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A 10- year-old, previously healthy child came to the emergency room for the evaluation of bloody diarrhea and diffuse 弥漫性 abdominal pain for 24 hours’. His mother said him eaten an hamburger at a fast food restaurant beside the school yesterday. Your diagnosis are …you must find the child’s….

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A 10- year-old, previously healthy child came to the emergency room for the evaluation of bloody diarrhea and diffuse弥漫性abdominal pain for 24 hours’. His mother said him eaten an hamburger at a fast food restaurant beside the school yesterday.

  • Your diagnosis are …you must find the child’s…


  • Name four genera of enterobacteriaceae that can cause gastrointestinal disease.

  • Name two genera that can cause hemorrhagic colitis出血性结肠炎

  • Name the group of E.coli that can cause gastroenteritis胃肠炎

  • what are the forms of salmonella沙门菌infection?

Enteric Bacilli, Vibrio, Campylobacter and Helicobacter

Enteric Bacilli associated with diseass




Suggested reading: your textbook

Chapters 10 of zhengren zhou

Suggested reading: your textbook

Chapters 10 of enjie luo

Suggested reading: your English

Textbook Chapters 15-17















Classification~29 genera, over 100 species.

General Information:

  • gram-negative bacilli.

  • peritrichous flagella (most)--- motile.

  • pili --- associated with attachment.

  • non-spore forming.

1. Similar shape


2. culture :EMB agar

facultative anaerobes.

form circular, convex凸的, and smooth colonies with distinct edges.

contain lactose and two dyes (eosin and methylene blue亚甲蓝)

+: purple colonies with green metallic sheen金属光泽 E. coli

-: colorless pathogenic bacteria



  • Isolated from fecal matter on agar containing

  • lactose and a pH indicator(中性红)

  • Colonies color

  • E. coli ferments lactose

  • Shigella, Salmonella and Yersinia are

  • non-fermenters

  • "Non-pathogenic" strains of E. coli (and other

    • lactose-positive enterics) are often present in

    • normal feces.

Biochemical reactions -- active and diverse

  • Oxidase氧化酶test: negative

  • They ferment glucose, often with gas


  • lactose fermentation is an important test for

    differentiating pathogenic enteric bacilli from non-pathogenic strains.

  • All Enterobacteriaceae isolated from other sites

    • which contain low numbers of bacteria

    • [e.g. urine],sterile [e.g. blood]

    • are identified biochemically

    • [e.g. the API 20E system]

Important serotypes can be differentiated by their:

  • O (lipopolysaccharide)

  • H (flagellar) antigens

  • K (capsular) antigens

However, serotyping is generally not performed in the

Routine常规clinical laboratory.

Antigenic Structure

  • Most are motile by peritrichous flagella --H antigens.

  • Capsule –Kantigen (Vifor Salmonella).

  • Cell envelope (wall)

  • LPS (endotoxin) –O antigen.

  • various outer membrane proteins.

  • Pili - various antigen types, some encoded by plasmids





  • G- rod bacilli

  • Habitat is the intestinal tract

  • Facultative anaerobes or aerobes

  • Ferment a wide range of carbohydrates

  • Possess complex Ags structure

  • Produce a variety of toxins and other virulence factors

(i) Escherichia coli 埃希菌属

At some level, E. coli and Shigella are


  • important properties: ferment lactose

  • laboratory diagnosis: MacConkey’ agar, EMB agar

Pathogenesis of E. coli

  • Transmission is by the fecal-oral route.

  • Pili (fimbriae) allow the bacteria to colonize the ileal mucosa.

  • Cytotonic enterotoxins watery diarrhea.

    tissue damage

  • Vero toxin

  • Hemolytic toxin

  • Others LPS, K Ag


  • intestinal tract infection

    • gastroenteritis 胃肠炎

  • systemic infection

    • septicemia 败血症,

    • meningitis 脑膜炎

  • urinary tract infection 泌尿道感染

    • Uropathogenic E.coli. UPEC

E. coli fimbriae

Type 1



  • galactose

    • glycolipids

    • glycoproteins

E.coli-urinary tract infection Is the leading cause of urinary tract infections which can lead to acute cystitis急性膀胱炎(bladder infection) and pyelonephritis肾盂肾炎(kidney infection).

