Altered susceptibility to the bactericidal effect of photocatalytic oxidation by TiO2 is related to colistin resistance development in Acinetobacter baumannii

Abstract

Multidrug-resistant Acinetobacter baumannii is a well-documented pathogen associated with hospital-acquired infections. In addition to multidrug resistance, A. baumannii can also become resistant to colistin, the antibiotic treatment of last resort, by the loss of the lipopolysaccharide from its outer membrane. Here, we demonstrate that the development of colistin resistance also increases the resistance of A. baumannii to titanium dioxide (TiO2) photocatalysis. Both colistin-sensitive A. baumannii (CSAB) and colistin-resistant A. baumannii (CRAB) were inactivated by TiO2 when irradiated by ultraviolet A (UV-A). The resistance of CRAB to TiO2 photocatalysis was 1.5 times higher than that of CSAB, as determined by either culture assay or quantification of leaked proteins after photocatalysis (p < 0.05). The results of two-dimensional gel electrophoresis led to the speculation that the high resistance of CRAB may be associated with a lack of sensitive targets and oxidative enzymes. This hypothesis was confirmed by antimicrobial assays with 25 mM hydrogen peroxide (H2O2) and 1.07 mM sodium hypochlorite (NaClO). CRAB was significantly more resistant to H2O2 and NaClO treatment than CSAB (p < 0.01), consistent with the results of the TiO2 inactivation experiment. Therefore, the antibiotic resistance profiles of bacterial strains should be considered before the use of strains as indicators to represent sanitary quality after TiO2 photocatalysis.

Altered susceptibility to air sampling stress by filtration is related to colistin resistance development inAcinetobacter baumannii

“…The evolution of cells to become CRAB, in contrast to CSAB, resulted in the complete loss of LPS production . Our previous study also confirmed the difference in LPS protein levels in CSAB and CRAB by two‐dimensional gel electrophoresis . In general, LPSs stabilize a bacterium's structure by acting as a protective impermeable barrier; however, lipid A of the LPS may be the specific target responsible for the lipid peroxidation of colistin.…”

“…The minimum inhibitory concentration (MIC) of colistin for the CRAB strain in this study was 32 μg/mL. We have used this CRAB strain for a bioaerosol study and TiO 2 susceptibility tests …”

“…High bacterial concentrations must be used because proteins from lower cell concentrations were difficult to observe by SDS‐PAGE. After the dehydration stress test, the filter eluates, containing CSAB and CRAB, were harvested by centrifugation (8000× g , 4°C, 10 minutes) for the protein leakage analysis, as in our previous study . Protein leakage was visualized by 15% SDS‐PAGE with silver staining (Sigma‐Aldrich, USA).…”

“…For instance, mutations in genes involved in reactive oxygen species (ROS) resistance increase the susceptibility of Escherichia coli to TiO 2 photocatalysis . Our previous studies have also demonstrated that when bacteria develop resistance to different types of antibiotics, their susceptibility to TiO 2 photocatalysis is altered …”

“…Although the A. baumannii concentration in air is not extremely high, it still poses a potential threat to human health as the infectious dose of A. baumannii is unknown. In addition, as A. baumannii may also have changed its susceptibility to various stresses while becoming antibiotic resistant, the reported concentrations of antibiotic‐resistant A. baumannii may be underestimated if the collection efficiency and sampling stress on airborne antibiotic‐resistant bacteria are not evaluated.…”