Pulmonary host defenses and oropharyngeal pathogens

Airway multidrug-resistant organisms in a population of tracheostomy and chronic ventilator-dependent children at a tertiary care pediatric hospital

OBJECTIVE/BACKGROUND

Children with tracheostomies are at an increased risk of bacterial respiratory tract infections. Infections caused by multidrug-resistant organisms (MDROs) are more difficult to treat and can result in severe complications. This study aimed to investigate the risk factors and sequelae of MDRO positivity in tracheostomy and chronic ventilator-dependent children.

METHODS

We performed a retrospective chart review of 75 tracheostomy and chronic ventilator-dependent children at St. Louis Children's Hospital. Data on demographics, respiratory cultures, hospitalizations, emergency department (ED) visits, and antibiotic usage were collected. We determined the frequency of MDRO positivity and compared the number of hospitalizations, number of ED visits, and antibiotic usage in patients with and without MDRO-positive cultures. Patient clinical variables were analyzed before and after MDRO acquisition.

RESULTS

We found 75.7% (56/74) of our participants had an MDRO-positive culture, with methicillin-resistant Staphylococcus aureus (MRSA, n = 36, 64%) and Pseudomonas aeruginosa (n = 8, 14%) being the most commonly detected organisms. Participants with a greater number of annual nonpulmonary admissions (odds ratio [OR] = 1.99, 95% confidence interval [CI] (1.21-3.29), p = 0.008], inpatient antibiotic courses [OR = 1.27, 95% CI (1.07-1.50), p = 0.006], total antibiotic courses [OR = 1.26, 95% CI (1.08-1.48), p = 0.004], and chronic antibiotic use [OR = 2.31, 95% CI (1.12-4.74), p = 0.03] were at an increased risk for MDRO positivity. Those who were MDRO-positive had more pulmonary admissions following MDRO acquisition compared those who were MDRO-negative [p = 0.005] but not more antibiotic usage or ED visits.

CONCLUSION

Frequent antibiotic usage and hospitalizations increase the risk of MDRO acquisition in children with tracheostomies and ventilator-dependence. Further antibiotic stewardship may help prevent resistant infections in technology-dependent children.

Type I IFNs mediate development of postinfluenza bacterial pneumonia in mice

Influenza-related complications continue to be a major cause of mortality worldwide. Due to unclear mechanisms, a substantial number of influenza-related deaths result from bacterial superinfections, particularly secondary pneumococcal pneumonia. Here, we report what we believe to be a novel mechanism by which influenza-induced type I IFNs sensitize hosts to secondary bacterial infections. Influenza-infected mice deficient for type I IFN-alpha/beta receptor signaling (Ifnar-/- mice) had improved survival and clearance of secondary Streptococcus pneumoniae infection from the lungs and blood, as compared with similarly infected wild-type animals. The less effective response in wild-type mice seemed to be attributable to impaired production of neutrophil chemoattractants KC (also known as Cxcl1) and Mip2 (also known as Cxcl2) following secondary challenge with S. pneumoniae. This resulted in inadequate neutrophil responses during the early phase of host defense against secondary bacterial infection. Indeed, influenza-infected wild-type mice cleared secondary pneumococcal pneumonia after pulmonary administration of exogenous KC and Mip2, whereas neutralization of Cxcr2, the common receptor for KC and Mip2, reversed the protective phenotype observed in Ifnar-/- mice. These data may underscore the importance of the type I IFN inhibitory pathway on CXC chemokine production. Collectively, these findings highlight what we believe to be a novel mechanism by which the antiviral response to influenza sensitizes hosts to secondary bacterial pneumonia.

