[Bone cement as a local antibiotic carrier]

BACKGROUND

There is widespread consensus that adjuvant local use of antimicrobial agents in combination with their systemic administration can better prevent and treat implant-associated musculoskeletal infections. The advantage of local antibiotics lies in their particular pharmacokinetics with initially high antibiotic concentrations at the implant site with only low systemic uptake.

AIM OF TREATMENT

The aim of local application is to protect the foreign bodies directly at the implantation site from bacterial colonization and biofilm formation (prophylaxis) and to support the eradication of an already established infection after surgical debridement (treatment). Since the observations of Prof. Buchholz, bone cement has been the most frequently used local carrier system.

APPLICATION

In cases of infection, surgeons should ideally work together with microbiologists, infectiologists or clinical pharmacists to determine which anti-infective agents are indicated systemically for the patient and which ones are indicated locally with PMMA cement, based on the pathogen(s) and antibiograms. However, for the anti-infective agents administered with bone cement, there is still uncertainty about which agents can be added to this carrier material and at what concentrations. Accordingly, the authors of this review article not only summarize the rationale and evidence for local antibiotic use but also elaborate on the points that must be considered for admixing these agents to the cement.

Patients at a high risk of PJI: Can we reduce the incidence of infection using dual antibiotic-loaded bone cement?

Prosthetic joint infection (PJI) is one of the most devastating complications of orthopedic surgery. However, not all patients are equally at the risk of severe infection. The incidences of PJI vary with the host and surgery-related risk factors. It is now generally accepted that some important medical comorbidities may predispose the patients to a high risk of PJI. Time-consuming and invasive surgical procedures, such as revision arthroplasties, are also associated with a high incidence of PJI, presumably due to the increased risk of surgical site contamination. Effective infection-preventing strategies should begin with identifying and optimizing the patients at a high risk of infection prior to surgery. Optimizing the operating room environment and antibiotic prophylaxis are also essential strategies that help minimize the overall incidence of infection in orthopedic surgery. The ideal antibiotic prophylaxis is still under debate, and discussions have emerged about whether variations or adjustments to the standard protocol are justified in patients at a high risk of infection. This also includes evaluating the possible benefits and risks of using high-dose dual antibiotic-loaded bone cement instead of low-dose single antibiotic-loaded bone cement in arthroplasty. This review summarizes the evidence showing that the combination of two local antibiotics in bone cement exerts a strong and longer-lasting antimicrobial effect against PJI-associated pathogens. This conclusion is consistent with the preliminary clinical studies showing a low incidence of PJI in high-risk patients undergoing cemented hemiarthroplasty, cemented revision, and primary arthroplasty if dual ALBC is used. These results may encourage clinicians to consolidate this hypothesis in a wider clinical range.

Infection Risk-Adjusted Antibiotic Prophylaxis Strategies in Arthroplasty: Short Review of Evidence and Experiences of a Tertiary Center in Spain

There is growing body of evidence that important patient-, procedure- and pathogen-related factors are linked to higher risks for prosthetic joint infections (PJI) following arthroplasty surgeries. The prior identification and optimization of such risk factors is considered paramount to minimize the incidence of these infections. Without any doubt, antibiotic prophylaxis remains one of the cornerstones among all preventive measures. However, the ideal antibiotic prophylaxis is still in debate and discussions have emerged, whether certain situations deserve adjustments or variations of the standard protocol taking into account antibiotic resistance surveillance data and patient risk factors for infections. This review aims to provide the reader with an overview of possible antibiotic prophylaxis strategies in response to these risks and discusses the clinical experiences so far obtained. We further present preliminary evidence that the use of a reinforced local antibiotic prophylaxis regimen with high-dose dual antibiotic-loaded bone cement may be an effective and easy-to-apply option in patients at high infection risks.

Risk assessment of antibiotic resistance development by antibiotic-loaded bone cements: is it a clinical concern?

Because of the risk of bacterial biofilm infections, prophylactic use of antibiotics in orthopaedic procedures involving the implantation of large prosthesis systems is considered mandatory.

A strategy based on the rationale that local antibiotics released from bone cement or other carriers establish a second antibacterial frontline in and around the prosthesis is considered complementary to the administration of systemic antibiotics.

