Comparative transcriptomic and phenotypic analysis of the responses of Bacillus cereus to various disinfectant treatments

Impact of benzalkonium chloride on anaerobic granules and its long-term effects on reactor performance

This study assessed the inhibitory and performance-degrading effects induced by the cationic surfactant benzalkonium chloride (BAC) on anaerobic granules during the long-term operation of a laboratory-scale expanded granular sludge bed (EGSB) reactor. To address the critical scientific problem of how BAC affects the efficiency of EGSB reactors, this research uniquely evaluated the long-term stress response to BAC by systematically comparing continuous and discontinuous inhibitor exposure scenarios. The novel comparison demonstrated that inhibitor concentration is of minor relevance compared to the biomass-specific cumulative inhibitor load in the reactor. After exceeding a critical biomass-specific cumulative inhibitor load of 6.1-6.5 mg BAC/g VS, continuous and discontinuous exposure to BAC caused comparable significant deterioration in reactor performance, including accumulation of volatile fatty acids (VFA), decreased removal efficiency, reduced methane production, as well as the wash-out, flotation, and disintegration of anaerobic granules. BAC exposures had a more detrimental effect on methanogenesis than on acidogenesis. Moreover, long-term stress by BAC led to an inhibition of protein production, resulting in a decreased protein-to-polysaccharide ratio of extracellular polymeric substances (EPS) that promoted destabilizing effects on the granules. Finally, hydrogenotrophic methanogenesis was triggered. Reactor performance could not be restored due to the severe loss of granular sludge.

Quaternary ammonium biocides promote conjugative transfer of antibiotic resistance gene in structure- and species-dependent manner

The linkage between biocides and antibiotic resistance has been widely suggested in laboratories and various environments. However, the action mechanism of biocides on antibiotic resistance genes (ARGs) spread is still unclear. Thus, 6 quaternary ammonium biocides (QACs) with different bonded substituents or alkyl chain lengths were selected to assess their effects on the conjugation transfer of ARGs in this study. Two conjugation models with the same donor (E. coli DH5α (RP4)) into two receptors, E. coli MG1655 and pathogenic S. sonnei SE6-1, were constructed. All QACs were found to significantly promote intra- and inter-genus conjugative transfer of ARGs, and the frequency was highly impacted by their structure and receptors. At the same environmental exposure level (4 × 10-1 mg/L), didecyl dimethyl ammonium chloride (DDAC (C10)) promoted the most frequency of conjugative transfer, while benzathine chloride (BEC) promoted the least. With the same donor, the enhanced frequency of QACs of intra-transfer is higher than inter-transfer. Then, the acquisition mechanisms of two receptors were further determined using biochemical combined with transcriptome analysis. For the recipient E. coli, the promotion of the intragenus conjugative transfer may be associated with increased cell membrane permeability, reactive oxygen species (ROS) production and proton motive force (PMF)-induced enhancement of flagellar motility. Whereas, the increase of cell membrane permeability and decreased flagellar motility due to PMF disruption but encouraged biofilm formation, maybe the main reasons for promoting intergenus conjugative transfer in the recipient S. sonnei. As one pathogenic bacterium, S. sonnei was first found to acquire ARGs by biocide exposure.

Detergent Chemistry Modulates the Transgression of Planetary Boundaries including Antimicrobial Resistance and Drug Discovery

Detergent chemistry enables applications in the world today while harming safe operating spaces that humanity needs for survival. Aim of this review is to support a holistic thought process in the design of detergent chemistry. We harness the planetary boundary concept as a framework for literature survey to identify progresses and knowledge gaps in context with detergent chemistry and five planetary boundaries that are currently transgressed, i.e., climate, freshwater, land system, novel entities, biosphere integrity. Our survey unveils the status of three critical challenges to be addressed in the years to come, including (i) the implementation of a holistically, climate-friendly detergent industry; (ii) the alignment of materialistic and social aspects in creating technical solutions by means of sustainable chemistry; (iii) the development of detergents that serve the purpose of applications but do not harm the biosphere in their role as novel entities. Specifically, medically relevant case reports revealed that even the most sophisticated detergent design cannot sufficiently accelerate drug discovery to outperform the antibiotic resistance development that detergents simultaneously promote as novel entities. Safe operating spaces that humanity needs for its survival may be secured by directing future efforts beyond sustainable chemistry, resource efficiency, and net zero emission targets.

Effect of dissolved organic matter on bacterial regrowth and response after ultraviolet disinfection

The effect of dissolved organic matter (DOM) on bacterial regrowth in water after disinfection using ultraviolet (UV) light emitting diodes (UVLEDs) is still unclear. Herein, the regrowth and responses of Vibrio parahaemolyticus and Bacillus cereus were investigated after being exposed to UVLEDs at combined wavelengths (265 and 280 nm) in a phosphate-buffered saline consisting of Suwannee River natural organic matter (SRNOM) and Suwannee River fulvic acid (SRFA). Low-molecular-weight (MW) organic compounds, which may form into intermediary photoproducts, and indicate bacterial repair metabolism, were characterized through non-target screening using orbitrap mass spectrometry. This study demonstrates the ability of the UVLEDs-inactivated cells to regrow. After UV exposure, a considerable upregulation of RecA was observed in two strains. With increasing the incubation time, the expression levels of RecA in V. parahaemolyticus increased, which may be attributed to the dark repair mechanism. Coexisting anionic DOM affects both the disinfection and bacterial regrowth processes. The time required for bacterial regrowth after UV exposure reflects the time needed for the individual cells to reactivate, and it differs in the presence or absence of DOM. In the presence of DOM, the cells were less damaged and required less time to grow. The UVLEDs exposure results in the occurrence of low-MW organic compounds, including carnitine or acryl-carnitine with N-acetylmuramic acid, which are associated with bacterial repair metabolism. Overall, the results of this study expand the understanding of the effects of water matrices on bacterial health risks. This can aid in the development of more effective strategies for water disinfection.

Comparative transcriptome analysis provides insights into the resistance regulation mechanism and inhibitory effect of fungicide phenamacril in Fusarium asiaticum

Fusarium asiaticum is a destructive phytopathogenic fungus that causes Fusarium head blight of wheat (FHB), leading to serious yield and economic losses to cereal crops worldwide. Our previous studies indicated that target-site mutations (K216R/E, S217P/L, or E420K/G/D) of Type I myosin FaMyo5 conferred high resistance to phenamacril. Here, we first constructed one sensitive strain H1S and three point mutation resistant strains HA, HC and H1R. Then we conducted comparative transcriptome analysis of these F. asiaticum strains after 1 and 10 μg·mL-1 phenamacril treatment. Results indicated that 2135 genes were differentially expressed (DEGs) among the sensitive and resistant strains. The DEGs encoding ammonium transporter MEP1/MEP2, nitrate reductase, copper amine oxidase 1, 4-aminobutyrate aminotransferase, amino-acid permease inda1, succinate-semialdehyde dehydrogenase, 2, 3-dihydroxybenzoic acid decarboxylase, etc., were significantly up-regulated in all the phenamacril-resistant strains. Compared to the control group, a total of 1778 and 2097 DEGs were identified in these strains after 1 and 10 μg·mL-1 phenamacril treatment, respectively. These DEGs involved in 4-aminobutyrate aminotransferase, chitin synthase 1, multiprotein-bridging factor 1, transcriptional regulatory protein pro-1, amino-acid permease inda1, ATP-dependent RNA helicase DED1, acetyl-coenzyme A synthetase, sarcoplasmic/endoplasmic reticulum calcium ATPase 2, etc., showed significantly down-regulated expression in phenamacril-sensitive strain but not in resistant strains after phenamacril treatment. In addition, cyanide hydratase, mating-type protein MAT-1, putative purine nucleoside permease, plasma membrane protein yro2, etc., showed significantly co-down-regulated expression in all the strains after phenamacril treatment. Taken together, This study provides deep insights into the resistance regulation mechanism and the inhibitory effect of fungicide phenamacril and these new annotated proteins or enzymes are worth for the discovery of new fungicide targets.

