Phenotyping and genotyping of streptococci in bovine milk in Argentinean dairy herds

Screening of bacteriocin associated genes of Streptococcus uberis strains

A wide variety of contagious and environmental bacteria can cause bovine mastitis worldwide. Antibiotic therapy is currently used for the treatment of the disease, although its intensive use leads to the emergence of resistant strains. Bacteriocins arise as potential antibacterial option for mastitis treatment. The aim of this work was to analyze bacteriocin associated genes as Streptococcus uberis ubericin A (ubaA), ubericin A immunity protein (ubaI), uberolysin A (ublA), Lantibiotic nisin-U (nsuA and nsuB) in 68 S uberis strains. Furthermore, the ability of the strains to inhibit important mastitis pathogens was assayed. Results showed that genes were present in combination and all the strains carried at least one gene. Seven bacteriocion associated gene patterns were identified. S. uberis strains were able to inhibit different mastitis pathogens and the greatest inhibition was observed in CNS strains. The results obtained provide new insights on antibacterial activity produced by S. uberis strains against different mastitis pathogens and could contribute to the development of strategies to treat intramammary infections.

Evaluation of environmental and nutritional factors and sua gene on in vitro biofilm formation of Streptococcus uberis isolates

The pathogenesis of Streptococcus uberis is attributed to a combination of extracellular factors and properties such as adherence and biofilm formation. The aim of this work was to evaluate the influence of different factors, additives and bovine milk compounds on S. uberis biofilm formation, as the presence of the sua gene by PCR. Additionally, extracellular DNA and the effect of DNaseI were evaluated in the biofilms yielded. Optimal biofilm development was observed when the pH was adjusted to 7.0 and 37 °C. Additives as glucose and lactose reduced biofilm formation as bovine milk compounds tested. PCR assay showed that not all the isolates yielded sua gene. Extrachromosomal ADN was found in cell-free supernatants, suggesting that DNA released spontaneously to the medium. The results contribute to a better understanding of the factors involved in biofilm production of this important pathogen associated with mastitis in order to promote the design of new therapeutic approaches.

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

Coagulase-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.

Development of an experimentally induced Streptococcus uberis subclinical mastitis in goats

Streptococcus uberis is a major environmental mastitis-causing pathogen. The infections are predominantly subclinical and are frequently undetected and untreated for extended periods of time. More information about the pathogenesis of S. uberis mastitis would be useful. To our knowledge, no experimental studies into the mastitis pathogenesis caused by S. uberis have been described in lactating goats. The aim of this study was to reproduce an experimentally induced S. uberis subclinical mastitis in lactating goats aimed to evaluate the inflammatory response, dynamics of infection and the pathological findings within the first hours of intramammary inoculation with S. uberis. Six Saanen goats in mid-lactation were inoculated with 1.7 × 10(8)cfu of S. uberis. Bacterial growth peaked in milk from challenged right mammary halves (RMH) at 4h PI. Shedding of viable bacteria showed a marked decrease at 20 h PI. Mean somatic cell counts in milk from the RMH peaked at 20 h PI. Inoculation with S. uberis was followed by a decrease in the mean total number of leukocytes. Signs and systemic symptoms were not evoked by intramammary inoculation. S. uberis could be isolated in tissue from all RMH. Histological examination of specimens of the RMH and lymph nodes of the goats showed an increased inflammatory response throughout the experiment. The histological findings correlated with the immunohistochemical detection of S. uberis in RMH. In conclusion, the experimental inoculation of S. uberis in lactating goats is capable of eliciting an inflammatory response and causing pathological changes, resulting in a subclinical mastitis. This investigation shows that goat might to represent a valuable model for the study of the mastitis pathogenesis caused by S. uberis.

Distribution of virulence-associated genes in Streptococcus uberis isolated from bovine mastitis

Streptococcus uberis is an important pathogen that has been implicated in bovine mastitis but the virulence factors associated with pathogenesis are not well understood. The aim of this work was to examine 11 putative and known virulence-associated genes by PCR in 78 S. uberis strains isolated from infected animals in Argentina. Additionally, the distribution of virulence patterns over various herds was determined. Not all genes were present in the strains but all of the detected virulence-associated genes were present in combination. Forty-seven (60.3%) isolates carried seven to 10 virulence-associated genes. Further analysis revealed 58 virulence patterns. Different patterns were found within the same herd and among herds, demonstrating that strains with different virulence patterns were able to cause mastitis. Despite the large number of strains with different virulence patterns, strains with identical patterns was found. Detection of virulence-associated genes in individual S. uberis strains isolated from infected animals revealed one to 10 virulence genes. This may indicate that other virulence factors could be involved. The present study reveals the occurrence and distribution of 11 virulence-associated genes among S. uberis isolates from bovine mastitis in various herds and contributes to a better understanding of the pathogenicity of this bacterium.