Non-aureus staphylococci and mammaliicocci isolated from bovine milk in Italian dairy farms: a retrospective investigation

Abstract

Non-aureus staphylococci and mammaliicocci (NASM) are associated with bovine mastitis and increased milk somatic cell count (SCC) but their relationships with mammary gland health at the species level are not clearly defined. Regional differences have also been reported in their specific prevalence. The implementation of MALDI-TOF MS in milk microbiology is generating large and dependable datasets with the potential of providing useful epidemiological information. We present the retrospective analysis of 17,213 milk samples sent to our laboratory in 2021–2022, including 13,146 quarter samples from cows with subclinical (SCM) or clinical mastitis (CM) from 104 farms, and 4,067 composite herd survey (HS) samples from 21 farms. NASM were isolated from 21.12% of SCM, 11.49% of CM, and 15.59% of HS milk samples. The three most frequently identified NASM in SCM milk were Staphylococcus chromogenes (33.33%), S. haemolyticus (26.07%), and S. epidermidis (10.65%); together with S. microti and S. hyicus, these species were significantly more prevalent in quarters with SCM (p < 0.05). The three most frequently identified NASM in CM milk were S. chromogenes (31.69%), S. haemolyticus (21.42%), and Mammaliicoccus sciuri (18.38%), although no significant associations were found between these NASM species and CM. The three most frequently identified NASM in HS milk were S. chromogenes (44.49%), S. epidermidis (17.84%), and S. haemolyticus (17.23%), with S. chromogenes being isolated in all the farms sending HS milk (100%). In conclusion, this retrospective study provides the first information on the NASM species isolated from cow milk in Italy, expanding our knowledge on the epidemiology of NASM at the species level and providing further insights into their relationships with mammary gland health in modern dairy farms.

An update on non-aureus staphylococci and mammaliicocci in cow milk: unveiling the presence of Staphylococcus borealis and Staphylococcus rostri by MALDI-TOF MS

“…Although not as frequently as S. chromogenes and S. haemolyticus, S. microti has also been isolated from CM, SCM, and HS milk. Our two surveys indicated percentages around 1% for CM, 4% for SCM and 1.5% for HS milk (Freu et al 2023;Addis et al 2024). A recent work reported that the identi cation by MALDI-TOF MS of NASM isolated from milk as S. microti might have been subjected to misclassi cation (Kløve et al 2023).…”

“…As in the case of S. borealis, differentiating S. rostri from S. microti and S. muscae is hampered by genetic similarity as well as by limitations in existing databases(Rosa et al 2022;Kløve et al 2023). In our previous retrospective studies, S. microti was the sixth most prevalent NASM in SCM and the ninth and tenth, respectively, in CM cases from US and Italy(Freu et al 2023;Addis et al 2024). In the present study, S. rostri accounted for 8.43% of all NASM identi ed in SCM, while S. microti was isolated only once, suggesting that previously reported S. microti might have actually been S. rostri and that the reported prevalence data for S. microti might have been overestimated.…”

“…In line with this, in two recent surveys from our research group the NASM most frequently isolated from clinical mastitis (CM) and SCM quarters were S. chromogenes and S. haemolyticus. S. haemolyticus was also frequently isolated from composite herd survey (HS) milk (Freu et al 2023;Addis et al 2024).…”

Divergent Immune Responses to Minor Bovine Mastitis-Causing Pathogens

“…Though dubbed “minor pathogens”, their true impact remains debated due to their presence in both healthy and infected quarters [ 2 ]. S. chromogenes leads the pack as the most common NASM isolates [ 3 , 4 , 5 ]. Among NASM, S. chromogenes , S. simulans , and S. xylosus all raise SCC, with S. chromogenes leading in causing persistent infections [ 6 ].…”