Comparative Genomic Analysis of Streptococcus dysgalactiae subspecies dysgalactiae Isolated From Bovine Mastitis in China

Comparative genomic analyses of Klebsiella pneumoniae K57 capsule serotypes isolated from bovine mastitis in China

Klebsiella pneumoniae can cause severe clinical mastitis in dairy cows, with K. pneumoniae type K57 (K57-KP) being the most common capsular serotype. To identify virulence factors and antimicrobial-resistance (AMR) genes of K57-KP with varying virulence, Galleria mellonella (greater wax moth) larvae were infected as a screening model to characterize virulence of 90 K57-KP strains, with 10 and 11 strains defined as virulent or attenuated, respectively, based on larval survival rates. Next, virulence of these 21 isolates was subsequently confirmed in adhesion and lactate dehydrogenase release assays, using bovine mammary epithelial cells cultured in vitro. Finally, genes associated with virulence and AMR were characterize with whole-genome sequencing. These 21 K57-KP strains were designated into 16 sequence types based on multi-locus sequence typing and allocated in phylogenetic analysis based on single nucleotide polymorphisms. We found great genetic diversity among isolates. In addition, adhesion-associated genes (e.g., fimA, sfaA, and focA) aminoglycoside-resistance genes (aph(6)-Id, strAB) were associated with virulence. This study provided new knowledge regarding virulence of K57-KP associated with bovine mastitis, which may inform development of novel diagnostic tools and prevention strategies for bovine mastitis.

Microbial Composition and Diversity of High-demand Street-vended Foods in Ecuador

Developing countries such as Ecuador carry a heavy food safety burden but reports on the microbiological quality of their foods are scarce. In this investigation, the microbial diversity of 10 high-risk and mass-consumption street-vended foods including bolones, encebollado, food dressings, ceviche, chopped fruits, fruit juices, fruit salads, cheese, raw chicken, and ground beef in Quito, Guayaquil, and Cuenca, three major population centers in Ecuador, were evaluated using 16S rRNA gene High Throughput Sequencing. In total, 1,840 amplicon sequence variants (ASVs) were classified into 23 phyla, 253 families, 645 genera, and 829 species. In the tested food samples, Proteobacteria and Firmicutes were the most abundant phyla accounting for 97.41% of relative abundance (RA). At genus level, 10 dominant genera were identified: Acinetobacter (12.61% RA), Lactococcus (12.08% RA), Vibrio (8.23% RA), Weissella (7.43% RA), Aeromonas (6.18% RA), Photobacterium (6.32% RA), Pseudomonas (3.92% RA), Leuconostoc (3.51% RA), Klebsiella (3.49% RA), and Cupriavidus (2.86% RA). The highest microbial diversity indices were found in raw chicken, encebollados, fruit salads, and fruit juices from Guayaquil and Cuenca. From sampled foods, 29 species were classified as food spoilage bacteria and 24 as opportunistic pathogenic bacteria. Two groups associated with human diseases were identified, including 11 enteric species and 26 species of fecal bacteria. The occurrence of recognized and opportunistic pathogenic bacteria, as well as enteric and fecal microorganisms, in the street-vended foods indicated extensive risks for the consumers' health. This study demonstrated the application of culture-independent amplicon sequencing in providing a more comprehensive view of microbial safety for street-vended food, which could be a useful tool to facilitate the control of foodborne diseases.

Metataxonomic analysis of milk microbiota in the bovine subclinical mastitis

Subclinical mastitis is one of the most widespread diseases affecting dairy herds with detrimental effects on animal health, milk productivity, and quality. Despite its multifactorial nature, the presence of pathogenic bacteria is regarded one of the main drivers of subclinical mastitis, causing a disruption of the homeostasis of the bovine milk microbial community. However, bovine milk microbiota alterations associated with subclinical mastitis still represents a largely unexplored research area. Therefore, the species-level milk microbiota of a total of 75 milk samples, collected from both healthy and subclinical mastitis-affected cows from two different stables, was deeply profiled through an ITS, rather than a traditional, and less informative, 16S rRNA gene microbial profiling. Surprisingly, the present pilot study not only revealed that subclinical mastitis is characterized by a reduced biodiversity of the bovine milk microbiota, but also that this disease does not induce standard alterations of the milk microbial community across stables. In addition, a flow cytometry-based total bacterial cell enumeration highlighted that subclinical mastitis is accompanied by a significant increment in the number of milk microbial cells. Furthermore, the combination of the metagenomic and flow cytometry approaches allowed to identify different potential microbial marker strictly correlated with subclinical mastitis across stables.

Molecular characterization of Streptococcus agalactiae and Streptococcus dysgalactiae causing bovine mastitis in the southern region of Bangladesh

Objective

This study was conducted to validate polymerase chain reaction (PCR) as a confirmatory diagnostic tool to find out the presence and frequency of Streptococcus agalactiae (S. agalactiae) and Streptococcus dysgalactiae (S. dysgalactiae) in mastitic milk samples obtained from dairy cows in the southern region of Bangladesh.

Materials and Methods

A total of 196 samples of bovine milk were collected from various dairy farms in the Chattogram metropolitan area of the southern part of Bangladesh. DNA extracted from isolates obtained by culturing California mastitis test (CMT)-positive mastitic milk samples (n = 146) on 5% sheep blood agar was used as a template for PCR. Two sets of specific primers based on the 16S rRNA gene were used to discriminate between S. agalactiae and S. dysgalactiae. Four PCR products were subjected to sequencing, followed by phylogenetic analysis.

Results

The PCR analyses revealed that out of the 146 CMT-positive milk samples tested, 29 samples were positive for S. agalactiae (19.86%), while 26 samples were positive for S. dysgalactiae (17.81%). Further sequence analysis of the corresponding PCR products and bioinformatics analysis verified the results.

Conclusion

The study proves the efficiency of PCR as a useful diagnostic approach to determine the presence and prevalence of S. agalactiae and S. dysgalactiae in mastitic milk samples obtained from dairy cows.