Absence of tmRNA Has a Protective Effect against Fluoroquinolones in Streptococcus pneumoniae

Abstract

The transfer messenger RNA (tmRNA), encoded by the ssrA gene, is a small non-coding RNA involved in trans-translation that contributes to the recycling of ribosomes stalled on aberrant mRNAs. In most bacteria, its inactivation has been related to a decreased ability to respond to and recover from a variety of stress conditions. In this report, we investigated the role of tmRNA in stress adaptation in the human pathogen Streptococcus pneumoniae. We constructed a tmRNA deletion mutant and analyzed its response to several lethal stresses. The ΔssrA strain grew slower than the wild type, indicating that, although not essential, tmRNA is important for normal pneumococcal growth. Moreover, deletion of tmRNA increased susceptibility to UV irradiation, to exogenous hydrogen peroxide and to antibiotics that inhibit protein synthesis and transcription. However, the ΔssrA strain was more resistant to fluoroquinolones, showing twofold higher MIC values and up to 1000-fold higher survival rates than the wild type. Deletion of SmpB, the other partner in trans-translation, also reduced survival to levofloxacin in a similar extent. Accumulation of intracellular reactive oxygen species associated to moxifloxacin and levofloxacin treatment was also highly reduced (∼100-fold). Nevertheless, the ΔssrA strain showed higher intracellular accumulation of ethidium bromide and levofloxacin than the wild type, suggesting that tmRNA deficiency protects pneumococcal cells from fluoroquinolone-mediated killing. In fact, analysis of chromosome integrity revealed that deletion of tmRNA prevented the fragmentation of the chromosome associated to levofloxacin treatment. Moreover, such protective effect appears to relay mainly on inhibition of protein synthesis, since a similar effect was observed with antibiotics that inhibit that process. The emergence and spread of drug-resistant pneumococci is a matter of concern and these results contribute to a better comprehension of the mechanisms underlying fluoroquinolones action.

Rapid microevolution of biofilm cells in response to antibiotics

“…In earlier studies, deletion of these genes led to increased susceptibility to a range of antibiotics and environmental stresses, 42 but increased resistance to fluoroquinolones, possibly due to a preventive effect on chromosome fragmentation. 43 Likewise, in our study a mutation in smpB could have decreased or abolished the activity of the protein, leading to similar effects specific to the fluoroquinolone ciprofloxacin.…”

“…These mutations emerged together in ciprofloxacin-exposed samples, were directly linked with ciprofloxacin resistance, and, according to the literature, might play a role in chromosome architecture and stability. 43,62…”

Bacterial Adaptation to Antibiotics through Regulatory RNAs

“…Also, trans-translation may be coordinated with other essential cotranslational processes such as protein folding and secretion. In S. pneumoniae, the lack of tmRNA protects bacteria against fluoroquinolones (83). In this species, deletion of tmRNA prevented chromosome fragmentation associated with levofloxacin treatment.…”

Absence of tmRNA Increases the Persistence to Cefotaxime and the Intercellular Accumulation of Metabolite GlcNAc in Aeromonas veronii

“…Although the deletion of ssrA strain promotes higher susceptibility to fosfomycin and ampicillin (Luidalepp et al, 2005), it does not significantly affect responses to ampicillin (de la Cruz and Vioque, 2001). In Streptococcus pneumoniae, tmRNA deficiency may reduce ROS production and chromosome breakage through the trans-translation process, thus increasing the tolerance to fluoroquinolones (Liliana et al, 2016). Herein, for the first time, the effect of the ssrA mutant was delineated on the persistence to cefotaxime.…”