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The in vitro antibacterial effect of permethrin and formaldehyde on Staphylococcus aureus
Philip Nikolic1, Poonam Mudgil1, John Whitehall1
1School of Medicine, Western Sydney University, Campbelltown, NSW, Australia.
Abstract:
Antibiotic-resistant strains of bacteria such as methicillin-resistant Staphylococcus aureus are a threat to human health, and effective treatment options against them are needed. This study aimed to determine whether the insecticide permethrin was capable of inhibiting the growth of S. aureus or if some other component of a permethrin cream was responsible for a decrease in scabies associated bacterial infection previously observed. Ten S. aureus strains were grown in the presence of permethrin and formaldehyde both alone and in combination with percent inhibition determined by viable counts. Also, a time-kill assay was conducted on S. aureus exposed to the same conditions. Finally, the morphology of S. aureus grown in the presence of permethrin was examined by scanning electron microscopy. Bacterial inhibition by permethrin ranged from 0% to 41% whereas inhibition by formaldehyde was 100%. The time-kill curves of permethrin exposed cells were very similar to the positive growth control while the formaldehyde and combination exposure showed complete inhibition even at the 0-hr time point. The scanning electron micrographs of permethrin grown S. aureus showed healthy cocci cells with no sign of cell damage. Our results show that permethrin is not capable of inhibiting the growth of bacteria enough for it to be termed bactericidal. Formaldehyde is a known antiseptic and therefore was responsible for the antibacterial effect observed after the use of permethrin cream.
Insights
Permethrin does not inhibit methicillin-resistant Staphylococcus aureus (MRSA) growth. Formaldehyde, an antiseptic in permethrin cream, was responsible for the observed antibacterial effects against MRSA.
Area of Science:
- Microbiology
- Bacteriology
- Dermatology
Background:
- Antibiotic-resistant bacteria, like methicillin-resistant Staphylococcus aureus (MRSA), pose significant health risks.
- Effective treatments against MRSA are urgently needed.
- Previous observations suggested a decrease in scabies-associated bacterial infections after permethrin cream use.
Purpose of the Study:
- To investigate the antibacterial efficacy of the insecticide permethrin against Staphylococcus aureus.
- To determine if permethrin or another component in permethrin cream inhibited bacterial growth.
- To identify the specific agent responsible for antibacterial effects in permethrin cream.
Main Methods:
- Ten strains of Staphylococcus aureus were cultured with permethrin and formaldehyde, alone and combined.
- Bacterial inhibition was quantified using viable counts and time-kill assays.
- Scanning electron microscopy examined Staphylococcus aureus morphology after exposure to permethrin.
Main Results:
- Permethrin exhibited limited bacterial inhibition (0%–41%), while formaldehyde demonstrated 100% inhibition.
- Time-kill assays showed permethrin-exposed cells behaved similarly to controls; formaldehyde and combination exposures resulted in complete inhibition.
- Scanning electron microscopy revealed no cell damage in permethrin-exposed Staphylococcus aureus.
Conclusions:
- Permethrin lacks sufficient bactericidal activity against Staphylococcus aureus.
- Formaldehyde, a known antiseptic, is the component responsible for the antibacterial effects observed with permethrin cream.
- This study clarifies that permethrin itself is not the antibacterial agent in the cream.