Ecotoxicity studies reveal that organic cations in dicamba-derived ionic liquids can pose a greater environmental risk than the herbicide itself

The following research provides novel and relevant insights into potential environmental consequences of combination of various organic cations with commercial systemic herbicide (dicamba), in accordance with a 'herbicidal ionic liquids' (HILs) strategy. Toxicity assays of five dicamba-based HILs comprising different hydrophobic and hydrophilic cations, namely choline [CHOL][DIC], ethyl betainate [BETC2][DIC], decyl betainate [BETC10][DIC], hexadecyl betainate [BETC16][DIC] and didecyldimethylammonium [DDA][DIC]), have been tested towards bacteria (Pseudomonas putida, Escherichia coli, Bacillus subtilis), algae (Chlorella vulgaris), fresh and marine water crustaceans (Daphnia magna, Artemia franciscana). The structure of respective substituents in the cation emerged as a decisive determinant of toxicity in the case of tested species. In consequence, small ions of natural origin ([CHOL] and [BETC2]) demonstrated toxicity numerous orders of magnitude lower compared to fully synthetic [DDA]. These results emphasize the role of cations' hydrophobicity, as well as origin, in the observed acute toxic effect. Time-dependent toxicity assays also indicated that betaine-type cations comprising an ester bond can rapidly transform into less harmful substances, which can generally result in a reduction in toxicity by even several orders of magnitude. Nonetheless, these findings challenge the concept of ionic liquids with herbicidal activity and give apparent parallels to adjuvant-dependent toxicity issues recently noted in typical herbicidal formulations.

The structure of biodegradable surfactants shaped the microbial community, antimicrobial resistance, and potential for horizontal gene transfer

While most household surfactants are biodegradable in aerobic conditions, their biodegradability may obscure their environmental risks. The presence of surfactants in a biological treatment process can lead to the proliferation of antimicrobial-resistance genes (ARG) in the biomass. Surfactants can be cationic, anionic, or zwitterionic, and these different classes may have different effects on the proliferation ARG. Cationic hexadecyltrimethyl-ammonium (CTAB), anionic sodium dodecyl sulfate (SDS), and zwitterionic 3-(decyldimethylammonio)-propanesulfonate inner salt (DAPS) were used to represent the three classes of surfactants in domestic household clean-up products. This study focused on the removal of these surfactants by the O₂-based Membrane Biofilm Reactor (O_2-MBfR) for hotspot scenarios (∼1 mM) and how the three classes of surfactants affected the microbial community's structure and ARG. Given sufficient O₂ delivery, the MBfR provided at least 98% surfactant removal. The presence and biodegradation for each surfactant uniquely shaped the biofilms' microbial communities and the presence of ARG. CTAB had by far the strongest impact and the higher ARG abundance. In particular, Pseudomonas and Stenotrophomonas, the two main genera in the biofilm treating CTAB, were highly correlated to the abundance of ARG for efflux pumps and antibiotic inactivation. CTAB also led to more functional genes relevant to the Type-IV secretion system and protection against oxidative stress, which also could encourage horizontal gene transfer. Our findings highlight that the biodegradation of quaternary ammonium surfactants, while beneficial, can pose public health concerns from its ability to promote the proliferation of ARG.

Enhance antibiotic resistance and human health risks in aerosols during the COVID-19 pandemic

Aerosols are an important route for the transmission of antibiotic resistance genes (ARGs). Since the 2019 (COVID-19) pandemic, the large-scale use of disinfectants has effectively prevented the spread of environmental microorganisms, but studies regarding the antibiotic resistance of airborne bacteria remain limited. This study focused on four functional urban areas (commercial areas, educational areas, residential areas and wastewater treatment plant) to study the variations in ARG abundances, bacterial community structures and risks to human health during the COVID-19 pandemic in aerosol. The results indicated the abundance of ARGs during the COVID-19 period were up to approximately 13-fold greater than before the COVID-19 period. Large-scale disinfection resulted in a decrease in total bacterial abundance. However, chlorine-resistant bacteria tended to be survived. Among the four functional areas, the diversity and abundance of aerosol bacteria were highest in commercial aera. Antibiotic susceptibility assays suggested elevated resistance of isolated bacteria to several tested antibiotics due to disinfection exposure. The potential exposure risks of ARGs to human health were 2 times higher than before the COVID-19 pandemic, and respiratory intake was the main exposure route. The results highlighted the elevated antibiotic resistance of bacteria in aerosols that were exposed to disinfectants after the COVID-19 pandemic. This study provides theoretical guidance for the rational use of disinfectants and control of antimicrobial resistance.

Bacterial drug-resistance and viability phenotyping upon disinfectant exposure revealed by single-nucleotide resolved-allele specific isothermal RNA amplification

Disinfectant abuse poses a risk of bacterial evolution against stresses, especially during the coronavirus disease 2019 (COVID-19) pandemic. However, bacterial phenotypes, such as drug resistance and viability, are hard to access quickly. Here, we reported an allele specific isothermal RNA amplification (termed AlleRNA) assay, using an isothermal RNA amplification technique, i.e., nucleic acid sequence-based amplification (NASBA), integrated the amplification refractory mutation system (ARMS), involving the use of sequence-specific primers to allow the amplification of the targets with complete complementary sequences. AlleRNA assay enables rapid and simultaneous detection of the single nucleotide polymorphism (SNP) (a detection limit, a LOD of 0.5 % SNP) and the viability (a LOD of 80 CFU) of the quinolone resistant Salmonella enterica. With the use of AlleRNA assay, we found that the quinolone resistant S. enterica exhibited higher survival ability during exposure toquaternary ammonium salt, 75 % ethanol and peracetic acid, which might be attributed to the upregulation of stress response-associated genescompared with the susceptible counterparts. Additionally, the AlleRNA assay indicated the potential risk in a high-frequency occurrence of viable but nonculturable (VBNC) quinolone resistant S. enterica induced by disinfectants due to the depression of ATP biosynthesis. The excessive usage of disinfectants during the COVID-19 pandemic should be carefully evaluated due to the latent threat to ecological and human health.

Quaternary ammonium compounds of emerging concern: Classification, occurrence, fate, toxicity and antimicrobial resistance

Amplified hygiene and precautionary measures are of utmost importance to control the spread of COVID-19 and future infection; however, these changes in practice are projected to trigger a rise in the purchase, utilisation and hence, discharge of many disinfectants into the environment. While alcohol-based, hydrogen peroxide-based, and chlorine-based compounds have been used widely, quaternary ammonium compounds (QACs) based disinfectants are of significant concern due to their overuse during this pandemic. This review presents the classification of disinfectants and their mechanism of action, focusing on QACs. Most importantly, the occurrence, fate, toxicity and antimicrobial resistance due to QACs are covered in this paper. Here we collated evidence from multiple studies and found rising trends of concern, including an increase in the mass load of QACs at a wastewater treatment plant (WWTP) by 331% compared to before the COVID-19 pandemic, as well as an increases in the concentration of 62% in residential dust, resulting in high concentrations of QACs in human blood and breast milk and suggesting that these could be potential sources of persistent QACs in infants. In addition to increased toxicity to human and aquatic life, increased use of QACs and accelerated use of antibiotics and antimicrobials during the COVID-19 pandemic could multiply the threat to antimicrobial resistance.

