Dual-species biofilm formation by Escherichia coli O157:H7 and environmental bacteria isolated from fresh-cut processing facilities

Biofilm formation is a mechanism adapted by many microorganisms that enhances the survival in stressful environments. In food processing facilities, foodborne bacterial pathogens, which many are poor biofilm formers, could potentially take advantage of this protective mechanism by interacting with other strong biofilm producers. The objective of this study was to determine the influence of bacteria native to fresh produce processing environments on the incorporation of Escherichia coli O157:H7 in biofilms. Bacteria strains representing 13 Gram-negative species isolated from two fresh produce processing facilities in a previous study were tested for forming dual-species biofilms with E. coli O157:H7. Strong biofilm producing strains of Burkholderia caryophylli and Ralstonia insidiosa exhibited 180% and 63% increase in biofilm biomass, and significant thickening of the biofilms (B. caryophylli not tested), when co-cultured with E. coli O157:H7. E. coli O157:H7 populations increased by approximately 1 log in dual-species biofilms formed with B. caryophylli or R. insidiosa. While only a subset of environmental isolates with strong biofilm formation abilities increased the presence of E. coli O157:H7 in biofilms, all tested E. coli O157:H7 exhibited higher incorporation in dual-species biofilms with R. insidiosa. These observations support the notion that E. coli O157:H7 and specific strong biofilm producing bacteria interact synergistically in biofilm formation, and suggest a route for increased survival potential of E. coli O157:H7 in fresh produce processing environments.

Nosocomial bloodstream infection and the emerging carbapenem-resistant pathogen Ralstonia insidiosa

Background

Ralstonia picketti, Ralstonia mannitolilytica, and Ralstonia insidiosa have recently been regarded as emerging pathogens of infectious diseases, in particular as the pathogens responsible for nosocomial infection in immunocompromised patients. R. insidiosa differs from R. picketti and R. mannitolilytica, and its related infections are rarely reported.

Methods

Clinical data from two nosocomial bloodstream infection cases were extracted and analyzed. The causable isolates were identified by the VITEK 2 Compact system, matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and molecular identification methods using PCR with universal and species-specific primers. Antimicrobial susceptibility testing was performed using the broth microdilution method. Both of the isolates were subjected to whole genome sequencing using a HiSeq X10 Sequencer. Antimicrobial resistance genes, virulence factors, and plasmid replicons were identified from assembled genomes. A real-time RT-PCR experiment and a cloning experiment were conducted to explore the related class D β-lactamase-encoding genes.

Results

Both patients recovered under therapy with antibiotics. Isolates were initially misidentified as R. mannitolilytica by the VITEK 2 Compact system rather than R. insidiosa, as identified by both MALDI-TOF MS and 16S rRNA gene sequencing. Both isolates were resistant to aminoglycosides, β-lactams, and polymyxin B. One isolate harboring bla_OXA-570 was resistant to carbapenems. The whole genome sequencing data confirmed species identification based on average nucleotide identity (ANI) and revealed two variants of class D β-lactamase-encoding gene bla_OXA (bla_OXA-573 and bla_OXA-574). The real-time RT-PCR experiment showed no difference in gene expression between bla_OXA-570 and bla_OXA-573 in our strains. The cloning experiment showed that variant OXA-573 had no carbapenem hydrolase activity.

Conclusions

We described two cases of nosocomial bloodstream infection caused by R. insidiosa strains. MALDI-TOF MS was cost-effective for rapid species identification. Clinicians should be aware that R. insidiosa can be resistant to commonly used antibiotics, even carbapenems.

