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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