Transcript Enterohemorrhagic E. coli

Enterobacteriaceae
Transmitted by the fecal-oral route
Primary pathogens
Organisms capable of causing
disease in anyone
Shigella
Opportunistic pathogens
Organisms that can only cause disease
under certain conditions or in certain hosts
E. coli
Salmonella
Yersinia
Providencia
Klebsiella
pneumoniae
Morganella
Proteus
Enterobacter
Senatia
Characteristics shared by all
members of family
Enterobacteriaceae
G-, non-spore forming rods
Peritrichous flagella
-shigella: nonmotile
Facultative anaerobe
Not fastidious
Active metabolism
- All ferment glucose;
- All reduce nitrates to nitrites;
- All oxidase negative
- Lactose fermentation: the key measure to isolate
and identify the Enterobacteriaceae
+: nonpathogenic
-: pathogenic
EMB plate
MacConkey agar
Triple sugar iron agar (TSI)
Antigenic structures
LPS (endotoxin) – O antigen.
Most are motile by peritrichous flagella --H antigens.
Capsule – K antigen ( Vi for Salmonella).
Cell envelope (wall)
various outer membrane proteins.
Pili - various antigen types, some encoded by plasmids
Enterobacteriaceae:
gastrointestinal diseases
– Escherichia coli
– Salmonella
– Shigella
– Yersinia entercolitica
Serotypes
• reference laboratory
– antigens
• O (lipopolysaccharide)
• H (flagellar)
• K (capsular)
O6:K15:H6
(I) Escherichia coli
Medical significance
Normal flora
E. coli is the
majority of GI
normal flora
Opportunistic
pathogen
pathogen
Extraintestinal
infection
Intestinal tract
infection
Urinary tract infection
Septicemia
Neonatal meningitis
ETEC
EIEC
EPEC
EHEC
EAggEC
Escherichia coli
• Toxins: two types of enterotoxin; Shiga-type toxin;
Enteroaggregative ST-like toxin; Hemolysins; Endotoxin
• Type III secretion system
• Adhesions: colonization factors ; both pili or fimbriae; nonfimbrial factors involved in attachment. There are at least 21
different types of adhesions.
• Virulence factors that protect the bacteria from host defenses:
Capsule/Iron capturing ability (enterochelin)
• Outer membrane proteins
What is the pathogenesis of these five
groups of pathogenic E. coli?
Gastroenteritis caused by E. coli
Enterotoxigenic E. coli (ETEC)
• A watery diarrhea, nausea, abdominal cramps and
low-grade fever for 1-5 days.
• Travellers diarrhea and diarrhea in children in
developing countries
• Transmission is via contaminated food or water.
• diarrhea like cholera
• milder
• nursery travellers diarrhea
• caused by LT, ST, or LT/ST.
Enterotoxigenic E. coli (ETEC)
• Heat labile toxin
• like choleragen
• Adenyl cyclase activated
• cyclic AMP
• secretion water/ions
• Heat stable toxin
• Guanylate cyclase activated
• cyclic GMP
• uptake water/ions
LT vs ST activity
Enteroinvasive E. coli (EIEC)
• The organism attaches to the intestinal mucosa via pili
• Outer membrane proteins are involved in direct penetration,
invasion of the intestinal cells, and destruction of the
intestinal mucosa.
• There is lateral movement of the organism from one cell to
adjacent cells.
• Symptoms include fever, severe abdominal cramps, malaise,
and watery diarrhea followed by scanty stools containing
blood, mucous, and pus.
• resembles shigellosis
Enteroinvasive E. coli (EIEC)
• Dysentery
- rearrangement of intracellular actin
- resembles shigellosis
- elder children and adult diarrhea
Enteropathogenic E. coli (EPEC)
• Malaise and low grade fever diarrhea, vomiting, nausea, nonbloody stools
• Bundle forming pili are involved in attachment to the intestinal
mucosa.
• This leads to changes in signal transduction in the cells,
effacement of the microvilli, and to intimate attachment via a
non-fimbrial adhesion called intimin.
• This is a problem mainly in hospitalized infants and in day
care centers.
Enteropathogenic E. coli (EPEC)
•
•
•
•
•
•
fever
infant diarrhea
vomiting
nausea
non-bloody stools
Destruction of surface microvilli
- loose attachment mediated by bundle forming pili (Bfp);
- Stimulation of intracellular calcium level;
- Rearrangement of intracellular actin
Enterohemorrhagic E. coli (EHEC)
• Hemorrhagic
– bloody, copious diarrhea
– few leukocytes
– afebrile
• Hemolytic-uremic syndrome
– hemolytic anemia
– thrombocytopenia (low platelets)
– kidney failure
Enterohemorrhagic E. coli (EHEC)
• Vero toxin
– “shiga-like”
•
Hemolysins
• younger than 5 years old,causing
hemorrhagic colitis
Enterohemorrhagic E. coli (EHEC)
• Usually O157:H7
Transmission electron
micrograph
Enteroaggregative E. coli (EaggEC)
• a cause of persistent, watery diarrhea with vomiting and
dehydration in infants.
