IE41893B1 - Improvements in methods and means for detection of microbiological organisms and other contaminants in fluids - Google Patents

Abstract

1494831 Measuring conductivity of milk D D A FRASER 2 Feb 1975 34129/74 Heading G1N Contaminated fluid, e.g. milk from a mastitis infected animal is detected by passing the fluid from different sources e.g. teats between the electrodes of separate conductivity cells, electrically energizing the cells, comparing the outputs of all cells with each other and detecting any differences. The electrical outputs may also be compared with a reference representing a healthy animal. Conductivity cells 2 mounted in the claw 1 of a milking machine are fed from oscillator 3 with 2À5 KHz A.C. The cell outputs are all compared by circuits AB-CD and, if any difference is found, a warning lamp 12R is illuminated. A "norm" is established for a milk sample from a healthy animal by adjusting potentiometer 4. Comparator 5, which includes a signal lamp then indicates if the conductivity of the milk varies from a norm, even if the outputs of all cells are the same. The comparators AB-CD each comprise a differential amplifier and a bi-stable circuit connected to the comparator output by a variable resistor which alters the trigger level permitting compensation for differences in cell parameter.

Description

The present invention relates to improved methods of and means for early detection of undesirable microbiological': organisms and other contaminants in materials Intended, for example, for human consumption, enabling the production or processing of such materials to be controlled in. such manner as to ensure the maintenance of quality standards and, in some cases to avoid conditions arising in which production yield is adversely effected. .10 The invention has particular, though not exclusive, application to the early detection of disease infection of living creatures and will now be described, by way of example, in relation to the detection of mastitis in milk-producing animals in the sub-clinical stage enabling corrective action to be taken before the infection has any significant effect upon the quality or quantity of milk yield.

It is well known that dairy cows have a natural resistance to mastitis and if such resistance proves even . temporarily ineffective the resultant increase in infection not only results in an undesirable contamination • of the milk produced but in a progressive reduction in milk yield. It is also known that in a dairy herd grazing, under natural conditions there is always a percentage of beasts in some stage of contracting, or naturally overcoming, mastitis so that the theoretical potential yield.of quality milk cannot be fully realised in that either the yield from infected beasts is below 2.41893 normal or toe mean quality, and thus the value for commercial purposes, oi tne herd yield is reduced, or both. It is thus of considerable commercial importance to dairy farmers that mastitis should be detected in the earliest possible stage to enable corrective action to be taken to maintain both quality and quantity of milk yield.

The invention is based upon consideration of the fact that infection is, at least initially, localised and it is thus possible to detect its presence by comparison of a number of spatially separated body fluids having characteristic electrical properties when free from the infection to be detected, to provide an indication of a 't change in such electrical properties of one of such fluids in relation to another, produced by the presence of infective organisms or their by-products in such one fluid.

It has been found, in applying the invention to the detection of mastitis in cows, that infection occurs preferentially in one teat and spreads to che others.

Even when more than one of the four teats is initially infected the extent of infection is usually different as between the different teats. Since the extent of infection determines the quantity of infective organism or by-product per unit of milk passing through an infected teat and such quantity in turn proportionally affects the electrical impedance characteristics of the milk, it is possible by comparison bridge techniques of sufficient sensitivity to detect mastitis even in the sub-clinical stage. Such detection can be caused to provide an indication that the beast being milked should be given treatment to cure the inftr.tinn and/or that ita milk should be isolated from the general yield of milk from the herd. The indication may be either a simple yes/no type indication or the actual departure of impedance from normal value may be quantitatively indicated and used in ascertaining the treatment necessary to abate infection.

In order to secure maximum sensitivity to the presence of infection it has been found desirable to use in the imbalance detection circuitry a predetermined threshold level and to include in the comparison network adjustable resistors in addition to the test electrode circuits for the individual teats. This is particularly important if it is desired also to detect the presence of infection in the very rare case where all the teats are infected to much the same degree and a simple comparison might otherwise fail to indicate the presence of infection. The threshold level has to be ascertained in relation to a norm for a particular herd grazing in a particular environment and can conveniently be achieved by tests designed to give a mean cell count, of staphylococcus or streptococcus for example, for a sample of the nri lk yield of the herd. The ascertainment of such a norm is also of assistance in determining the dosage of medication required to abate infection tp a tolerable level.

