Effects of heavy metals on bacterial growth, biochemical properties and antimicrobial susceptibility
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Date
2022
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Sokoine University of Agriculture
Abstract
Heavy metals are metallic elements that occur naturally and have high atomic weights and
densities that are five times greater than the density of water. Several studies have
demonstrated that metal contamination in natural environments could have an important
role in the development and spread of antimicrobial resistance. This is of particular
concern, considering that heavy metals usually occur at higher levels than pharmaceutically
produced antimicrobials. Also, the bio-accumulative and non-biodegradable nature of
heavy metals may result in long- term antimicrobial resistance selection pressure.
Therefore, this study assessed the effects of Copper, Cobalt, Cadmium, Zinc and Lead salts
on growth, biochemical properties and antimicrobial susceptibility of Escherichia coli,
Pseudomonas aeruginosa and Staphylococcus aureus to commonly used antimicrobials.
The selected bacteria were exposed to varying concentrations of the heavy metal salts
ranging from 1 ppm to 1 000 ppm after which growth was measured using a
spectrophotometer. The effect on biochemical properties and antimicrobial susceptibility
were also tested by the use of conventional biochemical tests and Kirby-Bauer disk
diffusion methods, respectively. Different heavy metals affected the growth of each
individual microorganism differently. Despite that, the growth of E. coli, P. aeruginosa
and S. aureus was observed to be inversely proportional to the concentrations of the heavy
metals used. Following exposure to heavy metals, E. coli and S. aureus showed no changes
in their biochemical properties but P. aeruginosa gave a positive urease result contrary to
the control. E. coli developed resistance to Levofloxacin, Meropenem and Tetracycline
while S. aureus to Azithromycin and Gentamicin and P. aeruginosa developed resistance
only to Meropenem. These results confirm the adverse effects of heavy metals on bacterial
growth and reveals that heavy metals can cause changes in some biochemical properties of bacteria that produce any of these properties under stressful growing conditions. This
research also supports the findings that heavy metals enhance the development of
antimicrobial resistance in otherwise antimicrobial sensitive strains of bacteria. This study
therefore, gives insight into the likely state of the proliferation of heavy metal induced
biochemical properties and antimicrobial resistance in heavy metal contaminated areas.
Description
Dissertation
Keywords
Heavy metals, Bacterial growth, Biochemical, Antimicrobial susceptibility