The gram-negative bacillary pneumonias

Polygenic prediction of educational attainment within and between families from genome-wide association analyses in 3 million individuals

We conduct a genome-wide association study (GWAS) of educational attainment (EA) in a sample of ~3 million individuals and identify 3,952 approximately uncorrelated genome-wide-significant single-nucleotide polymorphisms (SNPs). A genome-wide polygenic predictor, or polygenic index (PGI), explains 12-16% of EA variance and contributes to risk prediction for ten diseases. Direct effects (i.e., controlling for parental PGIs) explain roughly half the PGI's magnitude of association with EA and other phenotypes. The correlation between mate-pair PGIs is far too large to be consistent with phenotypic assortment alone, implying additional assortment on PGI-associated factors. In an additional GWAS of dominance deviations from the additive model, we identify no genome-wide-significant SNPs, and a separate X-chromosome additive GWAS identifies 57.

Coinfection of Clostridium perfringens and Escherichia coli in gas-producing perianal abscess diagnosed by 16S rDNA sequencing: a case report

BACKGROUND

Gas-producing perianal abscess raises the possibility of clostridial infection, with Clostridium perfringens being the most common causative agent, which is highly lethal if untreated timely. As the treatment of clostridial infections often differs from that of non-clostridial infections, which they may closely resemble, the importance of accurate pathogenic organism identification cannot be overemphasized. The 16S rDNA of bacteria is highly conserved within a species and among species of the same genus but demonstrates substantial variation between different species, thus making it a suitable genomic candidate for bacterial detection and identification.

CASE PRESENTATION

Here, we report the case of a 53-year-old patient who was admitted to the hospital for a gas-producing perianal abscess. The patient was managed with ceftizoxime and ornidazole and then received debridement and drainage at the lesion on the second day after admission. The bacterial cultures of the patient isolates from the debridement showed a coinfection of Escherichia coli and Enterococcus faecium. Although perianal redness and swelling subsided obviously after the surgery, the patient was febrile to 38.3℃ with his left upper thigh red and swollen, aggravated with tenderness and crepitus. Considering insufficient debridement and the risk of incorrect identification of pathogens, a second debridement and drainage were performed 4 days after the primary operation, and 16S rDNA sequencing of the isolates implicated Clostridium perfringens infection. Given the discrepancies in diagnostic results and the treatment outcomes, Enterococcus faecium was identified as sample contamination, and a diagnosis of coinfection of Clostridium perfringens and Escherichia coli in gas-producing perianal abscess was confirmed. The patient was then successfully treated with meropenem and vancomycin and was discharged at 27 days of admission.

CONCLUSIONS

This case represents the first report of coinfection of both clostridial and non-clostridial organisms in gas-producing perianal abscess and the first case reporting the use of 16S rDNA sequencing in the diagnosis of perianal abscess. Timely pathogen identification is critical for treating gas-producing perianal abscess and an antibiotic regimen covering both aerobic and anaerobic organisms is recommended before true pathogens are identified.

Aerobic Gram-negative Bacillary Pneumonia

Gram-negative bacilli (GNB) are a common cause of severe hospital-acquired pneumonia. Due to changes in the health care environment and selective antimicrobial pressure, these bacteria also are becoming a more common cause of pneumonia in venues outside of the traditional hospital setting and are increasingly resistant to antimicrobial agents. Risk factors for acquisition of GNB allow the clinician to efficiently identify patients who are likely to have pneumonia due to these pathogens. Available diagnostic techniques have a limited capacity to accurately detect GNB pulmonary infection. Yet, a pathogen specific diagnosis and knowledge of local resistance patterns are quintessential elements in formulating an effective treatment plan. This article reviews the epidemiologic characteristics, pathogenesis, and current management issues of GNB pneumonia.

Pneumonia in the elderly

Pneumonia is one of the commonest infections in elderly patients. The pathogens responsible for pneumonias in the elderly are the same as in younger adults. Because of associated cardiopulmonary disease and/or impaired host defenses, pneumonia in elderly patients is associated with increased mortality and morbidity compared to younger patients. The clinical importance of pneumonias in the elderly relates to age-dependent and pathologic changes in the immune system as well as the lungs. Pneumonias in the elderly may be classified, for clinical purposes, according to their location of acquisition, i.e. community-acquired pneumonias, nursing home-acquired pneumonias, or hospital-acquired pneumonias. The clinical presentation of pneumonias in the elderly may be difficult, due to pre-existing cardiopulmonary disease that mimics pneumonia. This review discusses the diagnostic and therapeutic approaches to elderly patients with pneumonia.

Enterobacter spp.: pathogens poised to flourish at the turn of the century

Knowledge of the genus Enterobacter and its role in human disease has expanded exponentially in recent years. The incidence of infection in the hospital and the community has increased. New clinical syndromes have been recognized. Enterobacter spp. have also been implicated as causes of other syndromes that traditionally have been associated almost exclusively with more easily treatable pathogens, such as group A streptococci and staphylococci. Rapid emergence of multiple-drug resistance has been documented in individual patients during therapy and in populations and environments with strong selective pressure from antimicrobial agents, especially the cephalosporins. Therapeutic options for patients infected with multiply resistant strains have become severely limited. Carbapenems or, alternatively, fluoroquinolones are the most predictively active options, although resistance to both classes has been observed on rare occasions. Enterobacter spp. appear well adapted for survival and even proliferation as the turn of the century approaches.

