Microbiology Chapter 15

What are the three categories of methods used to identify bacteria?

Phenotypic, Immunologic, Genotypic

What does phenotypic analysis involve?

Observation of microscopic and macroscopic morphology, physiology, and biochemical properties.

What is the main focus of immunologic methods in diagnosing infections?

Testing for the presence of specific antibodies to a suspected pathogen.

What are genotypic methods used for?

Examining the genetic material of the infecting organism.

What is a primary advantage of genotypic methods over phenotypic methods?

Culturing of microorganisms is not always necessary.

What is the significance of viable nonculturable (VNC) microbes?

They cannot be grown in the laboratory and are identified by genotypic methods.

What is the importance of specimen collection in diagnosing infections?

Success depends on how specimens are collected, handled, stored, and cultured.

What is a 'clean catch' urine sample?

A sample taken by washing the external urethra and collecting the urine midstream.

What should be avoided when collecting sputum samples?

Contamination with saliva.

What is the purpose of using sterile sample containers?

To prevent contamination from the environment or the patient.

What are the characteristics assessed in macroscopic morphology?

Appearance of colonies, texture, size, shape, and pigment.

What types of tests are performed on microbial isolates?

Tests to identify specific traits, enzymatic activities, and antibiotic susceptibility.

Why is rapid identification of microbes important in bloodstream infections?

It reduces the mortality risk associated with sepsis.

What is the role of antibody response in immunologic methods?

It is exploited for diagnostic purposes to identify pathogens.

What are some examples of physiological/biochemical characteristics used in identification?

Enzyme production, fermentation of sugars, and sensitivity to antibiotics.

What should be done before swabbing skin samples for culture?

Wounds should be cleansed to avoid collecting normal microbiota.

What is the significance of labeling and identifying specimens?

It is crucial for obtaining timely and accurate results.

What is a Gram stain an example of?

A phenotypic method of microbial identification.

What are some common laboratory techniques used in diagnosing infections?

Patient analysis for signs of infection, specimen collection, and analysis.

What is the importance of aseptic technique in specimen collection?

It prevents contamination and ensures accurate identification of the pathogen.

What factors can affect the identification of an infectious agent?

Specimen collection, handling, storage, and the presence of resident microbiota.

What is the difference between a 'dirty catch' and a 'clean catch' urine sample?

'Dirty catch' is first-voided urine, while 'clean catch' is collected midstream after cleaning the urethra.

What types of samples can be collected for microbial analysis?

Blood, cerebrospinal fluid, tissue fluids, skin, urine, sputum, and swabs from various sites.

What is the role of rapid methods of identification in infection management?

They promote correct diagnosis and treatment, especially in emergencies.

What is the mainstay of bacterial identification?

Physiological and biochemical characteristics.

How can contamination be avoided when collecting throat and nasopharyngeal samples?

Swabs should not touch the tongue, cheeks, or saliva.

What is the purpose of using laboratory kits in immunologic methods?

For immediate identification of a number of pathogens.

What is the significance of antibiotic resistance in treating infections?

It complicates the choice of appropriate antibiotics for treatment.

What is the purpose of entering results into a summary patient chart?

To use the results in assessment and treatment regimens.

Why is understanding lab results important in patient treatment?

It is imperative for successful treatment of patients.

What is the immediate method for determining microbial characteristics?

Direct microscopic observation of fresh or stained specimens.

What stains are most often used in direct examination of specimens?

Gram stain and Acid-fast stain.

What is the purpose of isolation media in microbial testing?

To enrich a pathogen present in small numbers or easily overgrown.

What is selective media used for?

To encourage the growth of only the suspected pathogen in nonsterile specimens.

What does differential media identify?

Definitive characteristics and fermentation patterns of bacteria.

What is the significance of obtaining pure cultures from isolation media?

It ensures subsequent identification steps will be accurate.

What does biochemical testing reveal about bacteria?

Physiological reactions to nutrients and substrates, indicating enzyme presence.

What does the MGIT system detect?

The growth of slow-growing Mycobacterium tuberculosis.

How does the MGIT system monitor growth?