Although less common as a consequence of the initially very high drug concentrations of local antibiotics in the tissues, a selection process of previous high resistance bacteria may occur, leading to antibiotic resistance.

The use of antibiotic combinations in bone cement is generally accepted to improve antibiotic efficacy and minimizes the treatment failure risk due to antibiotic resistance. This is important in septic revisions and/or in patients at particularly high risk of infection.

On an individual basis, the benefit of a lower infection probability with combined systemic and local antibiotic application should outweigh the risk of the selection of more resistant bacteria. Each prevented infection means that a complex and extended antibiotic therapy with risk of resistance development over time has been avoided.

On an epidemiological level there is no clinical evidence that the routine use of bone cement impregnated with appropriate bactericidal antibiotics promotes the widespread development of antibiotic resistance and thereby puts the successful treatment of a prosthetic joint infection at higher risk.

Cite this article: EFORT Open Rev 2019;4:576-584. DOI: 10.1302/2058-5241.4.180104

Dry-reagent-based PCR as a novel tool for laboratory confirmation of clinically diagnosed Mycobacterium ulcerans-associated disease in areas in the tropics where M. ulcerans is endemic

After tuberculosis and leprosy, Buruli ulcer (BU), caused by Mycobacterium ulcerans, is the third most common mycobacterial disease in immunocompetent humans. The disease occurs in tropical countries, with foci in West Africa, Central Africa, and the western Pacific. BU is defined as an infectious disease involving the skin and the subcutaneous adipose tissue characterized by a painless nodule, papule, plaque, or edema, evolving into a painless ulcer with undermined edges and often leading to invalidating sequelae. Due to the fundamental lack of understanding of modes of transmission, disease control in endemic countries is limited to early case detection through improved active surveillance and surgical treatment. The laboratory confirmation of BU is complicated by the absence of a diagnostic "gold standard." Therefore, misclassification and delayed diagnosis of BU may occur frequently, causing a considerable socioeconomic impact in terms of treatment costs due to prolonged hospitalization. In order to respond to the urgent need to develop reliable tools for early case detection and to overcome technical difficulties accompanying the implementation of diagnostic PCR procedures in tropical countries, a dry-reagent-based PCR formulation for the detection of M. ulcerans in diagnostic specimens has been developed at the Bernhard Nocht Institute for Tropical Medicine. Following technical and clinical validation, the assay has been successfully installed and field tested at the Kumasi Centre for Collaborative Research in Tropical Medicine, Kumasi, Ghana. Preliminary results show an excellent diagnostic sensitivity of >95%.

Dendritic cells (DC) activated by CpG DNA ex vivo are potent inducers of host resistance to an intracellular pathogen that is independent of IL-12 derived from the immunizing DC

We used the model of murine leishmaniasis to evaluate the signals enabling Ag-pulsed dendritic cells (DC) to prime a protective Th1 response in vivo. Bone marrow-derived DC (BMDC) that had been activated by TNF-alpha or CD40 ligation were not able to induce protection against leishmaniasis in susceptible BALB/c mice. In contrast, all mice vaccinated with a single dose of Leishmania major Ag-pulsed BMDC stimulated by prior in vitro exposure to CpG-containing oligodeoxynucleotides (ODN) were completely protected, had a dramatic reduction in parasite burden, and developed an Ag-specific Th1 response. Importantly, systemic administration of CpG ODN was not required. Protection mediated by ex vivo CpG ODN-activated and Ag-pulsed DC was solid, as documented by resistance to reinfection with a higher parasite dose, and long-lasting, as immunized mice were still protected against L. major challenge 16 wk after vaccination. A significantly increased level of protection could also be elicited in resistant C57BL/6 mice. Surprisingly, IL-12 expression by the immunizing BMDC was not required for induction of host resistance. In contrast, the availability of IL-12 derived from recipient cells was essential for the initial triggering of protective immunity by transferred BMDC. Together, these findings demonstrate that the type of stimulatory signal is critical for activating the potential of DC to induce a Th1 response in vivo that confers complete protection against an intracellular pathogen. Moreover, they show that the impact of activated DC on the initiation of a protective Th cell response in vivo may be independent of their ability to produce IL-12.

