Staphylococcus Lugdunensis, An Aggressive Coagulase-Negative Pathogen not to be Underestimated

Biofilms in Periprosthetic Orthopedic Infections Seen through the Eyes of Neutrophils: How Can We Help Neutrophils?

Despite advancements in our knowledge of neutrophil responses to planktonic bacteria during acute inflammation, much remains to be elucidated on how neutrophils deal with bacterial biofilms in implant infections. Further complexity transpires from the emerging findings on the role that biomaterials play in conditioning bacterial adhesion, the variety of biofilm matrices, and the insidious measures that biofilm bacteria devise against neutrophils. Thus, grasping the entirety of neutrophil-biofilm interactions occurring in periprosthetic tissues is a difficult goal. The bactericidal weapons of neutrophils consist of the following: ready-to-use antibacterial proteins and enzymes stored in granules; NADPH oxidase-derived reactive oxygen species (ROS); and net-like structures of DNA, histones, and granule proteins, which neutrophils extrude to extracellularly trap pathogens (the so-called NETs: an allusive acronym for "neutrophil extracellular traps"). Neutrophils are bactericidal (and therefore defensive) cells endowed with a rich offensive armamentarium through which, if frustrated in their attempts to engulf and phagocytose biofilms, they can trigger the destruction of periprosthetic bone. This study speculates on how neutrophils interact with biofilms in the dramatic scenario of implant infections, also considering the implications of this interaction in view of the design of new therapeutic strategies and functionalized biomaterials, to help neutrophils in their arduous task of managing biofilms.

Phenotypic and Genotypic Virulence Characterisation of Staphylococcus pettenkoferi Strains Isolated from Human Bloodstream and Diabetic Foot Infections

Staphylococcus pettenkoferi is a recently described coagulase-negative Staphylococcus identified in human diseases, especially in infections of foot ulcers in patients living with diabetes mellitus. To date, its pathogenicity remains underexplored. In this study, whole-genome analysis was performed on a collection of 29 S. pettenkoferi clinical strains isolated from bloodstream and diabetic foot infections with regard to their phylogenetic relationships and comprehensive analysis of their resistome and virulome. Their virulence was explored by their ability to form biofilm, their growth kinetics and in an in vivo zebrafish embryo infection model. Our results identified two distinct clades (I and II) and two subclades (I-a and I-b) with notable genomic differences. All strains had a slow bacterial growth. Three profiles of biofilm formation were noted, with 89.7% of isolates able to produce biofilm and harbouring a high content of biofilm-encoding genes. Two virulence profiles were also observed in the zebrafish model irrespective of the strains' origin or biofilm profile. Therefore, this study brings new insights in S. pettenkoferi pathogenicity.

Staphylococcus lugdunensis Uses the Agr Regulatory System to Resist Killing by Host Innate Immune Effectors

Coagulase-negative staphylococci (CoNS) are frequently commensal bacteria that rarely cause disease in mammals. Staphylococcus lugdunensis is an exceptional CoNS that causes disease in humans similar to virulent Staphylococcus aureus, but the factors that enhance the virulence of this bacterium remain ill defined. Here, we used random transposon insertion mutagenesis to identify the agr quorum sensing system as a regulator of hemolysins in S. lugdunensis. Using RNA sequencing (RNA-seq), we revealed that agr regulates dozens of genes, including hemolytic S. lugdunensis synergistic hemolysins (SLUSH) peptides and the protease lugdulysin. A murine bacteremia model was used to show that mice infected systemically with wild-type S. lugdunensis do not show overt signs of disease despite there being high numbers of bacteria in the livers and kidneys of mice. Moreover, proliferation of the agr mutant in these organs was no different from that of the wild-type strain, leaving the role of the SLUSH peptides and the metalloprotease lugdulysin in pathogenesis still unclear. Nonetheless, the tropism of S. lugdunensis for humans led us to investigate the role of virulence factors in other ways. We show that agr-regulated effectors, but not SLUSH or lugdulysin alone, are important for S. lugdunensis survival in whole human blood. Moreover, we demonstrate that Agr contributes to survival of S. lugdunensis during encounters with murine and primary human macrophages. These findings demonstrate that, in S. lugdunensis, Agr regulates expression of virulence factors and is required for resistance to host innate antimicrobial defenses. This study therefore provides insight into strategies that this Staphylococcus species uses to cause disease.

