Motile Aeromonas and Pseudomonas Septicemia

BACTERIA Motile Aeromonas and Pseudomonas Septicemia

I. Causative Agent and Disease hemorrhaging and necrosis of the fins is Motile bacterial septicemias are common. Exophthalmia and abdominal caused by Gram-negative bacteria distention with ascitic fluid may also be including Aeromonas and Pseudomonas present. Internally, the kidney may be with the Aeromonas hydrophila-complex soft and swollen and the spleen enlarged. and Pseudomonas fluorescens being Petechial hemorrhages may be present the most common species. The A. hy- internally in many tissues and the intes- drophila (liquefaciens) complex contains tines may be inflamed and filled with numerous biotypes and serotypes of yellow mucus or bloody fluid. A. hydrophila as well as A. sobria , A. caviae, A. shuberti and A. veronii. These IV. Transmission bacteria are ubiquitous in the aquatic These bacteria are among the normal environment and are found around the flora of healthy fish and are ubiquitous world in both fresh and brackish water, in the aquatic environment. They are but more commonly in freshwater. These particularly abundant in organically bacteria generally cause a systemic, polluted waters while infected carrier hemorrhagic disease in fish. Most of fish and other aquatic animals can serve these bacteria are considered opportu- as reservoirs. Transmission is horizontal nistic pathogens causing disease in fish from fish to fish or from contaminated compromised by stress or other patho- water. Water temperatures 10°C or above gens. Some species, most commonly P. favor these opportunistic pathogens. fluorescens and A. hydrophila, have been reported as primary fish pathogens in V. Diagnosis systems of high intensity fish culture. A presumptive diagnosis is made when fish exhibit characteristic clinical II. Host Species signs with tissue imprints, squashes or When less than optimum condi- blood smears containing Gram-negative, tions prevail, all freshwater fish species motile rod-shaped bacteria. A definitive are likely susceptible to these bacteria. diagnosis is made by isolation of the Among salmonids, rainbow trout and organism on appropriate bacteriological Chinook salmon are probably the most media followed by identification from susceptible to the A. hydrophila com- biochemical tests. plex. Both Aeromonas and Pseudomonas are pathogenic for other cold-blooded VI. Prognosis for Host vertebrates including frogs and reptiles Severely affected fish will die. and will infect mammals including man However, these bacteria are generally through wounds or when they are im- weak pathogens. Poor environmental munocompromised. conditions predispose fish to disease out- breaks which are self-resolving without III. Clinical Signs intervention by antibiotic therapy when Lethargy, low-level mortality and the source of stress is removed. When occasional cutaneous lesions on the body necessary, antibiotic therapy can be ef- surface may occur. Inflammation and fective, except some pseudomonads are erosion in and around the mouth with resistant to available aquaculture drugs.

30 BACTERIA

VII. Human Health Signifcance Some bacteria in these genera can cause disease in humans through wounds or when immunocompromised.

Petechial hemorrhages on ventral surface of a salmonid fsh with bacterial septicemia. 

Petechial hemorrhages of liver, pyloric caeca, gut and visceral fat (arrow) of a juvenile salmonid fsh with bacterial septicemia.