Dendritic cell (DC)-based protection against an intracellular pathogen is dependent upon DC-derived IL-12 and can be induced by molecularly defined antigens

Upon loading with microbial Ag and adoptive transfer, dendritic cells (DC) are able to induce immunity to infections. This offers encouragement for the development of DC-based vaccination strategies. However, the mechanisms underlying the adjuvant effect of DC are not fully understood, and there is a need to identify Ag with which to arm DC. In the present study, we analyzed the role of DC-derived IL-12 in the induction of resistance to Leishmania major, and we evaluated the protective efficacy of DC loaded with individual Leishmania Ag. Using Ag-pulsed Langerhans cells (LC) from IL-12-deficient or wild-type mice for immunization of susceptible animals, we showed that the inability to release IL-12 completely abrogated the capacity of LC to mediate protection against leishmaniasis. This suggests that the availability of donor LC-derived IL-12 is a requirement for the development of protective immunity. In addition, we tested the protective effect of LC loaded with Leishmania homolog of receptor for activated C kinase, gp63, promastigote surface Ag, kinetoplastid membrane protein-11, or Leishmania homolog of eukaryotic ribosomal elongation and initiation factor 4a. The results show that mice vaccinated with LC that had been pulsed with selected molecularly defined parasite proteins are capable of controlling infection with L. major. Moreover, the protective potential of DC pulsed with a given Leishmania Ag correlated with the level of their IL-12 expression. Analysis of the cytokine profile of mice after DC-based vaccination revealed that protection was associated with a shift toward a Th1-type response. Together, these findings emphasize the critical role of IL-12 produced by the sensitizing DC and suggest that the development of a DC-based subunit vaccine is feasible.

The method used to sample ulcers influences the diagnosis of cutaneous leishmaniasis

Before beginning treatment for cutaneous leishmaniasis, parasitological confirmation of the disease is required. The most commonly used diagnostic procedures are microscopy and culture of samples taken from the active edge of the lesion. In this study, we compared the sensitivity of previous diagnostic procedures with the polymerase chain reaction (PCR), using smears taken from the edge of the lesion and its centre. The sensitivity was greater with smears taken from the centre of the lesion, both for microscopical examination (85%) and for PCR (81%), compared to those obtained from the edge of the lesion (69% and 58% respectively). When PCR was carried out on biopsy material from the edge of the lesion the sensitivity was 63%.

Dendritic cell-based vaccination strategies: induction of protective immunity against leishmaniasis

The clinical symptoms caused by infections with Leishmania parasites range from self-healing cutaneous to uncontrolled visceral disease and depend not only on the parasite species but also on the type of the host's immune response. Infection of genetically susceptible mice with Leishmania major results in the development of disease-promoting T helper cells of type 2 (Th2). On the other hand, healing of lesions is dependent on the induction of Th1 cells producing interferon-gamma (IFN-gamma). The presence of interleukin 12 (IL-12) is known to be crucial for the differentiation of Th1 cells. Whereas IL-12 release and the T cell stimulatory functions of macrophages are down-regulated by L. major infection, dendritic cells (DC) exposed to L. major readily produce IL-12 and are highly potent antigen-presenting cells. Moreover, DC pulsed ex vivo with L. major antigen induce protection in otherwise susceptible mice against subsequent challenges with the parasites. The protection is long-lasting and correlates with a shift of the cytokine expression pattern towards a Th1 response. Thus, DC serve as immunomodulators in vivo and can be used as an effective adjuvant for vaccination against experimental leishmaniasis. Studies on the ability of DC to induce protective immunity to leishmaniasis may have important implications for the development of novel strategies for prophylactic and therapeutic immunizations against microbial pathogens.

Attenuated Toxoplasma gondii ts-4 mutants engineered to express the Leishmania antigen KMP-11 elicit a specific immune response in BALB/c mice

In order to test recombinant Toxoplasma as adjuvant and live vaccine carrier in the infectious disease model of murine experimental leishmaniasis, we engineered the attenuated, temperature-sensitive Toxoplasma gondii strain ts-4 to express the heterologous Leishmania antigen kinetoplastid membrane protein-11 (KMP-11). Transgenic ts-4 clones were obtained which express KMP-11 as cytoplasmatic protein or target it to the secretory pathway of the tachyzoites. Immunization of BALB/c mice with these stably transformed parasites elicited proliferative responses to both T. gondii antigen and recombinant KMP-11. When challenged with Leishmania major, we observed significant protection in animals that had been vaccinated with the KMP-11-expressing ts-4 mutants. The adjuvant attenuated only the onset of the Leishmania infection, but animals were ultimately not able to control the disease. Thus, our findings demonstrate that recombinant Toxoplasma has the potential to serve as an efficient vaccine carrier for cutaneous leishmaniasis. Furthermore, they establish a protective role for the antigen KMP-11 when given in such a vaccine formulation.