• That is autoagglutination in a ‘stacked brick’ arrangement.
• the bacteria adheres to the intestinal mucosa and elaborates
enterotoxins (enteroaggregative heat-stable toxin, EAST).
• The result is mucosal damage, secretion of large amounts of
mucus, and a secretory diarrhea.
Enteroaggregative E. coli (EaggEC)
• Mucous associated autoagglutinins cause aggregation of
the bacteria at the cell surface and result in the formation
of a mucous biofilm.
• The organisms attach via pili and liberate a cytotoxin
distinct from, but similar to the ST and LT enterotoxins
liberated by ETEC.
• Symptoms incluse watery diarrhea, vomiting, dehydration
and occasional abdominal pain.
Summary of E. coli strains
that cause gastroenteritis.
Organi
sm
Virulence factors
Adherence
ETEC
Colonization factors
of adherence
(CFAs)
Type 1 pili
EIEC
Type 1 pili
Afimbrial adhesins
EPEC
Bundle-forming pili
(BFP)
Type 1 pili
Intimin
Type 1 pili
Afimbrial adhesins
EHEC
EaggEC
Mucus-associated
autoagglutination
Type 1 pili
Toxins
invasion
Endotoxin
Noninvasive
Heat-labile enterotoxin
(LT)
Heat-stable enterotoxin
(ST)
Endotoxin
Very invasive
Type III
secretion
system
Endotoxin
Poorly invasive
serovar
O6:K15:H6
28
2, 55
Shiga toxin
Endotoxin
Probably poorly O157:H7
invasive
Endotoxin
Cytotoxin
(enteroaggregative STlike toxin)
Noninvasive
O42
organism
Site
Disease
pathogenesis
Traveler’s diarrhea, infant diarrhea Heat-stable and/or heatEnterotoxigenic E. Small
labile enterotoxins,
coli (ETEC)
intestine in under developed countries,
watery diarrhea, cramps, nausea,
low-grade fever
Enteroinvasive E.
coli (EIEC)
Fever, cramping, watery diarrhea
Large
intestine followed by development of
Enteropathogenic
E. coli (EPEC)
Infant diarrhea with fever, nausea,
Small
intestine vomiting, nonbloody stools
stimulate guanylate or
adenylate cyclase activity
with fluid and electrolyte
loss
Plasmid-mediated
invasion and destruction
dysentery with scant, bloody stools of epithelial cells lining
colon
plasmid-mediated
adherence and
destruction of epithelial
cells
Hemorrhagic colitis with severe
Mediated by cytotoxic
Enterohemorrhagi Large
c E. coli (EHEC) intestine abdominal cramps, watery diarrhea “vero-toxin”
initially, followed by grossly
bloody diarrhea, little or no fever,
hemolytic uremic syndrome (HUS)
Persistent infant diarrhea,
Enteroaggregative Small
E. coli (EAggEC) intestine sometimes with gross blood, lowgrade fever
Aggregative adherence
mediated by plasmid
Various Types of E. coli
“Nonintimate” association:
bacteria attach to host cell by bundleforming pili
Bacterial attachment:
signal transduction event stimulated;
host cell tyrosine kinase activated;
Ca2+ levels increase
“Intimate” contact:
pedestallike structure (composed of actin fibers)
forms in host cell under bacteria (intimin)
Escherichia coli
• In the diagnostic laboratory generally the groups are not
differentiated and treatment would be on symptomatology.
• Generally fluid replacement is the primary treatment.
• Antibiotics are generally not used except in severe disease or disease
that has progressed to a systemic stage (e.g.hemolytic-uremia
syndrome).
• Two major classes of pili are produced by E. coli : mannose sensitive
and mannose resistant pili. The former bind to mannose containing
glyocoproteins and the latter to cerebrosides on the host epithelium
allowing attachment. This aids in colonization by E. coli.
Sanitary significance
• Total bacterial
number: number of bacteria
contained per ml or gm of the sample; the standard
of drinking water is less than 100.
• Coliform bacteria index: the number of coliform
bacteria detected out per 1000 ml sample; the
standard of drinking water is less than 3
(II) Shigella
dysentery bacterium
Genral features
• Pili.
• Most strains can not ferment lactose; S. sonnei
can slowly ferment lactose.
• According to O antigen, 4 groups
• Easily causing drug-resistence.
Classification
Serogroup
Species
Number of serotypes
A
S. dysenteriae
10
B
S. flexneri
13
C
S. boydii
18
D
S. sonnei
1
The classification is based on O antigens
What disease is caused by Shigella species?
