FAQ

Fresh, preserved or frozen samples can be used. Clotted samples (due to extended storage at ambient temperature) may be used but clots should be removed before samples are diluted, as clots may cause pipetting errors.  Over time, sample exposure to proteolytic conditions will degrade the antibodies, and therefore samples should be frozen for long-term storage.

Yes, dilutions can be stored frozen. Make sure to thoroughly mix the sample by repeated pipetting before re-testing. A slight decline in antibodies may be occasionally observed.

The test has not yet been evaluated for goat and sheep milk samples, so at this stage, the use for goat and sheep milk samples is not recommended. There is, however, early indications that the test will work on milk from these other species.

A system that enables sanitation of cups after each cow is milked can be used instead of a milking order.  Establishing a ‘smart’ milking order or a ‘smart’ sanitation cycle where extra cleaning actions are put in place after milking of S. aureus-positive cows might also be possible.

There are typically two sources of sample carryover (from one cow to the next) in a routine milk recording or herd testing operation:

1. Milk meter carryover on-farm
2. Sample needle carryover at the milk testing laboratory

Both carryover sources present the possibility of pathogens in the first sample being transferred (or ‘carried over’) into the sample of the next animal. For direct pathogen detection methods such as microbial culture or PCR (where specific bacterial DNA are amplified and detected), this presents an opportunity for false-positive results.

The StaphGold™ ELISA test procedure involves a ten-fold dilution step during sample preparation. Should milk from a cow with high antibody levels be carried over, the subsequent sample will first be greatly diluted (approximately 100-fold) by the next milk sample, then diluted ten-fold during test sample preparation. Any remaining antibodies will therefore come in well under the limit of detection and thus generate a ‘Negative’ ELISA result for S. aureus. If the second animal has a somatic cell count below 250,000/mL, it would not be a candidate for StaphGold™ ELISA testing, in any case.

NB: Standard practice in a lab is to change pipette tips between samples.

Yes, very likely, although Koru has not looked specifically at antibody responses to certain genotypes. But we know that we can detect the antibody response to different S. aureus phenotypes that occur around New Zealand. 

For example, the StaphGold™ ELISA detects antibodies to typical coagulase-positive, haemolytic S. aureus strains, but it also detects antibodies to coagulase-positive or coagulase-negative non-haemolytic S. aureus strains. 

As we can detect antibodies to a range of different phenotypes, we believe that it is likely that we can detect antibodies to different S. aureus genotypes as well.

This depends on the stage of the lactation when the cure occurs. If the infection cures during the dry period, specific antibodies will not be detected, or detection will be below the test cut-off during the next lactation, except for the very early stage of the lactation.  Similarly, if the infection clears during the lactation and inflammation has subsided (as measured by SCC returning to normal levels), S. aureus-specific antibodies are not normally detected during the next herd test in four weeks.

Suspect positive cases should be retested during the next herd test.  If the re-test is negative, the animal can be considered negative. Conversely, a positive result indicates an infected animal.
In the meantime, suspect positive cows should be milked after the negative cows but before the confirmed ELISA-positive cows, to reduce the spread of infection.

Yes, because in many cases, an infection with S. aureus is already chronic, or is in the process of becoming chronic. In these animals, antibodies can be detected in milk, even though the elevation of the SCC was determined weeks earlier.  In the case that the infection has cured in the meantime and SCC have returned to normal, the test will return a negative result in any case.