Bacterial Colonization and Function in the Bowel

Gastroenterology No Responses »
Dec 072010
Bacteria colonize the colon because it contains elements that are critical for their growth: a warm, moist, stable environment with an abundant supply of nutrients both of exogenous (ie, dietary) and endogenous (ie, sloughed cells, mucus, secretions) origin. The resulting flora is among the most diverse in nature, incorporating over 400 different species of bacteria. It is replenished at a rate of 150 to 400 g daily, with each gram containing more than 1011 organisms.
Development of this complex ecosystem begins at birth. Initially, the colon is sterile and has a pH of 6.5 to 7.0. Within hours after birth, aerobes and facultative anaerobes (eg, Escherichia coli and Streptococcus) colonize to levels of 106 to 108 organisms per gram of feces. This results in an environment that is increasingly reduced in oxygen and thus favors the growth of strict anaerobes.
In breast-fed infants, Bifidobacterium appears by day 4 to 7, reaching levels of 108 to 1011 organisms per gram. Clostridium, Lactobacillus, and even Bacteroides also may colonize at this time. The presence of these organisms is associated with an acidic luminal pH of 5.1.
It has been noted that Bifidobacterium produces primarily lactate and acetate via lactose fermentation. The resulting milieu has been suggested to retard the growth of pathogenic bacteria such as E. coli and Salmonella and to promote the growth of Bifidobacterium.
In bottle-fed infants, the initial metabolic events differ. Strains of enterobacteria such as E. coli and Klebsiella pneumoniae predominate in a relatively neutral pH environment. By the end of the second week, in both breast- and bottle-fed infants, the rapid fluctuations both in bacterial numbers and in bacterial metabolic end products stabilize, and Bifidobacterium, Eubacterium, Clostridium, and Lactobacillus become the predominant species. This balance is maintained throughout adult life.
Under normal conditions, the presence of bacteria enhances colonic function. The primary Continue reading »
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Approach to the Child with Birth Defects

Genetics No Responses »
Dec 062010
In the mid-1960s, David W. Smith coined the term dysmorphology to describe the field of medicine devoted to the study of abnormal human development. His intent was to propose a term that both replaced teratology (whose literal meaning and reference to monsters was pejorative) and captured the essence of the discipline. The ability to recognize and interpret minor and major anomalies is an important skill that is required for evaluating a child with a birth defect.
A syndrome is a pattern of birth defects that are etiologically related and regularly recur in different individuals (eg, Down syndrome). In other areas of medicine, the word syndrome often refers to a specific set of symptoms that are not necessarily etiologically related (eg, nephrotic syndrome).
A sequence is a primary defect with a secondary cascade of structural changes.
Birth defects that represent a sequence are usually localized to a single body area. Whereas a sequence can often be misinterpreted as a group of malformations, more critical inspection reveals a single malformation and a subsequent disruption or deformation. For example, the Pierre Robin sequence is caused by a primary abnormality in mandibular development that produces disruption of palatal closure and secondary obstruction of the airway by the tongue. A sequence can occur in isolation or be a component of an underlying syndrome diagnosis. For example, about 20% of children with Pierre Robin sequence have a disorder of connective tissue called Stickler syndrome (characterized by joint hyperextensibility and myopia).
An association is two or more primary defects that occur in the same individuals more often than is expected by chance: Defining a group of defects as an association suggests that the anomalies are etiologically related to each other, yet the nature and mechanism of that relationship remains unclear. For example, children with defects of the vertebrae, anus, trachea and esophagus, radius, and kidneys (renal) are often labeled with the acronym VATER association. Associations tend to be etiologically heterogenous more often than syndromes, and fewer characteristics of an association are observed in each affected child.
Clinical Practice
The approach to a child with birth defects is multifaceted and includes the collection of phenotypic data, determination of the immediate and long-term issues of care, and the provision of the family with psychological support.
Phenotypic data that should be collected include detailed obstetrical, medical, and family histories, a comprehensive physical examination, and ancillary laboratory, physiological, or imaging studies. The gestational and birth history needs to include exposures to over-the-counter and prescription medications as well as illicit drugs, frequency and vigor of fetal movements, Continue reading »
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Viral Gastroenteritis in Children

Infectious Diseases No Responses »
Dec 062010
Infectious diarrhea is a leading cause of disease and death worldwide. During a 1-year period in Asia, Africa, and Latin America, it was estimated that 3 to 5 billion episodes of infectious diarrhea accounted for 5 to 10 million deaths. Rotaviruses; adenoviruses; small, round viruses (eg, Norwalk agent); caliciviruses; coronaviruses; and astroviruses are responsible for acute viral gastroenteritis. Rotaviruses, adenoviruses, and small, round viruses account for the majority of viral gastroenteritis in childhood.
Epidemiology
Since their initial identification as a cause of human disease in 1973, rotaviruses have been found to be the most important cause of acute gastroenteritis in infants and young children in all countries. Studies in the United States, England, Australia, Japan, and Bangladesh found that 34 to 63% of children hospitalized with acute diarrhea were infected with rotaviruses. Rotavirus causes 3 to 4 million cases of diarrhea, 500,000 outpatient visits, 50,000 hospitalizations, and approximately 40 deaths per year in the United States. Rotavirus-induced gastroenteritis primarily affects children 6 to 24 months of age, and most initial infections are symptomatic. The peak prevalence of the disease occurs between November and April in temperate climates, and year-round in tropical climates; infections are usually sporadic and occasionally epidemic. Rotaviruses are transmitted from person-to-person by the fecal-oral route, with an incubation period of 1 to 3 days.
Adenoviruses are probably the second most important cause of acute gastroenteritis in childhood. Disease is associated primarily with adenovirus types 40 and 41. These strains are now termed “fastidious” or “enteric” adenoviruses because they are difficult to propagate in cell culture. Similar to rotaviruses, enteric adenoviruses primarily infect children younger than 2 years of age, but unlike rotaviruses, adenovirus infections occur year-round. Although outbreaks in hospital nurseries have occurred, these viruses appear to be endemic rather than epidemic. Enteric adenoviruses have an incubation period of 3 to 10 days, which is longer than that for infection with either rotaviruses or small, round viruses.
In 1968, an outbreak of illness characterized by vomiting and fever occurred in a group of elementary school children in Norwalk, Ohio. Virus particles, 27 nm in diameter, were subsequently isolated from this outbreak by electron microscopy. Norwalk agent was the forerunner of a group of morphologically similar noncultivable agents named for the geographic location where they were found to cause disease (eg, Montgomery County agent, Hawaii agent). The morphologic similarity of a number of smaller viruses associated with gastroenteritis (including parvoviruses) led to the description of these agents as small, round viruses. Unlike rotaviruses and adenoviruses, infections with small, round viruses are usually epidemic and responsible for family and community-wide outbreaks of gastroenteritis in school-aged children, family contacts, and adults. Small, round viruses are transmitted by the fecal-oral route, with an incubation period of 1 to 2 days.
Clinical Manifestations
Rotavirus infection is characterized by diarrhea, fever, and vomiting. Occasionally, congestion Continue reading »
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