NKT cells play a limited role in the neutrophilic inflammatory responses and host defense to pulmonary infection with Pseudomonas aeruginosa

CD1d-restricted NKT cells are reported to play a critical role in the host defense to pulmonary infection with Pseudomonas aeruginosa. However, the contribution of a major subset expressing a Valpha14-Jalpha18 gene segment remains unclear. In the present study, we re-evaluated the role of NKT cells in the neutrophilic inflammatory responses and host defense to this infection using mice genetically lacking Jalpha18 or CD1d (Jalpha18KO or CD1dKO mice). These mice cleared the bacteria in lungs at a comparable level to wild-type (WT) mice. There was no significant difference in the local neutrophilic responses, as shown by neutrophil counts and synthesis of MIP-2 and TNF-alpha, in either KO mice from those in WT mice. Administration of alpha-galactosylceramide, a specific activator of Valpha14+ NKT cells, failed to promote the bacterial clearance and neutrophilic responses, although the same treatment increased the synthesis of IFN-gamma, suggesting the involvement of this cytokine downstream of NKT cells. In agreement against this notion, these responses were not further enhanced by administration of recombinant IFN-gamma in the infected Jalpha18KO mice. Our data indicate that NKT cells play a limited role in the development of neutrophilic inflammatory responses and host defense to pulmonary infection with P. aeruginosa.

Excessive matrix metalloproteinase-9 in the plasma of community-acquired pneumonia

BACKGROUND

It has been shown that matrix metalloproteinase-9 (MMP-9) is involved in the pathogenesis of various pulmonary inflammatory diseases. We determined the MMP-9 concentration in the plasma of community-acquired pneumonia (CAP) patients before and after antibiotic treatment.

METHODS

Gelatin zymography and ELISA analysis were used to measure MMP-9 activity and MMP-9 level, respectively, in 35 control subjects and 46 CAP patients.

RESULTS

WBC counts, neutrophils, MMP-9 activity and MMP-9 level were significantly higher in CAP patients compared with that of control subjects (P<0.001), while MMP-9 activity and MMP-9 level were returned to normal after the antibiotic treatment (P<0.001). In addition, MMP-9 level correlated positively with WBC counts and neutrophils number both before and after the antibiotic treatment.

CONCLUSIONS

MMP-9 may play an important role in the pathogenesis of CAP with a positive correlation with the number of neutrophils.

Limited role for interleukin-18 in the host protection response to pulmonary infection with Pseudomonas aeruginosa in mice

We report that clearance of Pseudomonas aeruginosa, accumulation of neutrophils, and synthesis of tumor necrosis factor alpha and macrophage inflammatory protein 2 in the infected lung were not largely different in interleukin-18 (IL-18) knockout or transgenic mice compared with control mice. Our results suggest a limited role for IL-18 in the host defense against P. aeruginosa.

Moraxella catarrhalis: from emerging to established pathogen

Moraxella catarrhalis (formerly known as Branhamella catarrhalis) has emerged as a significant bacterial pathogen of humans over the past two decades. During this period, microbiological and molecular diagnostic techniques have been developed and improved for M. catarrhalis, allowing the adequate determination and taxonomic positioning of this pathogen. Over the same period, studies have revealed its involvement in respiratory (e.g., sinusitis, otitis media, bronchitis, and pneumonia) and ocular infections in children and in laryngitis, bronchitis, and pneumonia in adults. The development of (molecular) epidemiological tools has enabled the national and international distribution of M. catarrhalis strains to be established, and has allowed the monitoring of nosocomial infections and the dynamics of carriage. Indeed, such monitoring has revealed an increasing number of B-lactamase-positive M. catarrhalis isolates (now well above 90%), underscoring the pathogenic potential of this organism. Although a number of putative M. catarrhalis virulence factors have been identified and described in detail, their relationship to actual bacterial adhesion, invasion, complement resistance, etc. (and ultimately their role in infection and immunity), has been established in a only few cases. In the past 10 years, various animal models for the study of M. catarrhalis pathogenicity have been described, although not all of these models are equally suitable for the study of human infection. Techniques involving the molecular manipulation of M. catarrhalis genes and antigens are also advancing our knowledge of the host response to and pathogenesis of this bacterial species in humans, as well as providing insights into possible vaccine candidates. This review aims to outline our current knowledge of M. catarrhalis, an organism that has evolved from an emerging to a well-established human pathogen.

