Academic journal article Journal of Health Population and Nutrition

Characterization of Ceftriaxone-Resistant Aeromonas Spp. Isolates from Stool Samples of Both Children and Adults in Southern India

Academic journal article Journal of Health Population and Nutrition

Characterization of Ceftriaxone-Resistant Aeromonas Spp. Isolates from Stool Samples of Both Children and Adults in Southern India

Article excerpt


The family Aeromonadaceae contains the members of the genus Aeromonas which are Gram-negative rods, facultative anaerobes and oxidase-positive. They are habitants of a wide range of aquatic environment like fresh, marine and estuarine water, as well as sewage where the bacterial ecosystem co-exists as well as are natural pathogens of aquatic life forms like fishes, etc. [1].

A number of Aeromonas species are described, but the taxonomy of the genus Aeromonas is confusing because of the lack of congruity between the phenotypic and genotypic characters. Now, several DNA hybridization methods are available based on which Aeromonas species are classified [1, 2]. Important Aeromonas species which are pathogenic for humans include Aeromonas hydrophila, Aeromonas sobria, Aeromonas trota, and Aeromonas caviae [1, 3, 4].

Today, Aeromonas species are considered not only pathogenic to cold-blooded animals and fishes, some of the species are pathogenic to animals and humans also, both immunocompetent and immunocompromised. The spectrum of infections caused by Aeromonas species varies from various intestinal manifestations to extra intestinal complications namely gastrointestinal tract syndromes, wound and soft tissue infections, urinary tract infections and rarely septicaemia [1, 2].

The role of Aeromonas as a gastrointestinal pathogen has been controversial as 1-4 % of asymptomatic individuals are known to harbour them in their gut. However, Aeromonas-associated acute bacterial gastroenteritis has been reported from across the world. The gastrointestinal manifestations can vary from an acute gastroenteritis presenting with an acute watery diarrhoea, choleraic illness to a more severe form accompanied by dysentery rarely leading to hemolytic uremic syndrome [1-4].

Susceptibility to the antibiotics varies according to the geographical area and the species of Aeromonas tested. Most of the isolates are generally susceptible to tetracyclines and quinolones though development of increasing resistance to third generation cephalosporins due to the production of beta-lactamases and extended spectrum beta-lactamases (ESBLs) has been noted in the recent years [2, 3, 5]. The current study was undertaken to characterize the third generation cephalosporin-resistant strains of Aeromonas spp. which were isolated from stool specimens.


The present study was a descriptive study conducted in a tertiary care centre in South India. All consecutive non-duplicate stool isolates of Aeromonas spp. resistant/intermediate to ceftriaxone by Kirby-Bauer disc diffusion method during a study period of 3 years from January 2010 to December 2012 were included in the study. These isolates were characterized phenotypically and genotypically for determining ceftriaxone resistance mechanisms.

Bacterial isolates

A total of 2780 stool samples were processed, out of which, 29 (1.04 %) Aeromonas spp. were identified. Total samples positive for other pathogens were Shigella (6.1 %), non-typhoidal salmonellae (1.29 %) and Vibrio cholerae (7 %) among the bacterial causes of diarrhoea, during the study period of 2 years using the cultural characteristics and standard biochemical reactions, followed by confirmation with respective antisera wherever applicable [6, 7]. In these 29 patients, no other pathogen was isolated, and Aeromonas spp. were the single pathogen isolated.

Antimicrobial susceptibility testing

Antimicrobial susceptibility testing of all the isolates was performed on Mueller-Hinton agar plates by standard Kirby-Bauer disc diffusion method as per the standard procedure mentioned in Clinical Laboratory Standards Institute guidelines for Aeromonas spp. [8]. The isolates were tested to the following panel of antibiotics including the beta-lactam and the non-beta lactam group of antibiotics namely ceftriaxone (30 ?g), ciprofloxacin (5 ?g), tetracycline (30 ?g), cotrimoxazole (1.25/23.75 ? …

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