The genus Legionella is a pathogenic group of Gram-negative bacteria that includes the species L. pneumophila, causing legionellosis. Legionella species typically exist in nature at low concentrations, in groundwater, lakes, and streams. Legionella are 0.3–0.9 μm wide and 2–20 μm long, depending on the age of the culture —fresh cultures of Legionella produce coccobacilli about 2–6 μm long, whereas older cultures may produce filamentous forms up to 20 μm long. L. pneumophila usually has limited motility, and some strains are completely non‑motile (Harrison & Taylor, 1988). They reproduce after entering man-made equipment, given the right environmental conditions.

It can become a health concern when it grows and spreads in human-made water systems like


  • Cooling towers (air-conditioning units for large buildings)
  • Hot tubs that aren’t drained after each use
  • Decorative fountains and water features
  • Hot water tanks and heater
  • Large plumbing systems
  • Showers and faucets

The bacteria live and grow in water systems at temperatures of 20 to 50 degrees Celsius (optimal 35 degrees Celsius). Legionella can survive and grow as parasites within free-living protozoa and within biofilms which develop in water systems. They can cause infections by infecting human cells using a similar mechanism to that used to infect protozoa.

It is common in many environments, including soil and aquatic systems, with at least 50 species and 70 serogroups identified. The bacterium, however, is not transmissible from person to person,(Winn WC 1996).

In 1976, an outbreak of severe pneumonia among the participants of the American Legion Convention in Philadelphia led to the description of Legionnaires’ disease by (Fraser et al. 1977). The disease was found to be caused by the bacterium Legionella pneumophila (Legionella after the legionnaires who were infected at the convention; pneumophila meaning “lung loving”), belonging to the family Legionellaceae. The generic term “legionellosis” is now used to describe these bacterial infections, which can range in severity from a mild, febrile illness (Pontiac fever) to a rapid and potentially fatal pneumonia (Legionnaires’ disease). Legionella has been retrospectively identified as the cause of outbreaks of Legionnaires’ disease since 1947 (Terranova, Cohen & Fraser, 1978; McDade, Brenner & Bozeman, 1979).

The most common form of transmission of Legionella is inhalation of contaminated aerosols produced in conjunction with water sprays, jets or mists. Infection can also occur by aspiration of contaminated water or ice, particularly in susceptible hospital patients.

Legionellosis is a generic term describing the pneumonic and non-pneumonic forms of infection with Legionella. The non-pneumonic form (Pontiac disease) is an acute, self-limiting influenza-like illness usually lasting 2–5 days. The incubation period is from a few and up to 48 hours. The main symptoms are fever, chills, headache, malaise and muscle pain (myalgia). No deaths are associated with this type of infection.

Before the development of an in vitro medium that could sustain legionellae (Feeley et al., 1978; Feeley et al., 1979), legionellae could only be grown by isolating them in guinea pigs or hen eggs (McDade et al., 1977; Morris et al., 1979). Currently, the preferred technique for checking other diagnostic methods is to grow the bacteria on direct culture. Primary isolation of Legionella spp. is carried out using a defined Legionella agar medium containing L-cysteine, such as Buffered Charcoal Yeast Extract (BCYE) agar. Supplements that reduce the background competing bacterial flora and yeasts may be added to increase selectivity of the media.

There are a number of manuals and laboratory procedures for the recovery of legionellae from environmental samples. In 1998, an international standard (International Organization for Standardization ISO 11731) was developed to incorporate the different strategies used by a number of institutions for efficient recovery and detection of legionellae (ISO, 2004).

Monitoring for legionellae is important for public health reasons to identify environmental sources which can pose a risk of legionellosis, such as evaporative cooling towers, hot- and cold-water distribution systems in buildings and associated equipment such as spa pools, dental units, air conditioning units, etc. Monitoring is also important for validation of control measures and ongoing verification that controls remain effective. Aqualytic Laboratories Limited has a program in place to carry out legionellae analysis in water using ISO 11731.We believe that deadlines are critical, time to market is imperative and mistakes are unacceptable.