Biology

General Characteristic of the species
Aeromonas species are ubiquitous water borne organisms. Aeromonas is a human pathogen causing extra-intestinal infection such as gastrointestinal infection, endocarditis, cellulites, wound infection, peritonitis, meningitis and supportive arthritis in patients, who are suffering from leukemia. Aeromonas hydrophila is a rod shaped, heterotrophic bacterium found mainly in warm climate in fresh, salt, marine, estuarine, chlorinated and un-chlorinated water.

Gram Reaction Aeromonas is a gram negative organism.
Respiration (aerobe or anaerobe)  Aeromonas hydrophila is able to live both in anaerobic and aerobic environment.

Sporulation Nonreverting beta-lactamase interrupts sporulation and cause fails to discharge free spores from sporangia. Endospores cannot be produced by Aeromonas hydrophila and it survives in 4 degree Celsius temperature.

Transient (is it normal flora in human body) Aeromonas has transient intestinal colonization of which there are many phenotypes of Aeromonas species during the life of first week of human body.
Scientific name of the pathogen Aeromonas hydrophila . The five pathogens of aeromonas hydrophila, A. veronii A. caviae, A. schubertii A. jandaei. A. sobria. Aeromonas subsp  strains are A.
218, 495A2, A1, A6,ATCC 14715  LMG 13663, ATCC 14715
Taxonomy, Species Aeromonas hydrophila, Unlprot,

Virulence factors and activity of each Aeromonas hydrophila is isolated from warmer areas of southern Italy, but it also can be taken from different sources like human diarrhea cases and sea sedimentary areas. It has characteristics of production of protein virulence factors such as cytotoxins, dermonecroting factor, cytotonic toxins, hemolysins so that it can bind to intestinal 407 cells in vitro.
Capsule Aeromonas salmonicida grows in medium which is having surplus glucose by carbon source and it tends to produce capsular and has contact with contaminated water exocellular polysaccharides in which the capsular polysaccharide is composed of rhamnose, N-acetylmannosamine and manuronic acid, glucose and mannose.

Toxin Aeromonas salmonicida exoenzyme, which is a protein toxin, belongs to the family of ADP-ribosylating toxin.

Enzymes Aeromonas secretes enzymes like -lactamases, lipases, hemolytic enterotoxins, proteases, chitinases, nucleases and amylases.

Pili Aeromonas hydrophila has fimbriae (pili) which help aceria to attach the host organism to invade the cells. Aerolysin are activated by A.hydrophila when it attaches to organs or cells.

Flagella  Aeromonas hydrophila has two distinctive features namely a polar flagellum to swim in liquid and multiple lateral flagella to swim over surface areas.

Disease description Necrotizing fascitis is uncommon and highly life threatening soft tissue infection with high mortality rate. It is also known as flesh eating disease. Aeromonas hydrophila infection may cause necrotizing fascitis in patients with bones, trauma in aquatic regions and in patients with immune suppressed system. In severe cases, it mainly develops myonecrosis of lower limb along with toxic shock. It is seen in wound infections due to direct contact with brackish water.

Pathology When the Aeromonas hydrophila bacterium enters the body of victim, travels in the blood steam and it is ready to produce Aerolysin Cytotoxic Enterotoxin. This toxin causes tissue damage and mediates the pathogenic mechanism. Aeromonas hydrophila is considered as opportunistic pathogens because it infects the host when immune responses grow weaker. Type 3 secretion systems (TTSS) play a vital role in aeromonas pathogenesis by exporting virulence factor directly mediated to host cell.

Symptoms The three main major symptoms are cellulites, ecthyma gangrenosum and myonecrosis. In this condition the lower limb has worsened oedema and dermatoneurosis of the whole lower extremity. Early symptoms which we find in cellulities are progressive skin change  like skin ulceration ,fluid filled blisters as bullae ,necrotizing eschar. This infection results in gangrene at the site of necrotizing soft tissue

There is sudden onset of redness and swelling along with pain at the site of the wound. Infection of it results in fever. Diarrhoea,abdominal cramps,vomting  .