Asymptomatic Periprosthetic Joint Infection of the Hip with High-Virulence Pathogens: Report of Two Cases

Periprosthetic joint infection (PJI) may be a life-threatening condition, particularly when caused by pathogens with high virulence, capable of developing secondary bloodstream infection. We report two cases of chronic PJI of the hip, one with Staphylococcus aureus in a 27-year-old female with severe anorexia, the other one with Staphylococcus lugdunensis in a 74-year-old female suffering from morbid obesity. Both infections did not cause relevant symptoms over time despite the absence of suppressive antibiotic treatment. To our knowledge, there are no similar cases described in the literature. While it remains difficult to recommend postponing treatment in such cases, this option may be an alternative to suppressive antibiotic therapy.

Staphylococcus lugdunensis in children: A retrospective analysis

Importance

Staphylococcus lugdunensis (S. lugdunensis) is a coagulase‐negative staphylococcus (CoNS), found commonly as skin flora in humans. While most species of CoNS are clinically benign, S. lugdunensis can exhibit a similar virulence to that of S. aureus. However, there is scant data concerning S. lugdunensis infection in the pediatric population.

Objective

To ascertain local S. lugdunensis infection rates and sensitivity patterns in the pediatric population.

Methods

A retrospective analysis was undertaken of all S. lugdunensis isolates across a 6‐year period from 2015 to 2020. Data were collected from electronic patient notes and laboratory records. Matrix‐assisted laser desorption ionization and time of flight mass spectrometry were used to identify isolates.

Results

Ninety‐six isolates of S. lugdunensis were identified from 86 patients. Of these, 34 isolates were treated as an infection. Twenty‐three (67.6%) were found to have skin as the primary source of infection. While the observed number was small, central nervous system (CNS) sources of S. lugdunensis infection appear to be a significant source: all three isolates cultured from cerebrospinal fluid were clinically managed as infection. All three were associated with ventriculoperitoneal (VP) shunt infection. No cases of S. lugdunensis infective endocarditis were identified. About 18.6% of S. lugdunensis isolates were resistant to flucloxacillin.

Interpretation

S. lugdunensis is an uncommon but significant cause of infection in the pediatric population and appears to be a rising cause of CNS infection, particularly when associated with VP shunts. Flucloxacillin is recommended locally as the first choice of antibiotic.

Enolase of Staphylococcus lugdunensis Is a Surface-Exposed Moonlighting Protein That Binds to Extracellular Matrix and the Plasminogen/Plasmin System

The coagulase-negative staphylococcal (CoNS) species Staphylococcus lugdunensis is unique in causing serious infections in humans that resemble those of Staphylococcus aureus rather than those of other CoNS species. The colonization and invasion of host tissue presupposes the presence of adherence factors, but only a few proteins mediating adhesion of S. lugdunensis to biotic surfaces are known yet. Here, we report on the functionality of the S. lugdunensis enolase (SlEno), which performs two distinct roles, first, as the metabolic enzyme of the glycolysis, and second, as an adherence factor to the extracellular matrix (ECM) of cells. Phylogenetic analyses of the SlEno confirmed their high conservation to enolases of other species and revealed a closer relationship to Staphylococcus epidermidis than to S. aureus. Using matrix-assisted laser desorption/ionization time of flight mass spectrometry and Western blot experiments, we identified SlEno to be located in the cytoplasm as well as on the cell surface of S. lugdunensis. Recombinantly generated and surface-associated SlEno showed the usual enolase activity by catalyzing the conversion of 2-phosphoglycerate to phosphoenolpyruvate but, in addition, also displayed strong binding to immobilized laminin, fibronectin, fibrinogen, and collagen type IV in a dose-dependent manner. We also showed a strong binding of SlEno to plasminogen (Plg) and observed a tissue plasminogen activator (tPA)-dependent conversion of Plg to plasmin (Pln) whereby the Plg activation significantly increased in the presence of SlEno. This interaction might be dependent on lysines of the SlEno protein as binding to Plg was inhibited by ε-aminocaproic acid. Furthermore, the enhanced activation of the Plg/Pln system by SlEno enabled S. lugdunensis to migrate through a fibrin matrix. This migration was about 10-fold higher than without exogenously added SlEno. Finally, we observed a significantly higher clearance of S. lugdunensis by freshly prepared granulocytes and in the presence of anti-SlEno antibodies. In conclusion, these data demonstrate for the first time a moonlighting function of the S. lugdunensis enolase, which is an underrated virulence factor for colonization and invasion of tissues. Hence, SlEno might be a potential vaccine candidate to prevent severe infections caused by this pathogen.

