Bacterial Diseases of Vegetable Crops: Leaf Spots & Blights


Bacterial Diseases of Vegetable Crops: Leaf Spots & Blights

Vegetable Crops Mating, large birds such as turkeys, especially if the fowl is stuffed, may persist despite the baking process; and organisms in eggs occasionally survive frying, scrambling, or boiling in the shell. The numerous by-products of the meat-packing industry, such as bone meal, fertilizer, domestic animal food, and fish meal, often contain salmonella and may serve as sources of infection, especially among lower animals… Finally, in considering potential sources of infection, household pets, including dogs, cats, birds, and turtles, should not be overlooked; all have been shown to harbor salmonellae.

Direct transmission from man to man without food as the intermediate source occurs occasionally Vegetable Crops. For example, a highly susceptible newborn may acquire the infection at birth from an infected mother or in the neonatal period from a nursery attendant. Several nursery and hospital outbreaks have been described in which infection appeared to be perpetrated by the airborne spread of salmonellae. Pathology. Death from Salmonella gastroenteritis occurs primarily in infants, the aged, and persons with underlying diseases. The intestinal mucosa is red and swollen and often shows petechial hemorrhages.

The pathologic findings in paratyphoid fever are qualitatively similar to those of typhoid fever, although the involvement of Peyer's patches is less prominent and ulcerations are much less frequent. Intestinal lesions are usually absent in patients with Salmonella bacteremia, and the findings are similar to those of any acute generalized infection. Blood-borne salmonellae may localize in almost any organ, producing single or multiple suppurative lesions. Pathogenesis. Multiplication of salmonellae in the intestinal tract' may cause inflammation of the intestinal mucosa and symptoms of gastroenteritis. Gastroenteritis is a true infection of the mucosa; ingestion of a large number of dead bacilli will not produce the disease.

Salmonellae multiplying in the intestinal tract occasionally gain access to the blood, producing transient bacteremia or localized ‘infections that can serve as soul ces of persistent bacteremia. The pathogenesis of enteric or paratyphoid fever is similar to that of typhoid fever. The prevalence of salmonellae in foods for human consumption makes it almost inevitable that man comes in contact with these organisms relatively frequently.

The outcome of such exposures depends on the characteristics of the Salmonella species, the number of bacteria ingested, and the status of the host. Every species of Salmonella has the capacity to produce asymptomatic infection, acute gastro-enteritis, bacteremia with or without localized infection, or paratyphoid fever. However, some species are much more likely to produce certain of these clinical syndromes than others. For example, anatomy usually prOduces inapparent infection or gastroenteritis and only rarely invades the blood. In contrast,choleraesuis only occasion-ally produces gastroenteritis or inapparent.

Vegetable Crops Cian but is a common cause of bacteremia or metastatic infection. Differences in pathogenicity are observed not only between species but also between strains of the same species. Limited information is available on the number of organisms required to produce salmonellosis in man. Experiments in volunteers suggest that a large number (approximately 106) of viable salmonellae are usually required to, produce gastro-enteritis in normal adults. A transient carrier state may follow ingestion of inocula 10 or 100 times smaller than those required to produce disease.

The resistance of the host also plays a major role in determining the wide range of responses from no disease to rapidly fatal illness observed in human salmonellosis. Local factors in the stomach and intestine may be the first lines of defense. It has been established that major gastric surgery, including subtotal gastrectomy, gastroenterostomy, and/or vagotomy, predisposes to Salmonella gastroenteritis. The mechanism of this effect is unknown but may be related to the reduced bactericidal activity of gastric juice or altered intestinal flora.

It has been shown in experimental Salmonella infections of mice that the microbial flora of the normal intestine exerts a protective action by suppressing the multiplication of salmonellae. In these studies, alteration of intestinal flora by anti-microbial drugs increased susceptibility to infection with S. Typhimurium 100,000 times, and resistance was restored by re-establishing the normal enteric flora. Prior antimicrobial therapy also apparently enhances the susceptibility of men to symptomatic intestinal infection with salmonella.

The incidence of severe Salmonella infections is increased in patients with certain underlying diseases. Another process, such as hepatic cirrhosis, lupus erythematosus, leukemia, lymphoma, or neoplasm, is present in one-third to one-half of patients with Salmonella bacteremia. These conditions are associated with a general depression of resistance to microbial invasion, and secondary infection is not unexpected. However, in a few diseases — acute bartonellosis, sickle cell anemia,• and, perhaps, malaria — there appears to be a pre-disposition to infection with salmonellae that exceeds any general susceptibility to other baCterial species.

The acute hemolytic phase of bartonellosis is complicated by the development of Salmonella bacteremia in as .many as 40 percent of cases. Patients with sickle cell anemia and other sickle hemoglobinopathies are unusually susceptible to invasion of the blood by salmonellae, and there is a strong tendency for .localization of infection in the bone. In fact, Salmonella species, not staphylococci account. for the vast majority of instances of osteomyelitis in patients with sickle cell anemia. Osteomyelitis is probably related to the localization of organisms in the areas of ischemia and necrosis of bone so common in sickle cell anemia this is but one example of the striking tendency of salmonellae to localize at sites of pre-existing.

The Relatively- Long Incubation Period Represents

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