Genotypic and phenotypic detection of capsular polysaccharides in Staphylococcus aureus isolated from bovine intramammary infections in Argentina

Staphylococcus aureus (n=157) isolated from intramammary infections in Argentine dairy areas were evaluated for presence of cap5 and cap8 loci. Isolates carrying cap5 and cap8 were serotyped using specific antisera. Sixty four percent of the isolates were genotyped as cap5 or cap8 and 50% of them expressed CP5 or 8.

Antimicrobial susceptibility of Staphylococcus aureus causing bovine mastitis in Argentine dairy herds / Sensibilidad a los antimicrobianos de Staphylococcus aureus causantes de mastitis bovina en rodeos lecheros de Argentina

We assessed the in vitro activity of selected antimicrobial agents against 95 Staphylococcus aureus strains causing both clinical and subclinical bovine mastitis belonging to 61 dairy farms from the Central dairy area of Argentina. Minimal inhibitory concentrations (MICs) of penicillin, oxacillin, gentamicin, erythromycin, enrofloxacin and florfenicol were estimated. In addition, the agar diffusion test was performed. MIC50 and MIC90 were as follows: penicillin, 0.05 and 4 µg/ml; oxacillin, 0.25 and 0.25 µg/ml; gentamicin, 0.25 and 0.5 µg/ml; erythromycin 0.125 and 0.25 µg/ml; enrofloxacin 0.25 and 0.5 µg/ml, and florfenicol 4 and 8 µg/ml. b-lactamase activity was detected in 89% of 46 penicillin- resistant strains. Apart from penicillin, antimicrobial resistance in S. aureus causing bovine mastitis remains rare in Argentine dairy farms.

Se evaluó la actividad in vitro de un grupo seleccionado de antimicrobianos contra 95 aislamientos de Staphylococcus aureus obtenidos de casos de mastitis bovina clínica y subclínica, en 61 rodeos lecheros de la cuenca central de Argentina. Fueron estimadas las concentraciones inhibitorias mínimas (CIM) de penicilina, oxacilina, gentamicina, eritromicina, enrofloxacina y florfenicol. Además se realizó la prueba de difusión en agar. Las CIM50 y CIM90 obtenidas fueron: penicilina 0,05 y 4 µg/ml; oxacilina 0,25 y 0,25 µg/ml; gentamicina 0,25 y 0,5 µg/ml; eritromicina 0,125 y 0,25 µg/ml; enrofloxacina 0,25 y 0,5 µg/ml y florfenicol 4 y 8 µg/ml. Se detectó actividad de b-lactamasa en el 89% de las cepas resistentes a la penicilina. A excepción de lo observado para penicilina, la resistencia a los antimicrobianos en S. aureus causantes de mastitis bovina en Argentina parece ser un fenómeno poco frecuente.

Intramammary infections during the periparturient period in Argentine dairy heifers / Infecciones intramamarias durante el periparto en vaquillonas en Argentina

Prevalence of intramammary infections at prepartum and postpartum in primigravid heifers from five dairy herds located in the central dairy area of Argentina was determined. Mammary secretion samples from 140 heifers (560 mammary quarters) were obtained 14 days prior to the expected calving day and within 7 days after parturition and subjected to bacteriological analysis. No clinical mastitis cases were detected during the study. The number of infected heifers in at least one mammary quarter at pre and postpartum was 87 (62.2%) and 53 (37.8%), respectively. The most prevalent mastitis pathogens at prepartum among samples yielding a positive bacteriological culture were coagulasenegative staphylococci (69.07%), Staphylococcus aureus (12.71%) and Streptococcus uberis (4.42%). A decrease on isolation frequency of coagulase-negative staphylococci (53.41%) and S. uberis (2.27%) was observed at postpartum, while that of S. aureus showed an increase (21.59%). Presence of intramammary infections appeared to be associated with some management conditions. These results highlighted the need to improve diagnosis and control measures in replacement heifers.

Se determinó la prevalencia al preparto y posparto de infecciones intramamarias causadas por organismos patógenos de mastitis en vaquillonas primíparas de cinco establecimientos lecheros ubicados en la cuenca central santafesina. Se tomaron muestras de secreción mamaria de 140 vaquillonas (560 cuartos mamarios) aproximadamente 14 días antes de la fecha probable de parto y dentro de los 7 días posparto, y se procesaron bacteriológicamente. No se detectaron casos de mastitis clínicas durante el estudio. El número de vaquillonas infectadas en al menos un cuarto mamario al preparto y posparto fue de 87 (62,2%) y 53 (37,8%), respectivamente. Los organismos patógenos más prevalentes al preparto entre las muestras con cultivo bacteriológico positivo fueron estafilococos coagulasa negativos (69,07%), Staphylococcus aureus (12,7%) y Streptococcus uberis (4,42%). Al posparto se observó un descenso en la frecuencia de aislamiento de estafilococos coagulasa negativos (53,41%) y S. uberis (2,27%), mientras que la de S. aureus mostró un aumento (21,59%). La presencia de infecciones intramamarias pareció estar asociada con algunas prácticas de manejo. Estos resultados ponen de manifiesto la importancia de hacer extensivo el diagnóstico y control de la enfermedad a las vaquillonas de reemplazo antes de su ingreso al rodeo en ordeño.

Susceptibilidad a antimicrobianos de cepas de estafilococos coagulasa positivos aisladas de mastitis bovina en la cuenca lechera central de la Argentina / Antimicrobial sensitivity of coagulase-positive staphylococcal strains isolated from bovine mastitis in the central dairy catchment area of Argentina

The activity of antimicrobial agents frequently used for treating bovine mastitis was determined against 101 coagulase-positive staphylococci isolated from bovine mammary secretion. The isolates were obtained from 39 dairy farms located in the central dairy area of Argentina. The disk diffusion method was used and the following antimicrobial agents were tested: penicillin, ampicillin, oxacillin, cephacetrile, penicillin + novobiocin, erythromycin, pirlimycin, novobiocin and neomycin. The highest levels of resistance were observed against penicillin and ampicillin (47.6), while the lowest against erythromycin (2), pirlimycin (4) and neomycin (2.9). No resistant strains against oxacillin, cephacetrile and penicillin + novobiocin were detected.

Influence of bacterial factors on proliferation of bovine mammary epithelial cells

Effects of bovine mastitis pathogen virulence factors on mammary epithelial cell function are not clearly understood. In this study, the effect of streptococcal lipoteichoic acid (LTA), streptokinase, and Escherichia coli lipopolysaccharide (LPS) on proliferation of a primary bovine mammary epithelial cell culture (BTE) and on an established bovine mammary epithelial cell line (MAC-T) was evaluated. Mammary epithelial cells were cultured in the presence of bacterial virulence factors for 48 h at 37 degrees C. BTE cell proliferation was inhibited by streptococcal LTA at 8 and 16 micrograms/ml whereas MAC-T cell proliferation was reduced significantly by concentrations of LTA > or = 2 micrograms/ml. Streptokinase had no effect on proliferation of either MAC-T or BTE cells and LPS inhibited proliferation of BTE but not of MAC-T cells. Effect of LTA and LPS on mammary epithelial cell proliferation could be relevant during the periparturient period when mammary glands are markedly susceptible to new intramammary infection and when mammary epithelial cells undergo extensive proliferation, differentiation and synthesis of milk components.