''Aeromonas hydrophila'' is a

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

, rod-shaped bacterium mainly found in areas with a warm climate. This bacterium can be found in fresh or brackish water. It can survive in

aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cellu ...

and

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...

environments, and can digest materials such as

gelatin Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...

and

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

. ''A. hydrophila'' was isolated from humans and animals in the 1950s. It is the best known of the species of ''

Aeromonas ''Aeromonas'' is a genus of Gram-negative, facultative anaerobic, rod-shaped bacteria that morphologically resemble members of the family Enterobacteriaceae. Most of the 14 described species have been associated with human diseases. The most imp ...

''. It is resistant to most common antibiotics and cold temperatures and is oxidase- and indole-positive. ''Aeromonas hydrophila'' also has a

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

relationship as gut flora inside of certain leeches, such as ''

Hirudo medicinalis ''Hirudo medicinalis'', the European medicinal leech, is one of several species of leeches used as "medicinal leeches". Other species of ''Hirudo'' sometimes also used as medicinal leeches include '' H. orientalis'', ''H. troctina'', and '' H. ...

''.

Structure

''Aeromonas hydrophila'' bacteria are Gram-negative, straight rods with rounded ends (bacilli to coccibacilli shape) usually from 0.3 to 1.0 μm in width and 1.0 to 3.0 μm in length. They can grow at temperatures as low as 4 °C. These bacteria are motile by a polar

flagellum A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

Pathology

Because of its structure, it is very toxic to many organisms. When it enters the body of its victim, it travels through the bloodstream to the first available organ. It produces

aerolysin In molecular biology, aerolysin is a cytolytic pore-forming toxin exported by ''Aeromonas hydrophila'', a Gram-negative bacterium associated with diarrhoeal diseases and deep wound infections. The mature toxin binds to eukaryotic cells and aggrega ...

, a cytotoxic enterotoxin that can cause tissue damage. ''A. hydrophila'', '' A. caviae'', and '' A. sobria'' are all considered to be opportunistic pathogens, meaning they rarely infect healthy individuals. ''A. hydrophila'' is widely considered a major fish and amphibian pathogen, and its pathogenicity in humans has been recognized for decades. The genomic insights of aeromonas could be a stepping stone into understanding of them

Pathogenic mechanism

The pathogenicity of ''Aeromonas'' species was believed to be mediated by a number of extracellular proteins such as aerolysin, lipase, chitinase, amylase, gelatinase, hemolysins, and enterotoxins. However, the pathogenic mechanisms are unknown. The recently proposed type-III secretion system (T3SS) has been linked to ''Aeromonas'' pathogenesis. T3SS is a specialized protein secretion machinery that exports virulence factors directly to host cells. These factors subvert normal host cell functions to the benefit of invading bacteria. In contrast to the general secretory pathway, the T3SS is triggered when a pathogen comes in contact with host cells. ADP-ribosylation toxin is one of the effector molecules secreted by several pathogenic bacteria and translocated through the T3SS and delivered into the host cytoplasm, which leads to interruption of the NF-κB pathway, cytoskeletal damage, and apoptosis. This toxin has been characterized in ''A. hydrophila'' (human diarrhoeal isolate), ''A. salmonicida'' (fish pathogen), and ''A. jandaei'' GV17, a pathogenic strain that can cause disease both in humans and fish.

Occurrence of exposure

''Aeromonas hydrophila'' infections occur most often during sexual changes,

stressor A stressor is a chemical or biological agent, environmental condition, external stimulus or an event seen as causing stress to an organism. Psychologically speaking, a stressor can be events or environments that individuals might consider demandin ...

s, changes in temperature, in contaminated environments, and when an organism is already infected with a virus or another bacterium. It can also be ingested through food products contaminated with the bacterium, such as seafood, meats, and even certain vegetables such as sprouts. It can also be transmitted by leeches.

Fish and amphibians

''Aeromonas hydrophila'' is associated with diseases mainly found in freshwater fish and

amphibians Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbore ...

, because these organisms live in aquatic environments. It is linked to a disease found in frogs called red leg, which causes internal, sometimes fatal hemorrhaging. When infected with ''A. hydrophila'', fish develop

ulcers An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caused by sloughing o ...

tail rot The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, r ...

fin rot A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

, and

hemorrhagic septicemia Haemorrhagic septicaemia is one of the most economically important pasteurelloses.De Alwis MCL (1999) Haemorrhagic septicaemia. Canberra: Australian Centre for International Agricultural Research. pp. 11–24.Carter GR and De Alwis MCL (1989) Hae ...

. Hemorrhagic septicaemia causes lesions that lead to scale shedding, hemorrhages in the gills and anal area, ulcers, exophthalmia, and abdominal swelling.

Human diseases

''Aeromonas hydrophila'' is not as pathogenic to humans as it is to fish and amphibians. One of the diseases it can cause in humans,

gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is an inflammation of the gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of energy, and dehydra ...

, occurs mostly in young children and people who have compromised immune systems or growth problems. This bacterium is linked to two types of gastroenteritis. The first type is a disease similar to

cholera Cholera is an infection of the small intestine by some strains of the bacterium ''Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting and ...

, which causes rice-water diarrhea. The other type is dysenteric gastroenteritis, which causes loose stools filled with blood and mucus. Dysenteric gastroenteritis is the most severe out of the two types and can last for several weeks. ''A. hydrophila'' is also associated with

cellulitis Cellulitis is usually a bacterial infection involving the inner layers of the skin. It specifically affects the dermis and subcutaneous fat. Signs and symptoms include an area of redness which increases in size over a few days. The borders of t ...

