ANTIBACTERIAL EFFECT OF SELENIUM, GERMANIUM, AND LITHIUM ON CLINICALLY IMPORTANT BACTERIA GROWING IN PLANKTONIC CULTURE AND BIOFILMS – SOME MEDICAL IMPLICATIONS

The antibacterial effects of lithium, selenium, and germanium were evaluated with respect to growth, biofilm formation, and mutational frequencies (MF), of Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli.
Selenium showed the highest antimicrobial and bactericidal activities as shown by zone of inhibition assay and scanning electron microscopy imaging (SEM). The SEM images showed that the metals in culture media led to cell disintegration that could have resulted in the leakage of cytoplasmic constituents, and cell dehydration. In biofilms, the combination of metal and antibiotics increased oxidative stress, mutational frequencies(MF), and formation of mutator phenotypes. Adding the antioxidant ascorbic acid reduced the S. aureus biofilm MF, but increased the MF of P. aeruginosa biofilm. Image analysis showed that metal and ascorbic acid cooperated in destroying cell structure pointing to the effectiveness of the antioxidant to prevent the formation of reactive oxygen species, oxidative stress, and bacterial DNA mutation rates. Generally, results showed that the antibacterial effect depended on the combinations of metal, antibiotic and antioxidant different and the bacterial strain being tested.
Biofilm cultures yielded adherent colony variants that differed in appearance and in the capability of the variants to form hypermutator phenotypes with relatively high MFs. There was perfect sequence alignment of an approximately 500 bases of the P. aeruginosa 16S rDNA fragment of the wild-type and colony variants. In contrast, the 16S rDNA sequence of S. aureus variant showed several mutations, deletions, and insertions, implying the high mutability of S. aureus when exposed to external factors.
Further studies should be conducted on the molecular basis of the antibacterial action and possible applications of selenium, germanium, and lithium in reducing antibiotic resistance, and biofilm infection. In addition, there is a need to understand bacterial adaptation to metals and their interaction with other antimicrobial agents in order to design effective drug therapies.