Larvae of Galleria mellonella are widely used for evaluating the virulence of microbial pathogens and for measuring the efficacy of anti-microbial agents and produce results comparable to those that can be obtained using mammals. In this work, the suitability of using G. mellonella larvae to measure the relative toxicity of a variety of food preservatives was evaluated. The response of larvae to eight commonly used food preservatives (potassium nitrate, potassium nitrite, potassium sorbate, sodium benzoate, sodium nitrate, sodium chloride, sodium nitrite and sodium acetate) administered by feeding or by intra-haemocoel injection was measured. A significant correlation between the LD50 (R (2) = 0.8766, p = 0.0006) and LD80 (R (2) = 0.7629, p = 0.0046) values obtained due to oral or intra-haemocoel administration of compounds was established. The response of HEp-2 cells to the food preservatives was determined, and a significant correlation (R (2) = 0.7217, p = 0.0076) between the LD50 values of the compounds administered by feeding in larvae with the IC50 values of the compounds in HEp-2 cells was established. A strong correlation between the LD50 values of the eight food preservatives in G. mellonella larvae and rats (R (2) = 0.6506, p = 0.0156) was demonstrated. The results presented here indicate that G. mellonella larvae may be used as a model to evaluate the relative toxicity of food preservatives, and the results show a strong positive correlation to those obtained using established cell culture and mammalian models.

The increasing incidence of human candidiasis and the tendency of Candida species to become resistant to existing chemotherapies are well-recognized health problems. The present study demonstrates the successful synthesis of novel triazole-amino acid hybrids with potent in vitro and in vivo inhibitory activity against Candida species. Particularly, compounds 68 and 70 showed potent in vitro activity against fluconazole (FLC) resistant as well as sensitive clinical isolates of Candida albicans. Time kill curve analysis of lead inhibitors 68 and 70 showed their fungistatic nature. Secretion of hydrolytic enzymes, mainly proteinases and phospholipases, decreased considerably in the presence of 68 and 70 indicating their interference in fungal virulence. TEM analysis of Candida cells exposed to compounds 68 and 70 clearly showed morphological changes and intracellular damage as their possible mode of action. A preliminary mechanistic study carried out on the two most effective inhibitors (68 and 70) revealed the inhibition of ergosterol biosynthesis thereby causing the cells to lose their integrity and viability. The selected compounds did not show significant cytotoxicity up to a concentration of 200 μg mL in the HEK293 cell line. An in silico analysis of 68 and 70 binding to a modeled C. albicans CYP51 showed critical H-bonding as well as hydrophobic interactions with the important active site residues indicating the basis of their anti-Candida role. Studies on the larvae of Galleria mellonella showed that the selected inhibitors (68 and 70) were non-toxic, did not provoke an immune response and significantly reduced Candida proliferation in vivo.

Despite the vast availability of antibiotics, bacterial infections remain a leading cause of death worldwide. In an effort to enhance the armamentarium against resistant bacterial strains, 1,2,3-triazole (5a–x) and sulfonate (7a–j) analogues of natural bioactive precursors were designed and synthesized. Preliminary screening against two Gram-positive (Streptococcus pneumoniae and Enterococcus faecalis) and four Gram-negative bacterial strains (Pseudomonas aeruginosa, Salmonella enterica, Klebsiella pneumoniae, and Escherichia coli) was performed to assess the potency of these analogues as antibacterial agents. Among all triazole analogues, 5e (derived from carvacrol) and 5u (derived from 2-hydroxy 1,4-naphthoquinone) bearing carboxylic acid functionality emerged as potent antibacterial agents against S. pneumoniae (IC50: 62.53 and 39.33 μg/mL), E. faecalis (IC50: 36.66 and 61.09 μg/mL), and E. coli (IC50: 15.28 and 22.57 μg/mL). Furthermore, 5e and 5u also demonstrated moderate efficacy against multidrug-resistant E. coli strains and were therefore selected for further biological studies. Compound 5e in combination with ciprofloxacin displayed a synergistic effect on multidrug-resistant E. coli MRA11 and MRC17 strains, whereas compound 5u was selective against E. coli MRA11 strain. Growth kinetic studies on S. pneumoniae and E. coli treated with 5e and 5u showed an extended lag phase. 5e and 5u did not show significant cytotoxicity up to 100 μg/mL concentration on human embryonic kidney (HEK293) cells. Transmission electron microscopic (TEM) analysis of bacterial cells (S. pneumoniae and E. coli) exposed to 5e and 5u clearly showed morphological changes and damaged cell walls. Moreover, these compounds also significantly inhibited biofilm formation in S. pneumoniae and E. coli strains, which was visualized by scanning electron microscopic (SEM) analysis. Treatment of larvae of Galleria mellonella (an in vivo model for antimicrobial studies) with 5e and 5u did not cause an alteration in the hemocyte density, thereby indicating lack of an immune response, and were nontoxic up to a concentration of 2.5 mg/mL.

A series of gold(I) pioneer complexes bearing N‐heterocyclic carbenes and steroid derivatives (ethynylestradiol and ethisterone) with the generic formula [Au(R2‐imidazol‐2‐ylidene)(steroid)] (where R=CH3 or CH2CH2OCH3) were synthesized, and the X‐ray structure of a rare of gold(I)–estradiol derivative is discussed. Toxicity studies reveal notable antibacterial activity of the gold‐based compounds, which is significantly increased in vivo by the presence of the estradiol unit. Toxicity profiling was estimated in vitro versus Gram‐positive (Staphylococcus aureus) and Gram‐negative (Escherichia coli) bacteria, and in vivo on Galleria mellonella larvae against E. coli.