Absence of COVID-19 associated mucormycosis in a tertiary intensive care unit in the Netherlands

Mucormycosis is a severe complication in critically ill COVID-19 patients. Throughout the pandemic, a notable prevalence of mucormycosis has been observed in the Indian population, whereas lower occurrences have been reported in Europe. However, limited data exist regarding its prevalence in Europe, which is potentially underestimated due to the low sensitivity of bronchoalveolar lavage (BAL) cultures. We aimed to evaluate the prevalence of mucormycosis in a high-risk critically ill COVID-19 population in the Netherlands, and to evaluate the potential benefit of adding Mucor PCR to BAL as part of routine follow-up. In this study, we included 1035 critically ill COVID-19 patients admitted to either one of the two ICUs at AmsterdamUMC between March 2020 and May 2022; of these, 374 had undergone at least one bronchoscopy. Following the AmsterdamUMC protocols, bronchoscopies were conducted weekly until clinical improvement was achieved. We cultured BAL fluid for fungi and used PCR and galactomannan testing to detect Aspergillus spp. Additionally, we retrospectively performed qPCR targeting Mucorales DNA in the BAL of 89 deceased patients. All cultures were negative for Mucorales, whereas 42 (11%) cultures were positive for Aspergillus. Furthermore, qPCR targeting Mucorales was negative in all 89 deceased patients. This study showed that pulmonary mucormycosis was not present in critically ill COVID-19 patients in two tertiary care ICUs. These results indicate routine Mucorales qPCR screening is not clinically necessary in a high-standard-of-care tertiary ICU in a low-endemic area.

Third-generation cephalosporin resistant gram-negative bacteraemia in patients with haematological malignancy; an 11-year multi-centre retrospective study

Objectives

Among patients with haematological malignancy, bacteraemia is a common complication during chemotherapy-induced neutropenia. Resistance of gram-negative bacteria (GNB) to third-generation cephalosporins (3GC) is increasing. In order to explore the value of using surveillance cultures to guide empirical treatment e.g. choosing between carbapenem versus ceftazidime- we aimed to assess the distribution of pathogens causing bacteraemia in patients with haematological malignancy, and the proportion of 3GC-resistant GNB (3GC-R GNB) bacteraemia that was preceded by 3GC-R GNB colonization.

Methods

Using 11 years of data (2008–2018) from the Dutch national antimicrobial resistance surveillance system, we assessed the prevalence of 3GC-R GNB in episodes of bacteraemia, and the proportion of 3GC-R GNB bacteraemia that was preceded by 3GC-R GNB colonization. Colonization was defined as availability of any GNB surveillance isolate in the year before, independent of the causative micro-organism (time-paired isolates).

Results

We included 3887 patients, representing 4142 episodes of bacteraemia. GNB were identified in 715/4142 (17.3%), of which 221 (30.9%) were 3GC-R GNB. In 139 of these 221 patients a time-paired surveillance culture was available. In 76.2% (106/139) of patients these surveillance cultures already showed 3GC-R GNB isolates in the year prior to the culture date of the 3GC-R GNB positive blood isolate.

Conclusions

This multi-centre study shows that in patients with haematological malignancy, the majority of 3GC-R GNB bacteraemia is preceded by 3GC-R GNB colonization. Prospective clinical studies are needed to assess the safety and benefits of the use of surveillance-cultures to guide empirical therapy to restrict the empirical use of carbapenems in this population.

[A woman with a neck abscess but no current fever]

A 28-year-old woman, originally from the Philippines, presented with a painful, fluctuating swelling of the neck, preceded by peeking fever. CT-imaging showed a multiloculated abscess. A chest X-ray did not show any abnormalities. Incision and drainage were performed. Both PCR and culture revealed an infection with Mycobacterium tuberculosis and the diagnosis of cervical tuberculous lymphadenitis was made.

Progressive disseminated histoplasmosis mimicking a flare of systemic lupus erythematosus: a European case report

Introduction:

Diagnosing progressive disseminated histoplasmosis (PDH) in patients with systemic lupus erythematosus (SLE) is diagnostically challenging. Since PDH is lethal when untreated, awareness of this infection in patients with SLE is of utmost importance. To the best of our knowledge, this is the first description of a case of PDH in a patient with SLE in Europe.

Case presentation:

A 56-year-old woman of Surinamese descent with a history of SLE, presented with fever and polyarthritis. Although a flare of SLE was suspected initially, cultures of bone marrow and broncho-alveolar lavage fluid grew Histoplasma capsulatum.

