Abstract:
This study aimed to investigate the impact of heavy metals, specifically iron (Fe), lead
(Pb), and zinc (Zn), on the antimicrobial efficacy of guava leaves collected from both
polluted and non-polluted areas. Topsoil samples were collected from both sites and
analyzed for heavy metal content using atomic absorption spectroscopy. The results
revealed significantly higher levels of iron in the polluted site than the non-polluted site.
In contrast, zinc concentrations were found to be higher in the non-polluted site. Mature
guava leaves were also collected from each site, from which crude extracts of guava
leaves were prepared by 48-hr maceration extraction in 95% ethanol. Intriguingly, the
crude extract from the polluted site exhibited larger zones of inhibition against S. aureus
and B. subtilis isolates. Linear regression models were then constructed to assess the
effects of heavy metal concentrations on the inhibitory activity of the extracts. The
analysis revealed a direct and significant effect of Fe on B. subtilis inhibition. In contrast,
Zn exhibited a significant inverse effect on the inhibition of B. subtilis. These findings
suggest that heavy metals have individual effects on the inhibitory activity of guava
leaves. Moderate levels of heavy metal-induced stress is known to enhance the
production of plant secondary metabolites, hence, strengthening antibacterial activity.
Meanwhile, metal deficiency or toxicity creates the opposite effect. Therefore, this
warrants further investigation on the heavy metal profile of other local medicinal plants
to elucidate the effects of pollution on their safety and antibacterial efficacy.