E.coli-Meningitis and Sepsis

  • Neonatal meningitis – is the leading cause of neonatal meningitis and septicemia with a high mortality rate. Usually caused by strains with the K1 capsular antigen.

Clinical Manifestations of gastroenteritis 胃肠炎

  • Depending on the virulence factors they possess, virulent Escherichia coli strains cause

    • noninflammatory diarrhea (watery diarrhea)

    • inflammatory diarrhea (dysentery with stools usually containing blood, mucus, and leukocytes粘液脓血便).

Summary of E.coli strains that cause gastroenteritis.






Enteropathogenic E. coli (EPEC).

  • fever

  • infantdiarrhea

  • vomiting

  • nausea

  • non-bloody stools

  • Destruction of surface microvilli微绒毛

  • loose attachment mediated by bundle forming pili (Bfp);

  • Stimulation of intracellular calcium level;

  • rearrangement of intracellular actin,

Transmission electron

micrograph of

Escherichia coli O157:H7

CDC/Peggy S. Hayes

Enterohemorrhagic E. coli (EHEC).

  • These are usually serotype O157:H7.

  • These organisms can produce a hemorrhagic

  • colitis (characterized by bloody and

  • diarrhea with few leukocytes in afebrile无热的

  • patients).

  • However, they are taking increasing importance

  • with the recognition of outbreaks caused by

  • contaminated hamburger meat.

  • The organisms can disseminate播散into the

  • bloodstream producing systemic

  • hemolytic-uremic syndrome (hemolytic anemia,

  • thrombocytopenia血小板减少(症)

  • and kidney failure肾衰竭).

Sanitary significance卫生学指标

  • Totoal bacterial number细菌总数: number of bacteria contained per ml or gm of the sample; the standard of drinking water is less than 100.

  • Coliform bacteria index大肠菌群指数

    the number of coliform bacteria detected out per 1000 ml sample; the standard of drinking water is less than 3

(ii) Shigella

Structure, Classification, and Antigenic Types

  • Shigellae are Gram-negative,

  • nonmotile,

  • facultatively anaerobic,

  • non-spore-forming rods.


  • A 25-year-old, previously healthy woman came to the emergency room for the evaluation of bloody diarrhea and diffuse abdominal pain of 24 hours’duration. She complained of nausea and had vomited twice. She reported no history of inflammatory bowel disease, previous diarrhea, or contact with other people with diarrhea. The symptoms began 24 hours after she had eaten an undercooked hamburger at a local fast food restaurant. Rectal examination直肠检查 revealed watery stool with gross blood. Sigmoidoscopy乙状结肠镜检查(术) showed diffuse mucosal erythema红斑 and petechiae瘀点 with a modest exudation渗出物 but no ulceration or pseudomembranes假膜,伪膜.


  • Name four genera of Enterobacteriaceae that can cause gastrointestinal disease. Name two genera that can cause hemorrhagic colitis.

  • What virulence factor mediates this disease ?

  • Name the five groups of E. coli that can cause gastroenteritis. What is characteristic of each group of organisms?

  • What are the four forms of Salmonella infection ?

  • Differentiate between disease caused by S.typhi and that caused bu S.sonnei?


4 Species;

S. flexneri,

S. boydii,

S. sonnei,

S. dysenteriae

All cause bacillary dysentery or shigellosis.

Shigellosis is bloody feces associated with

intestinal pain.

“pus” feces : mucus and blood ,leukocytes into the bowel.

Shigella are differentiated from the closely related Escherichia coli

  • failure to ferment lactose

  • The genus is divided into four serogroups with multiple serotypes:

    • A (S dysenteriae, 12 serotypes);

    • B (S flexneri, 6 serotypes);

    • C (S boydii, 18 serotypes); and

    • D (S sonnei, 1 serotype).

Pathogensis substance

  • All species are able to invade and multiply inside a wide variety of epithelial cells, including the enterocyte

  • Endotoxin

  • Shiga toxin, ST(exotoxin)

Chromosomally encoded

Neurotoxic, Enterotoxic and Cytotoxic

Enterotoxicity can make the disease clinically

appear as a diarrhea. The toxin inhibits protein synthesis (acting on the 60S ribosome and lysing 28S rRNA).

