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

Abstract

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 Agtolerant strains from the same source showed about 34% of resistance, with the predominance of monoresistance. 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.

Aspects of silver tolerance in bacteria: infrared spectral changes and epigenetic clues

“…Under metal-stressed conditions, bacteria evolve various strategies and develop tolerance to survive [26]. Although heavy-metal cations are important as trace elements in biochemical reactions, at higher concentrations they lead to toxic effects.…”

Proactive Approach for Safe Use of Antimicrobial Coatings in Healthcare Settings: Opinion of the COST Action Network AMiCI

“…The resistance genes may occur in bacterial chromosome or in plasmids and can be transmitted to other microbes via horizontal gene transfer similarly with antibiotic resistance genes [60]. For example, resistance genes for silver that have already been found in hospital environment [61,62] are located in mobile genetic elements easily transferable to other bacteria e.g., in (hospital) sewage systems [63]. Expression of biocide resistance genes has been associated with concurrent AMR [60,64].…”

Remediation of Heavy Metal-Contaminated Agricultural Soils Using Microbes

“…solubilization and reduction) of heavy metals (Gadd 2000 ;Gadd and Griffi ths 1977 ). Various studies have demonstrated that certain soil microbes are capable of reducing and solubilizing metals such as Cr, Fe, Hg, Ag, Mn, Te and U, making them more or less available for plant absorption and minimizing their phytotoxicity (Giller et al 1998 ;Lima de Silva et al 2012 ;Watts and Lloyd 2012 ;Lasat 2002 ;Kashefi and Lovley 2000 ). Numerous studies have also reported that microbes were helpful in decreasing plant toxicity of Cd, Zn and Cr (Bennisse et al 2004 ;Juwarkar et al 2007 ;Khan 2005 ).…”