Viability detection and quantification assay of waterborne pathogens by enrichment
View Patent ↗A process for detecting viable waterborne pathogens in a water sample, includes enriching a concentrate of bacteria from the sample and taking a first DNA extract at time T 0 and a second DNA extract at time T 2 after an incubation period. Real-time polymerase chain reaction performed on the DNA extracts yields respective cycle threshold values Ct. The change in Ct provides an indication of the targeted pathogen in the sample. An order of magnitude quantification of the sample can also be performed using a serial dilution technique on the T 0 DNA extract. The process has particular application for detecting Legionella , including viable but not culturable cells.
1 . A process for detecting presence of viable non-culturable targeted waterborne pathogens comprising:
(A) obtaining a liquid sample;
(B) collecting a concentrate of bacterial cells from the liquid sample;
(C) enriching the concentrate of bacterial cells to produce an enriched concentrate of bacterial cells;
(D) extracting a T 0 DNA extract from the enriched concentrate of bacterial cells at time T 0 ;
(E) storing the T 0 DNA extract;
(F) incubating the enriched concentrate of bacterial cells;
(G) extracting a T 2 DNA extract from the incubated enriched concentrate of bacterial cells at time T 2 ;
(H) analyzing the T 0 DNA extract with real-time Polymerase Chain Reaction (PCR) to determine a cycle threshold Ct value for the T 0 DNA extract;
(I) analyzing the T 2 DNA extract with real-time Polymerase Chain Reaction (PCR) to determine a cycle threshold Ct value for the T 2 DNA extract; and
(J) analyzing a difference in Ct value (ΔCt) between the T 0 DNA extract and the T 2 DNA extract to determine a qualitative assessment of the presence of viable but not culturable cells of the targeted waterborne pathogens in the liquid sample.
2 . The process of claim 1 wherein the qualitative assessment comprises determining if the ΔCt is greater than a cut-off value.
3 . The process of claim 2 wherein the cut-off value is ΔCt is greater than approximately 1.5.
4 . The process according to claim 1 comprising:
(A) obtaining the liquid sample from a water source; and
(B) neutralizing residual oxidants and antimicrobials within the liquid sample to obtain a substantially oxidant-free antimicrobial sample.
5 . The process according to claim 4 , wherein the sample is neutralized using a reducing agent.
6 . The process according to claim 5 wherein the reducing agent comprises at least one of sodium thiosulfate (Na 2 S 2 O 3 ) or sodium bisulfite.
7 . The process of claim 1 wherein collecting the concentrate of bacterial cells comprises performing a filter concentration on the liquid sample.
8 . The process of claim 7 wherein the filter concentration comprises using a membrane in a filtration unit, aseptically removing the membrane from the filtration unit and providing the membrane into an enrichment broth.
9 . The process according to claim 8 , wherein the membrane is a polycarbonate membrane.
10 . The process according to claim 9 , wherein the polycarbonate membrane is a track-etched membrane.
11 . The process according to claim 10 , wherein the polycarbonate membrane has a pore size of less than 0.25 μm.
12 . The process according to claim 4 , wherein the polycarbonate membrane has a diameter of about 47 mm or larger.
13 . The process according to claim 1 , wherein the concentrate of bacterial cells is enriched in a solution of growth medium.
14 . The process according to claim 13 , wherein the growth medium is a Buffered Yeast Extract media comprising Vancomycin, Polymyxin, Cycloheximide, Glycine, Iron pyrophosphate, L-cysteine, and Bovine serum albumin.
15 . The process according to claim 1 , wherein the T 0 DNA extract is stored at about −20° C.
16 . The process according to claim 1 , wherein the concentrate of bacterial cells is incubated at a temperature from 30° C. to 37° C.
17 . The process according to claim 1 , wherein the concentrate of bacterial cells is shaken at 50 rpm during the incubation period.
18 . The process according to claim 1 , when the Ct value of T 2 DNA extract is equal to or greater than the Ct value of T 0 DNA extract, the sample is assessed to not contain viable but not culturable cells of the targeted waterborne pathogens.
19 . The process according to claim 1 , when the Ct value of T 2 DNA extract is less than the Ct value of T 0 DNA extract, the sample is assessed to contain viable but not culturable cells of the targeted waterborne pathogens.
20 . The process according to claim 1 comprising:
(A) diluting the T 0 DNA extract;
(B) detecting PCR amplification by performing real-time PCR on the T 0 DNA extract dilution;
(C) repeating the diluting and detecting until no PCR amplification is detected;
(D) wherein the highest dilution of the T 0 DNA extract at which PCR amplification is detected provides an order of magnitude quantification of the viable but not culturable cells of the targeted waterborne pathogen in the liquid sample.
21 . The process according to claim 20 , when only the T 0 DNA extract shows PCR amplification, the quantification of the liquid sample is ≤1 Colony Forming Units (CFU)/ml.
22 . The process according to claim 20 , wherein the dilution is a serial dilution of 10-fold to 100-fold.
23 . The process according to claim 22 , wherein when only both the T 0 DNA extract and a 1:10 dilution of the T 0 DNA extract show PCR amplification, the quantification X of the liquid sample is 1<X≤10 CFU/ml.
24 . The process according to claim 22 , wherein when each of the T 0 DNA extract, the 1:10 dilution of the T 0 DNA, and a 1:100 dilution of the T 0 DNA show PCR amplification, the quantification X of the liquid sample is 10<X≤100 CFU/ml.
25 . The process according to claim 1 , wherein the targeted pathogen is Legionella.