Staphylococcus aureus is one of the main etiologic agents of contagious mastitis and it is able to cause significant economic losses in terms of reduced milk production and costs related to health interventions. Objective of this study was to characterize S. aureus strains isolated from high somatic cell counts herds in Piedmont region. Bulk tank milk samples were collected in 1,600 dairy herds (2 samples/month per 3 months) and the mobile geometric mean was evaluated in order to identify herds with higher somatic cells counts (SCC). During winter and spring periods two bulk tank milk samples were collected from a total of 79 selected herds with a SCC over 370,000/mL. Coagulase-positive staphylococci (CPS) were enumerated. Up to 3 strains were isolated from each sample, preferring those with different morphologycal characteristics. The microorganisms were then identified by mass spectrometry (MALDI-TOF). S. aureus strains were genotyped by RS-PCR, a method based on the amplification of the intergenic spacer 16S-23S rRNA and evaluated for the presence of Staphylococcal Enterotoxins genes. The majority of the samples (52.9%) had a concentration of CPS below the detection limit (<10 ufc/mL), while 33.1% showed CPS counts between 10 and 1,000 cfu/mL. Only in 2.9% of samples, the CPS couts was higher than 5,000 cfu/mL. A total of 181 S. aureus strains was isolated and molecular characterized. In this study, from the RS-PCR genotyping, 21 different genotypes were identified. The most prevalent was the GTB (No. 59), followed by its GTBI variant (No. 20) and by the GTBI (No. 14). Considering the different genotypes, including their own variants, the genotype B was identified in 50.3% of the isolated strains: 32.6% of the isolates was GTB, followed by the variants GTBI (11.0%), GTBII (3.3%) and GTBIII (3.3%). The 11.7% of the strains were found to be GTR, consisting of its variants GTRI (3.3%), GTRVI (3.3%), GTR (2.8%), GTRIX (1.7%) and GTRIV (0.6%). Considering both samplings carried out during the two seasons in the individual farms, it was not possible to isolate S. aureus strains in 46.8% of the farms involved in this study, although they had a high level of somatic cells in the reference period. In the 25.3% of the herds, a total of 6 S. aureus strains was isolated during the two samplings, while only 3 strains in the 18.9% of the farms. Only one genotype was detected in 52.4% of the herds, while in the 33.3% herds two different genotypes were isolated. In the remaining farms (14.7%), a greater number of genotypes was detected. Many strains harbored SEs genes, while 44% resulted non-enterotoxigenic. Sed-ser-sej profile was found in 21% of strains, followed by a combination of seg-sei (7%) and sea-sed-ser-sej (6%). GTB strains harbored sed-ser-sej (40%), sea-sed-ser-sej (10%), while the remainig (40%) resulted negative. This study highlighted that over 50% of the isolates was GTB, showing that this genotype is highly present in Piedmotese herds. However, it should be underlined that herds involved had high SCC (characteristic of the GTB). Study was funded by Regione Piemonte - Settore Agricoltura grant code 17P01 (Project title: Migliorlatte -Attività di ricerca ed innovazione nell'ambito del monitoraggio della qualità del latte bovino piemontese).
CHARACTERIZATION OF STAPHYLOCOCCUS AUREUS ISOLATED FROM HIGH SOMATIC CELL COUNT HERDS IN PIEDMONT
Paola Cremonesi;
2018
Abstract
Staphylococcus aureus is one of the main etiologic agents of contagious mastitis and it is able to cause significant economic losses in terms of reduced milk production and costs related to health interventions. Objective of this study was to characterize S. aureus strains isolated from high somatic cell counts herds in Piedmont region. Bulk tank milk samples were collected in 1,600 dairy herds (2 samples/month per 3 months) and the mobile geometric mean was evaluated in order to identify herds with higher somatic cells counts (SCC). During winter and spring periods two bulk tank milk samples were collected from a total of 79 selected herds with a SCC over 370,000/mL. Coagulase-positive staphylococci (CPS) were enumerated. Up to 3 strains were isolated from each sample, preferring those with different morphologycal characteristics. The microorganisms were then identified by mass spectrometry (MALDI-TOF). S. aureus strains were genotyped by RS-PCR, a method based on the amplification of the intergenic spacer 16S-23S rRNA and evaluated for the presence of Staphylococcal Enterotoxins genes. The majority of the samples (52.9%) had a concentration of CPS below the detection limit (<10 ufc/mL), while 33.1% showed CPS counts between 10 and 1,000 cfu/mL. Only in 2.9% of samples, the CPS couts was higher than 5,000 cfu/mL. A total of 181 S. aureus strains was isolated and molecular characterized. In this study, from the RS-PCR genotyping, 21 different genotypes were identified. The most prevalent was the GTB (No. 59), followed by its GTBI variant (No. 20) and by the GTBI (No. 14). Considering the different genotypes, including their own variants, the genotype B was identified in 50.3% of the isolated strains: 32.6% of the isolates was GTB, followed by the variants GTBI (11.0%), GTBII (3.3%) and GTBIII (3.3%). The 11.7% of the strains were found to be GTR, consisting of its variants GTRI (3.3%), GTRVI (3.3%), GTR (2.8%), GTRIX (1.7%) and GTRIV (0.6%). Considering both samplings carried out during the two seasons in the individual farms, it was not possible to isolate S. aureus strains in 46.8% of the farms involved in this study, although they had a high level of somatic cells in the reference period. In the 25.3% of the herds, a total of 6 S. aureus strains was isolated during the two samplings, while only 3 strains in the 18.9% of the farms. Only one genotype was detected in 52.4% of the herds, while in the 33.3% herds two different genotypes were isolated. In the remaining farms (14.7%), a greater number of genotypes was detected. Many strains harbored SEs genes, while 44% resulted non-enterotoxigenic. Sed-ser-sej profile was found in 21% of strains, followed by a combination of seg-sei (7%) and sea-sed-ser-sej (6%). GTB strains harbored sed-ser-sej (40%), sea-sed-ser-sej (10%), while the remainig (40%) resulted negative. This study highlighted that over 50% of the isolates was GTB, showing that this genotype is highly present in Piedmotese herds. However, it should be underlined that herds involved had high SCC (characteristic of the GTB). Study was funded by Regione Piemonte - Settore Agricoltura grant code 17P01 (Project title: Migliorlatte -Attività di ricerca ed innovazione nell'ambito del monitoraggio della qualità del latte bovino piemontese).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
