Legionella is able to remain in water as free-living planktonic bacteria or to grow within biofilms that adhere to the pipes. It is also able to enter amoebas or to switch into a viable but not culturable (VBNC) state, which contributes to its resistance to harsh conditions and hinders its detection in water. Factors regulating Legionella growth, such as environmental conditions, type and concentration of available organic and inorganic nutrients, presence of protozoa, spatial location of microorganisms, metal plumbing components, and associated corrosion products are important for Legionella survival and growth. Finally, water treatment and distribution conditions may affect each of these factors. A deeper comprehension of Legionella interactions in water distribution systems with the environmental conditions is needed for better control of the colonization. To this purpose, the implementation of water management plans is the main prevention measure against Legionella. A water management program requires coordination among building managers, health care providers, and Public Health professionals. The review reports a comprehensive view of the state of the art and the promising perspectives of both monitoring and disinfection methods against Legionella in water, focusing on the main current challenges concerning the Public Health sector.

A total of 273 Escherichia coli isolates from raw and treated municipal wastewaters were investigated to evaluate the frequency and persistence of antibiotic resistance and to detect the occurrence of conjugative R plasmids and integrons. The highest resistance rates were against ampicillin (22.71%), tetracycline (19.41%), sulfamethoxazole (16.84%) and streptomycin (14.28%).Multiple antibiotic resistance was present in 24.17% of the isolates. Several multiple antibioticresistant isolates proved to be able to transfer en bloc their resistance patterns by conjugative R plasmids with different molecular sizes and restriction profiles. Class 1 integrons of 1 or 1.5 kbp were found in 5 out of 24 representative multiresistant E. coli isolates. Although wastewater treatments proved to be effective in eliminating Salmonella spp. and in reaching WHO microbiological standards for safe use of wastewater in agriculture, they were ineffective in reducing significantly the frequency of plasmid-mediated multiple antibiotic resistance in surviving E. coli. Since multiple antibiotic-resistant bacteria carrying integrons and conjugative R plasmids can constitute a reservoir of antibiotic-resistance genes in wastewater reclaimed for irrigation, risks for public health should be considered. Bacterial strains carrying R plasmids and integrons could contaminate crops irrigated with reclaimed wastewater and transfer their resistances to the consumers' intestinal bacteria.

Molecular epidemiology at local scale in Sicily (Italy) of ampicillin resistance in Salmonella spp. isolates from municipal wastewater (n = 64) and clinical specimens (n = 274) is described in comparison with previously examined Escherichia coli isolates (n = 273) from wastewater. High prevalence of antibiotic resistance (28.9%) with highest resistance rates against ampicillin (22.7%) was observed in E. coli isolates. Different resistance rates were observed in Salmonella according to the serovars, with prevalences of the same order in both wastewater and clinical isolates belonging to the same serovar (e.g., 91.7% ampicillin resistance in wastewater isolates vs. 70.8% in clinical isolates of the Salmonella serovar Typhimurium and 0% ampicillin resistance in both wastewater and clinical isolates of the Salmonella serovar Enteritidis). The beta-lactam resistance gene bla(TEM) was present in both wastewater and clinical Salmonella spp. isolates, with the exception of Salmonella enterica serovar Typhimurium isolates with a typical six-drug resistance pattern AmpChlSulTeStrSp that had the bla(PSE-1) gene. The bla(TEM) gene was present in all the E. coli isolates but one had the bla(SHV) gene. Several E. coli and some Salmonella isolates were positive for class 1 integrons with variable regions of 1.0 or 1.5 kb containing aadA1, dfrA17-aadA5, or dfrA1-aadA1 gene cassettes, whereas Salmonella serovar Typhimurium isolates with the six-drug resistance pattern were positive for both 1.0 and 1.2 kb integrons. Polymerase chain reaction replicon typing demonstrated the presence of multireplicon resistance plasmids in several isolates of E. coli, containing two to four of the replicons IncF, IncI1, IncFIA, and IncFIB, whereas other isolates showed resistance plasmids with only IncF, IncP, or IncK replicons. Replicon IncI1 was detected in one Salmonella isolate, whereas other isolates belonging to different serovars had IncN replicons. Analysis of isolates from wastewater can be a useful epidemiologic tool to monitor the prevalence of antibiotic resistance and genetic elements related to antibiotic resistance in Salmonella clones circulating in the human population.

Biological contamination is a typical issue in water treatment. Highly concentrated microbial suspensions in a water flow may cause filter occlusion and biofilm formation, affecting the lifespan and quality of water purification systems and increasing the risk of nosocomial infections. In order to contrast the biofilm formation, most of the conventional strategies rely on the water chemical modification and/or on the use of filters functional coatings. The former is unsafe for huge chemicals spilling required; therefore, we focus on the second approach and we propose the use of a sulfonated pentablock copolymer (s-PBC, commercially named Nexar™) as innovative multifunctional coating for improving the performance of commercial water filters. S-PBC-coated polypropylene (PP) samples were tested against the pathogen Pseudomonas aeruginosa. The covering of PP with s-PBC results in a more hydrophilic, acid, and negatively charged surface. These properties avoid the adhesion and proliferation attempts of planktonic bacteria, i.e., the biofilm formation. Inhibition tests were performed on the as-modified filters and an evident antibacterial activity was observed. The results point out the possibility of using NexarTM as coating layer for filters with antifouling properties and a simultaneous ability to remove bacteria and cationic dyes from water.

Legionella pneumophila contamination of water systems is a crucial issue for public health. The pathogen is able to persist in water as free-living planktonic bacteria or to grow within biofilms that adhere to and clog filters and pipes in a water system, reducing its lifespan and, in the case of hospital buildings, increasing the risk of nosocomial infections. The implementation of water management is considered to be the main prevention measure and can be achieved from the optimization of water system architecture, notably introducing new materials and strategies to contrast Legionella biofilm proliferation and so prolong the water system functionality. In this research, we propose a new smart surface against L. pneumophila biofilm formation. This is based on an innovative type of coating consisting of a sulfonated pentablock copolymer (s-PBC, commercially named Nexar™) deposited on top of a polypropylene (PP) coupon in a sandwich filter model. The covering of PP with s-PBC results in a more hydrophilic, acid, and negatively charged surface that induces microbial physiological inhibition thereby preventing adhesion and/or proliferation attempts of L. pneumophila prior to the biofilm formation. The antibiofilm property has been investigated by a Zone of Inhibition test and an in vitro biofilm formation analysis. Filtration tests have been performed as representative of possible applications for s-PBC coating. Results are reported and discussed.