MOSullivan Microbial Strain Typing - Ministry of Health
Transcript of MOSullivan Microbial Strain Typing - Ministry of Health
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Microbial strain typing in surveillance and outbreak investigationMatthew O'Sullivan
Staff Specialist in Infectious Diseases and Clinical Microbiology
Senior Lecturer, Sydney Medical School
SYDNEY MEDICAL SCHOOL
CENTRE FOR INFECTIOUS DISEASES & MICROBIOLOGY, WESTMEAD HOSPITAL,
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Overview
› What is strain typing?
› Why do strain typing?
› Strain Typing in Infection Control
› Strain Typing Methods
› Typing Method Characteristics
› Strain Typing Interpretation
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What is strain typing?
Taxonomic Classifications
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What is strain typing?
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What is strain typing?
› Phenotype
Much variation is evident even within species
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What is strain typing?
› Phenotype
Much variation is evident even within species
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What is strain typing?
› Genotype
Much variation is evident even within species
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What is strain typing?
› Dividing organisms into groups below species level
- Using phenotypic or genotypic methods
What is strain typing?
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Why Do Strain Typing?
1. Study the evolution and population genetics
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Why Do Strain Typing?
1. Study the evolution and population genetics
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Why Do Strain Typing?
› Eg: Clostridium difficile ribotype 027
2. Detect strains of increased virulence
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EID 2012 17(6):976
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Why Do Strain Typing?
3.Identify source of infection
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Strain typing in infection control
› Incidence of organism
- A patient develops MRSA bacteraemia in the ICU 5 days after admission to
hospital after one negative MRSA screen. The prevalence of MRSA colonisation
in ICU patients is 25%
- A patient develops bacteraemia with KPC-producing Klebsiella pneumoniae 5
Is strain typing required to identify source of infection?
- A patient develops bacteraemia with KPC-producing Klebsiella pneumoniae 5
days after admission to hospital. The patient in the adjacent bed is known to be
colonised with KPC-producing Klebsiella pneumoniae. KPC producing organisms
have never been identified at the hospital before.
› Other characteristic markers?
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Strain Typing in Infection Control
Approaches
Retrospective
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Prospective
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Retrospective Strain Typing
Traditional way of utilising strain
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utilising strain typing in infection control
Strain Typing
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Case Definition
› Diagnosis
› Time
› Place
› Epidemiologic Parameters
› Strain type
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Prospective Strain Typing
Strain Typing
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Prospective typing increasingly utilised
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New MRSA isolates per day for hospital inpatients
Prospective Strain Typing
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New MRSA isolates per day for hospital inpatients
Prospective Strain Typing
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New Strain A MRSA isolates per day for hospital inpatients
Prospective Strain Typing
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New Strain G MRSA isolates per day for hospital inpatients
Prospective Strain Typing
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Strain typing methods
› Phenotypic
- Serotyping
- Streptococcus pneumoniae
- Phage typing
- Salmonella enterica
› Genotypic
- Pulse-field gel electrophoresis (PFGE)
- Many organisms (MRSA, VRE, MRAB)- Many organisms (MRSA, VRE, MRAB)
- PCR-ribotyping
- Clostridium difficile
- Multilocus variable number of tandem repeats analysis (MLVA)
- Salmonella enterica
- Binary typing
- Staphylococcus aureus
- Single locus sequence typing
- Stapylococcus aureus (spa)
- Multilocus sequence typing (MLST)
- Many organisms
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Typing Method Characteristics
› Discriminatory power
› Reproducibility
› Stability
› Typeability
› Ease of interpretation
› Ease of use
› Portability of results
› Turnaround time
› Throughput
› Cost
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Interpreting Strain Typing Results
A. Yes
B. No
Typing Results: All Part of Outbreak?
Maybe: Depends on discriminatory
power of typing system,
background prevalence of the strain
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background prevalence of the strain
type
Maybe: Depends on stability of the
typing system, how ‘different’ are
the strains
A. Yes
B. No
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Interpreting Strain Typing Results
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Interpreting Strain Typing Results
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Transmissible Resistance
Need to consider typing transmissible element as well as the ‘host’
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Conclusions
› Strain typing not necessary for infection control surveillance for all organisms
› Strain typing in infection control may be retrospective or prospective
› Characteristics of the available typing method must be considered before deciding to perform typingdeciding to perform typing
› Characteristics of the typing method must be considered in interpreting the results
› Typing does not provide a ‘Yes’ – ‘No’ answer, but a likelihood
› Transmissible resistance requires a different approach
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