4.1 Infections of the GI tract PART II Flashcards
What are enteric bacteria?
Give one thing they are resistant to?
The Enterobactericaea are a gram negative group of related bacteria that are known to reside in the intestines of the mammalian gut
They are resistant to bile salts and commonly have capsules
What are purpose of the LPS, O, K and H antigens of enteric bacteria
This classification of Salmonella based upon antigenic structure is known as the ________ scheme?
LPS (lipopolysaccharide): aids adherence and acts as an endotoxin
O-antigen: inhibits phagocytosis and provides a degree of heat stability
K-antigen: part of the capsule and creates a sticky layer to aid attachment to cellss of biofilm
H-antigen: ONLY present in bacteria containing flagellum (mobile) and allows adherence and protection from macrophages
Classified using the Kaufmann-White scheme
What is the most commonly found infection that co-exists with enterobacteria?
UTI’s
What are opportunistic pathogens give 2 examples
Found in normal microflora but have the potential to become pathogenic in situations such as a weakened immune system, altered microbiota and breached integumentary barriers
Examples:
- Escherichia Coli
- Klebsiella pneumoniae
- Proteus ss
- Citrobacter ss
What are obligate pathogens give 2 examples
Obligate pathogens always cause disease and can only survive and replicate within a host
Examples:
- Salmonella spp
- Shigella spp
- Yersinia spp
- Some E.Coli strains
What is meant by a ubiquitous organism?
What is meant by a facultative anaerobe?
What is meant by a strict/obligate aerobe?
Ubiquitous organism: organism that is present everywhere
Facultative anaerobe: is an organism that makes ATP by aerobic respiration when oxygen is available but can switch to anaerobic respiration if oxygen is absent
Strict aerobes: organisms that cannot make ATP in the absence of oxygen
Describe the structure of Salmonella
How are most grouped and how can they be sub-classified?
Where do they commonly reside
Salmonella is a gram-negative, facultative anaerobe that is rod-shaped, flagellated and belongs to the Enterobacteriaceae family
Nearly all grouped under S. enterica but can be further sub-classified based on their O (cell wall) and H (flagellar) antigens
They live in the intestinal tracts of warm and cold blooded animals but some species are ubiquitous.
What are the 2 main diseases caused by Salmonella in humans and what are they a result of?
Salmonella are the cause of two diseases called salmonellosis:
1) Enteric fever (typhoid): resulting from bacterial invasion in the bloodstream
2) Acute gastroenteritis: resulting from a food-borne infection
List 3 diseases caused by Salmonella and state specifically which strain causes these
1) S.typhi: typhoid fever (humans are the only host)
2) S. paratyphi A, B and C: paratyphoid fevers
3) S.typhimurium, S.montevideo, S.wien: cause salmonellosis
Salmonella is ingested in ______ food/water. The bacterium passes through the GIT and attaches to the ______ cells of the ______
It invades through the mucosa by endocytosis using ______ proteins on their surface AND induces ______ to persist in epithelial cells and macrophages
Inside the cell it produces enterotoxins leading to local ______ and then exits killing the host cell which triggers the symptoms of _________ and __________.
Salmonella is then shed in the ________ and after several days the symptoms alleviate without the need for specific therapy
Contaminated, M, jejunum, Invasin, phagocytosis, inflammation, abdominal cramps, diarrhoea, faeces
Typhoid fever occurs when salmonella temporarily enters the _______.
_______ may phagocytose but not digest S.Typhi and it can be carried to the _______, ______ and _______
In these locations it reproduces and re-enters the _______ where it travels and invades the ________, ________, and the _________ tissue of the bowel
blood, small intestine, WBCs, liver, spleen, bone marrow, blood, gallbladder, biliary system, lymphatic
What are the 4 stages of untreated Typhoid Fever and long does each last?
Each stage lasts about a week:
Stage 1: fever, bradycardia, malaise, headache, cough and epistaxis (25% of people)
Stage 2: continuing fever, bradycardia, distended abdomen, weight loss, dicrotic pulse (x2 beats) and delirium
Stage 3: high fevers + complications ➞ intestinal haemorrhage or perforation, encephalitis, dehydration, motionless
Stage 4: defervescence (very high fever) and potential death due to other complications that may arise
What complications of untreated Typhoid fever may lead to death?
