Pathogenic fungi synergistically cooperate with Serratia marcescens to increase cockroach mortality.

The abuse of chemical insecticides has led to strong resistance in cockroaches, and biopesticides with active ingredients based on insect pathogens have good development prospects; however, their slow effect has limited their practical application, and improving their effectiveness has become an urgent problem. In this study, the interaction between Serratia marcescens and Metarhizium anisopliae enhanced their virulence against Blattella germanica and exhibited a synergistic effect. The combination of S. marcescens and M. anisopliae caused more severe tissue damage and accelerated the proliferation of the insect pathogen. The results of high-throughput sequencing demonstrated that the gut microbiota was dysbiotic, the abundance of the opportunistic pathogen Weissella cibaria increased, and entry into the hemocoel accelerated the death of the German cockroaches. In addition, the combination of these two agents strongly downregulated the expression of Imd and Akirin in the IMD pathway and ultimately inhibited the expression of antimicrobial peptides (AMPs). S. marcescens released prodigiosin to disrupted the gut homeostasis and structure, M. anisopliae released destruxin to damaged crucial organs, opportunistic pathogen Weissella cibaria overproliferated, broke the gut epithelium and entered the hemocoel, leading to the death of pests. These findings will allow us to optimize the use of insect pathogens for the management of pests and produce more effective biopesticides.

Vairimorpha (Nosema) ceranae can promote Serratia development in honeybee gut: an underrated threat for bees?

The genus Serratia harbors opportunistic pathogenic species, among which Serratia marcescens is pathogenic for honeybees although little studied. Recently, virulent strains of S. marcescens colonizing the Varroa destructor mite's mouth were found vectored into the honeybee body, leading to septicemia and death. Serratia also occurs as an opportunistic pathogen in the honeybee's gut with a low absolute abundance. The Serratia population seems controlled by the host immune system, but its presence may represent a hidden threat, ready to arise when honeybees are weakened by biotic and abiotic stressors. To shed light on the Serratia pathogen, this research aims at studying Serratia's development dynamics in the honeybee body and its interactions with the co-occurring fungal pathogen Vairimorpha ceranae. Firstly, the degree of pathogenicity and the ability to permeate the gut epithelial barrier of three Serratia strains, isolated from honeybees and belonging to different species (S. marcescens, Serratia liquefaciens, and Serratia nematodiphila), were assessed by artificial inoculation of newborn honeybees with different Serratia doses (104, 106, and 108 cells/mL). The absolute abundance of Serratia in the gut and in the hemocoel was assessed in qPCR with primers targeting the luxS gene. Moreover, the absolute abundance of Serratia was assessed in the gut of honeybees infected with V. ceranae at different development stages and supplied with beneficial microorganisms and fumagillin. Our results showed that all tested Serratia strains could pass through the gut epithelial barrier and proliferate in the hemocoel, with S. marcescens being the most pathogenic. Moreover, under cage conditions, Serratia better proliferates when a V. ceranae infection is co-occurring, with a positive and significant correlation. Finally, fumagillin and some of the tested beneficial microorganisms could control both Serratia and Vairimorpha development. Our findings suggest a correlation between the two pathogens under laboratory conditions, a co-occurring infection that should be taken into consideration by researches when testing antimicrobial compounds active against V. ceranae, and the related honeybees survival rate. Moreover, our findings suggest a positive control of Serratia by the environmental microorganism Apilactobacillus kunkeei in a in vivo model, confirming the potential of this specie as beneficial bacteria for honeybees.

Importance of core microRNA pathway genes and microRNAs associated with the defense of Odontotermes formosanus (Shiraki) against Serratia marcescens infection.

MicroRNAs (miRNAs) are noncoding small regulatory RNAs involved in diverse biological processes. Odontotermes formosanus (Shiraki) is a polyphagous pest that causes economic damage to agroforestry. Serratia marcescens is a bacterium with great potential for controlling this insect. However, knowledge about the miRNA pathway and the role of miRNAs in O. formosanus defense against SM1 is limited. In this study, OfAgo1, OfDicer1 and OfDrosha were differentially expressed in different castes and tissues. SM1 infection affected the expression of all three genes in O. formosanus. Then, we used specific double-stranded RNAs to silence OfAgo1, OfDicer1 and OfDrosha. Knockdown of these genes enhanced the virulence of SM1 to O. formosanus, suggesting that miRNAs were critical in the defense of O. formosanus against SM1. Furthermore, we sequenced miRNAs from SM1-infected and uninfected O. formosanus. 33 differentially expressed (DE) miRNAs were identified, whereby 22 were upregulated and 11 were downregulated. Finally, the miRNA-mRNA networks were constructed, which further suggested the important role of miRNAs in the defense of O. formosanus against SM1. Totally, O. formosanus miRNA core genes defend against SM1 infection by regulating miRNA expression. This study elucidates the interactions between O. formosanus and SM1 and provides new theories for biological control.