Bacillary dysentery
shigellosis
Bacillary dysentery
• Source
- humans are the only reservoir
• Transmission
- the fecal-oral route
• Clinical findings
-watery diarrhea
-abdominal cramps
-tenesmus
-bloody stool with mucus and pus
-fever
• Clinical types
- acute dysentery
acute toxic dysentery
-chronic dysentery
Shigellosis
• within 2-3 days
– epithelial cell damage
• bloody feces
• intestinal pain
• pus
Shigellosis
• Invasiveness
• Endotoxin
• Exotoxin: Shiga toxin
- S. dysenteriae
- neurotoxic, enterotoxic and cytotoxic
Shiga toxin
• enterotoxic
• cytotoxic
• inhibits protein synthesis
– lysing 28S rRNA
Clinical significance
• man only "reservoir"
• mostly young children
– fecal to oral contact
– children to adults
• transmitted by adult food handlers
– unwashed hands
Clinical significance
• The infective dose required to cause infection is very low (10200 organisms).
• There is an incubation of 1-7 days followed by fever,
cramping, abdominal pain, and watery diarrhea (due to the
toxin)for 1-3 days.
• This may be followed by frequent, scant stools with blood,
mucous, and pus (due to invasion of intestinal mucosa).
• Is is rare for the organism to disseminate.
• The severity of the disease depends upon the species one is
infected with. S. dysenteria is the most pathogenic followed
by S. flexneri, S. sonnei and S. boydii.
immunity
• Primary immunity defense
- SIgA
• Immunity intensity
- Limited
- reasons
surface infection
various types
Diagnosis of Shigella infection
•
Specimen: stool.
•
Culture and Identification
•
Quick immunological methods:
- Immunofluorescent “ball” test;
- Coagglutination.
Prevention & Treatment
• streptomycin dependent (SD) dysentery
vaccine.
• manage dehydration
• patients respond to antibiotics , Problem of drugresistance
– disease duration diminished
Summary Shigella
• Shigella (4 species; S. flexneri, S. boydii, S. sonnei, S.
dysenteriae) all cause bacillary dysentery or shigellosis, (bloody
feces associated with intestinal pain).
• The organism invades the epithelial lining layer, but does not
penetrate.
• Usually, within 2-3 days, dysentery results from bacteria
damaging the epithelium lining layers of the intestine often with
release of mucus and blood (found in the feces) and attraction of
leukocytes (also found in the feces as "pus").
Summary Shigella
• Shiga toxin (chromosomally encoded) is neurotoxic, enterotoxic
and cytotoxic plays a role. The toxin inhibits protein synthesis
(acting on the 80S ribosome and lysing 28S rRNA).
• This is primarily a disease of young children occurring by fecal-
oral contact. Adults can catch this disease from children.
However it can be transmitted by infected adult food handlers,
contaminating food. The source in each case is unwashed hands.
Man is the only "reservoir".
• Patients with severe dysentery are usually treated with antibiotics
(e.g. ampicillin). In contrast to salmonellosis, patients respond to
antibiotic therapy and disease duration is diminished.
(III) Salmonella
Salmonella
•More than 2000 serotypes
•Transmitted by the fecal-oral routed
•Salmonellosis may present as one of several
syndromes including gastroenteritis, enteric
(typhoid) fever or septicemia.
•Zoonosis
Antigenic composition of Salmonella
• O antigen
• H antigen
• Vi antigen
- S. typhi and S. hirschfeldii
- Pathogenicity
- Screening of carriers (titer≥1:10)
- Inhibition of the agglutination of O Ags and the O Abs
The antigenic structures of salmonellae used in
serologic typing
Pathogenicity
• Virulence factors
• Endotoxin – may play a role in intracellular survival
• Capsule (for S. typhi and some strains of S. paratyphi)
• Adhesions – both fimbrial and non-fimbrial
• Enterotoxin - may be involved in gastroenteritis
• Outer membrane proteins - involved in the ability of Salmonella
to survive inside macrophages
• Flagella – help bacteria to move through intestinal mucous
Pathogenicity
• Virulence factors
• Type III secretion systems and effector molecules –
2 different systems may be found:
– One type is involved in promoting entry into intestinal
epithelial cells
– The other type is involved in the ability of Salmonella to
survive inside macrophages
Disease caused by Salmonella
Disease
Gastroenteritis
Septicemia
Enteric fever
pathogens
S. enteritidis,
S. typhimurium,
S. choleraesuis
S. choleraesuis, S. typhimurium,
S. enteritidis,
S. hirschfeldii
S. typhi,
S. paratyphi A,
S. schottmuelleri, S. hirschfeldii
Gastroenteritis
• The most common form of salmonellosis and
generally requires an 8-48 hour incubation period
and may last from 2-5 days.
