HK1223121B - Detector arrangement for blood culture bottles with colorimetric sensors - Google Patents

Description

Detector device for blood culture bottle with colorimetric sensor

The present application is a divisional application entitled "detector device for blood culture flask with colorimetric sensor" filed on 2011, 7/19, application No. 201180035365.2.

Cross Reference to Related Applications

The present application claims the benefit of U.S. provisional patent application No. 61/400,001 entitled "Detector Arrangement for blood culture Bottles With Colorimetric Sensors", filed on 20.7.2010.

Background

Bottles for culturing blood for the presence of microorganisms and related instruments for analyzing such bottles in a non-invasive manner are known in the art and described in the patent literature. See U.S. patents 5,858,769, 5,795,773, 4,945,060, 5,094,955, 5,164,796, 5,217,876 and 5,856,175. The bottles and instruments of the patents listed above are successfully commercialized by the present assignee under the trademark BacT/ALERT.

The vials described in these blood culture instruments utilize a colorimetric sensor placed in the bottom of the vial and in contact with the sample medium to determine the presence/absence of bacterial growth. Once the clinical/industrial sample is added to the liquid growth medium present in the vial and incubation occurs, the concentration of carbon dioxide increases as the number of microorganisms increases; carbon dioxide is a respiratory byproduct of bacterial growth. Alternatively, changes to the pH of the medium associated with the growth of the microorganisms may also be monitored by the sensor. The basic operation of the BacT/ALERT sensor and monitoring electronics is described in U.S. Pat. No. 4,945,060 and also in the Thorpe et al article "BacT/ALERT: an Automated Colorimetric microbiological Detection System", published in the journal of Clinical Microbiology (1990, 7 months, pp. 1608-12). The' 060 patent and the Thorpe et al article are incorporated by reference herein.

The basic colorimetric sensing system of the' 060 patent is shown in figure 1 of the drawings. A red Light Emitting Diode (LED) (4) is projected on the bottom of the BacT bottle (1). The colorimetric sensor (2) is placed on the bottom of the bottle (1). The LED light impinges on the sensor at a 45 degree angle relative to the bottom surface of the bottle (1). Most of the light penetrates the structure of the vial and impinges on the colorimetric sensor (2). Some of the light will reflect from the plastic bottle material and the sensor (2) at a 45 degree angle to the bottom surface of the bottle but in the opposite direction to the incident light (e.g., the angle of reflection equals the angle of incidence). Much of the remaining light is scattered from the surface and interior of the sensor. When separately, CO in a bottle₂Is changed from 0% to 100% and the color is changed from blueWhen changing to yellow, the sensor (2) changes its color. The silicon photodetector (5) "gazes" (i.e., continuously monitors the scattered intensity signal) at the area in the sensor (2) where the light from the LED interacts with the sensor. The intensity of the scattered light detected by the photodetector and the CO in the bottle (1)₂The levels are proportional. Fig. 1 also shows the related electronics including a current source (6), a current-to-voltage converter (7) and a low pass filter (8).

Fig. 2 is a graph of the signal received by the photodetector (5) of fig. 1. A fiber optic probe was used instead of the photodetector (5) in fig. 1 to collect data. The fiber optic probe is routed to an optical spectrometer that displays scattered light as a function of intensity (units of reflectance) and wavelength. The shape of each curve is at a specific CO₂Convolution of the LED intensity distribution at the level with the reflectivity of the colorimetric sensor (2).

When the silicon photodetector (5) of fig. 1 is replaced with a fiber optic probe, a photocurrent proportional to the integrated wavelength signal shown in fig. 2 is generated by the photodetector. In other words, the silicon photodetector (5) integrates the spectral response into a photocurrent. This photocurrent is in turn converted to a voltage signal using a transimpedance amplifier.

