344 Microbes and You 



are killed suspensions of bacteria in a concentration of about 

 one billion cells per milliliter. A combination of typhoid, para- 

 typhoid A, and paratyphoid B organisms (TAB vaccine) is 

 customarily administered to provide protection against all three 

 related organisms. Vaccination does not provide iron-clad pro- 

 tection from infection; this immunity is one of degree. Ingestion 

 of large numbers of Salmonella typhosa will result in disease, 

 but the vaccination will provide protection against minimal doses 

 of ingested organisms. The symptoms appear to be moderated 

 if a vaccinated person contracts the disease. 



SHIGELLA DYSENTERIAE 



Non-motile rods, 0.4—0.6 by 1.0-3.0 microns, occurring in 

 singles. Aerobic and facultative. Optimum growth temperature 

 37° C. Cause of dysentery in man and in monkeys. 



In contrast to most salmonellae, Shigella species are non-motile 

 and produce no gas when they ferment carbohydrates. The genus 

 is named for the Japanese, Shiga, who discovered the organisms in 

 1896. Other species were discovered in rapid succession. The 

 disease ranges from mild diarrhea to ulceration of the large bowel, 

 but bloodstream invasion does not normally take place. The 

 fatality rate is rather high in some epidemics, but by prompt 

 treatment with some of the newer drugs, the death rate has been 

 reduced. Vaccination is unsatisfactory. Even though Shigella 

 dysenteriae produces a true toxin, antitoxin appears to have little 

 or no useful effect in patients. 



This disease is extremely important as a cause of sickness in 

 tropical countries. The combination of poor sanitary facilities 

 and lack of proper personal cleanliness and hygiene is largely 

 responsible for the spread of bacillary dysentery, with an assist 

 from flies, cockroaches, and mice. 



Other diseases caused by gram negative rods and their 

 etiological agents include tularemia (Pasteurella tiilarensis), 

 BUBONIC PLAGUE (Pasteurella pestis), whooping cough (Hemo- 

 philus pertussis), and undulant fever (Brucella species). 



