Abstract
Although extensive research has been performed on bovine non-aureus staphylococci (NAS), several aspects such as bacteria-host interaction remain largely unstudied. Moreover, only a few mastitis pathogen challenge studies in cows have been conducted in the dry period, an important period that allows intramammary infection (IMI) to cure and new IMI to occur. We challenged 16 quarters of 4 Holstein Friesian cows at dry off with 100; 100 000 or 10 000 000 CFU of the udder-adapted S. chromogenes IM strain. Four quarters from one cow served as negative controls. Internally sealed quarters remained untouched, whereas non-sealed quarters were sampled 3 times during the dry period. After parturition, colostrum and daily milk samples were taken during the first week of lactation of all quarters. In total, 8 quarters appeared to be colonized, since S. chromogenes IM was recovered at least once during the experiment, as substantiated using Multilocus Sequence Typing. S. chromogenes IM shedding was highest in dry quarters inoculated with 10 000 000 CFU. Colonized quarters had the highest quarter somatic cell count (qSCC) in early lactation. Inoculated quarters (both colonized and non-colonized) had lower IL-6 and IL-10 concentrations in the dry period, whilst IFN-γ levels tended to be higher in colonized quarters compared to non-inoculated quarters. Also, IgG2 levels were higher in inoculated compared to non-inoculated quarters and the IgG2/IgG1 ratio was on average above 1. To conclude, we showed that dry quarters can be colonized with S. chromogenes IM, resulting in a shift towards a Th1 response in late gestation and early lactation characterised by an increased IgG2 concentration. However, further research is needed to confirm our findings.
Highlights
Non-aureus staphylococci (NAS) are the most frequently isolated bacteria from bovine mammary quarters either with or without subclinical mastitis [1,2,3,4,5] and have beenBeuckelaere et al Vet Res (2021) 52:137 typically cause a moderate increase in milk somatic cell count (SCC) [14] yet do not negatively impact milk yield [15,16,17], and can inhibit major mastitis pathogen growth in vitro [18]
The bacteria mainly belonged to the Corynebacterium spp. (9 quarters) in addition to non- Streptococcus uberis aesculin-positive cocci (EPC) (3 quarters), S. epidermidis (2 quarters), S. haemolyti‐ cus (1 quarter), S. hominis (1 quarter) and Bacillus spp. (1 quarter)
The aim of this study was to investigate our hypothesis i.e. that dry quarters from late gestation dairy cows can be colonized with the udder-adapted S. chromogenes IM strain
Summary
Non-aureus staphylococci (NAS) are the most frequently isolated bacteria from bovine mammary quarters either with or without subclinical mastitis [1,2,3,4,5] and have beenBeuckelaere et al Vet Res (2021) 52:137 typically cause a moderate increase in milk somatic cell count (SCC) [14] yet do not negatively impact milk yield [15,16,17], and can inhibit major mastitis pathogen growth in vitro [18]. Quarters from lactating heifers and cows have been challenged with S. chromogenes [12, 21], S. epidermidis or S. simulans [22] to investigate the host pro-inflammatory immune response and the effect on udder health [12, 21, 22], yet no experimental NAS challenge studies have been conducted in dry cows far. The dry period is very important for dairy cows as intramammary infections (IMI) present at the moment of dry off can cure yet non-lactating mammary quarters can become newly infected with potential negative effects for the start of the lactation [23, 24]. Immunization of quarters could lead to a modification of this maternal suppression of the proinflammatory Th1-response [26]
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