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Identification of Unknown Bacteria #127 and #128
#127: Shigella flexneri
#128: Streptococcus pyogenes
BIO 244
Introduction
, 2
Recognizing different types of bacteria is really important in microbiology. This is because
various bacteria can cause different diseases, react differently to antibiotics, and live in various
environments. Getting the identification right is super crucial in hospitals, as a wrong
identification can result in treatments that don’t work. In this lab experiment, two unknown
bacterial samples were identified using Gram staining, specific media, and other tests.
The Gram stain divides bacteria into two groups, Gram-positive and Gram-negative, depending
on their cell wall structure. Gram-positive bacteria have a thick layer of peptidoglycan that holds
onto the crystal violet dye, making them look purple, while Gram-negative bacteria have a
thinner peptidoglycan layer and an outer membrane, which makes them turn pink after they are
counterstained.
Selective and differential media like MacConkey agar are used to identify Gram-negative
bacteria and check if they can ferment lactose. Other tests, such as the Catalase, Urease, Triple
Sugar Iron (TSI), blood agar, 6.5% NaCl, and the BHIA 45 °C, give more details about the
bacteria which helps in their identification. The goal of this experiment was to find Unknown
#127 and Unknown #128 by using these methods.
Method
April 8
The two unknown bacterial samples were first looked at using Gram staining. A tiny bit of each
culture was carefully moved onto one glass slide (with two seperate circles drawn on the glass
slide), heat fixed, and stained with crystal violet, iodine, alcohol decolorizer, and safranin. After
that, the slides were checked under a microscope to see the Gram reaction and the shape of the
cells. Unknown #127 showed up as pink rod-shaped cells, which means it is a Gram-negative,
Identification of Unknown Bacteria #127 and #128
#127: Shigella flexneri
#128: Streptococcus pyogenes
BIO 244
Introduction
, 2
Recognizing different types of bacteria is really important in microbiology. This is because
various bacteria can cause different diseases, react differently to antibiotics, and live in various
environments. Getting the identification right is super crucial in hospitals, as a wrong
identification can result in treatments that don’t work. In this lab experiment, two unknown
bacterial samples were identified using Gram staining, specific media, and other tests.
The Gram stain divides bacteria into two groups, Gram-positive and Gram-negative, depending
on their cell wall structure. Gram-positive bacteria have a thick layer of peptidoglycan that holds
onto the crystal violet dye, making them look purple, while Gram-negative bacteria have a
thinner peptidoglycan layer and an outer membrane, which makes them turn pink after they are
counterstained.
Selective and differential media like MacConkey agar are used to identify Gram-negative
bacteria and check if they can ferment lactose. Other tests, such as the Catalase, Urease, Triple
Sugar Iron (TSI), blood agar, 6.5% NaCl, and the BHIA 45 °C, give more details about the
bacteria which helps in their identification. The goal of this experiment was to find Unknown
#127 and Unknown #128 by using these methods.
Method
April 8
The two unknown bacterial samples were first looked at using Gram staining. A tiny bit of each
culture was carefully moved onto one glass slide (with two seperate circles drawn on the glass
slide), heat fixed, and stained with crystal violet, iodine, alcohol decolorizer, and safranin. After
that, the slides were checked under a microscope to see the Gram reaction and the shape of the
cells. Unknown #127 showed up as pink rod-shaped cells, which means it is a Gram-negative,