By monitoring oxygen levels in a tube inoculated with patient sputum or blood.

Why is antimicrobial susceptibility testing important?

To determine which drugs will be effective in treatment, especially with rising resistance.

What is phage typing used for?

To identify bacteria when morphological and biochemical tests are insufficient.

How can clinical significance of cultures be determined?

By assessing if an isolate is clinically important or merely a contaminant.

What does a few colonies of E. coli in a urine sample indicate?

It can indicate normal biota.

What does a single colony of Mycobacterium tuberculosis suggest?

It is highly suggestive of disease.

What are the drawbacks of phenotypic methods?

Culturing takes time and may miss nonculturable organisms.

What does serology test for?

The presence of specific antibodies in serum, urine, and other fluids.

What is antiserum?

Blood serum containing antibodies against specific antigens.

What do agglutination reactions involve?

Interlinking of antigens by antibodies to form visible clumps.

What is the difference between agglutination and precipitation reactions?

Agglutination involves whole cells; precipitation involves soluble molecules.

What is immunochromatography?

A method that uses a lateral flow test to detect antigens in a sample.

How do lateral flow tests work?

Patient samples flow through a cartridge and encounter antibodies; binding indicates the presence of antigens.

What is the advantage of lateral flow antigen tests?

They provide rapid turnaround for virus tests without laboratory equipment.

What does antibody titer indicate?

The concentration of antibodies in a sample, reflecting the highest dilution of serum that still produces agglutination.

What is serotyping?

An antigen-antibody technique for identifying and classifying bacteria into serotypes using antisera against cell antigens.

What is the purpose of the Western Blot procedure?

To verify microbial-specific antigens or antibodies in a patient sample by separating proteins and detecting specific binding patterns.

Why is Western Blot often used after ELISA?

Because it is highly specific and serves as a confirmation test for less specific but more sensitive screening tests like ELISA.

What are fluorescent antibodies (FAbs)?

Monoclonal antibodies labeled by a fluorescent dye used in immunofluorescence testing.

What is the difference between direct and indirect immunofluorescence testing?

Direct testing uses fixed specimens exposed to FAb solutions, while indirect testing uses known antigens added to patient sera to visualize binding.

What is the Enzyme-Linked Immunosorbent Assay (ELISA)?

A test that uses an enzyme-linked indicator antibody to visualize antigen-antibody reactions on a solid support like a microtiter plate.

What does indirect ELISA detect?

Microbe-specific antibodies in patient sera.

What does direct ELISA detect?

Antigens in patient samples by using known antibodies.

What is the significance of PCR in infectious disease diagnosis?

PCR amplifies DNA or RNA from samples, allowing for the detection of minute quantities of nucleic acids.

What is Real-Time PCR (qPCR)?

A PCR method that uses fluorescent labeling to measure the level of fluorescence in real time during amplification.

What is hybridization in microbiology?

A technique that identifies microbes by analyzing segments of their genetic material using complementary probes.

What is Fluorescent in situ hybridization (FISH)?

A method that uses fluorescently labeled probes applied to intact cells to identify microbes based on glowing signals.

What is the tuberculin reaction?

An in vivo test where a purified protein derivative from Mycobacterium tuberculosis is injected to indicate previous exposure to tuberculosis.

What are the general features of effective serological tests?

They should have high specificity (focus on certain antibodies/antigens) and high sensitivity (detect minute quantities).

What does a high number of false positives indicate about a test's sensitivity?

It suggests an unacceptable level of sensitivity.

What is the purpose of new diagnostic strategies using patient blood?

To check for the presence of genes that indicate bacterial infection, helping to avoid unnecessary antibiotic prescriptions.

What is the role of imaging techniques in infection diagnosis?

To locate areas of localized infection in deep tissue, potentially avoiding invasive biopsies.

What is the significance of using computer chips in new detection systems?

They sense minute changes in electrical current that occur when antigen-antibody complexes are formed.

What is the main advantage of using PCR for diagnosis?

It can amplify even minute quantities of nucleic acids present in a sample within hours.

What is the main use of the CDC-supplied RT-PCR test for COVID-19?

To detect viral RNA from SARS-CoV-2.