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Aeromonas Postgraduate Seminar Maulana Azad Medical College Delhi

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  • In green: New species after last Koneman / Topley
  • Dhakensis in Dhaka, controversy to A. aquarorium
    In Red: Human Pathogens
  • Contd in next slide Antibiotic and IgA
  • Here we see the complicated course of Gastroenteritis
    See ref 7 for chronic colitis
    Ref 8 for HUS
  • In fact this is a benign picture where boys are playing on naturally water logged playgrounds. In mud football competition the field is artificially water logged and the view is also rather enjoyable, just with a little Aeromonas
  • use of medicinal leeches Hirudo medicinalis in conjunction with reimplantation or flap surgery. These leeches are applied to reduce congestion of blood and improve graft uptake
  • Also recommended to apply leech only in areas with good arterial blood supply. So that infection to necrotic part by Aeromonas doesn’t occur
  • Also continued in next slide
  • Also continued in next slide
  • 1 or 2 drops of oxidase reagent T-Meth-Para-Phen-Diamine-DiHcl on colonies Characteristics Black Discolouration
  • Aeromonas spp. are most easily confused in the laboratory with other oxidase-positive fermenters, i.e., Vibrio and Plesiomonas spp.
  • Aeromonas spp. are most easily confused in the laboratory with other oxidase-positive fermenters, i.e., Vibrio and Plesiomonas spp.
  • Chalk and board Esculin VP ++, +-, -+
  • Transcript

    • 1. Definition (Topley Wilson 10th Ed) Gram negative  Oxidase +  Catalase +  Facultative anaerobic rods  All are motile by means of a single polar flagellum Except: 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  Amylase peptidases,  DNase, proteases,  chitinase, chondroitinase,  hemolysins
    • 3. Classification & Taxonomy In mid 1970s the genus Aeromonas was divided into 2 groups:  PSYCHROPHILIC: only one spp – A. salmonicida , a fish pathogen. It is non motile & doesn’t grow at 37° C.  MESOPHILIC: all the other identified spp.  Mesophilic: A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, typically between 25 and 40 °C (77 and 104 °F).  Psychrophilic: Psychrophiles or cryophiles are extremophilic organisms that are capable of growth and reproduction in cold temperatures, ranging from −15°C to +10°C.
    • 4. Classification & Taxonomy…contd 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. Organism Human isolation (extraintestinal/fecal) Human pathogen (extraintestinal/fecal) Frequency in humans Pathogenic for animals, fish, and reptiles A. hydrophila complex A. hydrophila subsp. hydrophila Yes Yes Common Yes subsp. dhakensis b Yes Yes Rare No subsp. ranae No No — Yes A. bestiarum No/yes —/no Rare Yes A. salmonicida c No/yes No/no Rare subsp. salmonicida Yes subsp. achromogenes Yes subsp. masoucida Yes subsp. smithia Yes subsp. pectinolytica No Members of the genus Aeromonas
    • 6. Organism Human isolation (extraintestinal/fecal) Human pathogen (extraintestinal/fecal) Frequency in humans Pathogenic for animals, fish, and reptiles A. hydrophila complex A. hydrophila subsp. hydrophila Yes Yes Common Yes subsp. dhakensis b Yes Yes Rare No subsp. ranae No No — Yes A. bestiarum No/yes —/no Rare Yes A. salmonicida c No/yes No/no Rare subsp. salmonicida Yes subsp. achromogenes Yes subsp. masoucida Yes subsp. smithia Yes subsp. pectinolytica No Members of the genus Aeromonas
    • 7. Organism Human isolation (extraintestinal /fecal) Human pathogen (extraintestinal/ fecal) Frequency in humans Pathogenic for animals, fish, and reptiles A. caviae complex A. caviae Yes Yes Common Yes A. media No/yes —/yes Rare No A. eucrenophila Yes No/— Very rare No Members of the genus Aeromonas
    • 8. Organism Human isolation (extraintestinal/fecal) Human pathogen (extraintestinal/fecal) Frequency in humans Pathogenic for animals, fish, and reptiles A. veronii complex A. veronii bv. sobria Yes Yes Common Yes A. veronii bv. veronii Yes Yes Rare No A. jandaei Yes Yes/unknown Rare No A. trota Yes Neither Rare No A. schubertii Yes/no Yes/— Rare No A. encheleia Yes/no No/— One case No A. allosaccharophila No/yes —/no Very rare Yes A. sobria Neither — — No A. popoffii Yes Yes Very rare No A. culicicola No No — No A. simiae No No — No A. molluscorum No No — No A. bivalvium No No — No A. tecta Yes No Rare No A. piscicola No No — Yes
    • 9. Organism Human isolation (extraintestinal/fecal) Human pathogen (extraintestinal/fecal) Frequency in humans Pathogenic for animals, fish, and reptiles A. veronii complex A. veronii bv. sobria Yes Yes Common Yes A. veronii bv. veronii Yes Yes Rare No A. jandaei Yes Yes/unknown Rare No A. trota Yes Neither Rare No A. schubertii Yes/no Yes/— Rare No A. encheleia Yes/no No/— One case No A. allosaccharophila No/yes —/no Very rare Yes A. sobria Neither — — No A. popoffii Yes Yes Very rare No A. culicicola No No — No A. simiae No No — No A. molluscorum No No — No A. bivalvium No No — No A. tecta Yes No Rare No A. piscicola No No — Yes
