Brodie's abscess of the calcaneus due to Serratia marcescens.

Brodie's abscess is a subacute or chronic osteomyelitis characterised by an intraosseous abscess. It may present months to years after the inciting event. Staphylococcus aureus is the most common causative organism of Brodie's abscess, while Gram-negative bacteria are uncommon causative organisms. A combination of culture-directed antibiotics and surgical debridement is key to successful management. This case report describes a patient with a history of minor trauma preceding the development of Brodie's abscess of the calcaneus caused by Serratia marcescens This was managed successfully with surgical debridement, followed by oral antibiotics.

Trade-off between photosymbiosis and innate immunity influences cnidarian's response to pathogenic bacteria.

Mutualistic relationships with photosynthetic organisms are common in cnidarians, which form an intracellular symbiosis with dinoflagellates in the family Symbiodiniaceae. The establishment and maintenance of these symbionts are associated with the suppression of key host immune factors. Because of this, there are potential trade-offs between the nutrition that cnidarian hosts gain from their symbionts and their ability to successfully defend themselves from pathogens. To investigate these potential trade-offs, we utilized the facultatively symbiotic polyps of the upside-down jellyfish Cassiopea xamachana and exposed aposymbiotic and symbiotic polyps to the pathogen Serratia marcescens. Symbiotic polyps had a lower probability of survival following S. marcescens exposure. Gene expression analyses 24 hours following pathogen exposure indicate that symbiotic animals mounted a more damaging immune response, with higher levels of inflammation and oxidative stress likely resulting in more severe disruptions to cellular homeostasis. Underlying this more damaging immune response may be differences in constitutive and pathogen-induced expression of immune transcription factors between aposymbiotic and symbiotic polyps rather than broadscale immune suppression during symbiosis. Our findings indicate that in facultatively symbiotic polyps, hosting symbionts limits C. xamachana's ability to survive pathogen exposure, indicating a trade-off between symbiosis and immunity that has potential implications for coral disease research.

The function of OforOrco in the allogrooming behavior of Odontotermes formosanus (Shiraki) induced by Serratia marcescens Bizio (SM1).

Termites are consistently confronted with a complex microbial environment. In addition to the role of their innate immune system in resisting pathogen infection, social immune behavior also plays a significant role in helping termites withstand the stress caused by pathogenic microorganisms. The allogrooming behavior among different individuals is commonly observed in termites, and it plays a crucial role in the social immune interaction network. In the case of Odontotermes formosanus (Shiraki), Orco is specifically involved in detecting pheromones and volatile chemicals released by termites to communicate with each other. Nonetheless, the function of Orco in the social immunity remains unreported in O. formosanus. Consequently, in this study, we recorded the allogrooming behavior of O. formosanus workers under SM1 stress. The results indicated a significant increase in allogrooming behavior due to SM1 infection. The allogrooming behavior of workers under SM1 stress was significantly increased after the addition of soldiers. Compared with pronotum group treated by SM1, SM1 treatment of workers' heads significantly reduced the allogrooming behavior among workers. In addition, we found that SM1 could greatly increase the expression of OforOrco. Furthermore, interfering with OforOrco could markedly reduce the allogrooming behavior among workers under SM1 stress, and increase the mortality of worker under SM1 stress. This study demonstrated the significant role of OforOrco in the social immunity of O. formosanus, which offers a theoretical foundation for the advancement of research on termite RNA biopesticides, and the integration of RNA interference (RNAi) with pathogens. This study is valuable for elucidating the social immune behavior and interaction network of termites.

Anticancer and Immunomodulatory Activities of Prodigiosin Extracted and Purified from Serratia marcescens.