Conclusion:

This case report highlights that physicians should be aware of progressive disseminated histoplasmosis in patients with SLE treated with immunosuppressive agents. The signs and symptoms can easily mimic a SLE flare, which would then be treated with more aggressive immunosuppression. Failure to recognize the infection will therefore invariably lead to death of the patient. Progressive disseminated histoplasmosis is usually not recognized by doctors in non-endemic areas such as Europe. However, globalisation and more frequent intercontinental traffic of immunocompromised patients currently increases the incidence of histoplasmosis in these areas. It is therefore of life-saving importance that doctors are aware of the features of the infection in areas where H. capsulatum is not endemic.

Strategies to improve follow-up of children after surgery for cataract: findings from Child Eye Health Tertiary Facilities in sub-Saharan Africa and South Asia

PurposeWe sought to conduct a systematic literature review on follow-up of children with ocular surgical management (primarily childhood cataract) in developing countries. Second, we sought to determine the current practices regarding follow-up for clinical, optical, low vision, rehabilitation, and educational placement among children receiving surgical services at Child Eye Health Tertiary Facilities (CEHTF) in sub-Saharan Africa (SSA) and South Asia.MethodsA systematic literature review was conducted. Separately, we conducted a cross-sectional study among CEHTF in SSA and South Asia (India, Nepal, and Bangladesh) to assess current capacities and practices related to follow-up and educational placement.ResultsThe articles that met the systematic review eligibility criteria could be grouped into two areas: factors and strategies to improve post-operative follow-up and educational placement of children after surgery. Among the 106 CEHTF in SSA and South Asia, responses were provided by 75 CEHTF. Only 59% of CEHTF reported having a Childhood Blindness and Low Vision Coordinator; having a coordinator was associated with having appropriate follow-up mechanisms in place. Educational referral practices were associated with having a low-vision technician, having low-vision devices, and having donor support for these services.ConclusionsThe systematic literature review revealed evidence of poor follow-up after surgical interventions for cataract and other conditions, but also showed that follow-up could be improved significantly if specific strategies were adopted. Approaches to follow-up are generally inadequate at most facilities and there is little external support for follow-up. Findings suggest that funding and supporting a coordinator would assist in ensuring that good practices for follow-up (cell phone reminders, patient tracking, and reimbursement of transport) were followed.

A disc diffusion assay for detection of class A, B and OXA-48 carbapenemases in Enterobacteriaceae using phenyl boronic acid, dipicolinic acid and temocillin

Class A and B carbapenemases in Enterobacteriaceae may be detected using carbapenemase inhibition tests with boronic acid derivatives (BA) and dipicolinic acid (DPA)/EDTA, respectively. However, for OXA-48 (like) carbapenemases, no specific inhibitor is available. Because OXA-48 confers high-level temocillin resistance, a disc diffusion assay using temocillin as well as BA and DPA inhibition tests was evaluated for detection of class A, B and OXA-48 carbapenemases. The test collection included 128 well-characterized non-repeat Enterobacteriaceae isolates suspected of carbapenemase production; that is, with meropenem MICs ≥ 0.5 mg/L, including 99 carbapenemase producers (36 KPC, one GES, 31 MBL, four KPC plus VIM, 25 OXA-48, two OXA-162), and 29 ESBL and/or AmpC-producing isolates. PCR and sequencing of beta-lactamase genes was used as a reference test. Phenotypic carbapenemase detection was performed with discs (Rosco) containing meropenem (10 μg), temocillin (30 μg), meropenem + phenyl boronic acid (PBA), meropenem + DPA, meropenem + BA + DPA, and meropenem + cloxacillin (CL). Absence of synergy between meropenem and BA and/or DPA and a temocillin zone ≤10 mm was used to identify OXA-48. The sensitivity for identification of class A, B and OXA-48 carbapenemases was 95%, 90% and 100%, with 96-100% specificity. In non-Proteus species, the sensitivity for class B carbapenemase detection was 97%. All isolates without PBA or DPA synergy and a temocillin disc zone ≤10 mm were OXA-48 (like) positive. In conclusion, carbapenemase inhibition tests with PBA and DPA combined with a temocillin disc provide a reliable phenotypic confirmation method for class A, B and OXA-48 carbapenemases in Enterobacteriaceae.

