The in vitro antibacterial activity of a series of phosphanegold(I) dithiocarbamates, R 3 PAu[S 2 CN (iPr)CH 2 CH 2 OH] where R = Ph (2), Cy (3) and Et (4), against 25 strains of Gram-positive and Gram-negative bacteria were determined through the disk diffusion method, the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) and by time-kill assay. Compounds 2 and 3 have been shown to be specifically active against the tested Gram-positive bacteria, with MIC values ranging from 7.81 to 125 μg/ml. Compound 4 has a broadspectrum activity against 24 strains of Gram-positive and Gram-negative bacteria, with MIC values ranging from 0.98 to 1,000 μg/ml. Noteworthy was that 4, with a very low MIC value of 0.98 μg/ml, is particularly effective against methicillin-resistant Staphylococcus aureus (MRSA) and Bacillus sp., as effective as the standard antibiotic ciprofloxacin. In time-kill studies, the bacteriostatic and bactericidal activities of the tested compounds towards susceptible strains were similar to their characteristics determined by MBC/MIC ratios. In the time-kill assay, 2 and 3 showed only bactericidal activity towards the susceptible strains tested, whereas 4 revealed varying degrees of bactericidal and bacteriostatic activities, results indicating different antibacterial mechanisms are involved.
The phosphanegold(I) thiocarbamides, Ph 3 PAu{SC(OR)=NC 6 H 4 Me-4} for R = Me (1), Et (2) and iPr (3), have been shown to have essentially linear gold atom coordination geometries defined by phosphane-P and thiolate-S atoms, and exhibit minimum inhibitory concentration (MIC) values in the range of 1-37 μg/ml against four Gram-positive bacteria, namely Bacillus cereus, Enterococcus faecalis, Enterococcus faecium and Staphylococcus aureus; compounds 1-3 are less potent against a broad panel of 16 Gram-negative bacteria. As the minimum bactericidal concentration values were quite similar to the MIC values, compounds 1-3 are effective bactericidal agents. The specific action against the four Gram-positive bacteria suggests they function by inhibition of peptidoglycan synthesis.
Compact molecular structures of antimicrobial (R3PAu)2L (R = Et (1), Ph ((2) and Cy ((3); LH2 = {1,4-[MeOC(S)-N(H)]2C6H4}), arise from intramolecular Au⋯π(aryl) interactions, proven by theory to be attractive and 12 kcal mol–1 more stable than anticipated Au⋯O interactions.
Salmonella is an important food-borne pathogen causing disease in humans and animals worldwide. Salmonellosis may be caused by any one of over 2,500 serovars of Salmonella. Nonetheless, Salmonella enterica serovar Typhimurium and Salmonella enterica serovar Agona are the second most prevalent serovars isolated from humans and livestock products respectively. Limited knowledge is available about the virulence mechanisms responsible for diarrheal disease caused by them. To investigate the contribution of sopB, sopD and pipD as virulence factors in intracellular infections and the uniqueness of these bacteria becoming far more prevalent than other serovars, the infection model of Caenorhabditis elegans and phenotypic microarray were used to characterize their mutants. The strains containing the mutation in sopB, sopD and pipD genes were constructed by using latest site-specific group II intron mutagenesis approach to reveal the pathogenicity of the virulence factors. Overall, we observed that the mutations in sopB, sopD and pipD genes of both serovars did not exhibit significant decrease in virulence towards the nematode. This may indicate that these virulence effectors may not be universal virulence factors involved in conserved innate immunity. There are significant phenotypic differences amongst strains carrying sopB, sopD and pipD gene mutations via the analysis of biochemical profiles of the bacteria. Interestingly, mutant strains displayed different susceptibility to chemical stressors from several distinct pharmacological and structural classes when compared to its isogenic parental strains. These metabolic and chemosensitivity assays also revealed multiple roles of Salmonella virulence factors in nutrient metabolism and antibiotic resistance.
Forty-eight strains of Salmonella enterica subsp. enterica serovar Agona and 33 strains of Salmonella enterica subsp. enterica serovar Weltevreden were characterized by random amplified polymorphic DNA (RAPD) fingerprinting using 3 different arbitrary primer, Enterobacterial Repetitive Intergenic Consensus-Polymerase Chain Reaction (ERIC-PCR) and antimicrobial susceptibility testing. By using RAPD, 81 strains (44 strains of S. Agona and 33 strains of S. Weltevreden) can be clustered into 14 groups and 6 single isolates whereas ERIC-PCR produced 7 clusters and 3 single isolates. Thirteen antimicrobial agents were used and all the isolates were resistant to erythromycin and showed Multiple Antimicrobial Resistance indexes, ranging from 0.08 to 0.62. Poultry still remain as the common reservoir for multi-drug-resistant Salmonella. On the other hand, vegetables contaminated with S. Weltevreden showed a gain in antimicrobial resistance. Besides that, consistent antibiograms were observed from S. Weltevreden isolated at Kajang wet market on 2000/08/02.
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