Microbiology of the GIT Flashcards Preview

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Flashcards in Microbiology of the GIT Deck (23):

What is a gram-negative, non-spore forming, anaerobic bacteria that is found in the colon?

Bacteroides fragilis


What is meant by the term ‘obligate anaerobes’?

These microorganisms are unable to survive in the presence of oxygen (at least at atmospheric
pressure). They survive and thrive in the absence of oxygen.


Which parts of the GIT are predominantly anaerobic zones?

Parts of the mouth, small bowel and Colon


Describe four beneficial roles that bacteria play in the human GIT

o Prevent colonisation of pathogens
o Stimulate development of Mucosal associated lymphoid tissue
o Stimulate production of natural antibodies
o Kill non indigenous bacteria
o Assist in the digestion of certain polysaccharides
o Play a role in the synthesising of certain vitamins (B12, Vit K)


A man is involved in a fight and punches another person in the mouth. He has a small
laceration on his hand as a result. Why is this small wound potentially very serious?

The human mouth contains lots of bacteria (especially anaerobic) and even a small laceration
(especially if it involves a joint) can lead to a serious infection and possible joint destruction. It is
relatively common to see a hand laceration caused by this mechanism.


A man with a prosthetic heart valve needs some wisdom teeth removed. Explain why he
might receive prophylactic antibiotics?

This question is really just trying to reinforce the fact that the mouth contains a high concentration
of bacteria. Dental procedures (in fact even brushing and flossing) cause a bacteraemia (presence of
bacteria in the blood) which can increase the chances of a prosthetic heart valve being colonised by
these bacteria. Prosthetic heart valves can be colonised more easily than normal valves leading to
infection of the endocardial surface of the heart (infective endocarditis). Giving prophylactic
antibiotics is thought to reduce the duration of the bacteraemia and hence the likelihood of the
heart valve being colonised.


A twenty year old man goes to his GP with what he thinks is tonsillitis. The GP agrees that
it is. Should he be given antibiotics?

There is no right or wrong answer to this very common question, but it is worth noting that most
cases of Tonsillitis are caused by viruses. The decision to give antibiotics should not be a knee jerk
reaction (usually in response to a demanding patient) but based on the presence of Tonsillar
exudates or signs of secondary pharyngitis. Most people should just receive supportive treatments
to reduce their pain and fever and to maintain adequate hydration.


A 16 year old girl is brought to her GP by her mother with a twenty four hour history of profuse
vomiting with watery diarrhoea. The GP thinks this episode might be caused by the Norovirus
(formally known as the Norwalk virus). How is this virus spread?

Faeco-oral route by person-person contact or via aerolisation of virus


What is the normal incubation period of the norovirus?

Normally 1-2 days


What other symptoms other than vomiting and diarrhoes can be present in a Norovirus infection?

Apart from profuse vomiting (non bloody, Non bilious) and watery diarrhoea (non bloody)she may
have suffered abdominal cramps, headache and a low grade fever.


How would the GP assess whether this girl was dehydrated?

There are many ways. Common simple ones include the assessment of mucous membranes, skin
turgor and whether or not the person has sunken eyes. Signs of shock in severely dehydrated
patients will include tachycardia and tachypnoea. The girl might mention that she has not passed
much urine.


The GP wishes to reassure both this girl and her mother. What duration of symptoms is
likely from Norovirus and what are the treatment options for this illness?

The symptoms usually last 1-3 days and there is no specific treatment just supportive measures
surrounding correct fluid and electrolyte intake.


How would you define traveller’s diarrhoea?

Traveller’s diarrhoea is defined as the production of three or more loose watery stools during or
shortly after travelling abroad.


Entero-toxigenic E Coli (ETEC) is a common cause of traveller’s diarrhoea. What type of
bacteria is this?

Facultative anaerobic gram-negative bacilli


What type of diarrhoea is commonly associated with Entero-toxigenic E Coli (ETEC)?

Watery diarrhoea without blood or mucus


Briefly describe the mechanism by which this Entero-toxigenic E Coli (ETEC) causes diarrhoea?

ETEC bacteria colonize the mucosal surface of the small intestine. The bacteria use fimbrial adhesins
(projections from the bacterial cell surface) to bind enterocyte cells in the small intestine. Adhesion
to the mucosal epithelial cells allows for transfer of enterotoxins produced by ETEC bacteria which
stimulate the release of liquid from the cells lining the intestinal walls. ETEC make two toxins, heatlabile
(LT) and heat-stable (ST), that cause intestinal epithelial cells to secrete excess fluid. Some
strains produce only one of the toxins while others produce both.


What symptoms does Entero-toxigenic E Coli (ETEC) infection of the mucosal surface of the small colon produce?

ETEC infection results in the production of abundant watery diarrhea and abdominal cramping.
Other symptoms such as fever, vomiting, chills, headache, muscle aches, and bloating can also occur
but are less common. Illness usually lasts 3-4 days following exposure to the bacteria but can persist
for up to 3 weeks.


How can Entero-toxigenic E Coli (ETEC) infection be treated?

Supportive measures including rehydration tend to be sufficient for recovery, and
hospitalization or antibiotics are usually not required


Name two other common causes (other than ETEC) of traveller’s diarrhoea?

Salmonella spp


Name a normal vaginal commensal, which can convert glycogen to lactic acid creating an acidic environment which prevents other bacteria (like candida albicans) growing

Lactobacillus (gram-positive)


Which colonic bacteria can survive on perineal skin?

E coli
Enterococcus faecalis


Which microbes are the most common cause of UTIs?

1. E coli (primarily) (gram-negative bacilli)
2. Enterococcus faecalis (gram-positive cocci)
3. Then various gram-negative enteric bacilli (is something abnormal happening to get an infection of these?


Which two MSU Gram Stain results do not indicate a UTI?

Gram-positive bacilli
Gram-negative coccus