Postcardiac surgery infections

Interactions in bacterial biofilm development: a structural perspective

A community-based life style is the normal mode of growth and survival for many bacterial species. These cellular accretions or biofilms are initiated upon recognition of solid phases by cell surface exposed adhesive moieties. Further cell-cell interactions, cell signalling and bacterial replication leads to the establishment of dense populations encapsulated in a mainly self-produced extracellular matrix; this comprises a complex mixture of macromolecules. These fascinating architectures protect the inhabitants from radiation damage, dehydration, pH fluctuations and antimicrobial compounds. As such they can cause bacterial persistence in disease and problems in industrial applications. In this review we discuss the current understandings of these initial biofilm-forming processes based on structural data. We also briefly describe latter biofilm maturation and dispersal events, which although lack high-resolution insights, are the present focus for many structural biologists working in this field. Finally we give an overview of modern techniques aimed at preventing and disrupting problem biofilms.

Management of Cardiac Device Infections: A Retrospective Survey of a Non-Surgical Approach Combining Antibiotic Therapy with Transvenous Removal

Pacemakers (PMs) and implantable cardioverter defibrillators (ICDs) have become life-saving therapeutic tools for patients with cardiac arrhythmia. Complications include thrombosis, embolism and infections at a highly variable rate. Surgical removal of the infected device has been perceived as the only way to guarantee a successful outcome and to reduce the high risk of mortality. Recently, a transvenous extraction method has been developed to remove infected intracardiac leads without sternotomy. This survey was designed to evaluate the outcome of an approach combining antibiotic therapy with non-surgical transvenous complete removal for the management of cardiac device infections (CDIs). We reviewed case-histories of 121 patients (105 with PM and 16 with ICD infections). The aim of our retrospective survey was to ascertain that a non-invasive transvenous complete removal of the infected devices is safe and effective when associated with appropriate antibiotic therapy starting 10 days before the procedure and extending to at least three weeks after. The infected devices were successfully removed in all patients with a non-surgical transvenous technique. The infections were most frequently caused by coagulase-negative staphylococci (70%), Staphylococcus aureus (14%), and Gram-negative rods (12%). Polymicrobial infections were documented in 19 patients and represent 16% of all device-related infections. The removal of the devices was done during antibiotic therapy, administered for a median of 26 days (range 23 to 45 days). Neither fatalities nor relapse of infections were recorded in the patient population during the one-year follow-up visits. According to our experience, CDIs can be treated with antibiotic therapy and non-surgical removal of the entire infected device, thus allowing a successful reimplantation. This procedure prevents recurrent infections and operative mortality.

Recurrent bilateral breast abscesses after sternotomy

Median sternotomy is the most commonly used incision in cardiothoracic procedures. Development of breast abscess after sternotomy is a very rare situation. We present a case of sternal wound infection with recurrent bilateral breast abscess after sternotomy. Our case is the first and only case in the literature due to the presence of sternal wound infection with recurrent bilateral breast abscess after sternotomy.

Complete genome and transcriptomes of Streptococcus parasanguinis FW213: phylogenic relations and potential virulence mechanisms

Streptococcus parasanguinis, a primary colonizer of the tooth surface, is also an opportunistic pathogen for subacute endocarditis. The complete genome of strain FW213 was determined using the traditional shotgun sequencing approach and further refined by the transcriptomes of cells in early exponential and early stationary growth phases in this study. The transcriptomes also discovered 10 transcripts encoding known hypothetical proteins, one pseudogene, five transcripts matched to the Rfam and additional 87 putative small RNAs within the intergenic regions defined by the GLIMMER analysis. The genome contains five acquired genomic islands (GIs) encoding proteins which potentially contribute to the overall pathogenic capacity and fitness of this microbe. The differential expression of the GIs and various open reading frames outside the GIs at the two growth phases suggested that FW213 possess a range of mechanisms to avoid host immune clearance, to colonize host tissues, to survive within oral biofilms and to overcome various environmental insults. Furthermore, the comparative genome analysis of five S. parasanguinis strains indicates that albeit S. parasanguinis strains are highly conserved, variations in the genome content exist. These variations may reflect differences in pathogenic potential between the strains.

