Bacteria Subtyping Flashcards
Patient management or infection control distinguishes
Relapse from infection
Relapse is
Same bacteria
Reinfection is
Different bacteria
Criteria for evaluating typing system
Typeability Reproducibility Discriminatory power Ease of interpretation Cost Time
2 methods of sub typing
Phenotypic
Genotypic
Phenotypic subtyping
Biotyping
Antimicrobial susceptibility testing Serotyping
Bacteriophage typing
Whole cell or cell envelop protein profile Multilocus Enzyme Electrophoresis (MLEE)
Genotypic subtyping
Plasmid analysis
Restriction Fragment Length Polymorphism( RFLP)
Random Amplified Polymorphic DNA (RAPD) •
Amplified Fragment Length Polymorphism (AFLP) •
Ribotyping •
Pulsed-Field Gel Electrophoresis (PFGE) • Multilocus Sequence Typing (MLST) • Microarray (DNA chip)
What is MIC
Minimal inhibitory concentration
Lowest concentration of ab needed to inhibit growth of certain amount of bacteria
If MIC greater than or equal to resistance break point that means
Ab resistance
Antimicrobial susceptibility testing ( AST) is what kind of subtyping?
Phenotypic
Antimicrobial Susceptibility testing
Agar dilution Broth dilution/microdilution Disk diffusion test E-test Mininam inhibitory concentration (MIC)
The patterns of clearing around the bacteriophage spot indicate
The susceptibility of the test organism to different phases
Different patterns of clearing around the bacteriophage are compared to determine
Strain difference
Serotyping is based on
O antigen
H antigen
Serotyping is important in
Salmonella
E.Coli O157:H7
Listeria Monocytogenes
Strength of Ribotyping?
Rapid
Automated
Reproducible
Easy to interpret
Weakness of Ribotyping
Limited discriminatory power
Relative expensive
Insufficient database
What does PFGE do ?
Pulsed field Gel Electrophoresis
Target the whole bacteria genome to generate DNA fingerprints
Two innovations in the field of PFGE
- Imbedding cells in agarose before lysis
2. Use of alternating electric field direction
Identical PFGE patters means
Same clone
PFGE patters with 1-2 band difference
Clone related
PFGE patterns with >3 band difference
Different clones
Strength of PFGE
Discriminatory power
Reproducibility
Database developing
Easy to interpret
Weakness of PFGE
Tedious procedure/technical expertise
Moderate cost
What is Multi Locus Sequence Typing
MLST
Characterizing bacteria using the sequence of internal fragments of 7 house keeping genes
How many internal fragments are used in MLST
Approximately 450-500 bp
What are house keeping genes ?
Genes necessary for bacteria to survive
That means every bacteria has to have it