The fliR gene contributes to the virulence of S. marcescens in a Drosophila intestinal infection model.

Serratia marcescens is an opportunistic bacterium that infects a wide range of hosts including humans. It is a potent pathogen in a septic injury model of Drosophila melanogaster since a few bacteria directly injected in the body cavity kill the insect within a day. In contrast, flies do not succumb to ingested bacteria for days even though some bacteria cross the intestinal barrier into the hemolymph within hours. The mechanisms by which S. marcescens attacks enterocytes and damages the intestinal epithelium remain uncharacterized. To better understand intestinal infections, we performed a genetic screen for loss of virulence of ingested S. marcescens and identified FliR, a structural component of the flagellum, as a virulence factor. Next, we compared the virulence of two flagellum mutants fliR and flhD in two distinct S. marcescens strains. Both genes are required for S. marcescens to escape the gut lumen into the hemocoel, indicating that the flagellum plays an important role for the passage of bacteria through the intestinal barrier. Unexpectedly, fliR but not flhD is involved in S. marcescens-mediated damages of the intestinal epithelium that ultimately contribute to the demise of the host. Our results therefore suggest a flagellum-independent role for fliR in bacterial virulence.

Algal polysaccharide's potential to combat respiratory infections caused by Klebsiella pneumoniae and Serratia marcescens biofilms.

The growth of respiratory diseases, as witnessed through the SARS and COVID-19 outbreaks, and antimicrobial-resistance together pose a serious threat to humanity. One reason for antimicrobial resistance is formation of bacterial biofilms. In this study the sulphated polysaccharides from green algae Chlamydomonas reinhardtii (Cr-SPs) is tested for its antibacterial and antibiofilm potential against Klebsiella pneumoniae and Serratia marcescens. Agar cup assay clearly indicated the antibacterial potential of Cr-SPs. Minimum inhibitory concentration (MIC50) of Cr-SPs against Klebsiella pneumoniae was found to be 850 µg/ml, and it is 800 µg/ml in Serratia marcescens. Time-kill and colony-forming ability assays suggest the concentration-dependent bactericidal potential of Cr-SPs. Cr-SPs showed 74-100% decrease in biofilm formation in a concentration-dependent manner by modifying the cell surface hydrophobic properties of these bacteria. Cr-SPs have also distorted preformed-biofilms by their ability to interact and destroy the extra polymeric substance and eDNA of the matured biofilm. Scanning electron microscopy analysis showed that Cr-SPs effectively altered the morphology of these bacterial cells and distorted the bacterial biofilms. Furthermore reduced protease, urease and prodigiosin pigment production suggest that Cr-SPs interferes the quorum sensing mechanism in these bacteria. The current study paves way towards developing Cr-SPs as a control strategy for treatment of respiratory tract infections.

PsrA is a novel regulator contributes to antibiotic synthesis, bacterial virulence, cell motility and extracellular polysaccharides production in Serratia marcescens.

Serratia marcescens is a Gram-negative bacterium of the Enterobacteriaceae family that can produce numbers of biologically active secondary metabolites. However, our understanding of the regulatory mechanisms behind secondary metabolites biosynthesis in S. marcescens remains limited. In this study, we identified an uncharacterized LysR family transcriptional regulator, encoding gene BVG90_12635, here we named psrA, that positively controlled prodigiosin synthesis in S. marcescens. This phenotype corresponded to PsrA positive control of transcriptional of the prodigiosin-associated pig operon by directly binding to a regulatory binding site (RBS) and an activating binding site (ABS) in the promoter region of the pig operon. We demonstrated that L-proline is an effector for the PsrA, which enhances the binding affinity of PsrA to its target promoters. Using transcriptomics and further experiments, we show that PsrA indirectly regulates pleiotropic phenotypes, including serrawettin W1 biosynthesis, extracellular polysaccharide production, biofilm formation, swarming motility and T6SS-mediated antibacterial activity in S. marcescens. Collectively, this study proposes that PsrA is a novel regulator that contributes to antibiotic synthesis, bacterial virulence, cell motility and extracellular polysaccharides production in S. marcescens and provides important clues for future studies exploring the function of the PsrA and PsrA-like proteins which are widely present in many other bacteria.

