Enterobacteriaceae

ENTEROBACTERIACEAE

Enterobacteriaceae: gastrointestinal diseases    

Escherichia coli Salmonella Shigella Yersinia entercolitica

Antigenic structure – O antigen (lipopolysaccharide ,O-specific polysaccharide , somatic antigen ) –H antigen (flagella, flagellar antigen ) –K antigen (capsule, capsular antigen) –Vi antigen

鞭毛抗原 （H）

K 或 Vi 抗原

菌体抗原 (O)

Growth characteristics There is a simple distinction between pathogenic enteric bacteria and nonpathogenic enteric bacteria. –Pathogenic enteric bacteria such as Shigella and Samonella can not ferment lactose while nonpathogenic enteric bacteria such as Escherichia can ferment lactose.

E.coli colonies on EMB Agar.

Growth of gram-negative bacteria that cannot ferment lactose on EMB agar

Virulence of enterbacteriaceae •Pili –adherence of bacteria to human intestinal tract cells. •Endotoxin –LPS , lipid A

Diseases caused by Esherichia coli •E.coli is a member of the normal intestinal flora. It generally do not cause disease, and in the intestine, it may even contribute to normal function and nutrition. •This bacteria become pathogenic only when it reach tissues outsides of the normal intestinal flora sites.

Escherichia coli

Diseases caused by Esherichia coli •The most frequent sites of clinically important infection are urinary tract infection. •E.coli is the most common cause of urinary tract infection and accounts for approximately 90% of urinary tract infections . •Urethritis •Cystitis •Pyelonephritis

Intestinal Diseases Caused by Pathogenic E. coli Five classes (virotypes) of E. coli that cause diarrheal diseases are now recognized: 1.enterotoxigenic E. coli (ETEC), 2.enteroinvasive E. coli (EIEC), 3.enterohemorrhagic E. coli (EHEC), 4.enteropathogenic E. coli (EPEC), and 5. enteroaggregative E. coli (EAggEC).

Summary of E.coli strains that cause gastroenteritis.

Sanitary significance  Totoal 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

Shigella

Shigella  S. flexneri, S. boydii, S. sonnei, S. dysenteriae bacillary dysentery shigellosis bloody feces intestinal pain pus

General features  Pili.  Most strains can not ferment lactose; S. sonnei can slowly_ ferment lactose.  According to O antigen, 4 groups  Easily causing drug-resistence.

Shiga toxin  enterotoxic  cytotoxic  inhibits protein synthesis  lysing 28S rRNA

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.

Salmonella  Salmonellosis may present as one of several syndromes including gastroenteritis, enteric (typhoid) fever or septicemia.

The antigenic structures of salmonellae used in serologic typing

Salmonella  2000 antigenic "types”  genetically single species  S. enterica

 disease category  S. enteritidis  many serotypes

 S. cholerae-suis  S. typhi

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