Staphylococcus aureus and methicillin-resistant staphylococci and mammaliicocci in the bulk tank milk of dairy cows from a livestock-dense area in northern Italy

• Published in: Research in veterinary science 2025-01, Vol.182, p.105482, Article 105482
• Main Authors: Fusar Poli, Sara, Locatelli, Clara, Monistero, Valentina, Freu, Gustavo, Cremonesi, Paola, Castiglioni, Bianca, Lecchi, Cristina, Longheu, Carla Maria, Tola, Sebastiana, Guaraglia, Alessandro, Allievi, Carolina, Villa, Luca, Manfredi, Maria Teresa, Addis, Maria Filippa
• Format: Article
• Language: English
• Subjects: Animals; Anti-Bacterial Agents - pharmacology; Antimicrobial resistance; Cattle; Dairy herds; Dairying; Female; Italy - epidemiology; Mastitis, Bovine - epidemiology; Mastitis, Bovine - microbiology; Methicillin-Resistant Staphylococcus aureus - drug effects; Methicillin-Resistant Staphylococcus aureus - genetics; Methicillin-Resistant Staphylococcus aureus - isolation & purification; Milk - microbiology; Multidrug resistance; One health; Staphylococcal Infections - epidemiology; Staphylococcal Infections - microbiology; Staphylococcal Infections - veterinary; Staphylococci and mammaliicocci; Staphylococcus - drug effects; Staphylococcus - genetics; Staphylococcus - isolation & purification; Staphylococcus aureus - drug effects; Staphylococcus aureus - genetics; Staphylococcus aureus - isolation & purification
• ISSN: 0034-5288; 1532-2661; 1532-2661
• DOI: 10.1016/j.rvsc.2024.105482

Staphylococcus aureus is the main etiologic agent of contagious dairy cow mastitis, while non-aureus staphylococci and mammaliicocci (NASM) are the bacteria most frequently isolated from milk. Beyond their impact on animal health, NASM can harbor antimicrobial resistance (AMR) genes with potential for bidirectional transfer with S. aureus, and methicillin-resistant (MR) staphylococci (MRS) can raise significant One Health concerns. In our study, we evaluated the prevalence and characteristics of MRS in the bulk tank milk (BTM) of 88 dairy farms in the livestock-dense province of Lodi, Lombardy, northern Italy. S. aureus was isolated from 32.95 % of BTM samples, with the Ribosomal Spacer PCR (RS-PCR) genotype B being the most prevalent, identified in 37.93 % of S. aureus positive farms. All isolates carried the ica genes (icaA, icaB, icaC, icaD) indicating the potential to produce biofilm. MRS were isolated in 56.81 % of farms. According to MALDI-TOF MS analysis, the most prevalent MR species included S. epidermidis (MRSE, 35.59 %) followed by S. aureus (MRSA, 18.64 %), M. sciuri (15.25 %), S. saprophyticus (11.86 %), S. borealis (6.78 %), S. haemolyticus (5.08 %), M. fleurettii, (3.39 %), S. cohnii, and S. pettenkoferi (1.70 % each). Most MR isolates carried the mecA gene, while none carried mecC. The staphylococcal cassette chromosome mec (SCCmec) was predominantly type V in MRSA (45.45 %) and type IV in MRSE (61.90 %). Given their relevance to One Health, monitoring AMR in all staphylococci and mammaliicocci isolated from milk is essential for understanding the prevalence, characteristics, and transmission dynamics of MR gene pools within dairy herds. [Display omitted] •Staphylococci are the bacteria most frequently isolated from the milk.•Staphylococci can show methicillin resistance, making them a relevant One Health issue.•S. aureus was present in about one-third of the dairy farms.•Over half of the dairy farms harbored methicillin-resistant (MR) staphylococci.•S. epidermidis (MRSE) and S. aureus (MRSA) were the most prevalent MR species.