Decreasing Pasteurization Treatment Efficiency against Amoeba-Grown Legionella pneumophila—Recognized Public Health Risk Factor

Abstract

Legionellae are gram-negative bacteria most commonly found in freshwater ecosystems and purpose-built water systems. In humans, the bacterium causes Legionnaires’ disease (LD) or a Pontiac fever. In this study, the different waters (drinking water, pool water, cooling towers) in which Legionella pneumophila has been isolated were studied to assess the possible risk of bacterial spreading in the population. The influence of physical and chemical parameters, and interactions with Acanthamoeba castellanii on L. pneumophila, were analyzed by Heterotrophic Plate Count, the Colony-forming units (CFU) methods, transmission electron microscopy (TEM), and Sequence-Based Typing (SBT) analysis. During the study period (2013–2019), a total of 1932 water samples were analyzed, with the average annual rate of Legionella-positive water samples of 8.9%, showing an increasing trend. The largest proportion of Legionella-positive samples was found in cooling towers and rehabilitation centers (33.9% and 33.3%, respectively). Among the isolates, L. pneumophila SGs 2–14 was the most commonly identified strain (76%). The survival of Legionella was enhanced in the samples with higher pH values, while higher electrical conductivity, nitrate, and free residual chlorine concentration significantly reduced the survival of Legionella. Our results show that growth in amoeba does not affect the allelic profile, phenotype, and morphology of the bacterium but environmental L. pneumophila becomes more resistant to pasteurization treatment.

Multi-criterion analysis of the effect of physico-chemical microbiological agents on Legionella detection in hotel water distribution systems in Crete

“…Legionella show higher tolerance for heat when associated with amoeba and biofilms, thus showing the need to examine other prevention factors such as disinfectants and nutrient availability (Cervero-Arago et al, 2015). Knezevic et al recorded a statistically significant difference in the median temperature among the samples positive for Legionella and those negative for the bacterium, whether the water was warm or cold (Knezevic et al, 2022). The same study also concluded that L. pneumophila serogroup 1 showed a preference for higher temperatures compared to the rest serogroups.…”

“…Some other studies have shown a significant correlation between Legionella contamination and HPC at specific temperatures, for example at 30°C, while others have only associated the two parameters in certain temperatures and only for very high HPC values (>100 CFU/ml) revealing the need for HPC and biofilm to be examined with more parameters such as water stagnation (Bargellini et al, 2011;Volker et al, 2016). A recent study (Knezevic et al, 2022) reported that HPC was positively associated with Legionella only when HPC was recorded following incubation on blood agar plates at 36°C for four days. At less days of incubation or when yeast extract was used as a medium, no significant correlation was reported.…”

“…The chlorine levels of the water seem to correlate negatively with L. pneumophila growth except for serogroup 1 which seems to be more resistant to the disinfectant. Knezevic et al reported a simultaneous presence of chlorine along with Legionella, however the presence of the bacterium was reported at low to very low levels of the disinfectant (Knezevic et al, 2022).…”

Environmental Monitoring of Legionella in Hospitals in the Campania Region: A 5-Year Study

“…Favourable factors to the growth of this bacterium are temperatures between 25 °C and 45 °C (but ranges between 5.7 °C and 63.0 °C can determine its survival); stagnant water [ 10 ], in which Legionella in amoebae copiously reproduces [ 11 ]; low flow [ 12 ]; pH values between 5.5 and 9.2; biofilm and protozoa [ 2 ]; inorganic elements (iron, zinc and potassium) and organic and inorganic compounds [ 13 ]; existence of water systems of old facilities [ 14 ]; dead branches in complex water structures [ 15 ]; low total chlorine levels [ 16 ]; and low free residual chlorine levels [ 17 ]. In addition, man-made disasters [ 18 ], natural disasters, flooding [ 19 ], water system interruptions, changes in disinfection methods of water systems, and water network breaks [ 11 ] are risk factors for Legionella growth.…”