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Diagnostic Microbiology Chapter 5 Questions
with Accurate Answers
acute phase specimen correct answer Serum to detect patient antibody production to a particular pathogen should be collected when the disease is first suspected. This sample is known as the
Agglutination correct answer refers to the clumping or aggregation of cells, bacteria, or other particles coated with antigen or antibody with their corresponding antibody or antigen. The antigens or antibodies are attached to the surface of the particle by covalent bonds or electrical forces. In agglutination an aggregation of antibodies and antigens forms a visible framework. There are two stages to agglutination. In the first stage, known as sensitization, antigen combines with antibody. This reaction is not visible. In the second, or visible, reaction, a lattice forms between the antibody-coated particles. Antigens correct answer foreign compounds that stimulate an immune response, leading to the formation of proteins, known as antibodies automated systems in the lab correct answer - The MicroScan® System
- The Sensititre System
- BD PhoenixTM Automated Microbiology System
- The VITEK® System
- The MicroScan WalkAway
- Rapid Negative Identification Panel BBL Crystal System (BD BBLTM Diagnostics) correct answer is inoculated with one step, which then provides a closed system that is safe and easy to handle. Reagent addition and oil overlay are not needed in this panel design. This miniaturized identification system can identify almost 500 organisms.
The Crystal panels may be read manually or with the BBL Crystal Auto Reader, which uses a software program to read and print reports. There are panels for the identification of gram-negative bacilli, enterics, and nonfermenters and for gram-positive aerobic organisms. BD BBLTM EnterotubeTM II correct answer incorporates 15 standard biochemical tests contained in a compartmented tube designed to permit the simultaneous inoculation of 12 test media. This product system provides rapid, accurate identification of Enterobacteriaceae. This product contains several small pieces of agar substrates in a long plastic tube. The entire tube is inoculated with a long wire, which is enclosed in the system. After incubation and interpretation of results, a profile number is determined, which can be matched to a database. BD BBL Oxi/Ferm TubeTM II provides for the rapid identification of gram-negative oxidative and fermentative bacilli. BD Phoenix Automated Microbiology System correct answer uses the principle of nephelometry. It is a fully automated identification instrument that also can provide antimicrobial susceptibility testing. The system consists of disposable panels that combine identification and antimicrobial susceptibility testing. The instrument automatically takes readings every 20 minutes during incubation. The system measures colorimetric changes and changes in fluorescence intensity levels depending on the type of substrate.
Counterimmunoelectrophoresis correct answer is useful to detect small amounts of antibody and utilizes the principle of immunoelectrophoresis combined with an electrical current to decrease the reaction time. In this technique, solutions of antibody and sample are placed in small wells cut into agarose. A paper wick connects the two sides of the agarose to trays of buffer. An electrical current is applied through the buffer. The negatively charged bacterial antigens migrate to the positive electrode, while the neutral antibodies are carried by the weakly alkaline buffer to the negative electrode. At the zone of equivalence, antigen and antibody form a complex, and a visible band of precipitin forms. This method also has limited use because of its cost and is somewhat less sensitive than other methods, such as agglutination. direct immunofluorescence correct answer also called direct fluorescent antibody (DFA) the specimen is added to a microscopic slide. Next, fluoroscein-conjugated antibody is added to the slide. The specimen is incubated with the labeled antibody, at which time the antigen and antibody form a complex. Washing removes unbound antibody, and the excited fluorochromes emit visible light. DFA techniques detect only antigen. Applications include the detection of chlamydial antigen in urogenital specimens and the detection of Bordetella pertussis antigen in nasopharyngeal specimens. enzyme linked immunosorbent assays (ELISA) correct answer antibody or antigen is bound to an enzyme that is able to catalyze a reaction. The antibody-binding site remains free to react with antigen, and the enzyme catalyst remains unaltered during the reaction. The colored end product is then measured spectrophotometrically. Antigen can be detected using competitive ELISA techniques or noncompetitive techniques epitope correct answer The specific part of the antibody that reacts with the antigen
false positive correct answer Antibodies with low specificity may be associated with _______________ _____________ reactions; thus, high specificity is a desired antibody property Hemagglutination reaction correct answer use the aggregation of erythrocytes as a positive indicator high volume MicroScan correct answer can incubate up to 96 conventional panels Reagents are added automatically to the panels as needed, and the panels are read and interpreted and results printed. The incorporation of fluorescent labels into some of the substrates provides for bacterial identification within 2 hours. Each fluorescent substrate has a fluorophore attached to a phosphate, sugar, or amino acid compound. In fluorogenic reactions, if the enzyme is produced by the organism, it cleaves the fluorescent compound, releasing the fluorophore, and fluorescent is emitted. In fluorometric reactions, if the organism uses the substrate, the pH drops, and there is a decrease in fluorescence. latex agglutination correct answer is dependent on the proper pH, ionic strength of the reaction solution, and osmolarity. There may be false-positive reactions because of nonspecific antibodies or antibody-like compounds. Latex agglutination reactions are performed on cardboard slides or glass surfaces and are graded from 1+ to 4+. In addition to direct specimen testing, latex agglutination may be performed on bacteria isolated from cultures. Latex agglutination methods are rapid and are not labor intensive Latex correct answer Frequently used carrier molecule for agglutination
