Background 3 GI Flashcards
why is direct microscopy of no use with stool samples
heavy growth of normal flora
why is blood agar plate not used for stool samples
not possible to distinguish pathogen from normal flora
what type of media is used for stool samples
indicator media such as macconkey
samlonella and shigella are both
non lactose fermenters on macckoney agar
e.coli is usually a
lactose fermenter on macconkey
name a media which contains more inhibitory substances than macconkey
xld
on xld salmonella is a
red colony with a black centre
why does salmonella have a black centre in xld
becuase it produces H2s
what does shigella loook like on xld
red colony
e.coli looks like what on xld
it doesnt grow on xld
which pathogens are associated with gi infection in the uk?
salmonella, shigella and campylobacter
which pathogens are important to search for if the patient has travelled to an area where cholera is endemic?
vibrio
overseas travel would require the stool to be examined for
ova, cysts and parasites
campylobacter selective media is incubated for how many hours before it is examined?
48 hours
non lactose fermenters on the macconkey plate are picked off for biochemical testing such as the
oxidase test
the organisms that are oxidase negative are further tested biochemically e.g. a ____ test
urea
all urea negative isolates are
identified biochemically overnight
with the xld plate the red colonies are tested using
oxidase first
all oxidase negative isolates are tested further (from the xld plate) using
urea
the campylobacter selective media is examined for the presnece of colonies showing the
typical morphology of campylobacter species
suspicious colonies on the campylobacter are
gram stained and checked biochemically (oxidase)
if biochemistry identified salmonella and shigella colonies which tests are performed
agglutination tests to confirm the result using specific anti-sera
the most common subspecies of salmonella in the uk are
salmonella enteritidis and salmonella typhimurium
describe salmonella
gram negative rods, oxidase negative, non lactose fermenters on macconkey agar
typhoid is caused by
salmonella typhi
how is typhoid transmitted
contaminated water or by an asymptomatic carrier
shigella is also known as
bacillary dysentery
shigella is caused by
shigellae
the infective dose of shigellae is very
small
transmission of shigella is by
direct contact
what are the most common types of shigella in the uk?
shigella sonnei and shigella flexneri
describe shigellae
gram negative rods, oxidase neg, non lactose fermenters on macconkey agar
most common cause of gastro enteritis in the uk
campylobacter jejuni
what is the usual source of infection of campylobacter
poorly cooked poultry , contact with young animals
campylobacter enteritis usaully occurs in
adults and older children
symptoms of campylobacter enteritis are
severe bloody diarrhoea
describe campylobacter jejuni
microaerobic organism, thin curved gram neg rod, oxidase positive
verotoxin producing e.coli causes
haemorrhagic colitis and HUS Hemolytic uremic syndrome
what is e.coli usually tansmitted by
raw meat
e.coli O157 plated on sorbital macconkey doesnt ferment sorbitol so forms
colourless colonies
other e.coli colonies not o157 produce which colour colonies on sorbitol macconkey
dark pink
describe e.coli O157
gram negative rod, oxidase negative
what causes cholera
vibrio cholerae 01 or 01239
v cholerae produces a toxin causing secretions of fluids into intestine causes
severe diarrhoea
transmission by
water or food
vibrio cholera is isolated on which type of agar and which colour does it grow as
TCBS agar and grows as yellow colonies
describe v.cholera
gram neg curved rod and oxidase positive
rota virus causes 30-60% of GI infections in
infants
rota virus is rare in
children and adults
how is rotavirus transmitted
in nurseries and playgroups poor hand washing and hygiene
what is the most common waterborne disease in the uk?
cryptosporidiosis
what causes cryptosporidiosis and what exactly is it
cryptosporidium parvum is a parasite
how is cryptosporidium parvum excreted from a host
as a chemical resistant oocyst
how is cryptosporidium seen in the lab
by examining stool samples using ZN stain