Evaluation of penicillin G susceptibility testing methods for Staphylococcus lugdunensis

Background

Staphylococcus lugdunensis belongs to the CoNS group, but is regarded to be more virulent than most other CoNS. It is also remarkably susceptible to antibiotics, including penicillin G.

Objectives

To evaluate different methods for penicillin susceptibility testing, to assess penicillin susceptibility rates among S. lugdunensis and to describe the clinical presentation including antibiotic treatment.

Methods

Clinical isolates of S. lugdunensis were tested for penicillin susceptibility using disc diffusion according to CLSI (10 U disc) and EUCAST (1 U disc), assessment of zone-edge appearance, nitrocefin test and Etest for MIC determination. PCR of the blaZ gene was used as a reference method.

Results

Of the 112 isolates included in the study, 67% were susceptible to penicillin G according to blaZ PCR. The EUCAST disc diffusion test had 100% sensitivity, whereas the CLSI method had one very major error with a false-susceptible isolate. When zone-edge appearance was included in the assessment, the false-susceptible isolate was correctly classified as resistant. Foreign-body infection was the most common focus of infection, affecting 49% of the participants. Only 4% of the patients were treated with penicillin G.

Conclusions

Penicillin susceptibility is common in S. lugdunensis and the disc diffusion method according to EUCAST had a higher sensitivity than that of CLSI. Assessment of zone-edge appearance could increase the sensitivity of the disc diffusion test. Penicillin susceptibility testing and treatment should be considered in S. lugdunensis infections.

Virulence Factors in Coagulase-Negative Staphylococci

Coagulase-negative staphylococci (CoNS) have emerged as major pathogens in healthcare-associated facilities, being S. epidermidis, S. haemolyticus and, more recently, S. lugdunensis, the most clinically relevant species. Despite being less virulent than the well-studied pathogen S. aureus, the number of CoNS strains sequenced is constantly increasing and, with that, the number of virulence factors identified in those strains. In this regard, biofilm formation is considered the most important. Besides virulence factors, the presence of several antibiotic-resistance genes identified in CoNS is worrisome and makes treatment very challenging. In this review, we analyzed the different aspects involved in CoNS virulence and their impact on health and food.

Treatment of a Staphylococcus lugdunensis cervical epidural abscess

First reported in 1988, Staphylococcus lugdunensis is a virulent coagulase-negative Staphylococcus species often associated with endocarditis. This is the first case report describing this infection in the cervical spine. A 58-year-old, left-handed Caucasian woman with no significant medical history presented with neck and left arm pain. Neurological examination revealed mild left deltoid 4/5 weakness and myelopathy. She was found to have an epidural cervical spinal cord mass that was causing severe cord compression and underwent partial anterior cervical decompression of the mass. On entering what was believed to be the mass, yellow-tinged fluid was encountered. An abscess was immediately suspected, so the dura was not entered. The specimen sent for culture was identified a day later as S. lugdunensis A two-dimensional echocardiogram was negative for vegetations. A peripherally inserted central catheter line was placed and the patient discharged on 6 weeks of physical therapy and 6-8 weeks of intravenous cefazolin.

Successful bony integration of a porous tantalum implant despite longlasting and ongoing infection: Histologic workup of an explanted shoulder prosthesis

Infection associated with an implant is a complication feared in surgery, as it leads to loosening and dysfunction. This report documents an unexpected good bony integration of a porous tantalum shoulder prosthesis despite infection. A shoulder prosthesis with a porous tantalum glenoidal base plate was retrieved after 3 years of ongoing infection with Staphylococcus spp. Methyl-methacrylate embedded sections of the retrieved glenoidal component were analyzed by optical and scanning electron beam microscopy (SEM). Bone ongrowth and ingrowth were quantified. Bone had formed at the implant surface and within the open cell structure of the porous tantalum. The bone implant contact index was 32%. The bone ingrowth or relative bone area within the open structure was 8.2%, respectively 11.9% in the outer 50% of the thickness. Due to the section thickness, bone ongrowth could best be documented in SEM. Despite long-lasting and ongoing infection, the glenoidal base plate of the prosthesis showed good bony integration upon removal. The bone ingrowth into the porous tantalum was comparable to the values previously reported for the undersurface of retrieved proximal humerus resurfacing implants. Good integration of the implant however did not solve the problem of infection, and related morbidity. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2924-2931, 2018.

