What are the reactions of the Gram-positive and Gram-negative bacteria?
If the bacteria stays purple, they are Gram-positive. If the bacteria turns pink or red, they are Gram-negative. The two categories cause different types of infections: Gram-positive infections include methicillin-resistant Staphylococcus aureus (MRSA), strep infections, and toxic shock.
What is the effect of the decolorizing step on the Gram-positive and Gram-negative cell?
This step washes away unbound crystal violet, leaving Gram-positive organisms stained purple with Gram-negative organisms colorless. The decolorization of the cells is the most “operator-dependent” step of the process and the one that is most likely to be performed incorrectly. Rinse with water to stop decolorization.
What mistake could cause you to interpret a Gram-negative species as Gram-positive?
It is also possible for Gram-negatives to appear as Gram-positives. This can occur when the smear is too thick, resulting in Gram-negative bacteria not being fully decolorised during the decolorisation steps and appearing as Gram-positive bacteria. Other errors include: Smear improperly heat-fixed.
What is one mistake that might cause a false Gram-negative result?
Reduce water rinse time – Excessive washing can cause excessive decolorization. Crystal violet is susceptible to washout with water before binding to iodine, creating a false negative test.
What is the difference between the Gram-positive and Gram-negative bacteria cells?
Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives.
What is the difference between Gram-positive and Gram-negative bacteria quizlet?
Gram positive bacteria have lots of peptidoglycan in their cell wall which allows them to retain crystal violet dye, so they stain purple-blue. Gram negative bacteria have less peptidoglycan in their cell wall so cannot retain crystal violet dye, so they stain red-pink.
Which of the following describes the difference between Gram-positive and Gram-negative cells that causes them to stain differently after Gram staining?
Which of the following described the difference between gram-positive and gram-negative cells that causes them to stain differently after Gram staining? Gram-positive cells have a mycolic acid layer in their cell walls that holds in stain, whereas gram-negative cells lack this layer.
What is the effect of the decolorizing step in Gram-positive cell quizlet?
The decolorizing step removes the crystal violet from the gram-negative cell walls, but not the gram-positive walls.
Which factors can affect the results of a Gram stain?
The many variables that can affect this stain are age of the culture, amount of decolorizer used, the time of decolorization, the type of organism (acid-fast bacteria and spores do not stain well), thickness of the smear, and the general care of the stainer.
What are the main reasons for getting false positive or false negative in Gram stain?
Positive Gram stains with negative culture results could be due to fastidious or nonviable organisms and failure to order appropriate testing, such as anaerobe cultures. False-negative Gram stains could occur due to inadequate specimen or smear preparation or failure to examine an adequate number of fields.
What is the most common source of errors during the Gram stain procedure?
In this study, we present a review of over 6,000 Gram-stains and establish an error rate of around 3%, with the most common reason for error being an over-decolourisation step resulting in organisms that should be Gram-positive appearing as Gram-negative.
Which of the following describes the difference between gram-positive and gram-negative cells that causes them to stain differently after gram staining?
Which of the following described the difference between gram-positive and gram-negative cells that causes them to stain differently after Gram staining? Gram-positive cells have a mycolic acid layer in their cell walls that holds in stain, whereas gram-negative cells lack this layer.
What is the difference between gram-positive and gram-negative bacteria quizlet?
Gram positive bacteria have lots of peptidoglycan in their cell wall which allows them to retain crystal violet dye, so they stain purple-blue. Gram negative bacteria have less peptidoglycan in their cell wall so cannot retain crystal violet dye, so they stain red-pink.
What is the difference between a gram positive and gram negative bacteria?
Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives.
What is the major factor that determines if bacteria are gram positive or gram-negative?
The major difference between the two groups of bacteria is the thickness of the cell wall and the presence of an outer membrane in Gram negative bacteria only. The bacterial cell wall ranges from 20–80 nm thick for Gram positive and between 1.5–10 nm thick for Gram negative bacteria.
Why only Gram-negative cells undergo decolorization during the Gram staining procedure?
