Human oral defenses against gram-negative rods

Aspiration and infection in the elderly : epidemiology, diagnosis and management

Aspiration of the oropharyngeal or gastric contents by elderly persons often leads to lower respiratory tract infections, such as aspiration pneumonia or pneumonitis. The existence of dysphagia and aspiration in elderly patients are important factors in the occurrence of aspiration pneumonia, but are not sufficient to cause aspiration pneumonia in the absence of other risk factors. Salivary flow and swallowing can eliminate Gram-negative bacilli from the oropharynx in healthy persons. However, elderly persons may have diminished production of saliva as a result of medications and oral/dental disease, leading to poor oral hygiene and oropharyngeal colonisation with pathogenic organisms. When dysphagic patients aspirate pathogenic bacteria while swallowing food or liquids, they must also have decreased defences, such as impaired immunity or pulmonary clearance, in order to develop aspiration pneumonia.Elderly patients with cerebrovascular disease often have dysphagia that leads to an increased incidence of aspiration. It was previously reported that patients with silent cerebral infarction affecting the basal ganglia were more likely to experience subclinical aspiration and an increased incidence of pneumonia. Basal ganglia infarction leads to the impairment of dopamine metabolism and, as a consequence, a decrease of substance P in the glossopharyngeal nerve and sensory vagal nerves. Therefore, dysphagia and a decreased cough reflex may be induced by the impairment of dopamine metabolism in some elderly patients with cerebrovascular disease, suggesting that pharmaceutical agents which modulate dopamine metabolism may be able to improve swallowing and the cough reflex in patients with basal ganglia infarction. The main strategy for controlling aspiration and aspiration-related pulmonary infection in the elderly is to prevent aspiration of pathogenic bacteria along with the oropharyngeal or gastric contents. Because aspiration pneumonia in the elderly is related to certain risk factors, including dysphagia and aspiration, effective preventive measures involve various approaches, such as pharmacological therapy, swallowing training, dietary management, oral hygiene and positioning.

Lung infections and aging

Respiratory tract infections are the leading cause of death due to infectious disease in the elderly. Many factors, especially waning immune responses and the onset of age-associated organ dysfunction, likely account for an increase in susceptibility to respiratory tract infection in the elderly, and morbidity and mortality rates are substantially greater for the elderly when outcomes are compared to that of younger individuals. The presence of underlying disease states such as chronic obstructive pulmonary disease (COPD) or other organ system disease further increases the likelihood of developing severe pneumonia in the elderly population, and the frail elderly, particularly when institutionalized in chronic care facilities, are at high risk for developing severe and recurrent pneumonia. This article will discuss various factors associated with advanced age that predispose the elderly to respiratory infections and summarize current approaches to treatment and prevention.

Nosocomial pneumonia in children

Nosocomial pneumonia continues to be a leading cause of fatal nosocomial infection in the United States. Although there are differences in pathogens by age, the importance of nosocomial pneumonia is apparent in the adult population as well as in the pediatric patient groups. The ability to diagnose these infections utilizing clinical suspicion and microbiologic/rapid diagnostic tests will allow the clinician to effectively treat nosocomial pneumonia in the critically ill patient. Unfortunately, these treatment modalities and preventive measures have not kept pace with our understanding of the pathogenesis of this infection. The pediatric patient population presents several unique and specific infection control, diagnostic and treatment problems for the practicing clinician. The appropriate infection control and isolation policies for specific viral and multiple antibiotic resistant bacterial isolates remains a cornerstone in the prevention of nosocomial pneumonia. The judicious use of empiric antibacterial chemotherapy remains important in the treatment of patients with nosocomial pneumonia. However, in the pediatric patient population the recognition that viral and fungal etiologies are important causes of nosocomial pneumonia challenge the clinician to apply the appropriate diagnostic and effective treatment regimens in pediatric nosocomial pneumonias. The epidemiologic data for the clinician's own institution in regards to etiologic causes of nosocomial pneumonia, drug susceptibility patterns as well as the seasonal and patient distribution of these infections are critical. Nosocomial pneumonia will continue to remain a significant cause of morbidity, mortality, and hospital cost in the United States in the upcoming decades. The advent of new rapid diagnostic testing and improved treatment modalities for effective therapy and prevention will be aided by the advent of immunologic therapy for these disease states.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cancer chemotherapy on the human aerobic oropharyngeal flora