Although the BacT/ALERT sensing system of FIG. 1 is robust and has been used successfully in blood culture systems for many years, it has several aspects to be improved upon. First, if the blood culture bottle (1) moves in the chamber (e.g., shifts in the z-axis so that it moves away from the position of the photodetector), the system (as it is currently implemented) detects this movement as a decrease in intensity. However, this decrease in intensity is interpreted by the instrument as CO in the bottle₂A reduction in level, which may not actually occur. Because this effect is opposite to the effect of the increased reflectivity of the vial when the carbon dioxide content increases (meaning bacterial growth), it is possible for the system to treat a translated vial as not growing (i.e., a false negative condition).

Also, as the instrument ages in a clinical laboratory, the optical system may collect dust or optical material that changes over time experiencing reduced transmittance. For example, as plastics age, their transmission may decrease due to the effects of light, particulate build-up (dirt), or repeated use of cleaning agents. These effects will not affect the readings, but will appear as drift in the response of the system. Periodic calibration checks may compensate for this drift. Thus, there is a long felt but unmet need for a real-time monitor with transmission in the optical system and the ability to adjust or compensate for some of these sources of error, particularly if the vial is not fully installed in the container and is not at the nominal or home position (with some Z-axis displacement away from the optical detector arrangement).

Other prior art of interest includes the following U.S. patents: 7,193,717, 5,482,842, 5,480,804, 5,064,282, 5,013,155, 6,096,2726, 6,665,061, 4,248,536 and published PCT application WO 94/26874, published 11, 24, 1994.

Disclosure of Invention

According to an aspect of the present invention, there is provided a detection device for a blood culture bottle comprising a colorimetric sensor subject to pH or CO due to a sample medium within the blood culture bottle₂The color change caused by the change of (b), the detection device comprising:

a sensor LED illuminating the colorimetric sensor;

a reference LED illuminating the colorimetric sensor;

a control circuit for selectively and alternately activating the sensor LED and the reference LED; and

a photodetector that measures reflectance from the colorimetric sensor during selective and alternating illumination of the colorimetric sensor using the sensor LED and the reference LED and generates an intensity signal;

wherein the reference LED is selected to have a peak wavelength of illumination such that the intensity signal of the photodetector from the reference LED illumination is not substantially affected by a color change of the colorimetric sensor.

In some preferred embodiments, the reference LED has an illumination peak wavelength between 750 and 900 nm.

In some preferred embodiments, the detection device further comprises a computer receiving the intensity signal, the computer comprising a memory storing a calibrated relationship between the intensity signal of the reference LED as a function of the distance of the vial from the home position relative to the detection device.

In some preferred embodiments, the memory further stores a calibration relationship between the intensity signal of the sensor LED as a function of the distance of the bottle from the home position, and wherein the computer compensates for a drop in the intensity signal from the sensor LED due to the bottle being located a distance away from the home position according to the calibration relationship of the sensor LED and the reference LED.

According to another aspect of the present invention, there is provided a method for detecting a colorimetric sensor contained in a blood culture flask that is subject to pH or CO due to a sample medium within the blood culture flask₂The color change caused by the change, the method comprising the steps of:

alternately and repeatedly illuminating the colorimetric sensor with a sensor LED and a reference LED;

measuring reflectance from the colorimetric sensor due to illumination of the colorimetric sensor by the sensor LED and the reference LED using a photodetector, the photodetector responsively generating an intensity signal;

wherein the reference LED is selected to have a peak wavelength of illumination such that the intensity signal of the photodetector from the reference LED illumination is not substantially affected by a color change of the colorimetric sensor.

In some preferred embodiments, the reference LED has an illumination peak wavelength between 750 and 900 nm.

In some preferred embodiments, the method further comprises the steps of: storing in computer memory a calibration relationship between the intensity signals of the reference LED as a function of the distance of the vial from the home position relative to the sensor LED, the reference LED and the photodetector.

In some preferred embodiments, the method further comprises the steps of: storing in computer memory a calibration relationship between intensity signals of the sensor LED as a function of distance of the vial from a home position relative to the sensor LED, the reference LED and the photodetector.

In some preferred embodiments, the method further comprises the steps of: compensating for a drop in intensity signal from the sensor LED due to the vial being located a distance away from the home position based on a calibrated relationship of the sensor LED and the reference LED.

