Subclinical mastitis in sheep and goats is a silent problem. There are no visible signs, but it can affect up to 40% of the animals in the herd or flock. As it causes no obvious symptoms, it is not usually treated. However, a very important question arises: is there a link between subclinical mastitis and antibiotic resistance?
Antibiotic resistance is a great concern, as it makes infections more difficult to control. It is very important to know what bacteria are present on farms and which antibiotics they may be resistant to.
Staphylococci are the main cause of mastitis in sheep and goats. It is known that they can develop resistance, but are there differences between species? Is the risk of developing resistance the same in clinical and subclinical cases?
Some studies have confirmed that 45% of Staphylococcus strains may be resistant to antibiotics.
Illuminating study
A study was recently published which reports on the incidence of antibiotic-resistant Staphylococci in subclinical mastitis samples from sheep.
It was carried out on 12 dairy sheep farms in Greece, where a previous study had placed the incidence of subclinical mastitis at 52%.
What did the study reveal?
It studied 179 samples of subclinical mastitis, and the results were clear:
– 32% of the samples showed resistance to some antibiotic.
– Resistance to 11 different antibiotics was detected; in particular ampicillin, tetracycline, and penicillin, which are commonly used in the field.
– The risk of isolating Staphylococcus resistant to at least one antibiotic was 23.8%.
There was resistance in 1/3 of the samples taken during the study period.
One striking finding was that CNS (coagulase-negative Staphylococcus) showed more resistance than S. aureus. CNS were also resistant to more types of antibiotics, and all cases of multi-drug resistance corresponded to this group.
This is significant, because CNS often cause subclinical mastitis and are not usually treated. The above finding may be explained by the fact that animals receive antibiotics for other diseases, which could make them more susceptible to developing resistance.
More resistance was detected in CNS samples than with S. aureus. Moreover, most were resistant to multiple antibiotics.
Conclusions
The researchers point out a correlation:
The higher the risk of subclinical mastitis, the greater the likelihood of finding resistant Staphylococci.
These results underline the importance of rational use of antibiotics. The use of these drugs at incorrect doses or under incorrect protocols is known to be one cause of the emergence of resistant bacteria.
Mastitis prevention through management and vaccination can contribute significantly to reducing treatments.
Article written by:
Tania Perálvarez Puerta. Global Product Manager, Small Ruminants Franchise – HIPRA
References:
Charalambia K. Michael, et al. (2023) Longitudinal Study of Antibiotic Resistance of Staphylococci from Cases of Subclinical Mastitis in Sheep in Greece: Incidence and Risk Factors. Antibiotics 2023, 12, 1703. (https://pubmed.ncbi.nlm.nih.gov/38136737/).
