# Isothiocyanates: An Overview of Their Antimicrobial Activity against Human Infections
## 4 Isothiocyanates Antimicrobial Properties against Human Pathogens
### Clostridium Difficile and Clostridium Perfringens  
The genus _Clostridium_ is composed of several different Gram-positive, endospore-forming, anaerobic species, including two enteric pathogens, _Clostridium perfringens_ and _Clostridium difficile_, that can threaten human health [76]. Ingestion of contaminated food, dietary factors and the imbalance of intestinal microflora induced by antibiotic therapy [77; 78] can cause _Clostridium_ infections [79; 80]. The prevalence and severity of _C. difficile_ infections have boosted research efforts to detect new virulence factors and to develop new treatments and prevention regimens.  
In order to identify phytochemical compounds that preserve the natural intestinal microflora and ensure pathogen strain growth inhibition, [PERSON] and [PERSON] [47] evaluated the antimicrobial activity of phenethyl isothianate (PEITC) purified from _Sinapis alba_ seed oil against pathogenic _Clostridium_ species [47]. The results demonstrated that 2 mg/disc of PEITC inhibited _C. difficile_ ATCC 9689 and _C. perfringens_ ATCC 13124, with an inhibition zone >30 mm. The authors did not compare these results with those obtained using conventional antibiotics so the potential clinical efficacy of PEITC against infections of both _Clostridium_ strains cannot be indicated. Furthermore, hypothetical inhibitions towards the commensal bacteria (_Bifidobacterium bifidum_, _B. breve_, _B. longum_, _Lactobacillus acidophilus_ and _L. casei_) were evaluated and PEITC was shown not to affect the intestinal microflora. In order to understand if the chemical structure of ITCs may influence their antimicrobial activity against _Clostridia_ species, the authors [47] compared the results obtained using natural PEITC from _Sinapis alba_ seed oil extract with synthetic ITCs containing aromatic hydrocarbons (benzyl and benzoyl groups) and aliphatic hydrocarbons (acetyl-, allyl-, butyl-, ethyl- and methyl groups). Antimicrobial activity of natural PEITC was comparable to synthetic BITC using a similar dose (2 mg/disc). On the contrary, benzoyl ITC showed a decrease in growth-inhibiting activity against _Clostridia_. No growth inhibition properties were also observed using aliphatic ITCs such as AITC. These results suggested that aromatic ITC were favorites due to their ability to cross bacterial membrane structures and they probably could exert their antimicrobial activity better than aliphatic ITCs. Moreover, regarding aromatic ITCs, the decrease of inhibition activity observed for benzoyl ITC--that only differs from benzyl isothiamate by the presence of a carbonyl (-C=O) group--suggested that ITCs showed the highest activity against _Clostridia_ when only one benzyl group is involved [47].  
Regarding the resistant strains of _Clostridia_, [PERSON] and [PERSON] [81] assessed the antimicrobial activity of a horseradish root extract (containing 59.9% AITC, 35.8% PEITC and 1.5% 3-butenyl ITC) against _C. perfringens_ KCTC 3269 resistant strain compared to chlorhexidine digluconate used as a control [81]. The natural extract (MIC = 6.67 mg/mL and MBC = 16.67 mg/mL) inhibited _C. perfringens_ KCTC 3269 growth, but its efficiency was lower than that of the control antibiotic (MIC = 0.13 mg/mL and MBC = 0.21 mg/mL). In addition the authors evaluated the contribution of AITC to the slight antimicrobial property of horseradish root by comparing the antimicrobial activity of the natural extract with synthetic AITC (MIC = 8.33 mg/mL and BMC = 8.33 mg/mL). Natural extract and synthetic AITC showed similar antibacterial activity, suggesting that the AITC is the main horseradish ITC responsible for the slight antibacterial effect, despite the fact its effectiveness is very low. Although the antimicrobial assay and the used strains were not comparable, these results appear to be in agreement with [PERSON] and [PERSON] [47] who indicated the inability of the aliphatic AITC to counteract _Clostridia_ species.