a lower risk as those who do not
have this kind of continuous exposure (adaptive immunity ?). Human VTEC
infection in dairy farm families was negatively associated with age (P
< 0.05) and was not associated with clinical illness. Many dairy farm
residents experience subclinical immunizing VTEC infections at a young
age, which frequently involve non-O157 VTEC found in cattleref.
Argentina has the highest incidence of HUS in the world, 400 cases per
year, 7 times higher compared to other affected countries
UK : the techniques of ELISA and immunoblotting were used to examine a
total of 1667 serum specimens, from apparently healthy members of rural
communities in England, for antibodies to the LPS of E. coli O157
and VTs. 29 specimens from 22 individuals were shown to have antibodies
specific for
E. coli O157 LPS. Some of these lived on livestock
farms and had occupational contact with cattle, suggesting that personnel
working with farm animals may produce serum antibodies to the O157 LPS
antigens. 15 people had IgG class antibodies to O157 LPS, suggesting long-term
exposure to E. coli O157, and 5 people had serum antibodies, on
more than one occasion, showing evidence of persistent antibodies to O157
LPS. 13 specimens, from 12 of 22 individuals, also contained antibodies
to VT1, VT2, or both toxins. 10 specimens contained antibodies to VT1 and
VT2, 3 contained antibodies to VT2 onlyref.
In rural areas, most individuals carrying VTEC isolates were asymptomatic,
whereas in urban areas, a significant association was found between VTEC
isolation and diarrhea (p < 0.01)ref.
There is a greater level of exposure of dairy farm residents to VT-producing
E.
coli (VTEC) strains. The high rate of seropositivity to VT1 in farm
residents probably reflects the booster effect of repeated VTEC exposures
and argues against a sustained generalized immunosuppressive effect of
VT1. Seroepidemiological studies may help in assessing the level of exposure
of different populations to VTEC strainsref.
Cases in Cornwall and west Devon associated with animal contact included
farm visitors, holiday-makers, and members of farming families and farm
workersref.
157 cases (97 microbiologically confirmed : all phage type (PT) 21/28 and
produce verotoxin (VT) 2, with the exception of 1 case that is PT32 VT2),
65% in children of school age, occurred in Wales from 10 to 30 Sep 2005
in over 40 schools, with one death in a 5-year-old boy, caused by contamination
of sliced cooked meatref1,
ref2,
ref3,
ref4,
ref5
the finding of asymptomatic individuals with stool cultures positive for
a VTEC organism is not uncommon either in a cluster setting or an endemic
one. In one study, fecal samples from 350 farm workers on 276 dairy farms
and 50 abattoir employees from 7 different operations were examined for
the presence of VTEC O157 by an O157-specific enzyme-linked fluorescent
assay followed by immunoconcentration. VTEC O157 was isolated from 4 (1.1%)
of the farm workers. A 2nd stool sample was obtained from the positive
farm workers as well as from their household contacts. VTEC O157 was isolated
from the wife of one of them. The strains from the same household shared
the same Verocytotoxin genes profile, phage type and pulsed-field gel electrophoresis
pattern. The VTEC O157+ subjects had neither intestinal symptoms
at [that time] of sampling nor a history of bloody diarrhoea or renal failure.
Farm residents often develop immunity to VTEC O157 infection, possibly
due to recurrent exposure to less virulent strains of VTECref
Chronology of E. coli O157 outbreaks in Scotland :
1990 : an outbreak (16 cases, 4 HUS) of E. coli O157 infection was
associated with a restaurant in Lothian.
1992 : an outbreak (6 cases, 1 HUS) of E. coli O157 infection was
associated with a paddling pool.
1994 : an outbreak (22 cases) of E. coli O157 infection involved
6 health boards.
1996 : an outbreak (512 confirmed cases, 151 hospitalized; 34 HUS or TTP;
22 fatal) was traced to meat from a local butcher. 75% of the cases
were reported from Lanarkshire. During this period, 87 suspected or confirmed
cases were also registered in Forth Valley, Greater Glasgow and Lothian.