BACKGROUND: Prodigiosin is a naturally occurring compound produced by various bacteria, including Serratia marcescens. It is known for its diverse biological properties. The present study was conducted to extract and purify prodigiosin from Serratia marcescens and investigate its anticancer and immunomodulatory activities. METHODS: S. presence was isolated from soil samples and characterized. Different solvents were used to extract prodigiosin from Serratia marcescens. The cytotoxic activity of prodigiosin was tested against human rhabdomyosarcoma (RD), rat embryo fibroblasts (REF), and human breast cancer MDA-MB-231 (MDA) epithelial cell lines. Albino mice were divided into six groups: Negative control (normal saline); positive control (injected with 100 µ l of Serratia marcesence); groups A-D were injected with 100 µ l of prodigiosin (1, 3, 6, and 9 µ g/mouse, respectively). After 14 days of treatment, whole blood samples were collected for immunomodulatory analysis. RESULTS: The study found that the highest yield of prodigiosin (65-230 mg/l) was obtained with methanol as the extraction solvent. Prodigiosin had a cytotoxic effect on cancer cells, particularly against MDA epithelial cells. However, it did not have a cytotoxic effect on normal cells. Immunological analysis revealed significant differences (p ≤ 0.01) in absolute neutrophil counts between the positive control and prodigiosin-treated groups, with the highest value in group C and the lowest in group A. Immunological analysis showed significant differences in neutrophil counts, IL-4, and IL-10 levels between prodigiosin-treated groups and the control group. CONCLUSION: Serratia marcescens prodigiosin showed cytotoxic effects on cancer cells and boosted IL-10 and IL-4 serum levels, acting as an immunomodulator.

Functional dyeing of cellulose macromolecule/synthetic fibers two-component fabrics with sustainable microbial prodigiosins.

As an important cellulose macromolecular-based material, cotton/polyamide and cotton/polyester fabrics are widely utilized in the textile and garment field due to their combination of the advantages of both cotton and synthetic fibers, such as excellent breathability, hygroscopicity, and abrasion performance. However, the synthetic dyes used in fabric coloration are derived from non-renewable resources, and the long-time dyeing procedure poses large pollution problems. Herein, microbial prodigiosins fermented by Serratia marcescens were employed for cotton/polyamide and cotton/polyester fabric dyeing and functionalizing. The results demonstrated that the prodigiosins suspension exhibited outstanding stability. Synthetic fibers contributed significantly to the overall color of fabrics and provided good dimensional stability and durability. In contrast, cotton fibers imparted relatively lighter color but played an essential role in enhancing the softness and comfort of fabrics. The dyed fabrics presented bright overall color light with good uniformity. Furthermore, the antibacterial rates of the dyed cotton/polyamide and cotton/polyester fabrics were 87.31 % and 89.70 %, respectively. The UPF values of the dyed cotton/polyamide and cotton/polyester fabrics were recorded as 52.3 and 93.5, respectively. This study provided a novel approach for cleaner functional dyeing of cotton/synthetic fiber two-component fabrics using prodigiosins.

High sugar diets can increase susceptibility to bacterial infection in Drosophila melanogaster.

Overnutrition with dietary sugar can worsen infection outcomes in diverse organisms including insects and humans, through generally unknown mechanisms. In the present study, we show that adult Drosophila melanogaster fed high-sugar diets became more susceptible to infection by the Gram-negative bacteria Providencia rettgeri and Serratia marcescens. We found that P. rettgeri and S. marcescens proliferate more rapidly in D. melanogaster fed a high-sugar diet, resulting in increased probability of host death. D. melanogaster become hyperglycemic on the high-sugar diet, and we find evidence that the extra carbon availability may promote S. marcescens growth within the host. However, we found no evidence that increased carbon availability directly supports greater P. rettgeri growth. D. melanogaster on both diets fully induce transcription of antimicrobial peptide (AMP) genes in response to infection, but D. melanogaster provided with high-sugar diets show reduced production of AMP protein. Thus, overnutrition with dietary sugar may impair host immunity at the level of AMP translation. Our results demonstrate that dietary sugar can shape infection dynamics by impacting both host and pathogen, depending on the nutritional requirements of the pathogen and by altering the physiological capacity of the host to sustain an immune response.

Hosts manipulate lifestyle switch and pathogenicity heterogeneity of opportunistic pathogens in the single-cell resolution.

