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Diamidex’s microcolony counter is revolutionizing the way we identify and count bacteria.

It is easy to forget in the middle of the coronavirus pandemic that many other pathogenic microorganisms live in our environment. A recent article pointed out the risk of an outbreak of Legionnaire’s disease (collectively known as legionellosis with Pontiac fever) ensuing from the shutdown of commercial buildings (Shiffman, 2020). Legionnaire’s disease is an environment-related, acute respiratory infection caused by the Legionella bacteria, more specifically the Legionella pneumophila species. The disease is endemic to South-East Asia but surprisingly the incidence of legionellosis is lower than in most western nations (Liam et al., 2001).

A study by Yong et al. (2010) identified the presence of Legionella pneumophila in 75% of cooling towers sampled. The results were consistent with those observed in an earlier study by Ngow et al. (1992). Yong et al. suggest a few hypotheses to explain the frequent occurrence of L. pneumophila in water cooling towers. One relates to the warm and humid weather in Malaysia, but enhanced resistance to chlorine and ability to survive perennially in the environment is another. Despite these, surprisingly, no outbreaks of Legionella infection have been reported in Malaysia. In fact, a recent study confirmed that L. pneumophila accounts for a very small subset of pneumonia cases in a local Malaysian hospital (Lourdesamy Anthony AI et al., (2020). Nevertheless, it is worrying that cooling towers have such a high rate of Legionella contamination. Malaysia does not mandate routine screening of water from cooling towers but strongly encourages it. As demonstrated in Singapore, it is very effective in maintaining low levels of contamination.

Legionella bacteria count is performed in government laboratories or any laboratory accredited by the Singapore Ministry of Health. The count primarily uses the gold standard accredited traditional culture method (ISO 11731). However, the method usually takes between 10 to 14 days before a microbiologist can enumerate the bacteria, which represents the time necessary for the microcolony to become visible to the naked eye. The Pasteurian method remains to date the only reliable method to detect and count microorganisms. It is the reference in many industries that require monitoring of microorganisms, but it necessitates precious time. That was until Sam Dukan and his co-workers introduced a rapid detection and identification method of culturable Legionella pneumophila in Angewandte Chemie (Mas Pons J. et al., (2014)).

Their strategy relies on the specific metabolic incorporation of a modified molecule (DIAMIDEX proprietary sugar pLeg-N3) by growing Legionella pneumophila. Click chemistry is then used to reveal and enumerate the tagged bacterial colonies using fluorescence. This revolutionary method reduces the time of incubation to just 48 hours before microcolony enumeration. MICA, a piece of revolutionary optical equipment, is also part of the Diamidex technology and allows the detection of fluorescent microcolonies. Based on this technology, the MICA Legionella assay was developed that allows the semi-automatic counting of all culturable serogroups of L. pneumophila (Lp) with the help of dedicated software. The software uses machine learning to recognize specifically Lp microcolonies. The assay is extremely specific and sensitive in labelling culturable Lp only.

Going back to the legal requirements of counting Lp in cooling towers, these above-mentioned characteristics are extremely important. Firstly, because laboratories often have difficulty enumerating Legionella in dirty waters because of the presence of interfering flora. This often results in “uninterpretable results”. The short incubation time minimizes those uninterpretable results, as the interfering flora has no time to grow. Secondly, the results can be confidently reported since neither dead Lp, nor other bacterial species will be detected. The results are more accurate since all Lp microcolonies present are counted and not just a few representative ones.

When compared to the ISO 11731 standard, the DIAMIDEX technology demonstrates astounding accuracy and reliability. Additionally, it can provide results in CFU/mL or CFU/L*, thus resolving the normalization issues between regulatory analyses and routine/emergency analyses. Therefore, it allows a better Legionella risk assessment. Using this patented technology, Diamidex offers tailored solutions for a wide range of industries and markets. Whatever your needs are, there is always a MICA solution for you.

For more information, please visit Diamidex or contact us today!


  1. Shiffman, J. “Buildings Closed by Virus Face Another Risk: Legionnaires' Disease” Business Times, (28 Apr. 2020). Originally published by Reuters (24 Apr. 2020) Retrieved from Buildings closed by virus face another risk: Legionnaires' disease, Real Estate - THE BUSINESS TIMES

  2. Liam CK, Lim KH, Wong CM. Community-acquired pneumonia in patients requiring hospitalization. Respirology. 2001 Sep;6(3):259-64. doi: 10.1046/j.1440-1843.2001.00336.x. PMID: 11555386.

  3. Yong SF, Goh FN, Ngeow YF. Legionella species and serogroups in Malaysian water cooling towers: identification by latex agglutination and PCR-DNA sequencing of isolates. J Water Health. 2010 Mar;8(1):92-100. doi: 10.2166/wh.2009.002. PMID: 20009251.

  4. Ngeow YF, Tan CH, Lim SY. Legionella species isolated from cooling towers in Kuala Lumpur. Med J Malaysia. 1992 Mar;47(1):15-9. PMID: 1387443.

  5. Mas Pons, J., Dumont, A., Sautejeau, G., Fugier, E., Baron, A., Dukan, S. and Vauzeilles, B. (2014), “Identification of Living Legionella pneumophila Using Species‐Specific Metabolic Lipopolysaccharide Labeling”. Angew. Chem. Int. Ed., 53: 1275-1278.'

*Colonies Forming Units per milliliter / Colonies Forming Unit per liter

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