Serological versus molecular typing of surface-associated immune evading polysaccharide antigens-based phenotypes of Staphylococcus aureus

A novel dual-staining method for cost-effective visualization and differentiation of microbial biofilms

Microbial biofilms are intricate communities that pose significant challenges in clinical and microbiological settings due to their resistance to antibiotics and immune responses. Advanced microscopy techniques, such as scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and fluorescence microscopy, are often employed to visualize and differentiate between these biofilms. However, these methods are not feasible in all laboratories because of their high cost and complexity. In contrast, simpler techniques like crystal violet and Congo red staining fail to differentiate bacterial cells from the biofilm matrix. This study introduces a novel dual-staining method using Maneval's stain for microbial biofilm detection and differentiation. This simple, cost-effective method requires only basic equipment and minimal reagents, making it suitable for routine use across various settings. We applied the dual-staining method to various microbial species, including Staphylococcus aureus, Enterococcus faecalis, Candida albicans, Escherichia coli, and Pseudomonas aeruginosa. When compared with the microtiter plate assay, results showed strong agreement, with the dual-staining method effectively differentiating between bacterial cells and the surrounding biofilm matrix, displaying a distinctive blue polysaccharide layer surrounding the magenta‒red bacterial cells. This technique offers a viable alternative to more expensive and complex biofilm detection methods, with potential applications in clinical diagnostics and biofilm research.

Mammary Gland Pathology Subsequent to Acute Infection with Strong versus Weak Biofilm Forming Staphylococcus aureus Bovine Mastitis Isolates: A Pilot Study Using Non-Invasive Mouse Mastitis Model

Background

Biofilm formation by Staphylococcus aureus is an important virulence attribute because of its potential to induce persistent antibiotic resistance, retard phagocytosis and either attenuate or promote inflammation, depending upon the disease syndrome, in vivo. This study was undertaken to evaluate the potential significance of strength of biofilm formation by clinical bovine mastitis-associated S. aureus in mammary tissue damage by using a mouse mastitis model.

Methods

Two S. aureus strains of the same capsular phenotype with different biofilm forming strengths were used to non-invasively infect mammary glands of lactating mice. Biofilm forming potential of these strains were determined by tissue culture plate method, ica typing and virulence gene profile per detection by PCR. Delivery of the infectious dose of S. aureus was directly through the teat lactiferous duct without invasive scraping of the teat surface. Both bacteriological and histological methods were used for analysis of mammary gland pathology of mice post-infection.

Results

Histopathological analysis of the infected mammary glands revealed that mice inoculated with the strong biofilm forming S. aureus strain produced marked acute mastitic lesions, showing profuse infiltration predominantly with neutrophils, with evidence of necrosis in the affected mammary glands. In contrast, the damage was significantly less severe in mammary glands of mice infected with the weak biofilm-forming S. aureus strain. Although both IL-1β and TNF-α inflammatory biomarkers were produced in infected mice, level of TNF-α produced was significantly higher (p<0.05) in mice inoculated with strong biofilm forming S. aureus than the weak biofilm forming strain.

Conclusion

This finding suggests an important role of TNF-α in mammary gland pathology post-infection with strong biofilm-forming S. aureus in the acute mouse mastitis model, and offers an opportunity for the development of novel strategies for reduction of mammary tissue damage, with or without use of antimicrobials and/or anti-inflammatory compounds for the treatment of bovine mastitis.