Clinical breakpoint changes and their impact on surveillance of antimicrobial resistance in Escherichia coli causing bacteraemia

Dutch laboratories are currently changing their breakpoint criteria from mostly Clinical Laboratory and Standards Institute (CLSI) breakpoints to European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints. To evaluate the impact of these changes, we studied antimicrobial resistance trends of Escherichia coli in blood specimens from January 2008 to January 2012 using CLSI and EUCAST breakpoints and compared them with the antimicrobial susceptibility test (AST) interpretations reported by Dutch laboratories participating in the Infectious Disease Surveillance Information System for Antibiotic Resistance (ISIS-AR). ISIS-AR collects AST interpretations, including underlying minimal inhibitory concentrations (MICs) of routinely cultured bacterial species on a monthly basis from Dutch laboratories. MICs of Etests or automated systems were reinterpreted according to the CLSI 2009 and EUCAST 2010 guidelines. Trends in non-susceptibility (i.e. intermediate resistant and resistant) over time were analysed by the Cochran-Armitage test for trend. The effects of the change from CLSI to EUCAST breakpoints on non-susceptibility were small. There were no differences in non-susceptibility to amoxicillin, amoxicillin/clavulanic acid, cefuroxim, gentamicin and co-trimoxazol and only small differences (1-1.5%) for ciprofloxacin between AST interpretations by CLSI or EUCAST. However, for ceftazidime, and cefotaxime/ceftriaxone the proportion of non-susceptibility was substantially higher when EUCAST breakpoints were used (2-3%). The effects on time trends of the change in guidelines were limited, with only substantial differences for the oxymino-cephalosporins. Our study shows that the implementation of EUCAST breakpoints has a limited effect on the proportion of non-susceptible isolates and time trends in E. coli for most, but not all, antimicrobial agents.

Variability in clinical phenotype of severe haemophilia: the role of the first joint bleed

To quantify variation in clinical phenotype of severe haemophilia we performed a single centre cohort study among 171 severe haemophilia patients. Age at first joint bleed, treatment requirement (i.e. annual clotting factor use), annual bleeding frequency and arthropathy were documented. Because treatment strategies intensified during follow-up, patients were stratified in two age groups: patients born 1968-1985 (n = 91), or 1985-2002 (n = 80). A total of 2166 patient-years of follow-up were available (median 12.0 years per patient). Age at first joint bleed ranged from 0.2 to 5.8 years. Patients who had their first joint bleed later needed less treatment and developed less arthropathy. In patients born 1968-1985 during both on-demand and prophylactic treatment, the 75th percentile of annual joint bleed frequency was consistently four times as high as the 25th percentile. In both age groups variation in annual clotting factor use between 25th and 75th percentiles was 1.4-1.5 times for prophylaxis and 3.8 times for on-demand treatment. To conclude, the onset of joint bleeding is inversely related with treatment requirement and arthropathy and may serve as an indicator of clinical phenotype. Thus, providing a starting point for aetiological research and individualization of treatment.

Can long-term prophylaxis for severe haemophilia be stopped in adulthood? Results from Denmark and the Netherlands

Prophylaxis is the treatment of choice for children with severe haemophilia. As prophylaxis is especially important during the period of growth, the need for continued prophylaxis in adulthood should be considered. The aim of this study was to describe the incidence and outcome of stopping prophylaxis in patients with severe haemophilia who were offered prophylaxis during childhood. All patients with severe haemophilia (factor VIII/IX <0.01 IU/ml), born 1970-80, treated in two Danish and one Dutch treatment centre were studied. Data on discontinuation of prophylaxis, treatment, joint bleed frequency, clinical scores and radiological scores were collected. Eighty patients were studied. Median follow-up was 19 years (range 7-29). A total of 35% of patients discontinued prophylaxis at a median age of 21.5 years [interquartile range (IQR) 18.4-24.4], experiencing only three joint bleeds per year (IQR 1.4-8.7). Median clinical scores were similar in patients who discontinued prophylaxis [4 points (IQR 0-6)] and those who continued [3 points (IQR 1-6)], as were median Pettersson scores at 13 (IQR 1-24) vs. 13 points (IQR 5-23) respectively. In conclusion one-third of young adults with severe haemophilia on a prophylactic regimen discontinued prophylaxis in early adulthood, while maintaining a low joint bleed frequency and similar arthropathy after 4 years.

Early versus late treatment of posthaemorrhagic ventricular dilatation: results of a retrospective study from five neonatal intensive care units in The Netherlands

