Staphylococcus aureus endocarditis in preterm neonates

Successfully treated infective endocarditis caused by methicillin-resistant Staphylococcus Aureus in extremely low birth weight infant

Survival rates of preterm infants have improved in the past few decades, and central venous catheters play an important role in the intensive medical treatment of these neonates. Unfortunately, these indwelling catheters increase the risk of intracardiac thrombosis, and they provide a nidus for microorganisms during the course of septicemia. Herein, we report a case of persistent bacteremia due to methicillin-resistant Staphylococcus aureus in an extremely low birth weight (ELBW) infant, along with vegetation observed on an echocardiogram, the findings which are compatible with a diagnosis of endocarditis. The endocarditis was successfully treated with antibiotic therapy, and the patient recovered without major complications. We suggest a surveillance echocardiogram for ELBW infants within a few days of birth, with regular follow-up studies when clinical signs of sepsis are observed.

Phosphorylation of MgrA and its effect on expression of the NorA and NorB efflux pumps of Staphylococcus aureus

MgrA is a global regulator in Staphylococcus aureus that controls the expression of diverse genes encoding virulence factors and multidrug resistance (MDR) efflux transporters. We identified pknB, which encodes the (Ser/Thr) kinase PknB, in the S. aureus genome. PknB was able to autophosphorylate as well as phosphorylate purified MgrA. We demonstrated that rsbU, which encodes a Ser/Thr phosphatase and is involved in the activation of the SigB regulon, was able to dephosphorylate MgrA-P but not PknB-P. Serines 110 and 113 of MgrA were found to be phosphorylated, and Ala substitutions at these positions resulted in reductions in the level of phosphorylation of MgrA. DNA gel shift binding assays using norA and norB promoters showed that MgrA-P was able to bind the norB promoter but not the norA promoter, a pattern which was the reverse of that for unphosphorylated MgrA. The double mutant MgrA(S110A-S113A) bound to the norA promoter but not the norB promoter. The double mutant led to a 2-fold decrease in norA transcripts and a 2-fold decrease in the MICs of norfloxacin and ciprofloxacin in strain RN6390. Thus, phosphorylation of MgrA results in loss of binding to the norA promoter, but with a gain of the ability to bind the norB promoter. Loss of the ability to phosphorylate MgrA by Ala substitution resulted in increased repression of norA expression and in reductions in susceptibilities to NorA substrates.

Staphylococcus aureus Septicemia with a fatal transmural myocardial infarction in a 27-week-gestation twin infant: a case study

Septicemia, one of the major causes of morbidity and mortality in the neonatal period, often has a rapid and fulminant course. Low-birth-weight infants with persistent Staphylococcus aureus septicemia, possibly associated with percutaneous central venous catheters, may develop metastatic infections including endocarditis with large vegetations. This article describes a neonate with S. aureus bacteremia that resolved with treatment who died secondary to decreased left ventricular function. At autopsy, organizing microthrombi were seen within both atria, the left ventricle, and the left coronary arterial system. Extensive infarcts were noted throughout the entire myocardium of the left ventricle. It was suspected, but not proven, that the thrombotic sequelae from septicemia caused this neonate's death.

Frequency of infective endocarditis among infants and children with Staphylococcus aureus bacteremia

PURPOSE

The prevalence of infective endocarditis (IE) among children with Staphylococcus aureus bacteremia (SAB) is unknown. The objective of this study was to determine prospectively the prevalence of IE among pediatric patients with SAB in a large tertiary care center.

METHODS

Between July 1998 and June 2001, all children who developed SAB whose parent/guardian signed informed consent underwent echocardiography. Clinical and follow-up results were collected prospectively. Endocarditis was classified according to the modified Duke criteria.

RESULTS

Fifty-one children developed SAB during the study interval. Definite (6 patients [11.8%]) or possible (4 patients [7.8%]) IE was present in 10 of 51 (20%) children with SAB. Most children (73%) developed bacteremia as a consequence of an infected intravascular device. Children with underlying congenital heart disease had a significantly higher prevalence of definite or possible IE, compared with those with structurally normal hearts (53% vs 3%). All patients with definite IE had multiple positive blood cultures. Mortality was high among patients with and without IE (40% vs 12%).

CONCLUSIONS

In this study, the prevalence of definite IE among children with SAB was approximately 12% and was frequently associated with congenital heart disease and multiple positive blood cultures. The mortality for children with SAB and definite or possible S aureus IE is high.

Clinical microbiology of bacterial and fungal sepsis in very-low-birth-weight infants

Twenty percent of very-low-birth-weight (<1500 g) preterm infants experience a serious systemic infection, and despite advances in neonatal intensive care and antimicrobials, mortality is as much as threefold higher for these infants who develop sepsis than their counterparts without sepsis during their hospitalization. Outcomes may be improved by preventative strategies, earlier and accurate diagnosis, and adjunct therapies to combat infection and protect the vulnerable preterm infant during an infection. Earlier diagnosis on the basis of factors such as abnormal heart rate characteristics may offer the ability to initiate treatment prior to the onset of clinical symptoms. Molecular and adjunctive diagnostics may also aid in diagnosing invasive infection when clinical symptoms indicate infection but no organisms are isolated in culture. Due to the high morbidity and mortality, preventative and adjunctive therapies are needed. Prophylaxis has been effective in preventing early-onset group B streptococcal sepsis and late-onset Candida sepsis. Future research in prophylaxis using active and passive immunization strategies offers prevention without the risk of resistance to antimicrobials. Identification of the differences in neonatal intensive care units with low and high infection rates and implementation of infection control measures remain paramount in each neonatal intensive care unit caring for preterm infants.

Central venous catheter techniques in infants and children

PURPOSE OF REVIEW

The placement of central venous catheters is often necessary to facilitate optimal anaesthetic and perioperative management or for the long-term management of chronic underlying diseases. Insertion may be a challenge in selected patients, and the risk of infection, thrombosis, and other complications may result in significant risk factors.

RECENT FINDINGS

Ultrasound visualization of the cervical veins with Valsalva manoeuvres significantly increases the rate and safety of central venous cannulation, and decreases needle passes in paediatric patients even with experienced operators. Pericardial effusion with tamponade is a more frequent phenomenon than generally realized, and accurate location of the catheter-tip position is essential. The femoral venous approach has proved to be safe even in premature babies. Clear guidelines for infection control and the prevention of intravascular catheter-related infections in children have been established; however, the high incidence of nosocomial catheter-related infections requires effective prevention strategies. The impact of antimicrobial-impregnated central venous catheters on the prevention of bloodstream infections in children is not yet clear. Routine use of prophylactic antibiosis (i.e. vancomycin) to prevent catheter-related infection cannot be recommended. Thrombolytic therapy with recombinant tissue plasminogen activator is safe, efficient, well tolerated and effective for lysis of catheter-induced intravascular and intracardiac thrombi even in neonates. Embolized catheter fragments can be retrieved in neonates and children by non-surgical interventions using standard procedures applied by paediatric cardiologists.

SUMMARY

Despite a variety of new techniques, the major problem of central venous catheterization in neonates and children remains the prevention of catheter-related infection and infection control.