Host-microbe interactions are virtually bidirectional, but how the host affects their microbiome is poorly understood. Here, we report that the host is a critical modulator to regulate the lifestyle switch and pathogenicity heterogeneity of the opportunistic pathogens Serratia marcescens utilizing the Drosophila and bacterium model system. First, we find that Drosophila larvae efficiently outcompete S. marcescens and typically drive a bacterial switch from pathogenicity to commensalism toward the fly. Furthermore, Drosophila larvae reshape the transcriptomic and metabolic profiles of S. marcescens characterized by a lifestyle switch. More importantly, the host alters pathogenicity and heterogeneity of S. marcescens in the single-cell resolution. Finally, we find that larvae-derived AMPs are required to recapitulate the response of S. marcescens to larvae. Altogether, our findings provide an insight into the pivotal roles of the host in harnessing the life history and heterogeneity of symbiotic bacterial cells, advancing knowledge of the reciprocal relationships between the host and pathogen.

Enhanced bioremediation of soils contaminated with nicosulfuron using the bacterial complex A12.

AIMS: To construct an efficient bacterial complex to degrade nicosulfuron and clarify its degradative characteristics, promote the growth of maize (Zea mays), and provide a theoretical foundation for the efficient remediation of soil contaminated with nicosulfuron. METHODS AND RESULTS: Biocompatibility was determined by the filter paper sheet method by mixing Serratia marcescens A1 and Bacillus cereus A2 in a 1:1 ratio, yielding A12. The optimum culture conditions for the bacterial composite were obtained based on a three-factor, three-level analysis using response surface methodology, with 29.25 g l-1 for maltodextrin, 10.04 g l-1 for yeast extract, and 19.93 g l-1 for NaCl, which resulted in 92.42% degradation at 4 d. The degradation characteristics of A12 were clarified as follows: temperature 30°C, pH 7, initial concentration of nicosulfuron 20 mg l-1, and 4% inoculum. The ability to promote growth was determined by measuring the ratio of the lysosphere diameter (D) to the colony diameter (d), and the ability of the complex A12 to promote growth was higher than that of the two single strains. CONCLUSIONS: Nicosulfuron degradation in sterilized and unsterilized soils reached 85.4% and 91.2% within 28 d, respectively. The ability of the strains to colonize the soil was determined by extraction of total soil DNA, primer design, and gel electrophoresis. The bioremediation effect of A12 was confirmed by the maximum recovery of fresh weight (124.35%) of nicosulfuron-sensitive crop plants and the significant recovery of soil enzyme activities, as measured by the physiological indices in the sensitive plants.

Antimicrobial resistance of Serratia marcescens causing blood stream infections in a large University Hospital in Bulgaria, an 8-year analysis (2016-2023).

The aim of this study is to evaluate the antimicrobial susceptibility of invasive isolates of Serratia marcescens, associated with blood stream infections (BSIs) in patients hospitalized in Varna University Hospital, Bulgaria, as well as to identify the genetic mechanisms responsible for 3rd generation cephalosporin and carbapenem-resistance among these isolates. A total of 45 consecutive S. marcescens isolates, obtained from blood cultures of 45 patients with BSIs, hospitalized during an 8-year period (2016-2023) were included. Species identification and antimicrobial susceptibility testing were done by Phoenix (BD, USA) and Vitek 2 (BioMerieux, France) systems and the results were interpreted according to EUCAST guidelines. The genetic mechanisms of beta-lactam resistance were studied by PCR. During the study period, a total of 45 patients were diagnosed with S. marcescens-associated BSIs. All infections were defined as nosocomial, predominantly intensive care unit-acquired (42.2%) and 28.8% were central venous catheter-associated. The following antimicrobial resistance rates were found: ceftriaxone, piperacillin/tazobactam, 57.8%; ceftazidime, 55.6%; cefepime, trimethoprime/sulfamethoxazole, 53.3%; gentamicin, 48.8%; ciprofloxacin, 44.5%; amikacin, 15.6%; carbapenems, 2.2%. The blaCTX-M was identified in 88.9% of the tested 3rd generation cephalosporin resistant isolates. Among these, 50% were also blaTEM positive. The single carbapenem-resistant isolate harboured blaKPC, blaCTX-M1/9, blaCMY-2 and blaTEM. This study demonstrates S. marcescens as a problematic nosocomial pathogen and we report a KPC-producing S. marcescens clinical isolate from a BSI in Bulgaria.

