Chapter 25: Microbial Diseases of the Digestive System

• Anatomy and physiology• Normal flora• Upper digestive infections

– Bacterial– Viral

• Lower digestive infections – Bacterial– Viral– Protozoan

Anatomy and physiology

Normal Flora• Mouth

– A variety of species exist (aerobic and anaerobic)

– Bind to specific host cell receptors

• Intestines– Microorganisms make up 1/3 of the weight of

feces– Biochemical activities:

• Synthesis of vitamins• Degrade indigestible substances• Competitively inhibit pathogens

Upper digestive infections

• Bacterial– Dental Caries (tooth decay)– Periodontal disease– Trench Mouth (Vincent’s disease)

• Viral– Mumps

Tooth decay (dental caries)• Streptococcus mutans

• Formation of extracellular glucans from dietary sucrose

• Cariogenic dental plaque - acidity

• Control – fluoride and restricting dietary sucrose

Figure 25..3 b

Periodontal disease

• Inflammatory response to plaque bacteria

• Inflammation affects gums

• Dental calculus• Gingivitis –

Porphyromonas gingivalis

• Responsible for tooth loss in older people

Trench Mouth

• Synergistic infection – spirochetes and anaerobic bacteria

• Acute necrotizing ulcerative gingivitis

• Occurs at any age group (poor mouth care)

Summary of teeth and gum infections

• Paramyxovirus family• Enters through

respiratory tract • Infect different body

tissues:– Parotid glands– Meninges– Testicles

• Prevented with MMR vaccine

Mumps

Features of mumps

Lower digestive infections • Bacterial

– Heliobacter Peptic Ulcer Disease– Shigellosis– Salmonellosis – Cholera– Gastroenteritis

• Viral– Rotavirus

• Protozoan– Giardiasis – Cryptosporidiosis– Amoebic Dysentery

Heliobacter Peptic Ulcer Disease

• Helicobacter pylori • Gastric ulcer

Figure 11.11

Features of Helicobacter gastritis

Shigellosis

Figure 25.8

• Shigella spp. producing Shiga toxin

• Shiga toxin causes inflammation and bleeding

Features of shigellosis

Salmonellosis

Figure 25.9

• S. enterica Typhimurium

• Mortality (<1%) due to septic shock caused by endotoxin

• Typhoid fever

• Vaccine available

Features of salmonellosis

Cholera• Vibrio cholerae serotypes that produce

cholera toxin

• Toxin causes host cells to secrete Cl–, HCO–, and water

Figure 25.12

Features of cholera

Gastroenteritis

• Escherichia coli Gastroenteritis

• Campylobacter Gastroenteritis

• Yersinia Gastroenteritis

• Clostridium perfringens Gastroenteritis

• Bacillus cereus Gastroenteritis

Escherichia coli Gastroenteritis• Occurs as traveler's diarrhea and epidemic

diarrhea in nurseries• Four groups of pathogenic E. coli

– Enterotoxigenic– Enteroinvasive– Enteropathogenic– Enterohemorrhagic

• 50% of feedlot cattle may have enterohemorrhagic strains in their intestines – E. coli O157:H7 produce Shiga toxin

• O = cell wall antigen• H = flagellar antigen

Escherichia coli gastroenteritis

Campylobacter Gastroenteritis• Campylobacter jejuni

• Usually transmitted in cow's milk

• Most common cause of diarrhea

• Guillain – Barré syndrome

• Low infectious dose

Campylobacter Gastroenteritis

Other Gastroenteritis

• Yersinia Gastroenteritis– Y. enterocolitica and Y. pseudotuberculosis– Can reproduce at 4°C– Usually transmitted in meat and milk

• Clostridium perfringens Gastroenteritis– Grow in intestinal tract producing exotoxin

• Bacillus cereus Gastroenteritis– Ingestion of bacterial exotoxin produces mild

symptoms

Rotavirus• 3 million cases

annually • 1-2 day incubation,

1 week illness• Reovirus family• Main diarrheal

illness of infants and children

• Associated with traveler’s diarrhea

Giardiasis • Giardia lamblia• Drinking water contamination

by feces• Traveler’s diarrhea• Two forms

– Vegetative trophozoite– Resting form (cyst)

• survive chlorinated water

• Diagnosed by microscopic examination of stool for ova and trophozoite

Features of giardiasis

Cryptosporidiosis• Cryptosporidium parvum • Transmitted by oocysts in

contaminated water – difficult to remove by

filtration• Wide host range – human,

domestic animals• Diagnosed by acid-fast

staining of stool or presence of antibodies by FA or ELISA

• Treated with oral rehydration

Features of crytosporidiosis

Amoebic Dysentery• Entamoeba histolytica • Chronic – spread to the

liver and other organs• Two forms

– Ameba: feeds on RBCs and GI tract tissues

– Cyst (quadrinucleate cyst is infectious)

• Diagnosis by observing trophozoites in feces

• Treated with metronidazole

Features of Amoebic Dysentery