Microbiology Specimen Collection and Handling

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Questions and Answers

What type of microscopy is primarily used for morphologic examination of bacteria?

Brightfield microscopy (correct)

Electron microscopy

Fluorescence microscopy

Phase-contrast microscopy

Which prefix indicates that bacteria occur in pairs?

Diplo- (correct)

Strepto-

Mono-

Staphyl-

What color do gram-positive cocci (GPC) typically stain?

Pink

Green

Purple (correct)

Yellow

What is the shape of bacterial cells referred to as 'bacilli'?

Rod-shaped Signup and view all the answers

Which method is used to visualize the presence of bacteria on a microscope slide?

Smear preparation Signup and view all the answers

Which of the following staining methods provides valuable information for determining the purity of bacterial cultures?

Gram stain Signup and view all the answers

Which type of bacteria is identified as having a spiral shape?

Spirochetes Signup and view all the answers

What characteristic does a differential stain highlight in bacterial cells?

Chemical and structural properties Signup and view all the answers

What is the primary purpose of using solid media in microbiology?

To establish pure cultures and isolate microbes Signup and view all the answers

Which nutrient component is NOT typically found in liquid media?

Agar Signup and view all the answers

What is a key characteristic of the dilution streak technique?

It allows for the physical separation of colonies on a plate Signup and view all the answers

What temperature is optimal for growing E. coli in a microbiology incubator?

37°C Signup and view all the answers

In the dilution streak technique, how are subsequent streaks made?

Starting at the periphery and overlapping previous streaks Signup and view all the answers

Which of the following is a function of microbiology incubators?

To maintain consistent temperature for cell growth Signup and view all the answers

What type of media is suitable for growing microorganisms in varying nutrient conditions?

Nutrient broths Signup and view all the answers

What is the significance of agar in microbiological media?

It solidifies media and helps isolate colonies Signup and view all the answers

What is the primary reason for using refrigeration when storing microbiological specimens?

To prevent overgrowth of normal flora in the specimen Signup and view all the answers

Which statement correctly distinguishes solid media from liquid media in microbiology?

Solid media contains a solidifying agent, while liquid media contains no solidifying agent. Signup and view all the answers

What type of specimens are collected for microbiological examination?

Body fluids, cerebrospinal fluid, and swabs from various anatomical sites Signup and view all the answers

Why is immediate culture of freshly collected specimens not always practical?

Transport or handling delays can occur. Signup and view all the answers

What collection method may be used for particularly fragile organisms?

Providing the appropriate collection device and nutrient media to the patient Signup and view all the answers

How long can serum samples for serology testing be properly stored in the freezer?

Up to 1 week Signup and view all the answers

What equipment change in microbiology has contributed to a decrease in contamination?

Using disposable inoculating needles or loops Signup and view all the answers

What is a common storage issue for certain meningitis-causing bacteria in cerebrospinal fluid (CSF)?

Sensitivity to refrigeration Signup and view all the answers

What is the primary method used for isolating colonies from a urine sample?

Using a calibrated loop to streak the sample Signup and view all the answers

Which of the following is a characteristic of beta-hemolysis?

Complete lysis of red blood cells Signup and view all the answers

What culture media is recommended for the growth of anaerobic bacteria?

Columbia broth Signup and view all the answers

How should the collection site be cleansed before taking a blood culture sample?

With 70% alcohol and povidone-iodine solution Signup and view all the answers

Which of the following organisms is commonly isolated from blood cultures?

Klebsiella pneumoniae Signup and view all the answers

What characteristic distinguishes alpha-hemolysis from other types?

It results in a green discoloration around colonies Signup and view all the answers

Which test method can identify group A β-hemolytic streptococci in throat cultures?

PCR molecular diagnostic testing Signup and view all the answers

What is indicated by the presence of gamma-hemolysis on an agar plate?

No lysis of red blood cells Signup and view all the answers

What is indicated by the term 'susceptible' in antimicrobial susceptibility testing?

The antibiotic was effective in killing or stopping the growth of bacteria. Signup and view all the answers

What does the term 'resistant' mean in the context of antimicrobial susceptibility tests?

The antibiotic had no effect in stopping the growth of bacteria. Signup and view all the answers

What is the purpose of quality control (QC) in a microbiology laboratory?

To confirm the accuracy of test results and reliability of processes. Signup and view all the answers

What key difference exists between fungi and bacteria at the cellular level?

Fungi have a true nucleus and mitochondria, while bacteria do not. Signup and view all the answers

What characterizes the walls of fungal cells?

They contain chitin as a structural component. Signup and view all the answers

What is the minimum inhibitory concentration (MIC)?

The lowest concentration of an antibiotic that stops bacterial growth. Signup and view all the answers

How long should incubation typically last for observing zones of inhibition?

16 to 18 hours. Signup and view all the answers

Which of the following best describes yeasts in terms of their cellular structure?

Yeasts are single-celled organisms that reproduce by budding. Signup and view all the answers

Study Notes

Specimen Collection and Handling

Some organisms require special growth conditions for long-term viability and need to be rapidly placed in a suitable nutrient medium.
Some organisms are extremely fragile; therefore, appropriate collection devices and nutrient media are supplied directly to the patient.
Immediate culture of freshly collected specimens is not always practical, and storage is not suitable for all organisms.
Refrigeration prevents overgrowth of normal flora in specimens but is not appropriate for all organisms, such as anaerobic bacteria, CSF, and genital cultures for Neisseria.
Serum samples for serology testing can be stored in the freezer for 1 week before testing.