1996 (publication year) : an outbreak (711 cases) of Campylobacter
and E. coli O157 infections in Fife was caused by contaminated water.
1997 : an outbreak (37 cases) at Falkirk and District Royal Infirmary was
caused by E. coli O157 phage type 8.
1999 : an outbreak (8 cases) at a primary school in Aberdeenshire was ascribed
to unpasteurized goat cheese.
1999 : an outbreak (30 cases, 1 with HUS) at a school in the Grampian region
was ascribed to goat cheese.
1999 : an outbreak (6 cases) in Wester Ross (western coast) was traced
to contaminated water.
2000 : an outbreak (40 clinical cases, 2 confirmed) of E. coli O157
infection was reported at a scout camp.
2001 : an outbreak (30 cases, 2 HUS, 0 fatal) of E. coli O157 phage
type 1/28 infection in Lancashire was ascribed to cross-contamination
on a butcher shop counter.
2002 : an outbreak (5 cases) of E. coli O157 infection was reported
among members of a family in Aberdeenshire.
2002 : an outbreak (15 cases) of E. coli O157 infection was reported
among Highland campers.
2005 : an outbreak (10 confirmed, 5 suspected cases) was reported among
Scottish tourists returning from resorts on Turkey.
Notes: E. coli O157 infection accounts for > 90% of hemolytic-uremic
syndrome (HUS) cases in Scotland. 45 cases (7 fatal) of HUS were reported
during 2003 to 2004 - including 43 cases related to E. coli infection.
USA : causes about 73 000 illnesses and 61 deaths annually in USA (in Hawaii
: 9 cases in 2005, 10 cases in 2004, 9 cases in 2003). Escherichia coli
O157:H7 was isolated in 0.39% (range 0.07% to 2.13%) of diarrheal stools
in a multicenter survey conducted during 1990 to 1992 - isolation rates
were 0.13% in the South and 0.57% in the North. The true national incidence
is estimated at 725,000 per year, with 100 to 200 fatalities.
a major outbreak of hemorrhagic colitis involving 501 cases (151 hospitalized,
4 fatal) in Washington State during 1992 to 1993 was traced to hamburger.
E. coli O157:H7 is a leading cause of bloody diarrhea and of childhood
renal failure in this country. 204 children below age 5 died of E. coli
diarrhea during 1968 to 1991.
10,000 to 20,000 annual infections are estimated. 16 outbreaks were reported
during 1993, and 11 during January to June 1994. 1,420 cases of E. coli
O157:H7 infection were reported in 1994; 2,139 in 1995; 2,705 in 1996;
615 first half of 1997.
21 cases of post-diarrheal HUS were reported during the first half of 1997.
unpasteurized apple juice was implicated in 3 outbreaks (and 1 fatality)
during 1996.
alfalfa sprouts were responsible for 60 cases in Michigan (25 hospitalized;
2 HUS; none fatal) and 48 cases (11 hospitalized) in Virginia during 1997.
an outbreak of 15 cases during 1997 resulted in a massive recall of commercially-distributed
frozen beef patties.
Canada : in the spring of 2000, in Walkerton, a town of 5000 in southern
Ontario, an outbreak of E. coli O157:H7 infection claimed 7 lives
-- 6 adults and a child -- and over 200 were seen at local area hospitals
animal or human feces : secondary cases of E.coli O157 in a household
may still occur, since excretion of the bacillus in the stool of infected
children can be seen for as long as 3 weeks. Day care centers have long
been recognized as sites of E. coli O157 outbreaks. As with many
other enteropathogens found in day care center outbreaks, spread is frequently
hand-to-mouth or fomite to mouth, without any food or water source being
recognized. Toddlers are marvelous sharers of toys as well as fecally contaminated
hands. In one studyref,
all companion animal (pigs, dogs, parrot and iguanas (n = 48)) isolates
of E. coli O157 strains were Shiga-toxin negative. In anotherref,
the toxin producing strains from healthy companion animals constituted
a very heterogeneous group of E. coli, and many appeared to be specific
for their hosts. The absence of eae (attaching and effacing) sequences
in most animal STEC strains was felt to indicate that these strains are
less virulent for humans than the classical eae-positive enterohemorrhagic
types. The Shiga- like toxin II genes were frequent in these strains, were,
however, found in strains from healthy dogs, but were rarely found in isolates
from other animals. Disease can occur in companion animals, however, as
experimental inoculation of dogs was found to cause an illness similar
to hemolytic uremic syndrome in a non-O157 STEC strainref.
