Differences in the activity of methylene blue dye against bacteria and fungi

Dear editor, The pathogenic fungi and bacteria developed resistance to multiple antibiotics, making them difficult to treat with standard therapies. So, using alternative strategies such as dyes is urgent [1]. Methylthioninium chloride, commonly called methylene blue (MB), is a salt used as a dye and a medication is used to treat methemoglobinemia by converting/chemically reducing the ferric iron in hemoglobin to ferrous iron [2]. Candida albicans has served as the leading causal agent of life-threatening invasive infections, with mortality rates approaching 40% despite treatment [3]. Pseudomonas aeruginosa is the most common Gram-negative rod infection, especially in severely sick and vulnerable individuals [4]. Staphylococcus aureus remains one of the most involved bacteria in human diseases. S. aureus have intrinsic and acquired antibiotic resistance, making clinical infection management a real challenge, particularly in patients with comorbidity [5]. In the current study, a total of 30 S. aureus and P. aeruginosa isolated from wounds by culturing the specimens in three media (blood agar, MacConkey agar, and mannitol salt agar). C. albicans was isolated from three sites (vagina, oral, and urine) in 30 patients and cultured in Sabouraud dextrose agar and confirmed by germ tube test [6]. The good diffusion method is used to evaluate the activity of MB; the diameter of the inhibited growth is measured in millimeter. MB is considered active when the inhibition zone is more than or equal to 13 mm. All the statistical analyses was done using SPSS 26 software (SPSS Inc., Il, Chicago, USA) [7]. In the current study, the activity of MB against C. albicans isolates was 100%, while it was 81% on the bacterial infections (S. aureus and P. aeruginosa) (Fig. 1).Figure 1: Percentage of methylene blue activity.In this study, the median comparison of C. albicans and bacteria for MB activity was showed in Table 1. The efficacy of MB against C. albicans was 26 mm (26–28 mm) and for P. aeruginosa was 6 mm (0–22 mm) with significant difference (P≤0.0001). Activity of MB for S. aureus 22 mm (21–22 mm), which was higher than C. albicans with significant differences (P=0.001). These mean MB was more active against C. albicans less then against S. aureus and had the least activity against P. aeruginosa. Table 1 - Comparison medians of methylene blue activity for candida and bacteria Variables Groups Median, IQR (mm) P value* Methylene blue Candida albicans 26 (26–28) <0.0001 Pseudomonas aeruginosa 6 (0–22) Candida albicans 26 (26–28) 0.001 Staphylococcus aureus 22 (21–22) *Mann–Whitney U test. Another study mentions MB is known to have antibacterial activity. Numerous studies have found that MB has activity alone or in combination with various other compounds. For example, Sauer et al. [8] showed that combined with sodium citrate MB, it had in-vitro activity against P. aeruginosa, S. aureus, S. epidermidis, and C. albicans. Conclusion MB has more activity against yeast fungal infection 100% (C. albicans) than bacterial isolates 81% activity with statistically significant differences. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.