GI tract pathogens Flashcards
Define toxinoses
Disease in the absence of colonisation
E.G. Staph aureus food poisoning
Define botulism
A rare but life threatening infection which causes muscle paralysis
Causative agent of botulism
Clostridium botulinim
Gram- positive rod
Obligate anaerobe - (Oxygen is toxic for it)
Has spores which produces botulimun toxin in low oxygen environments
Clinical presentation of botulism
Blurred vision, drooping of eyelids, difficulty speaking
Diarrhea and vomiting may occur
Progresses to paralysis
Those who lose ability to breath, ventilation may be necessary
Prevention and treatment strategies for botulism
1)Prevention through proper food preparation
2) Children under 12 months should not be fed honey
3) Treatment involves administration of antitoxin
Antibiotics for wound botulism
What are some of the medical applications of botulinum toxin
Despite being the most dangerous toxin, it can be used for both therapeutic and cosmetic effects due to its ability to cause localised muscle paralysis.
Therapeutic uses involve :
1) Hemifacial spasms - involuntary contractions to one side of the face
2) Overactive bladder - reduces involuntary nladder contractions
Cosmetic:
Used in botox to reduce wrinkles
Give some features of E.coli
Gram- negative, rod shaped, facultative anaerobe (can survive with or without oxygen)
2 Strains of E.coli and what does each do?
E.coli is highly diverse as only 20% of genes are common to all the strains.
Commensal strains are harmless and help the host by producing vitamin K (needed for blood clotting) and preventing colonisation of the intestine by harmful bacteria.
Pathogenic strains can cause a disease if they acquire certain genetic elements like plasmids etc. These genetic elements can turn E.coli into virulent strains which can causes UTIS, Sepsis and gastroenteritis
Define pathovar
Subtype of same bacterial species (E.coli), which causes a specific disease in specific way.
How many pathovars of E.coli are there and which ones?
6
Enteropathogenic
Enterotoxigenic
Enterohaemorrhagic
Diffusely adherent
Enteroaggresive
Enteroinvasive
How are e.coli characterised?
Based on the presence of surface antigens.
O antigen : part of LPS
H antigen= flagellin
K antigen = the capsule
Even if two E. coli have similar O or H types, they might not be closely related genetically.
Pathotyping is a based on how the strains cause disease and is the common method of characterising E.coli strains.
What are sources and transmission of E.coli?
Transmission occurs due to :
Undercooked contaminated meat
Unpasterurised dairy products (i.e. no heat treament carried out to kill the bacteria)
Contaminated fruit and vegetables
Environmental factors i.e. faecal contamination
Sources - GI tract of humans, cattle, pig, fish
What are non-invasive E.coli pathotypes?
non-invasive strains of e.coli cause disease by staying on the surface of intestinal lining. There is no penetration through the epithelial layer.
The infection is localised
These strains secrete exotoxins which disrupt gut function without need to invade
Name some strains of non-invasive E.coli
Enterohaemorrhagic
Enteropathogenic
Enterotoxigenic
Name a strain of partially invasive E.coli
Enteroinvasive
What are 5 different types of viruses capable of causing viral gastroenteritis
Rotavirus, noravirus, adenovirus, saprovirus and astrovirus
Which virus is the most common in children and in adults
Rotavirus - in children
Norovirus- in adults
Rotavirus characteristics
- has 10 different species (A-J) A is the most common
- double stranded RNA virus
- contains 6 structural and 6 non structural proteins
Structural proteins help with cell entry
Non structural (NSP1) help with viral replication and innate immune response - classified using 2 key surface proteins : VP7 and VP4
What are clinical presentations of rotavirus
Symptoms depend on previous infections and subject age, ranging from asymptomatic to severe
Highly contagious, with symptoms onset within 24-72 hours
Nearly every child is infected with a rotavirus at least once by the age of five.
Immunity develops with each infection so subsequent infections are less severe, adults are rarely affected
Define Giardiasis
Diarrhoeal disease caused by protozoan parasite, giardia duodenalis.
infection is most common in children.
How is giardiasis spread.
Through cysts in contaminated water, food or by a faecal-oral route.
Cysts are very resistant and can survive for months in cold water and warm climates.
Both cycts and trophozoites are found in faeces (diagnosis)
Define cyptosoridosis
Watery diarrhea caused by parasite cryptosporidium spp.
How is cryptosporidium spread
Transmitted through infected water
Occasionally food sources such as chicken salad may act as vehicle for transmission.
Which 2 species are the most common in causing disease?
C.parvum and C.hominis
