A New Field Method for Enumerating Viable Legionella And Total Heterotrophic Aerobic Bacteria
Presentation at the 2007 Association of Water Technologies Convention and Exposition
A new field method for the quantitative determination of viable Legionella and total heterotrophic aerobic bacteria was evaluated in hundreds of laboratory experiments and from analysis of over two thousand field samplers in actual operating conditions. The method has been proven reliable for determining viable cell concentrations of Legionella pneumophila, Legionella species and total heterotrophic aerobic bacteria. In comparison to standard methods, the new protocol has been shown to be more accurate, faster and more convenient. Comparisons to other rapid methods are presented. Guidance is given for use of the new method within the context of hazard analysis and control to prevent legionellosis.
The patents pending Phigenics Validation Test® (PVT) is a “dipslide format” field sampler that has on its surfaces the standard growth media required for Legionella enumeration. The product is designed so that both viable Legionella and total heterotrophic aerobic bacteria counts can be obtained from the same test.More than two thousand PVT field samplers were analyzed in laboratory and field experiments to develop the method, simplify the protocol and compare results to the Standard Method. Laboratory experiments, split sample comparisons and case histories of field use under actual operating conditions document the features and benefits of the PVT.
Features of the PVT
The PVT is a field sampling protocol to obtain viable cell concentrations (as CFU/ml) for the following from the same sample:- total heterotrophic aerobic bacteria- Legionella pneumophila (serogroup 1)- Legionella pneumophila (serogroup 2-14)- non-pneumophila Legionella speciesData is obtained for the exact moment when the PVT field sampler contacts the water sample- shipment of water samples to the laboratory is not required- time required to obtain results is reduced 75-80% compared to the Standard Method for Legionella The PVT field sampler consists of a sterile plastic screw-capped container within which is held a paddle containing on one side buffered charcoal yeast extract agar enriched with α-ketoglutarate (BCYEα) and on the other side of the paddle, BCYEα agar plus the selective supplements glycine, vancomycin, polymyxin B, and cycloheximide (GVPC). Figure 1 shows the PVT field sampler.