Question

1)IN THE KIRBY-BAUER TEST, EXPLAIN HOW AND WHY INCREASE TURBIDITY(DENSITY) OF THE INOCULUM WILL AFFECT THE SIZE OF THE CLEAR AREA AROUND THE ANTIBIOTIC DISC) PLZ TYPE IN , THANK U

2)WHICH OF THE FOLOWING GENERA SHOULD BE TESTED FOR SPORES?A)E.COLI,B)MYCOBACTERIUM,C)CLOSTRIDIUM,D)STAPHYLOCOCCUS,E) MYCOPLAZMA.

THE LEAST AMOUNT OF ANTIBIOTIC REQUIRED TO INHIBIT BACTERIAL GROWTH IN AN OVERNIGHT CULTURE IS THE : maximum inhibitory concentration, maximum standard zone concentration, maximum inhibitory concentration,maximum lethal concentration ,maximum standard zone concentration.

Answer 1

First of all let's understand the basic concept behind this test. Kirby- Bauer test is a test to estimate how effective an antibiotic is against a specific pathogen species. In this method an agar plate is inoculated with an inoculum of bacterial culture. The density of this inoculum is standardized to match 0.5 McFarland turbidity standard (which roughly contains 150 million cells per mL). Then a filter paper disc impregnated with antibiotic is placed on agar plate and the bacteria are allowed to grow and then observed. The antibiotic diffuses into the agar medium resulting in inhibition of bacterial growth upto certain area(known as clear zone) around the disc (where concentration of antibiotic is high). The clear zone around the paper disc indicate the lethality of antibiotic. The more large the clear zone is, high is its effectiveness against that particular species of bacteria.

Now coming to the answer of question 1. If the inoculum density is high, it will definitely affect the clear zone. This is because high density/turbidity of inoculum means large number of bacteria and they will rapidly multiply to reach a critical mass and they can overpower the inhibitory effects of antibiotic. This could highly minimize the clear zone around paper disc.

Answer to Question 2. Out of all options, the correct one is (c) Clostridium. Rest of them do not produce spores. (Most of the spore forming bacteria belong to genus Bacillus and Clostridium of Phylum Firmicutes)

Answer to​​ question 3. The correct answer will be - minimum inhibitory concentration. This is the minimum concentration of antibiotic that is required to inhibit the bacterial growth in an overnight culture.

Hope you got your answers.

Thanks! Keep learning!