AUTHOR=Morovic Paula , Gonzalez Moreno Mercedes , Trampuz Andrej , Karbysheva Svetlana 

TITLE=In vitro evaluation of microbial D- and L-lactate production as biomarkers of infection

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1406350

DOI=10.3389/fmicb.2024.1406350

ISSN=1664-302X

ABSTRACT=<p>Mammalian cells produce and metabolize almost exclusively L-lactate, bacterial species have the capacity to produce both D-lactate and L-lactate. The aim of this study was to evaluate the intrinsic production of D- and L-lactate in the most common pathogenic microorganisms causing septic arthritis (SA) and periprosthetic joint infection (PJI) as a potential biomarker for the diagnosis of infection. Following microorganisms were grown according to ATCC culture guides and tested for production of D- and L-lactate: <italic>Staphylococcus aureus</italic> (ATCC 43300), <italic>Staphylococcus epidermidis</italic> (ATCC 35984), <italic>Enterococcus faecalis</italic> (ATCC 19433), <italic>Streptococcus pyogenes</italic> (ATCC 19615), <italic>Escherichia coli</italic> (ATCC 25922), <italic>Pseudomonas aeruginosa</italic> (ATCC 27853), <italic>Cutibacterium acnes</italic> (ATCC 11827), and <italic>Candida albicans</italic> (ATCC 90028). Pathogens were inoculated in 8 ml of appropriate liquid media and incubated as planktonic or biofilm form in either aerobic, anaerobic or CO<sub>2</sub> atmosphere up to 312 h. D- and L-lactate measurements were performed at different time points: 0, 6, 9, 12 and 24 h, then once per day for slow-growing pathogens. Samples were serially diluted and plated for colony counting. Liquid culture media without microorganisms served as a negative control. Production of D-lactate was observed in all tested microorganisms, whereas no L-lactate was detected in <italic>E. coli</italic>, <italic>P. aeruginosa,</italic> and <italic>C. albicans</italic>. Maximal concentration of D-lactate was produced by <italic>S. aureus</italic> (10.99 mmol/L), followed by <italic>E. coli</italic> (1.22 mmol/L), and <italic>S. epidermidis</italic> (0.48 mmol/L). Maximal L-lactate concentration was observed in <italic>S. pyogenes</italic> (10.12 mmol/L), followed by <italic>S. aureus</italic> (9.71 mmol/L), <italic>E. faecalis</italic> (2.64 mmol/L), and <italic>S. epidermidis</italic> (2.50 mmol/L). <italic>S. epidermidis</italic> bacterial biofilm produced significantly higher amount of D- and L-lactate compared to planktonic form (<italic>p</italic> = 0.015 and <italic>p</italic> = 0.002, respectively). Our study has demonstrated that the most common pathogenic microorganisms causing SA and PJI have the capability to generate measurable amounts of D-lactate in both planktonic and biofilm form, highlighting the practical value of this biomarker as an indicator for bacterial and fungal infections. In contrast to D-lactate, the absence of L-lactate production in certain tested bacteria, as well as in fungi, suggests that L-lactate is not eligible as a biomarker for diagnosing microbial infections.</p>