GI Infections- I have started reordering these cards, will finish soon. daniel Flashcards
Anaerobic organism responsible for GI infections
Clostridia (Gram +ve rod)
3 subspecies of clostridium responsible for GI infections
Botulinum Perfringens Difficile
Name of disease caused by Clostridium botulinum
Botulism
Clostridium botulinum: microscopic features
Gram +ve Rod-shaped Anaerobic Spore-forming Motile Produces the neurotoxin botulinum
How is Clostridium botulinum transmitted?
Botulinum toxin can be produced by the bacteria if present in canned/vacuum packed foods. Botulism is contracted if the toxin is ingested without inactivation by cooking. EMQ keywords: child eating honey, student eating beans from a dented can
How does botulism present?
Botulinum toxin blocks ACh release from peripheral nerves, causing a *descending* paralysis *The descending nature of paralysis differentiates from Guillain-Barré (differential diagnosis)
What is the treatment for botulism?
Botulism antitoxin
Clostridium perfringens: microscopic features
Gram +ve Rod-shaped Anaerobic Spore-forming
How does Clostridium perfringens cause GI infection?
Main culprit is reheated meat The “superantigen” clostridium perfringens enterotoxin (CPE) binds directly to the TCR and MHC outside the peptide binding site. The subsequent massive cytokine production by CD4 causes systemic toxicity and suppression of adaptive response
How does a clostridium perfringens infection present?
Acts on small bowel 8-16 hours incubation Watery diarrhoea Cramps Symptoms usually last 24 hours Can cause “gas gangrene” (gas producing muscle necrosis)
Clostridium difficile: microscopic features
Gram +ve Spore-forming Anaerobic Motile Long, irregular (often drumstick- or spindle-shaped) cells with a bulge at their terminal ends
How does C.diff cause GI infection?
Via 2 exotoxins, A and B
What is the name for the bowel inflammation caused by Clostridium difficile?
Pseudomembranous colitis
What iatrogenic factor can make a C.diff infection more likely?
Use of antibiotics, specifically cephalosporins and fluorquinolones
How is Clostridium difficile treated?
Metronidazole or vancomycin PO
2 aerobic organisms responsible for GI infections
Bacillus cereus (Gram +ve rod) Staphylococcus (Gram +ve)
How is bacillus cereus commonly ingested?
Reheated rice. Spores germinate while rice is at room temperature, then may not be killed by reheating
What is the incubation period for bacillus cereus?
Diarrhoeal form: 6-15 hours (related to raised cAMP level) Emetic form: 30 minutes to 6 hours (related to superantigen)
How does bacillus cereus infection present?
Either sudden vomiting or watery, non-bloody diarrhoea
What is the treatment for bacillus cereus?
None, self limiting
Subspecies of staphylococcus responsible for GI infections
Staph aureus
Staphylococcus microscopic features
Gram +ve Cocci Catalase +ve Coagulase +ve Appears in tetrads/clusters on Gram stain Beta haemolytic on blood agar
How does Staph aureus cause GI infection? (mode of action)
Produces enterotoxin - exotoxin that acts as a superantigen, releasing IL1 and IL2 which stimulate diarrhoea
What is the main virulence factor of Staph. aureus?
Protein A
How does Staph aureus infection present?
Prominent vomiting and watery, non-bloody diarrhoea
What is the treatment for Staph aureus?
None, self limiting
Lactose fermenting organism in Enterobacteriaceae family, responsible for GI infections
E(-scherichia) coli (Gram -ve, facultative anaerobe, oxidase -ve)
4 subspecies of E. coli
Enterotoxigenic E. coli (ETEC) Enteroinvasive E. coli (EIEC) Enterohemorrhagic E. coli (EHEC) Enteropathogenic E. coli (EPEC)
What does ETEC stand for?
