1. Definition(Topley Wilson 10th Ed) Gram negative Oxidase + Catalase + Facultative anaerobic rods All are motile by means of a single polar flagellumExcept: A. salmonicida & A. media : Non motile Nitrate reduction + Indole production +Except: A. schubertii : Indole -ve High salt conc. (6-7%) are inhibitory

2. Further Description (ASM Manual 10th Ed 2011)They are chemoorganotrophic, displaying oxidative and fermentative metabolism of glucose. Acid, and often acid with gas, is produced from many carbohydrates, especially glucose A variety of exoenzymes are produced Arylamidases esterases Amylasepeptidases, DNase,proteases, chitinase,chondroitinase, hemolysins 3. Classification & TaxonomyIn mid 1970s the genus Aeromonas was divided into 2groups: PSYCHROPHILIC: only one spp A. salmonicida , afish pathogen. It is non motile & doesnt grow at 37 C. MESOPHILIC: all the other identified spp. Mesophilic: A mesophile is an organism that grows bestin moderate temperature, neither too hot nor too cold,typically between 25 and 40 C (77 and 104 F). Psychrophilic: Psychrophiles or cryophiles areextremophilic organisms that are capable of growth andreproduction in cold temperatures, ranging from 15Cto +10C. 4. Classification & Taxonomycontd Order: Aeromonadales Family: Aeromonadaceae Other members of the Order: Oceanimonas and Tolumonas Aeromonas is the only one of these three genera that is pathogenic for humans. 5. Members of the genus AeromonasPathogenic for Human isolation Human pathogenOrganism Frequency in humansanimals, (extraintestinal/fecal) (extraintestinal/fecal) fish, and reptilesA. hydrophila complexA. hydrophilasubsp. hydrophilaYesYes CommonYessubsp. dhakensis b YesYes RareNosubsp. ranaeNo No YesA. bestiarumNo/yes /no RareYesA. salmonicida cNo/yes No/noRaresubsp. salmonicidaYessubsp.Yesachromogenessubsp. masoucidaYessubsp. smithiaYessubsp.Nopectinolytica 6. Members of the genus Aeromonas Pathogenic forHuman isolation Human pathogenOrganismFrequency in humansanimals,(extraintestinal/fecal) (extraintestinal/fecal)fish, and reptilesA. hydrophila complexA. hydrophila subsp. hydrophilaYesYesCommon Yes subsp. dhakensis b YesYesRare No subsp. ranaeNo No YesA. bestiarum No/yes /noRare YesA. salmonicida c No/yes No/no Rare subsp. salmonicidaYessubsp. Yesachromogenes subsp. masoucidaYes subsp. smithiaYes subsp. pectinolyticaNo 7. Members of the genus Aeromonas HumanHumanPathogenic forisolationpathogen Frequency inanimals, Organism (extraintestinal (extraintestinal/ humansfish, and/fecal)fecal)reptilesA. caviaecomplexA. caviae Yes YesCommon YesA. media No/yes/yes Rare NoA.YesNo/Very rareNoeucrenophila 8. Human isolation Human pathogenPathogenic for animals, Organism Frequency in humans(extraintestinal/fecal) (extraintestinal/fecal)fish, and reptilesA. veronii complexA. veronii bv. sobriaYes YesCommon Yes A. veronii bv. Yes YesRare NoveroniiA. jandaei Yes Yes/unknownRare NoA. trota YesNeither Rare NoA. schubertiiYes/noYes/Rare NoA. encheleia Yes/noNo/ One case No A. No/yes /noVery rareYesallosaccharophila A. sobriaNeither No A. popoffii Yes YesVery rareNo A. culicicola NoNo No A. simiae NoNo No A. molluscorumNoNo No A. bivalviumNoNo No A. tectaYes No Rare No A. piscicolaNoNo Yes 9. Human isolation Human pathogenPathogenic for animals, OrganismFrequency in humans (extraintestinal/fecal) (extraintestinal/fecal)fish, and reptilesA. veronii complexA. veronii bv. sobria Yes YesCommon YesA. veronii bv. veroniiYes YesRareNo A. jandaeiYes Yes/unknown Rare NoA. trotaYes Neither Rare No A. schubertii Yes/noYes/ Rare NoA. encheleiaYes/no No/ One case NoA. allosaccharophilaNo/yes /no Very rare YesA. sobria Neither No A. popoffiiYes Yes Very rare NoA. culicicola NoNo NoA. simiae NoNo NoA. molluscorumNoNo NoA. bivalviumNoNo NoA. tectaYes NoRare NoA. piscicolaNoNo Yes 10. Morphology and Cell Structures Straight, coccobacillary to bacillary cells withrounded ends 0.3 to 1.0 m in diameter and 1.0 to 3.5 m inlength. They can occur singly, in pairs, or, rarely, in shortchains. Most species are motile by a single, polarflagellum with a 1.7-m wavelength, butperitrichous flagella may be formed on solidmedia in young cultures and lateral flagellaoccur in some species. 