Gram-negative Facultatively-anaerobic Rods Flashcards
(48 cards)
What are the general characteristics of enterobacteriacea?
- Gram-negative
- Straight rods
- Motile (peritrichous), or non- motile
- Non-sporulating
- Facultative anaerobes
- Production of acid from glucose
- Catalase-positive Oxidase-negative
What is the major genera of enterobacteriacae?
- Escherichia
- Salmonella
- Shigella
- Citrobacter
- Proteus
History of Salmonella
- First identified in 1885 by Daniel Elmer Salmon (a vetinary surgeon)
- Theobald Smith was his assistant
- In 1990 Joseph Leon Ligneres proposed that the pathogen discovered by Salmon’s group be called Salmonella in his honor
Nomenclature
- 2600 different serotypes of salmonella (distinct variations within a species of bacteria)
- Split into salmonella bongori and Salmonella enterica (subdivided into 6 groups)
- Subroup I (enterica) is split into typhoid salmonella and non-typhoid salmonella
Typhoidal Salmonella
Salmonella typhi (tyhoid) has an incubation period of 8-14 days
Salmonella paratyphi A, B, or C (paratyphoid) has an incubation period of 8-14 days
They both spread in the sam eway:
They organism is ingested with contaminated food or water then it directly enters the bloodstream
Sympotoms: High fever, stomach ache, loss of appetite and rash
What are the generalised Characteristics of Salmonella?
- Gram-negative
- Facultative anaerobe
- Non-sporulating
- Peritrichous flagella
- diameters of ~0.7-1.5μm
- lengths of 2-5μm
- Growth:
Temp. 5.5 – 45.6°C (37°C) pH 3.8 – 9.5 (7-7.5)
Water activity (Aw) 0.99
Burden of Salmonella In The EU
Notification Pyramid For Gastrointestinal Infections
Pathogen-specific estimates of proportion foodborne from reported outbreaks, UK 2001-2008
The changing epidemiology of Salmonella
- 1940s : Lowest number of cases during World War II
- 1953-1954: saw a rapid increase of animal slaughter, a rise in meat and egg consumption
- 1959: highlighted a phenomenal surge in Salmonella infections linked to hens’ eggs
- 1980s: Enteritidis phage type 4 (PT4) was identified as the most prevalent serotype and the leading cause of foodborne infection was linked to shelled eggs
As a result of all eggs in the UK and USA were pasteurised and washed to effectively remove faecal contamination prior to packing
The changing epidemiology of Salmonella (1990s onwards)
1990s- Edwina Currys’ statement - sales of eggs plummeted 60% overnight
2002- introduction of the vaccine Nobilis Salenvac, which was administered to laying chickens
stimulates the production of maternally derived antibodies against S.Enteritidis in the chick before it hatches
All eggs laid from vaccinated hens are labelled with a red lion stamp and a best before date
Direct vs Indirect causes of food borne diseases
DIRECT: Contact with infected animals or environments
INDIRECT: Comtaminated- utensils, hands, food, water
What are the routes and reservoirs of salmonella transmission
Major routes: Farm animas→huaman food→Man
Minor routes: Animal importation→ Slurry/sewage environmental pollution→products eaten by animals
Foodborne outbreaks recorded in England and Wales from 1992 to 2008 showing causative agent by implicated food vehicles
- 20% salmonella cases attributed to meat and poultry
- 4.4% due to fish
What are the Signs & Symptoms of salmonella?
Nausea, vomiting, fever, diarrhoea and abdominal cramps
From 4-7 days illness ranges from mild to severe; most people recover without treatment
How does salmonella progress?
- Bacteria travel to small intestine adhere to lining; begin life cycle
- In severe cases, bacteria break through intestinal wall to bloodstream; can be deadly if not properly treater
What is the treatmentment for salmonella?
Oral or injected antibiotics, usually for 2 weeks
Salmonella in the body
Salmonella enters the body via consumption of contaminated foods
→Although human stomach acid can reduce and sometimes eliminate Salmonella spp, some bacteria get through to the intestine and then attach and penetrate the cells.
→Toxins produced by the bacteria (enterotoxin and cytotoxin) can damage and kill the cells that line the intestines, which results in intestinal fluid loss (diarrhea)
→Some Salmonella can survive in cells of the immune system and can reach the bloodstream, causing blood infection (bacteremia)
→Some Salmonella spp can enter the gallbladder, leaving the affected patient a chronic carrier of the organisms. Salmonella can then be shed with the bile from the gallbladder into the feces and then may infect other people
Salmonella Pathogenicity Island encoded type III secretion system
Salmonella has 5 pathogenicity islands in total
Pathogenicity island no.1- responsable for inflammation, diarhoeaand getting the cells into the intestines
Toxins released:
- SipA
- InJ
- SptP
- AvrA
- SopABDE
- sopE2
- SsH1
Pathogenicity island no.2: Spreading across intestine to other organs (systemic spread)
- SpiC
- SspH2
- SspH1
- SseBCD
Host pathogen interactions during pathogenesis
Describe the intracellular lifestyle of salmonella typhimurium (once engulfed)
- Vacuole formed during the engulfment of the bacterium by the host cell membrane
- A different type 3 secretion system is assembled and injects a different set of salmonella effectors across the vacuolar membrane to manipulate host function to protect the bacterium from host defences
- Thin filaments extend from the vacuole coeverd in salmonella effectors e.g SifA
- Now the baterium is safe and starts to replicate
- Salmonella triggers a profound inflammatory response
Salmonella’s type 3 secretion system
- Specialised needle like organelle (type 3 secretion system) to deliver its toxin directly into the host cells
- This system functions like a molecular syringe that injects the salmonella toxins as soon as it gets in contact with the host cell surface
- Toxins (effector proteins) include Sip A and SopE2 into the intestinal cells to manipulate the functions of cellular proteins and lipids
- As a result, the epitherlial cell membrane extends outward leading to the engulfment of the invading bacterium untill it is taken up completely into the interior of the host cell
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Food types tested in the laboratory
- Storage and Preparation of Samples
- Salmonella is not able to grow at low temperatures and samples should be refrigerated if they cannot be sent for analysis immediately.
- 25g food samples are cultured in detection testing
- dried foods require a resuscitation stage for sub-lethally damaged cells in non-selective pre-enrichment media, such as buffered peptone water
