Characterization of coagulase-negative staphylococci isolated from patients with infected hip prostheses: use of phenotypic and genotypic analyses, including tests for the presence of the ica operon

Correlation Analysis between Chronic Osteomyelitis and Bacterial Biofilm

Objective

To study the role of bacterial biofilm (BBF) in the formation of chronic osteomyelitis and its prevention and treatment.

Methods

In this paper, a large amount of relevant literature was searched for analysis and summary, and the key words "chronic osteomyelitis," "bacterial biofilm," "infection," and "debridement" were searched in databases, mainly CNKI, Wanfang, and Wipu. The search was conducted until December 2020. The role of bacterial biofilm formation in chronic osteomyelitis and its prevention were analyzed.

Results

Chronic osteomyelitis is formed mainly due to poor blood supply and drug-resistant bacteria, of which cellular biofilm is the most important cause. BBF forms on the surface of necrotic soft tissue and bone tissue, which has a protective effect on bacteria and greatly enhances their resistance to antibiotics, leading to difficulties in complete bacterial clearance and recurrent infections in osteomyelitis.

Conclusion

Through an in-depth study of the molecular biology and signal transduction of osteomyelitis biofilm, antibiotic biofilm treatment strategies and surgical debridement remain the focus of clinical translation of chronic osteomyelitis.

Characterization of methicillin-resistant Staphylococcus aureus strains in sewage treatment plants in Tehran, Iran

Multidrug-resistant Staphylococcus aureus strains have been commonly found in hospitals and communities causing wide ranges of infections among humans and animals. Typing of these strains is a key factor to reveal their clonal dissemination in different regions. We investigated the prevalence and dissemination of different clonal groups of S. aureus with resistance phenotype to multiple antibiotics in two sewage treatment plants (STPs) in Tehran, Iran over four sampling occasions. A total of 576 S. aureus were isolated from the inlet, sludge and outlet. Of these, 80 were identified as methicillin-resistant S. aureus (MRSA) and were further characterized using a combination of Phene Plate (PhP) typing, staphylococcal cassette chromosome mec (SCCmec), ccr types, prophage and antibiotic-resistant profiling. In all, eight common type (CT) and 13 single PhP type were identified in both STPs, with one major CT accounting for 38.8% of the MRSA strains. These strains belonged to three prophage patterns and five prophage types with SCCmec type III being the predominant type. Resistance to 11 out of the 17 antibiotics tested was significantly (P < 0.0059) higher among the MRSA isolates than methicillin-sensitive S. aureus (MSSA) strains. The persistence of the strains in samples collected from the outlet of both STPs was 31.9% for MRSA and 23.1% for MSSA. These data indicated that while the sewage treatment process, in general, is still useful for removing most MRSA populations, some strains with SCCmec type III may have a better ability to survive the STP process.

Plantaricin NC8 αβ exerts potent antimicrobial activity against Staphylococcus spp. and enhances the effects of antibiotics

The use of conventional antibiotics has substantial clinical efficacy, however these vital antimicrobial agents are becoming less effective due to the dramatic increase in antibiotic-resistant bacteria. Novel approaches to combat bacterial infections are urgently needed and bacteriocins represent a promising alternative. In this study, the activities of the two-peptide bacteriocin PLNC8 αβ were investigated against different Staphylococcus spp. The peptide sequences of PLNC8 α and β were modified, either through truncation or replacement of all L-amino acids with D-amino acids. Both L- and D-PLNC8 αβ caused rapid disruption of lipid membrane integrity and were effective against both susceptible and antibiotic resistant strains. The D-enantiomer was stable against proteolytic degradation by trypsin compared to the L-enantiomer. Of the truncated peptides, β1–22, β7–34 and β1–20 retained an inhibitory activity. The peptides diffused rapidly (2 min) through the bacterial cell wall and permeabilized the cell membrane, causing swelling with a disorganized peptidoglycan layer. Interestingly, sub-MIC concentrations of PLNC8 αβ substantially enhanced the effects of different antibiotics in an additive or synergistic manner. This study shows that PLNC8 αβ is active against Staphylococcus spp. and may be developed as adjuvant in combination therapy to potentiate the effects of antibiotics and reduce their overall use.

Plasma Fibrin Degradation Product and D-Dimer Are of Limited Value for Diagnosing Periprosthetic Joint Infection

BACKGROUND

Although the Musculoskeletal Infection Society introduced the use of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) as inflammatory markers for diagnosing periprosthetic joint infection (PJI), no single blood marker reliably detects infection before revision arthroplasty. We therefore posed 2 questions: (1) Are fibrin degradation product (FDP) and D-dimer of value for diagnosing PJI before revision arthroplasty? (2) What are their sensitivity and specificity for that purpose?

