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  1. 1. AEROMONAS A Presentation By Isaac U.M. Associate Professor & Head, Department of Microbiology, College of Medicine, International Medical & Technological University, Tanzania.
  2. 2. INTRODUCTION <ul><li>Aeromonas is a gram negative facultative anaerobic rod that morphologically resembles members of the family Enterobacteriaceae. </li></ul><ul><li>As with Vibrio , extensive reorganization of the taxonomy of these bacteria has occurred. </li></ul><ul><li>Fourteen species of Aeromonas have neen described most of which are associated with human disease. </li></ul><ul><li>The most important pathogenes are Aeromonas hydrophila, Aeromonas caviae, and Aeromonas veroni bivar sobria. </li></ul><ul><li>The organisms are ubiquitous in fresh and brackish water. </li></ul><ul><li>The two major diseases associated with Aeromonas are gastroenteritis and wound infections (with or without bacteremia). </li></ul>
  3. 3. HISTORY <ul><li>In the 1950s Aeromonas sp. were reported to be associated with children diarrhea. </li></ul><ul><li>Because the reports were in German language, it was not until early 1980s that the organisms were recognized as significant causes of gastroenteritis in children by Australian researchers. </li></ul><ul><li>Studies in volunteers in 1985 found no association between aeromonads and diarrhea in healthy adult volunteers. </li></ul><ul><li>However, the Aeromonas strains used in the study lack certain important virulence factors, adherence properties for example. </li></ul><ul><li>Although no more volunteer studies were carried out since then, there is strong epidemiological evidence that Aeromonas sp. are responsible for diarrhea in humans (including travelers’ diarrhea). </li></ul>
  4. 4. HABITAT <ul><li>Aeromonas species are indigenous to aquatic environment worldwide. </li></ul><ul><li>Aeromonads have been isolated from fresh water, chlorinated water, polluted water and occasionally marine environment and their numbers are highest at warm months. </li></ul><ul><li>Aeromonas species have also been isolated from store produce and meats and from environmental and seafood sources. </li></ul><ul><li>The organisms are associated with a wide variety of diseases in warm- and cold-blooded vertebrates, including frogs, fish, reptiles snakes, and birds. </li></ul>
  5. 5. TAXONOMY <ul><li>The genus Aeromonas consists of at least 14 species and 13 DNA hybridization groups (HG) or genospecies (Table 1). Aeromonas species can be grouped into two subdivisions: </li></ul><ul><li>1. Psychrophilic group: A. salmonicida . The only species in this group. It is a fish pathogen, nonmotile and do not grow at 37 o C. A. salmonicida have not been isolated from humans and, therefore, is not important in clinical microbiology. </li></ul><ul><li>2. Mesophilic group: A. hydrophila group. The organisms are motile and grow at 37 o C. It can be divided into 3 principal phenotypic groups (Phenons) which are equivalent to the species A. hydrophila , A. caviae and A. sobria (Table 1). </li></ul>
  6. 6. <ul><li>Table 1. </li></ul><ul><li>Phenotypic grouping of species and </li></ul><ul><li>DNA hybridization groups in the genus Aeromonas </li></ul><ul><li>____________________________________________________________________________ </li></ul><ul><li>DNA Hypbridization Phynotypic Group Named Species </li></ul><ul><li>Group (Genospecies) </li></ul><ul><li>____________________________________________________________________________ </li></ul><ul><li>1 A. hydrophila A. hydrophila </li></ul><ul><li>2 Unnamed </li></ul><ul><li>3 A. salmonicida </li></ul><ul><li>------------------------------------------------------------------------------------------------------------------------------- </li></ul><ul><li>4 A. cavaie A. caviae </li></ul><ul><li>5A A. media </li></ul><ul><li>5B A. media </li></ul><ul><li>6 A. eucrenophila </li></ul><ul><li>------------------------------------------------------------------------------------------------------------------------------- </li></ul><ul><li>7 A. sobria A. sobria </li></ul><ul><li>8/10* A. veronii biotype sobria </li></ul><ul><li>9 A. Jandaei </li></ul><ul><li>10/8* A. veronii biotype veronii </li></ul><ul><li>11 A. veronii-like </li></ul><ul><li>12 A. schubertii </li></ul><ul><li>13 Aeromonas group 501 </li></ul><ul><li>------------------------------------------------------------------------------------------------------------------------------ </li></ul><ul><li>14 A. trota </li></ul><ul><li>____________________________________________________________________________ </li></ul><ul><li>*DNA groups 8 and 10 have been shown to be identical </li></ul>
