Legionella cherrii

The bacterium was first discovered in 1982 by R. L. Tyndall and C. B. Duncan, who were a part of D.J. Brenner's team that discovered ten new species of Legionella.^[1] The isolation process initiated after collecting water samples and transferring them into guinea pig tissues before plating them onto buffered charcoal yeast extract agar.^[1] Afterwards, L. cherrii strains were cultured around 36 °C in an environment containing 2.5% carbon dioxide.^[1]

The genus Legionella is named after the 1976 pneumonia (Legionella pneumophila) outbreak at the American Legion convention at The Bellevue-Stratford Hotel in Philadelphia.^[4] The genus was previously unknown, but it was established three years later.^[4] The specific term cherrii is derived from the scientist William B. Cherry due to his contributions on the studies of Legionellae.^[1]

Legionella cherrii is rod-shaped and considered an oxidase-negative bacterium since it lacks cytochrome c oxidase and does not use oxygen in its electron transport chain.^[1] L. cherrii also has the ability to autofluoresce a bluish-white color which was tested by placing the specimen under a Woods lamp-a mechanism that uses backlight to highlight bacteria-and measured under 366 nm wavelengths.^[1] L. cherrii lacks the ability to reduce nitrate, does not contain a urease, and does not convert D-glucose to acid.^[1] However, L. cherrii can hydrolyze gelatin.^[5] When on a yeast extract agar plate, L. cherrii forms a dissolvable brown pigment containing tyrosine.^[5] One or a few flagella aid them in their motility.^[1] Legionella organisms’ dependence on L-cysteine and their unique fatty acids and isoprenoid ubiquinone distinguish them from other aerobic bacteria.^[6] Like other Legionella species, L. cherrii does not form spores and is an aerobic, Gram-negative bacterium.^[1] The genome size was sequenced using Illumina HiSeq 2000 and found to be 3.7 Mb.^[7] Scaffold assembly was conducted using whole genome shotgun sequencing and 13 scaffolds were found in the complete genome.^[7] The G/C content for this particular species of Legionella is 38.8 mol%.^[7] About 3,111 protein coding genes, four rRNA genes, and 36 tRNA genes were also discovered in the genome.^[7]

Various strains of L. cherrii were isolated in different areas in 1982.^[1] Strains ORW, ORB, and ORZ were discovered in Minnesota in a heated water sample.^[1] Another isolate, SC-65-C3, was found in a potable water stern on the island of St. Croix in the Virgin Islands.^[1] Legionella species are mostly found in freshwater environments.^[6] However, various strains of Legionella can congregate in water filtration systems, air conditioning units, humidifiers, and equipment used to combat respiratory infections.^[6]

To determine previously classified Legionella species' relatedness to L. cherrii, Brenner et al. hybridized DNA reactions using an in vitro method with phosphate (³²PO₄).^[1] A similar percentage of 94% or higher was found between the four L. cherrii strains.^[1] Reassociation criteria differed between 60 and 75 °C depending on the optimal or stringent growth of the bacteria.^[1] None to 0.5% divergence was found in related sequences.^[1] L. steigerwaltii was related to L. cherrii the most, and exhibited a 67% relatedness percentage.^[1] Following L. steigerwalti, L. dumofii (57%), L. anisa (56%), L. bozemanii (51%), and L. gormanii (47%) showed these levels of similarity.^[1] Although L. parisiensis is an autofluorescent species like L. cherrii, it only had a 24% relatedness to L. cherrii.^[1] Compared to other Legionella species, L. cherrii is 6-35% related.^[1]