Clinical outcomes and molecular genotyping of Staphylococcus aureus isolated from milk samples of dairy primiparous Mediterranean buffaloes (Bubalus bubalis)

Abstract

Staphylococcus aureus is one of the most important pathogens causing mastitis in dairy cows and in Mediterranean buffaloes. Genotype B (GTB) is contagious in dairy cows and may occur in up to 87% of cows of a dairy herd. It was the aim of this study to evaluate genotypes present, clinical outcomes, and prevalence of Staph. aureus in milk samples of primiparous Mediterranean dairy buffaloes. Two hundred composite milk samples originating from 40 primiparous buffaloes were collected from May to June 2012, at d 10, 30, 60, 90, and 150 d in milk (DIM) to perform somatic cell counts and bacteriological cultures. Daily milk yields were recorded. Before parturition until 40 to 50 DIM, all primiparous animals were housed separated from the pluriparous animals. Milking was performed in the same milking parlor, but the primiparous animals were milked first. After 50 DIM, the primiparous were mixed with the pluriparous animals, including the milking procedure. Individual quarter samples were collected from each animal, and aliquots of 1 mL were mixed and used for molecular identification and genotyping of Staph. aureus. The identification of Staph. aureus was performed verifying the presence of nuc gene by nuc gene PCR. All the nuc-positive isolates were subjected to genotype analysis by means of PCR amplification of the 16S-23S rRNA intergenic spacer region and analyzed by a miniaturized electrophoresis system. Of all 200 composite samples, 41 (20.5%) were positive for Staph. aureus, and no genotype other than GTB was identified. The prevalence of samples positive for Staph. aureus was 0% at 10 DIM and increased to a maximum of 22/40 (55%) at 90 DIM. During the period of interest, 14 buffaloes tested positive for Staph. aureus once, 6 were positive twice, and 5 were positive 3 times, whereas 15 animals were negative at every sampling. At 90 and 150 DIM, 7 (17.5%) and 3 buffaloes (7.5%), respectively, showed clinical mastitis (CM), and only 1 (2.5%) showed CM at both samplings. At 60, 90, and 150 DIM, 1 buffalo was found with subclinical mastitis at each sampling. At 30, 60, 90, and 150 DIM, 2.5 (1/40), 22.5 (9/40), 35 (14/40), and 10% (4/40) were considered affected by intramammary infection, respectively. Buffaloes with CM caused by Staph. aureus had statistically significantly higher mean somatic cell count values (6.06 ± 0.29, Log 10 cells/mL ± standard deviation) and statistically significantly lower mean daily milk yields (7.15 ± 1.49, liters/animal per day) than healthy animals (4.69 ± 0.23 and 13.87 ± 2.64, respectively), buffaloes with IMI (4.82 ± 0.23 and 11.16 ± 1.80, respectively), or with subclinical mastitis (5.47 ± 0.10 and 10.33 ± 0.68, respectively). Based on our knowledge, this is the first time that Staph. aureus GTB has been identified in milk samples of dairy Mediterranean buffaloes.

Efficacy of a polyvalent mastitis vaccine against Staphylococcus aureus on a dairy Mediterranean buffalo farm: results of two clinical field trials

“…Every year the animals were chosen by means convenience sampling from 80 primiparous in good health having 4 functional quarters, teats free of significant lesions, and with an estimated calving date to allow vaccination at predicted times before calving. Samples size was calculated by using the formula proposed by Thrusfield [19] considering the following values: study population (pregnant primiparous MB in farm, ~14% of entire herd – approximately stable parameter in both years considered), expected prevalence of positive primiparous MB for S. aureus (55%) [1], confidence interval 95% and desired absolute precision (5%).…”

“…After 90 DIM, milk yield and SCC values were evaluated at 150 and 240 DIM (close to dry off). As described by a previous study [1], a great variability to achieve the supposed drying-off time (daily milk yield < 0.5 L/day) was detected in the enrolled animals (from 240 to 260 DIM), as consequence, the last sample considered useful for the statistical and economic analysis was collected at 240 DIM.…”

“…Following the classification reported in previous studies [1, 23], the animals enrolled were defined as negative for S. aureus, affected by IMI or mastitis considering: presence/absence of clinical signs, SCC values, and microbiological status; briefly, MB producing milk with SCC below the threshold of 200 × 10 3 cells/mL and associated with BMC negative to S. aureus were considered and hereafter referred to as “healthy udder”; animals with analogous SCC values and positive BMC caused by S. aureus have been instead considered affected by IMI; moreover, buffaloes producing milk with SCC upon the threshold of 200 × 10 3 and positive BMC for S. aureus have been defined as affected by mastitis, with (clinical mastitis - CM) or without clinical signs (subclinical mastitis - SCM) [1, 23]. All the MB affected by mastitis (CM and/or SCM) due to S. aureus were considered in end-point phase and excluded from the study.…”

“…Mastitis represents one of the major causes of economic loss in dairy Mediterranean buffaloes (MB) because negatively influencing milk quality and yields of the animals affected [1, 2]. In MB mastitis is mainly caused by several contagious (e.g.…”

“…This bacteria typically colonizes the injured skin; damage of the teat end and faulty milking encourages migration of bacteria into the udder causing intramammary infections (IMI) and sometimes persisting for extended periods [4, 8, 9]. Some strains are particularly resistant to antibiotics [4] and moderate results were reported in an our previous study exploring the effects of an antibiotic selective treatment [1]. As a consequence, similarly to dairy cows additional strategies of herd health management including treatment or culling of affected animals, implementation of biosecurity measures and hygienic milking practices, have been recommended to prevent and control udder health problems related to S. aureus in MB farms [2].…”