Effect of Three Wound Dressings on Infection, Healing Comfort, and Cost in Patients With Sternotomy Wounds

STUDY OBJECTIVE

To compare three dressing types in terms of their ability to protect against infection and promote healing, patient comfort, and cost-effectiveness.

DESIGN

Prospective, randomized controlled trial.

SETTING

Major metropolitan, academically affiliated, tertiary referral center.

PATIENTS

Seven hundred thirty-seven patients were randomized to receive a dry absorbent dressing (n = 243) [Primapore; Smith & Nephew; Sydney, NSW, Australia], a hydrocolloid dressing (n = 267) [Duoderm Thin ConvaTec; Mulgrave, VIC, Australia], or a hydroactive dressing (n = 227) [Opsite; Smith & Nephew] in the operating theater on skin closure.

RESULTS

There was no difference in the rate of wound infection or wound healing between treatment groups. The Primapore dressing was the most comfortable and cost-effective dressing option for the sternotomy wound. Duoderm Thin dressings were associated with increased wound exudate (p < 0.001), poor dressing integrity (p < 0.001), more frequent dressing changes (p < 0.001), more discomfort with removal (p < 0.05), and increased cost (p < 0.001).

CONCLUSIONS

In the context of no additional benefit for the prevention of wound infection or the rate of wound healing for any of the three dressing products examined, dry absorbent dressings are the most comfortable and cost-effective products for sternotomy wounds following cardiac surgery.

Study of developed resistance due to antibiotic treatment of coagulase-negative Staphylococci

Coagulase-negative Staphylococci (CoNS) are a major cause of postoperative infections. These infections are often associated with foreign material implants and/or a compromised immune system in the patient. Multiresistant strains are increasingly common in the hospital environment and there is concern that the infections will become difficult or impossible to treat. This report is based on a study of 75 patients, with postoperative infections caused by CoNS after thoracic surgery. All patients were treated with surgical revision and antibiotic therapy. One or more bacterial cultures were made in each case, and the resistance pattern of the CoNS found was determined. The goal of the study was to evaluate possible relationships between antibiotic therapy and the appearance of resistance to antibiotics in CoNS found. To describe this relationship, three models were constructed and analyzed by multiple logistic regression. The results indicate an increased resistance to beta-lactam antibiotics and clindamycin after the use of cephalosporins. Also, the use of vancomycin or vancomycin in combination with rifampicin or fusidic acid increases the risk for development of resistance to beta-lactam antibiotics, ciprofloxacin, fusidic acid, clindamycin, netilmycin, and rifampicin. The hypothesis that a combination of antibiotics will curtail the development of resistance was not supported in this study.

Surgical treatment of pacemaker and defibrillator lead endocarditis: the impact of electrode lead extraction on outcome

BACKGROUND

Cardiac device (CD) endocarditis is an infrequent but potentially lethal infectious complication of permanent pacemakers or implantable cardioverter-defibrillators (ICDs), and mortality rates of 30 to 35% have been reported. Medical treatment has been suggested for the treatment of CD endocarditis, but there is increasing evidence that surgical treatment is to be preferred as the best approach to achieve eradication of the infection and reduce mortality.

OBJECTIVE

To evaluate the following: (1) the clinical and echocardiographic characteristics of patients with pacemaker or ICD endocarditis, (2) the outcome of this population depending on the mode of treatment (medical vs surgical treatment), and (3) the clinical, microbiological, echocardiographic, and therapeutic variables associated with patient outcome.

DESIGN

Prospective cohort study.

SETTING

Tertiary referral center in Barcelona, Spain.