METHODS

To answer these questions, we retrospectively enrolled 318 patients (129 with PJI [group A], 189 with aseptic mechanical failure [group B]) who underwent revision arthroplasty during 2013-2018. Receiver operating characteristic curves were used to determine maximum sensitivity and specificity of the 2 markers. Inflammatory and fibrinolytic markers were evaluated based on (1) the Tsukayama-type infection present and (2) the 3 most common PJI-related pathogens.

RESULTS

FDP and D-dimer levels were higher in group A than in group B: 4.97 ± 2.83 vs 4.14 ± 2.67 mg/L and 2.14 ± 2.01 vs 1.51 ± 1.37 mg/L fibrinogen equivalent units (FEU), respectively (both P < .05). Based on the Youden index, 2.95 mg/L and 1.02 mg/L FEU are the optimal FDP and D-dimer predictive cutoffs, respectively, for diagnosing PJI. Sensitivity and specificity, respectively, were 65.12% and 60.33% (FDP) and 68.29% and 50.70% (D-dimer). ESR, CRP, and interleukin-6 values were diagnostically superior to those of FDP and D-dimer.

CONCLUSION

The value of plasma FDP and D-dimer for diagnosing PJI is limited compared with traditional inflammatory markers (ESR, CRP, interleukin-6) before revision arthroplasty.

Rapid discrimination of Staphylococcus epidermidis genotypes in a routine clinical microbiological laboratory using single nucleotide polymorphisms in housekeeping genes

PURPOSE

Staphylococcus epidermidis colonies often display several morphologies and antimicrobial susceptibility patterns when cultured from device-related infections, and may represent one or multiple genotypes. Genotyping may be helpful in the clinical interpretation, but is time consuming and expensive. We wanted to establish a method for rapid discrimination of S. epidermidis genotypes for use in a routine microbiology laboratory.

METHODOLOGY

A real-time PCR targeting eight discriminatory class I or II single-nucleotide polymorphisms (SNPs) in six of the seven housekeeping genes was constructed. Post PCR, high-resolution melt (HRM) analysis using EvaGreen as fluorophore discriminated amplicons based on their percentage GC content.

RESULTS

In silico, 42 representative sequence types (STs), including all major MLST group and subgroup founders, were separated into 23 different cluster profiles with a Simpson's index of diversity of 0.97. By HRM-PCR, 11 commonly encountered hospital and outbreak STs were separated into eight HRM patterns.

CONCLUSION

This method can rapidly establish whether S. epidermidis strains belong to different genotypes. It can be used in patients with S. epidermidis infections, as an aid in outbreak investigations and to select strains for investigation with more discriminatory methods, saving workload and costs. Results may be obtained the same day as culture results. Its strength lies mainly in indicating differences, as some STs may have the same melt profile. Changes in S. epidermidis epidemiology may warrant alterations in the inclusion of SNPs. We believe this method can reduce the threshold for performing genotyping analysis on an increasingly important nosocomial pathogen.

Biofilm formation and antimicrobial susceptibility of staphylococci and enterococci from osteomyelitis associated with percutaneous orthopaedic implants

Staphylococci and enterococci account for most deep infections associated with bone-anchored percutaneous implants for amputation treatment. Implant-associated infections are difficult to treat; therefore, it is important to investigate if these infections have a biofilm origin and to determine the biofilm antimicrobial susceptibility to improve treatment strategies. The aims were: (i) to test a novel combination of the Calgary biofilm device and a custom-made susceptibility MIC plate (Sensititre^® ), (ii) to determine the biofilm formation and antimicrobial resistance in clinical isolates causing implant-associated osteomyelitis, and (iii) to describe the associated clinical outcome. Enterococci and staphylococci were characterized by microtitre plate assay, Congo Red Agar plate test, and PCR. Biofilm susceptibility to 10 antimicrobials and its relationship to treatment outcomes were determined. The majority of the strains produced biofilm in vitro showing inter- and intraspecies differences. Biofilms showed a significantly increased antimicrobial resistance compared with their planktonic counterparts. Slime-producing strains tolerated significantly higher antimicrobial concentrations compared with non-producers. All seven staphylococcal strains carried ica genes, but two did not produce slime. The degree of biofilm formation and up-regulated antibiotic resistance may translate into a variable risk of treatment failure. This new method set-up allows for the reproducible determination of minimum biofilm eradication concentration of antimicrobial agents, which may guide future antimicrobial treatment decisions in orthopaedic implant-associated infection. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2630-2640, 2017.