SigB modulates expression of novel SigB regulon members via Bc1009 in non-stressed and heat-stressed cells revealing its alternative roles in Bacillus cereus

BACKGROUND

The Bacillus cereus Sigma B (SigB) dependent general stress response is activated via the two-component RsbKY system, which involves a phosphate transfer from RsbK to RsbY. It has been hypothesized that the Hpr-like phosphocarrier protein (Bc1009) encoded by bc1009 in the SigB gene cluster may play a role in this transfer, thereby acting as a regulator of SigB activation. Alternatively, Bc1009 may be involved in the activation of a subset of SigB regulon members.

RESULTS

We first investigated the potential role of bc1009 to act as a SigB regulator but ruled out this possibility as the deletion of bc1009 did not affect the expression of sigB and other SigB gene cluster members. The SigB-dependent functions of Bc1009 were further examined in B. cereus ATCC14579 via comparative proteome profiling (backed up by transcriptomics) of wt, Δbc1009 and ΔsigB deletion mutants under heat stress at 42 °C. This revealed 284 proteins displaying SigB-dependent alterations in protein expression levels in heat-stressed cells, including a subgroup of 138 proteins for which alterations were also Bc1009-dependent. Next to proteins with roles in stress defense, newly identified SigB and Bc1009-dependent proteins have roles in cell motility, signal transduction, transcription, cell wall biogenesis, and amino acid transport and metabolism. Analysis of lethal stress survival at 50 °C after pre-adaptation at 42 °C showed intermediate survival efficacy of Δbc1009 cells, highest survival of wt, and lowest survival of ΔsigB cells, respectively. Additional comparative proteome analysis of non-stressed wt and mutant cells at 30 °C revealed 96 proteins with SigB and Bc1009-dependent differences in levels: 51 were also identified under heat stress, and 45 showed significant differential expression at 30 °C. This includes proteins with roles in carbohydrate/ion transport and metabolism. Overlapping functions at 30 °C and 42 °C included proteins involved in motility, and ΔsigB and Δbc1009 cells showed reduced motility compared to wt cells in swimming assays at both temperatures.

CONCLUSION

Our results extend the B. cereus SigB regulon to > 300 members, with a novel role of SigB-dependent Bc1009 in the activation of a subregulon of  > 180 members, conceivably via interactions with other transcriptional regulatory networks.

Impact of benzalkonium chloride, benzethonium chloride and chloroxylenol on bacterial antimicrobial resistance

This review examined 3655 articles on benzalkonium chloride (BKC), benzethonium chloride (BZT) and chloroxylenol (CHO) aiming to understand their impact on antimicrobial resistance. Following the application of inclusion/exclusion criteria, only 230 articles were retained for analysis; 212 concerned BKC, with only 18 for CHO and BZT. Seventy-eight percent of studies used MIC to measure BKC efficacy. Very few studies defined the term 'resistance' and 85% of studies defined 'resistance' as <10-fold increase (40% as low as 2-fold) in MIC. Only a few in vitro studies reported on formulated products and when they did, products performed better. In vitro studies looking at the impact of BKC exposure on bacterial resistance used either a stepwise training protocol or exposure to constant BKC concentrations. In these, BKC exposure resulted in elevated MIC or/and MBC, often associated with efflux, and at time, a change in antibiotic susceptibility profile. The clinical relevance of these findings was, however, neither reported nor addressed. Of note, several studies reported that bacterial strains with an elevated MIC or MBC remained susceptible to the in-use BKC concentration. BKC exposure was shown to reduce bacterial diversity in complex microbial microcosms, although the clinical significance of such a change has not been established. The impact of BKC exposure on the dissemination of resistant genes (notably efflux) remains speculative, although it manifests that clinical, veterinary and food isolates with elevated BKC MIC carried multiple efflux pump genes. The correlation between BKC usage and gene carriage, maintenance and dissemination has also not been established. The lack of clinical interpretation and significance in these studies does not allow to establish with certainty the role of BKC on AMR in practice. The limited literature and BZT and CHO do not allow to conclude that these will impact negatively on emerging bacterial resistance in practice.

Effect of peracetic acid solution on a nitrifying culture: Kinetics, inhibition, cellular and transcriptional responses

Peracetic acid (PAA) has been widely used as a disinfectant in many industries. However, information related to the potential inhibitory effect of PAA solutions (PAA and H₂O₂) on biological wastewater treatment processes is very limited. The work reported here assessed the effect of PAA and H₂O₂ solutions on nitrification kinetics and inhibition, cellular level responses and gene expression of a suspended-growth nitrifying culture. The initial ammonia removal and nitrate production rates significantly decreased at 1/0.14 to 3/0.42 mg/L PAA/H₂O₂. H₂O₂ up to 3 mg/L did not impact nitrification, cell viability or related respiratory activities; thus, the impact of the PAA solution is attributed to PAA alone or in some combination with H₂O₂. Nitrification inhibition by PAA was predominantly related to enzyme inhibition, rather than to loss of cell viability and/or cell lysis. PAA and H₂O₂ negatively affected Nitrosomonas but resulted in Nitrosospira enrichment. Most nitrogen metabolism-related genes (e.g., hydroxylamine oxidoreductase and nitrite oxidoreductase genes) as well as oxidase genes (e.g., cytochrome c oxidase, catalase-peroxidase, and peroxidase genes) were upregulated in PAA- and H₂O₂-amended cultures. Major ATPase genes were downregulated while ATP synthase genes upregulated under the effect of PAA and/or H₂O₂. Upregulation of ATP-dependent protease genes indicates protein damage predominantly caused by PAA rather than H₂O₂. The transcriptional level of genes related to cell division and DNA repair did not show a particular pattern; thus, cell division functionality and DNA integrity were not significantly affected by PAA or H₂O₂. The results of this study have significant implications in the design and operation of effective biological nitrogen removal systems for the treatment of PAA-bearing wastewater.

Comparative transcriptome analysis reveals the resistance regulation mechanism and fungicidal activity of the fungicide phenamacril in Fusarium oxysporum

Fusarium oxysporum (Fo) is an important species complex of soil-borne pathogenic fungi that cause vascular wilt diseases of agricultural crops and some opportunistic diseases of humans. The fungicide phenamacril has been extensively reported to have antifungal activity against Fusarium graminearum and Fusarium fujikuroi. In this study, we found that the amino acid substitutions (V151A and S418T) in Type I myosin FoMyo5 cause natural low resistance to phenamacril in the plant pathogenic Fo isolates. Therefore, we compared the transcriptomes of two phenamacril-resistant Fo isolates FoII5, Fo1st and one phenamacril-sensitive isolate Fo3_a after 1 μg/mL phenamacril treatment. Among the 2728 differentially expressed genes (DEGs), 14 DEGs involved in oxidation–reduction processes and MFS transporters, were significantly up-regulated in phenamacril-resistant isolates. On the other hand, 14 DEGs involved in ATP-dependent RNA helicase and ribosomal biogenesis related proteins, showed significantly down-regulated expression in both phenamacril-resistant and -sensitive isolates. These results indicated that phenamacril not only seriously affected the cytoskeletal protein binding and ATPase activity of sensitive isolate, but also suppressed ribosome biogenesis in all the isolates. Hence, this study helps us better understand resistance regulation mechanism and fungicidal activity of phenamacril and provide reference for the development of new fungicides to control Fo.

