GI Infections Flashcards
What is an obligate anaerobe? Give an example.
Organism which dies in the presence of oxygen
e.g. Bacteroides fragilis, Clostridium spp. (but these form spores which allow them to survive)
What is an obligate aerobe? Give an example.
Organism which must have oxygen to survive
e.g. Pseudomonas, Mycobacterium tuberculosis
What is a facultative anaerobe? Give an example.
Organism which prefers to utilise oxygen but can survive without it
e.g Gram-ve enteric bacteria (E. coli), Gram+ve skin bacteria (Staph.)
What anaerobic zones are present in the GI tract?
Parts of the mouth
- deep in the taste buds
- biofilm between teeth
- gingival crevice areas (gingiva = gums)
- peridontal pockets in people with peridontal disease (surrounding or encasing a tooth)
Small bowel
Colon
What are some functions of human colonic bacteria?
Synthesise and excrete vitamin K, B12, thiamine, more B vitamins
Prevent colonisation by pathogens
Kill non-indigenous bacteria
Stimulate development of MALT (caecum & Peyer’s patches)
Stimulate production of natural antibodies
Give some examples of spore-forming bacteria.
Bacillus anthrax
Clostridium tetani
Give examples of bacteria which can form biofilms.
Staphylococcus spp.
Streptococcus spp.
E. coli
Enterococcus spp.
Klebsiella pneumoniae
Pseudomonas aeruginosa
Name some aerobic cocci found in the GI tract.
Gram+ve:
- Staphylococcus
- Streptococcus
- Enterococcus
Gram-ve:
- Neisseria meningitidis
- Neisseria gonorrhoea
Name some anaerobic bacilli found in the GI tract.
Gram+ve: Clostridia spp. - tetani (endospores) - perfringens (gas gangrene) - difficile (pseudomembranous colitis)
Gram-ve:
Bacteroides fragilis
Name some aerobic bacilli found in the GI tract.
Gram+ve:
- Corynebacterium diptheria
- Bacillus anthrax
- Lactobacillus
- Mycobacterium tuberculosis
Gram-ve:
- Enteric bacteria (Escherichia coli, Pseudomonas, Proteus, Klebsiella, Salmonella, Shigella, Vibrio cholera, Campylobacter, Helicobacter pylori)
- Non-enteric bacteria (Haemophilus influenze, Bordetella pertussis, Brucella)
Name some types of microbes found in the mouth.
Lots of anaerobes e.g. Streptococcus, Staphylococcus, Candida, Lactobacillus, Enterococcus
What is noma/cancrum oris?
Severe ulcerative gingivitis which causes a gangrenous infection of the mouth which spreads to involve the face
Causes:
- systemically unwell
- malnourished
- dehydrated
- immunocompromised
What are some risk factors for oral thrush? What is the treatment?
Newborns Diabetics (glycosuria) Antibiotics Inhaled steroids Immune deficiency
Treatment:
- amphotericin lozenges
- nystatin suspension
What is the main bacterium implicated in dental caries and gingivitis?
Dental caries = Streptococcus mutans + lactobacilli (progression of dental decay)
note: S. mutans only causes caries in the presence of sugars (metabolises sucrose to lactic acid -> acid erosion of enamel)
Gingivitis =
- Porphyromonas gingivalis
- Aggregatibacter actinomycetemcomitans
What is Ludwig’s angina?
Severe inflammation caused by infection of both sides of the floor of the mouth (upper respiratory infection)
Infection colonises cervical lymph nodes -> ascending & descending cellulitis
-> massive swelling of the neck -> obstruction of airways -> larynx closes (-> do tracheostomy)
Where are the swab sites for MRSA?
Nose
Throat
Perineum
What is infective mononucleosis?
“glandular fever”
Epstein-Barr virus infection (10% due to cytomegalovirus infection)
Transmitted via saliva - “kissing disease”
- fever
- pharyngitis
- adenopathy
What microbes are found in the throat?
100% of patients:
- Streptococcus viridians
- Staphylococcus
- Neisseria meningitidis
<100% of patients:
- Streptococcus pyogenes
- Streptococcus pneumoniae
- Haemophilus influenzae
- Lactobacilli
- Corynebacterium diptheriae
- Candida albicans
What is the difference between bacteraemia and septicaemia?
BACTERIAEMIA = bacteria are rapidly cleared from the bloodstream by liver and spleen macrophages (no symptoms produced)
SEPTICAEMIA = bacteria are not cleared and multiply in the bloodstream -> sepsis develops
What are the common microbes implicated in tonsillitis?
70% viral:
- adenovirus
- rhinovirus
- Epstein-Barr virus
30% bacterial
- Streptococcus pyogenes (beta-haemolytic)
What is quinsy? How is it treated?
Pus in the space between the tonsil and the wall of the pharynx, causing severe pain, difficulty swallowing, and trismus (difficulty opening mouth)
- antibiotics
- surgical incision of abscess to release pus and aid breathing (!carotid artery behind tonsil)
What are the majority of the bacteria found in the colon?
95%-99% anaerobes
95%-99% of anaerobes are Bacteroides fragilis
Others:
- Escherichia coli
- Enterococcus faecalis
What is dirty surgery? How can this be combatted?
High risk of wound infection
e. g.
- colon (organisms present before procedure)
- old traumatic wounds/devitalised tissue
- existing infection/perforation (presence of bacteria is likely if we are operating on the small bowel in the first place)
Give prophylactic antibiotics for surgery on the colon
= metronidazole for anaerobes + broad spectrum (gentamicin, cephalosporins) for Gram-ve bacilli & Gram+ve cocci/
OR co-amoxiclav
What are the microbes implicated in perianal abscesses?
Infection of (mucous) anal gland
Bacteroides, E. coli, Enterococcus faecalis, Lactobacillus