Whilst of considerable commercial importance in relation to mastitis in dairy cattle the diagnostic 4. technique of the invention is clearly of much wider application and can usefully be employed wherever infection causes localised microbiological contamination of a body fluid which can be detected by a change in an electrical characteristic of the fluid and the fluid can be monitored as it flows in at least two separate channels in which contamination is unlikely to be equal due to the inherent localised nature of infection in its early stages. Thus the technique of the invention has application in the early diagnosis of disease in human beings as well as other animals, and in the early detection of contamination of fluids in the processing of such fluids or in the production of such fluids by natural or artificial production units. In this latter connection a dairy animal can be considered as a production unit and its milk production function as a manufacturing process requiring control and testing to ensure desired output quality and/or quantity in the same way as any industrial process for the production of fluids. Λ first aspect of the invention comprises a method of testing differential contamination of a fluid derived from three or more spatially separated sources said method comprising flowing fluid from each of said sources through an individual probe device to pass between a pair of electrodes having a predetermined spacing, electrically energizing said probe devices to yield electrical signals having a parameter indicative of an electrical characteristic of said fluid which varies in dependence upon the degree of contamination being tested for and applying such electrical signals to a comparsion device constructed to compare the signals from all pairs of probe devices to yield an indication of difference in said parameter between the signals applied there.to.

A second aspect of the invention comprises a method of detecting infection in a living animal having at least three spatially separated flow passages for a common body fluid susceptible to differential infection said method comprising causing the fluid flowing in each of the said passages to flow through a space between an individual pair of electrodes, electrically energizing said electrodes to yield individual electrical signals having a parameter indicative of an electrical characteristic of said fluid which varies in dependence upon the extent of contamination thereof due to the infection to be detected, and applying such electrical signals to a comparsion device constructed to compare the signals from all pairs of probe devices to yield an indication of difference in said parameter between the signals applied thereto.

A third aspect of the invention comprises a method of detecting differential infection of the teats of a milk producing animal having three or more teats during milking comprising causing the milk from each teat to'flow separately through a space between an individual pair of electrodes, electrically energizing the pairs of electrodes to yield - 6 41893 individual electrical signals indicative of the resistivity of the milk flowing from each teat and applying the signals obtained to a comparison means adapted to compare the signals from each of the electrode pairs with each other to yield an indication of difference in resistivity, of the milk from one or more teats in relation to that from any other teat thereby to indicate differential infection of the teats of the animal.

Apparatus for carrying out the invention comprises differential contamination detection apparatus comprising three or more probes each having a pair of electrodes disposed with a fluid flow channel of predetermined dimension therebetween, means for electrically energising said probes, means for comparing an electrical signal from each of said probes with that from any other of said probes and indicating means arranged to indicate when any such comparsion yields a difference signal.

Preferably such testing is effected by inserting in each of at least three channels through which the fluid flows, a test probe having spaced electrodes in such a manner that at least part of the fluid flows through the space between such electrodes, applying an electrical signal to flow through the fluid between the electrodes to produce a signal from each probe indicative of the electrical impedance of the fluid passing therethrough and applying such signals to the electrical comparison circuit to yield an out5 put signal indicative of difference in impedance and thus of greater contamination of the fluid in one channel than in the other.

The impedance of the fluid in either or both channels may also be compared with a norm either in a separate comparison circuit to which a signal indicative of a predetermined normal impedance is also applied or by incorporating in the comparison circuit used to compare the impedance signals derived from the two probes a threshold level set to such norm so that the circuit yields an out15 put signal when the impedance signal from both probes is abnormal though the two signals are not necessarily different.