NMR Hydrophilic Metabolomic Analysis of Bacterial Resistance Pathways Using Multivalent Antimicrobials with Challenged and Unchallenged Wild Type and Mutated Gram-Positive Bacteria

Multivalent membrane disruptors are a relatively new antimicrobial scaffold that are difficult for bacteria to develop resistance to and can act on both Gram-positive and Gram-negative bacteria. Proton Nuclear Magnetic Resonance (¹H NMR) metabolomics is an important method for studying resistance development in bacteria, since this is both a quantitative and qualitative method to study and identify phenotypes by changes in metabolic pathways. In this project, the metabolic differences between wild type Bacillus cereus (B. cereus) samples and B. cereus that was mutated through 33 growth cycles in a nonlethal dose of a multivalent antimicrobial agent were identified. For additional comparison, samples for analysis of the wild type and mutated strains of B. cereus were prepared in both challenged and unchallenged conditions. A C₁₆-DABCO (1,4-diazabicyclo-2,2,2-octane) and mannose functionalized poly(amidoamine) dendrimer (DABCOMD) were used as the multivalent quaternary ammonium antimicrobial for this hydrophilic metabolic analysis. Overall, the study reported here indicates that B. cereus likely change their peptidoglycan layer to protect themselves from the highly positively charged DABCOMD. This membrane fortification most likely leads to the slow growth curve of the mutated, and especially the challenged mutant samples. The association of these sample types with metabolites associated with energy expenditure is attributed to the increased energy required for the membrane fortifications to occur as well as to the decreased diffusion of nutrients across the mutated membrane.

In vitro virulence potential, surface attachment and transcriptional response of sublethally injured Listeria monocytogenes following exposure to peracetic acid

The disinfectant Peracetic acid (PAA) can cause high levels of sublethal injury to L. monocytogenes. This study aims to evaluate phenotypic and transcriptional characteristics concerning surface attachment and virulence potential of sublethally injured L. monocytogenes ScottA and EGDe after exposure to 0.75 ppm PAA for 90 min at 4°C and subsequent incubation in TSBY at 4°C. Results showed that injured L. monocytogenes cells (99% of total population) were able to attach (after 2 and 24h) on stainless steel coupons at 4°C and 20°C. In vitro virulence assays using human intestinal epithelial Caco-2 cells showed that injured L. monocytogenes could invade host cells but could not proliferate intracellularly. In vitro virulence response was strain-dependent; injured ScottA was more invasive than EGDe. Assessment of PAA-injury at the transcriptional level showed upregulation of genes (motB, flaA) involved in flagellum motility and surface attachment. The transcriptional response of L. monocytogenes EGDe and ScottA was different; only injured ScottA demonstrated upregulation of the virulence genes inlA and plcA. Downregulation of the stress-related genes fri and kat, and upregulation of lmo0669 was observed in injured ScottA. The obtained results indicate that sublethally-injured L. monocytogenes cells may retain part of their virulence properties as well as their ability to adhere on food processing surfaces. Transmission to food products and introduction of these cells in the food chain is therefore a plausible scenario that is worth taking into consideration in terms of risk assessment. Importance L. monocytogenes is the causative agent of listeriosis a serious food-borne illness. Antimicrobial practices, such as disinfectants used for the elimination of this pathogen in food industry can produce a sublethally injured population fraction. Injured cells of this pathogen, that may survive an antimicrobial treatment, may pose a food safety-risk. Nevertheless, knowledge regarding how sublethal injury may impact important cellular traits and phenotypic responses of this pathogen is limited. This work suggests that sublethally injured L. monocytogenes cells maintain the virulence and surface attachment potential and highlights the importance of the occurrence of sublethally injured cells regarding food safety.

Transcriptomic response of Campylobacter jejuni following exposure to acidified sodium chlorite

Chemical decontamination during processing is used in many countries to mitigate the Campylobacter load on chicken meat. Chlorine is a commonly used sanitizer in poultry processing to limit foodborne bacterial pathogens but its efficacy is limited by high bacterial loads and organic material. Acidified sodium chlorite (ASC) is a potential alternative for poultry meat sanitization but little is known about its effects on the cellular response of Campylobacter. In this study, the sensitivity of C. jejuni isolates to ASC was established. RNAseq was performed to characterize the transcriptomic response of C. jejuni following exposure to either chlorine or ASC. Following chlorine exposure, C. jejuni induced an adaptive stress response mechanism. In contrast, exposure to ASC induced higher oxidative damage and cellular death by inhibiting all vital metabolic pathways and upregulating the genes involved in DNA damage and repair. The transcriptional changes in C. jejuni in response to ASC exposure suggest its potential as an effective sanitizer for use in the chicken meat industry.

The antiseptic Miramistin: a review of its comparative in vitro and clinical activity

Miramistin is a topical antiseptic with broad antimicrobial action, including activity against biofilms and a clinical profile showing good tolerability. Miramistin was developed within a framework of the Soviet Union Cold War Space Program. It is available for clinical use in several prior Soviet bloc countries, but barely known outside of these countries and there is almost no mention of miramistin in the English literature. However, considering emerging antimicrobial resistance, the significant potential of miramistin justifies its re-evaluation for use in other geographical areas and conditions. The review consists of two parts: (i) a review of the existing literature on miramistin in English, Russian and Ukrainian languages; (ii) a summary of most commonly used antiseptics as comparators of miramistin. The oral LD50 was 1200 mg/kg, 1000 mg/kg and 100 g/L in rats, mice and fish, respectively. Based on the results of the review, we suggest possible applications of miramistin and potential benefits over currently used agents. Miramistin offers a novel, low toxicity antiseptic with many potential clinical uses that need better study which could address some of the negative impact of antimicrobial, antiseptic and disinfectant resistance.

Effect of ferrate and monochloramine disinfection on the physiological and transcriptomic response of Escherichia coli at late stationary phase

Biological mechanisms of disinfection not only vary by disinfectant but also remain not well understood. We investigated the physiological and transcriptomic response of Escherichia coli at late stationary phase to ferrate and monochloramine in amended lake water. Although ferrate and monochloramine treatments similarly reduced culturable cell concentrations by 3-log₁₀, 64% and 11% of treated cells were viable following monochloramine and ferrate treatment, respectively. This observed induction of viable but non-culturable (VBNC) state following monochloramine treatment but not ferrate is attributed to slower monochloramine disinfection kinetics (by 2.8 times) compared to ferrate. Transcriptomic analysis of E. coli at 15 min of exposure revealed that 3 times as many genes related to translation and transcription were downregulated by monochloramine compared to ferrate, suggesting that monochloramine treatment may be inducing VBNC through reduced protein synthesis and metabolism. Downregulation of universal stress response genes (rpoS, uspA) was attributed to growth-related physiological stressors during late stationary phase which may have contributed to the elevated expression levels of general stress responses pre-disinfection and, subsequently, their significant downregulation post-disinfection. Both disinfectants upregulated oxidative stress response genes (trxC, grxA, soxS), although levels of upregulation were time sensitive. This work shows that bacterial inactivation responses to disinfectants is mediated by complex molecular and growth-related responses.

Development of a Benzalkonium Chloride Based Antibacterial Paper for Health and Food Applications

Pathogenic bacteria and other microorganisms pose a potent threat to humans by causing various infectious diseases. To control the spread of infection, different antibacterial products have been developed. However, most of them are known to be associated with health hazards, environmental pollution, complex fabrication, and/or higher cost. To address these issues, in this study, a low cost, biodegradable and human skin compatible antibacterial paper has been developed. A quaternary ammonium compound, benzalkonium chloride (BKC) has been used for paper surface treatment. The concentration of aqueous solution of BKC coated on paper was varied from 0.1 wt% to 0.2 wt%. No external binder was required for coating BKC onto paper. The efficacy of the coated paper was investigated against Staphylococcus aureus ATCC 6538 and Escherichia coli ATCC 8739 bacterial strains. This antibacterial paper is highly effective against both strains with the concentrations of BKC being within the allowable limit for cytotoxic effects. The optimum concentration of BKC coated on paper can be considered as 0.15 wt%, as nearly 100% inhibition was achieved with it against both strains. The developed antibacterial paper is suitable for being used in the industry for disinfection and food packaging purposes, and also by the public for hand sanitization.

