Legionella colonization of water supply pipes is a significant public health problem. The objective of this work was to evaluate Legionella colonization in hotel hot water systems and to investigate the relationship between metal concentrations, piping materials (galvanized iron pipes and plastic pipes), and Legionella proliferation. Concentrations of calcium and magnesium ions and the presence of Legionella pneumophila were determined in a total of 108 water samples from the hot water systems of four hotels in Split-Dalmatia County over a 12-month period, and additional data on piping materials were collected. L. pneumophila was isolated in 23.1% of all samples—in 28.8% (15/52) of water samples from galvanized iron pipes and in 17.8% (10/56) of samples from plastic pipes. L. pneumophila serogroups 2–14 were isolated from all samples. This study found higher prevalence of L. pneumophila at higher concentrations of Ca and Mg ions (except for Mg and plastic pipes). The metal parts of the water supply may be important factors in Legionella contamination due to the possibility of lime scale or roughness of the pipes. Higher Ca and Mg ion concentrations increased the risk of Legionella colonization.

SUMMARY: Microorganisms in the air are part of the bioaerosol which is composed of different particles of biological substances, dust particles, bacteria cells and their portions, mould spores and a number of by-products of their metabolism. This research focuses on analysing the primary microclimate indicators (temperature and relative humidity) and the presence of microorganisms in the work environment (air). Measurements were taken after the process of sterilisation of infective waste over three months with the objective to determine the total number of aerobic mesophilic bacteria and the total number of moulds. The microclimate indicators were measured with an attested device. The study monitored the microbiological purity of the air in a given place using the sedimentation method, with samples subsequently processed in a microbiology lab in keeping with the prescribed standards. After incubation and following the counting of developed colonies on microbiological substrates (Tryptic soy agar and Sabouraud dextrose agar), different strains of bacteria and moulds were identified. The most common were Gram (+) sporogenes bacteria Micrococcus spp and Staphylococcus spp., and as for fungi the most commonly found were Aspergillus spp and Penicillium spp. It was found that temperature and relative humidity affect the total number of aerobic mesophilic bacteria and fungi which was confirmed using the Wilcoxon equivalent pairs test at the level of statistic significance p<0.05.

The presence and control of bacteria in water distribution systems (WDS) is a global problem that warrants appropriate water disinfection that minimizes exposure, especially to pathogenic microorganisms. Chlorine is commonly used for drinking water disinfection, but the chlorine dose used should be balanced with the need to minimize the formation of byproducts. Therefore, modeling of residual chlorine is an interesting alternative to improve and control disinfection. In this study, the presence of bacteria in water samples from a WDS was monitored regularly and used together with added chlorine to model bacteria and free residual chlorine. This paper presents the application of two empirical models for predicting residual chlorine concentration and bacterial counts in a WDS. The first is a multiple linear regression model and the second is a nonlinear artificial neural network (ANN). The development of both models is based on representative data obtained from the Split-Dalmatia County continuous WDS in Croatia. The obtained results indicate that the developed model ANN can successfully describe the relationship between residual chlorine and bacterial count and can be used for estimation of residual chlorine and total bacterial count in WDS.