Selection of colistin-resistant Acinetobacter baumannii isolates in postneurosurgical meningitis in an intensive care unit with high presence of heteroresistance to colistin

Colistin Resistance in Acinetobacter baumannii Is Mediated by Complete Loss of Lipopolysaccharide Production

“…Loss of LPS production in each of the strains tested resulted in high-level colistin resistance, clearly indicating that the interaction of colistin with LPS is critical for the bactericidal action of colistin against A. baumannii. The clinical significance of colistin-resistant strains has recently been highlighted with the report of the emergence of colistin resistance after colistin treatment of an infection caused by a heteroresistant A. baumannii strain (10). Here, we demonstrate in two independent strains of A. baumannii that selection of colistin-resistant strains from within an apparently susceptible population is due to the selection of lipid A biosynthesis mutants and that these mutants devoid of LPS are highly resistant to colistin.…”

“…Intriguingly, some A. baumannii isolates have been shown to display heteroresistance to colistin, where an apparently colistin-susceptible strain (based upon the MIC) harbors a small proportion of colistin-resistant cells (9,16). Under selective pressure both in vitro (33) and in vivo (10), heteroresistant A. baumannii strains can rapidly give rise to strains with high-level colistin resistance.…”

“…The treatment of these infections is hampered by the rapid rise in prevalence of A. baumannii strains that are resistant to almost all available antibiotics, including ␤-lactams, fluoroquinolones, tetracyclines, and aminoglycosides (23). In these multidrug-resistant (MDR) strains, colistin (also known as polymyxin E) is often the only remaining treatment (15), although colistin-resistant clinical isolates have already been reported (7,10,21). Intriguingly, some A. baumannii isolates have been shown to display heteroresistance to colistin, where an apparently colistin-susceptible strain (based upon the MIC) harbors a small proportion of colistin-resistant cells (9,16).…”

Clonal spread of multidrug-resistant Acinetobacter baumannii in eastern Taiwan

“…8e10 However, the reduced susceptibility to these three drugs in A baumannii has recently been reported in several countries. 11,12 Nevertheless, several studies have shown that tigecycline-or rifampicinbased regimens are more effective for treating severe infections caused by MDR A baumannii. 13,14 To date, no studies are available on the efficacy of rifampicin or combination rifampicin/colistin against A baumannii isolates in Taiwan, although rifampicin has been used for the long-term treatment of infections caused by Mycobacterium tuberculosis.…”

In vitro synergism of combinations of colistin with selected antibiotics against colistin-resistant Acinetobacter baumannii

“…For these strains, colistin, an old polimyxin antibiotic, frequently is the only remaining therapeutic option. Nevertheless, colistin-resistant A. b aumannii strains have been reported recently [1], [2], [3]. …”