Question

To be included in the formal lab report, this list is not inclusive of all the questions that should be answered in your formal lab report, but is rather to be used as a starting point. 1. State the clinical manifestations of infection by Salmonella enteric serovars? 2. With respect to the following media, briefly describe (1) their intended application, and (2) the biochemical principles of their use. a. Bismuth Sulfite agar b. Brilliant Green Sulfa agar c. Hektoen Enteric agar d. Xylose Lysine Deoxycholate agar e. Triple Sugar Iron agar 3. For all the various media types and tests used in this lab (not including the pre-enrichment and enrichment media), state what reaction indicates a positive result for Salmonella and for E. coli. 4. Why are the various foodstuffs used in this lab typically found to have high levels of bacteria and 5. 6. 7, more specifically Salmonella? Briefly describe the basis of serological identification and agglutination. Why are there so many serotypes of Salmonella enterica? why was the Rappaport-Vassiliadis Soya broth incubated at 42SC, whereas the nutrient broth for pre-enrichment was incubated at 37*C 8. What was the purpose of adding iodine to the Tetrathionate Briliant Green broth? 9. What is Lysine Iron agar (LIA) used for? Why does the LIA agar turn purple when lysine is decarboxylated? 10. Suggest 2 media that would successfully distinguish Salmonella enteric and Shigella spp. Why would you expect them to be similar or different?

Answer 1

Answer :

1) Typhoid fever is also called typhoid ,acute infectious disease caused by the bacterium salmonella enterica serovar typhi

The bacterium usually enters the body through the mouth by the ingestion of contaminated food or water ,penetrates the intestinal wall and multiplies in lymphoid tissue ,then enters the blood stream and causes bacteremia .

Clinical manifestations :

• Head ache .
• Malaise
• Generalized aching
• Fever
• Restlessness
• Loss of appetite
• Nose bleeds
• Cough
• Diarrhea
• Rashes of small rose colured spots on the trunk etc .

2) a) bismuth sulfite agar :

Intened Use : bismuth sulfite agar is a selective culture medium used For the isolation of salmonella typhi and other enteric bacilli

Principles :

Freshly precipitated bismuth sulfite acts together with brilliant green as the selective agent in this medium .

Gram positive organisms are inhibited and lactose -sucrose fermenting gram negative bacilli and shigella are suppressed .

Sulfur compunds provide a substract For hydrogen sulfide production .metallic salts formed in the medium in the presence of H2S stain the colony and the surrounding medium black or brown.

B)brilliant green sulfa agar :

Intended Use : hardy diagnostics BG sulfa is a selective medium recommended For the isolation of salmonella spp.other than S. Typhi and s.paratyphi

Priciples:

Salmonella species are ubiquitous in the environment .these enter gastrointestinal tract of animals due to consumption of contaminated feed .

Casein and meetone peptones provide nitrogen ,aminoacids and peptides necessary For bacterial growth .yeast extract is source of B-complex vitamins .sodium chloride is a source of essential electrolytes and maintains osmotic equilibrium .brilliant green due is a selective agent which inhibits gram positive bacteria and most gram negative bacilli .

C) hektoen enteric agar :

Intened Use : hektoen enteric agar is currently used as direct and indirect plating medium to recover gastrointestinal pathogens ,such as salmonella and shigella from food ,water and fecal samples suspected of containing these organisms .

Principles : hektoen enteric agar is a selective as well as differential media For the isolation and differentiation of enteric pathogens from clinical specimens .the presence of bile salts and dyes inhibits most gram positive organisms allowing onlt gram negative rods to grow on HE agar .

D) xylose lysine deoxycholate agar :

Intened Use : XLD agar is a srlective differential medium For the isolation of gram negative enteric pathogens from fecal specimens and other clinical material .

It is especially suitable For isolation of shigella and salmonella species .

Microbiological testing of foods ,water and dairy products .

Principle : XLD agar is both a selective and differential medium .it contains yeast extract as a source of nutrients and vitamins .it utilizes sodium deoxycholate as the selective agent and there fore is inhibitory to gram positive micro organisms

Xylose is incorporated into the medium since it is incorporated in to the medium since it is fermented by practically all enterics except For shigella and this property enables the differentiation of shigella species .

Lyesine is included to enable the salmonella group to be differentiated from the non pathogens since without lysine .

E) triple sugar iron agar :

Use : it is usef to differentiate gram negative enteric .

Enteric bacteria and other glucose fermenter first begin to metabolise glucose as glucose utilizing enzymes are present constututively and bacteria can gain the most energy by using simplest sugar .

Principles : triple sugar iron agar contains 3sugar glucose sucrose ,lactose in the ratio of 1:10 as the source of carbon as its name suggest .besides this the mediua also contains yeast and beef extract ,peptic digest of animal tissue and casein as the source of protein .the presence of fetrous sulphate and sodium thiosulphate fulfills the demand of sulphur and there is the indicator phenol red For the indication of change in the environment of the media due to production of acid or alkali .

The media is prepared in the form of slant containing a slant and butt region.