Enteric Gram-Negative Rods Enteric Gram-Negative Rods

((EnterobacteriaceaeEnterobacteriaceae))

SS plate

colored colonies (red)colored colonies (red) non-pathogenicnon-pathogenic

yes

nowhite colonieswhite colonies

pathogenicpathogenic

lactose fermentationlactose fermentation

•Mechanism: Non-pathogenic enteric bacilli can

ferment lactose to produce acidic by-products

while pathogenic enteric bacilli such as Shigella

and Salmonella can not.

•Media: SS-plate or EMB plate , TSI agar slants

•Basic components: lactose and a pH indicator

E. coli

Enterobacter Aerogenes

IMViC test

Indole testMethyl red (MR) testVoges-Proskauer (VP) testCitrate utilization test

Live in the intestinal tract of humans and animals

anaerobes

•opportunistic infection (E. coli)

septicemia

pneumonia

meningitis

urinary tract infections

•human pathogens (Salmonella and Shigella)

•community-acquired diseases

respiratory infections (Klebsiella pneumoniae)

urinary tract infection (E. coli and Proteus)

E. coli causes urinary tract infections such as acute cystitis and pyelonephritis

pili

capsule

enterotoxin: cause diarrhea and tissue

damage

endotoxin

H Ag (flagella)

somatic O Ag (lipopolysacchari

de)

K/Vi Ag (capsule)

Escherichia coli

Gram stain?

Motility?

lactose fermentation?

Antigens?

IMViC?

Transmission route?

virulence factors?

EnteroEnteroppathogenic athogenic E. coli E. coli ((EPECEPEC))

EnteroEnterottoxigenic oxigenic E. coli E. coli ((ETECETEC))

EnteroEnteroiinvasive nvasive E. coli E. coli ((EIECEIEC))

EnteroEnterohhemorrhagic emorrhagic E. coli E. coli ((EHECEHEC))

EnteroEnteroaggaggregative regative E.coli E.coli

((EAggECEAggEC))

Enteropathogenic E. coli (EPEC)

•Commonly associated with infant diarrhea.

•Characteristic lesion with destruction of

microvilli without invasion

•Clinical signs

Fever

diarrhea with non-bloody stools

Vomiting

nausea

Enterotoxigenic E. coli (ETEC)

•Cause "traveller’s diarrhea".

•Two types of plasmid-encoded toxins are produced:Heat labile toxins (LT), an adenyl cyclase which catalyze ATP to cAMP.

Heat stable toxins (ST), a guanyl cyclase to catalyze GTP to cGMP. cAMP/cGMP

are the intracellular second messagers. The former increases the secretion of

water and ions, and the latter inhibits ionic uptake.

•Clinical signs

watery diarrhea

Fever

nausea

Enteroinvasive E. coli (EIEC)

• Associated with elder children and adult diarrhea.

• Without flagella

• High virulence: a small number of EIEC can cause serious

illness

• Clinical signs

Acute inflammatory responses

tissue destruction

diarrhea with little fluid, a lot of blood and mucus

containing polymorphonuclear cells

•EHEC produces bacteriophage-mediated exotoxin. This toxin

is called as Vero toxin (VT) because of its cytotoxicity to

cultured Vero cells.

•In children, the disease may be progressed to a systemic

stage called as hemolytic uremic syndrome (kidney injury)

with 10% death rate.

•Clinical signs

serious abdominal pain

diarrhea which is initially watery but then becomes

bloody

Enterohemorrhagic E. coli (EHEC)

It produces enteroaggregative heat-stable toxin

(EAST) similar to the heat stable toxins of ETEC.

It produces mucous associated autoagglutinin which

causes aggregation of the bacteria and formation of

biofilm.

Clinical Signs

persistent, mucus-watery diarrhea

vomiting and dehydration in infants

Enteroaggregative E. coli (EAggEC)

ShigellaShigella

Gram stain?

motility?

Lactose fermentation?

ClassificationClassification

According to the difference of O antigen,

Shigella strains are divided into 4 groups:

S. dysenteriaeS. dysenteriae

S. flexneriS. flexneri

S. boydiiS. boydii

S. sonneiS. sonnei

Clinical findingsClinical findings Most common cause of bacterial dysentery in human

characteristic blood and mucus stools

Due to specific S-IgA, only invades intestinal mucosa and never enters bloodstream. But the endotoxin can be absorbed into bloodstream to cause endotoxemia.

Can cause toxic dysentery in children, display systemic toxic symptoms but no enteric symptoms. Has a a high death rate.

Virulent factorsVirulent factors pilus pilus

endotoxinendotoxin

exotoxin:exotoxin: Shigella dysenteriae can produce an

exotoxin called as shiga-toxin which is simmilar to

Vero toxin (VT) of EHEC. Shiga-toxin is enterotoxic,

cytotoxic and neurotoxic. So the dysentery ( 痢疾 )

caused by this microbe is more serious than that by the

other three groups.

