Streptococcus pneumoniae is a bacterium that can infect the upper respiratory tract and cause pneumonia, as well as infections in other parts of the body such as the bloodstream (bacteremia), lining of the brain and spinal cord (meningitis), bones (osteomyelitis), joints (arthritis), ears (otitis media) and sinuses (sinusitis).
Alcoholics and cigarette smokers are particularly susceptible to pulmonary infections caused by S. pneumoniae. A rodent study in the May issue of Alcoholism: Clinical & Experimental Research has found that alcohol consumption increases movement of S. pneumoniae toward the lungs, and that smoke exposure exacerbates the alcohol-induced increase in bacterial penetration.
"All of the infections caused by S. pneumoniae start with the bacterium colonizing or binding to cells in the upper part of the nose, which is called the nasopharynx," said Gentry-Nielsen, professor of microbiology and immunology at Creighton University School of Medicine, research microbiologist at the Omaha Veterans Affairs Medical Center, and corresponding author for the study. "The trachea that leads from the nasopharynx to the lungs is lined with cells that have hair-like projections called cilia. These cilia beat in an upward direction to sweep mucus and microorganisms like S. pneumoniae upward and prevent their movement into the lungs. Disease normally occurs when the immune system is compromised or the person is colonized with a new or especially virulent strain of S. pneumoniae that is able to evade the action of the cilia and travel from the nasopharynx into the lungs."
Gentry-Nielsen said that alcoholics are more susceptible to S. pneumoniae infections for several reasons. "They have a decreased gag reflex and an increased risk of movement of nasopharyngeal and gastric contents into their lungs, especially when they lose consciousness," she said. "Both of these defects provide additional opportunities for S. pneumoniae to enter their lungs. Host defenses within the lungs of alcoholics are also compromised, so they are not well equipped to handle the infection once the organisms reach the lungs. Cigarette smokers also have an increased susceptibility to pulmonary infections caused by S. pneumoniae. Smokers are much more likely to be colonized with the organism in their mouths and nasopharynx than non-smokers. Smoking also injures cilia and alters the efficiency of their beating so that bacteria entering the trachea have an increased likelihood of making their way into the lungs."
"Clinical studies of this type are complicated because at least 80 percent of human alcoholics smoke," added Gregory J. Bagby, Kai and Earl Rozas professor of physiology at Louisiana State University Health Sciences Center. "Controlled studies in animals are therefore critically important in identifying interactive and separate effects of these two agents. This group is one of the first to study this interaction in a systematic way and the present study on the interactive effects of cigarette smoke and alcohol on the mucociliary apparatus is the first study of its kind to my knowledge."
For 12 weeks, researchers exposed Sprague-Dawley rats (n=64) twice daily to either smoke generated from 30 cigarettes or room air. For the last five weeks of exposure, rats were fed liquid diets that contained 0, 16, 26 or 36 percent of their calories as alcohol. The rats were then infected intranasally with S. pneumoniae, and movement of the organisms into the lower respiratory tract was followed.