  7. 7. <ul><li>A number of putative virulence factors have been implicated in the patho-genesis of Aeromonas species. Genes that code for such factors have been described. These virulence markers are important to distinguish between potentially pathogenic and non-pathogenic strains. Aeromonas virulence factors include: </li></ul><ul><ul><li>Toxins: </li></ul></ul><ul><ul><ul><li>Hemolysins. </li></ul></ul></ul><ul><ul><ul><li>Cytotoxins. </li></ul></ul></ul><ul><ul><ul><li>Enterotoxins. </li></ul></ul></ul><ul><ul><li>Invasiveness. </li></ul></ul><ul><ul><li>Adherence. </li></ul></ul><ul><ul><li>Motility and lateral (polar) flagella: </li></ul></ul><ul><ul><ul><li>Recent studies have shown that lateral flagella production by Aeromonas is a pathogenic feature due to its enhancement of cell adherence, invasion and biofilm formation. </li></ul></ul></ul>VIRULENCE FACTORS
  8. 8. <ul><ul><li>Others: </li></ul></ul><ul><ul><ul><li>Proteases. </li></ul></ul></ul><ul><ul><ul><li>Outer membrane proteins. </li></ul></ul></ul><ul><li>Recently genes for putative type III secretion system (TTSS) were identified in Aeromonas . </li></ul><ul><li>As shown in other pathogenic Gram-negative bacteria, the TTSS plays an essential role in pathogenicity as it facilitates the delivery of toxins to host cells. </li></ul>VIRULENCE FACTORS
  9. 9. CLINICAL INFECTION <ul><li>Septicaemia: Mainly in immunocompromised individuals (e.g. patients with hepatobiliary disease). </li></ul><ul><li>Cellulitis and wound infections: Infections associated with exposure to contaminated water or after alligator bite. The infection usually results in gangrene-like syndrome. Also, in patients who went treatment with medicinal leech. </li></ul><ul><li>Diarrhoea: Most commonly watery in consistency and sometimes cholera-like of short duration. Occur in all ages but mainly in children less than 3 years. Several reports associated Aeromonas species with travelers’ and chronic diarrhoea. </li></ul><ul><li>Food poisoning: A number of food poisoning outbreaks have been reported. </li></ul><ul><li>Others: A wide range of infections that include: meningeal, sore throat, urinary tract, ear, endocarditis, septicemia, etc.. </li></ul>
  10. 10. LABORATORY DIAGNOSIS <ul><li>Media used: </li></ul><ul><ul><li>Blood agar (BA), </li></ul></ul><ul><ul><li>Ampicillin BA (ABA, 15mg/L) and </li></ul></ul><ul><ul><li>Alkaline peptone water (APW) for enrichment. </li></ul></ul><ul><ul><li>A wide range of other media are available commercially. </li></ul></ul><ul><li>Isolation: </li></ul><ul><ul><li>From stool: </li></ul></ul><ul><ul><ul><li>A loopful of liquid stool specimen is added to 10 ml APW and incubated at 37 ° C. After overnight incubation a loopful from APW is plated onto BA and another loopful onto ABA and incubated at 37 ° C overnight. </li></ul></ul></ul>
  11. 11. <ul><li>2. From blood: </li></ul><ul><ul><ul><li>10 ml of blood is inoculated into blood bottles and incubated at 37 ° C for up to 2 weeks. When growth is observed a loopful of culture is plated on BA and incubated at 37 ° C overnight. </li></ul></ul></ul><ul><ul><li>From wounds: </li></ul></ul><ul><ul><ul><li>A wound swab is plated directly on blood agar and on ampicillin blood agar (15mg/L) and the swab is then placed in APW. After incubation overnight a loopful from APW is plated on BA and another loopful onto ABA. Plates are incubated overnight at 37 ° C. </li></ul></ul></ul>LABORATORY DIAGNOSIS
  12. 12. <ul><li>Identification: </li></ul><ul><ul><ul><li>Suspected colonies are tested for oxidase. Oxidase-positive colonies are then identified using the Aerokey II identification scheme or other schemes </li></ul></ul></ul><ul><ul><ul><li>A number of PCR techniques are also available for identification of Aeromonas species. </li></ul></ul></ul>LABORATORY DIAGNOSIS
  13. 13. TREATMENT <ul><li>Aeromonas species are inherently resistant to  -lactams (chromosomally mediated). </li></ul><ul><li>Aeromonas species are usually susceptible to other antibiotics. </li></ul><ul><li>Drugs of choice include: </li></ul><ul><ul><li>Fluoroquinolones: Ciprofloxaxin, Norfloxacin </li></ul></ul><ul><ul><li>3 rd generation cephalosporins: Ceftriaxone, Cefuroxime </li></ul></ul><ul><ul><li>Trimehtoprim-sulfamethoxazole (TMP-SMZ) </li></ul></ul><ul><ul><li>Tetracyclines (TE) </li></ul></ul><ul><li>Due to emergence of resistance to TMP-SMZ and TE, antibiotic susceptibility should be performed for such drugs particularly in developing countries. </li></ul>
  14. 14. THANK YOU