Due to differences in the thickness of a peptidoglycan layer in the cell membrane between Gram positive and Gram negative bacteria, Gram positive bacteria (with a thicker peptidoglycan layer) retain crystal violet stain during the decolorization process, while Gram negative bacteria lose the crystal violet stain and …
Which step of the Gram stain is critical for differentiating between Gram-positive and Gram-negative cells Why is this step differential?
Both gram + and – bind to the crystal violet: the key step to their differentiation is the decolorization.
What are sources of error in Gram staining?
Sources of Error For example, the Gram stain will not detect organisms that exist within host cells (such as Chlamydia), organisms with no cell wall (such as Mycoplasma, Ureaplasma, and Rickettsia), and bacteria that are too small to be seen with light microscopy (such as Treponema).
What is the difference between Gram-positive and Gram-negative bacterial staining?
Gram positive bacteria have a thick peptidoglycan layer and no outer lipid membrane whilst Gram negative bacteria have a thin peptidoglycan layer and have an outer lipid membrane.
What are the factors that can affect the result of Gram stain?
The many variables that can affect this stain are age of the culture, amount of decolorizer used, the time of decolorization, the type of organism (acid-fast bacteria and spores do not stain well), thickness of the smear, and the general care of the stainer.
What would be the causes of a false positive result in a Gram stain?
Even occasional false-positive Gram stains should prompt review of laboratory methods. Our observations implicate dead bacteria in microbiologic reagents as potential sources of false-positive Gram stains.
What are some problems that can occur when performing a Gram stain?
Several factors may affect the results of Gram staining: If the smear is too thick, proper decolorizing will not be possible. If the smear is overheated during heat fixing, the cell walls will rupture. Concentration and freshness of reagents may affect the quality of the stain.
What the difference between a gram-positive and a gram-negative bacterial cell?
Gram-negative bacteria are surrounded by a thin peptidoglycan cell wall, which itself is surrounded by an outer membrane containing lipopolysaccharide. Gram-positive bacteria lack an outer membrane but are surrounded by layers of peptidoglycan many times thicker than is found in the Gram-negatives.
What is the difference between Gram positive and gram-negative bacteria quizlet?
Gram positive bacteria have lots of peptidoglycan in their cell wall which allows them to retain crystal violet dye, so they stain purple-blue. Gram negative bacteria have less peptidoglycan in their cell wall so cannot retain crystal violet dye, so they stain red-pink.
Which of the following describes the difference between Gram positive and gram-negative cells that causes them to stain differently after gram staining?
Which of the following described the difference between gram-positive and gram-negative cells that causes them to stain differently after Gram staining? Gram-positive cells have a mycolic acid layer in their cell walls that holds in stain, whereas gram-negative cells lack this layer.
What may be the effects of the following on the results of the Gram staining method under decolorization?
Over-decolorizing will lead to an erroneous result where gram-positive cells may stain pink to red indicating a gram-negative result, and under-decolorizing will lead to an erroneous result where gram-negative cells may appear blue to purple indicating a gram-positive result.
Which factors can affect the results of a Gram stain and why?
The many variables that can affect this stain are age of the culture, amount of decolorizer used, the time of decolorization, the type of organism (acid-fast bacteria and spores do not stain well), thickness of the smear, and the general care of the stainer.
Which of the following describes the difference between gram-positive and gram-negative cells that causes them to stain differently after Gram staining?
Which of the following described the difference between gram-positive and gram-negative cells that causes them to stain differently after Gram staining? Gram-positive cells have a mycolic acid layer in their cell walls that holds in stain, whereas gram-negative cells lack this layer.
What is the difference between Gram-positive and Gram negative bacterial staining?
Gram positive bacteria have a thick peptidoglycan layer and no outer lipid membrane whilst Gram negative bacteria have a thin peptidoglycan layer and have an outer lipid membrane.
Which of the following describes the difference between Gram-positive and Gram negative cells that causes them to stain differently after Gram staining?
Which of the following described the difference between gram-positive and gram-negative cells that causes them to stain differently after Gram staining? Gram-positive cells have a mycolic acid layer in their cell walls that holds in stain, whereas gram-negative cells lack this layer.