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Year : 2002  |  Volume : 20  |  Issue : 2  |  Page : 107-109

Aeromonas species isolated from cases of acute gastroenteritis

Dept. of Microbiology, Seth GS Medical College and KEM Hospital Parel, Mumbai - 400 012, India

Correspondence Address:
Dept. of Microbiology, Seth GS Medical College and KEM Hospital Parel, Mumbai - 400 012, India

 ~ Abstract 

A total of 67 Aeromonas strains were isolated as the sole bacterial pathogen from1485 patients with acute gastroenteritis. A. hydrophila (64.2%) was the predominant isolate followed by A. sobria (28.4%) and A.caviae (7.4%). Majority of the isolates were sensitive to gentamicin, nalidixic acid but were resistant to ampicillin. Minimum inhibitory concentration (MIC) of resistant strains of Aeromonas to ampicillin ranged from 80-1280 g/mL.

How to cite this article:
Vasaikar S, Saraswathi K, De A, Varaiya A, Gogate A. Aeromonas species isolated from cases of acute gastroenteritis. Indian J Med Microbiol 2002;20:107-9

How to cite this URL:
Vasaikar S, Saraswathi K, De A, Varaiya A, Gogate A. Aeromonas species isolated from cases of acute gastroenteritis. Indian J Med Microbiol [serial online] 2002 [cited 2021 Mar 8];20:107-9. Available from:

Aeromonas species are ubiquitous water borne organisms and in recent years have gained importance as human pathogens causing gastrointestinal infections and extra intestinal infections such as cellulitis, wound infection, peritonitis, endocarditis, osteomyelitis, meningitis and suppurative arthritis in patients with leukemia.[1],[2],[3],[4],[5],[6],[7] Aeromonas species have been reported more frequently from patients of acute diarrhea.[5],[7]
The present study was undertaken to assess the incidence of Aeromonas species, characterize and speciate the isolates and to study their sensitivity pattern in cases of acute gastroenteritis.

 ~ Materials and Methods Top

A total of 1485 faecal samples were collected from patients (adults as well as children) with acute diarrhea / dysentery attending the out patient department and those admitted in LTM general hospital, before starting the antibiotic therapy. The stool specimens were collected in sterile wide mouthed containers and rectal swabs in Cary - Blair transport medium. Detailed history with respect to duration and frequency of diarrhoea per day, pain in the abdomen, fever, vomiting and degree of dehydration were recorded in all the patients. During the same period, stool samples from 500 age and sex matched controls admitted in the hospital for illnesses other than gastroenteritis were also studied. The stool specimens were processed within two hours of collection. All the specimens were subjected to gross and microscopic examination (saline and iodine preparation) and screened for Aeromonas species as well as for other conventional bacterial enteric pathogens by standard bacteriological methods.[8] Viral etiology was not studied in our patients. The culture was done directly on MacConkey's agar, xylose lysine deoxycholate agar and ampicillin (10 g/mL) sheep blood agar.[8] Simultaneous enrichment was also done in gram negative broth and alkaline peptone water, incubated overnight at 37oC and then sub-cultured on the above mentioned media. Suspected colonies were identified as Aeromonas species as per standard laboratory methods[8] and speciated by biochemical tests as proposed by Popoff.[9] The isolates were subjected to antimicrobial sensitivity against ampicillin, tetracycline, chloramphenicol, co-trimoxazole, cefotaxime, gentamicin, nalidix acid and ciprofloxacin by the Kirby - Bauer disc diffusion technique on Mueller-Hinton agar. A control strain of E.coli (ATCC 25922) was used in parallel. The minimum inhibitory concentration (MIC) of ampicillin for the resistant Aeromonas isolates were determined by agar dilution method.[8]

 ~ Results Top

Aeromonas was isolated from 67 patients out of a total of 1485 patients with acute gastroenteritis. In the present study, the isolation rate of Aeromonas species was 4.51%. No other bacterial enteropathogens were isolated from these patients and the microscopic examination of the stool specimens did not reveal any pus cells, RBCs and parasites. Out of 67 strains, 49 (73.1%) were isolated from adults and 18 (26.9%) from pediatric age group. Aeromonas species were isolated in almost equal number in both sexes (33 males and 34 females).
Of the 67 isolates of Aeromonas, 43 were identified as A. hydrophila, 19 as A. sobria, and 5 as A. caviae. No Aeromonas species were isolated from the control group of 500 patients. Susceptibility pattern of 67 Aeromonas isolates is shown in the [Table - 1].
All the strains of A. hydrophila. A. sobria and A. caviae were sensitive to gentamicin, nalidixic acid, ciprofloxacin and cefotaxime. 34 strains of A. hydrophila (79%) were susceptible to chloram-phenicol, 33 (76.7%) to co-trimoxazole and 32 (74.4%) to tetracycline whereas A. sobria and A. caviae were susceptible to these antibiotics. Ampicillin sensitivity was only 14.9%. Minimum inhibitory concentration (MIC) of 57 resistant strains of A. hydrophila to ampicillin ranged from 80-1280 g/mL. Of these 57 strains 38 had MIC of 80 g/mL, 2 strains had 160 g/mL and one each had 320 g/mL, 640 g/mL, and 1280 g/mL. The MIC of 10 sensitive strains of A. hydrophila for ampicillin was 20 g/mL.
The main symptoms in patients with acute gastroenteritis due to Aeromonas species was watery diarrhoea of 2-8 days duration with an average of 8-10 stools/day. Low grade fever, vomiting and abdominal pain was encountered in 19% of the patients. None of the patients had any underlying disease or had received antibiotics two weeks prior to the onset of illness. All the 67 patients with Aeromonas infection were hospitalized and recovered uneventfully with parenteral rehydration and specific antibiotic treatment comprising of gentamicin and nalidixic acid or gentamicin and ciprofloxacin.