In some preferred embodiments, the compensating step comprises the steps of: determining a displacement value of the vial using the calibration relationship of the reference LED and using the calibration relationship of the sensor LED to adjust the intensity signal from the photodetector in accordance with the displacement value to correct for displacement of the vial.

An improved detection device for a blood culture flask containing a colorimetric sensor is disclosed.

The detection device includes a photodetector, a sensor LED and a reference LED, and a control circuit for selectively and alternately activating the sensor LED and the reference LED to illuminate the colorimetric sensor. The sensor LEDs function like the LEDs of fig. 1 and are used to determine the color change of the colorimetric sensor. The photodetector monitors the reflection from the sensor when illuminated by the sensor LED by monitoring the intensity changeAnd (5) emittance. The reference LED is selected to have a wavelength such that the intensity reading of the photodetector from illumination of the reference LED is not affected by the color change of the colorimetric sensor. Thus, the reference LED may be used as a reference, with the photodetector readings during illumination by the reference LED not being read by the CO in the bottle₂The effect of the change in concentration. It has been found that wavelengths in the near infrared (peak lambda of the LED between 750 and 950 nm) are suitable for the reference LED.

The reference LED is useful for indicating whether the distance between the vial and the detector subassembly has changed, whether ambient lighting conditions have changed, or whether anything within the physical optical path between the sensor LED, vial and photodetector has changed. Because the change in the reference LED is not dependent on the state of the colorimetric sensor, the reference LED can provide information about a change in the optical system that is not related to microbial growth, such that such non-growth related changes from the system can be distinguished from growth related changes. This feature helps reduce the false positive rate in the system and improves sensing accuracy and reliability.

In use, the sensor LED and the reference LED are illuminated alternately and repeatedly, for example in a time division multiplexed manner. The photodetector signals from such continuous illumination are fed to a computer. While the reference LED is illuminated, the computer monitors changes in the photodetector signal; these changes would indicate changes in vial position or optical system. For example, as the vial position in the detection system is offset from the original or nominal position, the computer may compensate the sensor LED signal based on the resulting calibration relationship between the sensor LED and reference LED signals.

Drawings

Figure 1 is a schematic representation of a known sensor and detector arrangement for a blood collection bottle as described in U.S. patent 4,945,060 (prior art).

FIG. 2 shows the wavelength and CO₂Colorimetric sensor on spectrometer as a function of concentration instead of the photosensor of figure 1Graph of the degree of reflection of (a).

Fig. 3 is a sensor and detector arrangement of a blood collection bottle according to the present disclosure.

FIG. 4 is 0-100% CO present in the bottle₂A plot of intensity signals from the photodetectors of fig. 3 over the range illuminated by the sensor LED and the reference LED of the colorimetric sensor.

FIG. 5 is a plot of the photodetector intensity signals of the sensor LED and the reference LED as a function of vial displacement from a nominal or home position, with the vial in its designed position proximate to the detection system of FIG. 3.

FIG. 6 is a graph of photodetector intensity signals of a sensor LED and a reference LED as a function of time during conditions of microbial growth within a vial.

Fig. 7 is a block diagram of an electronic device operating the sensor device of fig. 3.

FIG. 8 is a plot of the duty cycle of the reference and sensor LEDs of FIG. 3, illustrating a time division multiplexing method of operation. The width of the pulses representing the duty cycle is not drawn to scale; in one possible embodiment, the duty cycle is 33%: the time reference LED at 1/3 was illuminated, the time sensor LED at 1/3 was illuminated, and neither LED was illuminated at 1/3 to enable "dark" measurements.