In the application of the invention to the detection of mastitis at the sub-clinical stage of development in - 8 41893 dairy cattle, the probes are preferably incorporated in the teat cups or claw cavities of the milking apparatus, or in the flow channels leading from the teat cups or claw at a point before such channels merge, so that each probe monitors the milk drawn from an individual teat. It has been found by practical experimentation that satisfactory results are obtained when the probes are energised from a stabilized electrical oscillator operating at about 2,500 Hertz· It has also been found that in practically all cases of . mastitis the level of infection is different in at least two of the four teats of an animal for at least a period equal to that between successive mi1ki ngs so that comparison of the impedance of the milk drawn from each teat at each milking is an effective method of detecting the onset of mastitis. Further it has been found that this comparison technique is effective in indicating the presence of mastitis even when the general level of health of an animal is sub-normal due for example to a general infection. The constant monitoring to detect mastitis may also usefully serve to detect such general infection by comparing the individual probe signals with a reference signal corresponding to a norm representing the cell count obtained from a sample of pure milk from a healthy member of a particular herd» Since the ability of an animal to counteract mastitis without the aid of medication depends upon its general state of health the degree of departure from norm indicated by such monitoring can usefully serve to - 9 41883 indicate the probable need for medication to ensure a satisfactory milk yield. Any effects there may be of medication upon the milk produced by a treated animal will be the same for each teat so that the results of a teat-by-teat comparison method are not disturbed by such effects.

The various features and advantages of the invention will be apparent from the following description of apparatus for carrying out the invention as applied to the monitoring of milk production which apparatus is illustrated in the accompanying drawings.

Of these drawings:Figure 1 is a schematic diagram of a complete system embodying the invention, and Figure 2 is a schematic diagram of the electrical circuitry of a single comparison channel.

Eeferring to Figure 1, a conventional cluster of milking cups or a claw 1 is modified to the extent that a probe 2 consisting of two accurately spaced electrode members is incorporated in the individual milk duct leading from the individual teats of a beast being milked in such a manner that the milk flow passes continuously through the space between the electrode members when the milking apparatus is in operation. The cluster and probes for only one beast are shown but it will be apparent that these will be duplicated for each beast to be milked by the same milking apparatus at the - lo 41893 same time. An electronic oscillator 5 of conventional circuit configuration has its output connected to onfe electrode member of each probe 2 and the other electrode member of each probe is connected individually to three of six comparison units AB, AC, AB, BC, BB and CB in such manner that each of these unite receives the output signals of a different pair of the four probes. Additionally the output of oscillator 3 is applied through a norm setting potentiometer circuit 4 to a comparator 5 to which all the signals from the four probes are applied. The oscillator 3 is preferably connected in common to all the probes of all the clusters of the milking machine and the comparator 5 includes a single signal lamp IS arranged to be illuminated when the general signal level from the four probes associated with one beast exceeds the norm level set by potentiometer circuit 4. The comparison units AB to CB are each arranged to yield a zero signal output when the two signals they compare are equal and a difference signal output when the two Signals they compare are unequal and the output terminals at which the zero and difference signals appear are connected to an indicator unit 12 having a pair of differently coloured indicator lamps for each beast being milked by the milking apparatus.

Referring now to Figure 2, one of the comparison units AB to CB of Figure 1 is shown in greater detail as comprising a differential amplifier 10 to the inputs of which the output signals of two probes 2 are applied. The output of amplifier 10 ie developed across a potentiometer- 9 in the input circuit of an electronic switching device 11 which is arranged to respond to a first, lower level of input to energise a first one of ite outputs and de-energise or maintain de-energised a second one of its outputs and to respond to a second, higher, level of input to reverse the states of its 10 . first and second outputs. The first and second outputs of the switching circuits of all the comparison units AB to OD are connected iii common to respective first and second inputs of an indicator unit 12 which includes a pair of differently coloured signal lamps 12E and 12V IS arranged to he alternatively illuminated in dependence on which of the inputs of the unit 12 is energised.

