Rapid detection of replicating cells
The invention enables efficient, rapid, and sensitive enumeration of living cells by detecting microscopic colonies derived from in situ cell division using large area imaging. Microbial enumeration tests based on the invention address an important problem in clinical and industrial microbiology—the long time needed for detection in traditional tests—while retaining key advantages of the traditional methods based on microbial culture. Embodiments of the invention include non-destructive aseptic methods for detecting cellular microcolonies without labeling reagents. These methods allow for the generation of pure cultures which can be used for microbial identification and determination of antimicrobial resistance.
1. A method for detecting microcolonies of living target cells in a sample, the microcolonies having a measurement of less than 50 microns in at least two orthogonal dimensions, the method comprising the steps of:
(a) depositing living target cells present in the sample on a detection surface having at least one dimension of 1 cm or greater and a detection zone having a detection area;
(b) allowing the formation of one or more microcolonies of the target cells;
(c) illuminating the detection area using an external light source comprising a first light source and a liquid light-guide to direct light emitted by the first light source to the detection area; and
(d) detecting the one or more microcolonies using imaging optics based on light reflected by the one or more microcolonies or the detection area responsive to incidence of the light emitted by the first light source on the detection area without magnifying the detection area by more than five-fold.
2. The method of claim 1 , wherein the detecting detects a single microcolony on the detection surface.
3. The method of claim 1 , wherein the detecting detects overlapping or contiguous microcolonies.
4. The method of claim 1 , wherein the mean number of cells in the one or more microcolonies is less than 50,000 cells.
5. The method of claim 1 , wherein the cells in the one or more microcolonies remain competent to replicate following the detecting, and further comprising repeating steps (c) and (d) after a period in which cells are allowed to replicate to discern objects that change size over time from objects that do not change size over time.
6. The method of claim 1 , further comprising repeating steps (a)-(c) with one or more additional samples, wherein the repeating is automated.
7. The method of claim 1 , wherein the detecting detects at least one of light emitted, scattered, reflected, and absorbed as a result of illumination of the one or more microcolonies.
8. The method of claim 1 , wherein the detecting detects light reflected as a result of illumination of the one or more microcolonies.
9. The method of claim 1 , wherein the detecting detects fluorescence.
10. The method of claim 1 , wherein the detecting detects one or more naturally occurring optical properties of the one or more microcolonies.
11. The method of claim 10 wherein the one or more naturally occurring optical properties comprise at least one of autofluorescence, thermal radiation, optical absorbance, fluorescence polarization, optical reflectance, and light scattering.
12. The method of claim 1 , wherein the detecting employs at least one of a photoelectric detector, a photoelectric array detector, a photomultiplier tube detector, a photodiode detector, and a photosensitive film.
13. The method of claim 12 , wherein the photoelectric detector comprises a charge-coupled device (CCD) detector.
14. The method of claim 1 , further comprising the step, prior to or during step (c), of contacting the sample with a signaling moiety that associates either directly or indirectly with the target cells.
15. The method of claim 14 , wherein the signaling moiety has one of a fluorescent signaling character, a chromogenic signaling character, and a light-scattering signaling character.
16. The method of claim 14 , wherein the signaling moiety is a viability stain for staining living cells.
17. The method of claim 1 , further comprising the step, during or after step (d), of quantifying the number of microcolonies.
18. The method of claim 1 , wherein the external light source comprises an excitation filter-wheel to filter the light emitted by the first light source.
19. The method of claim 1 , further comprising the step, during or before step (d), of filtering the light reflected by the one or more microcolonies or the detection area.
20. The method of claim 19 , wherein the imaging optics comprises an emission filter-wheel to filter the light reflected by the one or more microcolonies or the detection area.