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Objectives: Bacteremia is a serious and potentially lethal condition. Staphylococcus aureus is a leading cause of bacteremia and methicillin-resistant S. aureus (MRSA) accounts for more than a third of the cases. Compared to methicillin-sensitive S. aureus, MRSA is more than twice as likely to be fatal. Furthermore, subpopulations of seemingly isogenic bacteria may exhibit a range of susceptibilities, often called heterogenous resistance. These heterogeneous antibiotic-resistant infections are often misdiagnosed as hospital-acquired secondary infections because there are no clinically used tests that can differentiate between homogeneous and heterogeneous antibiotic resistance. We describe the development and proof of concept of rapid bacterial identification using photoacoustic flow cytometry and labeled bacteriophages with the characterization and differentiation of heterogeneous antibiotic-resistant bacterial infections., Methods: In photoacoustic flow cytometry, pulsed laser light is delivered to a sample flowing past a focused transducer and particles that absorb laser light create an acoustic response. Optically labeled bacteriophage are added to a bacterial mixture that flows through the photoacoustic chamber. The presence of target bacteria is determined by bound labeled phage which are detected photoacoustically. Incubation of bacterial samples in the presence and absence of the antibiotic daptomycin creates a difference in bacterial cell numbers that is quantified using photoacoustic flow cytometry., Results: Four clinical isolates were tested in the presence and absence of daptomycin. Photoacoustic events for each isolate were recorded and compared to growth curves. Samples treated with daptomycin fell into three categories: resistant, susceptible, and heterogeneous resistant., Conclusions: Here we show a method to determine the presence of bacteria as a marker for bloodstream infection level and antibiotic sensitivity in less than 4 hours. Additionally, these results show an ability to identify heterogeneous resistant strains that are often misidentified., (© 2021 Wiley Periodicals LLC.)

Background and Objectives: Enumerating circulating tumor cells has been used as a method of monitoring progression of various cancers. Various methods for detecting circulating melanoma cells (CMCs) have been reported, but none has had sufficient sensitivity to determine if the presence of rare CMCs in the blood of Stage I-III melanoma patients predicts if those patients eventually develop metastatic disease., Study Design: We quantified CMCs in serial blood samples from 38 early stage melanoma patients to determine if CMC numbers predict development of metastatic melanoma. CMCs were enumerated using a photoacoustic flow cytometric detection system that uses a laser to induce high frequency acoustic signals in pigmented CMCs., Results: We observed that detection of greater than 2 CMCs/ml of blood from patients with Stage I-III melanoma predicts metastatic disease. Of the 11 patients we studied who had two or fewer CMCs detected at all time points tested, none progressed to metastatic disease over a mean follow-up of 1288 days. In contrast, 18 of the 27 patients (67%) having more than 2 CMCs/ml at one or more time points progressed to metastatic disease over a mean follow-up of 850 days., Conclusions: Photoacoustic flow cytometry can detect rare CMCs in the blood of Stage I-III melanoma patients and detectionof these cells is predictive of subsequent development of metastatic disease. Lasers Surg. Med., (© 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC.)