In setting the equipment up for use, the potentiometer circuit 4 is adjusted to give a reference signal equal to that which would result from the passage through 2o a sample of pure milk from the herd being milked in a probe of the form used in the equipment to establish a '’norm’’ level for the herd as one input to the comparator 5. The milk ducts in the cluster are filled either with a sample of pure milk from the herd, or a liquid having the same electrical '•impedance as such a sample, and the probes are energised from oscillator 3· The comparison units AB to CD are connected in turn to the indicator unit 12 and as each unit is connected its potentiometer 9 is adjusted if the high input indicator lamp 12B ie lit until such lamp is extinguished and the low input lamp 12V is lit. This adjustment eliminates any false indication due to the electrode spacing of the two probes concerned being sufficiently different to give significantly different output signals to the differential amplifier. This adjustment facility also enables a comparison unit to be checked by applying to its inputs reference signals having a predetermined difference in level, at which level of difference it is desired that the system should operate, and adjusting the potentiometer until the switch over between the lamps 12H. and 12W just occurs.

When milking starts the indications given by the indicator lamps during the first two or three seconds can be ignored since the first flush of milk may be contaminated for a variety of reasons not connected with the presence of mastitis. After that time, however, if any beast of a group being milked has contracted infection, the milk from its various teats will exhibit a difference in electrical impedance and such difference will result in at least one of the comparison units AB to CD yielding a difference signal output from its differential amplifier and the consequent energisation of the lamp 12E corresponding to the beast on the indicator unit 12.

As previously mentioned, the comparator 5 functions to 418 9 3 compare the four probe signals with a reference signal and this comparator yields an indication by illuminating an indicator lamp when any one or more of the probe signals differs from the reference signal by a predetermined amount. The comparator 5 conveniently comprises four differential amplifiers each having the reference signal from potentiometer 4 as one input and a different one of the four probe signals as its other input, and a single switching circuit responsive to a' predetermined difference signal output from any one of the four amplifiers. By suitable selection of the level of difference to which the comparator 5 responds, or by appropriate adjustment of the level of the reference signal, the comparator 5 may be rendered insensitive to the minimum level of infant-inn to which the comparison units AB to CD are adjusted, to respond and may, for example be rendered responsive to infection above a level at which, if it is mastitis, medication is considered to be essential to avoid increase or spread of infeetion.

If in addition to , or instead of, the lamp indication, the comparator 5 is arranged to give a quantitativeindication, for example by means of a meter showing the level of difference between the probe signals and the reference signal, it may conveniently serve as a guide to the amount or nature bf medication to be administered.

Thus the comparator 5 will serve to indicate I) a general level of infection; other than mastitis in the sub-clinical stage above a norm for the herd, and II) a level of mastitis necessitating medication, -ύ 41893 whether or not differential infection of the teats is present. The indicator unit Ί2, on the other hand, cannot serve to indicate infection which is not differential as between the teats but can serve to indicate mastitis at very much lower infection levels than would produce a response in comparator 5· In addition to providing a visual indication, the comparator 5 and/or the comparison units AB to CD may be arranged to control valves in the flow passages of the milking apparatus in Such a manner as to isolate milk from a beast yielding an indication of infection from tbe general output of the milking apparatus thereby automatically ensuring maintenance of quality of such output

Claims (21)

1. I . Λ method of testing differential contamination of a fluid derived from three or more spatially separated sources, said method comprising flowing fluid from each of said sources through an individual probe device to pass between a pair of electrodes having a predetermined spacing, electrically energising said probe devices to yield electrical signals having a parameter indicative of an electrical characteristic of said fluid which varies in dependence upon the degree of contamination being tested for, and applying such electrical signals to a comparison device constructed to compare the signals from all pairs of probe devices to yield an indication of difference in said parameter between the signals applied thereto.

