Aims:  To identify the causative agent of the mortality in the fish, Mugil cephalus, in Muttukadu lagoon. Methods and Results:  An enteric bacterium from the kidneys of moribund fish M. cephalus, was isolated and identified as Enterobacter cloacae (MK). Mugil cephalus was experimentally infected by this isolate and was re‐isolated from the kidneys of the moribund fish. Enterobacter cloacae isolates from the lagoon water (MW1, MW2 and reference strain ATCC 13047) and the reference strain were not able to induce similar pathogenesis. The putative factor imparting pathogenicity to the MK isolate was identified as a cationic molecule, which migrated towards the cathode on agarose gel electrophoresis. Conclusions:  The Ent. cloacae (MK) isolate harbouring a cationic factor was the causative agent for the mortality of M. cephalus, found in Muttukadu lagoon. Significance and Impact of the Study:  This study reveals that human enteric bacteria MK which is considered as nonpathogenic to fish, may become pathogenic to fish when it harbours this cationic factor. This cationic factor is found to be pathogenic to the fish M. cephalus leading to mortality. It was also found to be pathogenic to mice. Therefore, the shuttling of Ent. cloacae, harbouring cationic factor, between human and fish may be of human health importance.

Background: In recent decades, Pseudomonas aeruginosa has emerged as a multidrug-resistant bacteria by acquiring intrinsic resistance to a number of antimicrobial agents by uses distinctive resistant mechanisms to all the available antibiotics, which include metallo-β-lactamases (MBL) production, extended spectrum β-lactamase production, Amp C production, decreased permeability, altered penicillin binding proteins and rarely, and over expression of efflux pumps. Aims and Objectives: The aim of the study was to know the presence of IMP gene among P. aeruginosa isolates and to determine the carbapenem resistance mechanisms in carbapenem-resistant isolates of P. aeruginosa collected from sputum, blood, urine, pus, in Chennai, India. Materials and Methods: A total of 20 of non-repetitive clinical isolates of P. aeruginosa were collected and processed for biochemical tests and confirmed. Antibiotic susceptibility testing was determined by Kirby Bauer disc diffusion method. P. aeruginosa isolates were detected for the presence of bla IMP gene by polymerase chain reaction analysis. Results: Of the 20 clinical isolates of P. aeruginosa, 9/20 (45%) isolates were from sputum, 5/20 (25%) from blood, 3/20 (15%) from urine, and 3/20 (15%) from pus. Only 2/20 (10%) isolates showed sensitivity to imipenem. Other than that, for all other antibiotics isolates showed complete resistance 20/20 (100%). 17/20 (85%) clinical isolate of P. aeruginosa was found to possess bla IMP gene. Conclusion: The early detection of MBL-producing P. aeruginosa may help in appropriate antimicrobial therapy and avoid the development and dissemination of these multidrug-resistant strains. However, to derive a conclusion, a more number of isolates are recommended and even other types of genes are also screened.