Posthaemorrhagic ventricular dilatation (PHVD) in very preterm infants carries a poor prognosis. As earlier studies have failed to show a benefit of early intervention, it is recommended that PHVD be first treated when head circumference is rapidly increasing and/or when symptoms of raised intracranial pressure develop. Infants with PHVD, admitted to 5 of the 10 Dutch neonatal intensive care units were studied retrospectively, to investigate whether there was a difference in the time of onset of treatment of PHVD and, if so, whether this was associated with a difference in the requirement of a ventriculo-peritoneal (VP) shunt and/or neurodevelopmental outcome. The surviving infants with a gestational age <34 wk, born between 1992 and 1996, diagnosed as having a grade III haemorrhage according to Papile on cranial ultrasound and who developed PHVD were included in the study. PHVD was defined as a ventricular index (VI) exceeding the 97th percentile according to Levene (1981), and severe PHVD as a VI crossing the p 97 + 4 mm line. Ninety-five infants met the entry criteria. Intervention was not deemed necessary in 22 infants, because of lack of progression. In 31 infants lumbar punctures (LP) were done before the p 97 + 4 mm line was crossed (early intervention). In 20/31 infants, stabilization occurred. In 9 a subcutaneous reservoir was placed, with subsequent stabilization in 6. In 5/31 infants a VP shunt was eventually inserted. In 42 infants treatment was started once the p 97 + 4 mm line was crossed (late intervention). In 30 infants LPs were performed and in 17 of these a VP shunt was eventually inserted. In 11 infants a subcutaneous reservoir was immediately inserted and in 8 of these infants a VP shunt was needed. In one infant a VP shunt was immediately inserted, without any other form of treatment. Infants with late intervention crossed the p 97 + 4 mm earlier (p 0.03) and needed a shunt (26/42; 62%) more often than those with early intervention (5/31; 16%). Early LP was associated with a strongly reduced risk of VP-shunting (odds ratio = 0.22, 95% confidence interval: 0.08-0.62). The number of infants who developed a moderate or severe handicap was also higher (11/42; 26%) in the late intervention group, compared with those not requiring any intervention (3/22; 14%) or treated early (5/31; 16%).

CONCLUSION

In this retrospective study, infants receiving late intervention required shunt insertion significantly more often than those treated early. A randomized prospective intervention study, comparing early and late drainage, is required to further assess the role of earlier intervention.

[Pneumonia due to Legionella pneumophila in an immunocompromised child]

A one-year-and-seven-months-old boy was hospitalised because of fever, cough and general malaise. A diagnosed tonsillitis and pneumonia were treated with intravenous antibiotics. His clinical condition worsened despite antibiotic therapy. After immunologic investigations revealed both a cellular and a humoral immune disorder, a broncho-alveolar lavage was performed. The culture revealed Legionella pneumophila. Antibiotic treatment was then changed to erythromycin in combination with rifampicin, with a good response. Although rarely described in childhood, one should consider L. pneumophila as a possible pathogen in immunocompromised children presenting with pneumonia.

Fatty acid competition as a mechanism by which Enterobacter cloacae suppresses Pythium ultimum sporangium germination and damping-off

Interactions between plant-associated microorganisms play important roles in suppressing plant diseases and enhancing plant growth and development. While competition between plant-associated bacteria and plant pathogens has long been thought to be an important means of suppressing plant diseases microbiologically, unequivocal evidence supporting such a mechanism has been lacking. We present evidence here that competition for plant-derived unsaturated long-chain fatty acids between the biological control bacterium Enterobacter cloacae and the seed-rotting oomycete, Pythium ultimum, results in disease suppression. Since fatty acids from seeds and roots are required to elicit germination responses of P. ultimum, we generated mutants of E. cloacae to evaluate the role of E. cloacae fatty acid metabolism on the suppression of Pythium sporangium germination and subsequent plant infection. Two mutants of E. cloacae EcCT-501R3, Ec31 (fadB) and EcL1 (fadL), were reduced in beta-oxidation and fatty acid uptake, respectively. Both strains failed to metabolize linoleic acid, to inactivate the germination-stimulating activity of cottonseed exudate and linoleic acid, and to suppress Pythium seed rot in cotton seedling bioassays. Subclones containing fadBA or fadL complemented each of these phenotypes in Ec31 and EcL1, respectively. These data provide strong evidence for a competitive exclusion mechanism for the biological control of P. ultimum-incited seed infections by E. cloacae where E. cloacae prevents the germination of P. ultimum sporangia by the efficient metabolism of fatty acid components of seed exudate and thus prevents seed infections.

Pseudomonas syringae Hrp type III secretion system and effector proteins

Pseudomonas syringae is a member of an important group of Gram-negative bacterial pathogens of plants and animals that depend on a type III secretion system to inject virulence effector proteins into host cells. In P. syringae, hrp/hrc genes encode the Hrp (type III secretion) system, and avirulence (avr) and Hrp-dependent outer protein (hop) genes encode effector proteins. The hrp/hrc genes of P. syringae pv syringae 61, P. syringae pv syringae B728a, and P. syringae pv tomato DC3000 are flanked by an exchangeable effector locus and a conserved effector locus in a tripartite mosaic Hrp pathogenicity island (Pai) that is linked to a tRNA(Leu) gene found also in Pseudomonas aeruginosa but without linkage to Hrp system genes. Cosmid pHIR11 carries a portion of the strain 61 Hrp pathogenicity island that is sufficient to direct Escherichia coli and Pseudomonas fluorescens to inject HopPsyA into tobacco cells, thereby eliciting a hypersensitive response normally triggered only by plant pathogens. Large deletions in strain DC3000 revealed that the conserved effector locus is essential for pathogenicity but the exchangeable effector locus has only a minor role in growth in tomato. P. syringae secretes HopPsyA and AvrPto in culture in a Hrp-dependent manner at pH and temperature conditions associated with pathogenesis. AvrPto is also secreted by Yersinia enterocolitica. The secretion of AvrPto depends on the first 15 codons, which are also sufficient to direct the secretion of an Npt reporter from Y. enterocolitica, indicating that a universal targeting signal is recognized by the type III secretion systems of both plant and animal pathogens.