Detailed Description

The present invention relates to the use of secondary LEDs as light sources to compensate for non-emulsion sensor (LES) variations to the optical system. Fig. 3 shows a block diagram of an optical configuration. This configuration is used to test vial 1 with colorimetric LES 2 contained within vial 1. The arrangement includes a sensor LED 4, an IR reference LED 10 and a photodetector 5 which generates an intensity signal. Both LEDs 4 and 10 are angled at 45 degrees with respect to the bottom surface of the bottle as shown in fig. 3. The reflectance of the bottom of the vial and the LES 2 is continuously measured by means of a control circuit (42 of fig. 7) that selectively and alternately activates the sensor LED and the reference LED. For example, the sensing or red LED 4 is turned on and the reflected signal is measured by the photodetector 5. The sensing LED 4 is then turned off. The reference LED 10 is then illuminated and the same photodetector 5 measures the reflected light. It then extinguishes and the process repeats. This approach, also referred to as a time division multiplexing scheme, is shown in fig. 8 and will be described in more detail below.

As described above, the LEDs 4 and 10 are oriented at a 45 degree angle relative to the bottom of the bottle. This causes reflections from the bottom surface of the vial to not couple strongly into the photodetector 5. The angle of incidence is the angle of reflection, so that light striking the bottom of the bottle will exit at a 45 degree angle and will not strongly affect the photodetector readings (since scattered light from the LES is the only concern). The LED has a spatial emission angle of 15-17 degrees; that is, the LED emits light in a cone defined by a peak emission at half maximum power and a full-width angle; the angle of the cone is in the range of 15-24 degrees.

Tests were performed on various LED colors and it was found that the near infrared LED (peak wavelength from 750 to 950 nm) reflectance was slightly affected by LES color change. When CO is present₂All other wavelengths of light have a negative or positive change in reflectivity when the level changes from 0% to 100%. This effect is minimized at wavelengths beyond about 750nm (near infrared LED), as shown in table 1.

TABLE 1 CO Using for sensing (Red) and reference (IR) LEDs₂Output of the photodetector of the conical flask (volt)

Fig. 4 shows a graphical equivalent of table 1. The reference LED photodetector readings are plotted as line 20 and the sensor LED photodetector readings are plotted as line 22. When the carbon dioxide level in the bottle is from 0% CO₂Increase to 100% CO₂A large increase in the red LED signal 22 is seen on the curve (it changes from about 0.6 volts to almost 2 volts). All in oneThe reference LED signal 20 changes from 2.32 volts to 2.29 volts (30mV change), so it is very stable during the process of LES changing color.

To study the changes in the optical signal as a function of the position of the vial relative to the optical system, a calibration/test fixture consisting of a digital micrometer attached to the BacT/ALERT vial was constructed. The vial is first placed in the nominal (home) position in the BacT/ALERT shelf assembly so that it is as close to the optics as possible. A reading of the reflectance is taken and the vial is then displaced by adjusting the micrometer. The micrometer provides a precise small adjustment of the z-axis displacement (i.e., it moves the vial farther away from the optical system) so that the effect of the displacement can be quantified. The normalized change in the light signal as a function of displacement is schematically illustrated in fig. 5, again with the photodetector signal for the illumination of the reference LED being plotted as line 20 and the photodetector signal for the sensor LED being plotted as line 22. It is seen that the shift causes a linear displacement in the signal received by the photodetector. Although the sensor LED signal 22 and the reference LED signal 20 have different slopes of change, each is linear, so a relationship can be created to compensate for changes in the sensor LED based on changes in the reference LED detector output, for example due to displacement of the vial from a raw or nominal position. Calculating an equation for the curve in FIG. 5; the figures of merit for the equations together with the fitting parameters (R2) are listed below in table 2.

TABLE 2

Detector _ output (signal) 0.2652-0.2554x R2-0.9963

Detector _ out (reference) 0.5621-0.2384x R2 0.9999

Where x is the linear displacement distance (in inches)

Thus, by mapping the variation in intensity of the output of the reference LED, a shift value can be determined. Applying this value to the output of the sensor LED, the amount of intensity reduction can be quantified and compensated for.