Interventions to prevent pneumonia among older adults

Pneumonia is a common cause of death in older people. Antimicrobial drugs do not prevent pneumonia and, because of increasingly resistant organisms, their value in curing infection will become more limited. Establishing new strategies to prevent pneumonia through consideration of the mechanisms of this devastating illness is essential. The purpose of this review is to discuss how pneumonia develops in older people and to suggest preventive strategies that may reduce the incidence of pneumonia among older adults. Aspiration of oropharyngeal bacterial pathogens to the lower respiratory tract is one of the most important risk factors for pneumonia; impairments in swallowing and cough reflexes among older adults, e.g., related to cerebrovascular disease, increase the risk for the development of pneumonia. Thus, strategies to reduce the volumes and pathogenicity of aspirated material should be pursued. For example, since both swallowing and cough reflexes are mediated by endogenous substance P, pharmacologic therapy using angiotensin-converting enzyme inhibitors, which decrease substance P catabolism, may improve both reflexes and result in the lowering of the risk of pneumonia. Similarly, since the production of substance P is regulated by dopaminergic neurons in the cerebral basal ganglia, treatment with dopamine analogs or potentiating drugs such as amantadine (and, of course, prevention of cerebral vascular disease, which can result in basal ganglia strokes) should affect the incidence of pneumonia. The purpose of this review is to consider promising pharmacologic treatments as methods of preventing pneumonia in older adults and to review other proven strategies, e.g., infection control and cerebrovascular disease prevention that will lessen the incidence of pneumonia.

Impact of tracheotomy on colonization and infection of lower airways in children requiring long-term ventilation: a prospective observational cohort study

STUDY OBJECTIVES

Determination of the following: (1) colonization and infection rates in children requiring long-term ventilation initially via a transtracheal tube and subsequently via a tracheotomy; (2) the number of infection episodes per 1,000 ventilation days, during both types of artificial airways; and (3) routes of colonization/infection of the lower airways, ie, whether the pathogenesis was endogenous (via the oropharynx) or exogenous (via the transtracheal tube or tracheotomy).

DESIGN

Observational, cohort, prospective study over 2 1/2 years.

SETTING

Pediatric ICU (PICU), Royal Liverpool Children's National Health Service Trust of Alder Hey, a tertiary referral center.

PATIENTS

Twenty-two children requiring long-term mechanical ventilation initially transtracheally and subsequently via a tracheotomy.

INTERVENTION

Nil.

RESULTS

The lower airways were colonized in 71% of children during transtracheal ventilation; posttracheotomy, this was 95% (p=0.03). Children developed significantly fewer infections following colonization with a microorganism posttracheotomy (8/15 pretracheotomy vs 6/21 posttracheotomy; p=0.013). Throughout the study, there were a total of 17 episodes of infection, all of which were preceded by colonization. Haemophilus influenzae, Staphylococcus aureus, Acinetobacter baumannii, and Pseudomonas aeruginosa were the same four causative pathogens during mechanical ventilation both transtracheally and via tracheotomy. Forty-nine episodes of colonization were observed, 15 pretracheotomy and 34 posttracheotomy; of these, 12 (80%) and 19 episodes (56%), respectively, were primary endogenous, ie, present in the oropharynx on hospital admission and subsequently at tracheotomy. Only one colonization episode (7%) of exogenous pathogenesis was observed during transtracheal intubation, while 12 (35%) (p=0.02) occurred after tracheotomy. An equal number of secondary endogenous colonization episodes (two and three, ie, acquired in the oropharynx after PICU admission and after tracheotomy, respectively, were recorded.

CONCLUSIONS

(1) Despite a high level of hygiene, exogenous colonization without subsequent infection was common. (2) Although all patients were colonized, the infection rate was lower after tracheotomy. This may be due to enhanced immunity (medically stable) and improved tracheobronchial toilet. (3) Microorganisms in children with tracheotomy differ from those in adults.