Significance of Staphylococcus epidermidis in Health Care-Associated Infections, from Contaminant to Clinically Relevant Pathogen: This Is a Wake-Up Call!

Coagulase-negative staphylococci, particularly Staphylococcus epidermidis, have been recognized as an important cause of health care-associated infections. Concurrently, S. epidermidis is a common contaminant in clinical cultures, which poses a diagnostic challenge. An article in this issue of Journal of Clinical Microbiology (I. Tolo, J. C. Thomas, R. S. B. Fischer, E. L. Brown, B. M. Gray, and D. A. Robinson, J Clin Microbiol 54:1711-1719, 2015, http://dx.doi.org/10.1128/JCM.03345-15) describes a rapid single nucleotide polymorphism-based assay for distinguishing between S. epidermidis isolates from hospital and nonhospital sources, which represents an important contribution to the characterization and understanding of S. epidermidis health care-associated infections.

Prosthetic joint infection

Prosthetic joint infection (PJI) is a tremendous burden for individual patients as well as the global health care industry. While a small minority of joint arthroplasties will become infected, appropriate recognition and management are critical to preserve or restore adequate function and prevent excess morbidity. In this review, we describe the reported risk factors for and clinical manifestations of PJI. We discuss the pathogenesis of PJI and the numerous microorganisms that can cause this devastating infection. The recently proposed consensus definitions of PJI and approaches to accurate diagnosis are reviewed in detail. An overview of the treatment and prevention of this challenging condition is provided.

Antimicrobial activity of tigecycline alone or in combination with rifampin against Staphylococcus epidermidis in biofilm

Staphylococcus epidermidis is a commensal inhabitant of the healthy human skin, but in the recent years, it has been recognized as a nosocomial pathogen especially in immunocompromised patients. The pathogenesis of S. epidermidis is thought to be based on its capacity to form biofilms on the surface of medical devices, where bacterial cells may persist, protected from host defence and antimicrobial agents. Rifampin has been shown to be one of the most active antimicrobial agents in the eradication of the staphylococcal biofilm. However, this antibiotic should not be used in monotherapy. Therefore, one of the objectives of our research was to study the efficacy of the tigecycline/rifampin combination against methicillin-resistant S. epidermidis embedded in biofilms. Of the 80 clinically significant S. epidermidis isolates, 75 strains possess the ability to form a biofilm. These bacteria formed the biofilm via ica-dependent mechanisms. However, other biofilm-associated genes, including aap (encoding accumulation-associated protein) and bhp (coding cell wall-associated protein), were present in 85 and 29 % of isolates, respectively. The biofilm structures of S. epidermidis strains were also analyzed in confocal laser scanning microscopy (CLSM) and the obtained image demonstrated differences in their architecture. In vitro studies showed that the MIC value for tigecycline against S. epidermidis growing in the biofilm ranged from 0.125 to 2 μg/mL. Tigecycline in combination with rifampin demonstrated higher activity against bacteria embedded in biofilms than tigecycline alone.

Comparison of Staphylococcus epidermidis isolated from prosthetic joint infections and commensal isolates in regard to antibiotic susceptibility, agr type, biofilm production, and epidemiology

Staphylococcus epidermidis is the predominant bacterial species in the normal flora of the human skin and superficial mucosal membranes. However, it has also emerged as the most important pathogen in infections related to foreign-body materials, such as prosthetic joints and heart valves. The aims of this study were to characterise S. epidermidis isolated from prosthetic joint infections (PJI; n=61) and commensal isolates from healthy individuals (n=24) in regard to antimicrobial sensitivity, agr type, hld gene presence, biofilm production including presence of ica and aap genes involved in the biofilm formation process and epidemiology using both phenotypic (the PhenePlate-system) and genotypic [multilocus sequence typing (MLST)] methods. Among the PJI isolates, the majority (67%) were multidrug-resistant. Two major clusters of PJI isolates could be identified; 44% belonged to MLST sequence type (ST) 2, all but one were of agr type 1, and 31% were assigned ST215 and were of agr type 3. Of the commensal isolates, only one isolate was multidrug-resistant, and they were more molecular epidemiologically diverse with mainly MLST singletons and a maximum of 3 isolates assigned to the identical ST. Biofilm production was detected in 41% of the PJI isolates and 58% of the commensal isolates, with the aap gene (95%) more frequently detected than the ica genes (62%) in the biofilm-positive isolates. In conclusion, S. epidermidis isolated from PJIs and commensal isolates differed regarding antimicrobial sensitivity and molecular epidemiological typing using MLST, but not substantially in the distribution of agr types, biofilm production, or the presence of ica and aap genes.

