Effects of Ceftazidime Exposure on Phenotypic Characteristics of Pseudomonas Aeruginosa ATCC 9027

Pseudomonas aeruginosa is a well-known opportunistic Gram-negative bacterium that is responsible for several acute and chronic infections. This study investigated changes in the phenotype of P. aeruginosa under exposure to sub-MIC values of ceftazidime (Cz). The fully susceptible strain P. aeruginosa ATCC9027 was exposed to a sub-MIC level of Cz for 14 days to obtain Cz-E1 strain then cultured in an antibiotic-free medium for 10 consecutive days to obtain Cz-E2 strain. The Kirby-Bauer disk diffusion testing was used to determine the antibiotic susceptibility profile of obtained strains. The morphology of the strains was examined via colony morphology and scanning electron microscope (SEM). Two important virulence factors of P. aeruginosa, including pyoverdine and protease, were examined for production using a culture-based method. After being exposed to Cz, P. aeruginosa increased its Cz- MIC value 210 times ( from 4 to 1024 mg/L), and became highly resistant Cz. Moreover, it also exhibited resistance to other β-lactam antibiotics, including cefepime and piperacillin/tazobactam. Shape and size of P. aeruginosa altered in responding to Cz exposure. Colonies became smaller, with their diameter lesser than 3 mm. Cell length was significantly reduced in Cz-exposed strains compared to the initial train (from 1.98 ± 0.28 µm to 0.83 ± 0.07 µm, p-value < 0.05). Cz-E1 had a significant reduction of protease activity and pyoverdine production (p-value < 0.05). In conclusion, the results showed that the exposure of P. aeruginosa to sub-MIC values of Cz resulted in a increased betalactam resistance, reduced colony and shape size and decreased production of virulence factors.