Prevalence of genes encoding for staphylococcal leukocidal toxins among clinical isolates of Staphylococcus aureus from implant orthopedic infections

Comparison of Automated Ribotyping, spa Typing, and MLST in 108 Clinical Isolates of Staphylococcus aureus from Orthopedic Infections

108 isolates of Staphylococcus aureus, belonging to six large ribogroups according to the automated Ribo-Printer^® system, were studied with two highly used molecular methods for epidemiological studies, namely multi-locus sequence typing (MLST) and spa typing, followed by BURP and eBURST v3 analysis for clustering spa types and sequence (ST) types. The aim was to evaluate whether automated ribotyping could be considered a useful screening tool for identifying S. aureus genetic lineages with respect to spa typing and MLST. Clarifying the relationship of riboprinting with these typing methods and establishing whether ribogroups fit single clonal complexes were two main objectives. Further information on the genetic profile of the isolates was obtained from agr typing and the search for the mecA, tst genes, and the IS256 insertion sequence. Automated ribotyping has been shown to predict spa clonal complexes and MLST clonal complexes. The high cost and lower discriminatory power of automated ribotyping compared to spa and MSLT typing could be an obstacle to fine genotyping analyzes, especially when high discriminatory power is required. On the other hand, numerous advantages such as automation, ease and speed of execution, stability, typeability and reproducibility make ribotyping a reliable method to be juxtaposed to gold standard methods.

Epidemiology, resistance characteristics, virulence determinants, and treatment outcomes of Staphylococcus aureus bone and joint infections: a one-year prospective study at a tertiary care hospital in India

PURPOSE

The study was aimed to explore the differences between the Staphylococcus aureus osteosynthesis-associated infection (OAI) and non-implant related infections (NIRI) in terms of epidemiology, resistance characteristics, virulence determinants, treatment, risk factors, and outcome.

METHODS

A prospective study was conducted from 2018 through 2019. The phenotypic and genotypic characterization of S. aureus, risk factors, treatment, and outcome were compared.

RESULTS

A total of 60 patients were included. 50% had OAIs (70%) (p = .045). Overall, MRSA (OR 0.69; p = .020) and old age (OR 0.95; p = 0.035) were the important risk factors. Implanted patients presented with the features of chronic osteomyelitis (93.3%, p = 0.01). NIRI cases composed of only 66.7% of OM, and 55% of them were acute. OAI isolates were more frequently luk gene positives (50%) than isolates from the NIRI group (33.3%). Patients with OAI by luk positive isolates significantly had prolonged hospital stay (p = 0.043; OR-0.96, CI-0.91-1.0). Most of the NIRIs (60%) managed with antibiotics, but frequent surgical intervention (OR 10.68; p = .024) with prolonged systemic antibiotics (OR 1.07; p = .029) helped all OAIs to recover. Patients without implants were recovered in a higher number (83.3%).

CONCLUSION

Our study highlighted that the differences exist between the OAI and NIRI, specifically in terms of clinical features, distribution of luk genes, treatment approach, and outcome. Risk factors for both types of infection remained the same.

Anti-staphylococcus Antibiotics Interfere With the Transcription of Leucocidin ED Gene in Staphylococcus aureus Strain Newman

Antibiotics have been described to modulate bacterial virulence gene expression. This study aimed to assess the changes caused by anti-Staphylococcus agents in the transcription of leucocidin ED (lukED) gene of Staphylococcus aureus strain Newman in vitro and in vivo and to determine whether the altered expression is agr dependent. The bacteria were exposed to subinhibitory concentrations [1/2, 1/4, or 1/8 minimal inhibitory concentration (MIC)] of 11 antibiotics, and the expression of lukE and agr-effector RNAIII was determined using qRT-PCR. In vivo experiments were performed to evaluate the impact exerted by six representative antibiotics on the transcription of both genes. Molecular analysis showed that in vitro lukE transcription was dramatically promoted in the Newman strain exposed to sub-MICs of vancomycin, trimethoprim-sulfamethoxazole, clindamycin, gentamicin, daptomycin, and ciprofloxacin and considerably reduced when stimulated by cefazolin, erythromycin, rifampicin, tigecycline, and linezolid. In the murine abscess model, tigecycline significantly decreased the transcription of lukE and the bacterial numbers, whereas vancomycin increased them; although cefazolin increased the lukE expression (contrary to the in vitro effect), it had a remarkable role in reducing bacterial load. The correspondence analysis shows that RNAIII expression varied under seven of 11 antibiotics in vitro, and six drugs in vivo were consistent with lukE transcripts. In conclusion, our data show that anti-Staphylococcus antibiotics exert modulatory effects on lukE expression in vitro and/or in vivo, and the changed expression caused by some drugs may be involved with agr activity, thus providing a guide to choose appropriate agents to avoid promoting bacterial virulence in lukED-positive S. aureus infections.