Characteristics and Outcome of Twenty-Nine Implant-Related Infections of the Hand and Fingers: Results from a Twelve-Year Observational Study

BACKGROUND

Implant-related infections in hand surgery are dreaded complications, potentially leading to loss of finger joint function or amputation. Knowledge about the clinical presentation and treatment concepts of these infections is limited. The aim of this study is to present a consecutive series of patients with implant-related infections of the finger joints and wrist.

PATIENTS AND METHODS

We identified 25 patients with 29 implant-related infections. Infections were categorized as osteosynthesis-related infections (ORIs) or arthroplasty-related infections (ARIs). Further categorization included early and late post-operative (four weeks or less or more than four weeks after implantation) and exogenous and hematogenous infection.

RESULTS

Compared with patients with ARIs (n = 11), those with ORIs (n = 14) were predominantly male (n = 11), were younger (mean 43 vs. 65 years, p = 0.0023), had few or no comorbidities, and had an exogenous source of infection. Patients with ARIs were predominantly female with rheumatoid arthritis (n = 8) and had a hematogenous pathogenesis. Infections occurred late in 22 (88%) patients. The most commonly isolated micro-organism was Staphylococcus aureus (n = 12; 48%). All ORIs were treated with implant removal and a median antimicrobial treatment duration of 39 days (interquartile range [IQR] 28-50 days). In the ARI group, the implant was removed in three patients and exchanged in three patients (one-stage exchange in one patient, two-stage exchange in two patients). In five individuals, debridement and implant retention was performed. The median antimicrobial treatment duration for ARIs was 42 days (IQR 30-75 days). The median follow-up time was 96 days (IQR 42-258 days) and infection was cured or presumably cured in 22 patients (88%).

CONCLUSION

Our series shows distinct host and clinical patterns in ORIs and ARIs, supporting this categorization. The infection prognosis in ORIs is excellent with implant removal and antimicrobial treatment. Treatment concepts in ARIs are often derived from algorithms for periprosthetic joint infections of larger joints and need to be further elucidated.

The Staphylococcal Biofilm: Adhesins, Regulation, and Host Response

The staphylococci comprise a diverse genus of Gram-positive, nonmotile commensal organisms that inhabit the skin and mucous membranes of humans and other mammals. In general, staphylococci are benign members of the natural flora, but many species have the capacity to be opportunistic pathogens, mainly infecting individuals who have medical device implants or are otherwise immunocompromised. Staphylococcus aureus and Staphylococcus epidermidis are major sources of hospital-acquired infections and are the most common causes of surgical site infections and medical device-associated bloodstream infections. The ability of staphylococci to form biofilms in vivo makes them highly resistant to chemotherapeutics and leads to chronic diseases. These biofilm infections include osteomyelitis, endocarditis, medical device infections, and persistence in the cystic fibrosis lung. Here, we provide a comprehensive analysis of our current understanding of staphylococcal biofilm formation, with an emphasis on adhesins and regulation, while also addressing how staphylococcal biofilms interact with the immune system. On the whole, this review will provide a thorough picture of biofilm formation of the staphylococcus genus and how this mode of growth impacts the host.

Staphylococcus lugdunensis: a neglected pathogen of infections involving fracture-fixation devices

PURPOSE

Cases of fracture-fixation device infection involving Staphylococcus lugdunensis are not frequent. The clinical characteristics and the choice of treatment strategies of these infections are not obviously known to date.

METHODS

We performed a review of fracture-fixation device infection involving S. lugdunensis managed by our centres.

RESULTS

Among the 38 cases of fracture-fixation device infection involving S. lugdunensis, 53% were located in the tibia. Most of our cases (87%) were chronic infections. Purulent discharge, which occurred in 79% of cases, was the most frequent clinical symptom, followed by pain in 63%, local inflammation in 55%, and fever in 37%. Bacteremia and severe sepsis occurred in 10% and 18% of cases, respectively. Four cases (10%) were treated exclusively with antimicrobial treatment alone. Thirty-four cases (89%) were treated with a combination of surgery with antimicrobial therapy including surgical debridement, antibiotics and osteosynthesis device retention in six cases (16%), and osteosynthesis device removal in 27 cases (71%). The mean length of antibiotic treatment was 119 days. The relapse rate was high that was not related to selection of resistant strains. Polymicrobial infection had no impact on clinical outcome. A combination of surgery with antimicrobial therapy was identified as a significant prognostic factor associated with remission (p = 0.042).