The Pseudomonas syringae Hrp pathogenicity island has a tripartite mosaic structure composed of a cluster of type III secretion genes bounded by exchangeable effector and conserved effector loci that contribute to parasitic fitness and pathogenicity in plants

The plant pathogenic bacterium Pseudomonas syringae is divided into pathovars differing in host specificity, with P. syringae pv. syringae (Psy) and P. syringae pv. tomato (Pto) representing particularly divergent pathovars. P. syringae hrp/hrc genes encode a type III protein secretion system that appears to translocate Avr and Hop effector proteins into plant cells. DNA sequence analysis of the hrp/hrc regions in Psy 61, Psy B728a, and Pto DC3000 has revealed a Hrp pathogenicity island (Pai) with a tripartite mosaic structure. The hrp/hrc gene cluster is conserved in all three strains and is flanked by a unique exchangeable effector locus (EEL) and a conserved effector locus (CEL). The EELs begin 3 nt downstream of the stop codon of hrpK and end, after 2.5-7.3 kb of dissimilar intervening DNA with tRNA(Leu)-queA-tgt sequences that are also found in Pseudomonas aeruginosa but without linkage to any Hrp Pai sequences. The EELs encode diverse putative effectors, including HopPsyA (HrmA) in Psy 61 and proteins similar to AvrPphE and the AvrB/AvrC/AvrPphC and AvrBsT/AvrRxv/YopJ protein families in Psy B728a. The EELs also contain mobile genetic element sequences and have a G + C content significantly lower than the rest of the Hrp Pai or the P. syringae genome. The CEL carries at least seven ORFs that are conserved between Psy B728a and Pto DC3000. Deletion of the Pto DC3000 EEL slightly reduces bacterial growth in tomato, whereas deletion of a large portion of the CEL strongly reduces growth and abolishes pathogenicity in tomato.

The Avr (effector) proteins HrmA (HopPsyA) and AvrPto are secreted in culture from Pseudomonas syringae pathovars via the Hrp (type III) protein secretion system in a temperature- and pH-sensitive manner

We present here data showing that the Avr proteins HrmA and AvrPto are secreted in culture via the native Hrp pathways from Pseudomonas syringae pathovars that produce these proteins. Moreover, their secretion is strongly affected by the temperature and pH of the culture medium. Both HrmA and AvrPto were secreted at their highest amounts when the temperature was between 18 and 22 degrees C and when the culture medium was pH 6.0. In contrast, temperature did not affect the secretion of HrpZ. pH did affect HrpZ secretion, but not as strongly as it affected the secretion of HrmA. This finding suggests that there are at least two classes of proteins that travel the P. syringae pathway: putative secretion system accessory proteins, such as HrpZ, which are readily secreted in culture; and effector proteins, such as HrmA and AvrPto, which apparently are delivered inside plant cells and are detected in lower amounts in culture supernatants under the appropriate conditions. Because HrmA was shown to be a Hrp-secreted protein, we have changed the name of hrmA to hopPsyA to reflect that it encodes a Hrp outer protein from P. syringae pv. syringae. The functional P. syringae Hrp cluster encoded by cosmid pHIR11 conferred upon P. fluorescens but not Escherichia coli the ability to secrete HopPsyA in culture. The use of these optimized conditions should facilitate the identification of additional proteins traveling the Hrp pathway and the signals that regulate this protein traffic.

Creation and testing of a practical visual function assessment for use in Africa: correlation with visual acuity, contrast sensitivity, and near vision in Malawian adults

AIM

To develop and test a practical visual function assessment for use in developing countries.

METHODS

Using focus group discussions and interviews with eyecare workers and low vision specialists in Malawi, 13 questions related to visual characteristics of activities of daily living were designed. Patients presenting to an eye clinic were recruited and interviewed. Visual acuity, near vision, and contrast sensitivity were measured. Analysis sought to determine the degree of correlation between the vision indices and visual function.

