Milk Microbiota: What Are We Exactly Talking About?

The development of powerful sequencing techniques has allowed, albeit with some biases, the identification and inventory of complex microbial communities that inhabit different body sites or body fluids, some of which were previously considered sterile. Notably, milk is now considered to host a complex microbial community with great diversity. Milk microbiota is now well documented in various hosts. Based on the growing literature on this microbial community, we address here the question of what milk microbiota is. We summarize and compare the microbial composition of milk in humans and in ruminants and address the existence of a putative core milk microbiota. We discuss the factors that contribute to shape the milk microbiota or affect its composition, including host and environmental factors as well as methodological factors, such as the sampling and sequencing techniques, which likely introduce distortion in milk microbiota analysis. The roles that milk microbiota are likely to play in the mother and offspring physiology and health are presented together with recent data on the hypothesis of an enteromammary pathway. At last, this fascinating field raises a series of questions, which are listed and commented here and which open new research avenues

Phenotypic and genotypic characterization of Streptococcus uberis isolated from bovine subclinical mastitis in Argentinean dairy farms

The aim of this study was to investigate the phenotypic and genotypic characteristics of Streptococcus uberis isolated from subclinical mastitis (SCM) cases, and to examine the possible association between both characteristics. A total of 32 S. uberis were isolated from 772 quarter milk samples (SCM > 250,000 cells/ml) collected from 195 cows selected randomly from 18 dairy farms located in Argentina. The S. uberis strains were characterized phenotypically by the presence of virulence factors as plasminogen activator factor (PAF), hyaluronidase (HYA), capsule (CAP) and CAMP factor, and were further characterized genotypically by pulsed-field gel electrophoresis (PFGE). S. uberis strains expressed plasminogen activator factor, hyaluronidase or capsule (65.5 %, 56.3 %, 59.4 %, respectively), but only 25 % of isolates were CAMP factor positive. Thirteen different virulence profiles were identified on the basis of the combination of virulence factors. Eighteen PFGE patterns with 90% of similarity were identified among 32 S. uberis. A great diversity of virulence profiles and PFGE patterns were present among dairy farms. S. uberis strains with the same PFGE pattern showed different virulence profiles. Bovine S. uberis strains causing SCM included in the present study showed heterogeneity in regard to their phenotypic and genotypic characteristics, and the PFGE patterns are not associated with the virulence profiles.Caracterización fenotípica y genotípica de Streptococcus uberis aislados de mastitis bovina subclínica en tambos de Argentina. El objetivo de este estudio fue investigar las características fenotípicas y genotípicas de Streptococcus uberis aislados de casos de mastitis subclínica (MSC) y examinar la posible asociación entre ambas características. Un total de 32 cepas de S. uberis fueron aisladas de 772 muestras de leche de cuartos mamarios (MSC > 25 0000 células/ml) colectadas de 195 vacas seleccionadas al azar pertenecientes a 18 tambos lecheros localizados en Argentina. Las cepas de S. uberis fueron caracterizadas fenotípicamente sobre la base de la presencia de factores de virulencia tales como el factor activador del plasminógeno (FAP), la hialuronidasa (HIA), la cápsula (CAP) y el factor CAMP. Además, fueron caracterizadas genotípicamente por electroforesis de campos pulsados (PFGE). Las cepas de S. uberis expresaron el factor activador del plasminógeno, la hialuronidasa o la cápsula (65,5 %, 56,3 % y 59,4 %, respectivamente), pero solo el 25 % fueron CAMP positivas. Sobre la base de la combinación de los factores de virulencia se identificaron 13 perfiles de virulencia diferentes. Asimismo, se identificaron 18 patrones de PFGE con un 90 % de similitud entre las 32 cepas de S. uberis. Se presentó una gran diversidad de perfiles de virulencia y patrones de PFGE entre los tambos. Cepas con el mismo patrón de PFGE presentaron perfiles de virulencia diferentes. Las cepas de S. uberis causantes de MSC en bovinos incluidas en el presente estudio mostraron heterogeneidad con respecto a sus características fenotípicas y genotípicas, y los patrones de PFGE no estuvieron asociados con los perfiles de virulencia

Prevalence and antibiotic susceptibility of coagulase-negative Staphylococcus species from bovine subclinical mastitis in dairy herds in the central region of Argentina

AbstractCoagulase-negative staphylococci (CNS) are a common cause of bovine subclinical mastitis (SCM). The prevalence of CNS species causing SCM identified by genotyping varies among countries. Overall, the antimicrobial resistance in this group of organisms is increasing worldwide; however, little information exists about a CNS species resistant to antibiotics. The aim of the present study was to genotypically characterize CNS at species level and to determine the prevalence and antibiotic resistance profiles of CNS species isolated from bovine SCM in 51 dairy herds located in the central region of the province of Cordoba, Argentina. In this study, we identified 219 CNS isolates at species level by PCR-restriction fragment length polymorphism of the groEL gene. Staphylococcus chromogenes (46.6%) and Staphylococcus haemolyticus (32%) were the most prevalent species. A minimum of three different CNS species were present in 41.2% of the herds. S. chromogenes was isolated from most of the herds (86.3%), whereas S. haemolyticus was isolated from 66.7% of them. The broth microdilution method was used to test in vitro antimicrobial susceptibility. Resistance to a single compound or two related compounds was expressed in 43.8% of the isolates. S. chromogenes and S. haemolyticus showed a very high proportion of isolates resistant to penicillin. Resistance to two or more non-related antimicrobials was found in 30.6% of all CNS. S. haemolyticus exhibited a higher frequency of resistance to two or more non-related antimicrobials than S. chromogenes