Atomic force microscopy investigation of the morphology and topography of colistin-heteroresistant Acinetobacter baumannii strains as a function of growth phase and in response to colistin treatment.
The prevalence of infections caused by multidrug-resistant gram-negative Acinetobacter baumannii strains and the lack of novel antibiotics under development are posing a global dilemma, forcing a resurgence of the last-line antibiotic colistin. Our aim was to use atomic force microscopy (AFM) to investigate the morphology and topography of paired colistin-susceptible and -resistant cells from colistin-heteroresistant A. baumannii strains as a function of bacterial growth phase and colistin exposure. An optimal AFM bacterial sample preparation protocol was established and applied to examine three paired strains. Images revealed rod-shaped colistin-susceptible cells (1.65 +/- 0.27 microm by 0.98 +/- 0.07 microm) at mid-logarithmic phase, in contrast to spherical colistin-resistant cells (1.03 +/- 0.09 microm); the latter were also more diverse in appearance and exhibited a rougher surface topography (7.05 +/- 1.3 nm versus 11.4 +/- 2.5 nm for susceptible versus resistant, respectively). Cellular elongation up to approximately 18 microm at stationary phase was more commonly observed in susceptible strains, although these "worm-like" cells were also observed occasionally in the resistant population. The effects of colistin exposure on the cell surface of colistin-susceptible and -resistant cells were found to be similar; topographical changes were minor in response to 0.5 microg/ml colistin; however, at 4 microg/ml colistin, a significant degree of surface disruption was detected. At 32 microg/ml colistin, cellular clumping and surface smoothening were evident. Our study has demonstrated for the first time substantial morphological and topographical differences between colistin-susceptible and -resistant cells from heteroresistant A. baumannii strains. These results contribute to an understanding of colistin action and resistance in regard to this problematic pathogen.
Facility for Anti-Infective Drug Development and Innovation, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia.
Rachel L
RL
Soon
Roger L
RL
Nation
Patrick G
PG
Hartley
Ian
I
Larson
Jian
J
Li
D040981:Acinetobacter baumannii / Q000166:cytology* / Q000187:drug effects* / Q000254:growth & development; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003091:Colistin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial / Q000502:physiology*; D008826:Microbial Sensitivity Tests; D018625:Microscopy, Atomic Force
D000900:Anti-Bacterial Agents; D003091:Colistin