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Published on: November 4, 2016
Non-S. aureus staphylococci (NAS) in milk samples: Infection or contamination?
Johannes Hamel1, Yanchao Zhang1, Nicole Wente1
1University of Applied Sciences and Arts Hannover, Faculty II, Department of Bioprocess Engineering - Microbiology, Hannover, Germany.
Abstract:
Non-S. aureus staphylococci (NAS) are the most frequently isolated pathogens from bovine milk and can cause intramammary infections (IMI). They can also be found in teat canals, on bovine skin and in cows' environment, which may lead to unnoticed contamination of milk samples. The aim of this study was to investigate the role of NAS species as mastitis-causing pathogens or contaminants, and to identify possible differences between NAS species. A longitudinal study was conducted with consecutive milk sampling in five German dairy herds. Species identification was performed using matrix-assisted laser desorption ionization-time of flight mass spectrometry. Infections were distinguished from contaminations using two different definitions based on the repeated detection of an NAS species. Of 15 NAS species found, eight and ten, respectively, were associated with an IMI. Staphylococcus simulans and S. chromogenes were associated with IMI in more than 90 % of the findings. S. warneri, S. xylosus, S. microti, S. haemolyticus, and S. succinus seem to be frequent causes of IMI as well as contaminants. If a species-differentiation is available after cultivating NAS, the findings should be interpreted in consideration of the observations made in this study, whether it is more likely a question of a contaminant or a cause of intramammary infection. The bacteria shedding intensity of the NAS species with a more substantially adverse effect on udder health seems to be higher than that of the less important NAS pathogens.
Insights
Non-S. aureus staphylococci (NAS) frequently cause intramammary infections (IMI) in dairy cows. This study differentiates NAS species causing IMI from contaminants, aiding accurate diagnosis and treatment strategies for bovine mastitis.
Area of Science:
- Veterinary Microbiology
- Bovine Health
- Dairy Science
Background:
- Non-S. aureus staphylococci (NAS) are common in bovine milk, potentially causing intramammary infections (IMI) or contaminating samples.
- Distinguishing NAS as pathogens or contaminants is crucial for effective mastitis management in dairy herds.
Purpose of the Study:
- To investigate the role of various Non-S. aureus staphylococci (NAS) species in causing bovine intramammary infections (IMI) versus acting as sample contaminants.
- To identify potential differences in pathogenicity and shedding intensity among NAS species.
Main Methods:
- A longitudinal study involving consecutive milk sampling from five German dairy herds.
- Species identification of Non-S. aureus staphylococci (NAS) using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS).
- Application of two distinct definitions based on repeated NAS detection to differentiate infections from contaminations.
Main Results:
- Eight and ten NAS species were associated with intramammary infections (IMI), respectively, based on the applied definitions.
- Staphylococcus simulans and S. chromogenes were linked to IMI in over 90% of findings.
- Several NAS species, including S. warneri, S. xylosus, S. microti, S. haemolyticus, and S. succinus, were identified as both IMI causes and contaminants.
Conclusions:
- Species-specific identification of Non-S. aureus staphylococci (NAS) is vital for accurate interpretation of intramammary infection (IMI) findings in dairy cattle.
- Higher bacterial shedding intensity may correlate with NAS species having a more adverse impact on udder health.
- Understanding the pathogenic potential of different NAS species improves diagnosis and management of bovine mastitis.