Dendritic cells as vectors for vaccination against infectious diseases

Antigen presentation by dendritic cells (DCs) is critical for the induction of a specific immune response. The immunotherapeutic potential of antigen-pulsed DCs for the treatment of cancer has been confirmed in a number of experimental tumor models and in several preclinical trials. Recent advances in our understanding of the interaction of microbial pathogens with DCs have provided the basis to explore DCs as vaccine carriers for the induction of protective immune responses to infections. Support for this strategy comes from animal studies demonstrating that DCs, after ex vivo loading with microbial antigens, confer protection against microbial challenges in vivo. This may have important implications for the development of novel strategies for prophylactic or therapeutic immunizations against various microbial pathogens.

Diagnosis of cutaneous leishmaniasis in Colombia: the sampling site within lesions influences the sensitivity of parasitologic diagnosis

Parasitologic confirmation of cutaneous leishmaniasis is obligatory before chemotherapy can be considered. Direct microscopic examination of scrapings taken from indurated borders of ulcers has been routinely used as primary method of diagnosis. In this report we compared the sensitivity of examination of dermal scrapings taken from the bottoms of ulcers (BDS) with that of dermal scrapings taken from indurated active margins of lesions (MDS) in a total of 115 patients. The sensitivities of the microscopic examination were 90.4 and 78.3% for BDS and MDS samples, respectively. When the PCR method was used with a group of 40 patients, we also observed a higher sensitivity when BDS samples were examined (80.8% in BDS samples versus 57.7% in MDS samples). The improvement of the diagnostic sensitivity in the BDS samples appears to be related to the higher parasite load and more easily detectable morphology of amastigotes in the centers of the ulcers. Other parasitologic diagnostic methods, such as culture and histopathologic examination of biopsies, are less sensitive (67.5 and 64.3%, respectively). Aspirate culture, however, was shown to be the most sensitive method for the diagnosis of patients with chronic ulcers. When microscopic examinations of both MDS and BDS samples are combined, the sensitivity of diagnosis may rise up to 94%. We therefore recommend this method as a primary routine procedure for diagnosis of cutaneous leishmaniasis.

The gene encoding the metacyclogenesis-associated transcript Mat-1 is conserved in the genus Leishmania and shows a tendency to form dimers upon protein expression

The Leishmania infantum Mat-1 gene--recently described in L. major as a highly stage-specific, metacyclogenesis-associated transcript--has been cloned. The 420-bp Mat-1 coding region is conserved with respect to the L. major gene (82% sequence homology). Analysis of the predicted amino-acid sequence reveals structural motifs showing homology with the class of leucine-zipper transcription factors. Southern-blot hybridization analysis suggests that Mat-1 is a low-copy-number gene, probably consisting of two gene copies. The recombinant Mat-1 protein expressed in fusion with the Escherichia coli maltose-binding protein shows a tendency to form dimers in the presence of the leucine-rich C-terminal domain. Bacteria expressing the Mat-1 open reading frame are highly growth-attenuated and tend to delete or modify the insert, which suggests that expression of Mat-1 is toxic for the bacteria.