The effects of neutrophil-generated hypochlorous acid and other hypohalous acids on host and pathogens

Neutrophils are predominant immune cells that protect the human body against infections by deploying sophisticated antimicrobial strategies including phagocytosis of bacteria and neutrophil extracellular trap (NET) formation. Here, we provide an overview of the mechanisms by which neutrophils kill exogenous pathogens before we focus on one particular weapon in their arsenal: the generation of the oxidizing hypohalous acids HOCl, HOBr and HOSCN during the so-called oxidative burst by the enzyme myeloperoxidase. We look at the effects of these hypohalous acids on biological systems in general and proteins in particular and turn our attention to bacterial strategies to survive HOCl stress. HOCl is a strong inducer of protein aggregation, which bacteria can counteract by chaperone-like holdases that bind unfolding proteins without the need for energy in the form of ATP. These chaperones are activated by HOCl through thiol oxidation (Hsp33) or N-chlorination of basic amino acid side-chains (RidA and CnoX) and contribute to bacterial survival during HOCl stress. However, neutrophil-generated hypohalous acids also affect the host system. Recent studies have shown that plasma proteins act not only as sinks for HOCl, but get actively transformed into modulators of the cellular immune response through N-chlorination. N-chlorinated serum albumin can prevent aggregation of proteins, stimulate immune cells, and act as a pro-survival factor for immune cells in the presence of cytotoxic antigens. Finally, we take a look at the emerging role of HOCl as a potential signaling molecule, particularly its role in neutrophil extracellular trap formation.

Response of Pseudomonas aeruginosa to the Innate Immune System-Derived Oxidants Hypochlorous Acid and Hypothiocyanous Acid

The bacterial pathogen Pseudomonas aeruginosa causes devastating infections in immunocompromised hosts, including chronic lung infections in cystic fibrosis patients. To combat infection, the host’s immune system produces the antimicrobial oxidants hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN). Little is known about how P. aeruginosa responds to and survives attack from these oxidants. To address this, we carried out two approaches: a mutant screen and transcriptional study. We identified the P. aeruginosa transcriptional regulator, RclR, which responds specifically to HOCl and HOSCN stress and is essential for protection against both oxidants. We uncovered a link between the P. aeruginosa transcriptional response to these oxidants and physiological processes associated with pathogenicity, including antibiotic resistance and the type 3 secretion system.

Pseudomonas aeruginosa is a significant nosocomial pathogen and is associated with lung infections in cystic fibrosis (CF). Once established, P. aeruginosa infections persist and are rarely eradicated despite host immune cells producing antimicrobial oxidants, including hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN). There is limited knowledge as to how P. aeruginosa senses, responds to, and protects itself against HOCl and HOSCN and the contribution of such responses to its success as a CF pathogen. To investigate the P. aeruginosa response to these oxidants, we screened 707 transposon mutants, with mutations in regulatory genes, for altered growth following HOCl exposure. We identified regulators of antibiotic resistance, methionine biosynthesis, catabolite repression, and PA14_07340, the homologue of the Escherichia coli HOCl-sensor RclR (30% identical), which are required for protection against HOCl. We have shown that RclR (PA14_07340) protects specifically against HOCl and HOSCN stress and responds to both oxidants by upregulating the expression of a putative peroxiredoxin, rclX (PA14_07355). Transcriptional analysis revealed that while there was specificity in the response to HOCl (231 genes upregulated) and HOSCN (105 genes upregulated), there was considerable overlap, with 74 genes upregulated by both oxidants. These included genes encoding the type 3 secretion system, sulfur and taurine transport, and the MexEF-OprN efflux pump. RclR coordinates part of the response to both oxidants, including upregulation of pyocyanin biosynthesis genes, and, in the presence of HOSCN, downregulation of chaperone genes. These data indicate that the P. aeruginosa response to HOCl and HOSCN is multifaceted, with RclR playing an essential role.

IMPORTANCE The bacterial pathogen Pseudomonas aeruginosa causes devastating infections in immunocompromised hosts, including chronic lung infections in cystic fibrosis patients. To combat infection, the host’s immune system produces the antimicrobial oxidants hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN). Little is known about how P. aeruginosa responds to and survives attack from these oxidants. To address this, we carried out two approaches: a mutant screen and transcriptional study. We identified the P. aeruginosa transcriptional regulator, RclR, which responds specifically to HOCl and HOSCN stress and is essential for protection against both oxidants. We uncovered a link between the P. aeruginosa transcriptional response to these oxidants and physiological processes associated with pathogenicity, including antibiotic resistance and the type 3 secretion system.

Short- and Long-Term Transcriptomic Responses of Escherichia coli to Biocides: a Systems Analysis

The mechanisms of the bacterial response to biocides are poorly understood, despite their broad application. To identify the genetic basis and pathways implicated in the biocide stress response, we exposed Escherichia coli populations to 10 ubiquitous biocides. By comparing the transcriptional responses between a short-term exposure (30 min) and a long-term exposure (8 to 12 h) to biocide stress, we established the common gene and pathway clusters that are implicated in general and biocide-specific stress responses. Our analysis revealed a temporal choreography, starting from the upregulation of chaperones to the subsequent repression of motility and chemotaxis pathways and the induction of an anaerobic pool of enzymes and biofilm regulators. A systematic analysis of the transcriptional data identified a zur-regulated gene cluster to be highly active in the stress response against sodium hypochlorite and peracetic acid, presenting a link between the biocide stress response and zinc homeostasis. Susceptibility assays with knockout mutants further validated our findings and provide clear targets for downstream investigation of the implicated mechanisms of action.IMPORTANCE Antiseptics and disinfectant products are of great importance to control and eliminate pathogens, especially in settings such as hospitals and the food industry. Such products are widely distributed and frequently poorly regulated. Occasional outbreaks have been associated with microbes resistant to such compounds, and researchers have indicated potential cross-resistance with antibiotics. Despite that, there are many gaps in knowledge about the bacterial stress response and the mechanisms of microbial resistance to antiseptics and disinfectants. We investigated the stress response of the bacterium Escherichia coli to 10 common disinfectant and antiseptic chemicals to shed light on the potential mechanisms of tolerance to such compounds.

Aesthetic Alteration of Marble Surfaces Caused by Biofilm Formation: Effects of Chemical Cleaning

Despite the massive presence of biofilms causing aesthetic alteration to the façade of the Monza Cathedral, our team in a previous work proved that the biocolonization was not a primary damaging factor if compared to chemical-physical deterioration due to the impact of air pollution. Nonetheless, the conservators tried to remove the sessile dwelling microorganisms to reduce discolouration. In this research, two nearby sculpted leaves made of Candoglia marble were selected to study the effects of a chemical treatment combining the biocides benzalkonium chloride, hydrogen peroxide and Algophase® and mechanical cleaning procedures. One leaf was cleaned with the biocides and mechanically, and the other was left untreated as control. The impact of the treatment was investigated after 1 month from the cleaning by digital microscopy, environmental scanning electron microscopy, confocal microscopy and molecular methods to determine the composition and the functional profiles of the bacterial communities. Despite the acceptable aesthetic results obtained, the overall cleaning treatment was only partially effective in removing the biofilm from the colonized surfaces and, therefore, not adequately suitable for the specific substrate. Furthermore, the cleaning process selected microorganisms potentially more resistant to biocides so that the efficacy of future re-treatment by antimicrobial agents could be negatively affected.

