Technology

Analysis
Scientists performed the study in order to clarify the nature of infection and the dominant causative pathogens for subclinical mastitis that had widely affected cows in a dairy farm in north Rhine-Westphalia, Germany. The hypotheses under investigation was first, subclinical mastitis that is caused by Streptococcus canis is very rare and second, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and PCR gene amplification methods can accurately identify species specific characteristics of Lancefield serogroup G of Streptococcus canis  bacteria.

The study involved collecting milk samples from the affected lactating cows and subjecting them to laboratory analysis. The major techniques involved phenotypic and genotypic characterization of the bacteria present in the samples. For a start, a direct microscopic count was performed to determine the somatic cells count in the sample and this was followed by culturing and sub culturing methods on various agar plates to identify the various groups of bacteria present. The agar preparations distinguished Streptococcus from Enterococcus and Staphylococcus species all of which are present in cases of subclinical mastitis. The Streptococcus canis were further subjected to biochemical and phenotypic characterization tests.  The biochemical tests revealed sensitivity and resistance to various antibiotics, and hydrolysis activities on various carbohydrates. The PCR amplification methods further revealed the phenotypic and molecular characteristics of the S. canis. First, genomic DNA extraction was performed followed by PCR amplification of the encoded 16S ribosomal RNA segment using oligonucleotide primers then the fragments restricted by RFLP enzymes to generate species specific patterns. The necessary primers were used in amplification of species specific genes and this was in line with the universal data and DNA software in gene databases. A pulsed field gel electrophoresis was carried out for macrorestriction analysis of chromosomal DNA and this revealed that the bacterial species forming the group S. canis, were closely related. The results showed that S. canis was the predominant group of species that was identified in most of the case samples and therefore this disapproved the first hypothesis that S. canis is very rare in subclinical mastitis. However, it was noticed that this case is the largest subclinical mastitis outbreak caused by S. canis so far and this can be attributed to the high contagious ability of these species. All the same, the use of PCR amplification and RFLP analysis has been shown to accurately identify species-specific characteristics to almost 99 percent, therefore, agreeing with the second hypothesis.

The results from this study are of significance importance. The revelation of the genetic methods for species identification could point out that wrong diagnoses were being made in the past over the causative agent of subclinical mastitis, and that is why there was the speculation that S. canis is rare in subclinical mastitis. Exclusive phenotypic characterization could have limitations especially where species exhibit similar features to one another. Despite the time and high costs, future research should consider including genetic markers for all microorganisms especially the pathogenic ones to aid in accurate diagnosis of prevailing conditions. Also, the revelation that S. canis is sensitive to antibiotics such as penicillin G and amoxicillin-clavulanate can be of a great potential towards manufacture of antibiotics or vaccines that can combat the loss causing subclinical mastitis.

This article was an interesting read especially on the fact that it was very educative. The steps taken in the research are well sequenced making it easier to follow and understand. I chose this article because the research was based on a realistic case study. Diseases caused by Streptococcus are very common and this article can make a great reference for many clinical studies.