Enterobacteriaceae. Transmitted by the fecal-oral route Primary pathogens Organisms capable of causing disease in anyone Opportunistic pathogens Organisms

Enterobacteriaceae

Transmitted by the fecal-oral route

Primary pathogensOrganisms capable of causing

disease in anyone

Opportunistic pathogensOrganisms that can only cause disease

under certain conditions or in certain hosts

Shigella

Salmonella

Yersinia

Klebsiellapneumoniae

E. coli

Senatia

Morganella

Providencia

EnterobacterProteus

Characteristics shared by all Characteristics shared by all

members of family members of family

EnterobacteriaceaeEnterobacteriaceae

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

Extraintestinal infection

Urinary tract infectionSepticemia

Neonatal meningitis

pathogen

Intestinal tract infection

ETECEIECEPECEHEC

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; non-

fimbrial 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.

• 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

• 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


• Malaise and low grade fever diarrhea, vomiting, nausea, non-

bloody 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

• Vero toxin – “shiga-like”

• Hemolysins

• younger than 5 years old,causing

hemorrhagic colitis

Enterohemorrhagic E. coli (EHEC)

• Usually O157:H7

Transmission electron micrograph


• 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.

Enteroaggregative E. coli (EaggEC)

Summary of E. coli strains

that cause gastroenteritis.

Organism

Virulence factorsAdherence Toxins invasion serovar

ETEC Colonization factors of adherence (CFAs)Type 1 pili

Endotoxin Heat-labile enterotoxin (LT)Heat-stable enterotoxin (ST)

Noninvasive O6:K15:H6

EIEC Type 1 pili Afimbrial adhesins

Endotoxin Very invasiveType III secretion system

28

EPEC Bundle-forming pili (BFP)Type 1 piliIntimin

Endotoxin Poorly invasive 2, 55

EHEC Type 1 pili Afimbrial adhesins

Shiga toxinEndotoxin

Probably poorly invasive

O157:H7

EaggEC Mucus-associated autoagglutinationType 1 pili

EndotoxinCytotoxin (enteroaggregative ST-like toxin)

Noninvasive O42

organism Site Disease pathogenesis


Small intestine

Traveler’s diarrhea, infant diarrhea in under developed countries, watery diarrhea, cramps, nausea, low-grade fever

Heat-stable and/or heat-labile enterotoxins, stimulate guanylate or adenylate cyclase activity with fluid and electrolyte loss


Large intestine

Fever, cramping, watery diarrhea followed by development of dysentery with scant, bloody stools

Plasmid-mediated invasion and destruction of epithelial cells lining colon


Small intestine

Infant diarrhea with fever, nausea, vomiting, nonbloody stools

plasmid-mediated adherence and destruction of epithelial cells


Large intestine

Hemorrhagic colitis with severe abdominal cramps, watery diarrhea initially, followed by grossly bloody diarrhea, little or no fever, hemolytic uremic syndrome (HUS)

Mediated by cytotoxic “vero-toxin”

Enteroaggregative E. coli (EAggEC)

Small intestine

Persistent infant diarrhea, sometimes with gross blood, low-grade fever

Aggregative adherence mediated by plasmid

Various Types of E. coli

“Nonintimate” association:

bacteria attach to host cell by bundle-

forming 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) Shigelladysentery 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 (10-

200 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.

• Primary immunity defense - SIgA

• Immunity intensity - Limited

- reasons

surface infection

various types

immunity

Diagnosis of Shigella infection

• Specimen: stool.

• Culture and Identification

• Quick immunological methods:

- Immunofluorescent “ball” test;

- Coagglutination.

Prevention & Treatment

• manage dehydration

• patients respond to antibiotics , Problem of drug-

resistance

– disease duration diminished

• streptomycin dependent (SD) dysentery vaccine.

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(III) 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

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

Antigenic composition of Salmonella

The antigenic structures of salmonellae used in serologic typing

• Virulence factors

Pathogenicity

• 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

• Virulence factors

Pathogenicity

• 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 pathogens

Gastroenteritis S. enteritidis, S. typhimurium,

S. choleraesuis

Septicemia S. choleraesuis, S. typhimurium,

S. enteritidis, S. hirschfeldii

Enteric fever 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 (-)

The pathogenesis of typhoid

Enteric fever

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

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

Widal test

How to interpret the results of Widal test?

• Consider the manifestaton, course, history,

and local epidemiological conditions


TO<1:80,TH<1:160, PH<1:80 Normal value

TO≥1:80 & TH≥1:160 or

TO≥1:80 & PH≥1:80

Typhoid fever

Paratyphoid fever

TO≥1:80 & TH <1:160 or

TO≥1:80 & PH <1:80

Early stage of infection or cross-

reaction of O antigen with other

salmonellae

TO < 1:80 & TH ≥1:160 or

TO < 1:80 & PH ≥ 1:80

Vaccination or nonspecific memory

reaction


• Dynamic observation

-antibody titer give a rise gradually

-titer of convalescence serum≥4 times than that of

early specimen

• False negative

-pre-antobiotic

-immunosuppressed

Primary immunity defense

- CMI

Immunity intensity

- strong and permanent

immunity

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 self-limiting (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

Documents

Enterobacteriaceae. Transmitted by the fecal-oral route Primary pathogens Organisms capable of causing disease in anyone Opportunistic pathogens Organisms