Enterotoxigenic E. coli (Can also remember T=travellers)
How does ETEC cause travellers diarrhoea? (mode of action)
Produces 2 enterotoxins: heat-labile enterotoxin (LT) and heat-stable enterotoxin (ST) LT stimulates adenyl cyclase and cAMP ST stimulates guanylate cyclase
Which parts of the GI system do the ETEC entertoxins (LT and ST) act upon?
Jejunum and Ileum NOT the colon
What does EIEC stand for?
Enteroinvasive E. coli
What is the name of the disease caused by EIEC?
Invasive dysentery
What does EHEC stand for?
Enterohemorrhagic E. coli
What is the name of the toxin produced by EHEC?
Verotoxin
What does EPEC stand for?
Enteropathogenic E. coli (Can also remember P=paeds)
What paediatric disease is caused by EPEC?
Infantile diarrhoea
What is HUS and how is it caused?
Haemolytic-uremic syndrome Disease characterized by hemolytic anemia, acute kidney failure (uremia) and thrombocytopenia Usually caused by E. coli toxin O157:H7, a particularly infamous strain of the EHEC subspecies
What is the source of E. coli?
Human faeces - contaminated food/water
What is the treatment for E coli?
Usually self limiting and should avoid antibiotics. Occasionally ciprofloxacin may be rquired
3 non-lactose fermenting organisms in Enterobacteriaceae family, responsible for GI infections
Salmonella (Gram -ve rod) Shigella (Gram -ve, facultative anaerobe, non-spore-forming, non-motile, rods) Yersinia enterocolitica (Gram -ve, bacillus-shaped)
3 subspecies of salmonella
Typhi Paratyphi Enteritides
In relation to salmonella, what does Vi Ag stand for?
Vi (Virulence) antigen. Present on pathogenic strains of salmonella
What is the Kauffman–White classification?
A system that classifies the genus Salmonella into serotypes, based on their surface antigens
How many types of surface antigen can salmonella be classified by, and what are they?
3 types: O, H and Vi
Which gas is produced by salmonella and can therefore be used for detection?
Hydrogen sulphide (H2S)
Which compound should salmonella be grown on to encourage H2S production, and in which test is this used?
Ferrous sulfate Used in the triple sugar iron test
Name 3 media used for the selective growth of salmonella
Triple sugar iron (TSI) agar Xylose lysine deoxycholate (ZLD) agar Selenite F broth
Which 2 subspecies of salmonella cause enteric fever?
Typhi Paratyphi
Can enteric fever be carried by animals?
No, only human-human transmission (spread by eating or drinking food or water contaminated with the feces of an infected person)
What is enteric fever also known as?
Typhoid
Where in the body do salmonella typhi and paratyphi multiply?
Peryer’s patches (aggregations of gut associated lymphoid tissue, found in the ileum)
What percentage of the population are salmonella carriers and whereabouts in the body is it carried?
3% Carried in the gallbladder where salmonella is able to form a robust biofilm on gallstones
Give 2 symptoms of enteric fever
Slow onset fever Constipation
Give 6 clinical signs of enteric fever
Slow onset fever Relative bradycardia Splenomegaly Rose spots Anaemia Leukopaenia
What is the treatment for enteric fever (and salmonella enteritides if required)?
Ceftriaxone or ciprofloxacin
How is salmonella enteritides transmitted?
Poorly cooked poultry, eggs and meat
Which parts of the body are typically infected by salmonella enteritides?
Small and large bowel (Bacteraemia infrequent)
What is the main symptom of salmonella enteritides?
Self limiting non-bloody diarrhoea
Which parts of the GI system are affected by shigella, and how are they affected?
Distal ileum and colon Mucosal inflammation
Give 3 symptoms of shigella
Fever Pain Bloody diarrhoea
What is the name of the toxin that causes the symptoms of shigella?
Shiga enterotoxin
What is the treatment for shigella
Usually self limiting Antibiotics should be avoided, but ciprofloxacin if required
What is the disease caused by shigella also known as?
Dysentery
What is the name of the disease caused by yersinia enterocolitica?