Panton-Valentine Leukocidin Gene Detected in a Staphylococcus Aureus Strain Isolated from a Knee Arthroprosthesis Infection

This report focuses on the molecular characterization of a Staphylococcus aureus strain isolated from a knee arthroprosthesis infection and recognized retrospectively as a carrier of the Panton-Valentine leukocidin gene. The stored microbiological isolate, which belonged to the strain collection of the Research Unit on Implant Infections of the Rizzoli Orthopaedic Institute, was retrieved for molecular analysis. Genotyping was carried out, revealing an interesting profile. In addition to the positivity for the Panton-Valentine toxin gene, the results indicated that the isolate belonged to the agr III group and was endowed with bbp and cna genes, both encoding for staphylococcal adhesins that bind bone proteins. The strain had the mecA gene for methicillin resistance, even though it was unable to resist any of the β-lactam or other antibiotics. Its gene configuration matched that of other community-acquired methicillin-resistant and methicillin-susceptible Staphylococcus aureus (CA-MRSA and CA-MSSA) strains which have recently been reported worldwide. As far as we know, this is the first report on a PVL-positive S. aureus strain associated with an orthopedic implant (knee arthroprosthesis) infection.

Combating Implant Infections. Remarks by a Women's Team

Research on implant infections requires cooperative efforts and integration between basic and clinical expertises. An international group of women scientists is acting together in this field. The main research topics of the participants of this group are described. Formation of bacterial biofilms, antibiotic resistance and production of virulence factors like adhesins and toxins are investigated. New biomaterials, coatings and drugs designed to inhibit microbial adhesion are evaluated, and infection-resistant biomaterials are under study, such as a novel heparinizable polycarbonate-urethane (Bionate) or incorporation of diamino-diamide-diol (PIME) to reduce bacterial attachment. The correlation between biofilm production and the accessory-gene-regulator (agr) is investigated in Staphylococcus aureus. The ability to form biofilm has also been shown to be one of the important virulence factors of Enterococcus faecalis, favouring colonization of inert and biological surfaces. The study of quorum sensing has led to the discovery of a quorum sensing inhibitor termed RIP that suppresses staphylococcal biofilm and infections. The immune response and the local defence mechanisms of the host against implant-associated infections, activation and infiltration of immunocompetent cells into the sites of infection have been studied in patients with implant-associated osteomyelitis. Production of monoclonal antibodies (mAbs) as possible vaccines against the staphylococcal collagen-binding MSCRAMMs is in progress. (Int J Artif Organs 2008; 31: 858–64)

Influence of Material and Microtopography on the Development of Local Infection in vivo: Experimental Investigation in Rabbits

Polishing the surface of internal fracture fixation (IFF) implant materials can ease implant removal and reduce irritation to gliding tissues by reducing soft tissue adhesion and bony overgrowth. Thus, polishing the surface of these implants is expected to have significant clinical benefit in certain situations. The aim of the present study was to determine if polishing the surface of an IFF device influences susceptibility to infection.

The local infection rate associated with 4-hole 2.0 mm Synthes® locking compression plates (LCPs) composed of clinically available commercially pure titanium (cpTi) and titanium aluminium niobium (TAN) in their standard microrough form was compared with that of their test polished equivalents and also to clinically available electropolished stainless steel (EPSS). The LCPs were fixed in locking mode onto the tibia of mature, female New Zealand White rabbits and a clinical strain of Staphylococcus aureus was added to the implantation site. Twenty eight days after surgery the rabbits were euthanized and assessed for infection. The rank order based on descending ID50 was; polished TAN, standard TAN, standard cpTi, EPSS and finally polished cpTi, however, the ID50 values did not differ greatly between the groups with the same material. Using the LCP model in locking mode, polishing the surface of both cpTi and TAN was not found to influence the susceptibility to infection in our animal model.

