Effects of tendon injury on uninjured regional tendons in the distal limb: An in-vivo study using an ovine tendinopathy model.

Following injury to a tendon little is known about potential for pathology to develop in other regional tendons from overloading or altered function. The aim of this study was to investigate the gene expression and histopathological changes that occur 1) within the deep digital flexor tendon (DDFT) after injury to the superficial digital flexor tendon (SDFT) and 2) within the flexor tendons (SDFT and DDFT) after injury to the extensor tendons. Merino wethers [Ovis aries] (n = 18) were divided into three equal groups and underwent either partial transection of the SDFT, complete transection of the extensor tendons or were left as non-operated controls. Tendons were harvested and sampled regionally for gene expression (real time PCR) and histologic analysis eight weeks after surgery. Transection of the SDFT resulted in increased expression of collagen III, versican, biglycan, lumican and MMP1 (P<0.026 for all genes) within the DDFT. There was no effect of transecting the extensor tendons on the expression of any gene tested in either the SDFT or the DDFT. The DDFT had elevated histopathology scores induced by transection of the SDFT, eight weeks previously. There were minimal histological differences in either the SDFT or DDFT after transection of the extensor tendons. Transection of the SDFT results in a mild, subclinical tendinopathy within the DDFT with potential implications on treatment and rehabilitation of SDFT injuries. Injury to the extensor tendons has minimal measured effect on the SDFT or DDFT.

Comparison of outcomes of laparoscopic and open appendectomy in management of uncomplicated and complicated appendicitis.

BACKGROUND: Several studies have demonstrated the superiority of the laparoscopic approach in uncomplicated and complicated appendicitis with conflicting results. As a result the role of laparoscopy in the management of appendicitis in general and complicated or perforated appendicitis, in particular, is still undefined. METHODS: A retrospective, observational study design was used to analyze multicenter outcomes using the University HealthSystem Consortium database. A 3-year discharge data of all open appendectomy (OA) and laparoscopic appendectomy (LA) procedures from 2006 to 2008 in adult patients older than 18 years for complicated or uncomplicated appendicitis was accessed using International Classification of Diseases, Ninth Revision codes. Data on several surgical outcome measures such as observed mortality, overall patient morbidity, intensive care unit admission rate, 30-day readmission rate, length of hospital stay, and hospital costs were collected from the University HealthSystem Consortium database. Stratification by University HealthSystem Consortium-specific severity of illness groups and disease diagnosis of complicated or perforated and uncomplicated appendicitis was performed. RESULTS: A total of 40,337 appendectomy procedures performed during 2006 to 2008 in adult patients were included in the study. Laparoscopic appendectomy for uncomplicated appendicitis resulted in significantly better surgical outcomes. However, surprisingly, these outcomes resulted in comparable but not significantly reduced hospital costs (7825 ± 6,009 for LA vs 7841 ± 13,147 for OA; P > 0.05). Laparoscopic appendectomy for complicated or perforated appendicitis showed lower mortality, reduced overall morbidity (17.43% for LA vs 26.68% for OA; P < 0.001), relatively less 30-day readmission rate, fewer intensive care unit admissions, significantly shorter length of hospital stay (4.34 ± 4.84 days for LA vs 7.31 ± 9.43 for OA; P < 0.001), and reduced hospital costs (12,125 ± 14,430 for LA vs 17,594 ± 28,065 for OA; P < 0.001) compared with patients undergoing OA. On stratification for severity of illness in both complicated and uncomplicated appendicitis, laparoscopic appendectomy resulted in a greater or comparable clinical benefit than open appendectomy. Comparable clinical benefit was observed in minor severity patients and moderate and major/extreme severity patients showed vastly improved surgical outcomes with the laparoscopic approach. CONCLUSIONS: Laparoscopic appendectomy is superior or comparable to open appendectomy in terms of several surgical outcome measures for both uncomplicated and complicated appendicitis, across most illness severity groups. Thus, laparoscopic appendectomy may be the preferred technique, irrespective of appendicitis diagnosis or disease severity.

Differences in outcomes of laparoscopic gastric bypass.

BACKGROUND: Although several risk factors affecting weight loss outcomes with bariatric procedures have been identified, the effect of age, gender, race, and illness severity on postoperative outcomes of laparoscopic gastric bypass has not been extensively examined. METHODS: The University HealthSystem Consortium database is an administrative and financial database that provides information on the inpatient stay. A retrospective analysis of patient outcomes was performed using 4-year discharge data from the University HealthSystem Consortium database. RESULTS: A total of 37,765 patients underwent laparoscopic gastric bypass. The women exhibited significantly reduced mortality, morbidity, intensive care unit (ICU) admissions (9.87% male versus 6.73% female; P <.001), duration of hospitalization (2.72 ± 4.03 d for men versus 2.59 ± 2.88 d for women; P <.001), and hospital costs ($17,346 ± $15,397 for men versus $14,383 ± $11,170 for women; P <.001). Blacks demonstrated significantly greater 30-day readmission rates, duration of hospitalization, and costs compared with whites. Hispanics had lower ICU admission and hospital costs compared with whites. With increasing age, an increased risk of overall morbidity, ICU admissions, duration of hospitalization, and costs was observed. Compared with the minor severity group, the major/extreme severity group had significantly greater observed mortality, overall morbidity, ICU admissions, duration of hospitalization, and hospital costs. CONCLUSION: The present study identified gender, race, age, and illness severity as risk factors affecting postoperative outcomes after laparoscopic gastric bypass. Male gender and increasing age were overall associated with an increased risk of complications. Significant racial disparities in the outcome measures were observed with blacks having an increased risk of adverse events. Illness severity was shown to adversely affect the surgical outcomes in laparoscopic gastric bypass.

RF-Medisys: a radio frequency identification-based electronic medical record system for improving medical information accessibility and services at point of care.

This paper presents an innovative electronic medical records (EMR) system, RF-MediSys, which can perform medical information sharing and retrieval effectively and which is accessible via a 'smart' medical card. With such a system, medical diagnoses and treatment decisions can be significantly improved when compared with the conventional practice of using paper medical records systems. Furthermore, the entire healthcare delivery process, from registration to the dispensing or administration of medicines, can be visualised holistically to facilitate performance review. To examine the feasibility of implementing RF-MediSys and to determine its usefulness to users of the system, a survey was conducted within a multi-disciplinary medical service organisation that operates a network of medical clinics and paramedical service centres throughout Hong Kong Island, the Kowloon Peninsula and the New Territories. Questionnaires were distributed to 300 system users, including nurses, physicians and patients, to collect feedback on the operation and performance of RF-MediSys in comparison with conventional paper-based medical record systems. The response rate to the survey was 67%. Results showed a medium to high level of user satisfaction with the radiofrequency identification (RFID)-based EMR system. In particular, respondents provided high ratings on both 'user-friendliness' and 'system performance'. Findings of the survey highlight the potential of RF-MediSys as a tool to enhance quality of medical services and patient safety.

Does illness severity matter? A comparison of laparoscopic esophagomyotomy with fundoplication and esophageal dilation for achalasia.

INTRODUCTION: There is scarce evidence regarding optimal treatment options for achalasia in patients with varying illness severity risk. The objective of this study was to evaluate and compare outcomes with laparoscopic esophagomyotomy with fundoplication (LM) and esophageal dilation (ED) for hospitalized patients with different illness severity. METHODS: The University HealthSystem Consortium (UHC) is an alliance of more than 100 academic medical centers and nearly 200 affiliate hospitals. UHC's Clinical Data Base/Resource Manager (CDB/RM) allows member hospitals to compare patient-level risk-adjusted outcomes for performance improvement purposes. The CDB/RM was queried for patients with achalasia who underwent LM (n=1,390) or ED (n=492) during a 3-year period between 2006 and 2008. RESULTS: Overall esophageal perforation rates were significantly higher for ED (0.4% LM vs. 2.4% ED; p<0.001). Patients undergoing LM with minor/moderate illness severity showed higher morbidity (9.42% LM vs. 5.15% ED; p<0.05). However, LM patients in this illness severity group showed significantly lower 30-day readmission rate (0.38% LM vs. 7.32% ED; p<0.001) and length of stay (2.23±1.78 LM vs. 4.88±4.42 days ED; p<0.001), but comparable cost ($9,539 LM vs. $8990 ED; p>0.05). In the major/extreme illness severity group mortality was comparable (1.37% LM vs. 2.44% ED; p>0.05). Overall morbidity was significantly greater in LM (50.48% LM vs. 19.57% ED; p<0.001). However, the length of stay was significantly increased in the ED group (8.96±7.86 LM vs. 11.72±11.05 days ED; p=0.04). CONCLUSION: In hospitalized patients with minor/moderate illness severity, laparoscopic myotomy for achalasia showed comparable or better outcomes than ED. For major/extreme illness severity, dilation showed comparable or better profile for hospitalized achalasia patients. These results highlight the importance and impact of illness severity on outcomes of achalasia patients.

Critical elements and lessons learnt from the implementation of an RFID-enabled healthcare management system in a medical organization.

Healthcare services are complex and life-critical. One mistake in any procedure may lead to irremediable consequences; numerous researchers, thus, introduce information and communication technology to improve quality of services and enhance patient safety by reducing the medical errors. Radio frequency identification (RFID) is considered as one of the emerging tool assist in meeting the challenges of the present situation. In recent years, RFID has been applied in medical organizations for the purpose of managing and tracking medical equipment, monitoring and identifying patients, ensuring that the right medication is given to the right patient, and preventing the use of counterfeit medicine. However, most of the existing literature focuses on demonstrating how RFID can benefit the healthcare industry, whereas little attention has been given to the management issues involved in constructing an RFID project in medical organizations. In this paper, an exploratory case study is conducted in a medical organization to illustrate the development framework and critical issues that should be taken into consideration in the preparation, implementation and maintenance stage of constructing such a project. All the experiences and results discussed in this paper offer valuable and useful insights to steer those who would like to start their journey using RFID in medical organizations.

Experiences sharing of implementing Template-based Electronic Medical Record System (TEMRS) in a Hong Kong medical organization.

This paper aims to investigate the efficacy and feasibility of Template-based Electronic Medical Record System (TEMRS) and factors for its successful implementation. A TEMRS was designed and implemented in one core clinic of a Hong Kong professional multi-disciplinary medical services provider with four core clinics located in different parts of Hong Kong. Eight doctors participated in the study. Surveys and interviews were conducted to acquire the users' feedback and satisfaction level. The design, development, and the factors related to the success of the implementation of TEMRS were analyzed. In the study period, 3,032 cases were collected. The most encountered diagnosis were upper respiratory tract infection (50.59%), gastroenteritis (10.19%), dermatitis (5.87%), dyspepsia (5.28%) and rhinitis (4.82%). The system gained an overall satisfaction by the users and the most satisfied areas were rapid retrieving the necessary information of patient (75%) and fasten the diagnostic selection (75%). TEMRS is an enabling system which can reduce the user resistance in new technology with its flexibility. The consideration of cost, security, human, technical, data migration and standardization issues are essential in the implementation of the TEMRS and further research should be conducted to expand the TEMRS's implementation in health care system.

Safety, efficacy, and cost-effectiveness of common laparoscopic procedures.

BACKGROUND: Laparoscopic surgery has been shown to offer superior surgical outcomes for most abdominal surgical procedures. However, there is hardly any evidence on surgical outcomes with patient risk stratification. This study aimed to compare outcomes of common laparoscopic and open surgical procedures for varying illness severity. METHODS: A retrospective analysis of surgical outcomes for six commonly performed surgical procedures including cholecystectomy, appendectomy, reflux surgery, gastric bypass surgery, ventral hernia repair, and colectomy was performed using the University HealthSystem Consortium (UHC) Clinical Database/Resource Manager (CDB/RM). The 3-year discharge data for the six commonly performed laparoscopic surgical procedures were analyzed for outcome measures including observed mortality, overall patient morbidity, intensive care unit (ICU) admissions, 30-day readmissions, length of hospital stay, and hospital costs. RESULTS: In this study, 208,314 patients underwent one of six common surgical procedures by either the open or the laparoscopic approach. Overall, the laparoscopic approach showed significantly lower mortality, reduced morbidity, fewer ICU admissions and 30-day readmissions, shorter hospital stay, and significantly reduced hospital costs for all the procedures. At stratification by illness severity, the laparoscopic group showed better or comparable surgical outcomes across all the illness severity groups. However, the observed mortality was comparable for the minor and moderate severity patients between laparoscopic and open surgery for most procedures. The 30-day readmission rate for major/extreme severity patients was comparable between the two groups for most surgical procedures. CONCLUSIONS: This study demonstrated the superiority of laparoscopy over conventional open surgery across all illness severity risk groups for common surgical procedures. The results in general show that laparoscopic surgery is safe, efficacious, and cost-effective compared with open surgery and suggest that laparoscopic surgery should be the procedure of choice for all common surgical procedures, regardless of illness severity.

Professional Practice and Innovation: RF-MediSys: A Radio Frequency Identification-Based Electronic Medical Record System for Improving Medical Information Accessibility and Services at Point of Care.

This paper presents an innovative electronic medical records (EMR) system, RF-MediSys, which can perform medical information sharing and retrieval effectively and which is accessible via a 'smart' medical card. With such a system, medical diagnoses and treatment decisions can be significantly improved when compared with the conventional practice of using paper medical records systems. Furthermore, the entire healthcare delivery process, from registration to the dispensing or administration of medicines, can be visualised holistically to facilitate performance review. To examine the feasibility of implementing RF-MediSys and to determine its usefulness to users of the system, a survey was conducted within a multi-disciplinary medical service organisation that operates a network of medical clinics and paramedical service centres throughout Hong Kong Island, the Kowloon Peninsula and the New Territories. Questionnaires were distributed to 300 system users, including nurses, physicians and patients, to collect feedback on the operation and performance of RF-MediSys in comparison with conventional paper-based medical record systems. The response rate to the survey was 67%. Results showed a medium to high level of user satisfaction with the radiofrequency identification (RFID)-based EMR system. In particular, respondents provided high ratings on both 'user-friendliness' and 'system performance'. Findings of the survey highlight the potential of RF-MediSys as a tool to enhance quality of medical services and patient safety.

Primary and revisional laparoscopic adjustable gastric band placement in patients with hiatal hernia.

BACKGROUND: Limited evidence exists regarding the outcomes of patients undergoing laparoscopic adjustable band placement (LAGB) with hiatal hernia (HH) and concomitant hiatal hernia repair (HHR). The present study evaluated the safety, efficacy, and cost-effectiveness of primary LAGB (pLAGB) and revisional LAGB (rLAGB) in patients with HH. METHODS: The University HealthSystem Consortium is an alliance of >100 academic medical centers and nearly 200 affiliate hospitals. The University Health System Consortium database was queried for patients undergoing LAGB with and without HH from 2006 through 2009. RESULTS: The patients undergoing rLAGB had a significantly greater prevalence of HH than patients undergoing pLAGB (18.9% for pLAGB with HH versus 26.3% for rLAGB with HH; P <.001). The mortality (.04% for pLAGB without HH versus 0% for pLAGB with HHR; P >.05), morbidity (3.39% pLAGB without HH versus 2.63% for pLAGB HHR; P >.05), and length of stay (1.33 ± 2.25 days for pLAGB without HH versus 1.17 ± 0.56 days for pLAGB with HHR; P >.05) were comparable in the patients undergoing pLAGB with or without HHR. A trend was seen toward increased morbidity in patients undergoing rLAGB HHR than in those undergoing pLAGB HHR (2.63% for pLAGB HHR versus 13.33% for rLAGB HHR; P = .08). The length of stay (1.17 ± 0.56 days for pLAGB HHR versus 1.73 ± 1.49 days for rLAGB HHR; P <.01) and hospital costs ($12,178 ± 4451 for pLAGB HHR versus $14,616 ± 3538 for rLAGB HHR; P = .04) were increased for the rLAGB HHR group compared with the pLAGB HHR group. CONCLUSION: The results of the present study have demonstrated the safety of HHR concomitant with pLAGB. In addition, rLAGB was associated with increased morbidity and cost. These data suggest the safety, efficacy, and cost-effectiveness of crural repair of HH simultaneously with pLAGB.

Reoperative laparoscopic paraesophageal herniorrhaphy can produce excellent outcomes.

BACKGROUND: Patients undergoing laparoscopic paraesophageal herniorrhaphy present with various esophageal and extraesophageal symptoms. Given a recurrence rate of up to 44%, reoperative intervention is necessary on a number of patients. The goal of this study is to determine whether patients proceeding with reoperative laparoscopic paraesophageal herniorrhaphy experienced symptom resolution equal to or better than patients undergoing first-time repair. METHODS: A frequency-based symptom assessment consisting of 24 esophageal and extraesophageal reflux symptoms was developed and administered pre- and postoperatively to patients undergoing initial or reoperative paraesophageal herniorrhaphy during a 7-year period. A composite score for esophageal and extraesophageal symptoms was calculated. Retrospective analysis of patient records including diagnostic studies, and operative and postoperative progress notes was performed. Data were analyzed using appropriate statistical tests. RESULTS: In 195 patients, 89.9% of patients had resolved or improved individual symptom scores at 6 months postoperatively after primary or reoperative paraesophageal herniorrhaphy. Paraesophageal herniorrhaphy resulted in improvements of both esophageal (16.1±8.5 preoperatively versus 3.5±5.0 at 6 months postoperatively; p<0.001) and extraesophageal (8.6±7.5 preoperatively versus 2.2±5.1 at 6 months postoperatively; p<0.001) composite scores and all individual symptom scores (p<0.05). Preoperatively, patients undergoing reoperative surgery had significantly higher solid dysphagia and abdominal discomfort, but lower odynophagia scores. Furthermore, reoperative patients had significantly lower preoperative composite extraesophageal scores (6.1±7.2 reoperative versus 9.1±7.5 primary; p<0.05) and individual symptom scores in laryngitis, hoarseness, and coughing. Only heartburn in reoperative patients was significantly higher at 12 months postoperatively. Otherwise, there was no significant difference in individual or composite symptom scores between groups postoperatively. All scores had significant improvement postoperatively when compared with preoperative scores. CONCLUSIONS: Our data demonstrate that reoperative laparoscopic paraesophageal herniorrhaphy can produce excellent results, comparable to first-time repair.

In vivo miniature robots for natural orifice surgery: State of the art and future perspectives.

Natural orifice translumenal endoscopic surgery (NOTES) is the integration of laparoscopic minimally invasive surgery techniques with endoscopic technology. Despite the advances in NOTES technology, the approach presents several unique instrumentation and technique-specific challenges. Current flexible endoscopy platforms for NOTES have several drawbacks including limited stability, triangulation and dexterity, and lack of adequate visualization, suggesting the need for new and improved instrumentation for this approach. Much of the current focus is on the development of flexible endoscopy platforms that incorporate robotic technology. An alternative approach to access the abdominal viscera for either a laparoscopic or NOTES procedure is the use of small robotic devices that can be implanted in an intracorporeal manner. Multiple, independent, miniature robots can be simultaneously inserted into the abdominal cavity to provide a robotic platform for NOTES surgery. The capabilities of the robots include imaging, retraction, tissue and organ manipulation, and precise maneuverability in the abdominal cavity. Such a platform affords several advantages including enhanced visualization, better surgical dexterity and improved triangulation for NOTES. This review discusses the current status and future perspectives of this novel miniature robotics platform for the NOTES approach. Although these technologies are still in pre-clinical development, a miniature robotics platform provides a unique method for addressing the limitations of minimally invasive surgery, and NOTES in particular.

Femoral artery complications after cardiac catheterization: a study of patient profile.

BACKGROUND: Femoral artery complications after cardiac catheterization range from simple events to severe complications requiring invasive techniques or surgery with significant economic costs. This study evaluated early femoral arterial complications from percutaneous arterial access during diagnostic and interventional cardiac catheterizations in an era of widespread use of closure devices and intense anticoagulation. METHODS: Patients undergoing percutaneous cardiac catheterization via the femoral artery between August 2005 and December 2005 were identified using an ICD-9 patient database. Forty-six data points were extracted by retrospective chart review, including demographics, comorbidities, type of anticoagulation, procedural details, and postprocedural complications. Univariable analysis and binary logistic regression were used to determine factors associated with complications. RESULTS: Eighty-two of 579 patients (14%) suffered complications. The most common complications were hematomas (51 patients, 10%) and active bleeding (14 patients, 2.4%). Closure devices were used in 470 patients. After multivariable correction, use of preprocedural (odds ratio [OR]=5.65, 95% confidence interval [CI] 2.58-12.3, p<0.001) and intraprocedural (OR=4.88, 95% CI 1.95-12.3, p<0.001) antithrombotic agents (antiplatelet and/or anticoagulants), intraprocedural clopidogrel (OR=2.98, 95% CI 1.21-7.30, p=0.017), and postprocedural heparin (OR=29.4, 95% CI 3.56-250, p=0.002) were associated with increased risk. Coronary artery disease was associated with increased risk (OR=11.1, 95% CI 4.78-25.6, p<0.001), while use of a closure device (OR=0.263, 95% CI 0.125-0.553, p<0.001), male gender (OR=0.421, 95% CI 0.220-0.805, p=0.009), and prior catheterization (OR=0.033, 95% CI 0.012-0.095, p<0.001) were protective. CONCLUSION: With increasing numbers of complex coronary endovascular procedures and widespread use of high-dose multidrug antithrombotic therapy, femoral artery injuries will continue to be a significant risk for patients. Postprocedural monitoring with a high level of suspicion and use of vascular closure devices in high-risk patients may decrease the incidence of femoral artery complications. The use of vascular closure devices after low-risk procedures in male patients or those with previous ipsilateral catheterization might not be warranted but needs further study.

A malignant omental extra-gastrointestinal stromal tumor on a young man: a case report and review of the literature.

BACKGROUND: Gastrointestinal stromal tumors (GIST) are uncommon intra-abdominal tumors. These tumors tend to present with higher frequency in the stomach and small bowel. In fewer than 5% of cases, they originate primarily from the mesentery, omentum, or peritoneum. Furthermore, these extra-gastrointestinal tumors (EGIST) tend to be more common in patients greater than 50 years of age. Rarely do EGIST tumors present in those younger than 40 years of age. CASE PRESENTATION: We report a case of a large EGIST in a 27-year-old male. An abdominal pelvic computerized tomography imaging demonstrated an intra-abdominal mass of 22 cm, without invasion of adjacent viscera or liver lesions. This mass was resected en bloc with its fused omentum and an adherent portion of sigmoid colon. Pathology results demonstrated a malignant gastrointestinal stromal tumor with positive CD117 (c-kit) staining, and negative margins of resection, and no continuity of tumor with the sigmoid colon. Due to the malignant and aggressive nature of this patient's tumor, he was started on STI-571 as adjuvant chemotherapy. CONCLUSION: Stromal tumors of an extra-gastrointestinal origin are rare. Of the reported omental and mesenteric EGISTs in four published series, a total of 99 tumors were studied. Of the 99 patients in these series only 8 were under 40 years of age, none were younger than 30 years old; and only 5 were younger than 35 years old. Our patient's age is at the lower end of the age spectrum for the reported EGISTs. Young patients who present with an extra-gastrointestinal stromal tumor (EGIST), who have complete resection with negative margins, have a good prognosis. There is little data to support the role of STI-571 in adjuvant or neoadjuvant therapy after curative resection. Given the lack of data, the use of STI-571 must be individualized.

Localized reactive oxygen and nitrogen intermediates inhibit escape of Listeria monocytogenes from vacuoles in activated macrophages.

Listeria monocytogenes (Lm) evades being killed after phagocytosis by macrophages by escaping from vacuoles into cytoplasm. Activated macrophages are listericidal, in part because they can retain Lm in vacuoles. This study examined the contribution of reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI) to the inhibition of Lm escape from vacuoles. Lm escaped from vacuoles of nonactivated macrophages within 30 min of infection. Macrophages activated with IFN-gamma, LPS, IL-6, and a neutralizing Ab against IL-10 retained Lm within the vacuoles, and inhibitors of ROI and RNI blocked inhibition of vacuolar escape to varying degrees. Measurements of Lm escape in macrophages from gp91(phox-/-) and NO synthase 2(-/-) mice showed that vacuolar retention required ROI and was augmented by RNI. Live cell imaging with the fluorogenic probe dihydro-2',4,5,6,7,7'-hexafluorofluorescein coupled to BSA (DHFF-BSA) indicated that oxidative chemistries were generated rapidly and were localized to Lm vacuoles. Chemistries that oxidized DHFF-BSA were similar to those that retained Lm in phagosomes. Fluorescent conversion of DHFF-BSA occurred more efficiently in smaller vacuoles, indicating that higher concentrations of ROI or RNI were generated in more confining volumes. Thus, activated macrophages retained Lm within phagosomes by the localization of ROI and RNI to vacuoles, and by their combined actions in a small space

The Listeria monocytogenes hemolysin has an acidic pH optimum to compartmentalize activity and prevent damage to infected host cells.

Listeria monocytogenes is a facultative intracellular bacterial pathogen that escapes from a phagosome and grows in the host cell cytosol. The pore-forming cholesterol-dependent cytolysin, listeriolysin O (LLO), mediates bacterial escape from vesicles and is approximately 10-fold more active at an acidic than neutral pH. By swapping dissimilar residues from a pH-insensitive orthologue, perfringolysin O (PFO), we identified leucine 461 as unique to pathogenic Listeria and responsible for the acidic pH optimum of LLO. Conversion of leucine 461 to the threonine present in PFO increased the hemolytic activity of LLO almost 10-fold at a neutral pH. L. monocytogenes synthesizing LLO L461T, expressed from its endogenous site on the bacterial chromosome, resulted in a 100-fold virulence defect in the mouse listeriosis model. These bacteria escaped from acidic phagosomes and initially grew normally in cells and spread cell to cell, but prematurely permeabilized the host membrane and killed the cell. These data show that the acidic pH optimum of LLO results from an adaptive mutation that acts to limit cytolytic activity to acidic vesicles and prevent damage in the host cytosol, a strategy also used by host cells to compartmentalize lysosomal hydrolases.