RESULTS

The visual function questionnaire was easy to administer. Visual function correlated with visual acuity, contrast sensitivity, near vision, and patient reported visual problem. People with a higher frequency of "not applicable" responses had lower visual function scores. Multivariate modelling revealed that visual acuity and number of questions felt to be applicable were independently associated with visual function. Reducing the questionnaire to nine questions did not affect the degree of correlation with any of the visual indices.

CONCLUSION

The authors' visual function assessment correlates well with different measures of visual acuity. People with reduced vision for a prolonged period may no longer consider doing certain tasks and the number of questions considered appropriate by an individual may be an additional measure of visual function. Assessment of visual function by health workers may be a valuable tool in improving surgical uptake by encouraging both health personnel and patients to recognise that they have difficulties undertaking activities of daily living as well as a measure of monitoring and evaluating cataract outcomes.

Genetic polymorphism at the beta-tubulin locus among human and animal isolates of Cryptosporidium parvum

Sequence analysis of a fragment of the beta-tubulin gene was performed on 13 isolates of the parasite Cryptosporidium parvum, eight from humans and five from animals. A total of 12 synonymous substitutions and a deletion of two bases within the intron sequence were found. This genetic variation defined two alleles at the beta-tubulin locus, which can be identified by a simple polymerase chain reaction-restriction fragment length polymorphism assay. A total of 20 isolates were also tested using four available molecular markers. These analyses showed congruently that the C. parvum isolates segregate into two groups, one found exclusively in humans and the other found in both humans and animals. Since no recombinant genotypes were observed, the results are consistent with the hypothesis of a substantially clonal reproduction in this parasite.

A complete characterization of Ca5(PO4)3OH sputter-deposited films by ion beam analysis: RBS and ERD

RF magnetron sputter deposition was used to deposit thin calcium phosphate (hydroxyapatite) layers on titanium alloy substrate material. We determined the precise amount of calcium, phosphorus, oxygen, and hydrogen in these films by combining two ion-beam analysis techniques: Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD). Variables were power level, partial oxygen pressure, or additional water vapor. Also examined was the influence of additional bias power to the substrates during deposition and the effect of annealing on the final composition of the deposited layers. Measurements showed that the Ca/P ratio decreased with increasing oxygen pressure or decreasing sputtering power. In addition, the Ca/P ratio increased when a bias was applied to the substrates. The O/P ratio of the films decreased with additional oxygen pressure but increased when additional water vapor was applied during deposition. All as-deposited films showed a higher hydrogen content than stoichiometric HA. The hydrogen content in the films deposited with water vapor was more than 7 times higher than in the films deposited under pure argon conditions. After annealing, the hydrogen content decreased to about 3.5 at % whereas in stoichiometric HA the hydrogen content amounts to 4.5 at %. After annealing, the oxygen concentration in the film also decreased. We assume that hydrogen disappears out of the film as H2O during annealing. For the targets used in these experiments, sputter deposition at 400 W, with additional water vapor and annealing at 500 degrees C, produced films with a stoichiometry closest to that of hydroxyapatite.

Measurement and control of interface strength of RF magnetron-sputtered Ca-PO coating on Ti-6Al-4V substrates using a laser spallation technique

In previous studies, an RF magnetron sputter technique was developed for the production of thin calcium phosphate coating. Several deposition parameters were found to influence the growth rate and the stoichiometry of the coatings. For instance, deposition with additional oxygen pressure decreased the Ca to P ratio of the coatings to 1.67. For application of these coatings on actual Ti implants, it is important to know their adhesive tensile strength with the implant surface and how it varies with the deposition parameters. Motivated by these goals, the aim of this study was to measure the adhesive tensile strength of these coatings with Ti substrates and to study its variation with the deposition parameters. Since most mechanical characterization methods are incapable of providing a direct measure of the interface's fundamental strength, a novel laser spallation experiment was used to accomplish this task. In this experiment, a compressive stress pulse is generated on the back side of a substrate by impinging a 3-ns long Nd:YAG laser pulse. The stress pulse propagates through the substrate and is reflected into a tensile stress wave from the free surface of the coating deposited on its front surface. The returning tensile pulse pries off the coating if its amplitude is high enough. The peak interface tensile stress is computed by using the optically recorded free surface displacement of the coating. Because interface decohesion is accomplished at a strain rate of almost 10(7) s-1, all inelastic processes essentially are suppressed and the measured value essentially is the intrinsic tensile strength of the interface. Tensile strength values in the range of 500-900 MPa were recorded for the interfaces between sputter-deposited calcium-phosphate coatings and Ti substrates. To confirm the locus of failure, the spalled spots were examined using SEM and EDS. The variation in the measured values was related to the changes in the deposition conditions.

