AFB & Gram Stain Testing and Results
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Why AFB & gram stain test needed/ why AFB & gram stain test is done?
AFB and gram stain test is done to check for:
• The presence of bacteria and identify its basic type.
• Sometimes to identify a fungus.
• To classify bacteria grown in culture, to further identify with other tests and plan treatment accordingly.
When AFB & gram stain test is done?
• This test is done when your doctor suspects that you have a bacterial or fungal infection.
• This test can also be done along with the culture.
What sample is needed and how is it collected?
• The sample taken could be a sample of the pus, sputum, body fluids, and a swab of cells from the site of infection.
• The bacteria or fungi grown in culture.
The sample could be collected with the help of swab, needle, and syringe or directly into a sterile container.
What preparations are required before the gram stain test? / What are the preparations needed before the AFB & gram stain test?
No preparation is required before the test.
What is tested?
• Gram stain test is a lab test that is used to check for the presence of bacteria and sometimes fungi in a sample obtained from the site of infection. It provides quick results about the presence of bacteria or fungi and indicates its general type.
• The process of gram stain consists of applying a sample obtained from the infection site onto a glass slide which is then allowed to dry for sometimes. The slide is then applied with a special stain and checked under a microscope by the lab technician. If a sample is found to have any bacteria, then the test allows the categorization of these bacteria into different colors and shapes.
• Shape: The commonest found bacteria have a round (cocci) and rod (bacilli) shape.
• Color: In this test, the bacteria may develop purple or pink color and thus, are categorized as gram-positive or gram-negative bacteria respectively.
• More information can be obtained by checking if the round bacteria are present singly, in groups of two or four, or in clusters or in chains. Rod-shaped bacteria can be thick or thin, long or short, or may have enlarged spores at one end.
• Thus, the color, shape and other features obtained on gram stain allows us to get an idea of the type of bacteria causing infection. Some of the common gram-positive cocci are associated with upper respiratory tract infection. While some gram-negative bacteria are associated with urinary tract infection.
• Gram stain test is one of the initial tests that are done to help in identifying the probable bacterial type and make a possible assumption about it. However, it can’t typically confirm the exact bacterial type which is further established by means of other special tests. The tests that can be used for this purpose are culture, antigen, antibody, or molecular tests. A test call susceptibility test may also be done to check for the effectiveness of the antibiotic against the bacteria causing the infection.
What does the AFB & gram stain test result mean?
Here are the AFB & gram stain test results and details about them:
• Negative result: suggest that no bacteria could be seen in the sample collected. This may indicate the absence of bacteria and thus the absence of bacterial infection. Or, it may suggest a significantly low number of bacteria in the sample to be picked up the gram stain.
• Positive result: typically suggests the presence of bacteria and the report usually describes the findings on the seen under the microscope which can include:
• The type of bacteria: Gram-positive (purple) or Gram-negative (pink).
• The shape of the bacteria: rods (bacilli) or round (cocci).
• Grouping and arrangement of the bacteria, their size, relative quantity in the sample.
• Presence of bacteria inside (intracellular) or outside other cells (extracellular).
• Existence of red blood cells (RBC) and white blood cells (WBC) in the sample.
• In some cases presence of fungi in the sample which may be seen on Gram stain. Yeast may look as single cells that have buds, while mold may look like a plant-like branch which is called hyphae. Additional testing may be required to identify the specific type.
• These results when used with signs and symptoms and other clinical results helps the doctor to take decisions regarding the treatment, sometimes even before the result of culture becomes available.
• Gram stain results are considered preliminary and have a role in further directing the tests and confirming the results by means of tests such as culture, antigen, antibody tests.
• Following are the examples of some of the common bacteria that cause infections and how they appear on Gram stain:
• Gram-positive cocci: such as staphylococcus aureus may lead to skin infection and toxic shock syndrome and Streptococcus pneumoniae may result in pneumonia.
• Gram-negative cocci: such as Neisseria meningitides can cause meningitis, while Neisseria gonorrhea can lead to a sexually transmitted disease called gonorrhea.
• Gram-positive bacilli: bacillusanthracis known as (anthrax) may cause skin infections or pneumonia or listeriamonocytogenes may lead to foodborne illness.
• Gram-negative bacilli: many of them live in our gut and may cause diarrhea, blood infection, or urinary tract infection (UTI). One example of such bacteria isEscherichiacoli which is known to cause UTI.
• Many body fluids and sample site such as skin has normally existing usually harmless bacteria which needs to be differentiated with the one that causes infection.
• Some of the fluids such as CSF and blood normally don’t contain any bacteria. The presence of bacteria in these fluids typically suggests infection.
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