PATIENTS

All consecutive patients with infectious endocarditis (IE) admitted to the study institution between 1990 and 2001 were prospectively evaluated by a multidisciplinary treatment team, and a definite diagnosis of CD endocarditis was established when cases met pathologic or clinical criteria according to the Duke criteria.

RESULTS

A total of 31 patients, 25 men and 6 women aged 61 +/- 15 years (mean +/- SD), with pacemaker or ICD endocarditis were identified among 669 consecutive patients (4.6%) with IE. During the study period, a total of 3,768 pacemakers and 460 ICDs were implanted in the study institution. In 22 cases of pacemaker endocarditis, the pacemaker was implanted in our institution, and 9 cases were referred from other institutions (incidences of endocarditis on pacemaker and ICD implanted in our institution of 0.58% and 0.65%, respectively). Medical treatment without removal of the pacing system was initially performed on seven patients; all of them (100%) had relapses of endocarditis, and one patient died. The remaining 24 patients underwent surgical removal of the pacing system; 1 patient had one relapse, 3 patients died after surgical treatment, and the others were successfully cured with no relapses after a mean follow-up of 38 +/- 9 months. Clinical, echocardiographic, microbiological, and therapeutic variables were evaluated in association with prognosis. The only prognostic factor for failure of treatment or mortality was the absence of surgical treatment (p < 0.0001).

CONCLUSIONS

Electrode lead endocarditis occurred in < 1% of pacemaker and ICD implants. Conservative treatment without explantation of all hardware failed in all patients, and surgical treatment during antibiotic therapy was effective in eradication of infection but was associated with a 12.5% mortality. The only patient characteristic associated with treatment failure or death was the absence of surgical removal of all infected hardware. Complete extraction of the pacemaker or ICD should be considered as standard therapy for most patients with CD endocarditis.

Nosocomial infections occurring during receipt of circulatory support with the paracorporeal ventricular assist system

This retrospective study sought to report the spectrum of infections in a homogenous group of 39 patients who underwent implantation of the Thoratec paracorporeal ventricular assist device system (Thoratec Laboratories) in an emergency setting. Thirty-one of the 39 patients developed a total of 99 nosocomial infections (attack rate, 79.5%; incidence, 4.9 per 100 support-days). The lungs were the most frequently involved site (31.3%), and coagulase-negative Staphylococcus species were the pathogens most frequently isolated (16.2%). Infected patients required more transfusions and chest surgical revisions, as well as a longer duration of mechanical ventilation and a longer stay in the intensive care unit, compared with uninfected patients. Cox regression analysis revealed that chest surgical revision was the only independent risk factor for infection at any site (odds ratio, 2.6; 95% confidence interval, 1.2-5.7). There was no significant effect of infection on heart transplantation rate and overall survival.

Nosocomial cardiac infections

The most important nosocomial cardiac infections include nosocomial infective endocarditis on native and prosthetic valves, and nosocomial infections related to transvenous permanent pacemakers, implantable cardioverter-defibrillators and left ventricular assist devices. Although representing rare complications, they are of great importance because they are associated with high morbidity and mortality. Most of them are encountered in older-age groups, related to nosocomial invasive procedures performed within the preceding four to eight weeks of hospital admission. Nosocomial bacteraemia associated with infected central intravascular devices, genitourinary or gastrointestinal tract surgery and instrumentation, breaks in sterile surgical techniques at the implantation of prosthetic valves and cardiac devices as well as wound and skin infections, represent the most important risk factors. Staphylococcus aureus in native valve endocarditis and S. epidermidis in the presence of foreign bodies are the main implicated pathogens. However, because of the steeply increasing incidence of candidaemia in tertiary hospitals, nosocomial cardiac infections caused by Candida spp. have also been steadily increasing over the last decades. Diagnosis of nosocomial cardiac infections, particularly in the presence of foreign bodies, is often difficult because of the severity of patients' co-morbid illnesses and the co-existence of several risk factors. Diagnosis should be based on positive blood cultures and transoesophageal echocardiographic findings in febrile high-risk patients. Therapy necessitates a combination of antibiotics and surgical removal of foreign bodies. Prophylaxis should mainly target the prevention and/or appropriate treatment of bacteraemias secondary to infected intravascular devices, as well as application of prophylaxis guidelines whenever invasive hospital-based procedures are performed in high-risk individuals.

