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Identification methods for Legionella from environmental samples.
C Bartie1, S N Venter, L H Nel
1Immunology and Microbiology Section, National Centre for Occupational Health, P.O. Box 4788, Johannesburg, 2000, South Africa. bartid@health.gov.za
Water Research
|February 25, 2003
Summary
This study evaluated Legionella culturing methods for South Africa, finding a selective heat treatment approach most effective for detecting Legionella species in environmental samples. Re-incubation with amoebae also improved detection rates.
Area of Science:
- Environmental microbiology
- Diagnostic microbiology
Background:
- Standardized Legionella culturing methods are lacking in South Africa, leading to uncertainty in prevalence and species identification.
- Existing international methods (ISO, AS) and a most probable number (MPN) method show variable sensitivities and specificities for Legionella detection.
Purpose of the Study:
- To evaluate and compare the ISO, AS, and MPN methods for Legionella detection in South African environmental samples.
- To investigate the impact of sample pre-treatment (acid, heat) and re-incubation with autochthonous amoebae on culture outcomes.
- To provide guidelines for developing a standard Legionella culturing method for South Africa.
Main Methods:
- Environmental samples (industrial water, mine water, biofilm) were collected and concentrated via membrane filtration.
- Samples underwent different pre-treatments (none, acid, heat) and were cultured on four media (alphaBCYE, BMPA, MWY, GVPC).
- The effect of re-incubating sample concentrates with autochthonous amoebae was assessed.
Main Results:
- Legionella species were detected in 82% of evaluated environmental samples.
- A selective approach using heat treatment (not acid) combined with alphaBCYE and GVPC or MWY media was most effective.
- Legionella pneumophila serogroups 1-14 were the most prevalent species; 54% of samples exceeded 10(2) cfu/ml.
- Re-incubation with amoebae improved culturability in 50% of alphaBCYE and 25% of GVPC cultures.
Conclusions:
- A standardized selective culturing method incorporating heat treatment and specific media is recommended for South African Legionella diagnostics.
- Further optimization may involve re-incubation with autochthonous amoebae to enhance detection rates.
- Establishing a standard method is crucial for accurate Legionella surveillance in South Africa.