Staphylococcus (S.) aureus is considered as a major mastitis pathogen, with considerable epidemiological information on such infections while the epidemiology of coagulase-negative staphylococci (CNS) is more controversial. The aim of this study was to use matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) technology for identification of staphylococci isolated from bovine milk at species level and to characterize them in reference to presentation, somatic cell count (SCC), bacterial shedding (cfu) and antimicrobial resistance patterns. A total of 200 staphylococcal isolates (S. aureus n = 100; CNS n = 100) originating from aseptically collected quarter milk samples from different quarters of dairy cows were included in the study. They originated from cases of clinical (CM) and subclinical mastitis (SCM) or were isolated from milk with SCC ≤ 100,000 cells/mL in pure culture. We found staphylococci predominantly in cases of SCM (n = 120). In low-SCC cows, 12 S. aureus and 32 CNS isolates were detected. Eighteen percent of each were associated with CM. Eleven CNS species were identified, S. chromogenes (n = 26) and S. xylosus (n = 40) predominated. CNS, particularly those in low-SCC cows, showed higher MIC90 (minimal inhibitory concentration) values for penicillin, ampicillin, cefoperazone, pirlimycin and marbofloxacin. Based on the present results, a careful interpretation of laboratory results is recommended to avoid antimicrobial therapy of staphylococci without clinical relevance and to ensure prudent use of antimicrobials.

The present study describes an outbreak of Pseudomonas (P.) aeruginosa mastitis in a 20-cow dairy herd where throughout genotyping of isolates reusable udder towels were identified as the source of infection. Sampling of cows during three herd surveys and bacteriological culturing showed that P. aeruginosa was isolated from nine cows with a total of 13 infected quarters. Mastitis occurred as mild clinical or subclinical infection. P. aeruginosa was additionally isolated from a teat disinfectant solution, containing N-(3-aminopropyl)-N-dodécylpropane-1,3-diamine 1 as active component, and microfiber towels used for pre-milking teat preparation. Disc diffusion antimicrobial resistance testing revealed that all isolates were susceptible to piperacillin, piperacillin-tazobactam, ceftazidime, cefepime, aztreonam, imipenem, meropenem, tobramycin, amikacin, and ciprofloxacin. Thirty-two isolates of milk samples and 22 randomly selected isolates of one udder towel and of the teat disinfectant solution were confirmed as P. aeruginosa with matrix-assisted laser desorption, ionization time-of-flight mass spectrometry (MALDI Tof MS). Isolates were further characterized with rep-PCR and randomly amplified polymorphic DNA (RAPD) as well as with multiple locus variable-number tandem repeat analysis (MLVA). Results obtained in this study suggested that one single strain was responsible for the whole outbreak. The transmission occurred throughout a contaminated teat cleaning solution as a source of infection. The farmer was advised to change udder-preparing routine and to cull infected cows.

The present case report provides data on the phenotypic and genotypic properties of S. canis isolated from nine dairy cows with subclinical mastitis (SCC greater than 200,000 cells/mL in the quarter milk sample, no clinical signs) and from a cat living in the barn and reports the eradication of the pathogen from the herd with an automatic milking system. The isolates were identified using conventional bacteriology, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) and genetic relationships were investigated by multilocus sequence typing (MLST). Udder health management and hygiene instructions comprised the removal of the carnivores from the barn, strict monitoring of milking hygiene and techniques to avoid new infections via the milking robot, with simultaneous therapy for all infected cows. Phenotypic and genotypic properties of all isolates were identical. MLST revealed a unique sequence type (ST55) and a farmyard cat was identified as the most likely source of the S. canis infection in cows. The simultaneous treatment of all infected cows and management and hygiene improvements lead to a decreased SCC within four weeks.

The objective of this retrospective case-control study was to examine the relationship between E. coli-induced mastitis and acute laminitis in dairy cows. Correspondingly, the medical records of 93 cows diagnosed with E. coli mastitis between 2012 and 2023 were analysed. The cows were categorised into three groups: (1) cows with mastitis scores of 1 or 2 without signs of acute laminitis; (2) cows with a mastitis score of 3 without signs of acute laminitis; (3) cows with a mastitis score of 3 and exhibiting symptoms of acute laminitis. Out of the 93 cows with E. coli mastitis, 19 were assigned to group 1 (20.4%), 46 to group 2 (49.5%), and 28 to group 3 (30.1%). A total of 74 cows (79.6%) scored 3 for mastitis, but 28 cows (37.8%) were also diagnosed with acute laminitis. A higher mastitis score was significantly associated with a higher incidence of acute laminitis (p = 0.0004). E. coli mastitis showed a higher incidence in parity ≥ 3 (73.3% to 78.6%) and occurred in cows of all three groups mainly during the first third of lactation (53.6% to 75.6%). Cows in group 1 had a median survival time of 512 days, while for cows in groups 2 and 3, these values were 93 and 178 days, respectively. Regarding survival times, only a trend but no statistically significant difference (p = 0.221) was found among the cows in the three groups. This could possibly be explained by the fact that additional comorbidities were diagnosed in 53.6% to 65.2% of the cows from all three groups. It is concluded that cows with severe coliform mastitis have a higher risk of developing acute laminitis, and that a thorough clinical examination of the claws should always be performed to avoid overlooking acute laminitis, which accompanied the E. coli mastitis in approximately 38% of cases.