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Year 2 Medical Microbiology
medical microbiology enterobacteriae
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Cards (114)
What is the phylogenetic position of Enterobacterales?
Order:
Enterobacterales
Family:
Enterobacteriaceae
(Genera: Salmonella, Escherichia, Shigella)
Family:
Yersiniaceae
(Genus: Yersinia)
Phylum:
Proteobacteria
Order:
Campylobacterales
(Genera: Campylobacter, Helicobacter)
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What are the general morphological and biochemical characteristics of Enterobacterales?
29
genera including
Escherichia
,
Salmonella
,
Klebsiella
,
Enterobacter
Optimum temperature:
37
°C
Gram-negative
, non-spore forming
rods
Facultative
anaerobes
Catalase
positive
Oxidase
negative
Nitrate reductase
positive
Motile via
peritrichous flagella
(with a few exceptions)
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What is the G+C content and genome size of Enterobacteriaceae?
G+C content 38-60
%;
genome size
~
5 M bases
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What are the habitats and routes of infection for Enterobacteriaceae?
Habitats:
gastrointestinal
tract of humans, animals, and insects
Widespread
environmental contamination
: sewage, soil, water, plants,
food
Routes of infection:
oral
, via
wounds
,
urinary
tract,
respiratory
tract
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How many people are affected by food-borne illness in the UK each year?
1 million
people
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What percentage of urinary tract infections (UTIs) are caused by E. coli?
~
70%
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What are the general characteristics of the genus Salmonella?
2
species,
7
subspecies, >
2
,
600
serovars
Some serovars are
host-restricted
(e.g., Typhi for humans)
Most serovars infect a
wide
range of hosts (e.g., Typhimurium)
Classification of Salmonella species is
complex
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How can Salmonella be distinguished from E. coli and Shigella?
H2S
production
Acid
production during
carbohydrate
fermentation
Non-lactose
fermenter
Indole test
negative
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What color does Salmonella appear on XLD media?
Black
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What are the phases of typhoidal Salmonella infection?
1st phase:
slow fever
,
rose spots
,
mild bacteraemia
2nd phase:
organism reaches gallbladder
,
formation
of
ulcers
,
haemorrhage
,
death
(
20
%)
Typhoid state:
“muttering delirium”
or
“coma vigil”
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How many new cases of typhoid fever occur each year?
~
15 million
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What is the global burden of non-typhoid Salmonella (NTS) infection?
~
94 million
cases (155,000 deaths) each year
About
80 million
estimated as foodborne origin
UK data:
8-9,000
confirmed cases per year
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What are the predominant serovars of non-typhoid Salmonella?
Salmonella
Enteritidis
Salmonella
Typhimurium
Salmonella
Heidelberg
Salmonella
Newport
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What is the primary route of NTS Salmonella infection?
Faecal-oral transmission
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What are the main virulence factors of Salmonella?
Type
3
secretion systems (
T3SSs
)
SPI1
: invasion of
intestinal epithelial cells
SPI2
:
intracellular replication
and
systemic
infection
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What is the mechanism of UPEC infection?
Periurethral contamination
with
UPEC
can occur after
bowel movement
or during
sexual intercourse
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What are the types of urinary tract infections (UTIs) caused by UPEC?
Asymptomatic
bacteriuria
Cystitis
(bladder infection)
Pyelonephritis
(kidney infection)
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What percentage of women experience a UTI in their lifetime?
50%
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What is the major cause of CNS infections in infants under 1 month old?
Meningitis-associated E. coli
(
MNEC
)
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What are the symptoms of intestinal pathogenic E. coli (InPEC) infections?
Mild watery diarrhoea
(typically ETEC)
Dysentery
(typically EIEC)
Severe
bloody diarrhoea
(typically EHEC)
Persistent
diarrhoea (typically EPEC, EAggEC)
Vomiting
,
abdominal pain
,
fever
(all)
Haemolytic uraemic syndrome
(HUS) only
EHEC
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What are the characteristics of Enterotoxigenic E. coli (ETEC)?
Causes
watery
diarrhoea
High
infectious
dose: \(10^6\) organisms
Site of
damage
: small intestine; extracellular
Toxins
: LT and ST
Treatment
: self-limiting; oral rehydration
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What is the K-1 antigen synthesized by?
1 capsular
antigens
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Why is
K-1 antigen
considered a major
virulence
factor?
It is a
homopolymer
of
sialic acid
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In which populations are K-1 strains commonly found?
In the
GI
tract of
pregnant
women and
newborns
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What is the prevalence of gastrointestinal infections caused by intestinal pathogenic E. coli (InPEC) in the UK?
1
in
5
people are affected each
year
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How is InPEC transmitted?
By infected
food
and
water
or via
person-to-person
contact
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What symptoms are typically associated with ETEC infections?
Mild watery diarrhoea
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What symptoms are typically associated with
EIEC
infections?
Dysentery
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What symptoms are typically associated with EHEC infections?
Severe
bloody diarrhoea
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What symptoms are typically associated with
EPEC
and
EAggEC
infections?
Persistent diarrhoea
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What symptoms are common to all pathotypes of InPEC?
Vomiting
,
abdominal pain
, and
fever
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Which pathotype is associated with haemolytic uraemic syndrome (HUS)?
EHEC
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What are the characteristics of ETEC infections?
Symptoms:
Watery diarrhoea
Infectious dose:
High
(
10
^
6
organisms)
Site of damage:
Small intestine
;
extracellular
Toxins: LT and ST
Treatment:
Self-limiting
;
oral rehydration
;
antibiotics
(e.g. fluoroquinolones)
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What are the characteristics of EIEC infections?
Symptoms:
Dysentery
,
bloody
diarrhoea
Infectious dose:
High
(10^6-10^10 organisms)
Site of damage:
Colon
;
intracellular
Toxins: None
Treatment:
Oral rehydration
;
antibiotics
(e.g. azithromycin)
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What are the characteristics of EAggEC infections?
Symptoms:
Persistent
diarrhoea
Infectious dose:
High
(10^10 organisms)
Site of damage:
Colon
;
extracellular
Toxins:
SPATEs
(proteases),
enterotoxins
Treatment:
Self-limiting
;
oral rehydration
;
antibiotics
(rarely)
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What are the characteristics of EPEC infections?
Symptoms:
Diarrhoea
Infectious dose:
High
(10^8-10^10 organisms)
Site of damage:
Colon
;
extracellular
Toxins:
Proteases
Treatment:
Self-limiting
;
oral rehydration
;
antibiotics
(rarely)
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What are the characteristics of EHEC/STEC infections?
Symptoms:
Bloody diarrhoea
,
kidney
disease
Infectious dose:
Low
(
50-500
organisms)
Site of damage:
Colon
;
extracellular
Toxins:
Shiga
toxin (
Stx
)
Treatment: None at present
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What is the function of the type 3 secretion system (T3SS) in EPEC/EHEC?
It enables the bacterium to export
proteins
directly into the
host cell
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What is the primary cause of shigellosis worldwide?
flexneri
and
S. sonnei
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How many cases of shigellosis occur annually worldwide?
Over
190 million
cases
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