CONCLUSIONS

S. lugdunensis is probably involved in more infections than has been reported. Using appropriate microbiological methods laboratories should routinely identify the species of all coagulase-negative Staphylococci isolates involved in fracture-fixation device infection to better achieve the treatment strategies of fracture-fixation device infection involving S. lugdunensis.

Novel anti-staphylococcal and anti-biofilm properties of two anti-malarial compounds: MMV665953 {1-(3-chloro-4-fluorophenyl)-3-(3,4-dichlorophenyl)urea} and MMV665807 {5-chloro-2-hydroxy-N-[3-(trifluoromethyl)phenyl]benzamide}

PURPOSE

The treatment of device-related infections is challenging and current anti-microbial compounds have poor anti-biofilm activity. We aimed to identify and characterize novel compounds effective in the eradication of Staphylococcus aureus biofilms.

METHODOLOGY

Two novel compounds, MMV665953 {1-(3-chloro-4-fluorophenyl)-3-(3,4-dichlorophenyl)urea} and MMV665807{5-chloro-2-hydroxy-N-[3-(trifluoromethyl)phenyl]benzamide}, effective in killing S. aureus biofilms, were identified by screening of the open access 'malaria box' chemical library. The minimum bactericidal concentrations, half-maximal inhibition concentration (IC50) values and minimal biofilm killing concentrations effective in the killing of biofilm were determined against meticillin-resistant S. aureus and meticillin-sensitive S. aureus. Fibrin-embedded biofilms were grown under in vivo-relevant conditions, and viability was measured using a resazurin-conversion assay and confocal microscopy. The potential for the development of resistance and cytotoxicity was also assessed.

RESULTS

MMV665953 and MMV665807 were bactericidal against S. aureus isolates. The IC50 against S. aureus biofilms was at 0.15-0.58 mg l-1 after 24 h treatment, whereas the concentration required to eradicate all tested biofilms was 4 mg l-1, making the compounds more bactericidal than conventional antibiotics. The cytotoxicity against human keratinocytes and primary endothelial cells was determined as IC50 7.47 and 0.18 mg l-1 for MMV665953, and as 1.895 and 0.076 mg l-1 for MMV665807. Neither compound was haemolytic nor caused platelet activation. MMV665953 and MMV665807 derivatives with reduced cytotoxicity exhibited a concomitant loss in anti-staphylococcal activity.

CONCLUSION

MMV665953 and MMV665807 are more bactericidal against S. aureus biofilms than currently used anti-staphylococcal antibiotics and represent a valuable structural basis for further investigation in the treatment of staphylococcal biofilm-related infections.

Surgical outcomes of perforated and unperforated corneal descemetocele

OBJECTIVE

To compare the surgical outcomes of amniotic membrane transplantation (AMT) and penetrating keratoplasty (PK) in perforated and non-perforated corneal descemetocele.

METHOD

In this study, we retrospectively examined 48 eyes of 48 patients operated with AMT, and 32 eyes of 32 patients operated with PK for perforated and non-perforated descemetocele.

RESULTS

There were no significant differences between the two groups with regard to age, sex, laterality, follow-up duration, cause of descemetocele, and localization (p > 0.05). Thirty-six (75%) eyes in the AMT group and 17 (53.1%) eyes in the PK group were perforated prior to operation (p = 0.043). Surgical success was achieved in 35 (73%) of 48 eyes underwent AMT and 28 (87.5%) of 32 eyes underwent PK (p = 0.118). Perforation size was the only parameter significantly affecting surgical success (AMT p = 0.001, PK p = 0.003). The visual acuity was significantly better at the postsurgical period compared to the presurgical period in both groups (p = 0.003, p < 0.001). It was observed that the postsurgical change in the visual acuity score was significantly greater in the PK group (p = 0.001).

CONCLUSION

Penetrating keratoplasty is superior to AMT for achieving ocular surface integrity and enhancing visual acuity. Amniotic membrane transplantation saves time for patients and surgeons when donor cornea supply is limited and it allows PK to be performed at a quiet period when inflammation is suppressed.

