Abstract
Purpose :
Antibiotic resistance is an ever growing problem in clinical management of infections of the eye, including keratitis. We used photoacoustic flow cytometry to detect and classify keratitis as methicillin sensitive or resistant by testing clinical samples from patients.
Methods :
We developed photoacoustic flow cytometry to detect light absorbing particles under flow. This method induces acoustic waves in pigmented particles using laser irradiation, allowing for detection, enumeration, and capture. We acquired samples of Staphylococcus aureus from keratitis in 13 patients in the clinic. These Staphylococcus aureus samples were grown in the presence and absence of Oxacillin and were tested using photoacoustic flow cytometry. In order to create optical absorption in the S. aureus bacteria, purified bacteriophage SP1 virions were modified to incorporate Direct Red 81 dye. Bacteriophage SP1 has a broad host range and has been shown to infect approximately 98% of clinical S. aureus strains. We split each patient sample into two groups, those treated with oxacillin and those not treated. Modified bacteriophage SP1 were added to each group in equal amounts. Using photoacoustics, we then counted the number of bacteria with the expectation that methicillin sensitive samples treated with oxacillin would have greatly reduced numbers of bacteria.
Results :
We counted the photoacoustic events in all 13 treated and untreated samples. Detections ranged from 2 to 818 counts. We took the ratio of treated over untreated detections and performed k-means clustering into two groups. The two groups corresponded exactly to the methicillin sensitive and resistant groups determined by PCR for the MecA gene in all 13 strains.
Conclusions :
Photoacoustic flow cytometry has the ability to detect Staphylococcus aureus bacteria. By treating samples with antibiotic, it is possible to classify infections as sensitive or resistant, thus allowing for improved management of keratitis.
This is a 2021 ARVO Annual Meeting abstract.