By injecting an inoculum of Saccharomyces cerevisiae into the blood cultureFurther testing of the ability of the detector device of fig. 3 was performed in the bottle and the colorimetric sensor was monitored using sensor LED and reference LED optics as yeast was grown in the bottle. Figure 6 shows the growth curve for yeast growth-lag, exponential and stationary growth phases are shown. During growth (and changes in the response of the LES sensor), the reference LED signal 20 is seen to be unchanged, while the sensor LED signal 22 is due to CO as a result of microbial growth₂The concentration changes. The flatness of the curve 20 verifies the insensitivity of the photodetector readings to LES color changes during illumination of the reference LED. It further verifies the ability to monitor changes in the optical system while not being affected by bacterial growth.

Fig. 7 is a block diagram of the electronic device 30 of the embodiment of fig. 3. The electronic device 30 comprises an "optical package" 32 consisting of the sensor LED 4, the reference LED 10 and the photodetector 5. The output of the photodetector is converted to a digital signal in an a/D converter 34 and fed to a data acquisition system 36. The data acquisition system sends a signal to an LED control board 42 that includes control circuitry and an LED driver that sends a signal over conductors 44 and 46 to illuminate LEDs 4 and 10 in a time-multiplexed manner. The photodetector signals from the data acquisition system are sent to a computer 38, and the computer 38 may be part of the instrument containing the optical suite 32 of fig. 3 and 7 (the accompanying electronics such as filters and current-to-voltage converters are omitted from the figures, but may be present in the electronics).

The memory 40 stores calibration constants and the relationship between reference and sensor LED outputs derived from, for example, the fig. 5 curve and explained above in table 2. For example, the memory 40 stores a calibration relationship between the intensity signals of the sensor LEDs as a function of the distance of the bottle from the home position (curve 22 in fig. 5); the computer 38 compensates for the drop in intensity signal from the sensor LED due to the vial being located a distance away from the home position based on the calibrated relationship of the sensor LED and the reference LED.

Fig. 8 is a plot of the duty cycle of the reference LED 10 and sensor LED 4 of fig. 3, illustrating a time division multiplexing method of operation. The on and off status of the sensor LEDs is shown on line 50; the on and off states of the reference LEDs are shown in line 42. The width of the pulses representing the duty cycle is not necessarily drawn to scale and may vary. In one possible embodiment, the duty cycle is 33%: at time 3 at 1/3 the reference LED is illuminated, at time 1/3 the sensor LED is illuminated, and at time 3 at 1/3 both LEDs are not illuminated to enable a "dark" measurement to be taken.

Using the arrangement of fig. 3, it is also possible to compensate for dirt, drift, variations in the optical system, and aging of the optical material in the beam path. Since these occur over an extended period of time (expected to be of the duration of months), they will change very slowly. Compensation is achieved by saving data points from an initial calibration (e.g., from fig. 5) and comparing the photodetector signal of the emission level of the IR LED 10 to the initial value to compensate for degradation mechanisms in the optical system. This variation also applies to the sensor LED 4. For short period drift events, changes in the IR LED 10 that should be very stable over the growth cycle of the bacteria are monitored; any change in the IR LED performance, using the stored calibration relationship for example, causes an adjustment in the sensor LED photodetector reading accordingly.

The appended claims are further statements of the disclosed invention.

Claims (11)

1. A detection device for a blood culture bottle comprising a colorimetric sensor at the bottom of the blood culture bottle that is subject to pH or CO due to a sample medium within the blood culture bottle₂The color change caused by the change of (b), the detection device comprising:

a sensor LED illuminating the colorimetric sensor;

a reference LED illuminating the colorimetric sensor;

a control circuit for selectively and alternately activating the sensor LED and the reference LED; and

a photodetector that measures reflectance from the colorimetric sensor and from the bottom of the blood culture bottle during selective and alternating illumination of the colorimetric sensor using the sensor LED and the reference LED and generates an intensity signal;

wherein the reference LED and the sensor LED are positioned such that reflections from a bottom surface of the blood culture bottle are not strongly coupled into the photodetector, and wherein the reference LED is selected to have a peak wavelength of illumination between 750nm and 950nm such that the intensity signal of the photodetector from the reference LED illumination is not substantially affected by color changes of the colorimetric sensor,

wherein the reflectance from the reference LED measured by the photodetector varies according to:

movement according to the position of the blood culture flask, or

According to changes in ambient lighting conditions, or

According to a change in the physical light path between the sensor LED, the blood culture bottle and the photodetector, or

A change of the optical system and/or a change of the optical material in the beam path over time,

and wherein the reflectance from the sensor LED measured by the photodetector varies according to the color of the colorimetric sensor and the following information:

-said blood culture flask position, or

-a change in ambient lighting conditions, or

-a change in the physical light path between the sensor LED, the blood culture bottle and the photodetector, or

-a change of the optical system and/or a change of the optical material in the beam path over time.

