Enterobacteriaceae & Brucella
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Transcript of Enterobacteriaceae & Brucella
4.6 Enterobacteriaceae
Enteric Gram negative aerobes rods
Sub-grouping
LACTOSE FERMENTING(PINK PIGMENT IN MAC AGAR)
NON-LACTOSE FERMENTING(NO PINK PIGMENT IN MAC AGAR)
1. ESCHERICHIA2. KLEBSIELLA3. ENTEROBACTER4. CITROBACTER
1. SALMONELLA2. SHIGELLA3. PROTEUS4. MORGANELLA5. PROVIDENCIA6. SERRATIA
Morphology
Belongs to Gamma Proteobacteria Gram negativeRods1-4 X 0.6µmNon-sporing Have simple nutrition requirementsFacultative anaerobes
Important bacterial group, they are called enteric bacteria as it reflects the fact that they inhabit the intestinal tracts of humans and other animals.
Differentiation is based on biochemical reactions and differences in antigenic structure
Motility
Mostly surrounded by flagella (peritrichous) and are motile
Non-motile enterobacteriaceae are Shigella and Klebsiella
In Escherichia and Morganella, most of the strain are motile, but some are non-motile
Special case like Yersinia, contain species that are motile at 25oC but non-motile at 35 – 37oC.
Klebsiella E.coli
Culture
Most will grow in wide temperature range in ordinary culture media including NA and BA and selective media.
The selective media is incorporated with dyes and bile salts that inhibit G+ organisms and may suppress the growth of nonpathogenic species of Enterobacteriaceae
Eg: Selective media is required to recover Salmonella and Shigella On BA, enterobacteria produce large, shiny, grey colonies that may be hemolytic. Most grow well on a variety of lab media including a lot of selective and differential media originally developed for the selective isolation of enteric pathogens
Enterobacteriaceae
Many are differential on the basis of whether or not the organisms ferment lactose and/or produce H2S. Species that produce hydrogen sulphide often show a green colour around the subsurface colonies (Klebsiella) and capsulated strains (Escherichia) produce large mucoid colonies.
Catalase reaction vary among Enterobactericeae
E.coli
In nutrient agar In MacConkey agar
Klebsiella sp
In macconkey agar In blood agar
Salmonella sp
In ss agar In xld agar
Toxin production
Exotoxin (enterotoxin) is produced by Shigella dysenteriae and toxigenic strain of Escherichia coli (ETEC)
When lysed, enterobacteria will release endotoxin from their cell wall
*The feature above is applied to all Gram negative rods
Enterobacteriaceae
On CBA they all produce similar colonies that are relatively large and dull gray. They may or may not be hemolytic.
The three most useful media for screening stool cultures for potential pathogens are TSI, Lysine iron agar (LIA), and urea or phenylalanine agar.
The antigenic structure is used to differentiate organisms within a genus or species.
Three major classes of antigens are found:
Enterobacteriaceae
Somatic O antigens – these are the heat stable polysaccharide part of the LPS.
Variation from smooth to rough colonial forms is accompanied by progressive loss of smooth O Antigen.
Flagellar H antigens – are heat labile Envelope or capsule K antigens – overlay the surface O
antigen and may block agglutination by O specific antisera.
Boiling for 15 minutes will destroy the K antigen and unmask O antigens.
The K antigen is called the Vi (virulence) antigen in Salmonella typhi.
Antigenic Structure of Enterobacteriaceae
Antigenic structure of Enterobacteriacea
Assignments
Prepare notes on each of genus under enterobacteriaceae group. (10 genus)
All the notes should have the following criteria:
a) morphology,b)culture, c)biochemical tests d) serology test
Submit on 3rd of September 2012
4.7 BRUCELLA
Main species
Brucella melintensisBrucella abortusBrucella suis
Normal habitat
Obligate intracellular pathogens of animalsB. melitensis mainly found in goat and
sheepB. abotus infects cattleB. suis found in pigs and occasionally in
goatOther animal including horse, camel, eland
and wild rodents
Routes of infection
Mosquitoes helps in transfer Brucella from animal to human
Also by ingesting unpastuerized milk, meat or milk products, enter damaged skin or eyes, inhaled in airborne particles or aerosols and close contact with secretions.
Microscopic observation
Non-motileGram negativeCoccobaciliShow bipolar stainingRarely found in direct smear from
uncultured specimenOn Gram stain they appear as dense
clumps of Gram-negative coccobacilli and are exceedingly difficult to see.
Culture characteristics
Mostly cultured from blood of high fever patient(Brucellosis) Isolation is extremely rare in chronic brucellosis In all blood culture, they need carbon dioxide Blood culture should be kept in 4 – 6 weeks before result as no
organisms isolated To reduce the risk of contamination, use the diphasic medium
such as Castaneda or tryptic soy broth or agar Brucellae are aerobic with enriched of carbon dioxide
Biochemical tests Serology tests
Urease and hydrogen sulphide production
All brucella strains are catalase positive
Possess two antigens called A and M
Famous test serum: Rapid slide
agglutination test Tube agglutination
titration test
Serology test
It is crucial to be able to differentiate Brucella from Salmonella which could also be isolated from blood cultures and are Gram-negative. Testing for urease would successfully accomplish the task; as it is positive for the Brucella and negative for the Salmonella.