11. Morphology and Cell Structures 12. Type strain The type strain Aeromonas hydrophila subsp. hydrophila ATCC 7966 was the first aeromonad to be completely sequenced, annotated, published, and deposited in GenBank (as CP000462) This was followed just recently by the publication of the complete genome sequence of Aeromonas salmonicida subsp. salmonicida A449, an agent of furunculosis (a bacterial septicemia of salmonid fish), which was deposited in GenBank as NC 00938 13. Clinical significanceThe spectrum of human infections caused byAeromonas spp usually fall into the 4 broadcategories: Gastroenteritis Cellulitis and wound infection Septicemia Miscellanous 14. Clinical significance There are currently 20 named species but only 3 are of major clinical importance: A. hydrophila A. caviae A. veronii biovar sobria 15. GastroenteritisAeromonas was first isolated more than 60 years ago, but evidence implicating this genus as a cause of gastrointestinal disease has been amassed only since the early 1980s Aeromonas caviae is the predominant isolate from diarrheal stools, but in some geographic areas, A. hydrophila and A. veronii biovar sobria are frequently isolated as well 16. GastroenteritiscontdEvidence supporting a causative role in diarrheal disease includes: A higher carriage rate in symptomatic compared with asymptomatic individuals; An absence of other enteric pathogens in most symptomatic patients harboring Aeromonas species Identification of Aeromonas enterotoxins (although the absence of an animal model has hampered efforts to directly link toxin production with disease) 17. Gastroenteritis contdEvidence supporting a causative role in diarrheal disease also includes:Improvement of diarrhea with antibiotics active against Aeromonas species and clinical worsening with antibiotics ineffective against the organism; andEvidence of a specific secretory immune response (IgA) coincident with diarrheal disease. 18. Gastroenteritiscontd Diarrhea is usually watery and self-limited But some persons develop fever, abdominal pain, and bloody stools. Fecal leukocytes may be present. 19. Gastroenteritis contdOccasionally, diarrhea may be severe or protracted, and hospitalization may be necessary. Chronic colitis following acute Aeromonas- associated diarrhea has been reported in adults.Hemolytic uremic syndrome associated with Aeromonas enterocolitis has been described in infants and adults 20. Cellulitis & wound infectionMost Aeromonas soft tissue infections are caused by A. hydrophila.Trauma followed by exposure to fresh water (and not salt water, even though aeromonad density in seawater is similar to that in fresh water) usually, but not invariably, precedes infection.Cellulitis develops within 8 to 48 hours, and systemic signs are common. 21. Cellulitis & wound infectioncontdSuppuration and necrosis around the wound are frequent, and surgical dbridement is often necessary.Fasciitis, myonecrosis (occasionally associated with gas formation), and osteomyelitis may develop. 22. Cellulitis & wound infectioncontd Aeromonas soft tissue infections can develop after exposure to soil in association with crush injuries, and as a complication of burns, typicallywhen initial management of the burnincluded immersion in natural watersources. 23. Cellulitis & wound infectioncontdThere is one reported outbreak of A.hydrophila wound infections in participants ofa mud football competition in Australia. Thefield was prepared with water from anadjacent river. 24. In relation to HirudotherapyAeromonas soft tissue infection is a recognizedcomplication of the use of medicinal leeches inconjunction with reimplantation or flap surgery. 