Chapter 1 (Bacteria in Laboratory) Flashcards
Part 5
Methods for laboratory diagnosis of infectious diseases
- Biochemical test (conventional)
- Molecular methods of ID and characterization
- Immunochemical methods for Organism Detection
- Serologic diagnosis of infectious diseases
- Detection of antibacterial resistance
- Use of experimental laboratory animals
- Epidemiology (bacteriophage, serological typing)
Biochemical tests
- Enzyme based tests
- Presence of metabolic pathways
- Inhibitor profiles
Catalase, oxidase, indole (tryptophanase), urase, PYR (L-pyrrolidonnyl-B-naphthylamide), hippurate hydrolysis
Enzyme based tests
Oxidation-fermentation tests,
amino acid degradation (deamination, decarboxylation),
single substrate utilization (malonate, citrate)
Presence of metabolic pathways
Growth in the presence of various NaCl concentration, susceptibility to Optochin and bile solubility, ability to hydrolyze esculin, ethanol survival
Inhibitor profiles
Molecular methods of ID characterization
Nucleic acid based
Non-nucleic acid based analytic methods
- Nucleic acid hybridization
- Target nucleic acid amplification
- Polymerase chain reaction (PCR)
Nucleic Acid based
Chromatography (gas liquid chromatography)
Electrophoretic protein analysis
Non-nucleic acid based analytic methods
- Precipitin test
- Particle agglutination
- Immunofluorescent assays
- Enzyme immunoassay (EIA) / Enzyme Linked Immunosorbent Assay (ELISA)
- Radioimmunoassay (RIA)
Immunochemical methods for Organism Detection
- Agglutination
- Precipitation tests
- hemagglutination Inhibition
- Neutralization
- Complement fixation
- ELISA, FAT RIA, FIA
- Westernblot assay
Serologic diagnosis of Infectious diseases
Broth dilution
Mircodilution broth
MIC
MBC
- conventional
- commercial
- minimum inhibitory concentration
- minimum bactericidal concentration
- Agar dilution
- Agar dilution derivations
- Disk diffusion
- Diffusion in agar derivations
Conventional (1, 3)
Commercial (2, 4)
Purpose: Identifies bacterial strains based on their susceptibility to certain bacteriophages (viruses that infect bacteria).
Method: Different bacteriophages are applied to a bacterial culture. The areas where the bacteria are lysed (cleared by the phages) indicate susceptibility.
Application: Commonly used to differentiate strains within species such as Staphylococcus aureus and Salmonella.
Specificity: Highly specific for particular strains of bacteria.
Time: Relatively quick, as it involves culturing bacteria and applying phages, usually completed within a day or two
Bacteriophage typing
Purpose: Identifies bacterial strains based on the specific antigens present on their surfaces.
Method: Uses antibodies that bind to specific antigens on the bacterial cell surface. The binding can be detected through various methods like agglutination, precipitation, or ELISA (enzyme-linked immunosorbent assay).
Application: Widely used for a range of bacteria, including Escherichia coli, Streptococcus pneumoniae, and Neisseria meningitidis.
Specificity: Can be highly specific depending on the antibodies used.
Time: Can be rapid, especially with techniques like agglutination or ELISA, which can provide results within hours.
Serological typing
Deviation from the parent form in bacteria of the same species growing under different or identical condition
May affect all biologic properties of bacteria and may be temporary or permanent
Variation
Variations may appear either as a result of:
- Spontaneous mutation
- Induction by environmental factors
Variation types
- Morphologic
- Physiologic
- Genetic
Morphologic variation
- Pleomorphism
- Dissociation
- Cell structures
Genetic variations
- Mutation
- Gene exchange/ transfer and recombination
Variation in size, shape and appearance
Pleomorphism
Change in the type of colony formed on semisolid medium
Dissociation
- Formation tent to diminish w/ continued cultivation on artificial media and is restored by animal passage
- Presence/ absence is variable but numbers and location remain constant
- Formation is affected by environmental factors
- Bacterial forms w/ defective/ absent cell wall and are thus transparent and stain w/ difficulty
- Capsule
- Flagella
- Spores
- L-forms
Modification of the organism or part to make it for existence in conditions of its environment
Physiologic adaptation
Form adaptation which indicates a loss in the disease producing ability of a given organism
A highly pathogenic organism may be rendered temporarily/ permanently nonpathogenic of repeatedly subcultured on artificial lab medium
Attenuation
- Change in the original nucleotide sequence of a gene or genes within organism’s genome
- Change may involve a single DNA base or deletion/insertion of one or few nucleotide pairs
- Can be spontaneous
- Can be induced by chemical/physical factors o biologic factors
Mutation
Product of mutation
Mutant
Gene exchange/ transfer and recombination mechanisms
- Transformation
- Transduction
- Conjugation
