Why are Koh lyse gram negative?

Why are Koh lyse gram negative?

KOH easily dissolves the thin layer of peptidoglycan of the cell walls of gram negative bacteria. Disintergration of gram negative cell wall lyses the cell and release its contents, including the DNA. Thus, the cells are not lysed, the DNA is not released and no viscosity is observed.

What does koh do to Gram negative bacteria?

Gram-negative cell walls are broken down by 3% KOH and in turn release viscoid chromosomal material which causes the suspension to become thick and stringy. This reaction characterizes gram-negative bacteria.

What is a KOH test in microbiology?

For identification of Gram (-) bacteria. This test replaces the Gram stain. It is much quicker and easier to perform than the traditional Gram stain.

What is the gram reaction of Staphylococcus?

Staphylococci are gram-positive aerobic organisms. Staphylococcus aureus is the most pathogenic; it typically causes skin infections and sometimes pneumonia, endocarditis, and osteomyelitis. It commonly leads to abscess formation.

How does the KOH test work for Gram negative bacteria?

Like the Gram stain reaction, the KOH test is based on differences in the chemistry of the bacterial cell wall. In the presence of potassium hydroxide, Gram negative cell walls are broken down. KOH easily dissolves the thin layer of peptidoglycan of the cell walls of gram negative bacteria.

What do you need to know about KOH test?

It is a secondary test for identification of Gram (+) vs. Gram (-) cultures. 3% KOH dissolves cell walls of Gram (-) (thin layer of peptidoglycan), but does not affectGram (+) cell walls. Dissolution of Gram (-) cell wall lyses the cell and spills its contents,including the DNA.

Which is more accurate KOH or Gram stain?

It is much quicker and easier to perform than the traditional Gram stain. It is just as accurate. It is a secondary test for identification of Gram (+) vs. Gram (-) cultures. 3% KOH dissolves cell walls of Gram (-) (thin layer of peptidoglycan), but does not affectGram (+) cell walls.

What makes Koh viscous in a string test?

The KOH String Test relies on the differential resistance to 3% potassium hydroxide between gram positive and negative cells, where a portion of a colony is mixed with a small volume of 3% KOH. If the cells lyses, the liberated cellular DNA makes the mixture viscous or “stringy.”