Validation of a Streptococcus uberis mastitis model in late lactation
C.G.M. Scherpenzeel1, L. Heres1, E. van Engelen1 and Y.H. Schukken1
1Royal GD, Deventer, the Netherlands
WHY?
Streptococcus uberis (S. uberis) is a gram positive coccus that is known to cause mastitis in dairy cows. S. uberis can be found in the environment as well as on the skin of cows and can cause clinical and subclinical mastitis. Although S. uberis is renowned for causing mastitis shortly after calving, infections also occur in the dry period. The origin of these infections often lies in the end of the previous lactation or at the start of the dry period. Clinical mastitis caused by S. uberis can be treated with antibiotics and responds relatively well to treatment when treated immediately. However, when left untreated, chronic infections can persist and cause subclinical mastitis cases which are much harder to treat.
Aim
The aim of this study was to validate a Streptococcus uberis clinical mastitis model by evaluating whether two different promising strains of S. uberis, applied in two different ways (per teat dip and intramammary inoculation) were able to induce S. uberis mastitis in dairy cows in late lactation.
Materials
and Methods
The study consisted of one in-life study period. The study was designed as a within-cow comparison with quarter as experimental unit; all cows were healthy, with a low SCC and negative bacteriological results in a milk sample from each quarter. Per cow, three quarters were challenged, the fourth quarter was unchallenged. Two experimental groups of six cows (6 to 12 quarters per inoculation method) were included in this study. Cows were allocated to either study group A or study group B. One of both front quarters was intramammary challenged with approximately 200 cfu of S. uberis strain A (study group A) or B (study group B). The other front quarter was not challenged. In both groups, one of both hind quarters was challenged with a teat dip containing 108 cfu/ ml S. uberis strain A, the other hind quarter was challenged with a teat dip containing 108 cfu/ml S. uberis strain B. Royal GD has several well described S. uberis strains at its disposal in a bacteriobase. Nine strains of S. uberis were selected that were reported as inducing mild clinical mastitis symptoms whilst giving multiple positive S. uberis samples over time in one animal. These strains were analyzed using a IR Biotyper to determine filiation between strains. The two selected strains, were harvested from different farms and were of different clade, although they caused multiple infections in cows within these herds (no solitary cases). At SD0 (pm), SD1 (am and pm), SD2 (am and pm), SD3 (am and pm), SD4 (am and pm) and SD5 (am) the selected hind quarters for teat dip challenge were challenged with S. uberis strain A or B by
Clinical observations (incl. clinical score of cow and quarter, udder pressure, milk leakage, udder engorgement)
were infected with approximately 200 cfu of S. uberis strain A or B. Shortly, 2 mL of the prepared solution was aseptically intramammary applied using a blunt teat cannula.
Main results
The teat dip challenge with strain A persistently infected 6/12 quarters (50%), whereas teat dip challenge with strain B resulted in 9/12 persistently infected quarters (75%). In the unchallenged group (not inoculated), 5/12 quarters (41.2%) developed a persistent infection. The log transformed S. uberis counts showed that 37 out of 48 quarters had more than one milk sample with at least one log CFU S. uberis. Out of these 37 positive quarters, 8 quarters were of the
percentage of abnormal observations was higher (IMM A 14%, teat dip B 12%, IMM B 10%, teat dip A 8%) than in the nonchallenged quarters (6%).
Take home points
In conclusion both the teat dip method with S. uberis strain B (GD SUB B) and the intramammary method with S. uberis strain A (GD SUB A) were successful (i.e. 60% of the quarters) in inducing a persistent Streptococcus uberis infection in dairy cows. The teat dip challenge with strain A and B persistently infected 50%, respectively 75% of quarters. Surprisingly, in the unchallenged group (not inoculated), 41.2% of quarters also developed a persistent infection. This could be due to
c.scherpenzeel@gdanimalhealth.com www.gdanimalhealth.com
Figure 1. Timeline of measurements, challenges, sampling and observations in the study design of a Streptococcus uberis Mastitis model.