Identification of a novel mechanism of action of bovine IgG antibodies specific for Staphylococcus aureus

Novel luminescent affiprobes for molecular detection of Staphylococcus aureus using flow cytometry

AIMS

Diagnosis of Staphylococcus aureus is important in various diseases from hospital-acquired infections to foodborne diseases. This work reports two new luminescent affiprobes for specific detection of S. aureus.

METHODS AND RESULTS

To develop advanced luminescent affiprobes, enhanced green fluorescent protein (EGFP) was flanked by single and double repeats of ZpA963 affibody using molecular biology studies. The recombinant proteins including fluorescent monomeric affibody (fA₁ ) and fluorescent dimeric affibody (fA₂ ) were expressed in the bacterial expression system, purified and used to identify the S. aureus. Fluorescence microscope and flow cytometry results demonstrated that the treated samples with fA₁ and fA₂ had relatively high fluorescent mean intensities in comparison to the untreated S. aureus cells. Moreover, it was revealed that 'fA₂ ' affiprobe had lower dissociation constant value (about 25-fold) and was more effective for detection of S. aureus than the 'fA₁ ' affiprobe. In addition, the binding of the affiprobes for some other pathogenic bacteria i.e. Escherichia coli, Bacillus cereus, Enterococcus faecalis and Staphylococcus saprophyticus was examined. Expectedly, no cross-reaction was observed for binding the constructed affiprobes to these bacteria, eliminating possibilities for false positive results.

CONCLUSIONS

The results show that 'fA₁ ' affiprobe and 'fA₂ ' affiprobe are two new efficient luminescent affiprobes for detecting S. aureus.

SIGNIFICANCE AND IMPACT OF THE STUDY

We developed a new approach for detection of Staphylococcus aureus in a simple one-step process and in low concentrations of probes. In the best of our knowledge, this is the first study to direct detection of bacterial cells by affiprobes and may be used to develop new diagnostic kits.

Organic Selenium Ameliorates Staphylococcus aureus-Induced Mastitis in Rats by Inhibiting the Activation of NF-κB and MAPK Signaling Pathways

Mastitis is an economically important disease in dairy cows, which is often caused by Staphylococcus aureus (S. aureus). Selenium is an indispensable element for physiological function and contributes to reduce injury of the mammary glands in mastitis. However, adequate sources of selenium have always been an important consideration for livestock. Therefore, the study aimed to explore the protective effect and mechanism of Selenohomolanthionine (SeHLan) on mastitis induced by S. aureus. The S. aureus-induced rat model was established and three doses (0.2, 2, 20 μg/kg body weight/day) of dietary OS were supplemented. The bacterial load, histopathology, and myeloperoxidase (MPO) of the mammary glands were performed and determined. Cytokines, including interleukin (IL)-1β, TNF-α, and IL-6, were detected using qRT-PCR. The key proteins of NF-κB and MAPK signaling pathways were analyzed by Western blot. The results revealed that OS supplementation could reduce the recruitment of neutrophils and macrophages in mammary tissues, but did not decrease S. aureus load in the tissues. The overexpression levels of IL-1β, TNF-α, and IL-6 induced by S. aureus were inhibited after OS treatment. Furthermore, the increased phosphorylation of NF-κB and MAPKs proteins were also suppressed. The results suggest that dietary supplementation with adequate OS during pregnancy contributes to protect the mammary glands from injury caused by S. aureus and alleviate the inflammatory response.