Based on some observations i found that an imepenem resistant Pseudomonas aeruginosa had different colony morphology from its wild type. So, does this phenomenon occur in other bacteria? If yes what could be a possible explanation?
Colony morphology - particularly the colony size could vary depending on the nutritional factors and pressure of having been exposed to antibiotics invivo.
Its worth looking into the typing methods to see if there is any minor difference in the genotype.
A change in colony morphology could be readily explained by the fact that the particular antibiotic (imepenem) affects cell wall synthesis, and therefore resistance to it would likely allow the organism to grow, but perhaps not without some effect on the cell wall and therefore, colony morphology.
I had the same experience with a S.aureus that had colonized an immunocompromized patient, after 2 weeks of useless therapy it turned to be MRSA and the colony looked like strangly bigger, also at the optical microscope the bacterial cells looked "fatty" like they where swollen. I think it depends on the antimicrobial pressure, if you attack the cell wall synthesis when it becomes resistant it's possible that it affects the cell wall apparences. But I don't know the biochemical explanantion... Maybe some external components of the cell wall that the new resistant phenotype produce?
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