Streptococcus parasanguis fimbria-associated adhesin fap1 is required for biofilm formation

The sanguis streptococci are primary colonizers of the tooth surface and thus form the foundation for the complex multiple species biofilm known as dental plaque. In addition, these bacteria can colonize native and prosthetic heart valves and are a common cause of endocarditis. Little is known about the molecular mechanisms governing multiple or single species biofilm development within this group of organisms. Using an in vitro assay for biofilm formation, we determined that (i) Streptococcus parasanguis FW213 can form biofilms on inert surfaces such as polystyrene and (ii) environmental and nutritional factors, such as glucose, affect S. parasanguis biofilm formation. Several isogenic mutants of FW213 were tested in the biofilm assay. Strains containing mutations in fap1, a gene encoding a protein required for assembly of fimbriae, were deficient in biofilm formation. Mutants defective in recA, PepO endopeptidase activity, or the production of a fimbriae-associated protein, FimA, were still capable of biofilm formation. Phase-contrast microscopy was used to follow biofilm development by wild-type and fap1 mutant strains on plastic coverslips over time. Wild-type FW213 attached to the surface, formed aggregates of cells, and eventually formed a dense layer of cells that included microcolonies. In contrast, few fap1 mutant cells were observed attached to the surface, and no cell aggregates or microcolonies were formed. These results suggest that the long peritrichous fimbriae of FW213 are critical for the formation of biofilms on solid surfaces.

Saphenous vein graft infection: a fatal complication of postoperative mediastinitis

Infection and erosion of the saphenous vein graft with mediastinal hemorrhage is a rare but highly lethal complication of cardiac surgery. This is associated with a mortality rate of 50%. We present a patient who died during the postoperative period due to this complication.

Optimized performance of the Abiomed BVS 5000: adjustment of the pump height based on Doppler control of the flow pattern

The Abiomed BVS 5000 is an automatic volume-driven paracorporeal pulsatile assist device providing left, right or biventricular support. The paracorporeal position allows optical adjustment of filling volumes of the device, which determines the output of the system. A procedure to adjust for maximal stable flow has not yet been established. In vitro measurements have been performed to assess the flow and pressure characteristics of the Abiomed BVS 5000 by raising the preload in 5 mmHg steps before running the system. Doppler probes were placed at the inflow and outflow lines of the pump. After setting the afterload at 80 mmHg the assist device was started. Two measurements were performed to find optimal flow (based on Doppler control and optical adjustment). (1) By Doppler control a stable flow pattern was found at a preload of 25 mmHg with a mean atrial pressure of 5 mmHg and a mean flow of 5.3 +/- 0.7 l/min (mean +/- standard deviation) at the inflow and outflow sites (the console flow was 4.8 +/- 0.4 l/min with a frequency of 61.8 +/- 2.0 l/min). (2) Optical adjustment of the pump height gave rise to a preload of 35 mmHg where we recorded a maximal atrial pressure of 107 +/- 5.8 mmHg, a maximal retrograde flow of -4.3 +/- 1.2 l/min at the inflow and -1.2 +/- 0.4 l/min at the outflow site. The mean flow at the inflow and outflow sites was 5.1 +/- 0.5 l/min (the console flow was 4.6 +/- 0.3 l/min with a frequency of 59.6 +/- 2.6 Hz). At an initial afterload of 60 and 40 mmHg the system showed the same qualitative behaviour, but the results were less accurate. Optical adjustment of the pump height may result in an atrioventricular valve insufficiency with undetected retrograde flow and high atrial pressures. We conclude that a Doppler flow probe must be placed at the inflow site to guarantee maximal stable flow.