In silico characterization, docking, and simulations to understand host-pathogen interactions in an effort to enhance crop production in date palms.

Food safety remains a significant challenge despite the growth and development in agricultural research and the advent of modern biotechnological and agricultural tools. Though the agriculturist struggles to aid the growing population's needs, many pathogen-based plant diseases by their direct impact on cell division and tissue development have led to the loss of tons of food crops every year. Though there are many conventional and traditional methods to overcome this issue, the amount and time spend are huge. Scientists have developed systems biology tools to study the root cause of the problem and rectify it. Host-pathogen protein interactions (HPIs) have a promising role in identifying the pathogens' strategy to conquer the host organism. In this paper, the interactions between the host Rhynchophorus ferrugineus (an invasive wood-boring pest that destroys palm) and the pathogens Proteus mirabilis, Serratia marcescens, and Klebsiella pneumoniae are comprehensively studied using protein-protein interactions, molecular docking, and followed by 200 ns molecular dynamic simulations. This study elucidates the structural and functional basis of these proteins leading towards better plant health, production, and reliability.

Characterization of a new bacteriocin-like inhibitory peptide produced by Lactobacillus sakei B-RKM 0559.

The biopreservation strategy allows extending the shelf life and food safety through the use of indigenous or controlled microbiota and their antimicrobial compounds. The aim of this work was to characterize an inhibitory substance with bacteriocin-like activity (Sak-59) produced by the potentially probiotic L. sakei strain from artisanal traditional Kazakh horse meat product Kazy. The maximum production of Sak-59 occurred at the stationary phase of the L. sakei growth. Sak-59 showed inhibitory activity against gram-positive meat spoilage bacteria strains of Listeria monocytogenes, Staphylococcus aureus, and pathogenic gram-negative bacteria strains of Serratia marcescens and Escherichia coli, but not against the tested Lactobacilli strains. Sak-59 activity, as measured by diffusion assay in agar wells, was completely suppressed after treatment with proteolytic enzymes and remained stable after treatment with α-amylase and lipase, indicating that Sak-59 is a peptide and most likely not glycosylated or lipidated. It was concluded that Sak-59 is a potential new bacteriocin with a characteristic activity spectrum, which can be useful in the food and feed industries.

Comparative response of Spodoptera litura challenged per os with Serratia marcescens strains differing in virulence.

Host plays an important role in influencing virulence of a pathogen and efficacy of a biopesticide. The present study was aimed to characterize the possible factors present in Spodoptera litura that influenced pathogenecity of orally ingested S. marcescens strains, differing in their virulence. Fifth instar larvae of S. litura responded differently as challenged by two Serratia marcescens strains, SEN (virulent strain, LC50 7.02 103 cfu/ml) and ICC-4 (non-virulent strain, LC50 1.19 1012 cfu/ml). Considerable increase in activity of lytic enzymes protease and phospholipase was recorded in the gut and hemolymph of larvae fed on diet supplemented with S. marcescens strain ICC-4 as compared to the larvae treated with S. marcescens strain SEN. However, a significant up-regulation of antioxidative enzymes SOD (in foregut and midgut), CAT (in the midgut) and GST (in the foregut and hemolymph) was recorded in larvae fed on diet treated with the virulent S. marcescens strain SEN in comparison to larvae fed on diet treated with the non-virulent S. marcescens strain ICC-4. Activity of defense related enzymes lysozyme and phenoloxidase activity were also higher in the hemolymph of larvae fed with diet treated with S. marcescens strain SEN as compared to hemolymph of S. marcescens strain ICC-4 treated larvae. More number of over-expressed proteins was observed in the gut and hemolymph of S. marcescens strains ICC-4 and SEN treated larvae, respectively. Identification of the selected differentially expressed proteins indicated induction of proteins involved in insect innate immune response (Immunoglobulin I-set domain, Apolipophorin III, leucine rich repeat and Titin) in S. marcescens strain SEN treated larvae. Over-expression of two proteins, actin related protein and mt DNA helicase, were noted in S. marcescens treated larvae with very high levels observed in the non-virulent strain. Up-regulation of homeobox protein was noted only in S. marcescens strain ICC-4 challenged larvae. This study indicated that ingestion of non-virulent S. marcescens strain ICC-4 induced strong immune response in insect gut while there was weak response to the virulent S. marcescens strain SEN which probably resulted in difference in their virulence.