ERIC-PCR technique applied to monitoring and quantification of DNA damage during water disinfection process

In this work, we propose a novel application of ERIC-PCR technique to study DNA damage after ultraviolet radiation (UV) and peracetic acid (PAA) treatment for water disinfection purpose. The efficacy of both treatments on E. coli suspension was evaluated by two approaches: through monitoring of inactivation by conventional culture technique, and by analyzing DNA damage with ERIC-PCR. All the experiments were carried out in a batch reactor, using three intensities of UV-C radiation (10.5, 4.2 and 2.1 mW/cm2) and different PAA concentrations (4 to 16 ppm). Both treatments produced bacterial inactivation in a dose-response fashion. Based on the results of bacterial count we obtained an index of inactivation (INACI). For each sample, DNA extraction was performed and evaluated by ERIC-PCR. Qualitative modifications were observed in ERIC-PCR band patterns for all the UV-C radiation intensities used, but no changes were detected at any of the PAA concentrations. The banding pattern modifications observed are consequence of the interruption of Taq polymerase enzyme amplification-activity, caused by the presence of alterations on the DNA structure (dimer and hydrates formation). Furthermore, an index was proposed to measure DNA damage (DNADI) regarding the changes in the relative optical density values of the amplification products. A linear correlation was obtained with a high correspondence between the inactivation index (INACI) and the DNA damage index (DNADI), that was expressed as DNADI = 0.05881×INACI. This approach proves that ERIC-PCR is a feasible and valuable tool for detecting and quantifying DNA damage and it may provide a useful strategy for bacterial identification, tracking changes in DNA and providing reliable and reproducible data.

Oxidative Disinfectants Activate Different Responses in Vibrio parahaemolyticus

Vibrio parahaemolyticus is a prevalent seafoodborne enteropathogen that has become a global concern since the spread of its pandemic strain in 1996. This study investigates the responses of this pathogen to the oxidative disinfectants hydrogen peroxide, chlorine dioxide, and peracetic acid. Expression of the regulator genes oxyR and rpoS, determined by reverse transcription PCR, in V. parahaemolyticus wild-type, oxyR mutant, and rpoS mutant strains exhibited similar patterns in response to the tested oxidative disinfectants. The transcription of the rpoS gene was markedly enhanced in the oxyR mutant strain in the exponential phase. The expression of catalase KatE1 was tracked by using a LacZ fusion reporter in these strains. The experimental results revealed that KatE1 was a significant scavenger of hydrogen peroxide and peracetic acid in V. parahaemolyticus, and RpoS may partially compensate for the regulatory role of OxyR in the oxyR mutant strain. In contrast to its responses to hydrogen peroxide and paracetic acid, KatE1 was not the primary scavenger of chlorine dioxide in these V. parahaemolyticus strains. This study shows that these disinfectants activated a basic oxidative response in this pathogen with different features.

Benzalkonium Chlorides: Uses, Regulatory Status, and Microbial Resistance

Benzalkonium chlorides (BACs) are chemicals with widespread applications due to their broad-spectrum antimicrobial properties against bacteria, fungi, and viruses. This review provides an overview of the market for BACs, as well as regulatory measures and available data on safety, toxicity, and environmental contamination. We focus on the effect of frequent exposure of microbial communities to BACs and the potential for cross-resistant phenotypes to emerge. Toward this goal, we review BAC concentrations in consumer products, their correlation with the emergence of tolerance in microbial populations, and the associated risk potential. Our analysis suggests that the ubiquitous and frequent use of BACs in commercial products can generate selective environments that favor microbial phenotypes potentially cross-resistant to a variety of compounds. An analysis of benefits versus risks should be the guidepost for regulatory actions regarding compounds such as BACs.

The benzalkonium chloride resistant or sensitive phenotype of Listeria monocytogenes planktonic cells did not dictate the susceptibility of its biofilm counterparts

The main goal of this work was to approach food industry conditions in the comparison of the susceptibility of biofilms of Listeria monocytogenes to the biocides benzalkonium chloride (BAC) and peracetic acid (PAA). Twelve isolates of L. monocytogenes, including nine well characterized BAC resistant strains were used. Biofilms were produced on stainless steel coupons (SSC), at 11 °C (refrigeration temperature) or at 25 °C (room temperature), in culture media simulating clean (nutrient limiting) or soiled (nutrient rich) growth conditions. Neither different nutrient availability nor growth temperature showed significant effect (p > .05) on biofilm formation. PAA confirmed to be more effective than BAC in biofilm elimination. Biofilms formed under nutritional stress tended to differentiate more the response to BAC of the resistant or sensitive strains, but the resistant or sensitive phenotype of the planktonic cells did not dictate biofilm susceptibility.

Upregulation of peroxide scavenging enzymes and multidrug efflux proteins highlight an active sodium hypochlorite response in Pseudomonas fluorescens biofilms

The oxidative biocide sodium hypochlorite is among the most commonly used antimicrobial agents in the control of surface-attached microbial communities (biofilms). Clarifying the genetic response of microorganisms in biofilms to hypochlorite may contribute to improved biofilm control strategies. Here, RNA-seq was used to investigate the differential gene expression response of industrially relevant Pseudomonas fluorescens biofilms to sub-lethal concentrations of sodium hypochlorite. Pseudomonas biofilms responded to hypochlorite exposure with increased transcription of genes encoding peroxide scavenging enzymes (e.g., alkyl hydroperoxide reductase (Ahp) and hydroperoxide resistance protein (Ohr)), oxidative stress repair enzymes (e.g., the periplasmic sulfoxide reductase YedYZ complex), and multidrug efflux (e.g., MexEF pumps). In addition, genes involved in amino acid synthesis and energy metabolism were down-regulated following hypochlorite exposure. This work improves the current understanding of genetic response mechanisms to biocides and contributes to the optimization of biocides and application strategies.

Loss of Function in Escherichia coli Exposed to Environmentally Relevant Concentrations of Benzalkonium Chloride

Assessing the risk of resistance associated with biocide exposure commonly involves exposing microorganisms to biocides at concentrations close to the MIC. With the aim of representing exposure to environmental biocide residues, Escherichia coli MG1655 was grown for 20 passages in the presence or absence of benzalkonium chloride (BAC) at 100 ng/liter and 1,000 ng/liter (0.0002% and 0.002% of the MIC, respectively). BAC susceptibility, planktonic growth rates, motility, and biofilm formation were assessed, and differentially expressed genes were determined via transcriptome sequencing. Planktonic growth rate and biofilm formation were significantly reduced (P < 0.001) following BAC adaptation, while BAC minimum bactericidal concentration increased 2-fold. Transcriptomic analysis identified 289 upregulated and 391 downregulated genes after long-term BAC adaptation compared with the respective control organism passaged in BAC-free medium. When the BAC-adapted bacterium was grown in BAC-free medium, 1,052 genes were upregulated and 753 were downregulated. Repeated passage solely in biocide-free medium resulted in 460 upregulated and 476 downregulated genes compared with unexposed bacteria. Long-term exposure to environmentally relevant BAC concentrations increased the expression of genes associated with efflux and reduced the expression of genes associated with outer-membrane porins, motility, and chemotaxis. This was manifested phenotypically through the loss of function (motility). Repeated passage in a BAC-free environment resulted in the upregulation of multiple respiration-associated genes, which was reflected by increased growth rate. In summary, repeated exposure of E. coli to BAC residues resulted in significant alterations in global gene expression that were associated with minor decreases in biocide susceptibility, reductions in growth rate and biofilm formation, and loss of motility.IMPORTANCE Exposure to very low concentrations of biocides in the environment is a poorly understood risk factor for antimicrobial resistance. Repeated exposure to trace levels of the biocide benzalkonium chloride (BAC) resulted in loss of function (motility) and a general reduction in bacterial fitness but relatively minor decreases in susceptibility. These changes were accompanied by widespread changes in the Escherichia coli transcriptome. These results demonstrate the importance of including phenotypic characterization in studies designed to assess the risks of biocide exposure.

