Objective    To observe the surface characteristics of in vitro β-lactam resistant Pseudomonas aeruginosa  after treated with β-lactam resistant antibiotics.     Methods    A Pseudomonas aeruginosa strain was isolated from wound secretions with the K-B method to test its susceptibility to β-lactam resistant antibiotics. Morphology of the stain and its surface characteristics were observed with Gram staining under atomic force microscope (AFM).     Results    A β-lactam antibiotics resistant Pseudomonas aeruginosa strain was isolated. The strain after Gram staining was 10-fold longer (5.0 to 25.0 μm) and slightly less wider (0.3 to 0.8 μm) under atomic force microscope after K-B experiments. The strain was L-shaped. No change was found in the strain after Gram-negative staining. Atomic force microscopy showed more holes on surface of the strain under a scanning area of 500 nm×500 nm

which were further confirmed on the topographic maps (the depth was less than 10 nm before K-B test and greater than 30 nm after K-B test).     Conclusion    Atomic force microscopy can show the rough surface characteristics of Pseudomonas aeruginosa after K-B experiment

but cannot show them after Gram staining

indicating that AFM scanning can be used to observe microchanges on the surface of the strain.