Types of Microbiology Specimens

Various types of specimens are collected by microbiologists, including blood, body fluids, cerebrospinal fluid (CSF), inner ear fluids, respiratory samples, scrapings, stool, sputum, swabs of anatomical sites, and urine.

Basic Equipment and Techniques in Microbiology

The main difference between solid and liquid media in microbiology is the presence of a solidifying agent.
Solid media, such as agar, gelatin, or silica gel, is used to establish pure cultures, isolate microbes, and make agar slants and agar stabs.
Liquid media, also known as nutrient broths, are commonly used for growing microorganisms. Different nutrient components are added to the broths for the culture of a variety of microbes.

Culturing Techniques: Dilution Streak

The dilution streak technique involves a series of streaks across a solid media plate, diluting the sample to isolate individual colonies.
Each subsequent streak overlaps the previous one, resulting in a gradual decrease in the concentration of microorganisms.
The last streak typically contains colonies that are far enough apart to be considered individual colonies, facilitating isolation and identification.

Inoculating Needles and Loops

Previously reusable, inoculating needles and loops have become disposable to minimize contamination and ensure sterility.

Incubators

A microbiology incubator is a controlled environment for growing and maintaining microbial cultures, maintaining optimal temperature, humidity, gas composition, and sterility.
Temperature is critical for the growth of microorganisms, with different species requiring specific temperatures.
Humidity levels are essential for the growth of cells and must be maintained within the incubator.
The gas composition, especially CO2 and oxygen content, is critical for the growth of various cells.
Incubator sterility safeguards cultures from contamination.

Identification of Bacteria

Bacterial identification involves microscopic observations (smear preparation and staining), bacterial cultivation, and biochemical tests.
Smear preparations are prepared by spreading a specimen thinly on a glass microscope slide and allowing it to air dry.
Staining procedures, such as the Gram stain, provide valuable information about the morphology and characteristics of bacteria.
The Gram stain differentiates between gram-positive (purple) and gram-negative (pink) bacteria.
Simple stains, like methylene blue, are used to highlight cellular structures and shapes.

Morphology of Bacteria

Bacteria are classified by their shape and arrangement.
Spherical bacteria are referred to as cocci (singular: coccus).
Cocci are further categorized based on their arrangement: diplo- for pairs, strepto- for chains, and staphylo- for irregular clumps.
Rod-shaped bacteria are called bacilli (singular: bacillus).
Curved rods are known as vibrios.
Spiral-shaped bacteria include spirochetes and spirilla, with spirilla being thicker and more rigid, and spirochetes being thinner and more flexible.

Throat Cultures

Throat cultures are used to detect the presence of group A beta-hemolytic streptococci (Streptococcus pyogenes), which are a common cause of strep throat and other infections.
Methods for detecting group A beta-hemolytic streptococci include rapid detection methods (non-culture techniques) and culture on sheep blood agar.
The addition of a bacitracin disc (Taxo A) to sheep blood agar plates is used to identify group A beta-hemolytic streptococci.
Interpretation of throat culture plates involves examining colony morphology and hemolysis patterns on the agar.
hemolysis is classified as alpha (partial lysis, "greening"), beta (complete lysis), or gamma (no hemolysis).
Molecular diagnostic testing techniques, such as polymerase chain reaction (PCR), can be used to detect group A or group B streptococci by targeting specific DNA sequences.

Blood Cultures

Blood is normally sterile, so the presence of bacteria in blood indicates an infection, known as bacteremia.
The most frequently isolated bacteria from blood cultures include coagulase-negative staphylococci, Staphylococcus aureus, Enterococcus faecalis, Enterococcus faecium, Escherichia coli, Klebsiella pneumoniae, Streptococcus pneumoniae, Pseudomonas aeruginosa, Enterobacter cloaca, Salmonella typhi, and Acinetobacter baumannii.

Blood Culture Collection

Blood culture collection sites are thoroughly cleansed with 70% alcohol and povidone-iodine solution to reduce contamination.
Various culture media are used for blood cultures, including broth media (tryptic soy broth, brain heart infusion broth, thioglycolate broth), Columbia broth for anaerobic bacteria, pre-reduced peptone broths for anaerobic bacteria, and thio broths for anaerobic bacteria.

Antimicrobial Susceptibility Tests

Antimicrobial susceptibility tests determine the effectiveness of antibiotics against a specific microorganism.
Results are reported as susceptible (effective), intermediate (may be effective at higher doses or with different administration), or resistant (ineffective).
The minimum inhibitory concentration (MIC), which is the lowest concentration of an antibiotic that inhibits bacterial growth, is used to interpret susceptibility test results.

Quality Control in the Microbiology Laboratory

Quality control (QC) is essential in a microbiology laboratory to ensure the accuracy and reliability of test results.
This includes testing equipment, media, reagents, and specimens for consistency and contamination.
Equipment should be calibrated and maintained to ensure consistent performance and sterility.
Culture media must be tested for sterility and performance before use.
Reagents should be sterile.
Specimens must be collected, transported, and processed properly to maintain the quality and integrity of the specimen.
Antimicrobial susceptibility testing should be performed accurately, and profiles should be reviewed for each organism tested before reporting results.

Tests for Fungi (Mycology)

Fungi are eukaryotic organisms that include yeasts and molds.
Unlike bacteria, fungi have a true nucleus with a nuclear membrane and mitochondria.
Fungal cell walls are composed of chitin, not peptidoglycan, which is found in bacterial cell walls.
Yeasts are single-celled fungi that reproduce by budding.

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Description

This quiz covers essential practices in microbiology related to specimen collection and handling. You will learn about the types of specimens collected and the specific conditions required for different organisms. Understanding these concepts is crucial for laboratory accuracy and patient care.