15) Microbiology of GI Tract Flashcards
What are obligate aerobes?
Give an example
Must have oxygen to survive e.g Pseudomonas and Mycobacterium TB
What are obligate anaerobes?
Give an example
Die in the presence of oxygen e.g. Bacteroides fragilis, clostridial organisms
What are facultative anaerobes?
Give an example
Prefer oxygen but can live without it e.g. many gram-negative enteric bacteria such as E. Coli and gram-positive skin-dwellers such as Staphylococcus
What can clostridial organisms do to survive in oxygen?
Produce spores
What are the anaerobic zones of the GIT?
Parts of mouth - deep in taste buds, between teeth, gingival crevice areas
Small bowel
Colon
Why are human colonic bacteria important?
Synthesize and excrete vitamins that are absorbed by host e.g vit K, B12 and thiamine
Prevent colonisation by pathogens
Kill non-indigenous bacteria
Stimulate development of GALT (caecum and Peyer’s patches)
Stimulate production of natural antibodies
What are some features of bacteria that can allow them to survive and infect the GIT?
Endospores e.g. bacillus anthrax, clostridum tetani
Pili - adhere to epithelia
Biofilm
Why are biofilms on a prosthetic surface particularly dangerous?
No bloody supply close so difficult to get drugs to surface
What shape are the endospores of C. tetani?
Terminal drumstick
Give some examples of gram positive aerobic cocci:
Staphylococci, streptococci and enterococci
Give some examples of gram negative aerobic cocci:
Neisseria meningitidis and gonorrhoeae
Give some examples of gram positive aerobic bacilli:
Corynebacterium (diphtheria)
Bacillus (anthrax)
Lactobacillus
Mycobacterium TB
Give some examples of gram positive anaerobic bacilli:
Clostridia (tetani, perfringens, difficile)
Give some examples of gram negative enteric bacilli:
colon normal flora
E.coli, pseudomonas, klebsiella, salmonella, shigella, camplylobacter, helicobacter pylori Bacteroides fragilis (anaerobic)
Give some examples of gram negative non-enteric bacilli:
all aerobic
H. influenza, bordetella pertussis (whooping cough), brucella
What are the majority of mouth bacteria?
Anaerobes
What is noma/cancrum oris?
Bacteria causing tissue destruction, if individual is malnourished, dehydrated or immunocompressed
What causes oral thrush and how can it be treated?
Candida albicans
Amphotericin lozenges
What risk factors are there for oral thrush?
Newborns (immune system not developed) Diabetes Antibiotics Steroids Immune deficiency
What is dental caries and what organism causes it?
Teeth colonised by mouth bacteria and Strep. mutans
Causes cavities and teeth to break down
What bacteria causes parotitis?
S. aureus
What is Ludwig’s angina and what causes it?
Potentially life-threatening cellulitis or connective tissue infection of the floor of the mouth
Streptococci
What are the three swab sites for MRSA screening?
Nose, throat and perineum
What are the main bacteria found in the nose?
Staphylococcus and streptococcus
What are some of the main bacteria found in the throat?
Strep viridans
Strep pyogenes
Staphylococci
Neisseria meningitidis
When can Strep. viridans become a problem?
Dental procedures and teeth brushing where it can enter blood stream and stick to prosthetic surfaces
What percentage of tonsillitis is caused by viruses?
70% - adenovirus and rhinovirus
Which bacteria can cause tonsillitis?
Strep. pyogenes
What is quinsy?
Abscess between tonsil and wall of throat making eating and breathing hard
What are the main bacteria of the colon?
Anaerobes, particularly bacteroides and clostridial species, E. coli and enterococcus faecalis
Why is there a high risk of infection in gut surgery?
Abnormal numbers of bacteria
What prophylactic antibiotics can be given to reduce wound infections?
Metroniadazole and broad spectrum antibiotic (gentamicin or cephalosporin)
Co-amoxiclav
What is faecal peritonitis?
Faeces in peritoneal cavity, bacteria can enter blood
High mortality
What is a perianal abscess?
Glands in anal canal infected causing abscess around anus
What is an example of a normal vaginal commensal?
Lactobacillus
How does lactobacillus stop other micro-organisms from growing?
Converts glycogen into lactic acid, providing acidic environment
What happens if antibiotics kills lactobacillus?
Vaginal thrush
What organism is the most common cause of UTIs?
What is the next most common?
E. coli
Enterococcus faecalis
What would you be looking for on a MSU gram stain?
Gram neg bacilli (E. coli)
Gram pos cocci (Enterococci)
What is bacteraemia?
Bacteria rapidly cleared from bloodstream by liver/spleen macrophages, no symptoms
What is septicaemia?
Bacteria aren’t cleared and multiply in bloodstream
What does clostridium tetani cause?
Tetanus
What does clostridium dificile cause?
Pseudomembranous colitis
What does clostridium perfringes cause?
Gas/wet gangrene
What causes gastroenteritis?
Consumption of contaminated food or drink
What organisms can cause gastroenteritis?
Salmonella, campylobacter, listeria
What are the symptoms of gastroenteritis?
Vomiting and diarrhoea
What cause cholera and what are the symptoms?
Vibrio cholera leading mass movement of water and salt into lumen by secretion
Rice water diarrhoea and dehydration
What can helminth infestations cause?
Malabsorption
What can protozoal infections cause?
Giardia and cryptosporidium cause gastroenteritis
What cause traveller’s diarrhoea?
E. coli
What is the pathogenesis of traveller diarrhoea?
Heat stable or labile toxins released by E. coli resulting in watery diarrhoea
Usually self limiting
