Factors Affecting Antimicrobial Activity

Although it has become obvious that a fluorine atom in position 6 is the best substituent for antimicrobial activity, the reasons for this effect remain unclear. A comparative study of numerous quinolones seems to indicate that this F-substitution in position 6 affords both a better affinity with gyrase (2-17 times) and the best cell penetration (1-70 times).The presence of this fluorine lowers the basicity of the nitrogen-containing substituent in position 7, and this fact could play a role. However, there are multiple factors to take into account and interpretations must be carefully considered. Thus, replacing the fluorine atom by a chlorine in pefloxacin does not affect the activity on the enzyme, but a decrease of the bacterial activity is observed. This shows the importance of the pharmacokinetic factors. ... 

Secondary metabolites include essential oils, used in the flavour and fragrance industries. Essential oils are found in over 50 plant families and represent terpenoids and other aromatic compounds accumulating typically at relatively low concentrations (usually <1% of fresh weight, but can be up to 20%), but which have useful antimicrobial activity (Biavati el a/., 2003). Production of essential oils by plants is affected by many factors influencing plant growth. 

Unfortunately, the knowledge about the effects of mycotoxin exposure on the human microbiome is still limited and reported studies mainly refer to the role played by intestinal microflora in mycotoxin detoxification in animals. Nonetheless, mycotoxins may actually affect the gut microflora, as some of them exhibit antimicrobial activities in animals. In addition, it has been proven that chronic exposure to low doses of DON may induce a shift towards intestinal aerobic bacteria in pigs. Since the number and composition of intestinal microflora are significantly modified in inflammatory bowel diseases in humans, with an increase in the number of aerobic bacteria and a parallel decrease in the number of anaerobic bacteria, mycotoxin exposure might represent a potential risk factor for chronic intestinal inflammatory diseases. Since data supporting or contrasting these hypothesis are still poor, further studies should be addressed to better understand the role played by mycotoxins in the imbalance of intestinal microflora in humans. 

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