Perspectives on DNA Vaccines. Targeting Staphylococcal Adhesins to Prevent Implant Infections

DNA vaccines consist of a plasmid DNA genetically engineered to produce one or more proteins able to elicit protective immune responses against virulence factors of infectious pathogens. Once introduced into the cells of the host, a DNA vaccine induces a high production of antigens by the endogenous presence of the peptide codifying gene; improves antigen processing and presentation; may be able to simultaneously co-express multiple antigenic molecules; and, lastly, switches on both humoral and cellular immune responses. In this mini-review, we underscore the advantageous characteristics of DNA vaccines compared with traditional ones and provide summaries of some of the more recent studies on them, mainly focusing the possibility of their use in targeting the staphylococcal adhesins that play a key role in the first adhesive phase of implant infections.

Antibodies to S. aureus LukS-PV Attenuated Subunit Vaccine Neutralize a Broad Spectrum of Canonical and Non-Canonical Bicomponent Leukotoxin Pairs

S. aureus vaccine development has proven particularly difficult. The conventional approach to achieve sterile immunity through opsonophagocytic killing has been largely unsuccessful. S. aureus is highly toxigenic and a great body of evidence suggests that a successful future vaccine for this organism should target extracellular toxins which are responsible for host tissue destruction and immunosuppression. Major staphylococcal toxins are alpha toxin (a single subunit hemolysin) along with a group of bicomponent pore-forming toxins (BCPFT), namely Panton-Valentine leukocidin (PVL), gamma hemolysins (HlgCB and AB), LukAB and LukED. In our previous report, an attenuated mutant of LukS-PV (PVL- S subunit) named as “LukS-mut9” elicited high immunogenic response as well as provided a significant protection in a mouse sepsis model. Recent discovery of PVL receptors shows that mice lack receptors for this toxin, thus the reported protection of mice with the PVL vaccine may relate to cross protective responses against other homologous toxins. This manuscript addresses this issue by demonstrating that polyclonal antibody generated by LukS-mut9 can neutralize other canonical and non-canonical leukotoxin pairs. In this report, we also demonstrated that several potent toxins can be created by non-canonical pairing of subunits. Out of 5 pairs of canonical and 8 pairs of non-canonical toxins tested, anti-LukS-mut9 polyclonal antibodies neutralized all except for LukAB. We also studied the potential hemolytic activities of canonical and noncanonical pairs among biocomponent toxins and discovered that a novel non-canonical pair consisting of HlgA and LukD is a highly toxic combination. This pair can lyse RBC from different species including human blood far better than alpha hemolysin. Moreover, to follow-up our last report, we explored the correlation between the levels of pre-existing antibodies to new sets of leukotoxins subunits and clinical outcomes in adult patients with S. aureus bacteremia. We found that there is an inversed correlation between the antibody titer to sepsis for leukotoxins LukS-mut9, LukF-PV, HlgC, LukE and LukAB, suggesting the risk of sepsis was significantly lower in the patients with higher antibody titer against those toxins.

Internalization by osteoblasts of two Staphylococcus aureus clinical isolates differing in their adhesin gene pattern

Staphylococcus aureus is the leading etiologic agent of implant orthopedic infections. Until recently S. aureus was considered a mere extracellular pathogen; it then turned out to be able to invade eukaryotic cells. Adhesion of S. aureus to peri-prosthesis tissues represents the starting of the infection pathogenesis and the first step of the subsequent internalization of S. aureus by host cells. In the present work the experimental observations on two epidemic clinical strains differing in their adhesin pattern demonstrate the crucial role of the fibronectin-binding protein A in the internalization process and suggest that CNA and Bbp adhesins can play a synergistic role by acting in the initial adhesion of S. aureus to osteoblasts, thus favoring the subsequent FnBPA-mediated internalization.

The prevalence of genes encoding leukocidins in Staphylococcus aureus strains resistant and sensitive to methicillin isolated from burn patients in Taleghani Hospital, Ahvaz, Iran

BACKGROUND

Staphylococcus aureus has been recognized as an important human pathogen and is the major cause of nosocomial infections. Various strains of S. aureus produce bicomponent toxins such as LukE/D, and PVL. The toxins subunits bind to leukocyte cell membrane inducing trans-membrane pore formation and subsequent cell lysis. PVL is an example of these toxins and causes leukocyte destruction and tissue necrosis. It seems that S. aureus strains comprising LukE/D and PVL genes are more important in the disease process and associated with severe skin diseases, fatal pneumonia and osteomyelitis with high morbidity and mortality.

OBJECTIVE

The aim of this study was to determine the prevalence of genes encoding leukocidins in S. aureus strains resistant and sensitive to methicillin isolated from burn patients in Taleghani hospital, Ahvaz, Iran.

