Humoral immunity to SARS-CoV-2 in kidney transplant recipients and dialysis patients: IgA and IgG patterns unraveled after SARS-CoV-2 infection and vaccination.

BACKGROUND: Infection with SARS-CoV-2 in high-risk groups such as kidney transplant and dialysis patients is shown to be associated with a more serious course of the disease. Four years after the start of the COVID-19 pandemic, crucial knowledge on the immune responses in these patient groups is still lacking. Therefore, this study aimed at investigating the humoral immune response after a SARS-CoV-2 infection compared to vaccination as well as the evolution of immunoglobulins over time. METHODS: Kidney transplant recipients, patients on haemodialysis or on peritoneal dialysis and healthy controls were included in this longitudinal multicenter study. SARS-CoV-2 anti-RBD, anti-NP and anti-S1S2 immunoglobulin G (IgG) and A (IgA) as well as the neutralizing antibody capacity were measured. RESULTS: Kidney transplant recipients had a significantly better humoral response to SARS-CoV-2 after infection (86.4%) than after a two-dose mRNA vaccination (55.8%) while seroconversion was comparable in patients on haemodialysis after infection (95.8%) versus vaccination (89.4%). In individuals without prior COVID-19, the IgG levels after vaccination were significantly lower in kidney transplant recipients when compared to all other groups. However, the IgA titres remained the highest in this patient group at each time point, both after infection and vaccination. A history COVID-19 was associated with higher antibody levels after double-dose vaccination in all patient categories and, while decreasing, titres remained high six months after double-dose vaccination. CONCLUSION: Kidney transplant recipients had a more robust humoral response to SARS-CoV-2 following infection compared to a two-dose mRNA vaccination, while patients on haemodialysis exhibited comparable seroconversion rates. Notably, individuals with prior COVID-19 exhibited higher IgG levels in response to vaccination. Hybrid immunity is thus the best possible defence against severe COVID-19 disease and seems also to hold up for these populations. Next, it is not clear whether the higher IgA levels in the kidney transplant recipients is beneficial for neutralizing SARS-CoV-2 or if it is a sign of disease severity.

Asymptomatic bacteriuria in older adults: the most fragile women are prone to long-term colonization.

BACKGROUND: The diagnosis of urinary tract infections (UTIs) in institutionalized older adults is often based on vague symptoms and a positive culture. The high prevalence of asymptomatic bacteriuria (ABU), which cannot be easily discriminated from an acute infection in this population, is frequently neglected, leading to a vast over-prescription of antibiotics. This study aimed to identify subpopulations predisposed to transient or long-term ABU. METHODS: Residents in a long-term care facility were screened for ABU. Mid-stream urine samples were collected during two sampling rounds, separated by 10 weeks, each consisting of an initial and a confirmative follow-up sample. RESULTS: ABU occurred in approximately 40% of the participants and was mostly caused by Escherichia coli. Long-term ABU (> 3 months) was found in 30% of the subjects. The frailest women with urinary incontinence and dementia had drastically increased rates of ABU and especially long-term ABU. ABU was best predicted by a scale describing the functional independence of older adults. CONCLUSIONS: Institutionalized women with incontinence have ABU prevalence rates of about 80% and are often persistent carriers. Such prevalence rates should be considered in clinical decision making as they devalue the meaning of a positive urine culture as a criterion to diagnose UTIs. Diagnostic strategies are urgently needed to avoid antibiotic overuse and to identify patients at risk to develop upper UTI.

Acetoin synthesis acquisition favors Escherichia coli growth at low pH.

Some members of the family Enterobacteriaceae ferment sugars via the mixed-acid fermentation pathway. This yields large amounts of acids, causing strong and sometimes even lethal acidification of the environment. Other family members employ the 2,3-butanediol fermentation pathway, which generates comparatively less acidic and more neutral end products, such as acetoin and 2,3-butanediol. In this work, we equipped Escherichia coli MG1655 with the budAB operon, encoding the acetoin pathway, from Serratia plymuthica RVH1 and investigated how this affected the ability of E. coli to cope with acid stress during growth. Acetoin fermentation prevented lethal medium acidification by E. coli in lysogeny broth (LB) supplemented with glucose. It also supported growth and higher stationary-phase cell densities in acidified LB broth with glucose (pH 4.10 to 4.50) and in tomato juice (pH 4.40 to 5.00) and reduced the minimal pH at which growth could be initiated. On the other hand, the acetoin-producing strain was outcompeted by the nonproducer in a mixed-culture experiment at low pH, suggesting a fitness cost associated with acetoin production. Finally, we showed that acetoin production profoundly changes the appearance of E. coli on several diagnostic culture media. Natural E. coli strains that have laterally acquired budAB genes may therefore have escaped detection thus far. This study demonstrates the potential importance of acetoin fermentation in the ecology of E. coli in the food chain and contributes to a better understanding of the microbiological stability and safety of acidic foods.

