Changes of Intracellular Porphyrin, Reactive Oxygen Species, and Fatty Acids Profiles During Inactivation of Methicillin-Resistant Staphylococcus aureus by Antimicrobial Blue Light

Antimicrobial blue light (aBL) has attracted increasing interest for its antimicrobial properties. However, the underlying bactericidal mechanism has not yet been verified. One hypothesis is that aBL causes the excitation of intracellular chromophores; leading to the generation of reactive oxygen species (ROS) and the resultant oxidization of various biomolecules. Thus, monitoring the levels of redox-sensitive intracellular biomolecules such as coproporphyrins, as well as singlet oxygen and various ROS may help to uncover the physiological changes induced by aBL and aid in establishing the underlying mechanism of action. Furthermore, the identification of novel targets of ROS, such as fatty acids, is of potential significance from a therapeutic perspective. In this study, we sought to investigate the molecular impact of aBL treatment on methicillin-resistant Staphylococcus aureus (MRSA). The results showed that aBL (5–80 J/cm2) exhibited a bactericidal effect on MRSA, and almost no bacteria survived when 80 J/cm2 had been delivered. Further studies revealed that the concentrations of certain intracellular molecules varied in response to aBL irradiation. Coproporphyrin levels were found to decrease gradually, while ROS levels increased rapidly. Moreover, imaging revealed the emergence and increase of singlet oxygen molecules. Concomitantly, the lipid peroxidation product malondialdehyde (MDA) increased in abundance and intracellular K+ leakage was observed, indicating permeability of the cell membrane. Atomic force microscopy showed that the cell surface exhibited a coarse appearance. Finally, fatty acid profiles at different illumination levels were monitored by GC-MS. The relative amounts of three unsaturated fatty acids (C16:1, C20:1, and C20:4) were decreased in response to aBL irradiation, which likely played a key role in the aforementioned membrane injuries. Collectively, these data suggest that the cell membrane is a major target of ROS during aBL irradiation, causing alterations to membrane lipid profiles, and in particular to the unsaturated fatty acid component

Inactivation of Salmonella enterica Serovar Enteritidis on Chicken Eggshells Using Blue Light

Salmonella enterica serovar Enteritidis (S. Enteritidis) is a pathogen that poses a health risk. Blue light (BL), an emerging sanitization technology, was employed for the first time in the present study to inactivate S. Enteritidis on eggshell surfaces and its influence on maintaining eggshell freshness was investigated systematically. The results showed that 415 nm-BL irradiation at a dose of 360 J/cm2 reduced 5.19 log CFU/mL of S. Enteritidis in vitro. The test on eggshells inoculated with S. Enteritidis showed that a BL dose at 54.6 J/cm2 caused a 3.73 log CFU reduction per eggshell surface and the impact of BL inactivation could be sustained in post-5-week storage. The quality of the tested eggs (weight loss, yolk index, Haugh unit (HU) and albumen pH) demonstrated that BL treatments had negligible effects on the albumen pH of eggs. However, compared to the control, BL-treated eggs showed lower weight loss and higher HU after 5 weeks of storage at 25 °C and 65% humidity and yolk index in the control group could not be determined after 5 weeks of storage. Besides, the total amino acid content of the BL-treated egg was higher than the control, exhibiting an advantage of BL irradiation in maintaining the nutrient quality of whole eggs. The current study determined the efficacy of BL against S. Enteritidis on eggshell and suggested that BL could be an effective application in maintaining the freshness and quality of eggs

Comparison of lactic acid production and cell growth by using <i>Bacillus coagulans</i> NL01 and <i>Bacillus coagulans</i> GKN316 with different concentrations of condensed dilute-acid hydrolysate (CDH).

<p>(<b>A</b>) 25% hydrolysate; (<b>B</b>) 50% hydrolysate. The color of hydrolysate culture of <i>B</i>. <i>coagulans</i> NL01 (<b>B1</b>) and GKN316 (<b>B2</b>) after 24-h fermentation. Values are the average ± SD of three separate experiments.</p

Lactic Acid Production from Pretreated Hydrolysates of Corn Stover by a Newly Developed <i>Bacillus coagulans</i> Strain

<div><p>An inhibitor-tolerance strain, <i>Bacillus coagulans</i> GKN316, was developed through atmospheric and room temperature plasma (ARTP) mutation and evolution experiment in condensed dilute-acid hydrolysate (CDH) of corn stover. The fermentabilities of other hydrolysates with <i>B</i>. <i>coagulans</i> GKN316 and the parental strain <i>B</i>. <i>coagulans</i> NL01 were assessed. When using condensed acid-catalyzed steam-exploded hydrolysate (CASEH), condensed acid-catalyzed liquid hot water hydrolysate (CALH) and condensed acid-catalyzed sulfite hydrolysate (CASH) as substrates, the concentration of lactic acid reached 45.39, 16.83, and 18.71 g/L by <i>B</i>. <i>coagulans</i> GKN316, respectively. But for <i>B</i>. <i>coagulans</i> NL01, only CASEH could be directly fermented to produce 15.47 g/L lactic acid. The individual inhibitory effect of furfural, 5-hydroxymethylfurfural (HMF), vanillin, syringaldehyde and <i>p</i>-hydroxybenzaldehyde (pHBal) on xylose utilization by <i>B</i>. <i>coagulans</i> GKN316 was also studied. The strain <i>B</i>. <i>coagulans</i> GKN316 could effectively convert these toxic inhibitors to the less toxic corresponding alcohols <i>in situ</i>. These results suggested that <i>B</i>. <i>coagulans</i> GKN316 was well suited to production of lactic acid from undetoxified lignocellulosic hydrolysates.</p></div

Fermentation performance of <i>B</i>. <i>coagulans</i> GKN316 in the presence of the individual inhibitors.

<p>(<b>A</b>) Lactic acid production; (<b>B</b>) Inhibitor concentration. R₁ = H, Furfural→furfuryl alcohol; R₁ = CH₂OH, HMF→bis-hydroxymethylfuran (HMF alcohol); R₂ = H, R₃ = OCH₃ vanillin→vanillyl alcohol; R₂ = R₃ = OCH₃, syringaldehyde→syringaldehyde alcohol; R₂ = R₃ = H, <i>p</i>-hydroxybenzaldehyde (pHBal)→<i>p</i>-hydroxybenzyl alcohol. Values are the average ± SD of three separate experiments.</p

Lactic acid fermentation by <i>B</i>. <i>coagulans</i> GKN316 and <i>B</i>. <i>coagulans</i> NL01 from the three condensed hydrolysates.

<p>(<b>A</b>) <i>B</i>. <i>coagulans</i> GKN316, condensed acid-catalyzed steam-exploded hydrolysates (CASEH); (<b>B</b>) <i>B</i>. <i>coagulans</i> GKN316, condensed acid-catalyzed liquid hot water hydrolysate (CALH); (<b>C</b>) <i>B</i>. <i>coagulans</i> GKN316, condensed acid-catalyzed sulfite hydrolysate (CASH); (<b>D</b>) <i>B</i>. <i>coagulans</i> NL01, condensed acid-catalyzed steam-exploded hydrolysates (CASEH). Values are the average ± SD of three separate experiments.</p