METHODS

In an 11-month study, 203 staphylococci isolates were collected from burn patients. The isolates were examined by traditional culture method for detecting S. aureus strains and further confirmation with standard biochemical tests including catalase, coagulase and DNase. DNA was extracted from bacterial colony by simple boiling method. Using template DNA, the polymerase chain reaction technique (PCR) was used to detect mecA gene for detecting methicillin resistant S. aureus strains (MRSA), PVL and Luk-E/D genes.

RESULTS

Ninety-five (46.8%) out of total tested isolates were identified as S. aureus. Based on the results from PCR, 83 strains (87.36%), were mecA positive, so they were resistant to methicillin and the rest were sensitive to methicillin (MSSA). The prevalence of PVL and LukE/D genes in MRSA strains were (7.23%) and (66.26%) respectively. While this prevalence were (33.3%) for both genes in MSSA strains.

CONCLUSION

There were PVL and LukE/D positive MRSA isolates with high prevalence in evaluated hospital. Since resulting diseases from these bacteria are severe and may even lead to death, the prevention of disease progress is desired by early diagnosis and proper treatment.

Polymorphisms of agr locus correspond to distinct genetic patterns of virulence in Staphylococcus aureus clinical isolates from orthopedic implant infections

Staphylococcus aureus is the leading etiologic agent of orthopedic implant infections. It is endowed with the accessory gene regulator (agr) locus that modulates expression of many virulence genes. Four allelic groups of agr have been recognized within this bacterial species. Here, 200 S. aureus isolates from orthopedic implant infections, typed at the start depending on their agr group, were screened for the presence of adhesin and leukotoxin genes. Interestingly, specific virulence gene patterns emerged in association with agr groups. The most frequently observed agr groups, agr I and agr II, were associated with the presence of sdrE, fib (agr II more than agr I), fnbB (agr I more than agr II), and lukE/lukD (agr II more than agr I). The third more frequent agr group, agr III, differed clearly from agr I and II, exhibiting high prevalence of bbp, generally not harbored by agr I and II, and copresence of bbp with cna, whereas high prevalence of the tandem sdrE/fib marked definitely agr II (91% of agr II isolates), and, though less strictly, agr I, in which prevailed the peculiar fib/fnbB pattern. The only four isolates belonging to agr IV showed full copresence of bbp with fib. Results point out distinct patterns of virulence genes, which underlie distinct evolutive strategies associated to agr groups in S. aureus causing orthopedic implant infections.

Infection in fracture fixation: can we influence infection rates through implant design?

Musculoskeletal infection is one of the most common complications associated with surgical fixation of bones fractured during trauma. These infections usually involve bacterial colonisation and biofilm formation on the fracture fixation device itself, as well as infection of the surrounding tissues. Antibiotic prophylaxis, wound debridement and postsurgical care can reduce the incidence of, but do not prevent, these infections. Much research and development has been focussed on ways to further reduce the incidence of infection and in the following short review we describe our experiences investigating the contribution of the basic design of fracture fixation devices on the susceptibility to infection. It has been shown in animal studies that device size, shape, mode of action and material and topography play an interrelated role in the susceptibility to infection. Although direct extrapolation from animal studies to the clinical setting is difficult, close consideration of the design factors that can reduce the incidence of infection in animal models is expected to help minimise the incidence of infection associated with any clinically implemented fracture fixation device.

Molecular epidemiology of Staphylococcus aureus from implant orthopaedic infections: ribotypes, agr polymorphism, leukocidal toxins and antibiotic resistance

Staphylococcus aureus is a leading pathogen of implant-related infections. In the field of biomaterials a variety of alternative approaches are currently proposed for prophylaxis and treatment of implant infections, but little is known on the role of the different pathogenetic mechanisms and spreading strategies that lead selected S. aureus clones to prevail and become epidemic. This study aimed at identifying and characterizing the major clones in a collection of 200 S. aureus isolates from implant orthopaedic infections. Strain typing by automated ribotyping identified 98 distinct ribogroups. Ribogroups corresponded to specific accessory gene regulatory (agr) polymorphisms and possessed peculiar arrangements of toxins. The agr type II allele was more represented in epidemic clones, while agr type I in sporadic clones. A clear trend was observed, where epidemic clones resisted antibiotics more than sporadic ones. Conversely, the gene for lukD/lukE leukotoxin, found in 68% of the isolates, was unrelated to the level of clonal spreading. Surprisingly, the isolates of the most prevalent ribogroup were susceptible to almost all antibiotics and never possessed the lukD/lukE gene, thus suggesting the role of factors other than antibiotic resistance and the here investigated toxins in driving the major epidemic clone to the larger success.