The role of salivary function on oropharyngeal colonization

Aspiration of oropharyngeal flora is the most common route of acquiring Gram-negative pneumonia, a major nosocomial infection. Epidemiologic studies indicate that the elderly are at increased risk for developing these life-threatening pneumonias. The primary objective of this study was to determine the effects of salivary oral defenses against Gram-negative colonization. The study population consisted of 41 male outpatients, age 70 and older, seen at the Denver VAMC. The group included subjects with both diminished and normal salivary flow. Each subject answered a questionnaire regarding overall health, medication use, and symptoms of salivary dysfunction. We then collected whole saliva, unstimulated and stimulated parotid saliva, and performed a throat swab on each patient. For each throat culture, analysis was done to identify Gram-negative bacteria. Flow rates between colonized (n = 6) and noncolonized subjects (n = 34) were compared. While there were no significant differences in the flow rates between the two groups, a trend was noticed in that flow rates were lower for all three flow measures in the colonized group (whole, 22% decrease; unstimulated, 22% decrease; and stimulated, 28% decrease). These preliminary findings suggest that subjects with diminished salivary flow may possibly be at increased risk for oropharyngeal Gram-negative colonization. Research on the role that saliva plays in oropharyngeal bacterial colonization is continuing.

Recurrent Pseudomonas aeruginosa pneumonia in an intensive care unit

We reviewed the records of all patients in the intensive care unit (ICU) who had Pseudomonas aeruginosa pneumonia over a 2.5-year period. Of patients with P aeruginosa pneumonia, 20 of 34 survived the initial episode of pneumonia. Ten of these 20 developed recurrence. In the nonrecurrent group, nine of ten survived hospitalization, compared to only four of ten in the recurrent group. Comparing the recurrent to the nonrecurrent group, factors associated with recurrence were the APACHE 2 score (12.3 +/- 2.7 vs 8.6 +/- 4.2 [p less than 0.03]), APS score (7.0 +/- 3.5 vs 2.7 +/- 2.1 [p less than 0.01]), and chronic pulmonary disease (8/10 vs 2/10 [p less than 0.05]). The recurrent P aeruginosa group was younger (63 +/- 10 vs 74 +/- 11 years old [p less than 0.03]) and spent more time receiving mechanical ventilation (95 +/- 64 vs 26 +/- 36 days [p less than 0.01]), in the ICU (101 +/- 61 vs 33 +/- 35 days [p less than 0.01]), and in the hospital (144 +/- 77 vs 84 +/- 32 days [p less than 0.03]). Although not statistically significant, in the recurrent group, eight of ten patients had tracheostomy and seven of ten had COPD, vs three of ten and two of ten, respectively, in the nonrecurrent group. Recurrent P aeruginosa pneumonia in the ICU is associated with increased morbidity and mortality and does not appear to be related to the adequacy of antibiotic treatment. Chronic lung disease appears to predispose patients to recurrent P aeruginosa pneumonia.

Randomized clinical trial of aztreonam and aminoglycoside antibiotics in the treatment of serious infections caused by gram-negative bacilli

Aztreonam was compared with aminoglycoside antibiotics (tobramycin and amikacin) in a randomized, prospective, clinical trial in serious infections caused by gram-negative bacilli (GNB). A total of 43 evaluable patients with 47 infected sites were treated with aztreonam, and 41 evaluable patients were treated with aminoglycosides for 43 infections. Of patients treated with aztreonam, 17 were bacteremic, as were 12 of those treated with aminoglycosides. Clinical and microbiologic response rates were similar, except that only 5 of 11 patients with pneumonia were considered to be clinically cured with aminoglycoside therapy, while 5 of 6 patients with pneumonia treated with aztreonam were cured. Renal impairment was observed in 9 of 54 patients who received aminoglycoside antibiotics, but in only 2 of 53 patients treated with aztreonam. Hearing impairment developed in one patient treated with tobramycin. Transient elevations of serum transaminase levels occurred in 9 of 53 patients treated with aztreonam and in only 2 of 54 aminoglycoside-treated patients. Diarrhea and superinfection occurred with equal frequency in both groups. Serum concentrations of bactericidal activity could not be correlated with the outcome of therapy. Aztreonam appears to have comparable clinical efficacy with aminoglycoside antibiotics for the treatment of serious infections caused by aerobic and facultative GNB. Its use as a single agent for the treatment of serious lower respiratory infections caused by GNB warrants further evaluation.

Combination antimicrobial therapy

In spite of a large volume of data regarding the in vitro activity of single and combined antimicrobial activity, the clinical relevance of these studies is unclear. Few comparative trials of combined and single antibiotic therapy of human infection have been performed. Synergistic combination therapy has been shown to be beneficial in a few specific circumstances. Antagonistic combinations should be avoided in the treatment of meningitis, endocarditis, and infections of immunocompromised patients. The bactericidal titer of serum or spinal fluid should reflect adequacy of therapy of meningitis, endocarditis, and osteomyelitis, and adjustments can be made accordingly.