Ultrastructural changes caused by polymyxin B and meropenem in multiresistant Klebsiella pneumoniae carrying blaKPC-2 gene.

The ultrastructural alterations caused by polymyxin B and meropenem and by the association between polymyxin B and meropenem were investigated in two multiresistant isolates of Klebsiella pneumoniae (K3-A2 and K12-A2) carriers of blaKPC-2, coming from infection and colonization in patients in a public hospital in Recife, Brazil. The ultrastructural changes were detected by transmission electron microscopy and scanning. The susceptibility of the isolates to antimicrobials was tested by the disc diffusion method and microdilution in broth. The analysis by electron microscopy showed that the isolates presented morphological and ultrastructural cellular changes when subjected to a clinically relevant concentration of antimicrobials alone or in combination. When subjected to meropenem, they presented retraction of the cytoplasmic material, rupture of the cell wall and extravasation of the cytoplasmic content. When submitted to polymyxin B, the isolates showed condensation of the ribosomes, DNA clotting, cell wall thickening and the presence of membrane compartment. When subjected to polymyxin B and meropenem in combination, the isolates showed a higher intensity of the ultrastructural changes visualized. This is the first report of the ultrastructural changes caused by polymyxin B and meropenem in multiresistant isolates of K. pneumoniae carriers of the blaKPC-2 gene. It should be noted that even when the K. pneumoniae isolates were multiresistant carriers of the blaKPC-2 gene, they underwent important structural change owing to the action of polymyxin B and meropenem.