Expert guidance on target product profile development for AMR diagnostic tests.

Diagnostics are widely considered crucial in the fight against antimicrobial resistance (AMR), which is expected to kill 10 million people annually by 2030. Nevertheless, there remains a substantial gap between the need for AMR diagnostics versus their development and implementation. To help address this problem, target product profiles (TPP) have been developed to focus developers' attention on the key aspects of AMR diagnostic tests. However, during discussion between a multisectoral working group of 51 international experts from industry, academia and healthcare, it was noted that specific AMR-related TPPs could be extended by incorporating the interdependencies between the key characteristics associated with the development of such TPPs. Subsequently, the working group identified 46 characteristics associated with six main categories (ie, Intended Use, Diagnostic Question, Test Description, Assay Protocol, Performance and Commercial). The interdependencies of these characteristics were then identified and mapped against each other to generate new insights for use by stakeholders. Specifically, it may not be possible for diagnostics developers to achieve all of the recommendations in every category of a TPP and this publication indicates how prioritising specific TPP characteristics during diagnostics development may influence (or not) a range of other TPP characteristics associated with the diagnostic. The use of such guidance, in conjunction with specific TPPs, could lead to more efficient AMR diagnostics development.

Convergence of virulence and antimicrobial resistance in increasingly prevalent Escherichia coli ST131 papGII+ sublineages.

Escherichia coli lineage ST131 is an important cause of urinary tract and bloodstream infections worldwide and is highly resistant to antimicrobials. Specific ST131 lineages carrying invasiveness-associated papGII pathogenicity islands (PAIs) were previously described, but it is unknown how invasiveness relates to the acquisition of antimicrobial resistance (AMR). In this study, we analysed 1638 ST131 genomes and found that papGII+ isolates carry significantly more AMR genes than papGII-negative isolates, suggesting a convergence of virulence and AMR. The prevalence of papGII+ isolates among human clinical ST131 isolates increased dramatically since 2005, accounting for half of the recent E. coli bloodstream isolates. Emerging papGII+ lineages within clade C2 were characterized by a chromosomally integrated blaCTX-M-15 and the loss and replacement of F2:A1:B- plasmids. Convergence of virulence and AMR is worrying, and further dissemination of papGII+ ST131 lineages may lead to a rise in severe and difficult-to-treat extraintestinal infections.

Integrated regulation of acetoin fermentation by quorum sensing and pH in Serratia plymuthica RVH1.

During fermentation of sugars, a number of bacterial species are able to switch from mixed acid production to acetoin and 2,3-butanediol production in order to avoid lethal acidification of their environment, although the regulation of this switch is only poorly understood. In this study, we report the identification of the budAB structural operon, involved in acetoin production in Serratia plymuthica RVH1, and its activation by a LysR-type regulator encoded by budR, immediately upstream of this operon. In addition, the regulation of budR transcription was elucidated and found to be subject to negative control by BudR itself and to positive control by external stimuli such as N-(3-oxohexanoyl)-L-homoserine lactone (OHHL) quorum sensing signaling molecules and acetate. Interestingly, however, we observed that induction of budR transcription by OHHL or acetate did not require BudR, indicating the involvement of additional regulatory factors in relaying these environmental signals to the budR promoter.

Pseudomonas aeruginosa: a clinical and genomics update.