    • 10. Straight, coccobacillary to bacillary cells with rounded ends 0.3 to 1.0 μm in diameter and 1.0 to 3.5 μm in length. They can occur singly, in pairs, or, rarely, in short chains. Most species are motile by a single, polar flagellum with a 1.7-μm wavelength, but peritrichous flagella may be formed on solid media in young cultures and lateral flagella occur in some species. Morphology and Cell Structures
    • 11. Morphology and Cell Structures
    • 12.  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 Type strain
    • 13. The spectrum of human infections caused by Aeromonas spp usually fall into the 4 broad categories:  Gastroenteritis  Cellulitis and wound infection  Septicemia  Miscellanous Clinical significance
    • 14. There are currently 20 named species but only 3 are of major clinical importance:  A. hydrophila  A. caviae  A. veronii biovar sobria Clinical significance
    • 15. Aeromonas 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 Gastroenteritis
    • 16. Evidence 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) Gastroenteritis …contd
    • 17. Evidence 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; and Evidence of a specific secretory immune response (IgA) coincident with diarrheal disease. Gastroenteritis …contd
    • 18.  Diarrhea is usually watery and self-limited  But some persons develop fever, abdominal pain, and bloody stools.  Fecal leukocytes may be present. Gastroenteritis …contd
    • 19. Occasionally, 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 Gastroenteritis …contd
    • 20. Most 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. Cellulitis & wound infection
    • 21. Suppuration and necrosis around the wound are frequent, and surgical débridement is often necessary. Fasciitis, myonecrosis (occasionally associated with gas formation), and osteomyelitis may develop. Cellulitis & wound infection …contd
    • 22. Aeromonas soft tissue infections can develop  after exposure to soil  in association with crush injuries, and  as a complication of burns, typically when initial management of the burn included immersion in natural water sources. Cellulitis & wound infection …contd
    • 23. Cellulitis & wound infection …contd There is one reported outbreak of A. hydrophila wound infections in participants of a mud football competition in Australia. The field was “prepared” with water from an adjacent river.
    • 24. In relation to Hirudotherapy Aeromonas soft tissue infection is a recognized complication of the use of medicinal leeches in conjunction with reimplantation or flap surgery.
    • 25. In relation to Hirudotherapy  Aeromonas hydrophila and other Aeromonas species are normal inhabitants of the foregut of leeches.  Leeches lack the requisite proteolytic enzymes and are dependent on the symbiotic Aeromonas to digest the blood meal.  Aeromonas infection has developed in 7% to 20% of patients treated with leeches.  Prophylactic antibiotics now have been recommended at the time of leech application.  Mild wound infection, loss of flap,myonecrosis, and sepsis may ensue
    • 26. The 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. Septicaemia
    • 27. Taiwan Study…contd  Aeromonas hydrophila caused 60% of the bacteremias most of the other isolates that were identified by species were A. veronii subtype sobria and A. caviae. Most patients in this series were immunocompromised, including 54% who were cirrhotic and 21% who had an underlying malignancy. Septicaemia
    • 28. 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. Septicaemia
    • 29. The US Experience …contd: 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. Septicaemia
    • 30. A 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 Miscellaneous Infections
    • 31.  Endocarditis,  suppurative thrombophlebitis,  osteomyelitis,  urinary tract infection, prostatitis,  pneumonia including near-drowning– associated pneumonia,  LRTI, empyema, lung abscess,  URTI, tonsillitis, epiglottitis, otitis media  keratitis Miscellaneous Infections
    • 32. A. hydrophila epididymitis and bacteremia developed in a healthy man Before 24 hours he had sexual intercourse with his wife in their swimming pool Cultures obtained from the pool grew A. Hydrophila. Ref: Blair JE, Woo-Ming MA, McGuire PK: Aeromonas hydrophila bacteremia acquired from an infected swimming pool. Clin Infect Dis 1999; 28:1336-1337. Miscellaneous Infections
    • 33. Laboratory diagnosis  Selective Media for Id from Faeces:  Blood Agar (+/- Ampicillin) 10µg/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 diagnosis …contd  Modified cefsulodin-Irgasan-novobiocin (CIN) (4 μg/mL of cefsulodin versus 15 μg/ml in unmodified CIN) is also an excellent isolation medium for aeromonads. On this medium, Aeromonas colonies have a  pink center with an uneven, clear apron and are indistinguishable from Yersinia enterocolitica morphologically.
