Host Defenses Given the enormous number of microorganisms ingested with every meal, the normal host must combat a constant influx of potential enteric pathogens. Studies of infections in patients with alterations in defense mechanisms have led to a greater understanding of the variety of ways in which the normal host can protect itself against disease. Normal Flora The large numbers of bacteria that normally inhabit the intestine act as an important host defense by preventing colonization by potential enteric pathogens. Persons with fewer intestinal bacteria, such as infants who have not yet developed normal enteric colonization or patients receiving antibiotics,. | Chapter 122. Acute Infectious Diarrheal Diseases and Bacterial Food Poisoning Part 4 Host Defenses Given the enormous number of microorganisms ingested with every meal the normal host must combat a constant influx of potential enteric pathogens. Studies of infections in patients with alterations in defense mechanisms have led to a greater understanding of the variety of ways in which the normal host can protect itself against disease. Normal Flora The large numbers of bacteria that normally inhabit the intestine act as an important host defense by preventing colonization by potential enteric pathogens. Persons with fewer intestinal bacteria such as infants who have not yet developed normal enteric colonization or patients receiving antibiotics are at significantly greater risk of developing infections with enteric pathogens. The composition of the intestinal flora is as important as the number of organisms present. More than 99 of the normal colonic flora is made up of anaerobic bacteria and the acidic pH and volatile fatty acids produced by these organisms appear to be critical elements in resistance to colonization. Gastric Acid The acidic pH of the stomach is an important barrier to enteric pathogens and an increased frequency of infections due to Salmonella G. lamblia and a variety of helminths has been reported among patients who have undergone gastric surgery or are achlorhydric for some other reason. Neutralization of gastric acid with antacids or H2 blockers a common practice in the management of hospitalized patients similarly increases the risk of enteric colonization. In addition some microorganisms can survive the extreme acidity of the gastric environment rotavirus for example is highly stable to acidity. Intestinal Motility Normal peristalsis is the major mechanism for clearance of bacteria from the proximal small intestine. When intestinal motility is impaired . by treatment with opiates or other antimotility drugs anatomic abnormalities or .
