# Isothiocyanates: An Overview of Their Antimicrobial Activity against Human Infections
## 4 Isothiocyanates Antimicrobial Properties against Human Pathogens
### Pseudomonas Aeruginosa  
_Pseudomonas aeruginosa_ are aerobic Gram-negative bacteria that can colonize different environments. _P. aeruginosa_ is an opportunistic pathogen that is able to regulate biofilm formation and the release of different virulence factors in response to cell-to-cell signaling and environmental stimuli. Pathogenic and non pathogenic bacteria are able to produce biofilms. This statement plays an important role in the social communication of bacteria and their ability to survive in the natural environment. Although biofilms exert a positive role in a variety of ecosystems they are often associated to the survival of pathogens during antibiotic treatment leading to worse clinical outcomes [89]. Indeed, it is known that _P. aeruginosa_ strain biofilm producers show a greater resistance to common antibiotic treatment [90; 91; 92] and they are often associated to medical device colonization and nosocomial infections [93]. Many bacteria, including _Pseudomonas_ strains are equipped with a quorum sensing (QS) system able to control biofilm production and the release of different virulence factor in response to environmental stimuli. Specifically, the QS system detects environmental stimuli and releases signal molecules, defined as \"auto-inducers\" that contribute to the microbial pathogenicity [94]. At least two major QS systems--_las_ and _rhl_--have been identified in _P. aeruginosa_. The _las_ QS systems is composed by _lasI_, the autoinducer synthase gene responsible for the synthesis of the correlate (\(N\)-[3-oxododecanoylI]-L-homoserine lactone autoinducer, and the _lasR_ gene that codes for a transcriptional regulator that determines the transcription of QS genes including virulence factors.The _rhl_ system similarly consists of the pair RhlI/RhlR, which responds to \(N\)-butyrylhomoserine lactone (C4-HSL) [94; 95]. QS in _P. aeruginosa_ regulates not only biofilm production, but also the release of important virulence factor such as pyocyanin that affects the central nervous system, the urological and the vascular system inducing inflammatory effect [96] and rhamnoid involved in the _P. aeruginosa_ dissemination across human epithelia [97]. Over the years, multi-resistant strains of _P. aeruginosa_ biofilm producers have been isolated from patients. The acquisition of new resistance phenotypes underlines the need for new antibiotic therapeutic strategies and anti-biofilm molecular compounds [90; 92; 93; 98; 99]. The antimicrobial activity of total extracts and powdered juice from _Moringa oleifera_ leaf (fresh and dried) against _P. aeruginosa_ were investigated by [PERSON] et al. [62]. The aim of the study was to determine if fresh or dried leaf from _Moringa oleifera_ was able to counteract the growth of _P. aeruginosa_ (BMLRU1017) strain and also what was the most effective extraction method that ensure the best growth inhibition. [PERSON] et al. indicated that _Moringa oleifera_ leaf showed antimicrobial activity against _P. aeruginosa_ and especially the powder obtained from fresh leaf juice (1175 \(\upmu\)g/disc) had a higher inhibitory effect (IZ = 39.60 \(\pm\) 0.49 mm) compared to tetracycline control (IZ = 18.30 \(\pm\) 0.12 mm). Regarding the extracts, only fresh leaf (1175 \(\upmu\)g/disc) displayed antimicrobial activity, and no inhibition halo was observed using extracts from dried leaf. Moreover ethanol extract from fresh leaf showed strong antibacterial effect (IZ = 21.21 \(\pm\) 0.05) comparable to the antibiotic. Fresh leaf cold water extract (1175 \(\upmu\)g/disc) displayed only a slight antibacterial effect (IZ = 15.00 \(\pm\) 0.34 mm), while hot water extracts did not display antimicrobial activity [62]. Recently the effects of synthetic ITCs against different clinical isolates of _P. aeruginosa_ were investigated by [PERSON] et al. [48]. The authors tested the antimicrobial properties of synthetic AITC,BITC and PEITC against 105 clinical isolates of _P.