Sarah K. Parker

Thimerosal-Containing Vaccines and Autistic Spectrum Disorder: A Critical Review of Published Original Data

Objective. The issue of thimerosal-containing vaccines as a possible cause of autistic spectrum disorders (ASD) and neurodevelopmental disorders (NDDs) has been a controversial topic since 1999. Although most practitioners are familiar with the controversy, many are not familiar with the type or quality of evidence in published articles that have addressed this issue. To assess the quality of evidence assessing a potential association between thimerosal-containing vaccines and autism and evaluate whether that evidence suggests accepting or rejecting the hypothesis, we systematically reviewed published articles that report original data pertinent to the potential association between thimerosal-containing vaccines and ASD/NDDs. Methods. Articles for analysis were identified in the National Library of Medicines Medline database using a PubMed search of the English-language literature for articles published between 1966 and 2004, using keywords thimerosal, thiomersal, mercury, methylmercury, or ethylmercury alone and combined with keywords autistic disorder, autistic spectrum disorder, and neurodevelopment. In addition, we used the “related links” option in PubMed and reviewed the reference sections in the identified articles. All original articles that evaluated an association between thimerosal-containing vaccines and ASD/NDDs or pharmacokinetics of ethylmercury in vaccines were included. Results. Twelve publications that met the selection criteria were identified by the literature search: 10 epidemiologic studies and 2 pharmacokinetic studies of ethylmercury. The design and quality of the studies showed significant variation. The preponderance of epidemiologic evidence does not support an association between thimerosal-containing vaccines and ASD. Epidemiologic studies that support an association are of poor quality and cannot be interpreted. Pharmacokinetic studies suggest that the half-life of ethylmercury is significantly shorter when compared with methylmercury. Conclusions. Studies do not demonstrate a link between thimerosal-containing vaccines and ASD, and the pharmacokinetics of ethylmercury make such an association less likely. Epidemiologic studies that support a link demonstrated significant design flaws that invalidate their conclusions. Evidence does not support a change in the standard of practice with regard to administration of thimerosal-containing vaccines in areas of the world where they are used.

A novel class of microbial phosphocholine‐specific phospholipases C

In this report we describe the 1500‐fold purification and characterization of the haemolytic phospholipase C (PLC) of Pseudomonas aeruginosa, the paradigm member of a novel PLC/phosphatase superfamily. Members include proteins from Mycobacterium tuberculosis, Bordetella spp., Francisella tularensis and Burkholderia pseudomallei. Purification involved overexpression of the plcHR1,2 operon, ion exchange chromatography and native preparative polyacrylamide gel electrophoresis. Matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectrometry confirmed the presence of two proteins in the purified sample with sizes of 17 117.2 Da (PlcR2) and 78 417 Da (PlcH). Additionally, liquid chromatography electrospray mass spectrometry (LCMS) revealed that PlcH and PlcR2 are at a stoichiometry of 1 : 1. Western blot analysis demonstrated that the enzyme purifies as a heterodimeric complex, PlcHR2. PlcHR2 is only active on choline‐containing phospholipids. It is equally active on phosphatidylcholine (PC) and sphingomyelin (SM) and is able to hydrolyse plasmenylcholine phospholipids (plasmalogens). Neither PlcHR2 nor the M. tuberculosis homologues are inhibited by D609 a widely used, competitive inhibitor of the Bacillus cereus PLC. PlcH, PlcR2, and the PlcHR2 complex bind calcium. While calcium has no detectable effect on enzymatic activity, it inhibits the haemolytic activity of PlcHR2. In addition to being required for the secretion of PlcH, the chaperone PlcR2 affects both the enzymatic and haemolytic properties of PlcH. Inclusive in these data is the con‐clusion that the members of this PC‐PLC and phosphatase family possess a novel mechanism for the recognition and hydrolysis of their respective substrates.

Tissue Invasion by Entamoeba histolytica: Evidence of Genetic Selection and/or DNA Reorganization Events in Organ Tropism

Entamoeba histolytica infection may have various clinical manifestations. Nine out of ten E. histolytica infections remain asymptomatic, while the remainder become invasive and cause disease. The most common form of invasive infection is amebic diarrhea and colitis, whereas the most common extra-intestinal disease is amebic liver abscess. The underlying reasons for the different outcomes are unclear, but a recent study has shown that the parasite genotype is a contributor. To investigate this link further we have examined the genotypes of E. histolytica in stool- and liver abscess-derived samples from the same patients. Analysis of all 18 paired samples (16 from Bangladesh, one from the United States of America, and one from Italy) revealed that the intestinal and liver abscess amebae are genetically distinct. The results suggest either that E. histolytica subpopulations in the same infection show varying organ tropism, or that a DNA reorganization event takes place prior to or during metastasis from intestine to liver.

Purification and Characterization of Mycobacterial Phospholipase A: an Activity Associated with Mycobacterial Cutinase

We describe mycobacterial phospholipase A activity (MPLA) and, using reverse genetics, have associated this activity with putative mycobacterial cutinase. PLAs, which hydrolyze fatty acids on phospholipids, play a significant role in human inflammatory states and disease pathogenesis. In prokaryotes, the recognition of their role in virulence is more recent. Cutinases are serine esterases whose primary substrate is cutin, the waxy exterior layer of plants. Mycobacterium tuberculosis has maintained seven putative cutinases, though it should not encounter cutin; we demonstrate that known cutinases and MPLA cleave phospholipids in a PLA-type manner and also hydrolyze Tween. We analyzed cutinase motifs in mycobacteria and found the motif very prevalent. All mycobacteria tested had MPLA activity. These studies suggest an alternative use for putative cutinases by the M. tuberculosis group that is likely related to MPLA activity and lipid metabolism.

