DIAGNOSTIC MEDICAL MICROBIOLOGY

Diagnostic Medical Microbiology Case Studies

Diagnostic Medical Microbiology Case Studies

Introduction

The most common bacterial causes of diarrhea are E. coli O157:H7, Salmonella enteridis, Vibrio cholerae, and Shigella. Escherichia coli are bacteria of which the virulent strains can cause significant gastrointestinal morbidity and mortality (Su, 2005, 70). E. coli O157:H7 is the strain most well known to the general public for causing epidemics after ingestion of contaminated water and foods, including undercooked hamburgers, lettuce, and spinach. Acute viral gastroenteritis caused by rotavirus, hepatitis A, and poliomyelitis are examples of such viruses. The leading cause of diarrhea is viral gastroenteritis, a viral infection of the digestive tract. Infectious organisms causing diarrhea include viruses (rotavirus being the most common), bacteria (e.g., E. coli), and parasites (e.g., Giardia).

Bacterial infections of the intestines are a major cause of diarrhea, and impart a sizable disease burden on human populations, especially children, and especially in poor countries (Silvia, 2006, 62).

This report is based on the clinical and microbiological characteristics of seven patients with watery diarrhea who were found to have an unusual organism, resembling a large cryptosporidium, in their stool on examination for ova and parasites. The organism was identified by the Centers for Disease Control (CDC, Atlanta) as a cyanobacterium-like body.

The gastrointestinal system, particularly the small and large intestines, are naturally populated by hundreds of different strains of nonharmful bacteria, many of which help with digestion (Oijen, 2006, 82). Infectious diarrhea can be caused either when a harmful, nonnative, biological agent colonises the intestines or when one particular strain of native bacteria is favored over the others and takes over. This second pathway is exemplified by cases of bacterial overgrowth following the administration of antibiotics. The ingested antibiotics kill off most of the natural bacterial “flora” of the gut allowing a single disease causing variety to take over and proliferate.

Case 1

The patient had nausea but no abdominal cramps or fever. Routine stool cultures for bacteria and acidfast bacilli (see below) were negative; three examinations of stool for ova and parasites over 7 weeks showed nonrefractile, oval to round, acid-fast organisms that were 9 p,m in diameter.

Case 2

Stool cultures for bacteria and an examination for ova and parasites at the time of presentation were negative for enteric pathogens. The examination of five separate stool specimens over 3 weeks demonstrated spherical acid-fast organisms measuring 8-9 urn in diameter.

Case 3

Examination of three stool specimens, days, showed round ...