Aeromonas hydrophila: Introduction, Identification Features, Keynotes, and Aeromonas Footages

Introduction of Aeromonas hydrophila

Aeromonas hydrophila is a gram-negative, facultative anaerobe, rod-shaped motile(due to single polar flagellum) bacterium without capsule and spore having a size from 0.3-1.0 µm wide by 1.0-3.5 µm long. It is generally found in the aquatic environment. Its presence can not be ignored in drinking water, wastewater, sewage, and food. It is an emerging pathogen responsible for numerous clinical conditions. e.g. gastroenteritis, skin infections, peritonitis, bacteremia, meningitis, cholera-like illness, hemolytic uremic syndrome (HUS), and necrotizing fasciitis.

Biochemical Reactions of Aeromonas hydrophila

Basic Features	Properties
1. Gram Staining	Gram-Negative Rods (GNRs)
2. Spore	Non-Sporing
3. Capsule	Negative
4. Motility	Motile
5. Pigment	Tan to buff-color
6. Growth in potassium cyanide (KCN) medium	Positive
7. Catalase test	Positive
8. Oxidase test	Positive
9. Nitrate reduction test	Positive
10. MR (Methyl Red) test	Positive
11. VP (Voges- Proskauer) assay	Positive
12. OF (Oxidative-Fermentative) test	Positive
13. Gas	Positive (mostly)
14. H2S production	Positive
15. Indole formation	Positive
16. Urease/ urea hydrolysis test	Negative
17. Citrate/citrate utilization	Positive
18. DNase test	Positive
19. Glucose fermentation	Positive
20. Maltose fermentation	Positive
21. Lactose fermentation	Variable
22. Sucrose fermentation	Positive
23. Xylose fermentation	Negative
24. Mannitol fermentation	Positive
25. Acetate Utilization	Positive
26. ONPG (β-galactosidase)	Positive
27. Phenylalanine Deaminase (PDA)/PPA Test	Negative
28. Gelatin Hydrolysis	Positive
29. Esculin Hydrolysis test	Positive (mostly)
30. Lysine Decarboxylase Test	Positive
31. Ornithine Decarboxylase Test	Negative
32. Arginine Dihydrolase Test	Positive
33. Gelatin Hydrolysis/Liquefaction	Positive
34. Maximum Growth Temperature	41°C
35. Hemolysis on blood agar	Positive

Keynotes on Aeromonas

• Aeromonas hydrophila complex is a group of genera A. hydrophila A. bestiarum and A. salmonicida.
• It is an emerging pathogen.
• Aeromonas species grow at a range of temperatures from 0 to 42ºC.
• Common pathogenic species of Aeromonas are A. hydrophila, Aeromonas veronii, and Aeromonas schubertii.
• They possess many extracellular enzymes like proteases, lipases, nucleases, sulphatases, lecithinase, chitinase, amylase, and stapholysin.

Aeromonas Pictures

Aeromonas hydrophila beta-hemolytic colony on blood agar

Aeromonas hydrophila growth on MacConkey agar

Aeromonas in Hanging Drop Preparation

Aeromonas hydrophila colony characteristics on CLED agar

Further Readings

• https://www.researchgate.net/figure/biochemical-tests-of-A-hydrophila-isolates_tbl1_316660080
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4601520/
• https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/aeromonas-hydrophila
• https://catalog.hardydiagnostics.com/cp_prod/Content/hugo/Aeromonas.htm
• Al-shalah. L. AM, The study characters of Aeromonas hydrophila on some media. Mesop. environ. j., 2017, Special Issue A.;121-129.
• https://www.researchgate.net/figure/Biochemical-properties-of-Aeromonas-hydrophila_tbl1_231614040
• Garrity, George Brenner, Don J., Krieg, Noel R., Staley, James R. (2005). Bergey’s Manual of Systematic Bacteriology. Volume 2: The Proteobacteria, Part B: The Gammaproteobacteria.
• Sharon L. Abbott, Wendy K. W. Cheung, J. Michael Janda. The Genus Aeromonas: Biochemical Characteristics, Atypical Reactions, and Phenotypic Identification Schemes Journal of Clinical Microbiology Jun 2003, 41 (6) 2348-2357; DOI: 10.1128/JCM.41.6.2348-2357.2003
• https://www.uptodate.com/contents/aeromonas-infections