Images of susceptible (above: a, a', a''), intermediate (medium: b, b', b'') and resistant (below: c, c', c'') strains from E. coli incubated with 8/4 μg/ml and 32/16 μg/ml amoxicillin/clavulanic acid and processed by the technique to determine cell wall integrity. The strain is considered susceptible when its MIC is ≤ 8/4 and resistant when it is ≥ 32/16. a, b, c: control, without antibiotic. a', b', c': 8/4 μg/ml; a'', b'', c'': 32/16 μg/ml. Controls without antibiotic (a, b, c) show the bacteria unaffected by the lysis. After 8/4, only bacteria from the first strain, sensitive, appear lysed, showing the spread nucleoids (a'). After 32/16, first and second strains, sensitive and medium, respectively, show to be lysed (a'' and b''), whereas the third strain, resistant, appears not to be lysed (c''). Nevertheless, some isolated bacteria with damaged cell wall are visible. When the antibiotic is effective, besides the liberation of the nucleoids, it is observed a microgranular-fibrilar background of DNA fragments released by the bacteria.
Santiso et al. BMC Microbiology 2011 11:191 doi:10.1186/1471-2180-11-191