To this point, however, Shiga toxin producing E. coli disease in
dogs, cats or birds has not at all been an epidemiologic factor in human
cases. The closeness of dogs and cats to young children in a household
would
likely have produced such an association if such transmission occurred
commonly.
contaminated beef in undercooked fast-food hamburgers (people need to cook
hamburger thoroughly, to 155-160°F = 68-71°C to kill the bacteria).
The bacteria associated with the steak are usually external, meaning that
the pathogen would be killed by heat, which would not inactivate internal
bacteria. But since a lot of meat is injected with tenderizers or flavor-enhancing
solutions, the bacteria could be inoculated internally. Other transmissions
can occur via petting zoos
other material can be contaminated, including salad ingredients (leaf lettuce,
iceberg lettuce, mesclun lettuce, romaine lettuce, alfalfa and clover sprouts,
restaurant coleslaw), unpasteurized apple juice, or rarely spoled pasteruzied
milkref
landed directly in their mouth when air is dusty from the rafters, the
walls and the sawdust in the building
when people drink, or swim inref1,
ref2,
ref3,
tainted water
water -- either drunk or swum in -- may also be a vehicle for transmission
=> aspecific diarrhea
=> hemolytic
uremic syndrome (HUS) / Gasser syndromeref.
The risk of HUS developing after E. coli O157:H7 is < 15% (in
children < 10 years old, the highest risk group). Typically HUS develops
after 5 to 13 days of illness with the onset of diarrhea being day 1.
Although sometimes prolonged, the usual incubation period of E. coli
O157:H7
diarrhea after exposure is 3-4 daysref.
The gastrointestinal illness is usually quite prominent, but HUS has been
reported in patients with asymptomatic infection with the organismref1,
ref2.
Post-illness shedding of O157:H7 can be prolonged, contributing to secondary
cases, but it is probable that transmissibility is greatest during the
initial diarrheal phaseref.
=> asymptomatic infection with E. coli O157:H7 does occur but
is thought to be uncommon.
Therapy : the proceedings of a recent
seminar on this illness, published in March 2005 in The Lancetref,
categorically states that antimicrobial agents, antimotility agents, narcotics
(also antimotility), and non-steroidal anti-inflammatory agents (can diminish
renal blood flow) should be avoided.
although a number of studies, including an oft-cited one from the New England
Journal of Medicineref
suggest that antimicrobial therapy increases the risk of HUS, a more recent
meta-analysisref
revealed a pooled odds ratio of only 1.15 with CI95 of 0.79-1.68,
suggesting no higher risk. A thoughtful and analytic editorial in the same
issue of JAMA by Molbak and colleaguesref
agreed that the bottom line in this issue is not yet known and may relate
to the particular strain of O157, the antimicrobial used, and the timing
of antimicrobial treatment
regarding the use of antimotility agents, a retrospective analysis of 278
children who developed O157 enteritis during a 1993 outbreak in Washington
State USA had an odds ratio of 2.9 with CI 1.2-7.5ref.
