156 Handbook of herbs and spices
Cinnamon oil and its constituents (cinnamaledehyde and eugenol) have shown
antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, Enterococcus
faecalis, Staphylococcus aureus, Staphylococcus epidermis, Klebsiella pneumoniae,
Salmonella sp., and Vibrio parahaemolyticus (Chang et al., 2001). The volatile oils
of black pepper, clove, geranium, nutmeg, oregano and thyme – all of them containing
carvacrol – were effective against Enterococcus faecalis, Escherichia coli, Salm.
pullorum, Staph. aureus, Yersinia enterocolitica with the essential oil of thyme being
the strongest inhibitor (Dorman and Deans, 2000). Mint oil was bactericidal on
Staph. auerus, Salm. enteritidis and L. monocytogenes (Tassou et al., 1995, 2000).
Helander et al. (1998) have shown that carvacrol and thymol inhibited E. coli O157:H7
and Salm. enterica serovar typhimurium at MIC 3mM and 1mM respectively while
Kim et al. (1995a, b) found that 1.5% carvacrol was necessary to kill the pathogen.
Clove oil with its active principle eugenol inactivates Cl. perfingens and other
bacteria (Briozzo et al., 1988). Antibacterial effects have been reported for oregano,
black pepper, clove, thyme and the essential oil components thymol, carvacrol and
eugenol against Cl. sporogenes (Paster et al., 1990; Dorman and Deans, 2000) and
other bacteria such as E. coli, Staph. aureus and Salm. enterica ser. typhimurium
(Juven et al., 1994; Cosentino et al., 1999). The alcohol extract and the essential oil
from Curcuma longa inhibit the growth of Cl. septicum, Cl. novyi and Cl. sporogenes
(Lutomski et al., 1974). However, all these tests were performed in vitro with only a
limited number of tests performed in animals (Losa and Kohler, 2001).
Olive extract and its active compound oleuropein has also been proved to be
antimicrobial against pathogens such as Bacillus cereus, Staph. aureus, Salm. enteritidis,
L. monocytogenes (Nychas et al., 1990; Tassou et al., 1991, 2000; Tranter et al.,
1993; Tassou and Nychas, 1994, 1995a).
Plant extracts of Acacia catechu, Holarrhena antidysenterica, Peltophorum
pterocarpum, Psidium guajava, Punica granatum, Querqus infectoria, Uncaria gambir
and Walsura robusta demonstrated antibacterial activity against six strains of E. coli
O157:H7 with Querqus infectoria being the most active (Voravuthikunchai et al.,
2004). The antibacterial effect of Satureja montana L. (Lamiaceae) aromatic plant
and spice exhibited on important enteric bacterial pathogens, diarrhoeagenic E. coli,
Plesiomonas shigelloides, Shigella flexneri, Salm. Enterica serovar typhimurium,
Yersinia enterocolitica and Vibrio parahaemolyticus (Skocibusic and Bezic, 2003).
Maximum activity was observed against Shigella flexneri and E. coli. Shigella flexneri
is an important enteropathogen which causes a distinctive and complex disease,
bacillary dysentery, caused by invasion of the epithelial cells. The antimicrobial
properties of Shigella flexneri and Shigella sonnei are also possessed by cloves,
thyme, oregano, allspice, basil, rosemary and marjoram (Bagamboula et al., 2003).
Extracts of ginseng (Panax ginseng) roots and green tea (Thea sinensis) leaves
have been shown not only to enhance the growth of bifidobacteria but also to selectively
inhibit various clostridia (Ahn et al., 1990a, 1991). Recent in vivo investigations
using human volunteers have shown that intake of ginseng extract or green-tea derived
polyphenols favourably affected faecal microbiota (Ahn et al. 1990b; Okubo et al.,
1992).
10.3.1 Experimental assays
The experimental assays for testing the antimicrobial activity described in the literature
include: