Staphylococcus aureus AbcA transporter enhances persister formation under ß-lactam exposure.

We evaluated the role of Staphylococcus aureus AbcA transporter in bacterial persistence and survival following exposure to the bactericidal agents nafcillin and oxacillin at both the population and single-cell levels. We show that AbcA overexpression resulted in resistance to nafcillin but not oxacillin. Using distinct fluorescent reporters of cell viability and AbcA expression, we found that over 6-14 hours of persistence formation, the proportion of AbcA reporter-expressing cells assessed by confocal microscopy increased sixfold as cell viability reporters decreased. Similarly, single-cell analysis in a high-throughput microfluidic system found a strong correspondence between antibiotic exposure and AbcA reporter expression. Persister cells grown in the absence of antibiotics showed neither an increase in nafcillin MIC nor in abcA transcript levels, indicating that survival was not associated with stable mutational resistance or abcA overexpression. Furthermore, persister cell levels on exposure to 1×MIC and 25×MIC of nafcillin decreased in an abcA knockout mutant. Survivors of nafcillin and oxacillin treatment overexpressed transporter AbcA, contributing to an enrichment of the number of persisters during treatment with pump-substrate nafcillin but not with pump-non-substrate oxacillin, indicating that efflux pump expression can contribute selectively to the survival of a persister population.

Effect of PLGA hydrophilia on the drug release and the hypoglucemic activity of different insulin-loaded PLGA microspheres.

The effects of viscosity and hydrophilic characteristics of different PLGA polymers on the microencapsulation of insulin have been studied in vitro and in vivo after subcutaneous administration to hyperglycemic rats. Hydrophilic PLGA polymers produced a higher burst effect than the hydrophobic ones. Moreover, an incomplete insulin release was observed with the hydrophilic PLGA polymers in comparison with the hydrophobic ones. An explanation for that incomplete release can be the development of polymer-insulin interactions associated to the polymer hydrophilic/hydrophobic character, as detected by DSC analysis. Differences in the release rate of microsphere formulations lead to differences in the hypoglycemic action and the weight of animals. Hydrophobic PLGA was able to prolong the hypoglycemic action up to 4 weeks which is at least double than that obtained with hydrophilic PLGA of a similar viscosity. Comparing insulin microspheres with an immediate release formulation, microspheres can increase insulin relative bioavailability up to four times.

In vivo distribution and therapeutic efficacy of a novel amphotericin B poly-aggregated formulation.

OBJECTIVES: The purpose of this investigation is the study of toxicity, in vivo distribution and therapeutic activity against candidiasis of poly-aggregated amphotericin B, in two different formulations: not microencapsulated (P-AMB) or incorporated in albumin microspheres (MP-AMB). METHODS: The therapeutic efficacy and toxicity of amphotericin B formulations was studied in an immunocompetent murine model of systemic candidiasis. A pharmacokinetic study was also performed to measure the plasma, kidney, liver and spleen amphotericin B concentrations after administration of the three formulations to mice. RESULTS: The acute toxicity of P-AMB in mice is lower than that of the conventional amphotericin B reference formulation (D-AMB). The 50% lethal doses were increased at least eight times. Intravenous bolus administration of doses up to 40 mg/kg of body weight of poly-aggregated amphotericin B, either P-AMB or MP-AMB, did not produce acute symptoms of toxicity. Interestingly, in the pharmacokinetic study, significant (P < 0.05) lower plasma and kidney amphotericin B concentrations and higher liver and spleen amphotericin B concentrations were achieved after poly-aggregated amphotericin B formulation (P-AMB and MP-AMB) administration in relation to the reference formulation (D-AMB). At high amphotericin B doses, no significant differences in efficacy (P > 0.05) were observed among the formulations (D-AMB, P-AMB and MP-AMB). CONCLUSIONS: Although the efficacy in the candidiasis treatment was decreased as a consequence of amphotericin B aggregation, it can be compensated by the possibility of increasing the doses with lower nephrotoxicity. Moreover, due to its lower toxicity while maintaining its effectiveness, the poly-aggregated formulations (P-AMB and MP-AMB) have a better therapeutic index than the conventional formulation (D-AMB).

HPLC assay for determination of amphotericin B in biological samples.

A fast and selective HPLC method for assaying amphotericin B in biological samples was developed and validated. The chromatographic separation was achieved in less than 12 min on a reverse-phase C(18) column using an acetonitrile-acetic acid-water (52:4.3:43.7, v/v/v) mixture as mobile phase. The flow rate was 1 mL/min and the effluent was monitored at 406 nm. A linear response over the concentration range 0.1-10.0 microg/mL was obtained. Intra-day and inter-day RSDs were below 5% for all the sample types. This new HPLC method was applied to assay amphotericin B in plasma and several tissue samples such as kidney, liver, spleen and bone marrow. Application of this method to pharmacokinetic studies in mice and dog is provided.

Amphotericin B formulations and drug targeting.

Amphotericin B is a low-soluble polyene antibiotic which is able to self-aggregate. The aggregation state can modify its activity and pharmacokinetical characteristics. In spite of its high toxicity it is still widely employed for the treatment of systemic fungal infections and parasitic disease and different formulations are marketed. Some of these formulations, such as liposomal formulations, can be considered as classical examples of drug targeting. The pharmacokinetics, toxicity and activity are clearly dependent on the type of amphotericin B formulation. New drug delivery systems such as liposomes, nanospheres and microspheres can result in higher concentrations of AMB in the liver and spleen, but lower concentrations in kidney and lungs, so decreasing its toxicity. Moreover, the administration of these drug delivery systems can enhance the drug accessibility to organs and tissues (e.g., bone marrow) otherwise inaccessible to the free drug. During the last few years, new AMB formulations (AmBisome, Abelcet, and Amphotec) with an improved efficacy/toxicity ratio have been marketed. This review compares the different formulations of amphotericin B in terms of pharmacokinetics, toxicity and activity and discusses the possible drug targeting effect of some of these new formulations.

Does exposure to magnesium sulfate in utero decrease the risk of necrotizing enterocolitis in premature infants?

BACKGROUND: The objective of this study is to assess whether antenatal exposure to magnesium sulfate may decrease the risk of necrotizing enterocolitis in preterm infants. METHODS: We have compared the rate of magnesium sulfate exposure before birth among 23 consecutive infants diagnosed with necrotizing enterocolitis with that of 46 controls matched by gestational age at delivery and gender. Relevant obstetric and neonatal variables were compared between the two groups using chi-square and Fisher's exact test for categorical data, and one-way analysis of variance for continuous variables, with a two-tailed p-value <0.05 considered significant. RESULTS: No significant differences were present between the two groups in mode of delivery (p=0.9), rate of Apgar score at five minutes below seven (p=0.4), prenatal exposure to indocin (p=0.5) or steroids (p=0.6), or neonatal administration of surfactant (p=0.1). Similar proportions of babies with necrotizing enterocolitis and controls were diagnosed with respiratory distress syndrome (p=0.5), intraventricular hemorrhage grades three or four (p=0.9), and sepsis (p=0.6). Babies with necrotizing enterocolitis had a significantly longer hospital stay (74.6+/-64.0 vs. 41.9+/-37.0 days, p=0.01) and intubation period (31.4+/-24.1 vs. 16.8+/-15.6 days, p=0.01) than controls. The rates of prenatal exposure to magnesium sulfate were similar in the necrotizing enterocolitis and control groups (30% vs. 39% respectively, p=0.4). Power analysis demonstrated that 385 babies would be required in each group to reach statistical significance (alpha=0.05, beta=80%). CONCLUSION: In this retrospective case-control study, maternal administration of magnesium sulfate prior to delivery does not appear to confer a significant protective effect for the neonatal occurrence of necrotizing enterocolitis.

Chest radiograph heterogeneity predicts functional improvement with volume reduction surgery.

