# The Emergence of Antibioticstics Resistance Genes, Bacteria, and Micropollutants in Grey Wastewater
## 2 Emerging Pollutants
### Ecotoxicological Effects of EMPs  
Triclosan (TCS) is a common antimicrobial chemical in numerous PCPs (soaps, sanitizers, and toothpaste) [52] and is widely detected in aquatic environments at \(\mu\)g/L [53; 54] to mg/L level [55]. It can serve as an external pressure to co-select for triclosan resistance and antibiotic resistance in many bacteria [56; 57; 58]. Triclosan induces oxidative stress, causing genetic mutations in a few genes, such as _marR_, _frdD_, _fabI_, _acrR_, and _soxR_[59; 60; 61]. The gene _fabI_ is an acyl carrier protein reductase gene, a key enzyme in fatty acid synthesis in bacteria [62]. The interference with fatty acid synthesis results in modifications of the membrane structure, which causes less antibiotic uptake [63]. Subinhibitory concentrations of triclosan decrease the susceptibility of _E. coli_ to ciprofloxacin, kanamycin, and gentamicin due to alteration of the membrane structure and biofilm formation [64]. Likewise, _Stentrophomonas maltophilis_ exposed to triclosan resulted in overexpression of the multidrug efflux pump SmeDEF and reportedly reduced the susceptibility to chloramphenicol, tetracycline, and ciprofloxacin [65]. Similarly, _Salmonella enterica_ exposed to triclosan with increasing concentrations showed overexpression of the AcrAB efflux pump and reportedly reduced susceptibility to chloramphenicol, tetracycline, and ampicillin [66]. An efflux pump overexpression suggests the co-selective potential for more antimicrobial chemicals. In addition, _E. coli_ exposed to triclosan also resulted in overexpression of the multidrug efflux pump and a transcription of genes encoding beta-lactamases. In contrast, the expression of genes related to membrane permeability decreases [61]. [PERSON] et al. [67] documented that exposure to antimicrobials methyl-, ethyl-, propyl-, butylparaben, triclocarban, and triclosan increases ARGs in the microbiome. Parabens are widely used as preservatives in many pharmaceutical, food, and cosmetic products due to their low toxicity [68]. They are often used in small amounts and primarily prevent bacteria growth and prolong shelf life. The mode of action against microorganisms mostly interferes with cellular membrane transfer processes. The effectivity of the paraben is correlated with the size of the chemical; propylparaben is considered more active against most bacteria than methylparaben [69]. Propylparaben specifically induces the permeabilization of bacterial membranes, causing the release of potassium [70; 71]. The mechanisms of microbial resistance to parabens need to be better understood. Parabens are less active toward Gram-negative than Gram-positive bacteria [72; 73]. Paraben resistance has been linked to the cell wall characteristics and non-specific efflux systems [74]. However, so far, only a few cases of resistance to parabens have been reported, occurring in the specific strains of _P. aeruginosa_, _Burkholderia cepacia_, and _Cladosporium resinae_[68]. [PERSON] et al. [75] reported biodegradation of methyl- and propylparaben under aerobic and anoxic conditions, and benzoic acid was identified as one of the significant degradation products, thus reducing the efficacy of the compound. Tonalide and galaxolide are the most used synthetic fragrance compounds in various PCPs, such as detergents, perfumes, deodorants, skin creams, and soaps [76]. A tonalide concentration has been detected in wastewater treatment plants (WWTP), ranging between 0.086 and 12.5 \(\mu\)g/L and 0.043 and 16.6 \(\mu\)g/L for galaxolide [77]. They are moderately soluble in water and thus increase the possibility of accumulation in the environment [78]. Tonalide and galaxolide are volatile lipophilic compounds and can, therefore, relatively easily penetrate through the cell wall of microorganisms. They are more active against Gram-positive than Gram-negative bacteria [79].