- overwhelming infections
- pneumonia
- intestinal haemorrhage or perforation
- kidney failure
- peritonitis
What is meant by a ‘carrier’ of S.Typhi and why is this dangerous?
How would you treat?
A carrier is a healthy person who survived the disease, but still have the bacteria which are able to survive without causing further symptoms
Dangerous because carriers continue to spread the disease through excrement of their faeces without realising it
Treat with:
- prolonged antibiotics.
- removal of the gallbladder or site of the infection
Why may you remove gallbladder in a carrier of S. Typhi?
When spread through the bloodstream to distant sites, S.Typhi is able to establish a semi-permanent infection in the gallbladder meaning carriers can remain infected for years
What is shigella and what does it cause
What signs would be seen on infection, how is it transmitted and how would you treat
Shigella is gram (-), non-motile, non-spore forming, catalase (+) facultative anaerobe that causes Shigellosis
Signs: bloody faeces (dysentry) associated with intestinal pain
Mode of transmission is person-to-person
Treatment: manage dehydration, antibiotics for severe dysentery (e.g. ampicillin).
What are the 4 main species of Shigella?
group A ➞ shigella dysenteriae
group B ➞ shigella flexneri
group C ➞ shigella boydii
group D ➞ shigella sonnei
List 5 differences between diarrhoea and dysentery
1) diarrhoea presents as watery stool with NO blood, dysentery presents as mucoid stools may be blood
2) fever is less common in diarrhoea and more common in dysentery
3) diarrhoea affects small bowel, dysentery affects the colon
4) diarrhoea is viral cause, dysentery is mostly bacterial
5) diarrhoea doesn’t need antibiotics, dysentery almost always requires antibiotics
What enterotoxin is produced by shigella?
What is shigella’s mechanism of infection and how does this lead to dysentry?
What happens if shigella enters the blood?
Shigatoxin ➞ neurotoxic, enterotoxic and cytotoxic
1) bacteria are ingested and then invade the epithelial lining of intestines (does NOT penetrate)
2) multiplies in the small intestine and produces shigatoxin that inhibits host cell protein synthesis and damages epithelia
4) damage attracts leukocytes, triggers inflammation and causes release of mucus and blood leading to dysentery
If it enters the blood it can be phagocytosed very quickly and taken care of by our immune system. However, bacteria has adapted to only effect epithelial cells which allows a less effective host immune response
Give 6 ways in which various E.Coli strains can express pathogenicity?
1) O, H, K antigens
2) plasmids for virulence
3) shiga-like Toxin
4) type III secretion system
5) disrupt PM
6) receptors for attachment
What is meant by Type III secretion system that E.Coli has?
(T3SS) important virulence feature of Gram (-) bacteria that delivers effector proteins into host cells to subvert host cellular processes
List 3 conditions caused by E.coli
1) UTIs
2) neonatal meningitis: usually E. coli carrying the K1 capsular antigen (and group B strep)
3) Intra-abdominal infections (associated with intestinal perforation)
E.Coli can be classified by their virulence features and associated diseases ➞ what do the following classifications indicate
ETEC
EPEC
EIEC
EHEC
ETEC: enteroToxigenic, Travellers diarrhoea, produces 2 exotoxins HT (heat labile toxin) and ST (heat stable toxin) that cause infection that is non invasive and results in watery diarrhoea and NO fever….. similar to cholera
EPEC: enteroPathogenic, moderately invasive… similar to shigella
EIEC: enteroInvasive, causes dysentery and a host response that is clinically identical to shigella
EHEC: enteroHaemorrhagic, O157:H7 strain that produces the shigatoxin which stimulates an inflammatory response and can lead to haemolytic uraemic syndrome
What would the presence of blood and/or pus
cells in the faeces indicates?
An invasive infection with mucosal destruction ➞ Dysentery (NOT diarrhoea)