Microbial etiology of vertebral osteomyelitis/discitis amid the opioid epidemic.

OBJECTIVE: The primary goal of this study was to establish the current microbial trends in vertebral osteomyelitis/discitis (VOD) amid the opioid epidemic and to determine if intravenous drug use (IVDU) predisposes one to a unique microbial profile of infection. METHODS: The authors performed a retrospective cohort study consisting of 1175 adult patients diagnosed with VOD between 2011 and 2022 at a single quaternary center. Data were acquired through retrospective chart review, with pertinent demographic and clinical information collected. RESULTS: Staphylococcus aureus was the most cultured organism in both the IVDU and non-IVDU groups at 56.1% and 40.7%, respectively. In the IVDU cohort, Serratia marcescens was the next most prevalently cultured organism at 13.9%. CONCLUSIONS: The present study demonstrates that in the IVDU population S. marcescens is an organism of high concern. The potential for Serratia spp. infection should be accounted for when selecting empirical antimicrobial therapy in VOD patients.

Serratia marcescens ATCC 274 increases production of the red pigment prodigiosin in response to Chi phage infection.

Serratia marcescens is an opportunistic human pathogen that produces a vibrant red pigment called prodigiosin. Prodigiosin has implications in virulence of S. marcescens and promising clinical applications. We discovered that addition of the virulent flagellotropic bacteriophage χ (Chi) to a culture of S. marcescens stimulates a greater than fivefold overproduction of prodigiosin. Active phage infection is required for the effect, as a χ-resistant strain lacking flagella does not respond to phage presence. Via a reporter fusion assay, we have determined that the addition of a χ-induced S. marcescens cell lysate to an uninfected culture causes a threefold increase in transcription of the pig operon, containing genes essential for pigment biosynthesis. Replacement of the pig promoter with a constitutive promoter abolished the pigmentation increase, indicating that regulatory elements present in the pig promoter likely mediate the phenomenon. We hypothesize that S. marcescens detects the threat of phage-mediated cell death and reacts by producing prodigiosin as a stress response. Our findings are of clinical significance for two main reasons: (i) elucidating complex phage-host interactions is crucial for development of therapeutic phage treatments, and (ii) overproduction of prodigiosin in response to phage could be exploited for its biosynthesis and use as a pharmaceutical.

Probing the interaction between the metallo-ß-lactamase SMB-1 and ampicillin by multispectral approaches combined with molecular dynamics.

Metallo-ß-lactamases (MßLs) hydrolyze and inactivate ß-lactam antibiotics, are a pivotal mechanism conferring resistance against bacterial infections. SMB-1, a novel B3 subclass of MßLs from Serratia marcescens could deactivate almost all ß-lactam antibiotics including ampicillin (AMP), which has posed a serious threat to public health. To illuminate the mechanism of recognition and interaction between SMB-1 and AMP, various fluorescence spectroscopy techniques and molecular dynamics simulation were employed. The results of quenching spectroscopy unraveled that AMP could make SMB-1 fluorescence quenching that mechanism was the static quenching; the synchronous and three-dimensional fluorescence spectra validated that the microenvironment and conformation of SMB-1 were altered after interaction with AMP. The molecular dynamics results demonstrated that the whole AMP enters the binding pocket of SMB-1, even though with a relatively bulky R1 side chain. Loop1 and loop2 in SMB-1 undergo significant fluctuations, and α2 (71-73) and local α5 (186-188) were turned into random coils, promoting zinc ion exposure consistent with circular dichroism spectroscopy results. The binding between them was driven by a combination of enthalpy and entropy changes, which was dominated by electrostatic force in agreement with the fluorescence observations. The present study brings structural insights and solid foundations for the design of new substrates for ß-lactamases and the development of effective antibiotics that are resistant to superbugs.

Root Rot Management in Common Bean (Phaseolus vulgaris L.) Through Integrated Biocontrol Strategies using Metabolites from Trichoderma harzianum, Serratia marcescens, and Vermicompost Tea.