An extracellular Staphylococcus epidermidis polysaccharide: relation to Polysaccharide Intercellular Adhesin and its implication in phagocytosis

BACKGROUND

The skin commensal and opportunistic pathogen Staphylococcus epidermidis is a leading cause of hospital-acquired and biomaterial-associated infections. The polysaccharide intercellular adhesin (PIA), a homoglycan composed of β-1,6-linked N-acetylglucosamine residues, synthesized by enzymes encoded in icaADBC is a major functional factor in biofilm accumulation, promoting virulence in experimental biomaterial-associated S. epidermidis infection. Extracellular mucous layer extracts of S. epidermidis contain another major polysaccharide, referred to as 20-kDa polysaccharide (20-kDaPS), composed mainly out of glucose, N-acetylglucosamine, and being partially sulfated. 20-kDaPS antiserum prevents adhesion of S. epidermidis on endothelial cells and development of experimental keratitis in rabbits. Here we provide experimental evidence that 20-kDaPS and PIA represent distinct molecules and that 20-kDaPS is implicated in endocytosis of S. epidermidis bacterial cells by human monocyte-derived macrophages.

RESULTS

Analysis of 75 clinical coagulase-negative staphylococci from blood-cultures and central venous catheter tips indicated that 20-kDaPS is expressed exclusively in S. epidermidis but not in other coagulase-negative staphylococcal species. Tn917-insertion in various locations in icaADBC in mutants M10, M22, M23, and M24 of S. epidermidis 1457 are abolished for PIA synthesis, while 20-kDaPS expression appears unaltered as compared to wild-type strains using specific anti-PIA and anti-20-kDaPS antisera. While periodate oxidation and dispersin B treatments abolish immuno-reactivity and intercellular adhesive properties of PIA, no abrogative activity is exerted towards 20-kDaPS immunochemical reactivity following these treatments. PIA polysaccharide I-containing fractions eluting from Q-Sepharose were devoid of detectable 20-kDaPS using specific ELISA. Preincubation of non-20-kDaPS-producing clinical strain with increasing amounts of 20-kDaPS inhibits endocytosis by human macrophages, whereas, preincubation of 20-kDaPS-producing strain ATCC35983 with 20-kDaPS antiserum enhances bacterial endocytosis by human macrophages.

CONCLUSIONS

In conclusion, icaADBC is not involved in 20-kDaPS synthesis, while the chemical and chromatographic properties of PIA and 20-kDaPS are distinct. 20-kDaPS exhibits anti-phagocytic properties, whereas, 20-kDaPS antiserum may have a beneficial effect on combating infection by 20-kDaPS-producing S. epidermidis.

Alteration of the colonization pattern of coagulase-negative staphylococci in patients undergoing treatment for hematological malignancy

The aim was to prospectively describe the colonization pattern of coagulase-negative staphylococci (CoNS) and the relationship between colonizing and invasive CoNS isolates among patients undergoing treatment for hematological malignancy. Fourteen newly diagnosed patients were included with either multiple myeloma or acute leukemia. Patients were repeatedly sampled from nares, throat, axillae, and perineum, and the CoNS isolates obtained were phenotypically characterized together with blood isolates of CoNS using the PhenePlate system (PhP). During the treatment a gradual reduction in the heterogeneity of colonizing CoNS was observed as well as an inter-patient accumulation of phenotypically related and multi-drug-resistant CoNS. These clusters of CoNS persisted for 2-3 months after the end of therapy. Ten positive blood cultures of CoNS were obtained and in the majority of these cases CoNS of the same PhP type were found in superficial cultures collected prior to the blood culture sampling. In conclusion, the study shows that therapy for hematological malignancy is associated with a homogenization of colonizing CoNS isolates and that this acquired flora of CoNS is persistent several months after the end of therapy. Furthermore, the results suggest that the source of bloodstream infections of CoNS in hematological patients is colonizing CoNS of the skin and mucosa.

