Genetic relationships between respiratory pathogens isolated from dental plaque and bronchoalveolar lavage fluid from patients in the intensive care unit undergoing mechanical ventilation

Abstract

Background: Ventilator-associated pneumonia (VAP) is a leading cause of morbidity and mortality in patients hospitalized in intensive care units. Recent studies suggest that dental plaque biofilms serve as a reservoir for respiratory pathogens. The goal of this study was to determine the genetic relationship between strains of respiratory pathogens first isolated from the oral cavity and later isolated from bronchoalveolar lavage fluid from the same patient undergoing mechanical ventilation with suspected VAP.

Methods: Plaque and tracheal secretion samples were obtained on the day of hospital admission and every other day thereafter until discharge from the intensive care unit from 100 patients who underwent mechanical ventilation. Bronchoalveolar lavage was performed for 30 patients with suspected VAP. Pulse-field gel electrophoresis and multilocus sequence typing were used to determine the genetic relatedness of strains obtained from oral, tracheal, and bronchoalveolar lavage samples.

Results: Isolates of Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter species, and enteric species recovered from plaque from most patients were indistinguishable from isolates recovered from bronchoalveolar lavage fluid (i.e., had >95% similarity of pulse-field gel electrophoresis patterns). Nearly one-half of the Pseudomonas strains showed identical genetic profiles between patients, which suggested a common environmental source of infection.

Conclusions: Respiratory pathogens isolated from the lung are often genetically indistinguishable from strains of the same species isolated from the oral cavity in patients who receive mechanical ventilation who are admitted to the hospital from the community. Thus, dental plaque serves as an important reservoir for respiratory pathogens in patients who undergo mechanical ventilation.

Trial registration: ClinicalTrials.gov NCT00123123.

Conflict of interest statement

Potential conflicts of interest. All authors: no conflicts.

Figures

Figure 1

PFGE patterns with dendrogram for Staphylococcus aureus isolates. A genetic similarity index scale is shown above the dendrogram. Patient identification (Pt ID), sample site (Source), number of days after admission to the intensive care unit that the strain was isolated (Day), and multilocus sequence type (ST) are provided. USA100, USA200, USA400, USA800, and NCTC 8325 strains from the Centers for Disease Control and Prevention were used as reference strains. *Methicillin-resistant Staphylococcus aureus. For genotyping conditions, see Patients, Materials, and Methods. BAL, bronchoalveolar lavage; SG, supragingival dental plaque; TS, tracheal secretion.

Figure 2

PFGE patterns with dendrogram for Pseudomonas aeruginosa isolates. A genetic similarity index scale is shown above the dendrogram. Patient identification (Pt ID), sample site (Source), number of days after admission to the intensive care unit that the strain was isolated (Day), and multilocus sequence type (ST) are provided. P. aeruginosa PAO1 strain was used as the reference strain. To obtain optimal PFGE band patterns, different conditions of pulse time and running hours were used. For running conditions, see Patients, Materials, and Methods. BAL, bronchoalveolar lavage; SG, supragingival dental plaque; TS, tracheal secretion.

Figure 3

PFGE patterns with dendrogram for Escherichia coli isolates. A genetic similarity index scale is shown above the dendrogram. Patient identification (Pt ID), sample site (Source), and number of days after admission to the intensive care unit that the strain was isolated (Day) are provided. Escherichia coli K-12 strain was used as the reference strain. For running conditions, see Patients, Materials, and Methods. BAL, bronchoalveolar lavage; SG, supragingival dental plaque; TS, tracheal secretion.

Figure 4

PFGE patterns with dendrogram for other potentially pathogenic gram-negative bacilli. Patient identification (Pt ID), sample site (Source), number of days after admission to the intensive care unit that the strain was isolated (Day) are provided. λ DNA was used as the reference for standardization. For running conditions, see Patients, Materials, and Methods. BAL, bronchoalveolar lavage; SG, supragingival dental plaque; TS, tracheal secretion.