Since various agents used in cancer chemotherapy exhibit antimicrobial activity in vitro, we performed sequential quantitative cultures of saline gargles obtained from patients receiving cancer chemotherapy to determine if such chemotherapy alters the composition of the aerobic oropharyngeal flora. When we compared results of cultures obtained from 12 patients just before and at various times after receiving courses of cancer chemotherapy, we observed small, though significant reductions in the numbers of total bacteria, alpha-hemolytic streptococci and inhibitory streptococci two to seven days after courses of chemotherapy. A concomitant increase in the percentage of patients colonized by gram-negative bacilli occurred. Of the chemotherapeutic agents used to treat our subjects, only doxorubicin exhibited antimicrobial activity in vitro. All four alpha-hemolytic streptococci, but none of the seven strains of gram-negative bacilli examined, were inhibited by doxorubicin at concentrations of less than or equal to 12.5 mg/l. Doxorubicin had a modest enhancing effect on in vitro adherence of gram-negative bacilli to human embryonic lung cells. These data suggest that cancer chemotherapy might play a role in colonization of cancer patients by gram-negative bacilli by creating a microbiologic vacuum conducive to such colonization. In this way, cancer chemotherapy might contribute to the high incidence of gram-negative bacillary pneumonia among patients with malignant neoplasms.

Efficacy and safety of aztreonam-clindamycin versus tobramycin-clindamycin in the treatment of lower respiratory tract infections caused by aerobic gram-negative bacilli

A total of 80 patients were randomized to receive either aztreonam or tobramycin for the treatment of lower respiratory tract infections caused by gram-negative bacilli; all these patients received clindamycin concomitantly. A total of 53 patients were randomized to receive aztreonam-clindamycin; of these, 46 were clinically evaluable and 39 were bacteriologically evaluable. Of the 46 clinically evaluable patients, 41 were considered cured, 3 failed to be cured, and 2 died during the study period of unrelated causes. Of the 39 bacteriologically evaluable patients, 36 were considered cured, and 3 failed to be cured. There were 26 clinically evaluable patients in the group randomized to receive tobramycin-clindamycin. Of them, 22 patients were considered cured, 3 failed to be cured, and 1 died of unrelated causes during the study period. There were 18 bacteriologically evaluable patients in the tobramycin-clindamycin group; 17 were cured, and 1 failed to be cured. The most common pathogens isolated from the patients were Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa. All of the isolated organisms were susceptible to both tested antibiotics, except for a strain of Pseudomonas cepacia resistant to both tested antimicrobial agents and a strain of Enterobacter aerogenes and one of P. aeruginosa that were resistant to aztreonam. Very few adverse reactions related to the antibiotics were seen. These effects, when present, were transient and comparable in both studied groups, except for renal-function tests, which were altered in 7.7% of the patients randomized to receive tobramycin-clindamycin and in none of the patients randomized to receive aztreonam-clindamycin. Aztreonam-clindamycin is safe and effective for the treatment of lower respiratory tract infections caused by aerobic gram-negative bacilli when the organisms are susceptible.

The effect of selective decontamination of the digestive tract on colonisation and infection rate in multiple trauma patients

122 multiple trauma patients staying in the ICU for 5 or more days and needing mechanical ventilation were investigated to determine the effect of selective decontamination of the digestive tract on prevention of infection. The (retrospectively studied) control group of 59 patients received no antibiotic prophylaxis. The infection rate during ICU-stay was 81%. Most infections were caused by potentially pathogenic microorganisms (PPM) from the oral cavity or the intestines (i.e. endogenous infections). The oropharynx and the intestines were rapidly colonised with ICU-associated gram-negative bacilli. After 2 weeks more than 80% of patients were found colonised. This secondary colonisation of the digestive tract is a very important stage in the pathogenesis of infections. Sixty-three patients were selectively decontaminated with nonabsorbable antibiotics, administered through the gastric tube even if peristalsis was absent. Emphasis was laid on the selective decontamination of the oral cavity, using topical application of an antibiotic paste. With this technique the oral cavity was free of PPM within 3 days in most patients. No secondary colonisation was found. Rectal colonisation decreased significantly after 5 days. Secondary colonisation occurred in 9 patients with PPM sensitive to the antibiotics used. The prophylactic regimen included systemic cefotaxim, directed against early endogenous infection. The suppression and after some time the absence of the endogenous source of PPM resulted in a significant reduction of colonisation and infection. The total infection rate decreased to 16%.

Effect of decreased salivation and pH on the adherence of Klebsiella species to human buccal epithelial cells

To assess the role of reduced salivary flow and intraoral pH on gram-negative bacterial colonization of the oropharynx, we studied in vitro Klebsiella adherence to normal human buccal epithelial cells at various pH values and to buccal cells from patients with pathological xerostomia (decreased saliva flow). Reduced pH significantly increased adherence of Klebsiella pneumoniae 84 to normal buccal epithelial cells (P less than 0.001). In contrast, two clinical isolates of K. oxytoca showed no significant pH-dependent change in adherence. A corollary of this was that patients with pathological xerostomia had significantly increased adherence of K. pneumoniae 84 to their buccal epithelial cells as compared with normal controls (P less than 0.01). These results suggest that reduced salivary flow and the concomitant reduction of intraoral pH may predispose patients to bacterial colonization with K. pneumoniae.