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<p>This study investigated the concurrent infection of <i>Pseudomonas aeruginosa</i> and <i>Saprolegnia parasitica</i> in <i>Oreochromis niloticus</i> from Lake Manzala during the period from October to December 2023, employing phenotypic and genotypic characterizations of the isolated pathogens. Naturally infected fish displayed septicemic picture, fin rot, and the presence of cotton wool-like masses on the skin and fins. Water quality analysis revealed elevated salinity, unionized ammonia and nitrite levels, alongside with suboptimal water temperature. <i>P. aeruginosa</i> and <i>S. parasitica</i> were isolated from 30% and 31.8% of the clinically affected and moribund examined fish, respectively. Molecular analysis of <i>P. aeruginosa 16&#xa0;S-rDNA</i> and <i>S. parasitica ITS-rDNA</i> genes demonstrated a genetic similarity with their ancestral strains from the families <i>Pseudomonadaceae</i> and <i>Saprolegniaceae</i>, respectively. The pathogenicity of <i>P. aeruginosa</i> was confirmed through β-hemolysis and biofilm production. Antimicrobial susceptibility testing of <i>P. aeruginosa</i> indicated high susceptibility to colistin sulfate (100%) and meropenem (87.95%), with notable resistance to tetracycline (100%) and ampicillin (93.9%). Virulence gene analysis identified several key genes, including <i>tox</i>A (93.9%), <i>exo</i>S (66.7%), <i>las</i>B (45.45%), <i>phzM</i> (33.3%), <i>psl</i>A (33.3%), and <i>fli</i>C (42.4%). Resistance profiling revealed the presence of multiple antibiotic resistance genes, including <i>tet</i>A (100%), <i>bla</i><sub>TEM</sub> (93.9%), <i>bla</i><sub>CTX−M−1</sub> (81.8%), <i>bla</i><sub>OXA−1</sub> (54.4%), <i>qnr</i>A (30.3%), and <i>bla</i><sub>NDM−1</sub> (12.1%). Extensive drug resistance (XDR) and multiple drug resistance (MDR) phenotypes were observed in 12.1% and 27.3% of <i>P. aeruginosa</i> isolates, respectively, with high multiple antibiotic resistance (MAR) indices. Scanning electron microscopy (SEM) of skin lesions revealed extensive mycelial networks of <i>S. parasitica</i> on ulcerated skin surfaces. The co-occurrence of highly virulent, multidrug-resistant <i>P. aeruginosa</i> and <i>S. parasitica</i> underscores the complexity of treatment and highlights the need for targeted intervention strategies in aquaculture systems for disease prevention and control.</p>

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Synchronous natural infection of Nile tilapia (Oreochromis niloticus) by drug-resistant Pseudomonas aeruginosa and Saprolegnia parasitica: insights into water quality, phenotypic traits, and genotypic profiles

  • 期刊论文

  • 发表日期：

    2025年12月17日

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  • Reham M. El‑Tarabili,
  • Mahmoud E. Elsayed,
  • Hanan S. Khalefa,
  • Hanan Elghayaty,
  • Zainab Mohamed El Kattawy,
  • Mohamed Marzok,
  • Sherief M. Abdel-Raheem,
  • Hesham L. Ismail,
  • Dalia A. Abdel-moneam

摘要

This study investigated the concurrent infection of Pseudomonas aeruginosa and Saprolegnia parasitica in Oreochromis niloticus from Lake Manzala during the period from October to December 2023, employing phenotypic and genotypic characterizations of the isolated pathogens. Naturally infected fish displayed septicemic picture, fin rot, and the presence of cotton wool-like masses on the skin and fins. Water quality analysis revealed elevated salinity, unionized ammonia and nitrite levels, alongside with suboptimal water temperature. P. aeruginosa and S. parasitica were isolated from 30% and 31.8% of the clinically affected and moribund examined fish, respectively. Molecular analysis of P. aeruginosa 16 S-rDNA and S. parasitica ITS-rDNA genes demonstrated a genetic similarity with their ancestral strains from the families Pseudomonadaceae and Saprolegniaceae, respectively. The pathogenicity of P. aeruginosa was confirmed through β-hemolysis and biofilm production. Antimicrobial susceptibility testing of P. aeruginosa indicated high susceptibility to colistin sulfate (100%) and meropenem (87.95%), with notable resistance to tetracycline (100%) and ampicillin (93.9%). Virulence gene analysis identified several key genes, including toxA (93.9%), exoS (66.7%), lasB (45.45%), phzM (33.3%), pslA (33.3%), and fliC (42.4%). Resistance profiling revealed the presence of multiple antibiotic resistance genes, including tetA (100%), blaTEM (93.9%), blaCTX−M−1 (81.8%), blaOXA−1 (54.4%), qnrA (30.3%), and blaNDM−1 (12.1%). Extensive drug resistance (XDR) and multiple drug resistance (MDR) phenotypes were observed in 12.1% and 27.3% of P. aeruginosa isolates, respectively, with high multiple antibiotic resistance (MAR) indices. Scanning electron microscopy (SEM) of skin lesions revealed extensive mycelial networks of S. parasitica on ulcerated skin surfaces. The co-occurrence of highly virulent, multidrug-resistant P. aeruginosa and S. parasitica underscores the complexity of treatment and highlights the need for targeted intervention strategies in aquaculture systems for disease prevention and control.