Catalase expression is modulated by vancomycin and ciprofloxacin and influences the formation of free radicals in Staphylococcus aureus cultures

Ying Wang; Anni Bygvrå Hougaard; Wilhelm Erik Axel Paulander; Leif Horsfelt Skibsted; Hanne Ingmer; Mogens Larsen Andersen

doi:10.1128/aem.01199-15

Catalase expression is modulated by vancomycin and ciprofloxacin and influences the formation of free radicals in Staphylococcus aureus cultures

Ying Wang, Anni Bygvrå Hougaard, Wilhelm Erik Axel Paulander, Leif Horsfelt Skibsted, Hanne Ingmer, Mogens Larsen Andersen

6 Citations (Scopus)

Abstract

Detection of free radicals in biological systems is challenging due to their short half-lives. We have applied electron spin resonance (ESR) spectroscopy combined with spin traps using the probes PBN (N-tert-butyl-α-phenylnitrone) and DMPO (5,5-dimethyl-1-pyrroline N-oxide) to assess free radical formation in the human pathogen Staphylococcus aureus treated with a bactericidal antibiotic, vancomycin or ciprofloxacin. While we were unable to detect ESR signals in bacterial cells, hydroxyl radicals were observed in the supernatant of bacterial cell cultures. Surprisingly, the strongest signal was detected in broth medium without bacterial cells present and it was mitigated by iron chelation or by addition of catalase, which catalyzes the decomposition of hydrogen peroxide to water and oxygen. This suggests that the signal originates from hydroxyl radicals formed by the Fenton reaction, in which iron is oxidized by hydrogen peroxide. Previously, hydroxyl radicals have been proposed to be generated within bacterial cells in response to bactericidal antibiotics. We found that when S. aureus was exposed to vancomycin or ciprofloxacin, hydroxyl radical formation in the broth was indeed increased compared to the level seen with untreated bacterial cells. However, S. aureus cells express catalase, and the antibiotic-mediated increase in hydroxyl radical formation was correlated with reduced katA expression and catalase activity in the presence of either antibiotic. Therefore, our results show that in S. aureus, bactericidal antibiotics modulate catalase expression, which in turn influences the formation of free radicals in the surrounding broth medium. If similar regulation is found in other bacterial species, it might explain why bactericidal antibiotics are perceived as inducing formation of free radicals.

Original language	English
Journal	Applied and Environmental Microbiology
Volume	81
Issue number	18
Pages (from-to)	6393-6398
Number of pages	6
ISSN	0099-2240
DOIs	https://doi.org/10.1128/aem.01199-15
Publication status	Published - 2015

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10.1128/aem.01199-15

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Catalase expression is modulated by vancomycin and ciprofloxacin and influences the formation of free radicals in Staphylococcus aureus cultures. / Wang, Ying; Hougaard, Anni Bygvrå; Paulander, Wilhelm Erik Axel et al.
In: Applied and Environmental Microbiology, Vol. 81, No. 18, 2015, p. 6393-6398.

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abstract = "Detection of free radicals in biological systems is challenging due to their short half-lives. We have applied electron spin resonance (ESR) spectroscopy combined with spin traps using the probes PBN (N-tert-butyl-α-phenylnitrone) and DMPO (5,5-dimethyl-1-pyrroline N-oxide) to assess free radical formation in the human pathogen Staphylococcus aureus treated with a bactericidal antibiotic, vancomycin or ciprofloxacin. While we were unable to detect ESR signals in bacterial cells, hydroxyl radicals were observed in the supernatant of bacterial cell cultures. Surprisingly, the strongest signal was detected in broth medium without bacterial cells present and it was mitigated by iron chelation or by addition of catalase, which catalyzes the decomposition of hydrogen peroxide to water and oxygen. This suggests that the signal originates from hydroxyl radicals formed by the Fenton reaction, in which iron is oxidized by hydrogen peroxide. Previously, hydroxyl radicals have been proposed to be generated within bacterial cells in response to bactericidal antibiotics. We found that when S. aureus was exposed to vancomycin or ciprofloxacin, hydroxyl radical formation in the broth was indeed increased compared to the level seen with untreated bacterial cells. However, S. aureus cells express catalase, and the antibiotic-mediated increase in hydroxyl radical formation was correlated with reduced katA expression and catalase activity in the presence of either antibiotic. Therefore, our results show that in S. aureus, bactericidal antibiotics modulate catalase expression, which in turn influences the formation of free radicals in the surrounding broth medium. If similar regulation is found in other bacterial species, it might explain why bactericidal antibiotics are perceived as inducing formation of free radicals.",

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AU - Andersen, Mogens Larsen

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