Exercise 7 Flashcards
(9 cards)
What are the main benefits of the petri plate? Of the rodac plate?
Petri plates provide a large, solid surface area for bacterial colony formation and are useful for isolation and purification of bacteria. Rodac plates are press plates only. They are used to check surfaces, floors, walls.
Why must bottles of melted media be cooled to 50oC before pouring?
To reduce condensation and to provide easier handling.
Why must agar plates be inverted during incubation?
To avoid excessive condensation from lid.
At what temperature does tryptone soy agar (or NA) solidify?
42C
List the sources where you found Gram positive bacilli. Explain their presence and possible medical significance.
Many of the Gram + bacilli produce endospores which would be found in dust, on insects, tops of tables, the floor, in the air, etc. Endospore forming bacteria are commonly found in the soil and the endospores can be carried to almost any place by the wind or on dust. Endospores are very resistant. Disease causing endospore formers include Bacillus anthracis (anthrax), Clostridium tetani (tetanus), and others.
List the sources where you found Gram negative bacilli. Explain their presence and possible medical significance.
All Gram - bacilli possess endotoxins which allow them to survive in the water and soil, on insects, etc. They are most commonly found in aquatic environments because they can rapidly divide and their endotoxins can inhibit the development of others. Disease causing Gram negative bacilli include E. coli (colitis), Pseudomonas aeruginosa (cellulitis and skin infections), and Shigella boydii (shigellosis).
List the sources where you found Gram positive cocci. Explain their presence and possible medical significance.
Gram + cocci are commonly found on the skin and mucous membranes of man and animals. The body provides a natural environment for these commensals. Disease causing Gram + cocci include Staphylococcus aureus (skin and nosocomial infections) and Streptococcus pyogenes (strep throat, scarlet fever).
Are bacteria ubiquitous? Why? Define the term.
Bacteria are found literally everywhere and in every environment.
Why did we use Sabourauds dextrose agar (SDA) as a culture medium to test the floor or your shoe?
This medium is designed to promote the growth of molds and yeast. Some bacteria will grow but if molds and yeast are present on the floor or in the shoe they will slowly grow and be visible after 2 to 3 days.