Antimicrobial resistance (AMR) has become a global medical priority that needs urgent resolution. Pseudomonas aeruginosa is a versatile, adaptable bacterial species with widespread environmental occurrence, strong medical relevance, a diverse set of virulence genes and a multitude of intrinsic and possibly acquired antibiotic resistance traits. Pseudomonas aeruginosa causes a wide variety of infections and has an epidemic-clonal population structure. Several of its dominant global clones have collected a wide variety of resistance genes rendering them multi-drug resistant (MDR) and particularly threatening groups of vulnerable individuals including surgical patients, immunocompromised patients, Caucasians suffering from cystic fibrosis (CF) and more. AMR and MDR especially are particularly problematic in P. aeruginosa significantly complicating successful antibiotic treatment. In addition, antimicrobial susceptibility testing (AST) of P. aeruginosa can be cumbersome due to its slow growth or the massive production of exopolysaccharides and other extracellular compounds. For that reason, phenotypic AST is progressively challenged by genotypic methods using whole genome sequences (WGS) and large-scale phenotype databases as a framework of reference. We here summarize the state of affairs and the quality level of WGS-based AST for P. aeruginosa mostly from clinical origin.

Immunoglobin G/total antibody testing for SARS-CoV-2: A prospective cohort study of ambulatory patients and health care workers in two Belgian oncology units comparing three commercial tests.

BACKGROUND: Coronavirus disease (COVID-19) is interfering heavily with the screening, diagnosis and treatment of cancer patients. Better knowledge of the seroprevalence and immune response after Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection in this population is important to manage them safely during the pandemic. METHODS: 922 cancer patients, 100 non-cancer patients and 94 health care workers (HCW) attending the Multidisciplinary Oncology Unit of Antwerp University Hospital from 24th of March 2020 till 31st of May 2020, and the Oncology Unit of AZ Maria Middelares Hospital, Ghent, from 13th of April 2020 till 31st of May 2020 participated in the study. The Alinity® (A; Abbott) and Liaison® (D; DiaSorin) commercially available assays were used to measure SARS-CoV-2 IgG, while total SARS-CoV-2 Ig was measured by Elecsys® (R; Roche). RESULTS: In the overall study population IgG/total SARS-CoV-2 antibodies were found in respectively 32/998 (3.2%), 68/1020 (6.7%), 37/1010 (3.7%) and of individuals using the A, D or R test. Forty-six out of 618 (7.4%) persons had a positive SARS-CoV-2 polymerase chain reaction (RT-PCR) test. Seroprevalence in cancer patients (A:2.2%, D:6.2%, R:3.0%), did not significantly differ from that in non-cancer patients (A:1.1%, D:5.6%, R:0.0%), but was lower than the HCW (A:13%, D:12%, R:12%; respectively Fisher's exact test p = 0.00001, p = 0.046, p = 0.0004). A positive SARS-CoV-2 RT-PCR was found in 6.8% of the cancer patients, 2.3% of the non-cancer patients and 28.1% of the HCW (Fisher's exact test p = 0.0004). Correlation between absolute values of the different Ig tests was poor in the cancer population. Dichotomising a positive versus negative test result, the A and R test correlated well (kappa 0.82 p McNemar test = 0.344), while A and D and R and D did not (respectively kappa 0.49 and 0.57; result significantly different p McNemar test = <0.0001 for both). The rate of seroconversion (>75%) and median absolute antibody levels (A: 7.0 versus 4.7; D 74.0 versus 26.6, R: 16.34 versus 7.32; all >P Mann Whitney U test = 0.28) in cancer patients and HCW with a positive RT-PCR at least 7 days earlier did not show any differences. However, none (N = 0/4) of the patients with hematological tumours had seroconversion and absolute antibody levels remained much lower compared to patients with solid tumours (R: 0.1 versus 37.6, p 0.003; D 4.1 versus 158, p 0.008) or HCW (all p < 0.0001). CONCLUSION: HCW were at high risk of being infected by SARS-CoV-2 during the first wave of the pandemic. Seroprevalence in cancer patients was low in the study period. Although Ig immune response in cancer patients with solid tumours does not differ from healthy volunteers, patients with hematological tumours have a very poor humoral immune response. This has to be taken into account in future vaccination programmes in this population. SARS-CoV-2 antibody tests have divergent results and seem to have little added value in the management of cancer patients.

Blood Cytokine Analysis Suggests That SARS-CoV-2 Infection Results in a Sustained Tumour Promoting Environment in Cancer Patients.