2. The detection apparatus of claim 1, wherein the reference LED has an illumination peak wavelength between 750 and 900 nm.

3. A probe device according to claim 1 or 2, further comprising a computer receiving said intensity signals, said computer comprising a memory storing a calibrated relationship between said intensity signals of said reference LEDs as a function of the distance of said blood culture bottle from the original position relative to said probe device.

4. A detection device according to claim 3 wherein the memory further stores a calibrated relationship between the intensity signal of the sensor LED as a function of the distance of the blood culture bottle from the home position, and wherein the computer compensates for a drop in the intensity signal from the sensor LED due to the blood culture bottle being located a distance away from the home position based on the calibrated relationship of the sensor LED and the reference LED.

5. A method for detecting a colorimetric sensor contained in the bottom of a blood culture bottle that is subject to pH or CO due to a sample medium within the blood culture bottle₂The color change caused by the change, the method comprising the steps of:

alternately and repeatedly illuminating the colorimetric sensor with a sensor LED and a reference LED;

measuring reflectance from the bottom of the blood culture bottle and from the colorimetric sensor due to illumination of the colorimetric sensor by the sensor LED and the reference LED using a photodetector, the photodetector responsively generating an intensity signal;

wherein the reference LED and the sensor LED are positioned such that reflections from a bottom surface of the blood culture bottle are not strongly coupled into the photodetector, and wherein the reference LED is selected to have an illumination peak wavelength between 750nm and 950nm such that the intensity signal of the photodetector from illumination of the reference LED is not substantially affected by color changes of the colorimetric sensor,

wherein the reflectance from the reference LED measured by the photodetector varies according to:

movement according to the position of the blood culture flask, or

According to changes in ambient lighting conditions, or

According to a change in the physical light path between the sensor LED, the blood culture bottle and the photodetector, or

A change of the optical system and/or a change of the optical material in the beam path over time,

and wherein the reflectance from the sensor LED measured by the photodetector varies according to the color of the colorimetric sensor and the following information:

-said blood culture flask position, or

-a change in ambient lighting conditions, or

-a change in the physical light path between the sensor LED, the blood culture bottle and the photodetector, or

-a change of the optical system and/or a change of the optical material in the beam path over time.

6. The method of claim 5, wherein the reference LED has an illumination peak wavelength between 750 and 900 nm.

7. The method of claim 5, further comprising the steps of: storing in computer memory a calibration relationship between intensity signals of the reference LED as a function of distance of the blood culture bottle from a home position relative to the sensor LED, the reference LED and the photodetector.

8. The method of claim 6, further comprising the steps of: storing in computer memory a calibration relationship between intensity signals of the reference LED as a function of distance of the blood culture bottle from a home position relative to the sensor LED, the reference LED and the photodetector.

9. The method of claim 5, 6, 7 or 8, further comprising the steps of: storing in computer memory a calibration relationship between intensity signals of the sensor LED as a function of distance of the blood culture bottle from a home position relative to the sensor LED, the reference LED, and the photodetector.

10. The method of claim 9, further comprising the steps of: compensating for a drop in intensity signal from the sensor LED due to the blood culture bottle being located a distance away from the home position based on a calibrated relationship of the sensor LED and the reference LED.

11. The method of claim 10, wherein the compensating step comprises the steps of: determining a displacement value of the blood culture bottle using the calibration relationship of the reference LED and using the calibration relationship of the sensor LED to adjust the intensity signal from the photodetector in accordance with the displacement value to correct for displacement of the blood culture bottle.