Common bean (Phaseolus vulgaris L.) is an essential food staple and source of income for small-holder farmers across Africa. However, yields are greatly threatened by fungal diseases like root rot induced by Rhizoctonia solani. This study aimed to evaluate an integrated approach utilizing vermicompost tea (VCT) and antagonistic microbes for effective and sustainable management of R. solani root rot in common beans. Fourteen fungal strains were first isolated from infected common bean plants collected across three Egyptian governorates, with R. solani being the most virulent isolate with 50% dominance. Subsequently, the antagonistic potential of vermicompost tea (VCT), Serratia sp., and Trichoderma sp. was assessed against this destructive pathogen. Combinations of 10% VCT and the biocontrol agent isolates displayed potent inhibition of R. solani growth in vitro, prompting in planta testing. Under greenhouse conditions, integrated applications of 5 or 10% VCT with Serratia marcescens, Trichoderma harzianum, or effective microorganisms (EM1) afforded up to 95% protection against pre- and post-emergence damping-off induced by R. solani in common bean cv. Giza 6. Similarly, under field conditions, combining VCT with EM1 (VCT + EM1) or Trichoderma harzianum (VCT + Trichoderma harzianum) substantially suppressed disease severity by 65.6% and 64.34%, respectively, relative to untreated plants. These treatments also elicited defense enzyme activity and distinctly improved growth parameters including 136.68% and 132.49% increases in pod weight per plant over control plants. GC-MS profiling of Trichoderma harzianum, Serratia marcescens, and vermicompost tea (VCT) extracts revealed unique compounds dominated by cyclic pregnane, fatty acid methyl esters, linoleic acid derivatives, and free fatty acids like oleic, palmitic, and stearic acids with confirmed biocontrol and plant growth-promoting activities. The results verify VCT-mediated delivery of synergistic microbial consortia as a sustainable platform for integrated management of debilitating soil-borne diseases, enhancing productivity and incomes for smallholder bean farmers through regeneration of soil health. Further large-scale validation can pave the adoption of this climate-resilient approach for securing food and nutrition security.

Prolonged hospitalization signature and early antibiotic effects on the nasopharyngeal resistome in preterm infants.

Respiratory pathogens, commonly colonizing nasopharynx, are among the leading causes of death due to antimicrobial resistance. Yet, antibiotic resistance determinants within nasopharyngeal microbial communities remain poorly understood. In this prospective cohort study, we investigate the nasopharynx resistome development in preterm infants, assess early antibiotic impact on its trajectory, and explore its association with clinical covariates using shotgun metagenomics. Our findings reveal widespread nasopharyngeal carriage of antibiotic resistance genes (ARGs) with resistomes undergoing transient changes, including increased ARG diversity, abundance, and composition alterations due to early antibiotic exposure. ARGs associated with the critical nosocomial pathogen Serratia marcescens persist up to 8-10 months of age, representing a long-lasting hospitalization signature. The nasopharyngeal resistome strongly correlates with microbiome composition, with inter-individual differences and postnatal age explaining most of the variation. Our report on the collateral effects of antibiotics and prolonged hospitalization underscores the urgency of further studies focused on this relatively unexplored reservoir of pathogens and ARGs.

Host defense alteration in Caenorhabditis elegans after evolution under ionizing radiation.