Cytokines, chemokines, and (angiogenic) growth factors (CCGs) have been shown to play an intricate role in the progression of both solid and haematological malignancies. Recent studies have shown that SARS-CoV-2 infection leads to a worse outcome in cancer patients, especially in haematological malignancy patients. Here, we investigated how SARS-CoV-2 infection impacts the already altered CCG levels in solid or haematological malignancies, specifically, whether there is a protective effect or rather a potentially higher risk for major COVID-19 complications in cancer patients due to elevated CCGs linked to cancer progression. Serially analysing immune responses with 55 CCGs in cancer patients under active treatment with or without SARS-CoV-2 infection, we first showed that cancer patients without SARS-CoV-2 infection (n = 54) demonstrate elevated levels of 35 CCGs compared to the non-cancer, non-infected control group of health care workers (n = 42). Of the 35 CCGs, 19 were common to both the solid and haematological malignancy groups and comprised previously described cytokines such as IL-6, TNF-α, IL-1Ra, IL-17A, and VEGF, but also several less well described cytokines/chemokines such as Fractalkine, Tie-2, and T cell chemokine CTACK. Importantly, we show here that 7 CCGs are significantly altered in SARS-CoV-2 exposed cancer patients (n = 52). Of these, TNF-α, IFN-ß, TSLP, and sVCAM-1, identified to be elevated in haematological cancers, are also known tumour-promoting factors. Longitudinal analysis conducted over 3 months showed persistence of several tumour-promoting CCGs in SARS-CoV-2 exposed cancer patients. These data demonstrate a need for increased vigilance for haematological malignancy patients as a part of long COVID follow-up.

Digital dipstick: miniaturized bacteria detection and digital quantification for the point-of-care.

Established digital bioassay formats, digital PCR and digital ELISA, show extreme limits of detection, absolute quantification and high multiplexing capabilities. However, they often require complex instrumentation, and extensive off-chip sample preparation. In this study, we present a dipstick-format digital biosensor (digital dipstick) that detects bacteria directly from the sample liquid with a minimal number of steps: dip, culture, and count. We demonstrate the quantitative detection of Escherichia coli (E. coli) in urine in the clinically relevant range of 102-105 CFU ml-1 for urinary tract infections. Our format shows 89% sensitivity to detect E. coli in clinical urine samples (n = 28) when it is compared to plate culturing (gold standard). The significance and uniqueness of this diagnostic test format is that it allows a non-trained operator to detect urinary tract infections in the clinically relevant range in the home setting.

Horizontally acquired papGII-containing pathogenicity islands underlie the emergence of invasive uropathogenic Escherichia coli lineages.

Escherichia coli is the leading cause of urinary tract infection, one of the most common bacterial infections in humans. Despite this, a genomic perspective is lacking regarding the phylogenetic distribution of isolates associated with different clinical syndromes. Here, we present a large-scale phylogenomic analysis of a spatiotemporally and clinically diverse set of 907 E. coli isolates, including 722 uropathogenic E. coli (UPEC) isolates. A genome-wide association approach identifies the (P-fimbriae-encoding) papGII locus as the key feature distinguishing invasive UPEC, defined as isolates associated with severe UTI, i.e., kidney infection (pyelonephritis) or urinary-source bacteremia, from non-invasive UPEC, defined as isolates associated with asymptomatic bacteriuria or bladder infection (cystitis). Within the E. coli population, distinct invasive UPEC lineages emerged through repeated horizontal acquisition of diverse papGII-containing pathogenicity islands. Our findings elucidate the molecular determinants of severe UTI and have implications for the early detection of this pathogen.

Bacterial interactions in biofilms.

It is generally acknowledged that biofilms are the dominant lifestyle of bacteria, both in the natural environment as on manmade settings such as industrial and medical devices. This attached form of cell growth consists of slime matrix embedded bacteria of either a single, but mostly of multiple microbial species that form an interdependent structured community, capable of coordinated and collective behavior. Although research on multispecies biofilms is still in its infancy, this review will focus on these complex communities where cooperation and antagonism are keys to increase the fitness of the different species and where intercellular interactions and communication are means to achieve this goal.

[Urinary cultures fall short in institutionalized elderly patients]. / Urinekweken in verpleeghuis schieten tekort.

The diagnosis of urinary tract infections (UTI) in institutionalized elderly patients is complex, due to vague symptomatology. Moreover, the high prevalence of asymptomatic bacteriuria (ABU) is often ignored in clinical decision making, leading to a vast overprescription of antibiotics. Pragmatic clinical guidelines have been published to reduce the ordering of urinary cultures and prescription of antibiotics. Nitrite and leukocyte esterase dipstick tests have a high negative predictive value. Urinary cultures should only be ordered to guide antibiotic therapy after said decision has been taken based on clinical grounds. Apart from these pragmatic recommendations, current research is focussing on pathogen as well as host-derived factors. A smart combination of virulence factors and detection of immunological biomarkers could help clinicians to decide whether antibiotics should be initiated or not.

