Diagnostic Microbiology: Principles, Methods, and Laboratory Safety

Flashcards covering diagnostic microbiology philosophy, causes and manifestations of infection, diagnostic testing workflows, laboratory safety rules, and sterilization methods.

What two primary factors determine the clinical presentation and interaction between host and microorganism during an infection?

The interaction is affected by the host immune status and microbial virulence factors.

What composite of clinical and laboratory information is required to establish a diagnosis of an infectious disease?

Diagnosis requires a composite of history, physical examination, radiographic findings, and laboratory data.

What is the distinction between exogenous and endogenous microbial pathogens?

Exogenous pathogens are acquired from environmental or animal sources or from other persons, whereas endogenous pathogens arise from the host's normal flora.

What is the primary purpose and clinical role of Diagnostic Microbiology?

It is the tool that makes it possible to identify the exact pathogens of infectious diseases and determine the most optimal therapy at the level of individual patients.

What factors can make conventional, culture-based identification methods less reliable?

Transport of specimens under less than ideal conditions, prior use of antibiotics, and a small number of organisms.

What are the key diagnostic advantages of newer nucleic acid amplification and probe-based methods?

They mitigate the need for higher microbial load or viable, metabolically active organisms, shorten turnaround time, and can detect antibiotic resistance genes directly from the specimen to guide targeted therapy.

What are the three possible outcomes of microbial colonization?

1) Elimination of the microorganism without affecting the host; 2) Infection, in which the organisms multiply and cause an immune or other host response; and 3) A transient or prolonged carrier state.

At what point does microbial colonization transition into an infectious disease?

Infectious disease occurs when the microorganism causes tissue damage and loss of function of body systems.

Upon what information is initial empiric therapy based before definitive microbiologic identification is achieved?

It is based on the microbiologic epidemiology of the infection and the patient's presenting symptoms.

What are the five basic laboratory techniques involved in definitive microbiologic diagnosis?

1) Morphologic identification of the agent in stains of specimens or tissue sections (light and electron microscopy); 2) Cultivation and identification of the organisms; 3) Detection of microbial antigens by immunologic assay (latex agglutination, enzyme immunoassay [EIA]); 4) Detection of microbial DNA or RNA; and 5) Detection of an inflammatory or host immune response to the pathogenic agents.

What constitutes the laboratory "feedback" provided to healthcare providers during the diagnostic process?

Earliest reports of the results of individual steps in the isolation and identification of the causative agent, enabling clinicians to reevaluate diagnoses and adjust therapeutic programs.

According to the specimen collection and diagnosis pathway, which serologic and genetic tests are utilized to reach a definitive diagnosis?

Serologic tests include agglutination, complement fixation, and ELISA; genetic tests include hybridization of DNA and RNA.

What critical step follows a definitive diagnosis to finalize targeted treatment?

Antimicrobial susceptibility testing (or utilization of known susceptibility profiles).

What are the six specific laboratory safety admonitions listed for microbiology laboratories?

(1) Wear gloves; (2) Wash hands after working with infectious materials; (3) Disinfect all instruments immediately after use; (4) Use water to moisten specimen labels rather than the tongue; (5) Disinfect all contaminated waste before discarding; and (6) Report to appropriate personnel all accidents or exposures to infectious agents.

How is sterilization defined in the context of laboratory processing?

A process that kills all forms of microbial life, including bacterial endospores.

How does disinfection differ from sterilization?

Disinfection destroys pathogenic organisms but not necessarily all microorganisms, endospores, or prions (though some disinfectants kill endospores with prolonged exposure times).

What is decontamination?

The removal of pathogenic microorganisms so that items are safe to handle or dispose of.

What factors limit the success or degree of sterilization, disinfection, or decontamination in a healthcare setting?

Organic load (organisms, blood, or body fluids), type of organisms present, concentration and exposure time to the germicide, physical and chemical nature of the surface (hinges, cracks, rough or smooth surfaces), temperature, pH, humidity, and the presence of a biofilm.