Phage-based bacterial detection assay
Methods of detecting target bacteria are provided. In some embodiments the methods comprise exposing the sample to a phage capable of infecting a set of target bacteria and comprising a heterologous nucleic acid sequence encoding a marker. In some embodiments the target bacteria comprise Listeria . In some embodiments the target bacteria are all Listeria . Recombinant Listeria phage comprising a heterologous nucleic acid sequence encoding a marker are also provided as are useful combinations of such phage and articles of manufacture comprising such phage, among other things.
1. A composition comprising:
at least one recombinant phage capable of infecting at least one Listeria or Salmonella microbe obtained from an environmental sample, wherein the at least one recombinant phage comprises a heterologous nucleic acid sequence encoding a marker, and wherein the at least one recombinant phage is selected from the group consisting of LP48::ffluc, LP99::ffluc, LP101::ffluc, LP124::ffluc, LP125::ffluc, LP143::ffluc, A511::ffluc, P100::ffluc, LP40::nluc, LP124::nluc, LP125::nluc, A511::nluc, and P100::nluc; and
at least one aqueous solution suitable for propagation of the at least one recombinant phage in the at least one Listeria or Salmonella microbe, said solution comprising:
a) at least one nutrient;
b) at least one selective agent suitable to inhibit growth of at least one non-target microbe in said environmental sample;
c) at least one vitamin;
d) at least one divalent metal;
e) at least one buffering agent capable of maintaining the composition at pH 7.0-7.5; and
f) at least one agent suitable to neutralize a sanitizer present in said environmental sample, wherein said agent suitable to neutralize a sanitizer is selected from the group consisting of non-ionic detergents, oxygen scavengers and emulsifiers.
2. The composition of claim 1 , wherein the at least one recombinant phage is present in the composition at a concentration of 1×10 6 to 1×10 11 pfu/ml.
3. The composition of claim 2 , wherein the at least one recombinant phage is present in the composition at a concentration of 1×10 7 to 1×10 8 pfu/ml.
4. The composition of claim 3 , wherein the at least one recombinant phage is present in the composition at a concentration of 1.5×10 7 pfu/ml.
5. The composition of claim 4 , wherein the at least one recombinant phage comprises 3 recombinant phages and each recombinant phage is present in the composition at a concentration of 1.5×10 7 pfu/ml.
6. The composition of claim 1 , wherein the at least one nutrient comprises Brain Heart Infusion medium.
7. The composition of claim 1 , wherein the at least one selective agent is selected from the group consisting of LiCl, acriflavine, nalidixic acid, and cycloheximide.
8. The composition of claim 1 , wherein the at least one vitamin comprises yeast extract.
9. The composition of claim 1 , wherein the at least one divalent metal comprises CaCl 2 .
10. The composition of claim 1 , wherein the at least one buffering agent comprises HEPES buffer.
11. The composition of claim 1 , wherein the at least one aqueous solution comprises 1× Brain Heart Infusion medium; 0.5% LiCl; 0.002% nalidixic acid; 0.2% yeast extract; 2 mM CaCl 2 , 40 mM HEPES, pH 7.4; 1 mM sodium metabisulfite; 0.1% sodium thiosulfate; 0.5% Polysorbate 80; and 0.1% lecithin.
12. The composition of claim 1 , wherein the Listeria microbe is selected from the group consisting of Listeria innocua, Listeria monocytogenes, Listeria seeligeri, Listeria ivanovii, Listeria grayi, Listeria marthii, Listeria rocourti, Listeria welshimeri, Listeria floridensis, Listeria aquatic, Listeria cornellensis, Listeria riparia , and Listeria grandensis.
13. A kit comprising:
the composition of claim 1 ; and
a solid substrate capable of supporting adhesion by the at least one Listeria or Salmonella microbe.
14. A method of determining the presence or absence of a target microbe in an environmental sample, comprising:
collecting an environmental sample;
contacting the environmental sample with the composition of claim 1
and
assaying the phage-exposed environmental sample to detect the presence or absence of the marker to determine the presence or absence of the target microbe;
wherein the time from contacting the environmental sample with the recombinant phage to detecting the presence or absence of the target microbe is between 1 minute and 6 hours.
15. The method of claim 14 , wherein the time from contacting the environmental sample with the recombinant phage to detecting the presence or absence of the target microbe is between 1 minute and 4 hours.
16. The method of claim 15 , wherein the time from contacting the environmental sample with the recombinant phage to detecting the presence or absence of the target microbe is between 1 minute and 1 hours.
17. The method of claim 14 , wherein assaying the phage-exposed environmental sample to detect the presence or absence of the marker to determine the presence or absence of the target microbe comprises a lower limit of detection of 100 target microbe cells 30 minutes after contacting the environmental sample with the recombinant phage.
18. The method of claim 14 , wherein assaying the phage-exposed environmental sample to detect the presence or absence of the marker to determine the presence or absence of the target microbe comprises a lower limit of detection of 10 target microbe cells 60 minutes after contacting the environmental sample with the recombinant phage.
19. The method of claim 14 , wherein assaying the phage-exposed environmental sample to detect the presence or absence of the marker to determine the presence or absence of the target microbe comprises a lower limit of detection of a single target microbe cell 180 minutes after contacting the environmental sample with the recombinant phage.
20. The composition of claim 5 , wherein the three recombinant phages comprise LP40::nluc, LP124::nluc, and A511::nluc.
21. The composition of claim 1 , wherein the at least one aqueous solution suitable for propagation of the at least one recombinant phage in the at least one Listeria or Salmonella microbe, further comprises g) at least one agent to prevent the decomposition of luciferin.
22. The composition of claim 21 , wherein the at least one agent to prevent the decomposition of luciferin is selected from sodium thiosulfate, polysorbate 80, HEPES, and lecithin.