A trial like ALIC4E: why design a platform, response-adaptive, open, randomised controlled trial of antivirals for influenza-like illness?

ALIC4E is the first publicly funded, multicountry, pragmatic study determining whether antivirals should be routinely prescribed for influenza-like illness in primary care. The trial aims to go beyond determining the average treatment effect in a population to determining effects in patients with combinations of participant characteristics (age, symptom duration, illness severity, and comorbidities). It is one of the first platform, response-adaptive, open trial designs implemented in primary care, and this article aims to provide an accessible description of key aspects of the study design. 1) The platform design allows the study to remain relevant to evolving circumstances, with the ability to add treatment arms. 2) Response adaptation allows the proportion of participants with key characteristics allocated to study arms to be altered during the course of the trial according to emerging outcome data, so that participants' information will be most useful, and increasing their chances of receiving the trial intervention that will be most effective for them. 3) Because the possibility of taking placebos influences participant expectations about their treatment, and determining effects of the interventions on patient help seeking and adherence behaviour in real-world care is critical to estimates of cost-effectiveness, ALIC4E is an open-label trial.

Characterization of a luxI/luxR-type quorum sensing system and N-acyl-homoserine lactone-dependent regulation of exo-enzyme and antibacterial component production in Serratia plymuthica RVH1.

Quorum sensing by means of N-acyl-l-homoserine lactones (AHLs) is widespread in Gram-negative bacteria, where diverse AHLs influence a wide variety of functions, even in a single genus such as Serratia. Here we report the identification and characterization of the quorum sensing system of Serratia plymuthica strain RVH1. This strain isolated from a raw vegetable processing line produces at least three AHLs which were identified as N-butanoyl- (C4-HSL), N-hexanoyl- (C6-HSL) and N-(3-oxo-hexanoyl)-homoserine lactone (3-oxo-C6-HSL). The identified LuxI homolog SplI synthesizes 3-oxo-C6-HSL, and influences the production of C4-HSL and C6-HSL, as splI gene inactivation resulted in loss of 3-oxo-C6-HSL production and smaller amounts of C4-HSL and C6-HSL produced. SplI-dependent quorum sensing controls 2,3-butanediol fermentation (previously reported) and the production of an extracellular chitinase, nuclease, protease and antibacterial compound. The identity of the latter is not yet elucidated, but appears to be different from the known antibacterial compounds produced by Serratia strains. SplR, the homolog of the LuxR regulator, appears to act as a repressor of synthesis of extracellular enzymes and antibacterial compound and to autorepress its own expression, probably by binding to a 21bp lux box sequence.

N-acyl-L-homoserine lactone signal interception by Escherichia coli.

N-acyl-L-homoserine lactone (AHL) mediated quorum sensing is a widespread communication system in gram-negative bacteria which regulates a wide range of target genes in a cell density-dependent manner. Although Escherichia coli is not capable of synthesizing AHL molecules because it lacks an AHL synthase encoding gene, it does produce a predicted AHL receptor of the LuxR family, named SdiA. In this work, we used a promoter trap library to screen for E. coli MG1655 promoters whose expression was affected by synthetic N-hexanoyl-L-homoserine lactone (C6-HSL), and we identified six upregulated and nine downregulated promoters, which also responded to synthetic 3-oxo-N-hexanoyl-L-homoserine lactone (3-oxo-C6-HSL). The AHL responsiveness of these promoters was eliminated by knock-out of sdiA, and was temperature dependent, since the identified promoters showed a response at 30 degrees C but not, or only very weakly at 37 degrees C. In addition, in line with the observed induction of gadA encoding a glutamate decarboxylase, we could demonstrate an increased acid tolerance of E. coli upon exposure to C6-HSL. In conclusion, our work shows that E. coli has the capacity to alter its pattern of gene expression and its phenotypical properties in response to AHLs by means of the AHL responsive transcriptional regulator SdiA.

Isolation and functional analysis of luxS in Serratia plymuthica RVH1.