 ~ Discussion Top

In recent years, Aeromonas species have been recognized with increasing frequency as a cause of gastroenteritis in children and adults.[1],[2],[5],[7],[10] Incidence of Aeromonas species causing acute gastroenteritis ranges from 0.2% to 7.7%.[4] The isolation rate in the present study was 4.5% which correlates well with that of Ananthan and Alavandi (4.7%)[6] However, the incidence of Aeromonas species reported by Kuijper et al was less (3.7%)[12], whereas that by Kaur et al. was higher (7.7%)4 than in our study. From 1485 patients having acute gastroenteritis, 67 (4.51%) Aeromonas strains were isolated as the sole bacterial enteropathogen which is in concurrence with reports by other workers.2,7 In our study, A.hydrophila (64.2%) was the predominant isolate followed by A.sobria (28.4%) and A.caviae (7.4%). Several studies have shown similar preponderance of the species.[10],[11] However, Kaur et al have encountered A.caviae (83.8%) as the predominant isolate.[4]
Several investigators have determined the asymptomatic carrier rate to assess the role of Aeromonas species in diarrhoeal diseases. A faecal carriage rate of 0.5% to 3.2% has been reported.1,7 Agger et al showed that Aeromonas species were not associated with any of their 533 control group[2] which correlates well with our study where no Aeromonas strains were isolated from the control group (X2=22.04; p<0.001). The results of antibiotic sensitivity pattern of Aeromonas strains revealed 85.1% resistance to ampicillin, 16.4% to tetracycline and 14.9% to co-trimoxzole. The resistance to ampicillin is well documented.[13] In the present study, the level of resistance to ampicillin was of high order as compared to that reported by Richardson et al.[13]
In the developing countries Aeromonas induced diarrhoea is mainly toxigenic characterized by watery diarrhoea where as in the developed countries, the clinical spectrum varies from toxigenic diarrhoea to coliltis.[1],[3],[7] Earlier studies have shown enterotoxin production by A.hydrophila, A.sobria and A.caviae.3 In the present study, all the Aeromonas infected patients had watery diarrhoea suggesting the toxigenic nature of the organism. In all these patients Aeromonas was isolated as the sole bacterial enteropathogen in large numbers on primary isolation medium. Aeromonas infected patients recovered completely with treatment and repeat faecal cultures were negative. The present study reiterates the role of Aeromonas species as potential enteric pathogens in this geographical area. 

 ~ References Top

1.Von Gravenitz A, Mensch AH. The genus "Aeromonas" in human bacteriology report of 30 cases and review of literature. N Eng J Med 1968; 278:245-248.  Back to cited text no. 1    
2.Agger WA, McCormick JD, Gurwith MJ. Clinical and microbiological features of Aeromonas hydrophila associated diarrhoea. J Clin Microbiol 1985; 21:909-913.  Back to cited text no. 2    
3.Saraswathi K, Deodhar LP. Diarrhoea associated with Aeromonas hydrophila. Indian J Med Res 1986; 84:571-573.  Back to cited text no. 3    
4.Kaur G. Rodrigues S, Verenker MP. A study of Aeromonas in Goa. Indian J Med Microbiol 1999; 17:180-183.  Back to cited text no. 4    
5.Janda JM, Buttons EJ, Skinner CV, Calcaterra D. Phenotypic markers associated with gastrointestinal Aeromonas hydrophila isolates from symptomatic children. J Clin Microbiol 1983; 17:588-590.  Back to cited text no. 5    
6.Ananthan S, Alavandi SV. Biochemical characteristics and secretory activity of Aeromonas species isolated from children with gastroenteritis in Chennai. Indian J Med Res 1999; 109:136-240.  Back to cited text no. 6    
7.Sanyal SC, Sen PC, Tiwari IC, Bhatia BD, Singh SJ. Microbial agents in stools of infants and young children with and without acute diarrhoeal disease. J Trop Med Hyg 1977; 80:2-8.  Back to cited text no. 7    
8.Baron EJ, Peterson LR, Finegold SM. Conventional and rapid microbiological methods for identification of bacteria and fungi. In: Bailey & Scott's Diagnostic Microbiology, 10th ed. (The CV Mosby Co, St Louis) 1998:167-187.  Back to cited text no. 8    
9.Popoff MY. In: Genus III Aeromonas species. In: Bergey's Manual of Systematic Bacteriology, 9th ed. Kind NN, Halt, Eds. (The Williams and Wilkins Co, Baltimore) 1984:545-548.  Back to cited text no. 9    
10.Burke V, Gracy M, Robinson J, Peck D, Beaman J, Bundell C. The microbiology of childhood gastroenteritis. Aeromonas species and other infective agents. J Infect Dis 1983; 148:68-74.  Back to cited text no. 10    
11.Sack DA, Chowdhury KA, Hug A, Kay BA, Sayeed S. Epidemiology of Aeromonas and Plesiomonas diarrhoea. J Diarrhoeal Dis Res 1988; 6:107-112.  Back to cited text no. 11    
12.Kuijper EJ, Zanen HC, Peters MF. Aeromonas associated diarrhoea in the Netherlands. Ann Int Med 1987;104:640-641.  Back to cited text no. 12    
13.Richardson CJ , Robinson JO, Wagner LB, Burke V. Invitro susceptibility of Aeromonas species to antimicrobial Agents. J Antimicrob Chemother 1982; 9:267-274.  Back to cited text no. 13    
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