Identification and Elimination of the Clinically Relevant Multi-Resistant Environmental Bacteria Ralstonia insidiosa in Primary Cell Culture

In times of spreading multidrug-resistant bacteria, species identification and decontamination of cell cultures can be challenging. Here, we describe a mobile cell culture contaminant with “black dot”-like microscopic appearance in newly established irreplaceable hybridoma cell lines and its identification. Using 16S rRNA gene sequencing, species-specific PCRs, whole genome sequencing (WGS), and MALDI-TOF mass spectrometry, the contaminant was identified as the ubiquitous environmental and clinically relevant Gram-negative bacterium Ralstonia insidiosa (R. insidiosa), a strong biofilm producer. Further characterizations by transmission electron microscopy (TEM) and biochemical API test were not conclusive. Whole genome sequencing of our R. insidiosa isolate revealed numerous drug-resistance determinants. Genome-wide comparison to other Ralstonia species could not unambiguously designate our isolate to R. insidiosa (<95% average nucleotide identity) suggesting a potential novel species or subspecies, closely related to R. insidiosa and R. pickettii. After determining the antibiotic susceptibility profile, the hybridoma cell culture was successfully decontaminated with ciprofloxacin without affecting antibody production.

An outbreak of Ralstonia insidiosa bloodstream infections caused by contaminated heparinized syringes

INTRODUCTION

Ralstonia insidiosa, a gram-negative waterborne bacteria able to survive and grow in any type of water source, can cause nosocomial infections, and are considered emerging pathogens of infectious diseases in hospital settings. In this study, we report an outbreak of R. insidiosa at our center related to contaminated heparinized syringes.

MATERIAL AND METHODS

The present study was conducted in a tertiary care university hospital in Turkey. An outbreak analysis was performed between September 2021 and December 2021. Microbiological samples were obtained from environmental sources and from patient blood cultures. Species identification was performed using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). To investigate the clonality of strains, all confirmed isolates were sent to the National Reference Laboratory and pulsed-field gel electrophoresis (PFGE) was used to perform molecular typing.

RESULTS

Seventeen R. insidiosa isolates were identified from the blood cultures of 13 patients from various wards and intensive care units. Isolates from seven patient blood cultures and two heparinized blood gas syringes were characterized by PFGE. All isolates were found to belong to the same clone of R. insidiosa.

CONCLUSION

R. insidiosa was identified as the cause of a nosocomial infection outbreak in our hospital, which was then rapidly controlled by the infection-control team. When rare waterborne microorganisms grow in blood or other body fluid cultures, clinicians and the infection-control team should be made aware of a possible outbreak.

Enhanced biofilm formation in dual-species culture of Listeria monocytogenes and Ralstonia insidiosa

In the natural environments microorganisms coexist in communities as biofilms. Since foodborne pathogens have varying abilities to form biofilms, investigation of bacterial interactions in biofilm formation may enhance our understanding of the persistence of these foodborne pathogens in the environment. Thus the objective of this study was to investigate the interactions between Listeria monocytogenes and Ralstonia insidiosa in dual species biofilms. Biofilm development after 24 h was measured using crystal violet in 96-well microtiter plate. Scanning electron microscopy and cell enumeration were employed after growth on stainless steel coupons. When compared with their single species counterparts, the dual species biofilms exhibited a significant increase in biofilm biomass. The number of L. monocytogenes in co-culture biofilms on stainless steel also increased significantly. However, there was no effect on the biofilm formation of L. monocytogenes when cultured with R. insidiosa separated by a semi-permeable membrane-linked compartment or cultured in R. insidiosa cell-free supernatant, indicating that direct cell-cell contact is critical for this interaction.

Children with infectious pneumonia caused by Ralstonia insidiosa: A case report

BACKGROUND

Ralstonia is a Gram-negative non-fermentative bacterium widespread in nature, and includes four species, Ralstonia pickettii, Ralstonia solanacearum, Ralstonia mannitolilytica, and Ralstonia insidiosa, which were proposed in 2003. Ralstonia is mainly found in the external water environment, including municipal and medical water purification systems. This bacterium has low toxicity and is a conditional pathogen. It has been reported in recent years that infections due to Ralstonia are increasing. Previous studies have shown that most cases of infection are caused by Ralstonia pickettii, a few by Ralstonia mannitolilytica, and infections caused by Ralstonia insidiosa are rare.

CASE SUMMARY

A 2-year-old Chinese child suffered from intermittent fever and cough for 20 d and was admitted to hospital with bronchial pneumonia. Bronchoscopy and alveolar lavage fluid culture confirmed Ralstonia insidiosa pneumonia. The infection was well controlled after treatment with meropenem and azithromycin.