Mortality rate  Due to delayed treatment of septic shock there is an increase in morbidity and mortality rate. The positive predators of mortality confined by multivariate logistic regression analysis shows the presence of vibro infection, aeromonas infection, malignancy and hypotension. The presence of haemorraghic bullae is the negative predators of mortality rate. It significantly shows that there is decrease in mortality rate.

Population Effected The people who are believed to be susceptible having gastroenteritis, although it is more often seen in very young children.

People who are with impaired immune systems or underlying malignancy are  more susceptible to  severe infections would effect  by this bacterium.

Out comeThe outcome is frequent in which poor prognosis is seen in untreated fascitis  death and severe morbidity is high. In necrotizing fascitis mortality rate may be high 25. In patient with sepsis and renalfailure along with necrotizing fascitis mortality rate rate as high as  70. In multidrug resistance organisms and infection with MRSA may also have high morbidity and mortality rate.

Reservoir Aeromonas is predominantly found in salt and fresh water, sewage and soil. The bacterium is grown in warm climate, chlorinated, unchlorinated water and estuarine.

Mode of transmission Transmission occurs when it gets in contact with contaminated water, soil, food, feco oral route, injection of infected reptiles and fishes. It can also spread from person to person eg play groups, families etc.., where there is a breakdown of hand hygiene practices.

Season common for the disease Mainly it causes diseases during winter season.

Diagnosis Aeromonas hydrophila can be cultured and identified by necrotizing fascitis samples and blood.

Culture Real-time PCR is conducted to detect A.hydrophila ahh1 using DNA sample which was extracted from blood and isolated from necrotizing tissue in which ahh1 was positive.
Tissue biopsy It shows necrosis in the soft tissue muscles and fascia, subcutaneous abscess formation and hemorrhage and acute inflammation. In tissue culture it reveals that there is presence of both aerobic and anaerobic bacteria.

ELISA test In this three murine MAbs 6F6, 9C10 and 6H4 usually screened by r-28 antigen based enzyme linked immunosorbent assay able to recognize vp28 vial protein on western bolt. In this an antigen capture ELISA (AC-ELISA) is developed by MAbs virtue.

Antibody triter Aeromonas hydrophila in which serum human T-cell lymph tropic virus type III antibody titer is positive in stools culture, so the organism is susceptible.

Treatment Necrotizing fascitis can be promptly identified and the foremost surgical intervention is the only treatment available. After surgical intervention, that includes anti-biotic therapy and supportive care. If the condition of lower extremity is worsened with severe oedema then dermatoneurosis amputation at the thigh is the only possible way to keep the patient alive. Debriment of the infected necrotizing soft tissue and fasciotomies should be done. Then initially the septic shock should be treated in emergency department and later surgical intervention is suggestible. Blood pressure need to be stabilized by giving vasopressors and broad spectrum antibiotics to control infection.

Antibiotic therapy To control the infection substances like florenicol, tetracycline, chloramphenacol, sulfonamide, nitrofurane and pyrodinecarboxyli acid are used. Terramycin placed in fish food by the time of hatchery operations is one of the chemotherapeutic agents.

Drug susceptibility A.Hydrophila is septable to broad spectrum aminoglycosifdes, cabamapenems, tetracyclines, trimethoprim-sulfamethoxale and quinnoles, cephalosporine.

Resistance to Aeromonas hydrophila is resistant to Penicillin, ticarcillin, carbapencillin, ampicillin.
Susceptible to disinfectant 70 ethanol, 2 glutaral-dehydephenoles, iodines, 1 sodium hypochlorite and formaldehyde. Aeromonas hydrophila organism can be killed by using 2 calcium hypochlorite and 1sodium hypochlorite.

Immunization There is no specific vaccination to prevent this disease.
Conclusion Necrotizing fascitis is a rapidly progressive soft tissue infection mainly characterized by extensive myonecrosis of soft tissue and gangrenous lesion. Patients with clinical features of necrotizing fascitis should need deep biopsy specimen collected from necrotizing plaques to confirm the disease. To reduce the mortality and morbidity, the patient should immediately undergo surgical intervention.