Microbiology Flashcards
What is gastroenteritis
Diarrhea + vomiting due to enteric infections
What is dysentery
Diarrhea with blood / mucus
Infection at which part of GI tract causes large volume of diarrhea
Large intestine
What is considered as acute diarrhea
< 14 days
What is considered as chronic diarrhea
> 4 weeks
What is considered as traveller’s diarrhea
Diarrhea that develops during or within 10 days of returning from a resource limited country
Common pathogens causing traveller’s diarrhea
E. coli
Campylobacter
Shigella
Salmonella
List the bacteria causing gastroenteritis
Campylobacter Bacillus cereus Shigella Salmonella Staph. aureus E. coli
Which bacteria is the most common cause of gastroenteritis
Campylobacter
Which virus is the most common cause of gastroenteritis
Norovirus
List the viruses causing gastroenteritis
Rotavirus
Norovirus
Adenovirus
Gram stain of campylobacter
Gram negative bacillus
Which strain of campylobacter is the most common
C. jejuni
Symptoms caused by campylobacter
Watery /blood (30%) diarrhea + pain + fever
Which age group does campylobacter usually affect
young adults
How does campylobacter spread
from ingestion of
- uncooked poultry
- unpasteurized milk
- contaminated water
Incubation period of campylobacter
16 - 48 hours
What are the possible post Campylobacter infection conditions
Reactive arthiritis
Guillain Barre syndrome
What protein is reactive arthiritis associated to
HLA B27
When does Guillain Barre syndrome usually occur
1-2 weeks after infection
Gram stain of bacillus cereus
Gram positive bacillus
What toxins do bacillus cereus produce
Heat stable vomiting enterotoxin
Heat labile diarrheal toxin
What type of food does Bacillus cereus like
Starchy food left in room temperature overnight then reheated
Symptoms caused by bacillus cereus
Profuse vomiting +/- diarrhea
Why may diarrhea not occur in bacillus cereus infection
Because the enterotoxin that causes diarrhea is heat labile so does not tolerate heat when the starchy food is reheated
Incubation period of Bacillus cereus
0.5-6 hours for vomiting
8-12 hours for diarrhea
Gram stain of staphylococcus aureus
Gram positive
How does staphylococcus cause symptoms
Preformed toxin in poultry / milk / fish
toxin act on vomiting centre
Symptoms caused by staphylococcus aureus
Vomiting + diarrhea + nausea
maybe fever and pain
Incubation period of Staph. aureus
1-6 hours
Gram stain of Salmonella
gram negative
Bacteria in enterobacteriaceae family
E.coli Klebsiella Salmonella Shigella Citrobacter
Which type of salmonella causes gastroenteritis
Non-typhoidal salmonella
Examples of non-typhoidal salmonella
Salmonella enterica
Salmonella typhimurium
Transmission of salmonella
Ingestion of
- raw poultry
- raw egg
- unpasteurized milk
- contaminated fruits and veg
- contaminated water
- anal sex
Who are more at risk of salmonella infections
Haemochromatosis people
immunocompromised
infant sand adults
Why are haemochromatosis patients more at risk of salmonella infection
They have high iron levels. Salmonella needs iron to determine their virulence and pathogenicity
Symptoms caused by salmonella
Watery / bloody diarrhea + vomiting + fever + pain
Incubation period of salmonella
8 - 72 hours
Gram stain of shigella
Gram negative bacilli
Are enterobacteriaceae aerobic / obligate anaerobes / facultative anaerobic
Facultative anaerobic
Serotypes of shigella
Serogroup A
Serogroup B
Serogroup C
Serogroup D
Which serogroup of shigella is most pathogenic
A
Name of serogroup B of Shigella
S. flexneri
Name of serogroup A
S. dysenteriae
Which serogroup of shigella causes the mildest infection
D
What toxins do shigella produce
Shigella toxins (stx) - type 1 and 2
How does shigella toxin damage cells
Inhibit protein synthesis of the cell
Which STx is more potent
Type 2
Which age group is most commonly affected by shigella
young children
Transmission of shigella
From contaminated water / human to human
Symptoms caused by shigella
watery / bloody diarrhea + fever + pain
Which serogroup of shigella can cause HUS
S. dysenteriae (Serogroup A)
What is HUS (haematuria and renal failure)
Microangiopathic haemolytic anaemia + thrombocytopenia + kidney injury
Which STx is the most common cause of HUS
type 2
Which STx is more potent
Type 2
How does STx cause HUS
1) STx inhibits protein synthesis of the enterocyte
2) enterocyte dies, STx enters bloodstream
3) STx damage endothelial cells
4) causes platelet activation and aggregation
5) clot forms
6) STx carried to kidneys to cause haematuria, kidney injury
Which E.coli produces shiga toxin
E. coli 0157
Strains of E. coli