The humoral immune response to the kinetoplastid membrane protein-11 in patients with American leishmaniasis and Chagas disease: prevalence of IgG subclasses and mapping of epitopes

The kinetoplastid membrane protein-11 (KMP-11) is a major target of the humoral immune response during Leishmania-infections. The majority of sera from visceral leishmaniasis, mucocutaneous leishmaniasis and even some cutaneous leishmaniasis patients contain detectable IgG antibodies against KMP-11. We also provide evidence that this protein may act as a potent antigen in T. cruzi infections, since most Chagas sera show immunological cross-reactivity. Therefore, KMP-11 cannot be used as a specific diagnostical tool for the serodiagnosis of leishmaniasis in those regions where both, Leishmania and T. cruzi infections overlap geographically. When analyzing the subclass specificity of the antibody response to KMP-11 we observed the following order of reactivity: IgG1 > > IgG3 > IgG2 > IgG4, which is similiar to that seen in crude parasite extract. The mapping of antigenic determinants by using synthetic 20-mer peptides revealed the existence of predominantly conformational epitopes in leishmaniasis, while 50% of sera from Chagas patients reacted with a particular KMP-11 peptide. These results therefore suggest the presence of disease-specific B-cell epitopes.

Folding stability of the kinetoplastid membrane protein-11 (KMP-11) from Leishmania infantum

Kinetoplastid membrane protein-11 (KMP-11) is a major component of the cell surface of kinetoplastids, and acts as a potent B- and T-cell immunogen during Leishmania infection. Here we report that the Leishmania infantum KMP-11 secondary structure adopts mainly an alpha-helical conformation at pH 7.5 and that its urea- and thermally-induced unfolding constitute a fully reversible two-step process. This allows estimation of a half-denaturation temperature of approximately 65 degrees C, a delta GDH2O at 20 degrees C of approximately 14.63 kJ.mol-1, and an increment of the reaction heat of approximately 183.92 kJ.mol-1 and an entropy of approximately 543.4 J.mol-1.deg-1, respectively, for the native-denatured equilibrium of the KMP-11 in solution. We also report that the KPM-11 protein is induced to adopt a molten globule state at a pH range between pH 4 and pH 6. As a whole, the stability and the specific features of the denaturing effect induced by changes in pH are similar in KMP-11 to various other lipoproteins.

The expression of the Leishmania infantum KMP-11 protein is developmentally regulated and stage specific

Transcription of the gene coding for the KMP-11 protein of Leishmania infantum results in the production of a mature RNA transcript of 1.3 kb in length. The expression of KMP-11 mRNA is strongly down-regulated not only during the parasite growth from the logarithmic to the stationary phase but also during the differentiation transit from promastigotes to amastigotes. The estimated concentration of KMP-11 is one order of magnitude higher in promastigotes than in amastigotes. The analysis of the Triton X-114 phase partition of the protein shows that, in agreement with its predicted secondary structure, KMP-11 has an amphipathic nature since it is found in the aqueous as well as in the detergent phase. By fluorescence microscopy a defined pattern of distribution of the protein was observed only in promastigotes where KMP-11 is mainly located in the flagellum and the flagellar pocket.

Molecular and antigenic characterization of the Leishmania (Viannia) panamensis kinetoplastid membrane protein-11

The kinetoplastid membrane protein 11 (KMP-11) has been recently described in Leishmania (Leishmania) donovani as a major component of the promastigote membrane. Two oligonucleotide primers were synthesized to PCR-amplify the entire encoding region of New World Leishmania species. The Leishmania (Viannia) panamensis amplification product was clone, sequenced and the putative amino acid sequence determined. A remarkably high degree of sequence homology was observed with the corresponding molecule of L. (L) donovani and L. (L) infantum (97% and 96%, respectively). Southern blot analysis showed that the KMP-11 locus is conformed by three copies of the gene. the L. (V) panamensis ORF was subsequently clone in a high expression vector and the recombinant protein was induced and purified from Escherichia coli cultures. Immunoblot analysis showed that 80%, 77% and 100% sera from cutaneous, mucocutaneous and visceral leishmaniasis patients, respectively, recognized the recombinant KMP-11 protein. In a similar assay, 86% of asymptomatic Leishmania-infected individuals showed IgG antibodies against the rKMP-11. We proposed that KMP-11 could be used as a serologic marker for infection and disease caused by Leishmania in America.