BACKGROUND: Using a historical cohort study model, we tested the hypothesis that heterogeneity of emphysematous changes on the preoperative chest radiograph correlated with favorable outcome of lung volume reduction surgery. METHODS: The test population consisted of 21 patients with severe emphysema who were being treated at a 1,000-bed university-affiliated tertiary teaching hospital. A simple but quantitative index of heterogeneity has been devised, whereby the preoperative posteroanterior chest radiographic lung fields are divided into four geometric quadrants. Each quadrant is scored (0 to 4) for emphysematous changes by two radiologists blinded as to subsequent patient management and outcome. Criteria for determining presence of emphysema were hyperlucency, decreased vascular markings, and parenchymal crowding indicating compressed lung. Heterogeneity index is the sum of the two highest scores minus the two lowest, with a maximum index of 8 and a minimum of 0. Preoperative chest radiographs and postoperative changes in forced expiratory volume in 1 second were examined. RESULTS: The heterogeneity index was positively correlated with change in forced expiratory volume in 1 second after operation with an r2 of 0.31 and an average increase of 117 mL per unit increase in heterogeneity index (p < 0.009). CONCLUSIONS: This simple index of heterogeneity may be useful as a predictor of improved pulmonary function after lung volume reduction surgery.

Intermittent brachiocephalic vein obstruction secondary to a thymic cyst.

Mediastinal thymic cysts are usually asymptomatic and found incidentally on a routine chest roentgenogram. Rarely, they may cause symptoms of vascular obstruction. A 55-year-old woman presented with intermittent swelling in her left neck. The swelling was positional and was worse while supine and disappeared while upright. Evaluation revealed a thymic cyst causing extrinsic compression of the left brachiocephalic vein. The cyst was resected with complete resolution of the left neck swelling.

Methods of acute postcardiotomy left ventricular assistance.

OBJECTIVE: Despite many technological advances in cardiovascular surgery, some patients still experience postcardiotomy left ventricular (LV) failure that is refractory to both inotropic support and intra-aortic balloon pump (IABP) placement. The primary author (MJR) recently changed from inflow cannulation at the right superior pulmonary vein/left atrial junction to inflow cannulation at the dome of the left atrium. The purpose of this study was to compare data collected during placement of a left ventricular assist device (LVAD) at the junction of the right superior pulmonary vein with positioning the device in the dome of the left atrium. Experimental design, setting, and participants: the medical records of all patients undergoing cardiac surgery by one author (MJR) between 1994 and 1997 were retrospectively reviewed, and 4 patients requiring LVAD placement for short term postcardiotomy support were identified. Each patient's chart was reviewed for duration of LVAD support, average LVAD blood flows, pulmonary capillary wedge pressures (PCWP), preoperative characteristics, postoperative complications, and final outcome for the patients. RESULTS: Accessing the left atrium through the dome resulted in excellent blood flow through the LVAD and allowed for good LV decompression. Hemostasis remained the most common complication regardless of the technique employed; however, the enhanced visibility provided by accessing the left atrium via the dome made repairs less technically difficult. Three patients (75%) were able to be weaned from the LVAD and were discharged from the hospital to home. Two of these patients were cannulated via the left atrial dome making removal of the LVAD easier, thus exposing the patients to less additional operative time. One patient could not be weaned from LVAD support secondary to development of right ventricular failure requiring RVAD insertion and subsequent development of multiple organ failure syndrome. CONCLUSIONS: Patients requiring LV assistance following cardiopulmonary bypass surgery traditionally have high levels of morbidity and mortality. In spite of the complications associated with the placement of an assist device, we remain encouraged by the excellent LV decompression and systemic flows we achieved following implantation of the LVAD through the dome of the left atrium. The superior ease of implantation and decannulation provided better operative care and postoperative management for our patients.

Relation of the contractile reserve of hibernating myocardium to myocardial structure in humans.