Repurposing of antidiabetics as Serratia marcescens virulence inhibitors.

BACKGROUND: Serratia marcescens becomes an apparent nosocomial pathogen and causes a variety of infections. S. marcescens possess various virulence factors that are regulated by intercellular communication system quorum sensing (QS). Targeting bacterial virulence is a proposed strategy to overcome bacterial resistance. Sitagliptin anti-QS activity has been demonstrated previously and we aimed in this study to investigate the effects of antidiabetic drugs vildagliptin and metformin compared to sitagliptin on S. marcescens pathogenesis. METHODS: We assessed the effects of tested drugs in subinhibitory concentrations phenotypically on the virulence factors and genotypically on the virulence encoding genes' expressions. The protection of tested drugs on S. marcescens pathogenesis was performed in vivo. Molecular docking study has been conducted to evaluate the interference capabilities of tested drugs to the SmaR QS receptor. RESULTS: Vildagliptin reduced the expression of virulence encoding genes but did not show in vitro or in vivo anti-virulence activities. Metformin reduced the expression of virulence encoding genes and inhibited bacterial virulence in vitro but did not show in vivo protection. Sitagliptin significantly inhibited virulence factors in vitro, reduced the expression of virulence factors and protected mice from S. marcescens. Docking study revealed that sitagliptin is more active than metformin and fully binds to SmaR receptor, whereas vildagliptin had single interaction to SmaR. CONCLUSION: The downregulation of virulence genes was not enough to show anti-virulence activities. Hindering of QS receptors may play a crucial role in diminishing bacterial virulence.

Identifying the Molecular Targets of an Anti-pathogenic Hydroalcoholic Extract of Punica granatum Peel Against Multidrug-resistant Serratia marcescens.

BACKGROUND: Antibiotic-resistant members of the family Enterobacteriaceae are among the serious threats to human health globally. This study reports the anti-pathogenic activity of Punica granatum peel extract (PGPE) against a multi-drug resistant, beta-lactamase producing member of this family i.e. Serratia marcescens. OBJECTIVE: This study aimed at assessing the anti-pathogenic activity of PGPE against the gramnegative bacterial pathogen S. marcescens and identifying the molecular targets of this extract in the test bacterium. METHODS: Effect of PGPE on S. marcescens growth and quorum sensing (QS)-regulated pigment production was assessed through broth dilution assay. In vivo anti-infective and prophylactic activity of PGPE was assessed employing the nematode worm Caenorhabditis elegans as a model host. Differential gene expression in PGPE-exposed S. marcescens was studied through a whole transcriptome approach. RESULTS: PGPE was able to modulate QS-regulated pigment production in S. marcescens without exerting any heavy growth-inhibitory effect at concentrations as low as ≥2.5 µg/mL. It could attenuate the virulence of the test bacterium towards the worm host by 22-42% (p≤0.01) at even lower concentrations (≥0.5 µg/mL). PGPE also exerted a post-extract effect on S. marcescens. This extract was found to offer prophylactic benefit too, to the host worm, as PGPE-pre-fed worms scored better (34-51%; p≤0.001) survival in face of subsequent bacterial attack. Differential gene expression analysis revealed that PGPE affected the expression of a total of 66 genes in S. marcescens by ≥1.5 fold. CONCLUSION: The anti-virulence effect of PGPE against S. marcescens is multifaceted, affecting stress-response machinery, efflux activity, iron homeostasis, and cellular energetics of this bacterium notably. Among the major molecular targets identified in this study are LPS export transporter permease (LptF), t-RNA pseudouridine synthase (TruB), etc.

Using ceftazidime-avibactam for persistent carbapenem-resistant Serratia marcescens infection highlights antimicrobial stewardship challenges with new beta-lactam-inhibitor combination antibiotics.

