Institute for Microbiology, Medical Faculty of Masaryk University     and St. Anna Faculty Hospital
                                              in Brno







                             Agents of digestive system infections – I









                                         Digestive system

•       „a fruitful microbial garden“

•       Its both ends are the „buggiest“ parts of the body

•       in the colon: approx. 10^12 bacteria/g

•       Normal colonic flora: 99 % anaerobes (Bacteroides, Fusobacterium, Clostridium,
Peptostreptococcus),    only 1 % enteric bacteria (mostly E. coli) & enterococci

                                         Mouth cavity – I

Normal flora:

•         viridans (= α-haemolytic) streptococci (e.g. Streptococcus salivarius)

•         oral neisseriae (e.g. Neisseria subflava)

•         haemophili of very low pathogenity (e.g. Haemophilus parainfluenzae)



Dental plaque: adherent microbial layer at the tooth surface made up from living and dead bacteria
and their products together with components from the saliva



In essence, dental plaque is a biofilm

It cannot be washed off, only mechanically removed





                                              Biofilm

•        Bacteria can regulatethe quantity of their population by regulative compounds

•        Process – quorum sensing



•        More resistant to

–   desinfectants

–   antibiotics

–   immune rection



•        A product of normal flora                                                (which is
positive) and pathogens as well



                                         Mouth cavity – II

Dental caries: chronic infections caused by normal oral flora → localized destruction of tooth
tissue



Etiology: mouth microbes (mostly Strept. mutans) making acids from sucrose in food



Thrush (in Latin soor): Candida albicans              It occurs mostly in newborns



Herpetic stomatitis: primary infection with HSV 1



Ludwig´s angina: polymicrobial anaerobic infection of sublingual and submandibular spaces
(Porphyromonas, Prevotella etc.)

                                        Herpetic stomatitis

                                              Thrush

                                            C.albicans

                                            Oesophagus

Infections never in previously healthy individuals



Only in severely immunocompromised persons (AIDS):



•       Candida albicans

•       Cytomegalovirus (CMV)

                                              Stomach

Stomach = a sterilization chamber killing by means of HCl most of swallowed microbes



Exception: Helicobacter pylori

It produces a potent urease and by splitting tissue urea it increases pH around itself    (1
molecule of urea → 1 CO[2] + 2 NH[3])



H. pylori causes

•        chronic gastritis

•        peptic ulcers (Nobel price in 2005)

                                        Helicobacter pylori



                                   Biliary tree & the liver – I

Acute cholecystitis (colic, jaundice, fever): obstruction due to gallstones

Etiology: intestinal bacteria (E. coli etc.)

Complication: ascending cholangitis



Chronic cholecystitis: the most important is Salmonella Typhi (carriers of typhoid fever)



Granulomatous hepatitis: Q fever, tbc, brucellosis



                                   Biliary tree & the liver – II

Parasitic infections of the liver:

Amoebiasis (Entamoeba histolytica: liver abscess)

Malaria (the very first, clinically silent part of the life cycle of malaric plasmodia)

Leishmaniasis (Leishmania donovani: kala-azar, L. infantum)

Schistosomiasis (eggs of Schistosoma japonicum, less often S. mansoni)



                      Systemic infections which start in the digestive tract

Enteric fever (typhoid fever and paratyphoid fever): Salmonella Typhi, Salmonella Paratyphi A, B
and C

Listeriosis: Listeria monocytogenes

Peritonitis: colonic flora (Bacteroides fragilis + other anaerobes + mixture of facultative
anaerobes)

Viral hepatitis: HAV, HBV, HCV, HDV, HEV



                                     Small and large intestine

Bacterial overgrowth syndrome:

After surgery, depressed peristalsis, or gastric achlorhydria bacteria may overgrowth in the small
intestine → steatorrhea, deficiency of vitamin B[12], diarrhea, malabsorption of vitamins A and D



Diarrhea: increase in daily amount of stool water – common intestinal response to many agents



Dysentery: acute inflammation of the colon → abdominal pain & small-volume stools with blood, pus
and mucus

                                         Diarrheal disease

Infectious:

•       Bacterial (most frequent)

•       Viral

•       Parasitic

•       Mycotic



Non-infectious:

•       Food poisoning





                                           „Homework 1“
                        What is the name of the picture and of its author?