Control transmission

Dysentery is treated with antibiotics. But multiple drug resistance mediated by plasmids are common in many Shigella strains.

SalmonellaSalmonella

Gram stain?

Motility?

Lactose fermentation?

antigenic structures?

More than 2000 serotypes based on antigenic difference

Infect human (enteric fever)S. typhi

S. paratyphi A

S. schottmuelleri (S. paratyphi B)

S. hirschfeldii

Infect animal and human

S. choleraesuis

S. typhimurium

S. enteritidis

Virulent factorsVirulent factors

Vi antigen: Vi antigen: consisted of capsular

polysacchride. It resists phagocytosis and plays

an important role during invasion of Salmonella.

endotoxinendotoxin

enterotoxinenterotoxin

DiseasesDiseases

enteric fever (typhoid fever)

S. typhi S. paratyphi AS. schottmuelleri (S. paratyphi B)S. hirschfeldii

• Enteric fever (typhoid fever) is the most serious form of salmonella infection which only occurs in human.

• Carrier state is common

•In untreated patients, the death rate is 7% to 14%.

•Antibiotic therapy is essential, vaccines are not effective and not widely used.

1. The microbe initially invades intestinal mucosal

epithelium and propagate at the local.

2. The microbe penetrates into the bloodstream to cause

the first round of bacteremia with symptoms of fever,

general discomfort and pain.

3. The microbe enters many organs such as liver, spleen,

kidney, gall and marrow for further propagation.

4. The microbe penetrates into the bloodstream again to

cause the second round of bacteremia with serious

symptoms of high fever, swell of spleen and liver, rose-

colored spots in skin, and tissue injury.

enteric fever developmententeric fever development

enteric fever Diagnosis

1. Definitive diagnosis-bacteria culture

Blood @ first week

Stool and urine @ from the second week on

Marrow can be considered because of its high and permanent positive results.

enteric fever diagnosis2. Widal testa quantitative agglutination test using the known O antigen of S.typhi , and H antigens of S. typhi and S. paratyphi A/B to detect specific serum antibodies.

• For one single serum sample, The titers of anti-O antigen IgM 1:80 and/or anti-H antigen IgG 1:160.

• For two serum samples that collected with an interval of 5~7 days, 4-fold increase in titers of specific antibody.

DiseasesDiseasesGastroenteritis (food-poisoning)

S. choleraesuisS. typhimuriumS. enteritidis

• Gastroenteritis (food poisoning):

It is the most common Salmonella infection and usually transmitted from contaminated food. However, only a few of food poisoning-causing salmonella serotypes can produce enterotoxin.

DiseasesDiseases

Septicemia: commonly caused by

– S. hirschfeldii – S. typhimurium– S. choleraesuis

•Septicemia:

Many Salmonella serotypes can cause septicemia. This disease is commonly found in children or adult with low immunity.

Vibrio cholerae CholeraCholera

                                                 

IntroductionCholera caused by Vibrio cholerae is characterized by profuse watery diarrhea and serious vomiting which results in extreme loss of fluid and electrolytes, shock and kidney prostration. If patients are untreated, the death rate is as high as 60%.

Cholera: outbreak in India

IntroductionThere have been 8 great outbreaks in the world.

In 1991, a great outbreak (7th) started in Peru. There were more than a million patients in Central and South America. In 1992, another great outbreak (8th) started in India and then spread to all parts of Asia. Not serotype O1 but O139 caused this outbreak.

ClassificationClassification

O-antigen O-antigen

O1

non-O1/139

O139

classical biotype

El Tor biotype

Further typingFurther typing

Responsible for the 1st-6th great outbreaks

Responsible for the 7th great outbreak

Responsible for the 8th great outbreak in 1992

Cause cholera-like disease

high pH (pH8.5-9.0)

TCBS (thiosulfate-citrate-bile-sucrose) agar plate

Major virulent factors

Flagellum: offers an ability to penetrate enteric

mucus layer to reach the surface of host cells.

Pilus: adhesion

Cholera toxin: the most important virulent factor

which induce electrolyte and water

hypersecretion. This toxin is chromosomally

encoded and its molecule contains subunits A and

B.

Pathogenesis of cholera toxin

◇ Subunit B binds to its receptor (gangliosides) on the surface of epithelial cells and provides a channel allowing subunit A to enter host cell.

◇ Cellular proteinase lyses subunit A into peptides A1 and A2

Peptide A1 has activity of ADP-ribosylation to transfer ADP from NAD onto protein G which activates protein G

↓

Activated protein G induces cAMP overproduction

↓

A large number of cAMP induces electrolyte and water hypersecretion of cells

Dehydration!! ( 脱

水 )

the major cause of death…

Replace fluid and electrolyte ！！！-most important treatment

Antibiotics such as tetracycline additionally used

Vibrio parahemolyticusexists in raw sea-food and causes food poisoning in human It is halophilic and optimal NaCl concentration in media is 3.5% It produces hemolysin Can be rapidly killed by acid (eg. acetic acid)