Effect of Streptococcus mutans on the autofluorescence of pathogens causing aspiration pneumonia

•Streptococcus mutans influence the autofluorescence of some aspiration pneumonia pathogens.•Quantitative light-induced fluorescence detects pneumonia bacterial autofluorescence.•Microbial interactions are vital for developing reliable tools to detect pathogens. This study aimed to determine the autofluorescence characteristics influenced by interactions between Streptococcus mutans (SM) and pneumonia-related microorganisms using a quantitative light-induced fluorescence (QLF) technology. The microbial strains used were Acinetobacter baumannii (AB), Staphylococcus aureus (SA), Escherichia coli (EC), Candida albicans (CA), and SM. Fluorescence was captured using QLF technology. For single cultures, colonies were analyzed, and for cross-cultures, pixels at the point where the two microorganisms intersected and the adjacent areas of non-cross colonies were analyzed by measuring the red and green values (R/G ratio). The R/G ratio was analyzed using the Kruskal–Wallis H test and Mann–Whitney U test. AB showed red fluorescence only at 48 h when cultured alone, but had stronger redness from 120 h when cultured with SM. SA expressed red fluorescence throughout the 168 h when cultured alone, but redness was observed from 48 h when cultured with SM. EC showed no red fluorescence, either cultured alone or with SM. CA exhibited weak red fluorescence after 120 h when cultured alone, but not with SM. SM affects the fluorescence of the aspiration-pneumonia-associated pathogens AB and SA. These findings may serve as a basis for future detection of aspiration pneumonia-causing bacteria in the oral cavity.