Yersiniosis
What inflammatory affects does yersiniosis have on the GI system?
Enterocolitis Mesenteric adenitis w/necrotising granulomas
Give 2 potential complications of yersiniosis
Reactive arthritis Erythema nodosum
How is yersinia enterocolitica transmitted?
Food contaminated with animal faeces (many animals are a natural reservoir/carrier)
What is the preferred temperature of yersinia enterocolitica?
4C (cold enrichment)
3 “miscellaneous” bacterial organisms responsible for GI infections
Vibriosis (Gram -ve, comma shaped, late lactose fermenters, oxidase +ve) Campylobacter (Gram -ve, curved/comma/S-shaped/spiral, microaerophilic, oxidase-positive, catalase-positive, nonfermentative) Listeria monocytogenes (Gram +ve, facultative anaerobe, V/L shaped, beta haemolytic, aesculin +ve, tumbling motility)
3 protozoan organisms responsible for GI infections
Entamoeba histolytica Giardia lamblia Cryptosporidium parvum
Can mycobacteria cause GI infections?
Yes, especially in HIV +ve pts eg Mycobacterium tuberculosis, mycobacterium avium complex
5 viruses responsible for GI infections
Rotavirus Adenovirus Norovirus Poliovirus Enteroviruses - coxsackie, ECHO/echovirus (Enteric Cytopathic Human Orphan)
3 subspecies of vibriosis
Cholera Parahaemolyticus Vulnificus
Subspecies of campylobacter
Jejuni
Vibrio cholerae - microscopic features
Gram-negative comma-shaped bacterium Lives in brackish or saltwater.
What is the name of the disease caused by pathogenic strains of Vibrio cholerae?
Cholera
What is the pathomnemonic presenting feature of cholera?
Rice-water stool
How is cholera transmitted?
Via human faeces - therefore often involves shellfish (because they feed on sewage)
Describe the process by which Vibrio cholerae acts on the gut to cause diarrhoea
- Increase in cAMP - Opens Cl channels at the apical membrane of enterocytes - Efflux of Cl ions to the lumen, causing loss of H2O and electrolytes - Result is massive diarrhoea but no inflammation of the gut
What is the treatment for cholera?
Supportive
Vibrio parahaemolyticus - microscopic features
Gram-negative Curved Rod-shaped Found in brackish saltwater
How is vibrio parahaemolyticus often transmitted to humans?
Ingestion of raw/undercooked seafood Common in Japan
How does vibrio parahaemolyticus present?
3 days of diarrhoea Often self-limiting
Vibrio vulnificus - microscopic features
Gram-negative Motile Curved Rod-shaped
Who is likely to catch Vibrio vulnificus?
Shellfish handlers
How does Vibrio vulnificus usually present?
Cellulitis
How can Vibrio vulnificus present in HIV patients?
Fatal septicaemia with D+V
What is the treatment of choice for both Vibrio parahaemolyticus and Vibrio vulnificus?
Doxycycline
Campylobacter jejuni - microscopic features
Gram-negative Oxidase +ve Curved Helical/S-shaped Non-spore forming Microaerophilic Sensitive to nalidixic acid
How is Campylobacter jejuni ingested?
Drinking unpasteurised milk and from certain undercooked foods eg poultry
What does the Campylobacter jejuni prodrome include?
Headache and fever
What are the main GI symptoms of Campylobacter jejuni?
Abdo cramps Bloody foul-smelling diarrhoea
Give 2 serious complications associated with Campylobacter jejuni
Guillain Barre Reiter’s reactive arthritis
What is the treatment for Campylobacter jejuni?
Antibiotic use controversial - unclear whether benefit If required, erythromycin or ciprofloxacin in first 4-5 days
Listeria monocytogenes - microscopic features
Facultative anaerobe V or L shaped Beta haemolytic Aesculin +ve Tumbling motility
What is the name of the disease caused by Listeria monocytogenes?