Detection of Biofilms in Biopsies from Chronic Rhinosinusitis Patients: In Vitro Biofilm Forming Ability and Antimicrobial Susceptibility Testing in Biofilm Mode of Growth of Isolated Bacteria

Chronic rhinosinusitis (CRS) is the most common illness among chronic disorders that remains poorly understood from a pathogenic standpoint and has a significant impact on patient quality of life, as well as healthcare costs. Despite being widespread, little is known about the etiology of the CRS. Recent evidence, showing the presence of biofilms within the paranasal sinuses, suggests a role for biofilm in the pathogenesis. To elucidate the role of biofilm in the pathogenesis of CRS, we assessed the presence of biofilm at the infection site and the ability of the aerobic flora isolated from CRS patients to form biofilm in vitro. For selected bacterial strains the susceptibility profiles to antibiotics in biofilm condition was also evaluated.Staphylococci represented the majority of the isolates obtained from the infection site, with S. epidermidis being the most frequently isolated species. Other isolates were represented by Enterobacteriaceae or by species present in the oral flora. Confocal laser scanning microscopy (CLSM) of the mucosal biopsies taken from patients with CRS revealed the presence of biofilm in the majority of the samples. Strains isolated from the specific infection site of the CRS patients were able to form biofilm in vitro at moderate or high levels, when tested in optimized conditions. No biofilm was observed by CLSM in the biopsies from control patients, although the same biopsies were positive for staphylococci in microbiological culture analysis. Drug-susceptibility tests demonstrated that the susceptibility profile of planktonic bacteria differs from that of sessile bacteria in biofilms.

Bacterial Infection and Implant Loosening in Hip and Knee Arthroplasty: Evaluation of 209 Cases

The aim of this study was to evaluate bacteria species detected in a large number of patients treated for prosthetic joint infection of the hip and knee at a single specialized center. Furthermore, the rate of implant loosening was investigated in a time-dependent manner for the most frequently detected bacteria species. A retrospective analysis of patients (n = 209) treated for prosthetic joint infection of the hip and knee was performed. The following parameters were evaluated: C-Reactive Protein (CRP) concentration, microbiological evaluation of tissue samples, loosening of the implant, the time that had elapsed since the primary prosthetic joint replacement, and the duration since the last surgical intervention. Coagulase-negative Staphylococcus spp. were most frequently detected, followed by Staphylococcus aureus. Differences in CRP concentration were detected among various bacteria species. Osteolysis was not associated with one causative agent in particular. Patients who had undergone previous revision surgery had a higher probability of implant loosening. Coagulase-negative Staphylococcus spp. are the most common causative agents of prosthetic joint infection and show no significant differences with regard to implant loosening or the time-course when compared to S. aureus. Infections with Enterococcus spp. seem to develop faster than with other bacteria species. The risk of implant loosening increases with revision surgery, in particular in the hip joint.

Orthopedic implant infections: Incompetence of Staphylococcus epidermidis, Staphylococcus lugdunensis, and Enterococcus faecalis to invade osteoblasts

Septic failure is still the major complication of prosthetic implants. Entering host cells, bacteria hide from host immune defenses, shelter from extracellular antibiotics, and cause chronic infection. Staphylococcus aureus, the leading etiologic agent of orthopedic implant infections, is able to enter bone cells and induce osteoblast apoptosis, osteoclast recruitment, and highly destructive osteomyelitis. Staphylococcus epidermidis, Staphylococcus lugdunensis, and Enterococcus faecalis are opportunistic pathogens causative of implant-related infections. This study investigated the ability to internalize into osteoblastic MG63 cells of 22 S. epidermidis, 9 S. lugdunensis, and 21 E. faecalis clinical isolates from orthopedic implant infections. Isolates were categorized in clusters by ribotyping. Internalization assay was carried out by means of a microtiter plate-based method. S. epidermidis, S. lugdunensis, and E. faecalis strains turned out incompetent to enter osteoblasts, exhibiting negligible internalization into MG63 cells, nearly three orders of magnitude lower than that of S. aureus. Osteoblast invasion does not appear as a pathogenetic mechanism utilized by S. epidermidis, S. lugdunensis, or E. faecalis for infecting orthopedic implants. Moreover, it can be inferred that intracellularly active antimicrobials should not be necessary against implant infections caused by the three bacterial species. Finally, implications with the uptake of biomaterial microparticles by nonphagocytic cells are enlightened. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 788-801, 2016.

