Bacterial Colonization: Pathogenesis and Clinical Significance

Infectious Mechanisms Regulating Susceptibility to Acute Exacerbations of COPD

Acute exacerbations of COPD (AECOPD) are defined by clinical criteria, outlined in the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines [1]. These include an acute increase in one or more of the following cardinal symptoms, beyond day to day variability: dyspnea, increased frequency or severity of cough and increased volume or change in character of sputum, which represent an acute increase in airway inflammation. The role of infection in the pathogenesis of COPD, acute exacerbation and disease progression has been a clinical and research question for many years, and the pendulum has swung from infection as a major cause of acute exacerbation and COPD (British Hypothesis) [2], to infection as an unrelated epiphomenon in acute exacerbation [3–5], and back again to infection as integral in the development of AECOPD and likely an important contributor to COPD progression [6–19]. Upwards of 80 % of AECOPD are driven by infectious stimuli, with 40–50 % associated with bacterial infection and 30–50 % associated with acute viral infection, with some exacerbations having dual bacterial and viral causation [20]. Much of the advancement in our understanding of the role of infection is AECOPD is due to the advancement of clinical and research tools that have allowed researchers to accurately characterize the microbial pathogens, and better understand the host-pathogen interactions (Table 1).

Neutrophil elastase (NE) and NE inhibitors: canonical and noncanonical functions in lung chronic inflammatory diseases (cystic fibrosis and chronic obstructive pulmonary disease)

Proteases and antiproteases have multiple important roles both in normal homeostasis and during inflammation. Antiprotease molecules may have developed in a parallel network, consisting of "alarm" and "systemic" inhibitors. Their primary function was thought until recently to mainly prevent the potential injurious effects of excess release of proteolytic enzymes, such as neutrophil elastase (NE), from inflammatory cells. However, recently, new potential roles have been ascribed to these antiproteases. We will review "canonical" and new "noncanonical" functions for these molecules, and more particularly, those pertaining to their role in innate and adaptive immunity (antibacterial activity and biasing of the adaptive immune response).

Mechanisms and prevention of pneumonia in the elderly

Pneumonia is not only a major cause of death for elderly persons, but also imposes substantial personal morbidity and burdens on the health care system. An understanding of the pathogenesis of this serious illness could allow us to devise methods for curbing the incidence and severity of the disease. Pathophysiological issues and preventative measures are the subject of this review.

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.

[Protected bacteriologic brushing in patients with severe copd]

To determine the presence of germs and their concentration in a group of patients with severe chronic obstructive pulmonary disease (COPD) (FEV1 < 50%), some of whom were in stable condition and others of whom were in acute phase. Twenty-six patients with severe COPD (14 stable and 12 acute phase) were enrolled. None had received prior antibiotic or corticoid treatment. The stable patients had no signs or symptoms of exacerbation, whereas the acute-phase patients had increased dyspnea, sputum volume and purulence. The patients received aerosol rather than liquid anesthesia when PSB sampling was performed. A PSB finding was considered positive at a level > or = 10(3) CFU/ml. There were no significant differences between the groups with respect to age, sex, proportion of smokers and ex-smokers or packs per year. The only spirometric measure that was significantly different was (FEV1/FVC, which was lower in the acute-phase group (p < 0.05). Positive PSB findings were recorded for 57.1% of the stable patients and for 66.7% of the acute-phase patients (p = NS). H. influenzae was the microorganism found most often in both groups. The mean CFU/ml level was 8,625 in stable patients and 17,375 in acute-phase patients (p = NS). A large proportion of stable patients (57.1%) with severe COPD harbor significant concentrations of germs as revealed by PSB sampling. Germ concentrations were found in a non significantly greater number of acute-phase patients, confirming the lack of congruence between clinical status and bacteriological condition.

Technique for measurement of oropharyngeal clearance in the elderly

In elderly patients, gram negative bacterial colonization often preceeds nosocomial pneumonia. As we propose that a critical factor influencing this change from normal to gram negative predominance is an alteration in oral clearance, we designed this study to validate a technique for measurement of oropharyngeal clearance in a large number of nursing home residents. We modified a protocol of La Force et al who utilized an atomizer to radiolabel oropharyngeal secretions. We determined the output per spray of a DeVILBISS model 152 atomizer and found that 3 sprays of 5 mCi of 99mTc-HSA in 4 ml saline delivered 263 microCi in 0.21 ml. To measure clearance, we designed a portable, collimated ratemeter. It has a lead lined tapered aluminium frame 15 cm high, originating from a 7.5 cm rectangular base which is fitted to the scintillator. On the bench we demonstrated that this collimator, used to confine detection to the face, did not alter sensitivity and linearity of the ratemeter in our specific experimental conditions. When the ratemeter was collimated and its window off, its sensitivity was 5 times greater than the gamma camera with no loss of linearity. However, distance had a significant effect on the ratemeter's sensitivity whereas it had little effect on the gamma camera. Finally, in thirteen patients we assessed the ratemeter's accuracy in measurement of oropharyngeal clearance by comparing curves obtained simultaneously from the ratemeter and gamma camera. While each curve had its own characteristics, both devices provided remarkably similar data and there were no significant differences (r = 0.967, p < 0.0001). We conclude that oropharyngeal clearance can be conveniently and accurately studied in elderly patients at the bedside with a collimated ratemeter. The high sensitivity provides a measure of clearance with low levels of radioactivity exposure, allowing repeated studies over time.

