Complexes of bacteria‐recognizing engineered phage lysin and red‐colored bacteria microparticles as optical bioprobes for simple, rapid, naked‐eye detection of syphilis‐specific antibodies from clinical samples

Abstract Serological detection of syphilis‐specific antibodies is the most widely used clinical method for diagnosing syphilis. However, the current methods in clinical practice are too diverse, complicating result interpretation and wasting medical resources. To meet the resultant demand for a simple fast naked‐eye detection method, we employed the bacterial cell‐binding domain (CBD) of bacteriophage lysin to functionalize bio‐microparticles (engineered non‐culturable red‐colored Staphylococcus aureus bacteria), forming a bioprobe that can detect the syphilis‐specific antibodies from human serum in 5 min with naked eyes. Specifically, CBD is bioengineered by fusion with one of three antigens of the syphilis‐causing bacteria Treponema pallidum separately. The three resulting fusion proteins bind to the bacteria surface through the CBD motif, generating a bioprobe with the antigens exposed. When the bioprobe is added to the serum samples collected from the syphilis patients, the syphilis‐specific antibodies bind the antigens on the bioprobes and cross‐link them, forming eye‐visible red aggregates for the naked‐eye antibody detection. The bioprobe was validated on 209 clinical samples, revealing its high clinical sensitivity and specificity. Exploiting the natural biorecognition between the bacteria‐specific phage‐derived species and the phage host bacteria represents a promising strategy for producing facile probes for rapid point‐of‐care testing of infectious diseases.