Mycobacterium tuberculosis Rv3802c encodes a phospholipase/thioesterase and is inhibited by the antimycobacterial agent tetrahydrolipstatin.

The cell wall of M. tuberculosis is central to its success as a pathogen. Mycolic acids are key components of this cell wall. The genes involved in joining the α and mero mycolates are located in a cluster, beginning with Rv3799c and extending at least until Rv3804c. The role of each enzyme encoded by these five genes is fairly well understood, except for Rv3802c. Rv3802 is one of seven putative cutinases encoded by the genome of M. tuberculosis. In phytopathogens, cutinases hydrolyze the waxy layer of plants, cutin. In a strictly mammalian pathogen, such as M. tuberculosis, it is likely that these proteins perform a different function. Of the seven, we chose to focus on Rv3802c because of its location in a mycolic acid synthesis gene cluster, its putative essentiality, its ubiquitous presence in actinomycetes, and its conservation in the minimal genome of Mycobacterium leprae. We expressed Rv3802 in Escherichia coli and purified the enzymatically active form. We probed its activities and inhibitors characterizing those relevant to its possible role in mycolic acid biosynthesis. In addition to its reported phospholipase A activity, Rv3802 has significant thioesterase activity, and it is inhibited by tetrahydrolipstatin (THL). THL is a described anti-tuberculous compound with an unknown mechanism, but it reportedly targets cell wall synthesis. Taken together, these data circumstantially support a role for Rv3802 in mycolic acid synthesis and, as the cell wall is integral to M. tuberculosis pathogenesis, identification of a novel cell wall enzyme and its inhibition has therapeutic and diagnostic implications.

Guidance for the knowledge and skills required for antimicrobial stewardship leaders.

Antimicrobial stewardship programs are increasingly recognized as critical in optimizing the use of antimicrobials. Consequently, more physicians, pharmacists, and other healthcare providers are developing and implementing such programs in a variety of healthcare settings. The purpose of this guidance document is to outline the knowledge and skills that are needed to lead an antimicrobial stewardship program. It was developed by antimicrobial stewardship experts from organizations that are engaged in advancing the field of antimicrobial stewardship.

Implementation of Rapid Molecular Infectious Disease Diagnostics: the Role of Diagnostic and Antimicrobial Stewardship

ABSTRACT New rapid molecular diagnostic technologies for infectious diseases enable expedited accurate microbiological diagnoses. However, diagnostic stewardship and antimicrobial stewardship are necessary to ensure that these technologies conserve, rather than consume, additional health care resources and optimally affect patient care. Diagnostic stewardship is needed to implement appropriate tests for the clinical setting and to direct testing toward appropriate patients. Antimicrobial stewardship is needed to ensure prompt appropriate clinical action to translate faster diagnostic test results in the laboratory into improved outcomes at the bedside. This minireview outlines the roles of diagnostic stewardship and antimicrobial stewardship in the implementation of rapid molecular infectious disease diagnostics.

Hepatic amebiasis: a reminder of the complications.

The complications of amebic liver abscess are underappreciated in developed countries and are often misdiagnosed. We report a 16-month-old male child with amebic liver abscess, initially misdiagnosed with pneumonia, who became critically ill with peritoneal, pleural and pericardial extension, and gastric perforation. In addition to highlighting the complications of amebic liver abscess, this case demonstrates the value of PCR testing as a diagnostic and molecular tool.

Handshake Stewardship: A Highly Effective Rounding-Based Antimicrobial Optimization Service.

Background: Implementation of an antimicrobial stewardship program is recommended as one solution to combat increasing antimicrobial resistance. Most antimicrobial stewardship programs use preauthorization or restrictive strategies recommended in national guidelines. We describe a unique, rounding-based strategy, handshake stewardship. Handshake stewardship is distinguished by: (1) lack of restriction and preauthorization, (2) review of all prescribed antimicrobials and (3) a rounding-based, in-person approach to feedback by a pharmacist–physician team. Methods: We retrospectively measured antimicrobial use hospital-wide and by unit during preimplementation, planning, and postimplementation phases of the handshake stewardship approach to determine the efficacy of this strategy in decreasing use in a freestanding children’s hospital. All antimicrobials prescribed on the inpatient services between October 2010 and September 2014 were included in the review. Monthly antimicrobial use (hospital-wide and by unit) was measured in days of therapy per 1000 patient days (DOT/1000 PD). Results: Overall antimicrobial use decreased by 10.9% during the 4 years of the analysis (942 to 839 DOT/1000 PD, P < 0.01), with an impact of 10.3% on antibacterials (750 to 673 DOT/1000 PD, P < 0.01). Vancomycin use decreased by 25.7% (105 to 78 DOT/1000 PD, P < 0.01). Meropenem use decreased by 22.2% (45 to 35 DOT/1000 PD, P = 0.04) without a compensatory increase of other antipseudomonal agents. Decreased usage was observed both hospital-wide and on individual units for most agents. Conclusions: The handshake stewardship approach is an effective strategy for an antimicrobial stewardship program, as demonstrated by the widespread and significant decrease in antimicrobial use after implementation.

Primary and Postprimary or Reactivation Tuberculosis: Time to Revise Confusing Terminology?

AJR 2009; 192:W198 0361–803X/09/1924–W198