Important contribution of the novel locus comEB to extracellular DNA-dependent Staphylococcus lugdunensis biofilm formation

The coagulase-negative species Staphylococcus lugdunensis is an emerging cause of serious and potentially life-threatening infections, such as infective endocarditis. The pathogenesis of these infections is characterized by the ability of S. lugdunensis to form biofilms on either biotic or abiotic surfaces. To elucidate the genetic basis of biofilm formation in S. lugdunensis, we performed transposon (Tn917) mutagenesis. One mutant had a significantly reduced biofilm-forming capacity and carried a Tn917 insertion within the competence gene comEB. Site-directed mutagenesis and subsequent complementation with a functional copy of comEB verified the importance of comEB in biofilm formation. In several bacterial species, natural competence stimulates DNA release via lysis-dependent or -independent mechanisms. Extracellular DNA (eDNA) has been demonstrated to be an important structural component of many bacterial biofilms. Therefore, we quantified the eDNA in the biofilms and found diminished eDNA amounts in the comEB mutant biofilm. High-resolution images and three-dimensional data obtained via confocal laser scanning microscopy (CSLM) visualized the impact of the comEB mutation on biofilm integrity. The comEB mutant did not show reduced expression of autolysin genes, decreased autolytic activities, or increased cell viability, suggesting a cell lysis-independent mechanism of DNA release. Furthermore, reduced amounts of eDNA in the comEB mutant biofilms did not result from elevated levels or activity of the S. lugdunensis thermonuclease NucI. In conclusion, we defined here, for the first time, a role for the competence gene comEB in staphylococcal biofilm formation. Our findings indicate that comEB stimulates biofilm formation via a lysis-independent mechanism of DNA release.

Polysaccharide intercellular adhesin in biofilm: structural and regulatory aspects

Staphylococcus aureus and Staphylococcus epidermidis are the leading etiologic agents of implant-related infections. Biofilm formation is the main pathogenetic mechanism leading to the chronicity and irreducibility of infections. The extracellular polymeric substances of staphylococcal biofilms are the polysaccharide intercellular adhesin (PIA), extracellular-DNA, proteins, and amyloid fibrils. PIA is a poly-β(1-6)-N-acetylglucosamine (PNAG), partially deacetylated, positively charged, whose synthesis is mediated by the icaADBC locus. DNA sequences homologous to ica locus are present in many coagulase-negative staphylococcal species, among which S. lugdunensis, however, produces a biofilm prevalently consisting of proteins. The product of icaA is an N-acetylglucosaminyltransferase that synthetizes PIA oligomers from UDP-N-acetylglucosamine. The product of icaD gives optimal efficiency to IcaA. The product of icaC is involved in the externalization of the nascent polysaccharide. The product of icaB is an N-deacetylase responsible for the partial deacetylation of PIA. The expression of ica locus is affected by environmental conditions. In S. aureus and S. epidermidis ica-independent alternative mechanisms of biofilm production have been described. S. epidermidis and S. aureus undergo to a phase variation for the biofilm production that has been ascribed, in turn, to the transposition of an insertion sequence in the icaC gene or to the expansion/contraction of a tandem repeat naturally harbored within icaC. A role is played by the quorum sensing system, which negatively regulates biofilm formation, favoring the dispersal phase that disseminates bacteria to new infection sites. Interfering with the QS system is a much debated strategy to combat biofilm-related infections. In the search of vaccines against staphylococcal infections deacetylated PNAG retained on the surface of S. aureus favors opsonophagocytosis and is a potential candidate for immune-protection.

Staphylococcus lugdunensis gluteal abscess in a patient with end stage renal disease on hemodialysis

A 57-year-old end stage renal disease patient on hemodialysis (HD) presented with sepsis secondary to right buttock abscess and overlying cellulitis. She was started on broad-spectrum antibiotic therapy and underwent incision and drainage with marked improvement. Her cultures grew methicillin-resistant Staphylococcus lugdunensis. This bacterium is more virulent than other coagulase negative staphylococci and has been implicated in causing a variety of serious infections but it has been underreported as a cause of skin infections in HD patients and possible other patient populations.

Brain Abscess due to Staphylococcus lugdunensis in the Absence of Endocarditis or Bacteremia

Staphylococcus lugdunensis has been recognized to be a microorganism potentially more virulent than other coagulase-negative staphylococci. We report the case of a patient who presented with a single, large, right, frontoparietal abscess that evolved despite conventional antibiotic treatment. Bacteremia and endocarditis were excluded. After surgical treatment, S. lugdunensis sensible to trimethoprim-sulfamethoxazole was isolated, and the patient responded favorably to treatment. Although the ability of S. lugdunensis to produce brain abscesses has been recognized, we report a case of a brain abscess in the absence of bacteremia or endocarditis.