    • 35. Laboratory diagnosis  Oxidase + Thus quickly excluded from Enterobacteriaceae  Motile  Indole + This excludes Pseudomonas  OF test: Aeromonads utilize glucose fermentatively, thus excluded from Pseudomonas 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  Moeller’s lysine, ornithine, and arginine tests and by fermentation of m-inositol
    • 37. Aeromonas in Blood Agar Ref: http://www.microbiologyatlas.kvl.dk Medium sized to large, smooth colonies, which are white, or especially in older cultures, buff in colour. The colonies have an entire margin. The same Blood Agar plate examined with transmitted light. The colonies are surrounded by a wide haemolysis zone.
    • 38. Laboratory diagnosis  6.5% NaCl: Distinguishes from Vibrio fluvialis causing similar infections  Resistance to vibriostatic agent O/129 : 150 μg of the vibriostatic agent 2,4- diamino-6,7-diisopropylpteridine differentiates from all other Vibrios
    • 39. Aeromonas in Blood-MAC Agar Ref: http://www.microbiologyatlas.kvl.dk
    • 40. Id of Species
    • 41. Biochemical identification of Aeromonas to complex level No. of strains identified as belonging to Test A. hydrophila complex (A. hydrophila, A. bestiarum, A. salmonicida) A. caviae complex (A. caviae, A. media, A. eucrenophila) A. veronii complex (A. veronii HG8, bA. jandaei, A. schubertii, A. trota) Esculin 87 (92, 81, 85) 71 (76, 55, 78) 0 Voges-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.  The clinically relevant Aeromonas spp are uniformly resistant to penicillin and ampicillin  Often resistant to cefazolin and ticarcillin  Usually but not invariably susceptible to third- generation cephalosporins, aztreonam, and carbapenems.  Resistance to cefotaxime has developed on therapy.  Sensitivity to piperacillin and ticarcillin-clavulanate is variable. Antimicrobial Susceptibility and resistance patterns
    • 44. Aeromonas spp produce as many as three β- lactamases, 1. A Bush group 2d penicillinase 2. A group 1 cephalosporinase 3. and a metallocarbapenemase Some isolates exhibit coordinated expression of these β-lactamases after both induction and selection of derepressed mutants. Antimicrobial Susceptibility and resistance patterns
    • 45. Despite the presence of a carbapenemase imipenem MIC typically remain low, although A. jandaei and A. veronii subtype veronii can display imipenem resistance. Unlike most carbapenemases, the Aeromonas metallocarbapenemases have narrow substrate profiles and specifically hydrolyze carbapenems. Antimicrobial Susceptibility and resistance patterns
    • 46. There 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. Antimicrobial Susceptibility and resistance patterns
    • 47. Fluoroquinolones are highly active against Aeromonas spp, although the existence of nalidixic acid–resistant 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. Antimicrobial Susceptibility and resistance patterns
    • 48. Antimicrobial Susceptibility and resistance patterns Susceptibility a Antibiotic agent Resistant Ampicillin (except A. trota [100% susceptible]), A. caviae [35% susceptible] Variable Ticarcillin or piperacillin (except A. veronii bv. veronii [100% resistant], A.trota [100% suscep-tible]) Cephalothin Cefazolin Cefoxitin (except A. veronii bv. veronii [100% susceptible]) Cefuroxime Ceftriaxone Cefotaxime Susceptible Ciprofloxacin 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

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