25. In relation to Hirudotherapy Aeromonas hydrophila and other Aeromonas speciesare normal inhabitants of the foregut of leeches. Leeches lack the requisite proteolytic enzymesand are dependent on the symbiotic Aeromonas todigest the blood meal. Aeromonas infection has developed in 7% to 20% ofpatients treated with leeches. Prophylactic antibiotics now have beenrecommended at the time of leech application. Mild wound infection, loss of flap,myonecrosis,and sepsis may ensue 26. SepticaemiaThe mortality rate for Aeromonas sepsis is 30% to 50%.Taiwan Study: till date the biggest Cochrane evidence:Aeromonas bacteremia and sepsis are uncommon, but in the largest series reported to date, 143 Aeromonas bacteremias, including 104 that were monomicrobial, occurred in one institution in Taiwan over a 10-year period. 27. SepticaemiaTaiwan Studycontd Aeromonashydrophila caused 60% of the bacteremiasmost of the other isolates that were identified by species were A. veronii subtype sobria and A. caviae.Most patients inthisseries were immunocompromised, including 54% who were cirrhotic and 21% who had an underlying malignancy. 28. Septicaemia The US Experience:There was a similar distribution of Aeromonas species in a study of 53 Aeromonas blood isolates collected from 27 medical centers in the United States over a 10-year period. Most patients were immunocompromised, and underlying malignancy was much more common than liver disease in this series. Most patients with Aeromonas sepsis do not present with diarrhea. Interestingly, about one third of Aeromonas bacteremias are nosocomial. 29. SepticaemiaThe US Experiencecontd:Aeromonas has been recovered from hospital water supplies, and clusters of nosocomial Aeromonas bacteremia have been described.However, in one study in which molecular typing was performed, many different genotypes were found.So, mostly the nosocomial cases were not epidemiologically linked, and endogenous gut flora was the presumed source. 30. Miscellaneous InfectionsA variety of other infections caused by Aeromonas species have been reported, including:intra-abdominal abscess,pancreatic abscess,hepatobiliary infection,spontaneous bacterial peritonitis in patients with cirrhosis,Meningitis 31. Miscellaneous Infections Endocarditis, suppurative thrombophlebitis, osteomyelitis, urinary tract infection, prostatitis, pneumonia including near-drowning associated pneumonia, LRTI, empyema, lung abscess, URTI, tonsillitis, epiglottitis, otitis media keratitis 32. Miscellaneous Infections A. hydrophila epididymitis and bacteremiadeveloped in a healthy manBefore 24 hours he had sexual intercourse with his wife in their swimming poolCultures obtained from the pool grew A. Hydrophila.Ref: Blair JE, Woo-Ming MA, McGuire PK: Aeromonas hydrophilabacteremia acquired from an infected swimming pool. Clin InfectDis 1999; 28:1336-1337. 33. Laboratory diagnosis Selective Media for Id from Faeces: Blood Agar (+/- Ampicillin) 10g/mL added Alk Peptone Water (pH 8.6) : overnight enrichment recommended, then S/C CIN Agar - originally developed for Yersinia enterocolitica Enteric Agars: Deoxycholate MAC XLD Agar 34. Laboratory diagnosiscontd Modified cefsulodin-Irgasan-novobiocin (CIN) (4 g/mL of cefsulodin versus 15 g/ml in unmodified CIN) is also an excellent isolation medium for aeromonads.On this medium, Aeromonas colonies have a pink center with an uneven, clearapron and are indistinguishablefrom Yersinia enterocoliticamorphologically. 35. Laboratory diagnosis Oxidase + Thus quickly excluded fromEnterobacteriaceae Motile Indole + This excludes Pseudomonas OF test: Aeromonads utilize glucosefermentatively, thus excluded fromPseudomonas again 36. Laboratory diagnosis most clinically relevant species are beta- hemolytic, including an increasing number of A. caviae strains, beta-hemolytic colonies on blood agar should be screened with oxidase and a spot indole test Plesiomonas is easily differentiated from Aeromonas by positive reactions in Moellers lysine, ornithine, and arginine testsand by fermentation of m-inositol 37. Aeromonas in Blood Agar Ref: http://www.microbiologyatlas.kvl.dkMedium sized to large, smooth The same Blood Agar plate examinedcolonies, which are white, or with transmitted light. The coloniesespecially in older cultures, buff in are surrounded by a wide haemolysiscolour. The colonies have an entire zone.margin. 