BACKGROUND: Adaptation to a stressor can lead to costs on other traits. These costs play an unavoidable role on fitness and influence the evolutionary trajectory of a population. Host defense seems highly subject to these costs, possibly because its maintenance is energetically costly but essential to the survival. When assessing the ecological risk related to pollution, it is therefore relevant to consider these costs to evaluate the evolutionary consequences of stressors on populations. However, to the best of our knowledge, the effects of evolution in irradiate environment on host defense have never been studied. Using an experimental evolution approach, we analyzed fitness across 20 transfers (about 20 generations) in Caenorhabditis elegans populations exposed to 0, 1.4, and 50.0 mGy.h- 1 of 137Cs gamma radiation. Then, populations from transfer 17 were placed in the same environmental conditions without irradiation (i.e., common garden) for about 10 generations before being exposed to the bacterial parasite Serratia marcescens and their survival was estimated to study host defense. Finally, we studied the presence of an evolutionary trade-off between fitness of irradiated populations and host defense. RESULTS: We found a lower fitness in both irradiated treatments compared to the control ones, but fitness increased over time in the 50.0 mGy.h- 1, suggesting a local adaptation of the populations. Then, the survival rate of C. elegans to S. marcescens was lower for common garden populations that had previously evolved under both irradiation treatments, indicating that evolution in gamma-irradiated environment had a cost on host defense of C. elegans. Furthermore, we showed a trade-off between standardized fitness at the end of the multigenerational experiment and survival of C. elegans to S. marcescens in the control treatment, but a positive correlation between the two traits for the two irradiated treatments. These results indicate that among irradiated populations, those most sensitive to ionizing radiation are also the most susceptible to the pathogen. On the other hand, other irradiated populations appear to have evolved cross-resistance to both stress factors. CONCLUSIONS: Our study shows that adaptation to an environmental stressor can be associated with an evolutionary cost when a new stressor appears, even several generations after the end of the first stressor. Among irradiated populations, we observed an evolution of resistance to ionizing radiation, which also appeared to provide an advantage against the pathogen. On the other hand, some of the irradiated populations seemed to accumulate sensitivities to stressors. This work provides a new argument to show the importance of considering evolutionary changes in ecotoxicology and for ecological risk assessment.

Making a Pathogen? Evaluating the Impact of Protist Predation on the Evolution of Virulence in Serratia marcescens.

Opportunistic pathogens are environmental microbes that are generally harmless and only occasionally cause disease. Unlike obligate pathogens, the growth and survival of opportunistic pathogens do not rely on host infection or transmission. Their versatile lifestyles make it challenging to decipher how and why virulence has evolved in opportunistic pathogens. The coincidental evolution hypothesis postulates that virulence results from exaptation or pleiotropy, i.e. traits evolved for adaptation to living in one environment that have a different function in another. In particular, adaptation to avoid or survive protist predation has been suggested to contribute to the evolution of bacterial virulence (the training ground hypothesis). Here, we used experimental evolution to determine how the selective pressure imposed by a protist predator impacts the virulence and fitness of a ubiquitous environmental opportunistic bacterial pathogen that has acquired multidrug resistance: Serratia marcescens. To this aim, we evolved S. marcescens in the presence or absence of generalist protist predator, Tetrahymena thermophila. After 60 d of evolution, we evaluated genotypic and phenotypic changes by comparing evolved S. marcescens with the ancestral strain. Whole-genome shotgun sequencing of the entire evolved populations and individual isolates revealed numerous cases of parallel evolution, many more than statistically expected by chance, in genes associated with virulence. Our phenotypic assays suggested that evolution in the presence of a predator maintained virulence, whereas evolution in the absence of a predator resulted in attenuated virulence. We also found a significant correlation between virulence, biofilm formation, growth, and grazing resistance. Overall, our results provide evidence that bacterial virulence and virulence-related traits are maintained by selective pressures imposed by protist predation.

Urease-producing bacteria with plant growth-promoting ability that may tolerate and remove cadmium from aqueous solution.

Urease-producing bacteria (UPB) are widely present in soil and play an important role in soil ecosystems. In this study, 65 UPB strains were isolated from cadmium (Cd)-polluted soil around a lead-zinc mine in Yunnan Province, China. The Cd tolerance, removal of Cd from aqueous solution, production of indoleacetic acid (IAA) and plant growth-promoting effects of these materials were investigated. The results indicate that among the 65 UPB strains, four strains with IAA-producing ability were screened and identified as Bacillus thuringiensis W6-11, B. cereus C7-4, Serratia marcescens W11-10, and S. marcescens C5-6. Among the four strains, B. cereus C7-4 had the highest Cd tolerance, median effect concentration (EC50) of 59.94 mg/L. Under Cd 5 mg/L, S. marcescens C5-6 had the highest Cd removal from aqueous solution, up to 69.83%. Under Cd 25 mg/kg, inoculation with B. cereus C7-4 significantly promoted maize growth in a sand pot by increasing the root volume, root surface area, and number of root branches by 22%, 29%, and 20%, respectively, and plant height and biomass by 16% and 36%, respectively, and significantly increasing Cd uptake in the maize roots. Therefore, UPB is a potential resource for enhancing plant adaptability to Cd stress in plants with Cd-polluted habitats.