Polysaccharide intercellular adhesin in biofilm: structural and regulatory aspects

Staphylococcus aureus and Staphylococcus epidermidis are the leading etiologic agents of implant-related infections. Biofilm formation is the main pathogenetic mechanism leading to the chronicity and irreducibility of infections. The extracellular polymeric substances of staphylococcal biofilms are the polysaccharide intercellular adhesin (PIA), extracellular-DNA, proteins, and amyloid fibrils. PIA is a poly-β(1-6)-N-acetylglucosamine (PNAG), partially deacetylated, positively charged, whose synthesis is mediated by the icaADBC locus. DNA sequences homologous to ica locus are present in many coagulase-negative staphylococcal species, among which S. lugdunensis, however, produces a biofilm prevalently consisting of proteins. The product of icaA is an N-acetylglucosaminyltransferase that synthetizes PIA oligomers from UDP-N-acetylglucosamine. The product of icaD gives optimal efficiency to IcaA. The product of icaC is involved in the externalization of the nascent polysaccharide. The product of icaB is an N-deacetylase responsible for the partial deacetylation of PIA. The expression of ica locus is affected by environmental conditions. In S. aureus and S. epidermidis ica-independent alternative mechanisms of biofilm production have been described. S. epidermidis and S. aureus undergo to a phase variation for the biofilm production that has been ascribed, in turn, to the transposition of an insertion sequence in the icaC gene or to the expansion/contraction of a tandem repeat naturally harbored within icaC. A role is played by the quorum sensing system, which negatively regulates biofilm formation, favoring the dispersal phase that disseminates bacteria to new infection sites. Interfering with the QS system is a much debated strategy to combat biofilm-related infections. In the search of vaccines against staphylococcal infections deacetylated PNAG retained on the surface of S. aureus favors opsonophagocytosis and is a potential candidate for immune-protection.

Staphylococcus lugdunensis: A Rare Pathogen for Osteomyelitis of the Foot

Staphylococcus lugdunensis is an aggressive gram-positive bacteria that can lead to devastating infections in humans. S. lugdunensis has been associated with rare cases of osteomyelitis of the vertebra, prosthetic implants, and endocarditis. Reports of this organism associated with osteomyelitis of the foot or ankle have been infrequent. We present a unique case of acute osteomyelitis of a foot caused by S. lugdunensis after a patient stepped on a thorn. Our case is unique, because the radiographic changes were noted within 4 days, despite normal plain films and magnetic resonance images on the day of admission. This finding suggests the aggressiveness and virulence of S. lugdunensis. In addition, we report the first case of foot osteomyelitis as a result of isolated S. lugdunensis that involved 2 distinct specimens with 2 different antibiotic sensitivity reports.

Staphylococcus lugdunensis: Novel Organism causing Cochlear Implant Infection

A majority of cochlear implant infections are caused by Staphylococcus aureus or Pseudomonas aeruginosa. Reported here is a pediatric patient with a cochlear implant infection caused by methicillin-resistant Staphylococcus lugdunensis, a coagulase-negative Staphylococcus that has only recently been determined to be clinically relevant (1988). Unlike other coagulase-negative Staphylococcus, it is more aggressive, carrying a greater potential for tissue destruction. In pediatrics, the organism is uncommon, poorly described, and generally pan-susceptible. Described herein is the presentation and management of this unusual organism in a pediatric setting.

A review of the biomaterials technologies for infection-resistant surfaces

Anti-infective biomaterials need to be tailored according to the specific clinical application. All their properties have to be tuned to achieve the best anti-infective performance together with safe biocompatibility and appropriate tissue interactions. Innovative technologies are developing new biomaterials and surfaces endowed with anti-infective properties, relying either on antifouling, or bactericidal, or antibiofilm activities. This review aims at thoroughly surveying the numerous classes of antibacterial biomaterials and the underlying strategies behind them. Bacteria repelling and antiadhesive surfaces, materials with intrinsic antibacterial properties, antibacterial coatings, nanostructured materials, and molecules interfering with bacterial biofilm are considered. Among the new strategies, the use of phages or of antisense peptide nucleic acids are discussed, as well as the possibility to modulate the local immune response by active cytokines. Overall, there is a wealth of technical solutions to contrast the establishment of an implant infection. Many of them exhibit a great potential in preclinical models. The lack of well-structured prospective multicenter clinical trials hinders the achievement of conclusive data on the efficacy and comparative performance of anti-infective biomaterials.