Interfacial phenomena: an in vitro study of the effect of calcium phosphate (Ca-P) ceramic on bone formation

In previous studies we developed a RF magnetron sputter technique for the production of thin Ca-P coatings. With this technique coatings can be produced that vary in Ca/P ratio as well as in structural appearance. The aim of this investigation was to obtain more understanding of the biological behavior of these coatings by way of in vitro experiments. The effect of noncoated titanium (Ti) and three different Ca-P-sputtered surfaces on the proliferation and differentiation (morphology and matrix production) of osteoblast-like cells was studied. Proliferation was determined using counting procedures; morphology was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fluorescent markers and energy-dispersive X-ray microanalysis (EDX) were used to obtain quantitative and compositional information about the resultant calcified extracellular matrix (ECM). Results demonstrated that proliferation of the osteoblast-like cells was significantly (p < 0.05) higher on noncoated than on Ca-P-coated samples. On the other hand, more mineralized ECM was formed on the coated surfaces. In addition, TEM confirmed that the cells on the coated substrates were surrounded by ECM with collagen fibers embedded in crystallized, needle-shaped structures. On the basis of these findings, we concluded that: (1) the investigated Ca-P sputter coatings possess the capacity to activate the differentiation and expression of osteogenic cells, and (2) bone formation proceeds faster on Ca-P surfaces than on Ti substrates. Further, this bone-inductive effect appeared to be dependent on the Ca-P ratio of the deposited coatings.

Mechanical and histologic evaluation of Ca-P plasma-spray and magnetron sputter-coated implants in trabecular bone of the goat

To aim of this study was to investigate the bone response to calcium phosphate (Ca-P) plasma-spray and radiofrequency magnetron sputter-coated implants with comparable roughness. Therefore, tapered conical screw designed implants were installed in the trabecular bone of the femurs of nine goats. They were provided with two types of coatings, a plasma-spray dual coating of fluorapatite and hydroxyapatite (FA/HA-PS) and a titanium plasma-spray coating, covered with an amorphous Ca-P magnetron sputtercoating (TPS/Ca-P-a). These implants were evaluated histologically and mechanically after 3 months of implantation. A well-controlled method to apply and measure a torsional force to load the screw-type implants to the point of failure was introduced. All implants healed uneventful and were well fixed. No significant difference (Student t test, p > 0.05) for the torsional failure force was measured for both type of coatings. Nevertheless, SEM revealed differently situated fracture planes. Light microscopy showed intimate bone-implanted contact for both types of coatings; original drill margins were still visible. A lamellar type of bone with some remodeling lacunae was shown. Histomorphometry revealed a higher percentage of bone contact for the FA/HA-PS-coated implants (students t test, p < 0.05). Measurement of the amount of bone revealed more bone mass around TPS/Ca-P-a-coated implants (analysis of variance and Turkey multiple comparison, p < 0.05).

Evaluation of plasma-spray and magnetron-sputter Ca-P-coated implants: an in vivo experiment using rabbits

The bone response to different plasma-spray and magnetron-sputter calcium phosphate (Ca-P)-coated implants was evaluated in a rabbit animal model. Four types of Ca-P coatings have been investigated: a plasma-spray Ca-P coating (HA-PS), a heat-treated plasma-spray Ca-P coating (HA-PS/ht), an amorphous magnetron-sputter coating (Ca-P-a), and a crystalline magnetron-sputter coating (CA-P-c). Seventy-two specially designed cylindrical implants were inserted in the lateral and medial femoral condyles of 18 New Zealand White rabbits. The four differently coated implants were positioned in one animal according to a split-plot design. After implantation periods of 3, 6, and 9 weeks, the bone-implant interface was evaluated histologically. Besides descriptive light microscopical evaluation, quantitative histomorphometrical measurements were done to determine bone contact and the amount of bone surrounding the implant-bone interface. Light microscopical examination revealed that all types of coatings followed the same process of bone healing. Measurements of bone contact at 6 and 9 weeks did not reveal significant differences between the various coatings. For the amount of bone, in a circular region at a certain distance from the implant, the Ca-P-c-coated implants showed a significantly greater amount of bone after 6 weeks of implantation than did the other three Ca-P coatings. At 9 weeks this difference could no longer be measured. On the basis of these findings we concluded that magnetron-sputtered Ca-P coatings show the same process of bone healing as the plasma-sprayed Ca-P coatings when inserted into the trabecular femoral bone of rabbits.