Acetylcholine receptor epsilon-subunit deletion causes muscle weakness and atrophy in juvenile and adult mice

In mammalian muscle a postnatal switch in functional properties of neuromuscular transmission occurs when miniature end plate currents become shorter and the conductance and Ca2+ permeability of end plate channels increases. These changes are due to replacement during early neonatal development of the gamma-subunit of the fetal acetylcholine receptor (AChR) by the epsilon-subunit. The long-term functional consequences of this switch for neuromuscular transmission and motor behavior of the animal remained elusive. We report that deletion of the epsilon-subunit gene caused in homozygous mutant mice the persistence of gamma-subunit gene expression in juvenile and adult animals. Neuromuscular transmission in these animals is based on fetal type AChRs present in the end plate at reduced density. Impaired neuromuscular transmission, progressive muscle weakness, and atrophy caused premature death 2 to 3 months after birth. The results demonstrate that postnatal incorporation into the end plate of epsilon-subunit containing AChRs is essential for normal development of skeletal muscle.

Expression of the mouse and rat mas proto-oncogene in the brain and peripheral tissues

We isolated the mas proto-oncogene from a mouse genomic library. Sequence analysis showed that it contains an open reading frame without intervening sequences. The amino acid sequence deduced confirms the seven-transmembrane-domain structure and exhibits 97% and 91% amino acid homology with the rat and the human Mas, respectively. In mice and rats, mas mRNA was detected in the testis, kidney, heart, and in the brain regions: hippocampus, forebrain, piriform cortex, and olfactory bulb. Testicular mas mRNA from rats increases markedly during development, while cerebellar mRNA is high postnatally but completely disappears at later stages. We conclude that the product of the mouse mas gene may be involved in the development of the brain and testis.

Characterization of the functional role of E-box elements for the transcriptional activity of rat acetylcholine receptor epsilon-subunit and gamma-subunit gene promoters in primary muscle cell cultures

The expression of gamma and epsilon subunits of the acetylcholine receptor from mammalian skeletal muscle is regulated independently during myogenic differentiation and innervation. Genomic DNA fragments containing 5'-flanking sequences of the epsilon-subunit and gamma-subunit genes were characterised by a series of 5' deletions fused to the chloramphenicol-acetyltransferase gene and transiently expressed by transfection of primary cultures of rat muscle cells and non-muscle cells. A 6.3-kb epsilon-subunit fragment can be reduced to yield a 270-bp fragment that confers 5-10-times higher expression levels in muscle cells compared to in non-muscle cells. The region composed of nucleotides -185 to -128 increases the transcriptional activity moderately while the 14-bp palindrome containing a single E box at nucleotides -88 to -83 may interact with the promoter but has no enhancer properties in muscle cells. From a 1.1-kb genomic fragment of the gamma-subunit gene, 167 bp were sufficient for muscle-specific expression. Two promoter-proximal E-box elements enhance promoter activity in muscle and mediate transactivation by myogenic factors. Myogenin and myf5 were much more efficient than MRF4 or MyoD1 which exerted only little transactivation. Cotransfection experiments show that increased expression of Id in primary muscle cells inhibits chloramphenicol-acetyltransferase expression mediated by the gamma-subunit gene promoter and support the view that myogenic factors play an important role in the transcriptional regulation of the gamma-subunit gene.

Two adjacent E box elements and a M-CAT box are involved in the muscle-specific regulation of the rat acetylcholine receptor beta subunit gene

We have isolated and analysed the 5' flanking region of the rat acetylcholine receptor (AChR) beta subunit gene and determined regulatory elements that confer muscle specificity. Deletion mapping revealed a minimal TATA-box-less promoter region containing an initiator motif. An 85-bp fragment has been shown to promote high muscle-specific expression of a chloramphenicol acetyltransferase (CAT) reporter construct upon transfection in primary muscle cells. This sequence can be functionally dissected in a basal muscle-specific promoter element carrying a M-CAT box that is flanked at the 5' end by an enhancer element with two binding sites for myogenic factors. Point mutations in the M-CAT box cause the loss of transcriptional activity of the basal promoter fragment. The enhancer activity depends on the presence of both E boxes that cooperate in a synergistic fashion. We therefore conclude that the control of muscle-specific and developmental expression of the rat AChR beta subunit gene requires both regulatory elements, the M-CAT box and two adjacent E boxes, located in close proximity to each other. Cotransfection experiments in NIH3T3 cells demonstrate that the rat AChR beta subunit gene can be transactivated by myogenic factors displaying a preference for myogenin, as well as MRF4 and myf5 compared to a clearly weaker responsiveness to MyoD1.