Photometers are placed at angles to the turbid suspension, and the scattering of light is measured. Noncompetitive ELISA correct answer sandwich techniques are used more often than competitive techniques and also can be used to detect antibody. ELISA methods are sensitive and economical, are not labor intensive, and do not require expensive instrumentation Rapid Negative Identification Panel correct answer uses 36 tests and can identify up to 150 species. Currently, identification systems are available for gram-positive bacteria, gram-negative bacteria, yeast, anaerobes, Haemophilus, and Neisseria. Susceptibility testing is available for gram-negative and gram-positive bacteria. The fluorometric system allows for rapid identification results within 2 hours for certain bacteria. The rapid colorimetric system can identify other microorganisms within 4 hours, and susceptibility results are available in 4 to 7 hours. The system uses microtiter trays that contain fluorescent-labeled substrates containing a synthetic and metabolic component. A halogen quartz incandescent lamp is focused on the trays. If the organism produces the enzyme to act on a substrate, the synthetic moiety is released, which enables it to fluoresce. The degree of fluorescence is measured using a fluorometer. Some of the substrates contain fluorescent pH indicators, which emit or fail to emit fluorescence when the pH changes. Real time PCR correct answer is based on PCR technology and utilizes small automated systems that combine target nucleic acid amplification with the qualitative or quantitative measurement of amplified product.
These systems use instruments or platforms that utilize amplification with real-time detection of the product. Real-time PCR has many advantages, which include the ability to detect the amplified target nucleic acid by fluorescent-labeled probes as the hybrids form. Cross-contamination between samples is lessened because amplification and product detection occur in one reaction vessel. Real- time PCR methods also can measure the amount of amplicon and, thus, can quantify the number of copies of target nucleic acid in the original specimen. Real-time PCR requires less time than does conventional PCR because of the use of fluorescent probes and their very rapid thermal cycling. Remel's RapIDTM System correct answer provides a variety of identification products that use enzyme technology; most require 4-hour incubation. Reagents are impregnated in wells in a clear plastic tray. The RapIDTM One uses 19 substrates to identify over 70 oxidase- negative, gram-negative bacilli (Enterobacteriaceae), and the RapIDTM NF Plus is used to identify oxidase-positive enteric organisms as well as nonfermenting gram-negative bacilli. There are also identification systems available for identification ofCorynebacterium and other gram- positive coryneform bacilli (RapIDTM CB Plus) and for Neisseria, Moraxella, Haemophilus, and similar organisms (RapIDTM NH). The RapIDTM Staph Plus provides for the identification of 40 staphylococci and related genera, and the RapIDTM STR System identifies β-hemolytic streptococci and viridans streptococcus. RapIDTM Yeast Plus provides for a 4-hour identification of yeasts. Databases are available for each test system Reverse transcriptase PCR (RT-PCR) correct answer is used to amplify RNA targets.
The reaction is washed again to remove any unlabeled antibody, and an enzyme substrate is added. Typical substrates are orthophenylenediamine for horseradish peroxidase and nitrophenyl phosphate for alkaline phosphatase. In a positive reaction the enzyme complex will act on the substrate, converting it to a colored end product. The intensity of the color, which is read spectrophotometrically, is proportional to the amount of antibody or antigen in the original sample. Specificity correct answer refers to the ability of an antibody to distinguish between antigens that have very small differences VITEK 2 correct answer is an automated microbiology system utilizing growth-based technology and is currently available in three formats:
- The VITEK® 2 compact is recommended for low- to middle-volume clinical and industrial laboratories, and
- VITEK® 2-60 and VITEK® 2 XL are adapted for clinical microbiology laboratories. VITEK System correct answer 1.) Computer based 2.) Uses the Vitek Card
- Lab evaluation identifies most clinically significant bacteria and yeast and also performs qualitative and quantitative antibiotic susceptibility tests Can also be used for antibiotic susceptibility testing for gram-positive and gram-negative organisms. A gram-positive or gram-negative susceptibility card is inoculated, and the reader measures the amount of light passing through each well hourly for 15 hours. As the organism grows, the amount of light transmitted decreases.
Increased turbidity and resulting decreased transmission of light usually indicate the organism is resistant to the antibiotic. A growth curve is developed based on the decline of the percentage of transmission. MICs can be determined based on the growth curve and slope of the curve.