The newer beta-lactam-inhibitor combination (BLIC) antibiotics are available in South Africa (SA) for the treatment of carbapenem-resistant Enterobacterales infections. We describe the successful use of ceftazidime-avibactam (CA) for the treatment of a child with persistent carbapenem-resistant Serratia marcescens bacteraemia, and the challenges faced using this lifesaving antibiotic, including access to susceptibility testing, procurement process, cost and complexity of deciding when, how and for how long to use it. Furthermore, the burden of carbapenem resistance is increasing in SA, and inappropriate use of CA and other newer BLIC antibiotics, such as ceftolozane-tazobactam, will inevitably endanger their longevity. A careful balance must be struck between removing unnecessary obstacles and delays in initiating these antibiotics for life-threatening infections, and additional antimicrobial stewardship-guided interventions aimed at preserving their therapeutic use.

Differential susceptibility of airway and ocular surface cell lines to FlhDC-mediated virulence factors PhlA and ShlA from Serratia marcescens.

Introduction. Serratia marcescens is a bacterial pathogen that causes ventilator-associated pneumonia and ocular infections. The FlhD and FlhC proteins complex to form a heteromeric transcription factor whose regulon, in S. marcescens, regulates genes for the production of flagellum, phospholipase A and the cytolysin ShlA. The previously identified mutation, scrp-31, resulted in highly elevated expression of the flhDC operon. The scrp-31 mutant was observed to be more cytotoxic to human airway and ocular surface epithelial cells than the wild-type bacteria and the present study sought to identify the mechanism underlying the increased cytotoxicity phenotype.Hypothesis/Gap Statement. Although FlhC and FlhD have been implicated as virulence determinants, the mechanisms by which these proteins regulate bacterial cytotoxicity to different cell types remains unclear.Aim. This study aimed to evaluate the mechanisms of FlhDC-mediated cytotoxicity to human epithelial cells by S. marcescens.Methodology. Wild-type and mutant bacteria and bacterial secretomes were used to challenge airway and ocular surface cell lines as evaluated by resazurin and calcein AM staining. Pathogenesis was further tested using a Galleria mellonella infection model.Results. The increased cytotoxicity of scrp-31 bacteria and secretomes to both cell lines was eliminated by mutation of flhD and shlA. Mutation of the flagellin gene had no impact on cytotoxicity under any tested condition. Elimination of the phospholipase gene, phlA, had no effect on bacteria-induced cytotoxicity to either cell line, but reduced cytotoxicity caused by secretomes to airway epithelial cells. Mutation of flhD and shlA, but not phlA, reduced bacterial killing of G. mellonella larvae.Conclusion. This study indicates that the S. marcescens FlhDC-regulated secreted proteins PhlA and ShlA, but not flagellin, are cytotoxic to airway and ocular surface cells and demonstrates differences in human epithelial cell susceptibility to PhlA.

Sotolon is a natural virulence mitigating agent in Serratia marcescens.

Serratia marcescens is an emerging opportunistic bacterium that can cause healthcare-associated infections. The high rate of multidrug resistance and the ability to produce a set of virulence factors, by which it can produce infectious diseases makes it urgent to find an alternative approach to the treatment of such infections. Disarming of virulence by targeting of quorum sensing (QS) as the regulating mechanism of virulence is a promising approach that has no effect on bacterial growth that is considered a key factor in emergence of resistance. This study was designed to investigate the ability of sub-inhibitory concentrations (sub-MICs) of sotolon to attenuate virulence of a clinical isolate of S. marcescens. Sotolon at 25 and 50 µg/ml inhibited 35.2 and 47.5% of biofilm formation, respectively. The inhibition of swimming motility were 41.4 and 69.3%, while that of swarming motility were 77.6 and 86.8% at 25 and 50 µg/ml, respectively. Moreover, sotolon reduced prodigiosin production by 76.6 and 87.6% at concentrations of 25 and 50 µg/ml, respectively. Protease activity was reduced by 25 µg/ml of sotolon by 54.8% and was completely blocked at 50 µg/ml. The relative expression of genes regulating virulence factors decreased by 40% for fimA, 29% for fimC, 59% for flhC, 57% for flhD, 39% for bsmB, 37% for rssB, 49% for rsmA, 54% for pigP, and 62% for shlA gene in the presence of 50 µg/ml sotolon. In conclusion, sotolon is an anti-virulence agent that could be used for the treatment of S.marcescens hospital-acquired infections.