In those who did not develop HUS, there was no difference in the median
duration of diarrhea among children who received antimotility agents, but
the median duration of bloody diarrhea was longer (4 vs. 3 days, p <
0.05). In another study of 118 E. coli O157 enteritis casesref,
a relative risk of 44.11 was found for those receiving prolonged antimotility
agents with CI 8.48-229.4.
avoiding unnecessary surgery if the patient presents with significant abdominal
pain and bloody diarrhea or just gross blood, which might suggest an ischemic
colitis in an adult or an intussusception
in a child
intravenous plasma expansion with fluids could lower the risk of developing
hemolytic uremic syndromeref
Prevention : cook very well ground beef, avoid
cross-contamination, practice correct personal hygiene
Web resources : International
VTEC/STEC Club (IVC)
uropathogenic Escherichia
coli (UPEC) (O1, O2, O4, O6, O7, O75), which also produce :
cytotoxic necrotizing factors (CNF) p115CNF1 and 2, which
catalyze deamidation of the Gln residue at position 63 of Rho to Glu. This
amino acid change produces a dominant active Rho protein unable to hydrolyze
bound GTP.
peculiar K Ags
type 1 fimbriae
adhesive type 1 pili have a crucial role during infection by mediating
the attachment to and potentially the invasion of host tissue. These filamentous,
highly oligomeric protein complexes are assembled by the 'chaperone–usher'
pathway, in which the individual pilus subunits fold in the bacterial periplasm
and form stoichiometric complexes with a periplasmic chaperone molecule
that is essential for pilus assembly. The chaperone subsequently delivers
the subunits to an assembly platform (usher) in the outer membrane, which
mediates subunit assembly and translocation to the cell surface. The periplasmic
type 1 pilus chaperone FimC binds non-native pilus subunits and accelerates
folding of the subunit FimG by 100-fold. Moreover, the FimC–FimG complex
is formed quantitatively and very rapidly when folding of FimG is initiated
in the presence of both FimC and the assembly-competent subunit FimF, even
though the FimC–FimG complex is thermodynamically less stable than the
FimF–FimG complex. FimC thus represents a previously unknown type of protein-folding
catalyst, and simultaneously acts as a kinetic trap preventing spontaneous
subunit assembly in the periplasmref.
P fimbriae / pyelonephritis-associated pili (PAP) binds specifically
to D-Gal-D-Gal disaccharides
contained in the P blood group Ag on RBCs and on surfaces of uroepithelial
cells in approximately 99% of the population (remaining 1% never experience
E.
coli UTI)
a-hemolysins, pore forming on all kinds of blood
cells
b-hemolysins, chemotaxis inhibitor
UPECs are embedded within pod-like bulges with cytoplasm of urothelial
cells whose shells contain uroplakin
and a fibrous polysaccharide matrix similar to biofilms found in ECM. Based
on the degree of protrusion into the bladder lumen, the biofilms approximately
double the volume of each infected cell
=> urinary
tract infections (UTI) and colibacilluria
Cytolysin A (ClyA), a pore-forming toxin with hemolytic and cytolytic
properties : it exported from the bacterial cells in outer-membrane vesicles
constantly discharged from the surface of the cell during bacterial growth
that can fuse with mammalian target cells and subsequently discharge their
toxic cargo. Periplasmic ClyA is kept in monomeric form by a disulphide
bond, whereas the relevant cysteine residues are reduced in the protein
from the vesicles, which oligomerize to form the large complexes suggested
to be the active form of pore assemblies. Since the redox status of periplasmic
proteins depends on the activity of specific membrane-bound and periplasmic
disulphide bond isomerases/oxidases, that ClyA can bypass this thiol-redox
pathway suggests that bacteria can sort proteins when forming vesicles,
excluding certain periplasmic proteins such as those catalyzing the formation
of disulphide bonds.
=> osteomyelitis => acute
cholecystitis => ecthyma
gangrenosum => the colonic mucosa of patients with colorectal
carcinoma (CRC)
but not normal colonic mucosa is colonized by intracellular E. coli
:
bacterial concentrations of 103-105 CFU/mL were detected
in biopsy specimens from both malignant and macroscopically normal tissue
in 90% and 93% of patients with adenoma and carcinoma, respectively.
E.
coli and coli-like bacteria were shown to colonize the colonic
mucosa in 82% of these patients. The gentamicin protection assay indicated
that E. coli was partially intracellular in 87% of patients with
adenoma and carcinoma and in none of the controlsref => colibacillosis gravidarum : severe infection with Escherichia
coli during pregnancy.
Prevention : homologous
hyperimmune serum.
Web resources :