. It also causes diseases such as

myonecrosis Gas gangrene (also known as clostridial myonecrosis and myonecrosis) is a bacterial infection that produces tissue gas in gangrene. This deadly form of gangrene usually is caused by ''Clostridium perfringens'' bacteria. About 1,000 cases of gas g ...

and

eczema Dermatitis is inflammation of the Human skin, skin, typically characterized by itchiness, erythema, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become lichenification, thick ...

in people with compromised or suppressed (by medication) immune systems. In very rare cases, ''A. hydrophila'' can cause

necrotizing fasciitis Necrotizing fasciitis (NF), also known as flesh-eating disease, is a bacterial infection that results in the death of parts of the body's soft tissue. It is a severe disease of sudden onset that spreads rapidly. Symptoms usually include red or p ...

Outbreaks

Though ''A. hydrophila'' can cause serious disease, large scale outbreaks have not been reported. Outbreaks among vertebrates have occurred. One such incident occurred in Puerto Rico inside the intestinal tracts of lizards. Some 116 different strains were found in the lizards. On May 1, 1988, a small outbreak happened in California. The 225 isolates in 219 patients caused their hospital admissions. Confidential morbidity report cards were used to report the cases to the local health departments. Investigations were conducted, and reports were sent to the California Department of Health Services for diagnosis and methods in treatment.

Treatments

''Aeromonas hydrophila'' can be eliminated using a 1%

sodium hypochlorite Sodium hypochlorite (commonly known in a dilute solution as bleach) is an Inorganic chemistry, inorganic chemical compound with the chemical formula, formula NaOCl (or NaClO), comprising a sodium cation () and a hypochlorite anion (or ). It may ...

solution or 2%

calcium hypochlorite Calcium hypochlorite is an inorganic compound with formula Ca(OCl)2. It is the main active ingredient of commercial products called bleaching powder, chlorine powder, or chlorinated lime, used for water treatment and as a bleaching agent. Thi ...

solution. Brage et al., 1990 recommends fluoroquinolone administration as prophylactic treatment during medicinal leech application.

Antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...

s such as

chloramphenicol Chloramphenicol is an antibiotic useful for the treatment of a number of bacterial infections. This includes use as an eye ointment to treat conjunctivitis. By mouth or by injection into a vein, it is used to treat meningitis, plague, cholera, a ...

florfenicol Florfenicol (marketed by Schering-Plough Animal Health under the trade name Nuflor) is a fluorinated synthetic analog of thiamphenicol, mainly used in veterinary medicine. As a generic, it is now available worldwide. Indications In the United ...

tetracycline Tetracycline, sold under various brand names, is an oral antibiotic in the tetracyclines family of medications, used to treat a number of infections, including Acne vulgaris, acne, cholera, brucellosis, plague (disease), plague, malaria, and sy ...

sulfonamide In organic chemistry, the sulfonamide functional group (also spelled sulphonamide) is an organosulfur group with the structure . It consists of a sulfonyl group () connected to an amine group (). Relatively speaking this group is unreactive. ...

nitrofuran Nitrofurans are a class of drugs typically used as antibiotics or antimicrobials. The defining structural component is a furan ring with a nitro group. Drugs Members of this class of drugs include: * Antibacterials (antibiotics) ** Difurazone ...

derivatives, and

Pyridinecarboxylic acids A pyridinecarboxylic acid is any member of a group of organic compounds which are monocarboxylic derivatives of pyridine. Pyridinecarboxylic acid comes in three isomers: *Picolinic acid (2-pyridinecarboxylic acid) *Nicotinic acid (3-pyridinecarbox ...

are used to eliminate and control the infection of ''A. hydrophila''.

Terramycin Oxytetracycline is a broad-spectrum tetracycline antibiotic, the second of the group to be discovered. Oxytetracycline works by interfering with the ability of bacteria to produce essential proteins. Without these proteins, the bacteria cannot ...

is placed in fish food during hatchery operations as another

chemotherapeutic Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemotherap ...

agent in preventing ''A. hydrophila''. S.I. Paul et al. (2021) isolated and identified probiotic ''Bacillus subtilis'' strain WS1A that can inhibit the growth of pathogenic ''Aeromonas'' in fish. ''Bacillus subtilis'' strain WS1A produces different types of potential

antimicrobial peptides Antimicrobial peptides (AMPs), also called host defence peptides (HDPs) are part of the innate immune response found among all classes of life. Fundamental differences exist between prokaryotic and eukaryotic cells that may represent targets for a ...

. Fish (''Labeo rohita'') fed with extracellular products of ''Bacillus subtilis'' strain WS1A develop disease resistance against motile ''Aeromonas'' septicemia. ''Bacillus subtilis'' strain WS1A boosts immunity of treated fish. This strain was isolated from

marine sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through ...

of Saint Martin's Island in the

Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...

Bangladesh Bangladesh (}, ), officially the People's Republic of Bangladesh, is a country in South Asia. It is the eighth-most populous country in the world, with a population exceeding 165 million people in an area of . Bangladesh is among the mos ...

References

External links

''Aeromonas hydrophila ATCC7966''Type strain of ''Aeromonas hydrophila'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{DEFAULTSORT:Aeromonas Hydrophila Aeromonadales Bacterial diseases of fish Bacteria described in 1901