Virulence of silver-resistant mutant of Klebsiella pneumoniae in burn wound model

Antibacterial effect of silver nanoparticles on antibiotic resistant E. coli O157:H7 isolated from some dairy products

Food safety is a worldwide health goal so foodborne diseases are a main health concern. A total 150 of dairy products samples (locally made yoghurt, ice cream and Talaga cheese) (50 for each type) were examined for E.coli O157:H7 detection and PCR confirmation using fliCH7 gene. E. coli O157:H7 was detected at 18%, 4%, 8% respectively, in samples. The isolates showed broad antibiotic resistance against vancomycin (84.6%), penicillin G (76.9%), cloxacillin (69.2%) and tetracycline (61.5%). Because of increasing number of microorganisms that are resistant to multiple antibiotics causing continuing economic losses in dairy manufacturing, there is an urgent need for development of alternative, cost-effective, and efficient antimicrobial agents to overcome antimicrobial resistance. Here, silver nanoparticle (AgNPs) solution was prepared, identified by transmission electron microscopy (TEM) with an average size 26.5 nm and examined for bactericidal activity against E. coli O157:H7 by using well diffusion assay. The mean inhibition zones of 25 and 50 µg/ml concentrations of Ag-NPs were 15.0±1.2 and 20.9±1.4 mm, respectively. In addition, the statistical analysis showed highly significant differences in the bactericidal effect of different Ag-NPs concentrations on E. coli O157:H7 strains. Bacterial sensitivity to nanoparticles is a key factor in manufacture, so nanoparticles were considered suitable for long life application in food packaging and food safety.

Heavy metal tolerance (Cr, Ag AND Hg) in bacteria isolated from sewage

Samples of sewage from a university hospital and a chemistry technical school were analysed for the percentage of bacterial tolerance to chromium (Cr), silver (Ag) and mercury (Hg). Additionally, we investigated the effect of these metals on pigmentation and on some enzymatic activities of the metal tolerant strains isolated, as well as antimicrobial resistance in some metal tolerant Enterobacteriaceae strains. Tolerance to Cr was observed mainly in Gram positive bacteria while in the case of Ag and Hg the tolerant bacteria were predominately Gram negative. Hg was the metal for which the percentage of tolerance was significantly higher, especially in samples from the hospital sewage (4.1%). Mercury also had the most discernible effect on color of the colonies. Considering the effect of metals on the respiratory enzymes, one strain of Ag-tolerant Bacillus sp. and one of Hg-tolerant P. aeruginosa were unable to produce oxidase in the presence of Ag and Hg, respectively, while the expression of gelatinase was largely inhibited in various Gram negative strains (66% by Cr). Drug resistance in Hg-tolerant Enterobacteriaceae strains isolated from the university hospital sewage was greater than 80%, with prevalence of multiple resistance, while the Ag-tolerant strains from the same source showed about 34% of resistance, with the predominance of mono-resistance. Our results showed that, despite the ability of metal tolerant strains to survive and grow in the presence of these elements, the interactions with these metals may result in metabolic or phisiological changes in this group of bacteria.