EHEC
EIEC
ETEC
EAIC
Which strain does E.coli 0157 belong to
EHEC enterohaemorrhagic
Transmission of E.coli 0157
from
- contaminated water
- unpasteurised milk
- contaminated meat and veg
- human to human
Which age groups do E.coli 0157 most commonly affect
young children below 5 years old
elderly
Incubation period of shigella
1 - 2 days
Incubation period of E. coli
3- 4 days
What should you must do after discovering e.coli 0157
Notify health protection unit
Which E. coli strains are related to traveller’s diarrhea
ETEC
EAIC
Which E. coli strain produces shiga like toxin
EIEC
Management of gastroenteritis
Rehydration is key
Antibiotics are reserved for immunosuppressed / elderly / systemically unwell patients
Antibiotics against campylobacter
Macrolide - erythromycin
What type of antibiotic is macrolide
Broad spectrum antibiotic
Antibiotics against salmonella and shigella
Ciprofloxacin (levofloxacin)
Which virus causing gastroenteritis is associated with daycare exposure
Rotavirus
Transmission of rotavirus
person - person
faecal - oral
Which age group is most commonly affected by rotavirus
Young children
What may develop post rotavirus infection
Malabsorption, causing more diarrhea
How to diagnose rotavirus
PCR in faeces
Symptoms caused by rotavirus
watery diarrhea + vomiting + fever
What pathogens do not cause bloody diarrhea
Bacillus cereus
Rotavirus
Staph. aureus
EIEC
Type of vaccine for rotavirus
Live attenuated
Transmission of norovirus
faecal - oral
droplet
Effect of norovirus on healthy vs frail
Self limiting in healthy people but can cause kidney injury in frail
Symptoms caused by norovirus
explosive diarrhea + vomiting + fever + myalgia
What is special about norovirus
Symptoms come abruptly and unpredictably
Incubation period of norovirus
< 24 hours
How is norovirus diagnosed
PCR on vomit
What immune cells are for protection against worms
Eosinophils
Mast cells
What immune cells are for protection against bacteria
T lymphocytes
B lymphocytes
Complement system
What immune cells are for protection against viruses
T lymphocytes
B lymphocytes
What immune cells are for protection against fungi
T lymphocytes
eosinophils
What immune cells are for protection against protozoa
t lymphocytes
eosinophils
Which pathogens causes dysenteric gastroenteritis
E.coli 0157
Campylobacter
Salmonella
Shigella
What are the characteristics of enterobacteriaceae
Gram negative bacilli Oxidase negative Glucose fermenting Facultative anaerobic Non spore forming
What agar is used to test for lactose
Macconkey agar
Which enterobacteriaceae are lactose negative
Shigella
Salmonella
Which enterobacteriaceae are lactose positive
Klebsiella
Citrobacter
E.coli
What molecular tests are used to classify bacteria
MALDI-TOF
16sRNA
What does MALDI-TOF look at
mass spectrometry, analyses protein components in cell wall
Gram positives in GI tract
Candida
Strep. viridans
Staphylococci
Where are gram positives mostly located
In mouth, only few in stomach
Timeline of septic shock
Infection -> SIRS -> Sepsis -> Septic shock
What is SIRS and what causes it
Systemic inflammatory response syndrome; caused by infection / burns / trauma / injury / pancreatitis
What are the signs that show SIRS
HR = <90 Temp = >38 or <36 RR = >20 WCC = >12000
What is sepsis
Organ dysfunction caused by a dysregulated host response to infection
What causes of SIRS do not cause sepsis
Burns / trauma / injury / pancreatitis; sepsis must be due to infection
What pathogens are commonly found in hospitals
Staphylococcus aureus (often MRSA)
E. coli
Klebsiella
Pseudomonas
What should be monitored when giving gentamicin
Renal function
Complications of gastroenteritis
Post infectious IBS Sepsis / septic shock Acute kidney injury HUS Dehydration Guillain Barre / reactive arthritis - campylobacter
Gram stain for C. difficile
Gram positive
When does C.difficile become infectious
When the normal gut flora becomes suppressed by broad spectrum antibiotics
What drug increases risk of C.difficile infection
Any broad spectrum antibiotics
PPI
Complication of C.difficile
toxic megacolon
Symptoms and signs of C.difficile infection
abdominal pain
Diarrhea
Raised WCC
Neutrophilia
Treatment of C.difficile
oral vancomycin
Second line treatment of C.difficile
oral fidaxomicin
Third line treatment of C.difficile
Oral vancomycin + IV metronidazole
What is the treatment for recurrent C.difficile infection
Faecal microbiota transplant
Antibiotic for travellers diarrhea due to E. coli
Rifaximin
Which antibiotics are highly associated with C.difficile infection
Cephalosporins - ceftriaxone
Clindamycin
Co-amoxiclav