Microbial responses to transient shock loads of quaternary ammonium compounds with different length of alkyl chain in a membrane bioreactor

Extensive applications of quaternary ammonium compounds (QACs) in household and industrial products inevitably lead to their release into wastewaters; however, little attention has been paid to the acute effects on activated sludge. In this work, we investigated the responses of microorganisms in a membrane bioreactor (MBR) to transient shock loads of QACs with different alkyl chain length and their impacts on MBR performance. Results showed that QACs affected microbial viability and caused damage to key enzymes (e.g., ammonium monooxygenase and nitrite oxidoreductase), inhibiting organic matter degradation and nitrogen removal. The presence of QACs also caused negative influences on dehydrogenase activity, catalase and superoxide dismutase, thus increasing the production of reactive oxygen species. Moreover, QACs with longer alkyl chains and/or benzyl groups bonded to the nitrogen atom could induce a more severe damage to cell integrity and microbial viability. The interaction with QACs also induced the release of organic matters and the changes of adhesion properties of microbial products, resulting in aggravated membrane fouling in MBRs. Our results demonstrate the acute negative effects of QACs on activated sludge, and special attention should be paid to the performance of biological wastewater treatment processes subject to the shock loads of QAC-bearing industrial streams.

Genomic and Transcriptomic Insights into How Bacteria Withstand High Concentrations of Benzalkonium Chloride Biocides

Benzalkonium chlorides (BAC) are commonly used biocides in broad-spectrum disinfectant solutions. How microorganisms cope with BAC exposure remains poorly understood, despite its importance for disinfection and disinfectant-induced antibiotic resistance. To provide insights into these issues, we exposed two isolates of an opportunistic pathogen, Pseudomonas aeruginosa, to increasing concentrations of BAC. One isolate was preadapted to BAC, as it originated from a bioreactor fed with subinhibitory concentrations of BAC for 3 years, while the other originated from a bioreactor that received no BAC. Replicated populations of both isolates were able to survive high concentrations of BAC, up to 1,200 and 1,600 mg/liter for the non- and preadapted strains, respectively, exceeding typical application doses. Transcriptome sequencing (RNA-seq) analysis revealed upregulation of efflux pump genes and decreased expression of porins related to BAC transport as well as reduced growth rate. Increased expression of spermidine (a polycation) synthase genes and mutations in the pmrB (polymyxin resistance) gene, which cause a reduction in membrane negative charge, suggested that a major adaptation to exposure to the cationic surfactant BAC was to actively stabilize cell surface charge. Collectively, these results revealed that P. aeruginosa adapts to BAC exposure by a combination of mechanisms and provided genetic markers to monitor BAC-resistant organisms that may have applications in the practice of disinfection.IMPORTANCE BAC are widely used as biocides in disinfectant solutions, food-processing lines, domestic households, and health care facilities. Due to their wide use and mode of action, there has been rising concern that BAC may promote antibiotic resistance. Consistent with this idea, at least 40 outbreaks have been attributed to infection by disinfectant- and antibiotic-resistant pathogens such as P. aeruginosa However, the underlying molecular mechanisms that bacteria use to deal with BAC exposure remain poorly elucidated. Elucidating these mechanisms may be important for monitoring and limiting the spread of disinfectant-resistant pathogens. Using an integrated approach that combined genomics and transcriptomics with physiological characterization of BAC-adapted isolates, this study provided a comprehensive understanding of the BAC resistance mechanisms in P. aeruginosa Our findings also revealed potential genetic markers to detect and monitor the abundance of BAC-resistant pathogens across clinical or environmental settings. This work contributes new knowledge about high concentrations of benzalkonium chlorides disinfectants-resistance mechanisms at the whole-cell genomic and transcriptomic level.

Pseudomonas aeruginosa defense systems against microbicidal oxidants

The most abundant oxidants controlling bacterial colonization on mucosal barrier epithelia are hypochlorous acid (HOCl), hypobromous acid (HOBr) and hypothiocyanous acid (HOSCN). All three oxidants are highly antimicrobial but little is known about their relative efficacies, their respective cellular targets, or what specific responses they elicit in bacteria. To address these important questions, we directly tested the individual oxidants on the virulent Pseudomonas aeruginosa strain PA14. We discovered that HOCl and HOBr work almost interchangeably, impacting non-growing bacterial cultures more significantly than actively growing bacteria, and eliciting similar stress responses, including the heat shock response. HOSCN treatment is distinctly different, affecting primarily actively growing PA14 and evoking stress responses suggestive of membrane damage. What all three oxidants have in common, however, is their ability to cause substantial protein aggregation. This effect became particularly obvious in strains lacking polyphosphate, a newly recognized chemical chaperone. Treatment of PA14 with the FDA-approved anti-inflammatory drug mesalamine, which has recently been shown to attenuate polyP production in a wide range of bacteria, effectively decreased the resistance of PA14 toward all three oxidants, suggesting that we have discovered a novel, targetable defense system in P. aeruginosa.

Assessment of chlorine tolerance profile of Citrobacter species recovered from wastewater treatment plants in Eastern Cape, South Africa

This present study assessed the chlorine tolerance of some Citrobacter species recovered from secondary effluents from the clarifiers of two wastewater treatment plants in the Eastern Cape, South Africa. The bacterial survival, chlorine lethal dose and inactivation kinetics at lethal doses were examined. Inactivation of the test bacteria (n = 20) at the recommended dose of 0.5 mg/l for 30 min exposure showed a progressive reduction in bacterial population from 4 to 5 log reduction and residuals ranged between 0.12 and 0.46 mg/l. The bactericidal activity of chlorine increased at higher dosages with a substantial reduction in viability of the bacteria and complete inactivation of the bacterial population at a lethal dose of 0.75 and 1.0 mg/l in 30 min. For the inactivation kinetics, bactericidal activity of chlorine increased with time showing a 3.67-5.4 log reduction in 10 min, 4.0-5.6 log reduction in 20 min and above 6.3 log reductions to complete sterilization of bacterial population over 30 min for all the entire test Citrobacter isolates used in this study. Furthermore, there was a strong correlation (R ² > 0.84) between bacteria inactivation and increase in contact time. This study appears to have provided support for laboratory evidence of bacterial tolerance to chlorine disinfection at current recommended dose (0.5 mg/l for 30 min), and chlorine concentration between 0.75 and 1.0 mg/l was found to have a better disinfecting capacity to check tolerance of Citrobacter species.

CRISPR Perturbation of Gene Expression Alters Bacterial Fitness under Stress and Reveals Underlying Epistatic Constraints

The evolution of antibiotic resistance has engendered an impending global health crisis that necessitates a greater understanding of how resistance emerges. The impact of nongenetic factors and how they influence the evolution of resistance is a largely unexplored area of research. Here we present a novel application of CRISPR-Cas9 technology for investigating how gene expression governs the adaptive pathways available to bacteria during the evolution of resistance. We examine the impact of gene expression changes on bacterial adaptation by constructing a library of deactivated CRISPR-Cas9 synthetic devices to tune the expression of a set of stress-response genes in Escherichia coli. We show that artificially inducing perturbations in gene expression imparts significant synthetic control over fitness and growth during stress exposure. We present evidence that these impacts are reversible; strains with synthetically perturbed gene expression regained wild-type growth phenotypes upon stress removal, while maintaining divergent growth characteristics under stress. Furthermore, we demonstrate a prevailing trend toward negative epistatic interactions when multiple gene perturbations are combined simultaneously, thereby posing an intrinsic constraint on gene expression underlying adaptive trajectories. Together, these results emphasize how CRISPR-Cas9 can be employed to engineer gene expression changes that shape bacterial adaptation, and present a novel approach to synthetically control the evolution of antimicrobial resistance.