Role of interleukin-8 in community-acquired pneumonia: relation to microbial load and pulmonary function

In pneumonia local phagocyte activation is crucial for clearing of pathogenic microorganisms. In this context alveolar macrophage interleukin-8 secretion, phagocyte oxidative response and concentrations of lavage proteins were quantified, including interleukin-8, in 31 patients with pneumonia, 13 age matched patients with peripheral lung consolidation and six healthy volunteers; these findings were related to the impairment of gas exchange and the bacterial load in the alveolar space. Increased interleukin-8 levels were found in bronchoalveolar lavage fluid (BALF) and in alveolar macrophage supernatants from patients with pneumonia (214 ng/10(5) AM +/- 121 vs 71 ng/10(5) AM +/- 35 and 66 ng/10(5) AM +/- 30, p < 0.05). Interleukin-8 release from alveolar macrophages correlated with the upregulated spontaneous luminol enhanced oxidative response of pulmonary phagocytes but not with the neutrophil count in BALF. In pneumonia patients a significant difference was found between patients with 10(4) or more colony forming units (CFU)/ml BALF of one pathogen and patients with less CFU or nonspecific microbiological results (261 ng/10(5) AM +/- 89 vs 179 ng/10(5) AM +/- 81 and 7.5 ng/ml BALF +/- 17 vs 0.44 ng/ml BALF +/- 1, p < 0.05). Further, a negative correlation between interleukin-8 release of alveolar macrophages and the arterial pO2 at the time of BALF could be demonstrated (r = -0.47, p < 0.05). The results demonstrate local cellular activation in community-acquired pneumonia, which is related to the bacterial load in the alveolar space and to impairment of gas exchange. This is consistent with the hypothesis that pulmonary phagocytes play a central role in the pathogenesis of bacterial pneumonia, contributing not only to bacterial clearing but also to local tissue damage.

The course of nosocomial oropharyngeal colonization in patients recovering from acute respiratory failure

We sought to determine the duration of nosocomially acquired Gram-negative bacilli (GNB) oropharyngeal colonization following hospitalization for acute respiratory failure (ARF). We selected 24 inpatients recovering from ARF who had positive oropharyngeal cultures for GNB. Follow-up cultures were obtained at the time of hospital discharge, and 2 and 4 weeks afterwards. The prevalence of GNB colonization in these patients was 14/21 (67 percent) at the time of hospital discharge and 14/23 (60 percent) 2 weeks afterwards. Both rates were greater than the control population's 7/30 (23 percent, p < 0.02 and < 0.05, respectively). Four weeks after hospital discharge, the prevalence of colonization had fallen to 7/19 (37 percent) which was not significantly different from that of controls. Five of 24 subjects were rehospitalized during the follow-up period. Pneumonia was diagnosed in only two of the five and both proved to be due to pathogens other than GNB. We conclude that the prevalence of GNB oropharyngeal colonization following ARF approaches control levels within four weeks of hospital discharge. We speculate that a post-ARF patient's risk for GNB pneumonia similarly declines.

Development and immunophenotyping of the pharyngeal tonsil (adenoid) in cattle

Immunoperoxidase staining and electron and light microscopy were used to characterize the development of the pharyngeal tonsil in 98 cattle aged between 30 days of gestation and 12 years. The rugae of the pharyngeal tonsil were poorly formed before 95 days of gestation. Microvillous (M) cells associated with intra-epithelial leucocytes (lympho-epithelium) were scattered among ciliated and goblet cells covering most of the surface in post-natal animals. Intra-epithelial leucocytes were rare in fetuses, but ciliated and M cells could be distinguished. Leucocytes of the lamina propria started to accumulate at approximately 120 days of gestation. A loose accumulation of mononuclear cells progressed into a B-cell rich upper and T-cell rich lower layer, with typical lymphoid tissue organization in post-natal animals and lymphoid involution in aged cattle. Primary lymphoid follicles formed at 5 months of gestation, but germinal centres did not form until 2 to 4 weeks after birth. Except for null cells, the relative number of cells staining for each leucocyte phenotype or MHC class II antigen increased with age, especially during the neonatal period. The early development, strategic location and specialized structure of the pharyngeal tonsil suggest an important role in modulating inhaled antigens in cattle. Fetal and neonatal calves had minimal lymphoid tissue priming, as indicated by lack of secondary follicles, low MHC class II expression and few intra-epithelial leucocytes. The phenotypic differences may be relevant to the increased susceptibility of calves to infectious diseases shortly after birth.