Autoinducer-2 (AI-2) is a signalling molecule proposed to act as a 'universal' signal for interspecies communication, regulating niche-specific genes with diverse functions in various bacteria. We have previously reported the production of AI-2 in strains from different Serratia species and recently, the luxS gene of two Serratia strains was isolated and shown to affect distinct phenotypes. In the current work, we have identified the luxS gene of Serratia plymuthica RVH1, and studied its effect on the N-acyl-L-homoserine lactone-regulated 2,3-butanediol fermentation, production of extracellular protease, chitinase, nuclease and antibacterial compound, and on biofilm formation. None of these phenotypes was affected by luxS knockout. However, overexpression of the luxS gene in RVH1, which was accompanied by an increased production of AI-2, resulted in a slower growth. This growth retardation was also observed when RVH1 was grown in spent culture medium from the AI-2-overproducing strain, but not in spent culture medium from the luxS knockout strain. These results suggest that luxS primarily fulfils a metabolic role and may not regulate a coordinated behaviour controlled by cell-to-cell signalling in S. plymuthica RVH1.

The endotracheal tube microbiome associated with Pseudomonas aeruginosa or Staphylococcus epidermidis.

Ventilator-associated pneumonia (VAP) is one of the commonest hospital-acquired infections associated with high mortality. VAP pathogenesis is closely linked to organisms colonizing the endotracheal tube (ETT) such as Staphylococcus epidermidis and Pseudomonas aeruginosa, the former a common commensal with pathogenic potential and the latter a known VAP pathogen. However, recent gut microbiome studies show that pathogens rarely function alone. Hence, we determined the ETT microbial consortium co-colonizing with S. epidermidis or P. aeruginosa to understand its importance in the development of VAP and for patient prognosis. Using bacterial 16S rRNA and fungal ITS-II sequencing on ETT biomass showing presence of P. aeruginosa and/or S. epidermidis on culture, we found that presence of P. aeruginosa correlated inversely with patient survival and with bacterial species diversity. A decision tree, using 16S rRNA and patient parameters, to predict patient survival was generated. Patients with a relative abundance of Pseudomonadaceae <4.6% and of Staphylococcaceae <70.8% had the highest chance of survival. When Pseudomonadaceae were >4.6%, age of patient <66.5 years was the most important predictor of patient survival. These data indicate that the composition of the ETT microbiome correlates with patient prognosis, and presence of P. aeruginosa is an important predictor of patient outcome.

Characterizing the in vitro biofilm phenotype of Staphylococcus epidermidis isolates from central venous catheters.

Central venous catheter (CVC)-related infections are commonly caused by Staphylococcus epidermidis that is able to form a biofilm on the catheter surface. Many studies involving biofilm formation by Staphylococcus have been published each adopting an own in vitro model. Since the capacity to form a biofilm depends on multiple environmental factors, direct comparison of results obtained in different studies remains challenging. This study characterized the phenotype (strong versus weak biofilm-producers) of S. epidermidis from CVCs in four different in vitro biofilm models, covering differences in material type (glass versus polymer) and nutrient presentation (static versus continuous flow). A good correlation in phenotype was obtained between glass and polymeric surfaces independent of nutrient flow, with 85% correspondence under static growth conditions and 80% under dynamic conditions. A 80% correspondence between static and dynamic conditions on polymeric surfaces could be demonstrated as well. Incubation time had a significant influence on the biofilm phenotype with only 55% correspondence between the dynamic models at different incubation times (48h versus 17h). Screening for the presence of biofilm-related genes only revealed that ica A was correlated with biofilm formation under static but not under dynamic conditions. In conclusion, this study highlights that a high level of standardization is necessary to interpret and compare results of different in vitro biofilm models.

Genotypic and phenotypic characterization of a biofilm-forming Serratia plymuthica isolate from a raw vegetable processing line.

Recently, we isolated from a raw vegetable processing line a Serratia strain with strong biofilm-forming capacity and which produced N-acyl-L-homoserine lactones (AHLs). Within the Enterobacteriaceae, strains of the genus Serratia are a frequent cause of human nosocomial infections; in addition, biofilm formation is often associated with persistent infections. In the current report, we describe the detailed characterization of the isolate using a variety of genotypic and phenotypic criteria. Although the strain was identified as Serratia plymuthica on the basis of its small subunit ribosomal RNA (16S rRNA) gene sequence, it differed from the S. plymuthica type strain in production of pigment and antibacterial compounds, and in AHL production profile. Nevertheless, the identification as S. plymuthica could be confirmed by gyrB phylogeny and DNA:DNA hybridization.