Abstract
This study aimed to investigate the prevalence, antibiogram of Pseudomonasaeruginosa (P.aeruginosa), and the distribution of virulence genes (oprL,exoS, phzM, and toxA) and the antibiotic-resistance genes (blaTEM, tetA, and blaCTX-M). A total of 285 fish (165 Oreochromisniloticus and 120 Clariasgariepinus) were collected randomly from private fish farms in Ismailia Governorate, Egypt. The collected specimens were examined bacteriologically. P. aeruginosa was isolated from 90 examined fish (31.57%), and the liver was the most prominent infected organ. The antibiogram of the isolated strains was determined using a disc diffusion method, where the tested strains exhibited multi-drug resistance (MDR) to amoxicillin, cefotaxime, tetracycline, and gentamicin. The PCR results revealed that all the examined strains harbored (oprL and toxA) virulence genes, while only 22.2% were positive for the phzM gene. On the contrary, none of the tested strains were positive for the exoS gene. Concerning the distribution of the antibiotic resistance genes, the examined strains harbored blaTEM, blaCTX-M, and tetA genes with a total prevalence of 83.3%, 77.7%, and 75.6%, respectively. Experimentally infected fish with P.aeruginosa displayed high mortalities in direct proportion to the encoded virulence genes and showed similar signs of septicemia found in the naturally infected one. In conclusion, P.aeruginosa is a major pathogen of O.niloticus and C.gariepinus.oprL and toxA genes are the most predominant virulence genes associated with P.aeruginosa infection. The blaCTX-M,blaTEM, and tetA genes are the main antibiotic-resistance genes that induce resistance patterns to cefotaxime, amoxicillin, and tetracycline, highlighting MDR P.aeruginosa strains of potential public health concern.
Highlights
This study aimed to investigate the prevalence, antibiogram of Pseudomonas aeruginosa (P. aeruginosa), and the distribution of virulence genes and the antibioticresistance genes
A total of 285 fish samples represented as 165 O. niloticus (70 apparently healthy and 95 moribunds) and 120 C. gariepinus (55 apparently healthy and 65 moribunds) were collected randomly; (5 sampling points at two months interval) from two private freshwater farms located at Ismailia Governorate, Egypt over the period of July 2018 to February 2019
The clinical inspection revealed that 95 O. niloticus (95/165, 57.5%) and 65 C. gariepinus (65/120, 54.1%) were moribund and showed the signs of hemorrhagic septicemia
Summary
This study aimed to investigate the prevalence, antibiogram of Pseudomonas aeruginosa (P. aeruginosa), and the distribution of virulence genes (oprL, exoS, phzM, and toxA) and the antibioticresistance genes (blaTEM, tetA, and blaCTX-M). Concerning the distribution of the antibiotic resistance genes, the examined strains harbored blaTEM, blaCTX-M, and tetA genes with a total prevalence of 83.3%, 77.7%, and 75.6%, respectively. The blaCTX-M, blaTEM, and tetA genes are the main antibiotic-resistance genes that induce resistance patterns to cefotaxime, amoxicillin, and tetracycline, highlighting MDR P. aeruginosa strains of potential public health concern. Pseudomonas aeruginosa is a part of normal fish microbiota, under stressful conditions Such as malnutrition and overcrowding the bacteria have become highly opportunistic and pathogenic, causing serious illness including, hemorrhagic septicemia, gill necrosis, abdominal distension, splenomegaly, friable liver, and congested k idney[6]. P. aeruginosa is an aerobic Gram-negative motile, non-spore-forming rods, catalase, and oxidase-positive[7] This bacterium possesses many virulence-related determinants including cell-mediated and secreted virulence types. The molecular typing of most inherited antibiotic-resistance genes should be performed to avoid the emergence of antibiotic-resistant strains that have a global health c oncern[14]
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