A respiratory commensal bacterium acts as a risk factor for Mycoplasma gallisepticum infection in chickens.

Commensal microbiota has been shown to play an important role in local infections. However, the correlation between host respiratory microbiota and Mycoplasma gallisepticum (MG) infection is not well characterized. Here, the results of 16S rRNA sequencing showed that MG infection correlated with alteration in respiratory microbiota of chickens characterized by decreased richness and diversity. To explore whether respiratory microbiota contributed to MG infection, an antibiotics cocktail was used to deplete respiratory microbiota. It has been found that depletion of respiratory Gram-positive and Gram-negative bacteria promoted MG infection, as reflected in the form of increased MG colonization, pro-inflammatory cytokines and proteins expression, and severe lung damage compared to the control group. Importantly, depletion of Gram-negative bacteria in respiratory tract mitigated MG infection, which indicated that certain Gram-negative bacteria may promote MG infection. By reconstitution of individual cultivable respiratory tract bacteria in antibiotic-treated chickens, a respiratory commensal microbe Serratia marcescens was identified to facilitate MG infection. We further found that Serratia marcescens may promote MG infection by downregulating Mucin 2 (MUC2) and tight junction related gene mRNA expression levels in trachea and lung tissues. Together, our data demonstrated that MG infection induced disturbed respiratory microbiota and the specific respiratory commensal bacterium Serratia marcescens could promote MG infection, and thus expand our understanding of the pathogenesis of MG infection.

Synergistic effects of Cinnamomum cassia L. essential oil in combination with polymyxin B against carbapenemase-producing Klebsiella pneumoniae and Serratia marcescens.

Multidrug resistance prompts the search for new sources of antibiotics with new targets at bacteria cell. To investigate the antibacterial activity of Cinnamomum cassia L. essential oil (CCeo) alone and in combination with antibiotics against carbapenemase-producing Klebsiella pneumoniae and Serratia marcescens. The antimicrobial susceptibility of the strains was determined by Vitek® 2 and confirmed by MALDI-TOF/TOF. The antibacterial activity of CCeo and its synergism with antibiotics was determined using agar disk diffusion, broth microdilution, time-kill, and checkboard methods. The integrity of the bacterial cell membrane in S. marcescens was monitored by protein leakage assay. CCeo exhibited inhibitory effects with MIC = 281.25 µg.mL-1. The association between CCeo and polymyxin B showed a decrease in terms of viable cell counts on survival curves over time after a 4 hour-treatment with a FIC index value of 0.006. Protein leakage was observed with increasing concentrations for CCeo and CCeo + polymyxin B treatments. CCeo showed antibacterial activity against the studied strains. When associated with polymyxin B, a synergistic effect was able to inhibit bacterial growth rapidly and consistently, making it a potential candidate for the development of an alternative treatment and drug delivery system for carbapenemase-producing strains.

Bactericidal and Antiproliferative Effects of Peripheral Parenteral Nutrition Solutions with Sodium Bisulfite on Pathogenic Microorganisms in Catheter Lumens.

Catheter-related bloodstream infections (CRBSIs) due to pathogenic microorganisms pose a major threat to patients requiring parenteral nutrition (PN). Additives contained in medicines and foods have antiproliferative and bacteriostatic effects on pathogenic microorganisms. Therefore, PN solutions containing additives may also have an antibacterial effect. However, so far, there have been no reports on or observations of a PN solution with bactericidal activity. In this study, we assessed several nutrition solutions with antimicrobial activities and investigated their effects on pathogenic microorganisms colonizing catheter lumens. We selected the highly acidic Plas-Amino® (PA), which contains a large amount of sodium bisulfite as a preservative and potentially has an antimicrobial effect. In this study, we used the following pathogenic bacteria as the main causatives of CRBSIs: Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Serratia marcescens, Pseudomonas aeruginosa, and Candida albicans. We then created a catheter lumen microorganism contamination model and evaluated the antibacterial effect of PA; we found that all bacteria in the control group grew significantly in the catheter lumen in a time-dependent manner at 48 and 72 h. On the other hand, we demonstrated that PA has bactericidal effects on S. aureus, S. epidermidis, B. cereus, S. marcescens, and P. aeruginosa in the catheter lumen and confirmed that it has a remarkable antiproliferative effect on C. albicans. Hence, we concluded that highly acidic PN solutions that contain a preservative like sodium bisulfite have bactericidal and growth inhibition effects on microorganisms in the catheter lumens of patients with CRBSIs and patients with totally implantable central venous access devices, in whom it is difficult to remove the catheter.

