It was a little disconcerting to this reviewer to find that the reason certain bacteria are classified as either Gram positive or Gram negative relates to a staining technique!
Gram-positive bacteria will retain the stain’s crystal violet color, while Gram-negative bacteria will end up either red or pink in this process to classify the bacteria. (We recommend reading Wikipedia’s article1 on Gram-negative bacteria for a better understanding of the process.)
Actually, it’s a little more technical than just this colorful bacterial reaction to staining. Gram-positive bacteria have a “thicker peptidoglycan layer in their cell wall beneath the cell membrane” . . . while the “thinner peptidoglycan of Gram-negative bacteria are more resistant to antibiotics than Gram-positive due to their relatively impermeable lipid [fat] based bacterial outer membrane.”2
The take-home message here is that Gram-negative bacteria are more likely to develop resistance to antibiotics.
Our study today comes to us from scientists at the Department of Molecular Biology and Biotechnology, Atomic Energy Commission, Damascus, Syria.
The study begins by noting that “Medicinal plants are considered new resources for producing agents that could act as alternatives to antibiotics in the treatment of antibiotic-resistant bacteria. The aim of this study was to evaluate the antibacterial activity of 28 plant extracts and oils against four Gram-negative bacterial species.”3
This study is available for downloading at no charge at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3895893/pdf/ijms-39-36.pdf. The reader will find tables that list the 10 plant extracts and 18 essential oils that were tested against the four Gram-negative bacteria: Escherichia coli 0157:H7, Yersinia enterocolitica 09, Proteus spp., and Klebsiella pneumoniae.
The reader will easily recognize the killer E. coli (the tragic fast-food hamburger incidents come to mind). Yersinia enterocolitica 09 is a zoonotic disease (afflicting both humans and animals), Proteus spp. often causes urinary tract infections and can be deadly for immunocompromised individuals, and Klebsiella pneumoniae. This Gram-negative killer can be found harmlessly in the normal flora of the mouth, skin, and intestines. But, “it can cause destructive changes to human lungs if aspirated.”4 This bacterial species is especially deadly when the antibiotic-resistant strain is contracted in health care settings among patients with weakened immune systems.
Plant Extracts and Essential Oils That Eradicate the Negatives!
Table 2 of this study explains that of the 10 plant extracts, eight of them, “O. syriacum L., T. syriacus, S. aromaticum, C. zeylanicum, L. nobilis L., J. foetidissima, A. sativum L., and M. fragrans had good antibacterial activities against the Gram-negative bacteria, whereas the rest of the studied extracts were ineffective.”5
The essential oils that proved effective were Origanum syriacum L. (Syrian oregano), Thymus. syriacus Boiss (a Syrian thyme), Syzygium aromaticum L. (clove), and Cinnamomum zeylanicum L. (a synonym for Cinnamomum verum, cinnamon oil). The researchers stated, “It can be logically assumed that the above-mentioned plant extracts and oils have bactericidal effect on Gram-negative bacteria, especially against Proteus spp. and K. pneumoniae.”6
We loved that the researchers recognized an essential oil fact perhaps not known well enough! “Since the antibacterial effectiveness of medicinal plants varies dramatically depending on the phytochemical characteristics of plant families and subfamilies, it is not surprising to note the difference in this efficacy even when using samples taken from the same plant, but from two different regions.”7
Al-Marini, op cited.