Analytical instrument for evaluating microbial contamination of an object
An instrument for ascertaining a viable aerobic microbe count at t o employing a two-point calibration curve of t threshold to TVC for each type of sample. One point on the calibration curve is the x-intercept value (i.e., an estimated or experimental value for the logarithm of the minimum viable aerobic microbe count at commencement of testing (t o ) in a sample effective for causing the sample to reach t Threshold substantially instantaneously upon commencement of incubation). The other point is ascertained experimentally from a sample having a smaller known viable aerobic microbe count at t o .
1. An analytical instrument comprising an O 2 sensor and a microprocessor in electrical communication with the sensor, wherein the instrument is effective for (i) periodically ascertaining an O 2 concentration of an incubating sample taken from an object, (ii) determining a time period t Threshold from a time t o at which incubation of the sample commenced to a time at which an ascertained O 2 concentration for the sample first falls below a threshold value, (iii) correlating t Threshold to a viable aerobic microbe count in the sample prior to incubation, utilizing the linear equation:
y=mx+b (Eq. 1)
wherein:
x=logarithm of the viable aerobic microbe count per unit weight of, volume of or area swabbed to obtain a sample at t o
y=t Threshold
x-intercept=(−b/m)=an estimated or experimental value for the logarithm of the minimum viable aerobic microbe count at t o in a sample effective for causing the sample to reach t Threshold substantially instantaneously upon commencement of incubation, and
m (slope)=(y 2 −y 1 )/(x 2 −x 1 ) wherein:
x 1 and y 1 are ascertained experimentally by establishing t Threshold for a sample taken from an object having a known x, and
x 2 and y 2 are values of x and y at the x-intercept (−b/m, 0), and
(iv) transmitting a correlated value of x to a peripheral device.
2. The instrument of claim 1 wherein the logarithms are natural logarithms.
3. The instrument of claim 1 wherein the instrument is programmed to ascertain an O 2 concentration of the incubating sample at least once every 2 hours.
4. The instrument of claim 1 wherein the instrument is programmed with an O 2 concentration threshold value of between a 25% and 75% decrease from the O 2 concentration at t o .
5. The instrument of claim 1 wherein the instrument correlates t Threshold to a viable aerobic microbe count in a sample prior to incubation by solving the linear equation for x.
6. The instrument of claim 1 wherein the instrument correlates t Threshold to a viable aerobic microbe count in a sample prior to incubation by use of a look-up table.
7. The instrument of claim 1 wherein the instrument further includes at least a user interface and the x-intercept is an experimental value input by a human.
8. The instrument of claim 1 wherein the instrument further includes at least a user interface and the x-intercept is an estimated value between 6 and 10 input by a human.
9. The instrument of claim 1 wherein the sensor comprises an oxygen sensitive photoluminescent dye having a luminescent lifetime and a reader effective for determining O 2 concentration in an environment in fluid communication with the dye by measuring fluouresence of the oxygen sensitive dye.
10. The instrument of claim 9 wherein luminescent lifetime of the oxygen sensitive dye changes in response to changes in the O 2 concentration of the incubating sample.
11. The instrument of claim 10 wherein the oxygen-sensitive photoluminescent dye is embedded within an oxygen-permeable hydrophobic polymer matrix capable of being placed in physical contact with a sample taken from an object.