Staphylococcus aureus Strain Newman Photoinactivation and Cellular Response to Sunlight Exposure

Abstract

Sunlight influences microbial water quality of surface waters. Previous studies have investigated photoinactivation mechanisms and cellular photostress responses of fecal indicator bacteria (FIB), including Escherichia coli and enterococci, but further work is needed to characterize photostress responses of bacterial pathogens. Here we investigate the photoinactivation of Staphylococcus aureus (strain Newman), a pigmented, waterborne pathogen of emerging concern. We measured photodecay using standard culture-based assays and cellular membrane integrity and investigated photostress response by measuring the relative number of mRNA transcripts of select oxidative stress, DNA repair, and metabolism genes. Photoinactivation experiments were performed in both oxic and anoxic systems to further investigate the role of oxygen-mediated and non-oxygen-mediated photoinactivation mechanisms. S. aureus lost culturability much faster in oxic systems than in anoxic systems, indicating an important role for oxygen in photodecay mechanisms. S. aureus cell membranes were damaged by sunlight exposure in anoxic systems but not in oxic systems, as measured by cell membrane permeability to propidium iodide. After sunlight exposure, S. aureus increased expression of a gene coding for methionine sulfoxide reductase after 12 h of sunlight exposure in the oxic system and after 6 h of sunlight exposure in the anoxic system, suggesting that methionine sulfoxide reductase is an important enzyme for defense against both oxygen-dependent and oxygen-independent photostresses. This research highlights the importance of oxygen in bacterial photoinactivation in environmentally relevant systems and the complexity of the bacterial photostress response with respect to cell structure and transcriptional regulation.IMPORTANCE Staphylococcus aureus is a pathogenic bacterium that causes gastrointestinal, respiratory, and skin infections. In severe cases, S. aureus infection can lead to life-threatening diseases, including pneumonia and sepsis. Cases of communityacquired S. aureus infection have been increasing in recent years, pointing to the importance of considering S. aureus transmission pathways outside the hospital environment. Associations have been observed between recreational water contact and staphylococcal skin infections, suggesting that recreational waters may be an important environmental transmission pathway for S. aureus. However, prediction of human health risk in recreational waters is hindered by incomplete knowledge of pathogen sources, fate, and transport in this environment. This study is an in-depth investigation of the inactivation of a representative strain of S. aureus by sunlight exposure, one of the most important factors controlling the fate of microbial contaminants in clear waters, which will improve our ability to predict water quality changes and human health risk in recreational waters.KEYWORDS Staphylococcus aureus, coastal waters, enterococci, fecal indicator bacteria, photoinactivation

Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches

“…faecalis, 124,127 and the msrA gene in S. aureus. 126 On the other hand, the obligate anaerobe Bacteroides thetaiotaomicron was inactivated faster than a suite of seven other Gram-positive and Gram-negative bacteria under oxic and anoxic conditions; although it possesses oxidative stress response genes, they may not have been activated in this study when grown under anoxic conditions. 155 Evidence of damage to lipids and proteins was found in a study of Acinetobacter and Pseudomonas exposed to UVB and UVA wavelengths.…”

“…faecalis, 126 suggesting that non-pigmented enterococci may still be a conservative indicator of pathogenic bacteria.…”

“…faecalis and Staphylococcus aureus by natural sunlight was also shown to be much faster under oxic conditions than anoxic conditions. 126,127 Most mechanistic studies have been carried out only under aerobic conditions, under which it is difficult to separate direct and indirect endogenous mechanisms. For this reason, and because the mechanisms clearly interact, they are discussed together.…”

“…faecalis and Staphylococcus. 126,127 Based on the prior discussion of mechanisms, loss of these membrane functions is likely a result of damage to components of the electron transport chain and other transmembrane proteins that contain either chromophores or accessible iron. Simultaneous with membrane damage, damage to cytoplasmic proteins has also been documented.…”

Dead or Alive? Molecular life-dead distinction in human stool samples reveals significantly different composition of the microbial community

“…However, the samples were exposed to air (21% oxygen) for a short period of time during dilution and PMA treatment, which might affect the viability of the microbial community 2 . However, we cannot think of any chemical process, which would, in the dark but in presence of air, induce immediate cell wall/cell membrane damage, and thus affect the outcome of the PMA treatment 63 , so that we did not evaluate the impact of the oxygen in the ambient air on our results. In this regard, the study setup was performed according to feasibility and common practice, and the samples were treated with PMA without delay, but under normal atmosphere.…”