Isolation and identification of two Serratia marcescens strains from silkworm, Bombyx mori.

Bacterial septicemia commonly occurs and usually cause huge losses in sericulture industry. Here, two pathogenic bacterial strains were isolated from dead silkworm and named as ZJ-1 and ZJ-2. Phenotypic and genotypic analysis results revealed that both of these two strains are closely related to Serratia marcescens (S. marcescens). The morphological as well as physiological and biochemical characteristics of ZJ-1 were accordant with S. marcescens mentioned in Bergey's manual of determinative bacteriology, whereas ZJ-2 showed some discrepancies such as the utilization of malonate and starch, fermentation of maltose and sucrose, and tests of urease, etc. Surprisingly, ZJ-2 could produce red pigment at high temperature (37°) but ZJ-1 could not. Besides, by analyzing the lethal concentration 50 (LC50) of ZJ-1 and ZJ-2, it was found that the virulence of ZJ-2 was lower than that of ZJ-1. These results revealed that ZJ-1 and ZJ-2 were two different strains of S. marcescens and that ZJ-2 was expected to be a safe (low-toxicity) and efficient strain for the production of red pigment. Nonetheless, further research in molecular level is needed to understand the regulation mechanism of pigment production and infection of ZJ-2.

The contest of microbial pigeon neighbors: Interspecies competition between Serratia marcescens and the human pathogen Cryptococcus neoformans.

In nature, microorganisms often exhibit competitive behavior for nutrients and limited space, allowing them to alter the virulence determinants of pathogens. The human pathogenic yeast Cryptococcus neoformans can be found organized in biofilms, a complex community composed of an extracellular matrix which confers protection against predation. The aim of this study was to evaluate and characterize antagonistic interactions between two cohabiting microorganisms: C. neoformans and the bacteria Serratia marcescens. The interaction of S. marcescens with C. neoformans expressed a negative effect on biofilm formation, polysaccharide capsule, production of urease, and melanization of the yeast. These findings evidence that competition in mixed communities can result in dominance by one species, with direct impact on the physiological modulation of virulence determinants. Such an approach is key for understating the response of communities to the presence of competitors and, ultimately, rationally designing communities to prevent and treat certain diseases.

The Serratia marcescens Siderophore Serratiochelin Is Necessary for Full Virulence during Bloodstream Infection.

Serratia marcescens is a bacterium frequently found in the environment, but over the last several decades it has evolved into a concerning clinical pathogen, causing fatal bacteremia. To establish such infections, pathogens require specific nutrients; one very limited but essential nutrient is iron. We sought to characterize the iron acquisition systems in S. marcescens isolate UMH9, which was recovered from a clinical bloodstream infection. Using RNA sequencing (RNA-seq), we identified two predicted siderophore gene clusters (cbs and sch) that were regulated by iron. Mutants were constructed to delete each iron acquisition locus individually and in conjunction, generating both single and double mutants for the putative siderophore systems. Mutants lacking the sch gene cluster lost their iron-chelating ability as quantified by the chrome azurol S (CAS) assay, whereas the cbs mutant retained wild-type activity. Mass spectrometry-based analysis identified the chelating siderophore to be serratiochelin, a siderophore previously identified in Serratia plymuthica Serratiochelin-producing mutants also displayed a decreased growth rate under iron-limited conditions created by dipyridyl added to LB medium. Additionally, mutants lacking serratiochelin were significantly outcompeted during cochallenge with wild-type UMH9 in the kidneys and spleen after inoculation via the tail vein in a bacteremia mouse model. This result was further confirmed by an independent challenge, suggesting that serratiochelin is required for full S. marcescens pathogenesis in the bloodstream. Nine other clinical isolates have at least 90% protein identity to the UMH9 serratiochelin system; therefore, our results are broadly applicable to emerging clinical isolates of S. marcescens causing bacteremia.