Molecular Characterization of Staphylococcus aureus Isolates from Intramammary Infection in Pre-Calved Dairy Heifers and Cows

CAMUSSONE, C.; MOLINERI, A.I.; SIGNORINI, M.L.; NEDER, V.E.; CALVINHO, L.F.

La Plata

Congreso; V Reunión Anual de la Red latinoamericana de Investigación en Mastitis; 2019

Red Latinoamericana de Investigación en Mastitis

IntroductionStaphylococcus aureus is a frequent cause of intramammary infection (IMI) in lactating cows in Argentina (Dieser et al., 2014) and has also been detected in mammary secretions of periparturient dairy heifers (Calvinho et al., 2007). Although prevalence of S. aureus IMI in the lactating herd is considered a risk factor for presence of IMI in pre-calved heifers, there is scarce information about relatedness between S. aureus populations from lactating cows and pre-calved heifers secretion. The aim of this study was to evaluate genetic relationships between S. aureus isolates from pre-calved heifers and lactating cows from two dairy herds from different regions of Argentina.Materials and MethodsFrom both herds (H) S. aureus isolated from mammary secretions of pre-calved dairy heifers obtained approximately 20 days before the expected calving date (n=14 H1 and n=5 H2), and from lactating cows (n=19 H1 and n=18 H2) were analyzed.Clonality of S. aureus isolates was assessed by PFGE of SmaI-digested chromosomal DNA fragments. Cluster similarity was set in 80%. Within a cluster, isolates with identical PFGE band patterns were considered to have indistinguishable genotypes. The presence of cap5 and cap8 loci, genes for α-toxin (hla), β-toxin (hlb), Clumping factors A (ClfA) and B (ClfB), Fibronectin Binding Proteins A (FnBPA) and B (FnBPB), and genes from the intercellular adhesion locus, IcaA and IcaD, were evaluated by PCR. Associations between origin of isolate (cow versus heifer) and cluster, and associations between origin of isolate and presence of a given virulence factor was examined. Statistical significance was tested by Chi-square or two-sided Fisher?s exact test (InfoStat software).Results and DiscussionAnalysis within herdsSimilar to previous findings (Haveri et al., 2008; Castelani et al., 2013), S. aureus isolates in each dairy herd were grouped in few main clusters. In H1, analysis showed 3 PFGE clusters: A (genotypes a1, a2, a3, a4), B, and C. Isolates of cluster A were present in higher proportion in heifers (93.3%) than cows (6.7%) (P< 0.001), while clusters B and C were only present in cows. In H2, analysis showed two clusters, D (genotypes d1, d2, d3, d4) and E (genotypes e1, e2, e3). Cluster E was only present in heifers (P= 0.011), while cluster D was present in higher proportion in cows (94.7%) than heifers (5.3%) (P= 0.001). Results agree with those of Castelani et al. (2013), who found that a S. aureus isolated from a heifer at pre-partum carried a different pulsotype than those found in lactating cows in the same herd, suggesting the existence of different sources of S. aureus infection for pre-calved heifers and lactating cows.Regarding virulence factors, all S. aureus in H1 evaluated were positive for hla, hlb, ClfA, ClfB, FnBPA, IcaA, and IcaD. All isolates in cluster A, were cap5 positive. Seven from 8 isolates in genotype B were cap8 positive; while the remaining one was cap5 positive. Eight from 10 isolates in genotype C were cap5 positive, while the two remaining isolates were cap8 positive. The sample origin was associated with the presence of FnBPB; being more frequent in isolates from cows (94.7%) than from heifers (0%) (P