Microbiology 3 - Gram staining & KOH test

Which of the following is TRUE? (more than 1 answer)

• In Gram POSITIVE bacteria the cell wall is made up of 90% peptidoglycan

• In Gram POSITIVE bacteria the cell wall have high amount of teichoic acids

• In Gram NEGATIVE  bacteria, peptidoglycan constitutes 10% of the cell wall.

• In Gram NEGATIVE  bacteria, have an outer membrane called lipo-polysaccharides (LPS)

1) Based on the shape and arrangement shown in the micrograph, the bacteria is most likely to be ___________.

• streptococci

• staphylococci

• streptobacillus

• diplobacilli

2) Based on the Gram staining results shown, the bacteria is __________.

• Gram positive

• Gram negative

• I can't remember...

3) The following shows the steps involved in Gram staining. Rearrange the steps to show the CORRECT procedure.

• ABCD

• BADC

• CDAB

• CADB

4) What is the purpose of alcohol wash in Gram staining?

• Fix the bacterial cells to microscope slide by denaturation

• Ensure no contaminants by killing other microbes present.

• Remove the crystal violet stain in Gram positive bacteria so that these cells can be stained by safranin.

• Wash off the crystal violet-iodine complex by degrading the LPS layer of Gram negative bacteria.

5) _________ is a rapid test to determine Gram reaction. Gram _____ have thinner cell wall and thus easily lysed and ____ exude from cells which are visible by lifting

• NAOH test ; positive ; protein strands

• NAOH test ; negative ; protein strands

• NAOH test ; negative ; DNA strands

• KOH test ; negative ; protein strands

• KOH test ; negative ; DNA strands

6) The following diagram shows the structure of cell wall and cell membrane in _______ bacteria.

• Gram positive

• Gram negative

• both Gram positive and Gram negative

• I am unsure...

The result of KOH test is:

• Positive

• Negative

 Bacterium Y turns purple after Gram staining. Which statement is correct about bacterium Y?

• It will not give a sticky strand when tested with 3% KOH.

• It has lipopolysaccharide in its cell wall.

• It does not take up safranin dye.

• Its cell wall is thinner.

Which of the following is a Gram negative bacteria?

• A

• B