الفهرس 
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Abstract
Summary and Conclusion
Bacteria in most environments exist as structured communities of sessile cells embedded in a self-produced polymeric matrix known as biofilms. They are responsible for more than 80% of hospital-acquired and community acquired infections. P.aeurginosa is an important example of biofilm producing pathogen. Biofilm formation is considered as a virulence factor. It‟s extremely difficult to be eradicated, since they are shielded from the host defense mechanisms as phagocytes and antibodies, as well as antibiotics. Searching for alternative approaches for prevention and eradication of biofilm associated infections are therefore urgently needed.
This study aimed to test the effect of Lactobacillus acidophilus, a probiotic Lactobacilli, against the growth and biofilm formation/removal of the preformed one by different P.aeruginosa isolates to be used as an alternative or adjuvant to antibiotics.
Thirty-five isolates of P. aeurginosa were obtained from 135 urine samples from catheterized and un-catheterized patients admitted to ICUs of Ain Shams University EL-Demerdash hospital and suffered from UTI.
All samples were cultured on MacConkey’s and CLED agar media then the isolated organisms were identified by conventional microbiological methods.
Antibiotic susceptibility testing of the P. aeruginosa isolates was done using Kirby Bauer disc diffusion method according to CLSI guidelines, (2018). The isolates of P. aeruginosa showed a high resistance to cefepime and tobramycin (91.4%) followed by imipenem and Piperacillin/Tazobactam (85.7%), ciprofloxacin, levofloxacin and meropenem (82.9%), ceftazidime (77.1%), amikacin (68.6%), gentamycin (51.4%) and no resistance to aztreonam was detected.
Testing the antibacterial effect of L. acidophilus on the growth of the isolated strains of P. aeruginosa was done by using agar well diffusion method. The growth of P.aeruginosa strains were significantly inhibited by the cell-free supernatants of L.acidophilus by 88.6%.
The isolated P. aeruginosa strains were tested for their ability to form biofilm using microtitre plate assay. Out of the 35 isolates, 12 (34.3%) were strong biofilm producers, 12 (34.3%) were moderate biofilm producers, 9 (25.7%) were weak biofilm producers. The remaining 2 isolates (5.7%) were non biofilm producers.
The effect of L.acidophilus cell free supernatant was tested on the biofilm forming ability of the isolates using microtitre plate assay and the optical densities were compared before and after mixing the isolates with L. acidophilus cell free supernatant. There was statistically significant
Summary and Conclusion
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difference between the OD readings before and after adding L.acidophilus cell free supernatant (P<0.001).
The effect of L.acidophilus cell free supernatant was also tested on the preformed biofilm removal or reduction in biomass. There was statistically significant difference between the OD readings before and after adding L.acidophilus cell free supernatant on the preformed biofilms (P<0.001). This effect is less powerful than its ability to inhibit biofilm formation from the start. This may indicate that L. acidophilus may have a more powerful preventive role in biofilm formation by P. aeruginosa than to cure infections when biofilm is already established.
In conclusion, the present work illustrates that - although P. aeruginosa is hardly to be eradicated by a lot of antibiotics- L. acidophilus has the ability of biofilm inhibition/removing, in addition to their broad antibacterial effect that proposes them as a potent probiotics for bio-control of different antibiotic resistant biofilm producing P.aeruginosa strains.