Prandial aspiration and pneumonia in an elderly population followed over 3 years

The purpose of our study was to prospectively determine pneumonia frequency and correlate it with prandial liquid aspiration and feeding status in frail elderly nursing home residents. Initially, 152 patients had video swallowing examinations (81 oropharyngeal dysphagia, 19 thoracic dysphagia, 52 without dysphagia). Those diagnosed with oropharyngeal impairment were subsequently managed with swallowing therapy or artificial feeding modalities. Patients were followed for 3 years (unless they expired earlier) and clinical courses were categorized according to the degree of prandial aspiration and feeding (PAF) status. Subjects with new lung infiltrates persisting for at least 5 days with appropriate clinical findings were diagnosed as having pneumonia and were classified according to the PAF status months in which these findings occurred. Fifty-six pneumonias were diagnosed during 4,280 months with the following frequencies: no aspiration months 0.6%; minor aspiration months 0.9%; major aspiration/oral feeding months 1.3%; major aspiration/artificial feeding months 4.4%, p < 0.001. Our results indicate that there is not a simple and obvious relation between prandial liquid aspiration and pneumonia. Artificial feeding does not seem to be a satisfactory solution for preventing pneumonia in elderly prandial aspirators.

The pathogenesis of ventilator-associated pneumonia: I. Mechanisms of bacterial transcolonization and airway inoculation

Ventilator-associated pneumonia (VAP) is an infection of the lung parenchyma developing in patients on mechanical ventilation for more than 48 h. VAP is associated with a remarkably constant spectrum of pathogenic bacteria, most of which are aerobic Gram-negative bacilli (AGNB) and, to a lesser extent Staphyloccus aureus. Most authorities agree that VAP develops as a result of aspiration of secretions contaminated with pathogenic organisms, which appear to be endogenously acquired. These pathogens gain access to the distal airways by mechanical reflux and aspiration of contaminated gastric contents and also by repetitive inoculation of contaminated upper airway secretions into the distal tracheobronchial tree. Persistence of these organisms in the upper airways involves their successful colonization of available surfaces. Although exogenous acquisition can occur from the environment, the rapidity at which critically ill patients acquire AGNB in the upper airways in conjunction with the low rate of AGNB colonization of health-care workers exposed to the same environment favors the presence of endogenous proximate sources of AGNB and altered upper airway surfaces that are rendered receptive. Proximate sources of AGNB remain unclear, but potential sites harboring AGNB prior to illness include the upper gastrointestinal tract, subgingival dental plaque, and the periodontal spaces. Following illness or antibiotic therapy, competitive pressures within the oropharynx favor AGNB adherence to epithelial cells, which lead to oropharyngeal colonization. Similar dynamic changes in contiguous structures (oropharynx, trachea, sinuses, and the upper gastrointestinal tract) lead to the transcolonization of these structures with pathogenic bacteria. Following local colonization or infection, these structures serve as reservoirs of AGNB capable of inoculating the lower airways. As the oropharynx becomes colonized with AGNB, contaminated oropharyngeal secretions reach the trachea, endotracheal tube, and ventilator circuit. Contaminated secretions pooled above the endotracheal tube cuff gain access to the trachea and inner lumen of the endotracheal tube by traversing endotracheal tube cuff folds. Amorphic particulate deposits containing AGNB form along the endotracheal tube and are capable of being propelled into the distal airways by ventilator-generated airflow or by tubing manipulation. Bacteria embedded within this type of amorphous matrix are particularly difficult for the host to clear. If host defenses fail to clear the inoculum, then bacterial proliferation occurs, and the host inflammatory response progresses to bronchopneumonia.(ABSTRACT TRUNCATED AT 400 WORDS)

Pathology of shigellosis and its complications

One hundred and thirty-three colonic biopsies of proven cases of Shigella colitis were examined and post-mortem examinations were carried out on 29 fatal cases at the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR, B) hospital between 1988 and 1992. The distribution of pathological lesions and the spectrum of histopathological changes in the intestinal tract of these patients, and the features of intestinal and extra-intestinal complications of shigellosis are presented. Septicaemia, hyponatraemia, hypokalaemia and hypoglycaemia were present in a high percentage of these cases. All but two patients were malnorished at the time of autopsy. Shigellosis patients rapidly became hypoproteinaemic and were susceptible to other infections including opportunistic infections. Mortality amongst shigellosis patients admitted to our hospital continues to be high in spite of adequate antibiotic and supportive therapy.