This study utilized urease-producing bacteria screened from the soil of lead zinc mining areas in Yunnan, China as the research object, enriching the microbial resources in Yunnan. In addition, this article verified the IAA production ability and cadmium removal ability of urease-producing bacteria, and screened out bifunctional urease-producing bacteria that have potential in cadmium pollution control and plant growth promotion.

Within-host transition to GES-55 during a GES-6-producing Serratia marcescens outbreak: Emergence of ceftazidime-avibactam resistance and increased susceptibility to carbapenems.

OBJECTIVES: To describe the in vivo emergence of ceftazidime-avibactam resistance in GES-type carbapenemases and to characterize an unusual outbreak of GES-6-producing Serratia marcescens during the COVID-19 pandemic in Spain. METHODS: Retrospective study to describe a GES-CPSM outbreak based on whole genome sequencing and antimicrobial susceptibility testing (AST). Transferability of blaGES-carrying plasmid was assessed by conjugation experiments. RESULTS: In December 2020, we identified a cluster of S. marcescens harbouring blaGES-6 involving 9 patients. Whole-genome sequence analysis revealed a clonal relationship (≤3 SNPs) between the first isolates identified in each of the evolved patients and environmental samples with GES-CPSM detection. Plasmid analysis showed that the blaGES-6 gene was located in an IncQ3-type plasmid. Triparental mating experiments using a helper plasmid demonstrated mobilization of the blaGES-6-carrying plasmid. Our results also demonstrate within-host evolution in S. marcescens isolates, leading to a transition from blaGES-6 to the new blaGES-55, caused by the P162S mutation, in a subsequent infection in one of the affected patients. In blaGES-55 we identified emergence of ceftazidime-avibactam resistance along with an increase of carbapenems susceptibility. This patient had been treated with a 14-day course of ceftazidime-avibactam. AST of the transformants bearing blaGES-6 and blaGES-55 plasmids, confirmed susceptibility variation affecting ceftazidime-avibactam and carbapenems. CONCLUSIONS: We report an unusual outbreak of GES-6 whose incidence is becoming increasing. Transition from GES-6 to GES-55 may readily occur in vivo leading to ceftazidime-avibactam resistance, which brings to the fore the critical need for developing more accurate diagnosis tools for detection of GES ß-lactamases and optimise the use of antimicrobials.

Whole-genome sequencing analysis of multidrug-resistant Serratia marcescens isolates in an intensive care unit in Brazil.

INTRODUCTION: Serratia marcescens is an opportunistic pathogen found ubiquitously in the environment and associated with a wide range of nosocomial infections. This multidrug-resistant bacterium has been a cause of concern for hospitals and healthcare facilities due to its ability to spread rapidly and cause outbreaks. Next generation sequencing genotyping of bacterial isolates has proven to be a valuable tool for tracking the spread and transmission of nosocomial infections. This has allowed for the identification of outbreaks and transmission chains, as well as determining whether cases are due to endogenous or exogenous sources. Evidence of nosocomial transmission has been gathered through genotyping methods. The aim of this study was to investigate the genetic diversity of carbapenemase-producing S. marcescens in an outbreak at a public hospital in Cuiaba, MT, Brazil. METHODOLOGY: Ten isolates of S. marcenses were sequenced and antibiotic resistance profiles analyzed over 12 days. RESULTS: The isolates were clonal and multidrug resistant. Gentamycin and tigecycline had sensitivity in 90% and 80% isolates, respectively. Genomic analysis identified several genes that encode ß-lactamases, aminoglycoside-modifying enzymes, efflux pumps, and other virulence factors. CONCLUSIONS: Systematic surveillance is crucial in monitoring the evolution of S. marcescens genotypes, as it can lead to early detection and prevention of outbreaks.

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.