Anti-bacterial activity of peppermint (Mentha piperita) extracts against some emerging multi-drug resistant human bacterial pathogens

Various plant extracts have great potential against infectious agents and can be used for therapeutic purposes. This study was carried out to evaluate the antimicrobial activities of peppermint (Mentha piperita) extracts against 10 multidrug resistant (MDR) pathogenic bacterial clinical isolates.The antibacterial activities of ethanol, methanol, ethyl acetate and chloroform peppermint extracts were assessed using the standard minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) methods. Overall, the ethyl acetate extract of peppermint had strong growth inhibitory effects on the tested pathogens, followed by the chloroform, ethanol and methanol extracts. The inhibitory activity of the ethyl acetate extract against all Gram-negative pathogens was higher than that of chloroform (10-80 mg/ml), methanol (10- > 80 mg/ml) and ethanol (40- > 80 mg/ml). The lowest MIC value was seen for Streptococcus pyogenes (1.25 mg/ml for ethyl acetate extract), followed by methicillin-resistant Staphylococcus epidermidis (MRSE) and Enterococcus faecalis (2.5 mg/ml for ethyl acetate extract).The MBC values of all extracts were higher than the corresponding MIC values for the majority of pathogens. This study highlights the potential antibacterial activity for M. piperita extracts, especially the ethyl acetate extract, against MDR S. pyogenes, E. faecalis, methicillin-resistant Staphylococcus aureus (MRSA), MRSE and carbapenem-resistant E. coli, and Klebsiella pneumonia clinical isolates. Further in vitro and in vivo studies on a large number of clinical isolates of MRSA, Acinetobacter baumannii and Stenotrophomonas maltophilia are necessary to further investigate and standardize the inhibitory effect of peppermint extracts against these emerging pathogens.