3. Expression of results in antimicrobial studies

Regarding the expression of the results, the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and inhibition percentage of growth are cited by researchers as the most common measurements of antimicrobial performance. In this sense, there are two primary categories for measuring an antimicrobial agent: bactericidal or bacteriostatic. Bacteriostatic refers to an agent that prevents the growth of bacteria and a bactericidal agent kills bacteria, but a complete separation of these definitions might be further pursued. This difference only applies under strict laboratory conditions and is inconsistent for a particular agent against all bacteria; indeed, it can be influenced by growth conditions, bacterial density, test duration, and extent of reduction in bacterial numbers. Furthermore, bacteriostatic activity has been defined as an MBC/MIC ratio of 4, but numerous technical problems and other factors can affect the determination of that ratio and may have an important impact on the interpretation of the in vivo situation. Although MBC and MIC data may provide information on the potential action of antibacterial agents in vitro, it is necessary to combine this information with pharmacokinetic and -dynamic data to provide more meaningful predictions of efficacy in vivo [49]. Considering this information, no pharmacokinetic or -dynamic studies have been conducted involving the Taraxacum genus to date. The majority of the research (not only as an antimicrobial agent, but also as an important medicinal plant) has been performed from a traditional perspective, based on centuries of oral traditions. Only in recent decades has Taraxacum been subjected to a considerable amount of tests, principally due to its anti-inflammatory and anti-carcinogenic properties [50]. The antimicrobial properties of this genus have been widely known, but only very general studies have been performed to date, with information that is difficult to interconnect as the action mechanisms and the specific compounds involved have not yet been elucidated. Nevertheless, all the data gathered here provides a promising case for the advantageous commercial usage of this genus.

for in vitro conditions frequently cannot be reached in vivo because the infecting microorganisms are never exposed to constant concentrations of an antimicrobial agent. Microorganisms in vivo are subject to competition from other microorganisms present in the tissue, so decreased microbial activity might be due to this competition rather than directly related to the antimicrobial activity of the plant extract. Moreover, temperature, pH, and humidity are more difficult to control in an in vivo system. Another issue to consider is that microorganisms in a microtiter plate are in the form of a suspension, whereas bacteria associated with different illnesses naturally form biofilms (organ and tissue infections, dental plaque, etc.), representing an extra challenge for antimicrobial agents [1]. Until now, only studies regarding fruit and vegetable infections have shown a parallel between in vitro and in vivo responses to Taraxacum extracts (Chapter 1; see Section 2.2.2), but

*Taraxacum* Genus: Extract Experimental Approaches http://dx.doi.org/10.5772/intechopen.72849 289

The following sections are referred and discussed in accordance with the information provided in Table 2 (see Chapter 1) and Figure 1. It should be noted that the impact of the parameters mentioned in these sections, except for solvent selection, on the antimicrobial properties of the

Scientific criteria should be used in the selection of the sample material. To avoid the use of random criteria, the selection of plants should be made from an ethnopharmacological perspective. All the species tested need to be perfectly described and identified, including location, season, date, and time of day harvested. The use of commercial samples should be limited to cases of standardized extracts or defined phytomedicines [3]. The phytochemical composition of Taraxacum (and plants in general) is known to depend on the season in which

activity

Negative antimicrobial activity

studies in animal tissues and organs have not yet been performed directly.

Taraxacum parts mentioned in the text Number of extracts tested Positive antimicrobial

Total 232 152 80

Table 2. Summary of the antimicrobial results regarding Taraxacum plant parts tested in main studies.

Root 51 17 11% 34 43% Leaves 38 28 18% 10 13% Flower 13 10 7% 3 4% Honey 6 4 3% 2 3% Herb 3 3 2% 0 0% Aerial 32 24 16% 8 10% Whole plant 8 0 0% 8 10% No information 81 66 43% 15 19%

5. Factors affecting antimicrobial activity of extracts

Taraxacum genus has not yet been studied.

5.1. Plant material collection

Considering this general approach, most of the research regarding Taraxacum indicates MIC values and inhibition percentages measured in relation to area (in solid cultures) or optical density (in broth cultures). The MBC values were not identified in the consulted references. An observation was made that the MIC definition sometimes differed between publications, another obstacle for data comparison. Some MIC definitions are: "the lowest concentration of the tested products that inhibited the development of microorganisms" [40]; "the lowest concentration required to show a marked inhibition of mycobacterial growth at 72 h" [43]; "the lowest concentration of the compound to inhibit the growth of microorganisms" [19]; and "the lowest sample concentration at which no pink color appeared" [15]. This indicates that MIC values are relative to each study and is compounded by the fact that the complete procedure (including extraction process and sample manipulation) is not standardized and varies considerably among the authors. Furthermore, due to the different solubilities and stabilities of the various compounds in the solvent and the sensitivity of the antimicrobial activity assay performed, directly comparing MIC values is difficult and sometimes confusing. As further examples, in three different studies, the authors reported MIC values in the 0.05–5.0 mg range for ethanol, methanol, or water extracts against S. aureus using broth microdilution or agar diffusion method as bioassays [13, 17, 34]. This meant that only MIC values could be used as a comparison against the positive control under the same conditions and may only be considered as an initial screening for further antimicrobial approaches; it cannot provide a reliable comparison between studies. The MIC/ MBC ratio might be an option for making antimicrobial activity more independent of assay conditions if similar extraction conditions and sample manipulation have been performed.