• Symptoms include nausea, vomiting and diarrhea
(non-bloody stool). Salmonella enteritidis is the
most common isolate.
• poultry, eggs. no human reservoir
• self-limiting (2 - 5 days)
Gastroenteritis
• The most common form of salmonellosis (70%)
• Self-limited (2-5 d)
• Not enter into blood
• Culture
- blood (-)
- stool (+)
Septicemia
• Salmonella septicemia (bacteremia) may be
caused by any species but S. choleraesuis is
common.
• This disease resembles other G- septicemias and
is characterized by a high, remittent fever with
little gastrointestinal involvement.
Septicemia
• 5-10% of salmonellosis
• Intestinal manifestations: often absent
• Culture
- blood (+)
- stool (-)
Enteric fever
The pathogenesis of typhoid
Enteric or typhoid fever
• Enteric or typhoid fever occurs when the bacteria leave the
intestine and multiply within cells of the reticuloendothelial
system.
• The bacteria then re-enter the intestine, causing
gastrointestinal symptoms.
• Typhoid fever has a 10-14 day incubation period and may last
for several weeks.
• Salmonella typhi is the most common species isolated from
this salmonellosis.
• Human reservoir: carrier state common
• Contaminated food: water supply
• Poor sanitary conditions
Typhoid -Therapy
• Antibiotics
– essential
• Vaccines
Vi (capsular) antigen :protective
What does the pathogenesis imply in terms
of collection of clinical samples?
Diagnosis
• Specimens
a) Enteric fever: blood, bone marrow, stool, urine.
b) Food poisoning: stool, vomitus, suspected food.
c) Septicemia: blood.
• Culture and identification
• Widal test
Widal test
A quantitative agglutination test for typhoid and
paratyphoid, in which detects a patient’s
antibodies to the specific O antigen of S. typhi
and H antigens of S. typhi, S. paratyphi A, S.
schottmuelleri and S. hirschfeldii
How to interpret the results of
Widal test?
• Consider the manifestaton, course, history,
and local epidemiological conditions
How to interpret the results of
Widal test?
TO<1:80,TH<1:160, PH<1:80
Normal value
TO≥1:80 & TH≥1:160 or
Typhoid fever
TO≥1:80 & PH≥1:80
Paratyphoid fever
TO≥1:80 & TH <1:160 or
Early stage of infection or cross-
TO≥1:80 & PH <1:80
reaction of O antigen with other
salmonellae
TO < 1:80 & TH ≥1:160 or
Vaccination or nonspecific memory
TO < 1:80 & PH ≥ 1:80
reaction
How to interpret the results of
Widal test?
• Dynamic observation
-antibody titer give a rise gradually
-titer of convalescence serum≥4 times than that of
early specimen
• False negative
-pre-antobiotic
-immunosuppressed
immunity

Primary immunity defense
- CMI

Immunity intensity
- strong and permanent
Salmonella
• Using appropriate antibodies more than 2000 antigenic “types”
have been recognized. There are, however, only a few types that are
commonly associated with characteristic human diseases (most
simply referred to as S. enteritidis, S. cholerae-suis and S. typhi).
• Salmonellosis, the common salmonella infection, is caused by a
variety of serotypes (S. enteritidis) and is transmitted from
contaminated food (such as poultry and eggs). It does not have a
human reservoir and usually presents as gastroenteritis (nausea,
vomiting and non-bloody stools). The disease is usually selflimiting (2-5 days). Like Shigella they invade the epithelium and do
not produce systemic infection. In uncomplicated cases of
salmonellosis, which are the vast majority, antibiotic therapy is not
useful. S. choleraesuis (seen much less commonly) causes
septicemia after invasion. In this case, antibiotic therapy is required.
.
Salmonella
• The severest form of salmonella infections "typhoid" (enteric
fever), caused by Salmonella typhi.
• The organism is transmitted from a human reservoir or in the water
supply (if sanitary conditions are poor) or in contaminated food.
• It initially invades the intestinal epithelium and during this acute
phase, gastrointestinal symptoms are noted. The organism
penetrates, usually within the first week, and passes into the
bloodstream where it is disseminated in macrophages. Typical
features of a systemic bacterial infection are noted. The septicemia
usually is temporary with the organism finally lodging in the gall
bladder. Organisms are shed into the intestine for some weeks. At
this time the gastroenteritis (including diarrhea) is noted again. The
Vi (capsular) antigen plays a role in the pathogenesis of typhoid.
• A carrier state is common; thus one person e.g. a food handler can
cause a lot of spread. Antibiotic therapy is essential. Vaccines are
not widely effective and not generally used
Summary
• Common members of Enterobacteriaceae to
cause human diseases
• Common properties of Enterobaceriaceae
• The medical significance of E. coli
• The opposite traits of Shigella and Salmonella
in terms of pathogenesis and immunity
• Widal test: definition, result determination