Question

How Specimen will be obtained, and streak plates done
Name of Unknown	Bacillus Species
Description of colonies and Hemolysis
Colony of Agar Plate
Gram stain results under the microscope
Name a Genus and Species
One example of skin disease

Answer 1

Answer: The specimen obtained for streak plating the organism is either water or soil, (air exposure method is far unrelated to this streaking method). For collecting specimen just wear a sterile glove and/or use a spatula, forceps to pick the sample from marked location.

The soil or water sample collected is to be serially diluted using Phosphate buffer up to 10^-4. (For bacteria the dilution is 10^-7 and for fungus, it is 10^-4). The sample is to be diluted as there can be a huge amount of bacterial cells present in the sample.

Streak Plating Method: It is a technique used to isolate a pure strain or specie of micro-organism, mostly bacteria. It was developed by Loeffler and Gaffky in Koch's laboratory.

The technique is basically streaking the bacterial colony over a new agar plate using a sterile inoculating loop until a pure strain of the organism is not seen on the plate forming colonies.

There are different types of streaking method used in microbiology lab:

1. T Streak: T-streak, as the name suggests, has a T-shape, but the streaking is not done in T shape, instead, a T is imagined on the plate to make three spaces and then the inoculating loop is run over three different places one by one. The area to be inoculated at last would have clean and segregated bacterial colonies as most of the bacterial cells will be rubbed on the first and second area.
2. Quadrant Method: Quadrant streaking is the most used streaking method in any laboratory, in this method the person has to dip the inoculating loop in the diluted sample once and streak 2-3 line horizontally in one side motion and away from the center, then turn the plate 90 degrees and repeat the same to completely make a square (quadrant).
3. Discontinuous Streaking Method: This streaking method is used to separate a colony from a mixture of colonies already growing on an agar plate. The inoculating loop with a colony picked from the agar plate is streaked over a part of the quadrant in a back and forth motion and repeated like a quadrant streaking. It is named discontinuous streaking because of the appearance of colonies on the agar plate which is discontinuous.

(Since the last part of the question is one example of skin disease, So we will take Bacillus subtilis as our specimen to answer the next two questions)

Description of Colonies and Hemolysis:

Bacillus subtilis forms a circular colony, with opaque and rough appearance, the color of the colony is fuzzy white or yellow with jagged edges.

They display hemolysis, (hemolysis is a process of breaking or rupturing the red blood cells). It is performed by streaking the colony on Blood agar and if the organism contains blood rupturing enzyme then it is said to be displaying hemolysis.

Colony on Agar Plate: Round, white colonies.

Gram Stain Results under the microscope:

The Bacillus species are rod-shaped, endospore producing, aerobic or facultatively anaerobic, Gram-Positive bacterial species but sometimes they turn Gram-negative with age.

Genus: Bacillus

Species: Subtilis

Skin Infection: Bacteriamia caused by Bacillus subtilis.