A newly developed assay to study the minimum inhibitory concentration of Satureja spinosa essential oil.
OBJECTIVE
The minimum inhibitory concentration (MIC) of Satureja spinosa essential oil against Staphylococcus aureus, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica, Salmonella serovar Enteritidis PT4 and Bacillus cereus was comparatively assessed with an established optical density method as well as a novel impedimetric method.


RESULTS
The impedimetric analysis takes into account information of microbial growth, such as detection time, maximum conductance, and slope of the conductance curve. For each pathogen two levels of inoculation were studied, a high (10(5) CFU ml(-1)) and a low level (10(2) CFU ml(-1)). Non-linear regression analysis was used to fit the data using a modification of a previously published model, from which a more exact value can be obtained for the MIC. Both methods gave similar MICs as shown by t-test statistical analysis. Salm. Enteritidis seems to be the least sensitive to the action of S. spinosa essential oil followed by L. monocytogenes, E. coli, B.cereus and Staph. aureus. The MICs of low inoculum were lower than that of high inoculum.


CONCLUSIONS
The new impedimetric assay of MIC of essential oils can be considered a reliable rapid method for screening antimicrobial effectiveness of natural additives.


CONCLUSIONS
Determination of the minimum inhibitory concentration of an essential oil with the simple conductance technique and further study of the mode of action of its components is a good combination for obtaining additional knowledge for industrial application of such natural additives.
Laboratory of Microbiology and Biotechnology of Foods, Department of Food Science and Technology, Agricultural University of Athens, Athens, Greece.
N G
NG
Chorianopoulos
R J W
RJ
Lambert
P N
PN
Skandamis
E T
ET
Evergetis
S A
SA
Haroutounian
G-J E
GJ
Nychas
D000900:Anti-Bacterial Agents / Q000032:analysis* / Q000494:pharmacology; D001409:Bacillus cereus / Q000187:drug effects; D015169:Colony Count, Microbial / Q000379:methods; D019453:Escherichia coli O157 / Q000187:drug effects; D005516:Food Microbiology; D008089:Listeria monocytogenes / Q000187:drug effects; D008826:Microbial Sensitivity Tests / Q000379:methods; D009822:Oils, Volatile / Q000032:analysis* / Q000494:pharmacology; D019779:Salmonella enterica / Q000187:drug effects; D012477:Salmonella enteritidis / Q000187:drug effects; D031362:Satureja / Q000737:chemistry*; D013211:Staphylococcus aureus / Q000187:drug effects
D000900:Anti-Bacterial Agents; D009822:Oils, Volatile