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.

Protected specimen brush in the assessment of ventilator-associated pneumonia. Selection of a certain lung segment for bronchoscopic sampling is unnecessary

The protected specimen brush (PSB) with quantitative cultures is one of the most reliable techniques for assessing pneumonia in mechanically ventilated (MV) patients. The need to select a certain lung segment for bronchoscopic sampling is still debated. We investigated whether the results of PSB specimens collected within an area radiographically involved with pneumonia (inv-PSB) differed from the results of PSB specimens collected within a lung area without radiographic abnormalities (non-inv-PSB) in 39 MV patients with suspected pneumonia. The comparison of bacterial titers of inv-PSB and non-inv-PSB cultures did not disclose significant differences. Agreement regarding the diagnosis of pneumonia according to recommended diagnostic threshold was observed in 34 of 39 patients (87.1 percent). These results which are in accordance with the pathophysiology of ventilator-associated pneumonia and histologic studies do not support the need to select a certain lung segment for bronchoscopic sampling in most MV patients with suspected pneumonia.

Prevention of nosocomial infection in critically ill patients by selective decontamination of the digestive tract. A randomized, double blind, placebo-controlled study

OBJECTIVE

To evaluate the effect of a method of Selective Decontamination of the Digestive Tract (SDD) on colonization, nosocomial infection (NI), bacterial resistance, mortality and economic costs.

DESIGN

Randomized, double blind, placebo controlled study.

SETTING

Polyvalent intensive care unit (ICU) of a tertiary care hospital with 27 beds.

PATIENTS

101 patients with > 3 days of mechanical ventilation and > 5 days of stay, without infection at the start of the study. 47 belonged to the Treated Group (TG) and 54 to the Placebo Group (PG).

INTERVENTIONS

The TG was given Cefotaxime i.v. (6 g/day) for the first four days and an association of Polymyxin E, Tobramycin and Amphotericin B at the oropharyngeal and gastrointestinal level throughout the whole stay.

RESULTS

In the TG, colonization by gram-negative agents at oropharyngeal, tracheal and gastrointestinal level fell significantly. There was a significant drop in the overall, respiratory and urinary NI (26% vs 63%, p < 0.001; 15% vs 46%, p < 0.001; 9% vs 31%, p < 0.01). The overall mortality and NI related mortality was less in the TG (21% vs 44%, p < 0.05; 2% vs 20%, p < 0.01). The economic costs, mechanical ventilation time and length of stay were similar. The percentage of bacterial isolations resistant to Cefotaxime and Tobramycin was greater in the TG (38% vs 15% and 38% vs 9%, p < 0.001).

CONCLUSIONS

colonization by gram-negative bacilli, NI and the mortality related to it can be modified by SDD. Continuous bacteriological surveillance is necessary.

Concentrations of temafloxacin in serum and bronchial mucosa

The bronchial mucosal concentrations of temafloxacin hydrochloride were determined in specimens obtained at fibreoptic bronchoscopy and compared with simultaneous serum concentrations. The 18 patients studied were given an oral dose of 400 mg b.i.d for three days to achieve steady state levels. The mean serum concentration was 6.9 mg/l (SD 2.5 mg/l) and the mean bronchial mucosal concentration 12.2 mg/kg (SD 4 mg/kg). The mucosal levels exceeded those required to inhibit most of the common respiratory pathogens, including Streptococcus pneumoniae and Pseudomonas aeruginosa. These data support the use of temafloxacin for therapy of bronchial infections.

Aspiration and the elderly

Aspiration is prevalent in the elderly but its association with impairment of oral intake and gastroesophageal reflux is often misunderstood. This paper describes the causes, pathophysiology, and consequences of aspiration and their unique features in aged persons. It also explains how videofluoroscopic evaluation can assess current function while limiting factors that result in misinformation. The management of aspiration is discussed, emphasizing the importance and difficulties in maintaining functional well-being and possible complications of therapy.

Concentrations of cefixime in bronchial mucosa and sputum after three oral multiple dose regimens

In a study of 58 patients the concentrations of cefixime, a new oral cephem antibiotic, in bronchial mucosa were 35-40% of the concentrations found in simultaneously collected serum samples. The antibiotic was often undetectable in sputum despite a highly sensitive assay.

Infection v. colonisation

The interaction between bacteria and the human respiratory tract is complex and while the concept of three states, namely sterility, colonisation, and infection is clinically convenient it is inevitably in oversimplification. Evidence from both clinical and laboratory observations has led to some ideas about the relationship between colonisation and infection and while these are helpful in defining the steps involved, the decision of whether and when to start new treatment remains one of clinical judgement. This article reviews the evidence from lung disease both in and out of an intensive care unit and attempts to define the frontier between infection and colonisation in different clinical settings.