Alcaligenes is a genus ofGram-negative,aerobic,rod-shaped bacteria in the order ofBurkholderiales, family Alcaligenaceae.^[1]

Alcaligenes
Alcaligenes faecalis,flagella stain
Scientific classification
Domain:	Bacteria
Kingdom:	Pseudomonadati
Phylum:	Pseudomonadota
Class:	Betaproteobacteria
Order:	Burkholderiales
Family:	Alcaligenaceae
Genus:	Alcaligenes Castellani & Chalmers 1919
Species
A. aquatilis A. endopyhticus A. faecalis A. nematophilus A. pakistanensis

The type species,A. faecalis, was first isolated from stale beer byJohannes Petruschky in 1896.^[2] However, formal description was only finished in 1919 by Castellani and Chalmers.^[3]The nameAlcaligenes has its origin inArabic andGreek and means "alkali-producing".^{[4][clarification needed]}

Several species were previously placed inAlcaligenes, but have since been moved to more appropriate genera.A. aestus,A. aquamarinus,A. cupidus,A. pacificus andA. venustus were first reclassified to the genusDeleya and later merged intoHalomonas in the class ofGammaproteobacteria.Other species were reassigned within the order ofBurkholderiales.A. denitrificans,A. piechaudii,A. ruhlandii andA. xylosoxidans are currently placed inAchromobacter,^[5]A. latus inAzohydromonas,^[6]A. eutrophus inWautersia,^[7] andA. paradoxus inVariovorax.^[8]

Species ofAlcaligenes are rods, coccal rods, or cocci, sized at about 0.5-1.0 x 0.5-2.6 μm. The slender rods are slightly curved, capsule forming, not spore-forming.^[9] They are usually motile with amphitrichousflagella and rarely nonmotile. They tend to be colorless.

Alcaligenes species are obligately aerobic, but some can undergo anaerobic respiration if nitrate is present. They arenon-fermenting.^[10]

Alcaligenes species have been used for the industrial production ofnonstandard amino acids.^[11]

Species ofAlcaligenes typically occur in soil and water or decaying materials and dairy products.A. faecalis is commonly found in the intestinal tracts of vertebrates, and is found as a harmless saprophyte in 5% – 19% of the human population.^[12]

Infections fromAlcaligenes species are uncommon and largely opportunistic.^[13][14]A. faecalis is a known causing agent of nosocomialbacterial sepsis in immunocompromised patients by contaminated hemodialysis or intravenous fluid.^[14]Cases ofmeningitis,peritonitis,^[15]enteric fever,appendicitis,cystitis,chronic suppurative otitis media,abscesses,arthritis,pneumonitis andendocarditis^[16] associated withAlcaligenes have been reported,^{[clarification needed]} including azoonotic infection fromferrets.^[16]An increased recovery rate ofAlcaligenes species from patients withcystic fibrosis was reported in 2001,^[17] though the most commonly identified strainA. cylosoxidans has since been transferred toAchromobacter.

A. faecalis infections can pose a challenge due to considerable resistance to commonly used antibiotics.^[18] The resistance is driven by the production of β-lactamases (such as OXA-10 and PER-1), efflux pumps like the AcrAB-TolC system, and mutations in thegyrA andparC genes, which decrease fluoroquinolone effectiveness. The bacterium also forms biofilms on medical devices, providing protection against both antibiotics and the host immune system. In recent years, extensively drug-resistant (XDR) strains have emerged, showing very limited susceptibility to most available antibiotics.^[1]

• Madigan M; Martinko J, eds. (2005).Brock Biology of Microorganisms (11th ed.). Prentice Hall.ISBN 978-0-13-144329-7.
• Holt, John G. (1994).Determinative Bacteriology (9th ed.). Maryland: Williams & Wilkins. p. 75.ISBN 978-0-683-00603-2.

• Alcaligenes at Kenyon College.