Influence of annealing temperature on RF magnetron sputtered calcium phosphate coatings

The effect of different annealing temperatures on the characteristics of thin calcium phosphate coatings fabricated by radiofrequency magnetron sputtering was studied. Annealing of the as-sputtered films was necessary to change the amorphous coating to a crystalline coating. The films were annealed for 2 and 4 h at 400, 600, 800, 1000 and 1200 degrees C under dry argon or argon and water vapour flow. After annealing, the structure and the chemical composition of these films were characterized with incident light microscopy, Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), and Fourier transform infrared absorption spectrometry (FTIR). Incident light microscopy showed cracks in the coatings annealed at a higher temperature than 400 degrees C. RBS revealed that the as-sputtered coatings had a high Ca/P ratio which decreased with increasing annealing temperature. After annealing at a temperature of 600 degrees C or more the XRD showed crystalline hydroxyapatite (HA) coatings. However, the second phase, present in the coatings, changed from tetra-calcium phosphate to calcium oxide to beta-tri-calcium phosphate with increasing annealing temperature. FTIR measurements showed the existence of OH- and PO- bonds in all coatings, although the PO- bonds varied for different annealed coatings, from the PO- bonds due to HA to PO- bonds due to other calcium phosphates. From the results of this study we suggest that 600 degrees C is probably the best annealing temperature to obtain a better characterization and understanding of the coating.

Biological evaluation of the effect of magnetron sputtered Ca/P coatings on osteoblast-like cells in vitro

A rat bone marrow cell culture was used to evaluate the osteogenic potential of amorphous and crystalline thin calcium phosphate (Ca/P) coatings. The coatings were deposited on titanium discs using a radiofrequency magnetron sputter procedure. Amorphous and crystalline plasma spray Ca/P coated and noncoated titanium discs served as reference material. The cellular behavior was analyzed with quantitative (attachment and proliferation rates) and qualitative (scanning electron microscopy) techniques. No significant differences were found in cell attachment and proliferation rates between the various materials. Scanning electron microscopy showed extracellular matrix formation after 18 days of culture on amorphous plasma-sprayed and the two types of magnetron sputtered coatings. Furthermore, no severe degradation of the magnetron sputtered coatings was observed. They even appeared to induce apatite formation. On basis of the results, we conclude that magnetron sputtering appears to be a promising method to manufacture bioactive ceramic coatings.

Influence of discharge power level on the properties of hydroxyapatite films deposited on Ti6A14V with RF magnetron sputtering

The effects of discharge radiofrequency (RF) power and film thickness were studied on the characteristics of Ca5(PO4)3OH (hydroxyapatite) thin films fabricated by RF magnetron sputtering. The structure and chemical composition were investigated with alpha-step (thickness), scanning electron microscopy (SEM), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), and infrared absorption spectrometry (FTIR). The films were analyzed as-sputtered and after annealing at 550 degrees C under argon flow. SEM showed that the film surfaces had no cracks or other defects. X-ray diffraction showed that the deposited films were amorphous with low-discharge RF power, and crystalline with high-discharge RF power. After annealing, all the films had the same crystalline structure as apatite. However, the RBS measurements revealed that all films had a higher calcium-phosphate ratio than standard synthetic hydroxyapatite. Furthermore, statistical testing of the RBS data revealed the existence of only a weak correlation between the Ca/P ratio and the discharge power level. Although all sputtered films showed phosphate bonds in the infrared spectrum, only after annealing did the OH bonds of hydroxyapatite become visible.

Study of the surface characteristics of magnetron-sputter calcium phosphate coatings

Plasma-sprayed hydroxylapatite coatings on metals such as titanium have been investigated for many years and have shown a good biocompatibility when implanted in bony tissues. Radiofrequency magnetron sputtering was used as an alternative method to deposit thin films of hydroxylapatite on titanium substrates. X-ray diffraction demonstrated that the sputtered layer was crystalline with a preferred (001) crystallographic orientation with the C-axis perpendicular to the substrate surface. Scanning electron microscopy showed that the deposited films had a uniform and dense structure. The calcium phosphate ratio varied between 1.5 and 2.0, as determined by energy-dispersive X-ray analysis. The in vitro dissolution appeared to be determined by the degree of the coating's crystallinity.

Kinetic properties of hydrogenase isolated from Desulfovibrio vulgaris (Hildenborough)

Hydrogenase of Desulfovibrio vulgaris shows nonlinear kinetics in hydrogen production with both the natural electron carrier, cytochrome c3, and the artificial donor, methyl viologen semiquinone. Increasing concentrations of salt progressively inhibit the hydrogen production, as do increasing amounts of dimethylsulfoxide (Me2SO). Hydrogen consumption activity does not change up to 30% (v/v) of Me2SO. Preincubation in Me2SO up to 55% (v/v) does not affect the hydrogen uptake or production. The production activity of the enzyme shows an optimum around pH 6. When plotted as a function of redox potential the activity can be fitted to a Nernst equation with n = 1. Midpoint potentials calculated at various values follow approximately the hydrogen electrode to pH 6. Thereafter, there is a shift of about 40 mV to higher redox potentials.