Listeriosis
Give 5 symptoms of listeriosis
Watery diarrhoea Cramps Headache Fever Little vomiting
Name a serious complication of listeriosis
Meningitis
In which foods is Listeria monocytogenes commonly found?
Unpasteurised ready-to-eat food eg pate and soft cheese
Which 2 groups of people should especially avoid the foods at risk of Listeria monocytogenes infection?
Pregnant women and immunocompromised
What is the treatment for listeriosis?
Ampicillin (generally first choice) OR Ceftriaxone OR Cotrimoxazole
Entamoeba histolytica - microscopic features
Anaerobic Parasitic protozoan
Which group is particularly at risk of Entamoeba histolytica infection?
MSM (faeco-oral transmission)
What does “histolytica” literally mean?
Tissue destroyer
As well as GI infection, where else can Entamoeba histolytica cause abscesses?
Liver
Entamoeba histolytica can exist in 2 forms, what are they?
Trophozoite (active, motile stage) Cyst (non-motile)
Which form of Entamoeba histolytica exists outside the host and allows the parasite to be transmitted?
Cyst
Which form of Entamoeba histolytica only exists within the host or in fresh loose stool and causes the symptoms of infection?
Trophozoite stage
How many nuclei exist in the mature Entamoeba histolytica cyst?
4
What can be seen on histology in an Entamoeba histolytica infection?
A flask-shaped ulcer
List 5 symptoms of Entamoeba histolytica
Dysentery Wind Tenesmus Chronic weight loss RUQ pain (due to liver abscesses)
How is Entamoeba histolytica investigated/diagnosed?
Stool microscopy
What is the treatment for Entamoeba histolytica?
Metronidazole + paromycin (if luminal disease)
In EMQ land, which patient groups are more likely to be infected with the protozoan Giardia lamblia?
Travellers Hikers MSM Psychiatric inpatients (?because they eat poo?)
Fun fact: what is giardiasis also known as (in the US)?
Beaver fever
What are the two stages of the giardia life cycle?
Trophozoite (active form) and cyst (resistant, most likely to be the form that’s ingested, causing infection)
Microscopic features of the giardia trophozoite
Anaerobic, flagellated and pear-shaped
How is giardia transmitted?
Commonly from drinking water contaminated with faeces containing cysts
How does giardiasis affect GI function?
Causes malabsorption of protein and fat This leads to foul smelling non-bloody diarrhoea
How is Giardia lamblia identified?
Stool microscopy ELISA String test (gelatin capsule with an attached thread is swallowed then withdrawn. If present, trophozites may be released)
Which part of the GI system does the protozoan Cryptosporidium parvum infect?
Jejunum
Who is most likely to be infected with Cryptosporidium parvum?
Immunocompromised Fun fact: Cryptosporidium parvum is the organism most commonly isolated in HIV-positive patients presenting with diarrhoea
What is the test for Cryptosporidium parvum?
Modified Kinyoun acid fast stain (other stains also used) Oocytes can then be seen on microscopy of the stool
What is the name of the disease caused by Cryptosporidium parvum infection?
Cryptosporidiosis
What is the treatment for cryptosporidiosis?
Paromycin OR Nitazoxanide (in children)
Which 2 viruses cause secretory diarrhoea in children?
Rotavirus Adenovirus
Which strains of adenovirus cause non-bloody diarrhoea
Types 40 and 41
What is the difference between secretory and inflammatory diarrhoea?
Secretory - no white cells in stool sample Inflammatory - Neutrophils in sample
List 4 bacteria that cause *secretory* diarrhoea
Vibrio cholerae Enterotoxigenic E. coli (ETEC) Enterohemorrhagic E. coli (EHEC) Enteropathogenic E. coli (EPEC)
List 4 bacteria that cause *inflammatory* diarrhoea
Campylobacter jejuni Enteroinvasive E. coli (EIEC) Non typhoidal salmonella serotypes Shigella species