2. A method of detecting infection in a living animal having at least three spatially separated flow passages for a common body fluid susceptible to differential infection said method comprising causing the fluid flowing in each of said passages to flow through a space between an individual pair of electrodes, electrically energising said electrodes to yield individual electrical signals having a parameter indicative of an electrical characteristic of said fluid which varies in dependence upon the extent of contamination thereof due to the infection to be detected, and applying such electrical signals to a comparison device constructed to compare the signals from all pairs of probe devices to yield an indication of difference in said parameter between the signals applied thereto. - 16 41893

3. A method of detecting differential infection of the teats of a milk-producing animal having three or more teats during milking comprising causing the milk from each teat to flow separately through a space between an individual pair of electrodes, electrically energising the pairs of electrodes to yield individual electrical signals indicative of the resistivity of the milk flowing from each teat, and applying the signals obtained to a comparison means adapted to compare the signals from each of the electrode pairs with each other to yield an indication of difference in resistivity of the milk from one or more teats in relation to that from any other teat thereby to indicate differential infection of the teats of the animal.

4. A method as claimed in claim 1 or 2 wherein the electrical characteristic of the fluid utilized is electrical impedance. .

5. A method as claimed in any one of claims 1 to 4 including the step of comparing said electrical signals with a reference signal indicative of a norm of contamination or infection and applying any difference signal, indicating a predetermined departure from norm,to an indicator device.

6. A method as claimed in any one of claims 1 to 5 wherein the energisation of said electrodes is effected with alternating current at a frequency of 2,500 Hertz. - 17 41893

7. A method as claimed in claim 5 including the preliminary step of adjusting the comparison means utilized to compare the signals from individual electrode pairs with each other to respond to a significantly lower 5 difference than the comparison means utilized to compare such signals with said reference signal.

8. Differential contamination detection apparatus comprising 3 or more probes each having a pair of electrodes disposed with a fluid flow channel of predetermined io dimensions therebetween, means for electrically energising said probes, means for comparing an electrical signal from each of said probes with that from any other of said probes, and indicating means arranged to indicate when any such comparison yields a difference signal. 15

9. Apparatus as claimed in claim 8 including a comparator arranged to compare electrical signals from said probes with a reference signal and to yield an indication when the level of any one of said probe signals departs from the level of said reference signal by more than a 2o predetermined amount.

10. Apparatus as claimed in claim 8 or 9 including an electrical oscillator arranged to energise said probes.

11. Apparatus as claimed in claim 8, 9 or 10 wherein said means for comparing said probe signals with each other comprises a series of separate comparison means each arranged to compare a different pair of probe signals.

12. Apparatus as claimed in claim 11 wherein each 5 of said comparison means comprises a differential amplifier and a switching device responsive to a first, lower, level of output from said amplifier to yield a first output and responsive to a second, higher, level of output of said amplifier to yield a second output in place of 10 said first output. 1

13. Apparatus as claimed in claim 12 including an indicator unit arranged to respond to said first output to provide a first indication and to respond to said second output to provide a second indication different from said 15 first indication.

14. Apparatus as claimed in claim 12 or 13 wherein each said comparison means includes a potentiometer settable to determine the level of output from said amplifier at which said switching device switches from yielding said first 20 output to yielding said second output.

15. Apparatus as claimed in claim 13 wherein said indicator unit is arranged to respond to said second output of any one of said comparison units. - 19 41893

16. Apparatus as claimed in claim 10 as appendant to claim 9. Wherein the output of said oscillator is applied to a potentiometer device settable to provide a portion of said oscillator output as said reference signal to said comparator. 5

17. Apparatus as claimed in claim 9 or in any one of claims 10. To 16 as appendant to claim 9 wherein said comparator includes indicating means adapted to provide a quantitative indication of departure from norm.

18. Differential contamination apparatus as claimed in claim10 8 substantially as herein described with reference to the accompanying drawings;

19. A method of detecting differential contamination of a fluid according to claim 1 derived from spatially separated sources substantially as herein described.

11. 15 20. A method of detecting infection in a living animal according to claim 2, substantially as herein described.

21. A method of detecting differential infection of the teats of a milk producing animal according to .claim 3 substantially as herein described.