CONCLUSION

Ralstonia infections are increasing, and we report a rare case of Ralstonia insidiosa infection in a child. Clinicians should be vigilant about Ralstonia infections.

Transcriptomic and metabolomic analyses to study the key role by which Ralstonia insidiosa induces Listeria monocytogenes to form suspended aggregates

Ralstonia insidiosa can survive in a wide range of aqueous environments, including food processing areas, and is harmful to humans. It can induce Listeria monocytogenes to form suspended aggregates, resulting from the co-aggregation of two bacteria, which allows for more persistent survival and increases the risk of L. monocytogenes contamination. In our study, different groups of aggregates were analyzed and compared using Illumina RNA sequencing technology. These included R. insidiosa under normal and barren nutrient conditions and in the presence or absence of L. monocytogenes as a way to screen for differentially expressed genes (DEGs) in the process of aggregate formation. In addition, sterile supernatants of R. insidiosa were analyzed under different nutrient conditions using metabolomics to investigate the effect of nutrient-poor conditions on metabolite production by R. insidiosa. We also undertook a combined analysis of transcriptome and metabolome data to further investigate the induction effect of R. insidiosa on L. monocytogenes in a barren environment. The results of the functional annotation analysis on the surface of DEGs and qPCR showed that under nutrient-poor conditions, the acdx, puuE, and acs genes of R. insidiosa were significantly upregulated in biosynthetic processes such as carbon metabolism, metabolic pathways, and biosynthesis of secondary metabolites, with Log2FC reaching 4.39, 3.96, and 3.95 respectively. In contrast, the Log2FC of cydA, cyoB, and rpsJ in oxidative phosphorylation and ribosomal pathways reached 3.74, 3.87, and 4.25, respectively. Thirty-one key components were identified while screening for differential metabolites, which mainly included amino acids and their metabolites, enriched to the pathways of biosynthesis of amino acids, phenylalanine metabolism, and methionine metabolism. Of these, aminomalonic acid and Proximicin B were the special components of R. insidiosa that were metabolized under nutrient-poor conditions.

A case of meningitis caused by Ralstonia insidiosa, a rare opportunistic pathogen

BACKGROUND

Ralstonia is a genus of Gram-negative opportunistic bacteria that can survive in many kinds of solutions and cause a variety of infections. Ralstonia spp. have increasingly been isolated and reported to cause infections in recent years, thanks to the development of identification methods such as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and gene sequencing. However, infections caused by Ralstonia insidiosa are still rare. Only a few cases of respiratory infections and bloodstream infections have been reported, none of which involved meningitis. To the best of our knowledge, this is the first reported case of meningitis caused by R. insidiosa worldwide. It is necessary to report and review this case.

CASE PRESENTATION

We report a case of meningitis caused by R. insidiosa following lumbar surgery in China. The patient exhibited symptoms of headache, dizziness, and recurrent fever. The fever remained unresolved after empiric antibiotic therapy with intravenous cefotaxime and vancomycin in the initial days. Cerebrospinal fluid (CSF) culture yielded Gram-negative non-fermentative bacteria, which were identified as R. insidiosa. As there was a lack of antibiotic susceptibility testing results, clinical pharmacists conducted a literature review to select appropriate antibiotics. The patient's condition improved after receiving effective treatment with intravenous cefepime and levofloxacin.

CONCLUSIONS

Uncommon pathogens, such as R. insidiosa, should be considered in postoperative central nervous system (CNS) infections, particularly in cases with unsatisfactory results of empiric anti-infective therapy. This is the first reported case of meningitis caused by R. insidiosa worldwide. MALDI-TOF MS provides rapid and accurate identification of this pathogen. The antibiotic susceptibility testing results of R. indiosa may be interpreted based on the breakpoints for Pseudomonas spp., Burkholderia cepacia spp., and Acinetobacter spp. Our case presents a potential option for empiric therapy against this pathogen, at least in the local area. This is crucial to minimize the severity and mortality rates associated with meningitis. Standardized antibiotic susceptibility testing and breakpoints for the Ralstonia genus should be established in the future as cases accumulate. Cefepime and levofloxacin may be potential antibiotics for infections caused by R. indiosa.