Differences in Antibiotic-Induced Oxidative Stress Responses between Laboratory and Clinical Isolates of Streptococcus pneumoniae

Abstract

Oxidants were shown to contribute to the lethality of bactericidal antibiotics in different bacterial species, including the laboratory strain Streptococcus pneumoniae R6. Resistance to penicillin among S. pneumoniae R6 mutants was further shown to protect against the induction of oxidants upon exposure to unrelated bactericidal compounds. In the work described here, we expanded on these results by studying the accumulation of reactive oxygen species in the context of antibiotic sensitivity and resistance by including S. pneumoniae clinical isolates. In S. pneumoniae R6, penicillin, ciprofloxacin, and kanamycin but not the bacteriostatic linezolid, erythromycin, or tetracycline induced the accumulation of reactive oxygen species. For the three bactericidal compounds, resistance to a single molecule prevented the accumulation of oxidants upon exposure to unrelated bactericidal antibiotics, and this was accompanied by a reduced lethality. This phenomenon does not involve target site mutations but most likely implicates additional mutations occurring early during the selection of resistance to increase survival while more efficient resistance mechanisms are being selected or acquired. Bactericidal antibiotics also induced oxidants in sensitive S. pneumoniae clinical isolates. The importance of oxidants in the lethality of bactericidal antibiotics was less clear than for S. pneumoniae R6, however, since ciprofloxacin induced oxidants even in ciprofloxacin-resistant S. pneumoniae clinical isolates. Our results provide a clear example of the complex nature of the mode of action of antibiotics. The adaptive approach to oxidative stress of S. pneumoniae is peculiar, and a better understanding of the mechanism implicated in response to oxidative injury should also help clarify the role of oxidants induced by antibiotics. Streptococcus pneumoniae is an opportunistic colonizer of the nasopharynx and the causative agent of many serious diseases, such as pneumonia, sepsis, meningitis, and otitis media (1, 2). Antimicrobial therapy based on ␤-lactam antibiotics is the recommended treatment regimen against pneumococcal diseases (3-5). However, resistance is now common in many countries, resulting into a shift toward the use of other molecules, including respiratory fluoroquinolones and third-generation cephalosporins (6-11). While the rates of resistance to these alternative agents remain globally low, some countries are nonetheless experiencing decreased susceptibilities (6,8,(12)(13)(14)(15)(16), and a precise understanding of the mode of action (MOA) of antibiotics and of the cellular response that they induce should prove useful for the prevention of further resistance.Bactericidal antibiotics have been proposed to contribute to bacterial death through a common mechanism involving reactive oxygen species (ROS) as a common effector (17-24). While generating great enthusiasm regarding novel therapeutic strategies (25, 26), this unified model remains a matter of debate given recent contradictory findings about the role of oxi...

Influence of Reactive Oxygen Species onDe NovoAcquisition of Resistance to Bactericidal Antibiotics

“…The decreased ROS concentrations in adapted cells could also promote the development of resistance through ROS-induced mutagenesis (25), as ROS induced by bactericidal antibiotics have been shown to result in oxidation of the nucleotide pool (26,27). Similar results were obtained in a Streptococcus pneumoniae strain resistant to either penicillin, ciprofloxacin, or kanamycin (28). In contrast to wild-type S. pneumoniae, cells resistant to one of those three bactericidal antibiotics did not respond by producing ROS upon exposure to another.…”

The Gac/Rsm Signaling Pathway of a Biocontrol Bacterium, Pseudomonas chlororaphis O6

“…However, the higher levels of Mn-superoxide dismutase was detected in the GacS mutant (Kang et al, 2004). These findings suggest that the Gac/Rsm regulon helps PcO6 survive under oxidative stress and other unfavorable environments, such as when challenged by antibiotics produced by other microbes (Dridi et al, 2015).…”

The Role of Reactive Oxygen Species in Antibiotic-Induced Cell Death in Burkholderia cepacia Complex Bacteria

“…However, for the Bcc strains tested we could not find a correlation between the MIC and the production of ROS. Dridi et al (2015) found that whether or not resistance led to a decreased ROS production in clinical isolates of Streptococcus pneumoniae differed between laboratory-derived and naturally-selected antibiotic resistant mutants, suggesting the antibiotic induced production of ROS is not universal and varies according to the genetic background of the strains [ 38 ].…”