Shigella attachment and penetration

  • Within 2-3 days

  • Epithelial cell damage

ShigellaClinical Manifestations

  • Symptoms of shigellosis include

    • abdominal pain,

    • Tenesmus 里急后重,下坠,

  • watery diarrhea, and/or dysentery (multiple scanty, bloody, mucoid stools).

  • Other signs may include abdominal tenderness, fever, vomiting, dehydration.


  • Patients with severe dysentery are usually treated with antibiotics (e.g. ampicillin氨苄西林).

  • Mild diarrhea is often not recognized as shigellosis.

  • Managing dehydration is of primary concern.


It can be transmittedby fecal-oral contact.

Food hands contaminating food.

Adults can catch this disease from children.

The source in each case is unwashed hands.

Man is the only "reservoir".

(iii) Salmonella沙门氏菌

Only a few types that are commonly associated

with characteristic human diseases -

1. S. enteritidis

2. S. cholerae-suis

3. S. typhi

Salmonella typhi

  • The organism is transmitted from:

1. a human reservoir

2. in the water supply (if sanitary conditions

are poor)

3. in contaminated food

  • It initially invades the intestinal epithelium and

  • during this acute phase, gastrointestinal

  • symptoms are noted.


  • Virulence factors

    a. Invasiveness:


    -Vi antigens, anti-phagocytosis

    b. Endotoxin:

    c. Exotoxin: (some)

    -enterotoxin, like ETEC’s.

The antigenic structures of salmonellae used in serologic typing

Clinical disease

a. Enteric fever

b. Enteritis (or food poisoning)

c. Septicemia

S. typhi → small intestine

penetrate across the mucosa

multiplication in phagocytes

the first bacteremia

multiplication in phagocytes of some organs

the second bacteremia

(carrier state) gall bladder high fever, leukopenia, low pulse

reinvasion of the gut mucosa

↓ hypersensitivity

intestinal hemorrhage or perforation穿孔



S. typhi

rose rash


胆囊---肠道---粪排菌/肠 壁淋巴组织




皮肤----血栓出血--玫瑰疹rose rash










  • Septicemia

  • -occurs 10-14 days

  • lasts 7 days

  • gall bladder

  • shedding, weeks

  • acute phase, gastroenteritis


Enteric fever

  • S. typhi - typhoid fever

    S. paratyphi - paratyphoid fever

  • incubation period: 1~2 weeks

  • typical duration: 3~5 weeks

Enteric fever

Enteritis (Food poisoning)

  • the most common Salmonella infection.

  • common causative agents:

    S. typhimurium, S. enteritidis and S. choleraesuis.

  • manifestations:

    low fever, nausea, vomiting, diarrhea.

  • a self-limited disease, lasting for 3~5 days.


  • the common causative agent:

    S. choleraesuis

    S. typhimurium

    S. enteritidis.


  • manifestations:

    fever, chill, and some local infection.

  • intestinal symptoms : little or no

Laboratory Diagnosis

  • A. Specimens

    a) Enteric fever: blood, bone marrow, stool, urine.

    b) Food poisoning: stool, vomitus, suspected food.

    c) Septicemia: blood.

  • B. Culture and identification

  • C. Widal test

Bacteriologic Methods

  • Serologic diagnosis ---- Widal test


    A quantitative agglutination test forenteric fever, 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.


Typhoid -Therapy

  • Antibiotics

  • Vaccines

    Vi (capsular) antigen :protective




This chapter will focus on

  • Definitions

    • Widal test

  • Questions

    1. What are the common properties of the Enterobacteriaceae?

    2. What are the medically important genera of the Enterobacteriaceae? What diseases are caused by them?

    3. What is the importance of lactose fermentation in distinguishing between certain genera of the Enterobacteriaceae?

    4. What are the 5 serotypes of E. coli causing diarrhea? What is the pathogenesis of them?

    5. What are the medically important species of Salmonella? What diseases are caused by them?

    6. What is the pathogenesis of typhoid?

    7. what is the medical significance of Widal test? How to interpret the results of the test?

Isolation Rate for Salmonella enteritidis

by Region, United States, 1974-1994 CDC

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