BACKGROUND: Although dobutamine echocardiography (DE) is widely used to assess myocardial viability in humans, little is known about the relation between contractile reserve and myocardial structure. METHODS AND RESULTS: We evaluated 20 patients with coronary disease (64+/-13 years old, ejection fraction 28+/-7.5%) with DE (up to 40 micrograms . kg(-1). min(-1)), rest-redistribution (201)Tl single photon emission CT, and quantitative angiography before bypass surgery. During surgery, patients underwent transmural myocardial biopsies (n=37) guided by transesophageal echocardiography to determine the extent of interstitial fibrosis and intracellular and interstitial proteins by histopathology and immunohistochemistry. Among the 37 segments biopsied, 16 recovered function as assessed 2 to 3 months later. Segments with postoperative functional recovery had more wall thickening at low-dose DE (28% versus 3%, P<0.001), higher thallium uptake (69% versus 48%, P=0.03), and less interstitial fibrosis (2% versus 28%, P<0.001). Quantitative angiographic parameters did not predict recovery of function. Segments with DE viability (contractile reserve and/or ischemia) had less fibrosis (2.7% versus 28%, P<0.001), less vimentin and fibronectin (both P<0.01), more glycogen (P=0.016), and higher thallium uptake (64% versus 35.5%, P<0.05) than those without viability. Viable segments by both DE and thallium had less fibrosis (1%) than those viable by 1 of the 2 techniques (9%) or not viable by both (28%, P=0.005). Thickening at low-dose DE correlated well with the extent of interstitial fibrosis (r=-0.83, P<0.01). CONCLUSIONS: Contractile reserve during DE correlates inversely with the extent of interstitial fibrosis and the amount of fibronectin and vimentin and directly with rest-redistribution thallium uptake.

The anatomical aspects of minimally invasive cardiac valve operations.

Cadaveric dissections were carried out to examine the relationship of the cardiac valve structures to the surface anatomy of the chest as it relates to our approaches to minimally invasive valvular operations. The techniques of upper hemisternotomy and lower hemisternotomy as used at our institution are described.

Effect of extended cross-clamp time during thoracoabdominal aortic aneurysm repair.

BACKGROUND: In previous studies of the neurologic outcome of patients undergoing thoracoabdominal aortic aneurysm repair with the simple cross-clamp technique, cross-clamp time of greater than 30 minutes was identified as an important risk factor. We retrospectively examined the effect of clamp time of 30 minutes or greater on outcome for patients undergoing repair with the addition of surgical adjuncts. METHODS: Between February 1991 and June 1996 we operated on 370 patients for thoracoabdominal or descending thoracic aortic aneurysm. Two hundred seventy-one of these patients with cross-clamp times of 30 minutes or greater were included in this study. One hundred twelve patients underwent simple cross-clamp repair, whereas 159 were operated on with the surgical adjuncts of distal aortic perfusion and cerebrospinal fluid drainage. RESULTS: By multivariate analysis, acute dissection, surgical adjuncts, and aneurysm extent proved most significant in overall patient outcome. The overall rate of early neurologic deficits was 23 of 271 (8.5%). For highest risk patients with type II thoracoabdominal aortic aneurysms, the rate of neurologic deficits was 11 of 29 (38%) for cross-clamp versus 6 of 82 (7.3%) for adjunct operation patients (odds ratio = 0.13; p < 0.001). CONCLUSIONS: The adjuncts of cerebrospinal fluid drainage and distal aortic perfusion decreased the risk of extended cross-clamp time during thoracoabdominal aortic aneurysm repair, particularly for highest risk type II.

Thoracic and thoracoabdominal aortic aneurysm repair using cardiopulmonary bypass, profound hypothermia, and circulatory arrest via left side of the chest incision.