Effects of exposure to quaternary-ammonium-based biocides on antimicrobial susceptibility and tolerance to physical stresses in bacteria from organic foods

In the present study, a collection of 76 biocide-sensitive bacterial strains isolated from organically produced food were adapted by repeated exposure to increasing concentrations of the quaternary ammonium compounds (QACs) benzalkonium chloride (BC) and hexadecylpyridinium chloride (HDP). The sensitivity of both wildtype strains and their corresponding QAC-adapted strains to other biocides and to antibiotics was studied. QAC tolerance increased in 88.2% of strains for BC and in 30.3% of strains for HDP, with increases in minimum inhibitory concentrations between 2 and over 100 fold. Adaptive resistance was stable after 20 subcultures in biocide-free medium for 7 and 5 of the BC- and HDP-adapted strains, respectively. Adaptation to BC and HDP also reduced the susceptibility to other biocides, mainly hexachlorophene (CF), didecyldimethylammonium bromide (AB), triclosan (TC) and chlorhexidine (CH). BC-adapted strains showed increased antibiotic resistance to ampicillin (AM) followed by sulfamethoxazol (SXT) and cefotaxime (CTX), and some showed increased sensitivity to ceftazidime (CAZ), CTX, AM and STX. Changes in antibiotic resistance in HDP-adapted strains were more heterogeneous and strain-dependent. Main efflux pump genes detected in QAC-adapted strains were acrB, sugE, norC, qacE and qacH, as well as antibiotic resistance genes aac(6_)-Ie-aph(2_)-Ia, aph(2_)-Ic, ant(4_)-Ia, lsa, mrsA/B, ereA, ermB and cat. Membrane anisotropy experiments revealed that QAC adaptation induced an increase in membrane rigidity in the case of BC, while response to HDP was more heterogeneous and strain-dependent. Growth capacity was significantly higher in some QAC-adapted strains and strain-dependent changes in heat tolerance were also detected in QAC-adapted strains. Gastric acid or bile resistances do not seem to be influenced by QAC adaptation.

Antibiofouling Polyvinylidene Fluoride Membrane Modified by Quaternary Ammonium Compound: Direct Contact-Killing versus Induced Indirect Contact-Killing

Widespread applications of membrane technology call for the development of antibiofouling membranes. For the traditional contact-killing strategy, the antibacterial action is restricted to the surface: the membrane loses its antibiofouling efficacy once its surface is completely covered with a fouling layer. However, in this study, polyvinylidene fluoride (PVDF) microfiltration membranes blended with quaternary ammonium compound (QAC) exhibited a surprisingly lasting antimicrobial activity in the vicinity of the membrane surface. The results indicated that QAC was capable of driving surface segregation with a high structural stability, and the QAC modified membrane shows clear antibacterial effects against both Gram-positive and Gram-negative bacteria. Covering the modified membrane surface by an abiotic alginate layer resulted in a loss of antibacterial efficiency by 86.2%. In contrast, the antibacterial efficiency was maintained after developing a biofilm of Staphylococcus aureus of 30 μm in thickness. The current study may suggest that bacteria affected by contact-killing might interact with other bacteria in the vicinity, resulting in retarded biofilm growth. The antibiofouling effect and associated mechanism of the QAC modified membrane were further validated in a membrane bioreactor during long-term operation.

Similar Microbial Consortia and Genes Are Involved in the Biodegradation of Benzalkonium Chlorides in Different Environments

Benzalkonium chlorides (BACs) are emerging pollutants. Identification of microorganisms and the genes involved in the biodegradation of BACs is crucial for better understanding the fate of BACs in the environment and developing treatment strategies. Four microbial communities degrading BACs were developed from sewage (SEW), activated sludge (AS), soil (SOIL) and sea sediment (SEA) samples. According to 16S rRNA pyrosequencing and shotgun metagenome sequencing analyses, the most abundant species represented uncharacterized members of the Pseudomonas and Achromobacter genera. BAC biotransformation rates of the enriched microbial communities were 2.8, 3.2, 17.8, and 24.3 μM hr(-1) for SEA, AS, SOIL, and SEW, respectively, and were positively correlated with the relative abundance of a particular Pseudomonas sp. strain, BIOMIG1. The strain BIOMIG1 mineralizes BACs at a rate up to 2.40 μmol hr(-1) 10(-11) cells. Genomes of four BAC degrading and nondegrading BIOMIG1 phenotypes were sequenced and differentially compared with each other. As a result, a gene cluster encoding for transporters, an integrase and a dioxygenase were involved in BAC biotransformation. Our results suggest that BIOMIG1 plays a key role on the fate of BACs in the environment and genes, other than those reported to date, are involved in BAC biotransformation in various habitats.

Efflux pump induction by quaternary ammonium compounds and fluoroquinolone resistance in bacteria

Biocides, primarily those containing quaternary ammonium compounds (QAC), are heavily used in hospital environments and various industries (e.g., food, water, cosmetic). To date, little attention has been paid to potential implications of QAC use in the emergence of antibiotic resistance, especially fluoroquinolone-resistant bacteria in patients and in the environment. QAC-induced overexpression of efflux pumps can lead to: cross resistance with fluoroquinolones mediated by multidrug efflux pumps; stress response facilitating mutation in the Quinolone Resistance Determining Region; and biofilm formation increasing the risk of transfer of mobile genetic elements carrying fluoroquinolone or QAC resistance determinants. By following the European Biocidal Product Regulation, manufacturers of QAC are required to ensure that their QAC-based biocidal products are safe and will not contribute to emerging bacterial resistance.

Predictive Studies Suggest that the Risk for the Selection of Antibiotic Resistance by Biocides Is Likely Low in Stenotrophomonas maltophilia

Biocides are used without restriction for several purposes. As a consequence, large amounts of biocides are released without any control in the environment, a situation that can challenge the microbial population dynamics, including selection of antibiotic resistant bacteria. Previous work has shown that triclosan selects Stenotrophomonas maltophilia antibiotic resistant mutants overexpressing the efflux pump SmeDEF and induces expression of this pump triggering transient low-level resistance. In the present work we analyze if two other common biocides, benzalkonium chloride and hexachlorophene, trigger antibiotic resistance in S. maltophilia. Bioinformatic and biochemical methods showed that benzalkonium chloride and hexachlorophene bind the repressor of smeDEF, SmeT. Only benzalkonium chloride triggers expression of smeD and its effect in transient antibiotic resistance is minor. None of the hexachlorophene-selected mutants was antibiotic resistant. Two benzalkonium chloride resistant mutants presented reduced susceptibility to antibiotics and were impaired in growth. Metabolic profiling showed they were more proficient than their parental strain in the use of some dipeptides. We can then conclude that although bioinformatic predictions and biochemical studies suggest that both hexachlorophene and benzalkonium chloride should induce smeDEF expression leading to transient S. maltophilia resistance to antibiotics, phenotypic assays showed this not to be true. The facts that hexachlorophene resistant mutants are not antibiotic resistant and that the benzalkonium chloride resistant mutants presenting altered susceptibility to antibiotics were impaired in growth suggests that the risk for the selection (and fixation) of S. maltophilia antibiotic resistant mutants by these biocides is likely low, at least in the absence of constant selection pressure.