Evaluation of CHROMagar Acinetobacter and MacConkey media for the recovery of Acinetobacter baumannii from soil samples.

The opportunistic pathogen Acinetobacter baumannii occupies niches in human and veterinary clinics and other environments. This comparative study was designed to assess the recovery rate of Ac. baumannii from 20 soil samples collected in Germany (from which Ac. baumannii had been previously isolated) on selective CHROMagar Acinetobacter (CMA) and MacConkey Agar (MCA). Suspected Ac. baumannii were confirmed by detection and sequencing of blaOXA-51-like genes. Overall, the recovery rate of Ac. baumannii from both media was similar. Out of the 20 soil samples enriched in mineral salt medium (MM) plus 0.2% acetate for 5 h, Ac. baumannii was recovered from 12 (60%) on CMA and 11 (55%) on MCA, and from 14 (70%) with both selective media after enrichment for 24 h. Typical and distinct colonies of Ac. baumannii were more often observed on CMA with soil enriched in MM for 5 h, while on MCA distinct colonies were more obvious after 24 h. In five soil samples (25%), strains harbouring different OXA-51-like variants were recovered on MCA. Late lactose fermentation (48 h) was observed on MCA. The study suggests that no single growth medium would efficiently recover Ac. baumannii from all soil samples.

Impact of zinc uptake regulator Zur on the susceptibility and oxidative stress response of Acinetobacter baumannii to antibiotics.

Zinc is a highly coveted redox-inactive micronutrient required for the growth and virulence of Acinetobacter baumannii. In this study, the role of the zinc uptake regulator Zur in the susceptibility and oxidative stress response of A. baumannii to antibiotics was evaluated. Inactivation of zur increased the susceptibility of A. baumannii AB5075 to colistin, gentamicin, rifampicin and tigecycline. Furthermore, activities of superoxide dismutase and catalase decreased significantly in the Δzur mutant compared with the parental strain. Colistin, gentamicin, rifampicin and tigecycline raised the superoxide anion radical (·O2-) and hydrogen peroxide (H2O2) contents of the Δzur mutant compared with the parental strain. In addition, the antibiotics lowered glutathione and concomitantly raised glutathione disulphide levels in the Δzur mutant. All of the antibiotics, except tigecycline, significantly raised the NAD+/NADH and ADP/ATP ratios in A. baumannii. We conclude that decreased capability of the Δzur mutant to detoxify reactive oxygen species increased its susceptibility to antibiotics.

Contributions of ferric uptake regulator Fur to the sensitivity and oxidative response of Acinetobacter baumannii to antibiotics.

Ferric uptake regulator (Fur) is important in the regulation of bacterial iron metabolism and uptake of Fe from the environment. We evaluated the contribution of fur to the sensitivity and oxidative response of A. baumannii to antibiotics. Deletion of fur increased the sensitivity of A. baumannii AB5075 to colistin, gentamicin, rifampicin and tigecycline. Furthermore, activities of superoxide dismutase and catalase in Δfur mutant decreased significantly compared to the parental strain. Conversely, •O2- and H2O2 accumulate in colistin, gentamicin, rifampicin or tigecycline-treated Δfur mutant compared to the parental strain. Ferrous ion (Fe2+) content of Δfur mutant increased compared to the parental strain. Fe chelator 2,2'-bipyridyl lowered the sensitivity of A. baumannii to the antibiotics. The antibiotics, except tigecycline, raised the NAD+/NADH and ADP/ATP ratio of Δfur mutant compared to the WT. Glutathione content of Δfur mutant was significantly depleted compared to parental strain following exposure to the antibiotics. We conclude that decreased capability of Δfur mutant to detoxify reactive oxygen species raised its susceptibility to antibiotics through Fenton chemistry.

Monitoring polycyclic aromatic hydrocarbon metabolites in human urine: extraction and purification with a sol-gel glass immunosorbent.

A new, rapid method for selective extraction of hydroxylated polycyclic aromatic hydrocarbons metabolites (OH-PAHs) in human urine was developed using an immunosorbent of anti-pyrene antibodies which were encapsulated in a sol-gel glass (SGG) matrix. Resulting chromatograms after immunoextraction of urine samples and HPLC analysis of the extracts were free from matrix interferences. The LODs for the determination of OH-PAHs in these difficult samples were in the low-ppt range (1-16 ng/L). In addition to its high selectivity, the immunosorbent proved to be robust and reusable. Obtained recoveries in spiked urine samples ranged from 83 to 107% for the hydroxyphenanthrene and hydroxypyrene compounds under investigation, while recovery for 3-hydroxybenzo[a]pyrene was only 45-62%. In a biomonitoring study, the SGG immunosorbent was successfully used for trace-level analysis of OH-PAHs in 20 human urine samples. Results were compared to data obtained by an independent reference analysis method and revealed good correlation between both methods.