Resolution of Staphylococcus aureus biofilm infection using vaccination and antibiotic treatment

Staphylococcus aureus infections, particularly those from methicillin-resistant strains (i.e., MRSA), are reaching epidemic proportions, with no effective vaccine available. The vast number and transient expression of virulence factors in the infectious course of this pathogen have made the discovery of protective antigens particularly difficult. In addition, the divergent planktonic and biofilm modes of growth with their accompanying proteomic changes also demonstrate significant hindrances to vaccine development. In this study, a multicomponent vaccine was evaluated for its ability to clear a staphylococcal biofilm infection. Antigens (glucosaminidase, an ABC transporter lipoprotein, a conserved hypothetical protein, and a conserved lipoprotein) were chosen since they were found in previous studies to have upregulated and sustained expression in a biofilm, both in vitro and in vivo. Antibodies against these antigens were first used in microscopy studies to localize their expression in in vitro biofilms. Each of the four antigens showed heterogeneous production in various locations within the complex biofilm community in the biofilm. Based upon these studies, the four antigens were delivered simultaneously as a quadrivalent vaccine in order to compensate for this varied production. In addition, antibiotic treatment was also administered to clear the remaining nonattached planktonic cells since the vaccine antigens may have been biofilm specific. The results demonstrated that when vaccination was coupled with vancomycin treatment in a biofilm model of chronic osteomyelitis in rabbits, clinical and radiographic signs of infection significantly reduced by 67 and 82%, respectively, compared to infected animals that were either treated with vancomycin or left untreated. In contrast, vaccination alone resulted in a modest, and nonsignificant, decrease in clinical (34% reduction) and radiographic signs (9% reduction) of infection, compared to nonvaccinated animal groups untreated or treated with vancomycin. Lastly, MRSA biofilm infections were significantly cleared in 87.5% of vaccinated and antibiotic-treated animals, while antibiotics or vaccine alone could not significantly clear infection compared to controls (55.6, 22.2, and 33.3% clearance rates, respectively). This approach to vaccine development may lead to the generation of vaccines against other pathogenic biofilm bacteria.

Partial atlE sequencing of Staphylococcus epidermidis strains from prosthetic joint infections

Partial atlE sequencing (atlE nucleotides 2782 to 3114 [atlE(2782-3114)]) was performed in 41 Staphylococcus epidermidis isolates from prosthetic joint infections (PJIs) and 44 isolates from skin as controls. The atlE(2782-3114) allele 1 (type strain sequence) was significantly more frequent in PJI strains (38/41 versus 29/44 in controls; P = 0.0023). Most PJI strains were positive for mecA, icaA/icaD, and IS256, and most belonged to the sequence type 27 subgroup, suggesting the involvement of few related clones.

Biofilm formation by Propionibacterium acnes is a characteristic of invasive isolates

Propionibacterium acnes is a common and probably underestimated cause of delayed joint prosthesis infection. Bacterial biofilm formation is central in the pathogenesis of infections related to foreign material, and P. acnes has been shown to form biofilm both in vitro and in vivo. Here, biofilm formation by 93 P. acnes isolates, either from invasive infections (n = 45) or from the skin of healthy people (n = 48), was analysed. The majority of isolates from deep infections produced biofilm in a microtitre model of biofilm formation, whereas the skin isolates were poor biofilm producers (p <0.001 for a difference). This indicates a role for biofilm formation in P. acnes virulence. The type distribution, as determined by sequencing of recA, was similar among isolates isolated from skin and from deep infections, demonstrating that P. acnes isolates with different genetic backgrounds have pathogenic potential. The biofilm formed on plastic and on bone cement was analysed by scanning electron microscopy (EM) and by transmission EM. The biofilm was seen as a 10-mum-thick layer covering the bacteria and was composed of filamentous as well as more amorphous structures. Interestingly, the presence of human plasma in solution or at the plastic surface inhibits biofilm formation, which could explain why P. acnes primarily infect plasma-poor environments of, for example, joint prostheses and cerebrospinal shunts. This work underlines the importance of biofilm formation in P. acnes pathogenesis, and shows that biofilm formation should be considered in the diagnosis and treatment of invasive P. acnes infections.

Osteomyelitis and the role of biofilms in chronic infection

Understanding the mechanisms implicated in the initial attachment, development, and maturation of a biofilm phenotype are of tremendous importance for their effect on the medical, industrial, and public health arenas. This review explores the current understanding of the nature of biofilms and the impact that molecular interactions between the bacteria themselves, as well as between bacteria and the host, may have on biofilm development and phenotype using the nonmotile Gram-positive coccus, Staphylococcus aureus, as an example.