الفهرس 
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Abstract
Pseudomonas aeruginosa is a common cause of nosocomial infections. It can causes serious infections as blood stream infections, urinary tract infections, wound infections and ventilator associated pneumonia especially in patients admitted to critical care units such as intensive care units.
Treatment of infections caused by P. aeruginosa is challenging because of its resistance to a large number of antimicrobial agents and extracellular matrix of biofilms which is one of the leading factors that can reduce the penetration of antibiotics and contribute to the evolution of resistance.
Nanoparticles are nowadays considered a viable alternative to antibiotics and seem to have a high potential to solve the problem of the emergence of bacterial multidrug resistant P. aeruginosa.
The aim of this work the present study was to isolate P.aeruginosa isolates from patients admitted to Menoufia university Hospitals, determine antibiotic susceptibility patterns of the isolated P.aeruginosa with ESβls detection ,detection of biofilm-producing P.aeruginosa strains phenotypically and genotypically (pslA and lasR genes),also assessment of the relationship between the ability of biofilm production and antibiotic resistance and finally evaluate the anti-bacterial and anti-biofilm activity of silver nano particles on P.aeruginosa isolates.
This study was perfomed in Medical Microbiology and immunology department, Faculty of medicine, Menoufia University from March 2021 to August 2022. Two hundred and eighty-three clinical samples were collected and processed according to standard microbiological methods. P. aeruginosa were further identified using Vitek-2 system.
Antibiogram was done to all P. aeruginosa
by modified Kirby Bauer disk diffusion method and for extended-spectrum β-lactamases. Biofilm production was detected by modified congo red agar methods and for genes essential to initiate and maintain biofilm structure (pslA and lasR genes), conventional PCR was used. The antibacterial and anti-biofilm effect of commercially available silver nano particles was also tested
A total 50 P. aeruginosa isolates were obtained from different clinical samples. P. aeruginosa were mostly isolated from burn unit (60%) and patients stayed in hospital for more than 10 days (68%), exposed to invasive procedures (100%) and had associated co-morbidities (64%).
About 92% of P. aeruginosa isolates were resistant to Piperacillin and ciprofloxacin while 62% and 52% of isolates were resistant to ceftazidime, and gentamicin respectively. On the other hand, 68%, 60% were sensitive to meropenem and imipenem respectively. About 54% of isolated P. aeruginosa were ESβls producers. All ESβL-producing P. aeruginosa isolates were resistant to piperacillin, ceftazidime, cefepime and azetronam (100%).
Regarding biofilm, 44% of isolated P. aeruginosa were biofilm producers with higher antibiotic resistance and ESβL-production among biofilm producing isolates.
The prevalence of pslA and lasR genes among P. aeruginosa isolates were (52%) and (48%) respectively, about 20/22 (90.9%) of the biofilmproducing P. aeruginosa isolates were positive for the pslA gene while only 6/28 (21.4%) of non-biofilm producers had pslA gene. About 18/22 (81.8%) of the biofilm-producing P. aeruginosa isolates were positive for the lasR gene compared to only6/28 (21.4%) in non-biofilm-producers.
Regarding to the antibacterial effect of AgNPs, higher concentrations were needed for bacterial growth inhibition in biofilm producers. MIC in biofilm producers ranged from 6.25 to 25 µg/ml, of which 36.4% had MIC of 25 μg/ml. On the other hand, the range of MIC in non-biofilm producers was (6.25 - 25 µg/ml), and 75% of them had MIC of 6.25 µg/ml.
Maximal inhibition of biofilm formation occurred at a concentration of 25 µg/ml of AgNPs. On the other hand, only 40.9% of biofilm were inhibited at a concentration of 6.25 μg/ml.