Abstract
Legionella spp are the causative agents of Legionnaires’ diseases, which is a pneumonia of important public health concern. Ubiquitous freshwater and soil inhabitants can reach man-made water systems and cause illness. Legionella enumeration and quantification in water systems is crucial for risk assessment and culture examination is the gold standard method. In this study, Legionella recovery from potable water samples, at presumably a low concentration of interfering microorganisms, was compared by plating on buffered charcoal yeast extract (BCYE) and glycine, vancomycin, polymyxin B, cycloheximide (GVPC) Legionella agar media, according to the International Standard Organization (ISO) 11731: 2017. Overall, 556 potable water samples were analyzed and 151 (27.1%) were positive for Legionella. Legionella grew on both BCYE and GVPC agar plates in 85/151 (56.3%) water samples, in 65/151 (43%) on only GVPC agar plates, and in 1/151 (0.7%) on only BCYE agar plates. In addition, GVPC medium identified Legionella species other than pneumophila in six more samples as compared with the culture on BCYE. Although the medians of colony forming units per liter (CFU/L) detected on the BCYE and GVPC agar plates were 2500 and 1350, respectively (p-value < 0.0001), the difference did not exceed one logarithm, and therefore is not relevant for Legionella risk assessment. These results make questionable the need to utilize BCYE agar plates to analyze potable water samples.
Highlights
Legionella is a water-born pathogen widely spread in man-made water systems, responsible for a severe pneumonia and a flu-like illness, named Legionnaires’ disease (LD) and the Pontiac fever, respectively
Potable water samples were analyzed according to the ISO1173: 2017, in order to compare the Legionella recovery obtained by plating on buffered charcoal yeast extract (BCYE) and GVPC agar plates
We observed that GVPC was more efficient in detecting Legionella than BCYE medium
Summary
Legionella is a water-born pathogen widely spread in man-made water systems, responsible for a severe pneumonia and a flu-like illness, named Legionnaires’ disease (LD) and the Pontiac fever, respectively. At the present time, 62 Legionella spp. have been identified and less than a half were pathogenic, Legionella pneumophila was surely the most frequently found in LD cases. Outbreak investigations have widely demonstrated that the most frequent sources of infection are water systems of different buildings, such as hotels or hospitals and, showers, cooling towers, and spa pools [5,6]. The timely identification of the source of an infection is of great importance to prevent clusters or outbreaks and culture examination is the gold standard for the analyses of water samples. Molecular methods have been demonstrated to be highly sensitive and specific, as well as able to detect all Legionella species and serogroups, they remain impracticable for Legionella enumeration because they detect DNA of both living and dead bacteria [7,8]
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