38. Laboratory diagnosis 6.5% NaCl: Distinguishes from Vibriofluvialis causing similar infections Resistance to vibriostatic agent O/129 :150 g of the vibriostatic agent 2,4-diamino-6,7-diisopropylpteridinedifferentiates from all otherVibrios 39. Aeromonas in Blood-MAC AgarRef: http://www.microbiologyatlas.kvl.dk 40. Id of Species 41. Biochemical identification of Aeromonas to complex levelNo. of strains identified as belonging toA. veroniiA. hydrophilaA. caviae complex complexcomplex(A. veronii HG8, bA.Test (A. hydrophila, A. (A. caviae,jandaei, bestiarum,A. media, A.A. schubertii, A.A. salmonicida) eucrenophila) trota)Esculin 87 (92, 81, 85) 71 (76, 55, 78) 0Voges-Proskauer 75 (88, 63, 62) 0 54 (88, 87, 17, 0)Glucose (gas) 81 (92, 69, 77) 16 (0, 0, 78) 87 (92, 100, 0, 69)L-Arabinose 93 (84, 100, 100) 96 (100, 100, 78) 4 (12, 0, 0, 0) 42. Exception Factsheet All are Motile except: A. salmonicida A. media All are Indole + except: A. schubertii All are Arg decarb + Ornith -ve except: A. veronii biovar veronii All are VP + Lysine decarb +ve except: A. caviae complex: VP ve Lysine decarb -ve 43. Antimicrobial Susceptibility andresistance patterns The clinically relevant Aeromonas spp are uniformlyresistant to penicillin and ampicillin Often resistant to cefazolin and ticarcillin Usually but not invariably susceptible to third-generation cephalosporins, aztreonam, andcarbapenems. Resistance to cefotaxime has developed on therapy. Sensitivity to piperacillin and ticarcillin-clavulanate isvariable. 44. Antimicrobial Susceptibility and resistance patterns Aeromonas spp produce as many as three - lactamases,1. A Bush group 2d penicillinase2. A group 1 cephalosporinase3. and a metallocarbapenemase Some isolates exhibit coordinated expression of these -lactamases after both induction and selection of derepressed mutants. 45. Antimicrobial Susceptibility and resistance patternsDespite the presence of a carbapenemase imipenem MIC typically remain low, although A. jandaei and A. veronii subtype veronii can display imipenem resistance.Unlikemostcarbapenemases, the Aeromonas metallocarbapenemases have narrow substrate profiles and specifically hydrolyze carbapenems. 46. Antimicrobial Susceptibility and resistance patternsThere are reports of increasing resistance to tetracycline and trimethoprim-sulfamethoxazole.In one report, tigecycline was active against 200 of 201 isolates.Aminoglycosides are usually active, with resistance to tobramycin being more common than resistance to gentamicin or amikacin. 47. Antimicrobial Susceptibility andresistance patternsFluoroquinolones are highly active against Aeromonas spp, although the existence of nalidixic acidresistant strains containing mutations in the gyrA gene raise concern that fluoroquinolone resistance could easily develop.Aeromonas species harboring a conjugative plasmid that confers multiple antibiotic resistance have been identified. 48. Antimicrobial Susceptibility andresistance patternsSusceptibility aAntibiotic agentResistantAmpicillin (except A. trota [100% susceptible]), A. caviae [35% susceptible] Ticarcillin or piperacillin (except A. veronii bv. veronii [100% resistant],Variable A.trota [100% suscep-tible]) Cephalothin Cefazolin Cefoxitin (except A. veronii bv. veronii [100% susceptible]) Cefuroxime Ceftriaxone CefotaximeSusceptibleCiprofloxacin c Gentamicin Amikacin Tobramycin (A. veronii bv. veronii [42% resistant]) Imipenem (A. jandaei [65% resistant], A. veronii bv. veronii [67% resistant]) Trimethoprim-sulfamethoxazole 49. THANK YOU