Microbiology Flashcards
What is considered mild diarrhoea?
3 or few stools per day ( without abdominal or systemic symptoms)
What is considered moderate or severe diarrhoea?
4 or more stools per day associated with [abdominal symptoms (cramps, nausea, vomiting, tenesmus) systemic symptom (fever, malaise, dehydration)].
What is Dysentery?
Passage of frequent , small- volume stools accompanied by blood, mucus, abdominal pain (cramping) and tenesmus. (ineffectual and painful straining at stool.
What are the most common sources of Dysentry?
- Shigella spp.
- Campylobacter spp
- Enteroinvasive Escherichia Coli
- Salmonella enteritidis (?)
- Yersinia enterocolitica (?)
- Antibiotic –associated diarrhoea Clostridium difficile
What type of bacteria is Shigella?
Gram - negative bacilli
What type of Shigella is seen primarily in underdeveloped countries?
Shigella flexneri
“They can’t flex because they’re underdeveloped “
What type of Shigella is the most common in the industrial world ?
Shigella sonnei
Shigella outbreaks normally occur in?
- Homosexuals men
- Under conditions of crowding
- Where personal hygiene is poor, such as in jails, institutions for children, daycare centres, mental hospitals and crowded refugee camps.
What is the infectious dose for Shigella?
10-100 or 100-200 Low infectious dose
What type of cells does the Shigella bacteria adhere and invade?
M cells in Peyer’s patches.
From what type of bacteria is Shiga toxin produced in?
Shigella dyenteriae type 1
What is the Shiga Toxin?
This toxin is a subunit protein composed of one A subunit and five B subunits with binding specificity for a specific microvillus membrane glycolipid receptor
Fill in the blanks. “In relation to the Shiga toxin, The glycolipid receptor for the B subunit are located on __________.”
The villus cells
True or False? The glycolipid receptor for the B subunit are located on the villus cells and NOT the crypt cells, thereby impairing sodium adsorption without affecting chloride secretion and leading to net luminal fluid accumulation.
TRUE!!
What does the A unit for the Shigella Toxin cleaves ?
The A subunit enzymatically cleaves the 28S ribosomal RNA of the 60S ribosomal subunit in eukaryotic cells with resultant inhibition of protein synthesis .
Haemolytic - uremic syndrome , Toxic Megacolon , Disseminated intravascular coagulation (DIC) & Sepsis is associated with which type of Shigella?
Shigella Dysenteriae Type 1
What is Reiter’s syndrome?
It is a post infectious arthropathy-the triad of nongonococcal urethritis, conjunctivitis and arthritis, frequently with mucocutaneous lesions.
What is the culture used for the diagnosis of Shigella?
MacConkey (indicator).
How is the culture presented for Shigella?
Shigella forms a non-lactose fermenting pale coloured or colourless and transparent colonies.
What is the preffered drug of choice to treat Shigella?
Antimicrobial therapy
For cases in which susceptibility is unkown or an ampicillin-resistant strain is isolated, Bactrim is the drug of choice.
What is Food Poisoning?
A non-specific term applied to the syndrome of acute anorexia, nausea and vomiting +/- diarrhoea that is attributed to food intake especially if it afflicts groups of persons. It may or may not be accompanied by fever.
What are chemically - related food poisonings?
- Ackee, mushroom poisoning
- Heavy metals eg. Copper, Zinc, Selenium, Cadmium
- Toxic fish poisoning eg. Shellfish - saxitoxin - clams, oysters - ciguatera - ciguatoxin-snapper - barracuda 4. Chinese Restaurant syndrome –MSG
- Salt petre: methaemoglobinemia
What is the pathophysiology for non- inflammatory diarrhoea from food posoining?
It is caused by action of enterotoxins on the secretory mechanisms of the mucosa of the SI without invasion (watery, no leukocytes)
What is the pathophysiology for inflammatory diarrhoea from food posioning?
It is caused by cytoyoxins on the mucosa leading to invasion & destruction. Colon or distal small bowel involved.
* Diarrhoea bloody with leukocytes.
What is the time period for clinical presentation of chemical poisoning?
Within 30 minutes
What is the time period for clinical presentation of Preformed toxin ?
Within 1-6 hours
What are the steps in the investigation of outbreaks due to food poisoning?
1.Identify index case
2. Proper clinical history
3. Determine I.P. eg. Illness
4. Identify common foods eaten
5. Determine food specific attack rates for everything served
What are the specimens to be collected from patients with suspected food poisoning ?
Stool
Vomitus
Blood
What are the specimens to be collected from Foodhandlers with suspected food posioning?
Stool
Nose
Hand
True or False? Most cases of Food-Poisoning are self- limiting.
TRUE!!
What are indications for antibiotic treatment for Food poisoning?
- Fever of >38C plus…
- Faecal leukocytes +blood or mucus in stool
- Isolation of some organisms eg Shigella, S typhi
- Immunocompromised patients
Fill in the blanks. “ Salmonella is a genus in the family _________.”
Enterobacteriaceae
True or False? Salmonella is a gram- positive cocci in chains.
FALSE!! Gram-negative rods
What type of Salmonella species is a contaminant found in marijuana?
S. munchen
Which type of Salmonella species can be found in eggs?
S. enteritidis
Salmonella Dublin is mostly associated with what substances?
Milk , cow liver
What are the three kinds of surface antigens for Salmonella?
- Flagellar or ‘H’ antigen
- Somatic or polysaccharide ‘O’ antigen
- Polysaccharide Vi antigen in S. typhi/paratyphi
What is the laboratory diagnosis used for Salmonella using a stool sample?
MacConkey agar & SS ( Salmonellla / Shigella )agar - non lactose fermenting colonies
What are the most common sites for Intra-abdominal infections?
- Peritoneal cavity
- Retroperitoneal space
What are the two types of Intra-abdominal infections?
- Diffuse ( Peritonitis)
- Localized ( Abscesses)
What are the most common locations for Intra peritoneal abscesses?
1.Pelvic space
2.Perihepatic spaces
3.Within lesser sac
4.Paracolic gutter
What are the different types of visceral abscesses?
Hepatic
Renal
Splenic
Tubo-Ovarian
What are the types of Infective Peritonitis?
Primary & Secondary
What are the types of Peritonitis?
- Infective
- Chemical
- Combination fo 1& 2