PURPOSE: Although some authors advocate hypothermic circulatory arrest for spinal cord protection in descending thoracic and thoracoabdominal repair, this method has been associated with high morbidity and mortality rates in other studies. The safety and effectiveness of this surgical adjunct were evaluated. METHODS: Between February 1991 and April 1997, 409 patients underwent thoracic or thoracoabdominal aortic repair. Because of an inability to gain proximal aortic control because of anatomic or technical difficulty, hypothermic circulatory arrest was used in 21 patients (4.9%). Thirteen patients were men, 8 were women, and the median age was 57 (range, 21 to 81 years). Four patients (19%) had Marfan's syndrome, and 1 had aortitis. Seven patients (33%) had aortic dissection (4 chronic type A, 2 chronic type B, 1 acute B), and 1 had aortic laceration. All but 6 patients had hypertension. Fifteen patients (73%) were operated on for repair of the distal arch and descending thoracic aorta, 4 (19%) for repair of the distal arch and thoracoabdominal aorta, and 2 for repair of either the thoracoabdominal or descending thoracic aorta alone. Surgery for 9 patients (43%) also included bypass grafts to the subclavian or innominate arteries. Six operations (29%) were urgent. RESULTS: The overall 30-day mortality rate was 29% (6 of 21 patients). Among urgent patients, the mortality rate was 50% (3 of 6 patients) versus 20% (3 of 15) for elective patients. Of the remaining 15 patients, renal failure occurred in 1 (7%) and heart failure in 2 (13%). Ten patients (67%) had pulmonary complications. Encephalopathy occurred in 5 patients (33%) and stroke in 2 (13%), and spinal cord neurologic deficit developed in 2 (13%). The median recovery was 28 days (range, 10 to 157 days). CONCLUSION: Hypothermic circulatory arrest did not reduce the incidence of deaths and morbidity to a rate comparable with our conventional methods. We recommend the judicious application of this method in rare instances when proximal control is not feasible or catastrophic intraoperative bleeding leave the surgeon with no other option.

Operation for acute and chronic aortic dissection: recent outcome with regard to neurologic deficit and early death.

BACKGROUND: We reviewed our experience in the repair of acute and chronic aortic dissection with regard to early neurologic deficit and death. METHODS: Between February 1991 and June 1996, we performed 206 operations on 195 patients for aortic dissection. Ascending or arch repair, or a combination (type A dissection) was performed on 92 of 206 patients (45%); 44 of 92 (48%) were acute dissection and 48 of 92 (52%) were chronic. Descending or thoracoabdominal repair (type B dissection) was performed on 114 of 206 patients (55%); 22 of 114 (19%) were acute and 92 of 114 (81%) were chronic. RESULTS: Among type A cases, strokes occurred in 6 of 92 patients (7%) overall; 4 of 44 (9%) were acute cases and 2 of 48 (4%) were chronic (p < 0.34). Early deaths for type A were 11 of 92 (12%) overall; 9 of 44 (20%) acute and 2 of 48 (4%) chronic (p < 0.02). In type B cases, neurologic complications were 15 of 114 (13%) overall; 7 of 22 (32%) were acute cases and 8 of 92 (9%) were chronic (p < 0.004). Early deaths for type B were 12 of 114 (11%) overall; 3 of 22 (14%) acute and 9 of 92 (10%) chronic (p < 0.6). Preoperative hypotension was significant in acute type A patients, with strokes in 2 of 7 (29%) hypotensives compared with 2 of 37 (5%) normotensives (p < 0.05) and early death in 4 of 7 (57%) hypotensives versus 5 of 37 (14%) normotensives (p < 0.009). CONCLUSIONS: Morbidity and mortality for repair of chronic dissection types A and B were acceptable. Preoperative hypotension in acute type A dissection was a major predisposing factor toward stroke (29% versus 5%, p < 0.05). Acute type B dissection had acceptable mortality (14%) but a high rate of neurologic complications (32%).

Mitral valve injury from blunt trauma.

Mitral valve injury from blunt trauma to the chest is an uncommon entity. We report a case of mitral valve injury after a fall, and its repair. The English literature is reviewed from the earliest report in 1873 to the present. The diagnosis, types of injury and surgical correction are discussed.

New developments in mitral valve repair.

The etiology of mitral valve disease is changing. The predominance of rheumatic pathology has given way to degenerative pathology in an increasingly elderly population. Mitral valve conservation by repair rather than replacement has several advantages. Repair is associated with a lower incidence of thromboembolism, hemolysis, and infectious endocarditis. For patients in sinus rhythm, thromboembolism is rare and anticoagulation can be discontinued. Repair also is associated with improved long-term survival. This article reviews the current literature on different types of surgical techniques for repair of the mitral valve and discusses future trends.