Virulence Factor Genes and Cytotoxicity of Streptococcus agalactiae Isolated from Bovine Mastitis in Poland

Current research update on group B streptococcal infection related to obstetrics and gynecology

Group B streptococcal (GBS) is a Gram-positive bacterium that is commonly found in the gastrointestinal tract and urogenital tract. GBS infestation during pregnancy is a significant contributor to maternal and neonatal morbidity and mortality globally. This article aims to discuss the infectious diseases caused by GBS in the field of obstetrics and gynecology, as well as the challenges associated with the detection, treatment, and prevention of GBS.

Antibacterial activity and mechanism of chelerythrine against Streptococcus agalactiae

Streptococcus agalactiae (S.agalactiae), also known as group B Streptococcus (GBS), is a highly infectious pathogen. Prolonged antibiotic usage leads to significant issues of antibiotic residue and resistance. Chelerythrine (CHE) is a naturally occurring benzophenidine alkaloid and chelerythrine chloride (CHEC) is its hydrochloride form with diverse biological and pharmacological activities. However, the antibacterial mechanism of CHEC against GBS remains unclear. Thus, this study aims to investigate the in vitro antibacterial activity of CHEC on GBS and elucidate its underlying mechanism. The antibacterial effect of CHEC on GBS was assessed using inhibitory zone, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) assays, as well as by constructing a time-kill curve. The antibacterial mechanism of CHEC was investigated through techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM), measurement of alkaline phosphatase (AKP) activity, determination of Na+ K+, Ca2+ Mg2+-adenosine triphosphate (ATP) activity, observation of membrane permeability, and analysis of intracellular reactive oxygen species (ROS) and mRNA expression levels of key virulence genes. The results demonstrated that the inhibition zone diameters of CHEC against GBS were 14.32 mm, 12.67 mm, and 10.76 mm at concentrations of 2 mg/mL, 1 mg/mL, and 0.5 mg/mL, respectively. The MIC and MBC values were determined as 256 μg/mL and 512 μg/mL correspondingly. In the time-kill curve, 8 × MIC, 4 × MIC and 2 × MIC CHEC could completely kill GBS within 24 h. SEM and TEM analyses revealed significant morphological alterations in GBS cells treated with CHEC including shrinkage, collapse, and leakage of cellular fluids. Furthermore, the antibacterial mechanism underlying CHEC's efficacy against GBS was attributed to its disruption of cell wall integrity as well as membrane permeability resulting in extracellular release of intracellular ATP, AKP, Na+ K+, Ca2+ Mg2+. Additionally CHEC could increase the ROS production leading to oxidative damage and downregulating mRNA expression levels of key virulence genes in GBS cells. In conclusion, CHEC holds potential as an antimicrobial agent against GBS and further investigations are necessary to elucidate additional molecular mechanisms.

Characterization of Virulence Factors and Antimicrobial Susceptibility of Streptococcus agalactiae Associated with Bovine Mastitis Cases in Thailand

Streptococcus agalactiae is a contagious pathogen that causes bovine mastitis. The ability of S. agalactiae to cause widespread mastitis relies on bacterial virulence factors. In this study, we detected 10 virulence determinants associated with mastitis pathogenicity using conventional PCR. The antimicrobial susceptibility of 100 S. agalactiae isolates from 13 Thai dairy herds was assessed using the Kirby-Bauer disk diffusion susceptibility test. All strains had at least three virulence factors responsible for invasion, adhesion, and infection (fbsB, bibA, and cfb, respectively). The predominant virulent profile of S. agalactiae strains revealed the presence of fbsA, fbsB, bibA, cfb, and cyl (n = 96). Most strains were sensitive to penicillin, ampicillin, amoxicillin-clavulanic acid, cefotaxime, ceftiofur, erythromycin, sulfamethoxazole-trimethoprim, and vancomycin. However, all strains were resistant to aminoglycosides, including kanamycin and gentamicin attributed to the unnecessary antimicrobial use. Furthermore, we identified seven multidrug resistant (MDR) S. agalactiae strains among four dairy herds, of which, two were vancomycin resistant. Our study provides profiles for virulence factors and antimicrobial susceptibility, which are beneficial for the clinical monitoring, prevention, and control of bovine mastitis in dairy cattle in Thailand. Moreover, we emphasize the need for awareness regarding the judicious use of antimicrobials on dairy farms.

Evaluation of Streptococcus species isolated from subclinical sheep mastitis by molecular methods and determination of virulence factors and antimicrobial resistance genes

Streptococcus (S.) species are important pathogens that cause mastitis in sheep. The study aimed to examine Streptococcus species in sheep milk with subclinical mastitis, assessing their prevalence, antimicrobial resistance, and virulence genes. A total of 200 milk samples were collected from sheep farms in İzmir's five districts. Out of 32 (28.6%) Streptococcus isolates identified by phenotypic methods, 25 were genotypically identified as S. uberis, 5 as S. agalactiae, and 2 as S. dysgalactiae. Disk diffusion was used to determine the antimicrobial resistance of the isolates. PCR was employed to identify antimicrobial resistance and virulence genes in the isolates. The highest resistance was found for cloxacillin (100%), and the highest sensitivity was found for florfenicol (84%). The most common resistance gene combination was tetM+tetS (3/32) for S. uberis in 9.4%. A total of five virulence genes were detected. GapC+sua (56.2%) constituted the most common gene pattern. The highest virulence gene gapC was detected in 78.1% (25/32) of the isolates. The cylE gene was not detected (0%) in the isolates. Streptococcus species may play a role in mastitis in sheep, emphasising the need for meticulous hygienic milking practices.