OBJECTIVEMechanical ventilation support is a very important method for the salvage of serious patients. However, it can result in the formation of an adherent matrix of bacteria on the surfaces of implanted materials which is termed "biofilm". Biofilm is dense bacterial communities attached to a solid surface and surrounded by an exopolysaccharide matrix. One of the most important features of bacterial biofilm is their resistance to antimicrobial agents and host immune system components. As a consequence, diseases involving biofilm are generally chronic and difficult to treat. The present study was conducted to explore the relationship between ETT-biofilm and the lower respiratory infection by observing microbial colonization and associated biofilm accumulation on the surface of endotracheal tubes (ETTs) removed from neonates treated with intubated mechanical ventilation.

METHODSTwenty neonates undergoing mechanical ventilation (from January to June in 2005) were recruited into this study. Clinical data about lower respiratory infection for each case were collected. ETTs were collected at the first time of extubation. A sterile control tube was also processed. For each ETT, a 1-cm-long cross-sectional segment was divided into two portions for both scanning electron microscopy (SEM) and aerobic/anaerobic cultures. The presence of biofilm on the surface of ETTs were examined by SEM, meanwhile, bacteria harvested from the surface of ETTs and the secretions of lower respiratory tract were isolated, identified and assessed on antimicrobial susceptibility, respectively.

RESULTSThe diagnosis on admission of the twenty cases included: neonatal respiratory distress syndrome (10), meconium aspirate syndrome (2), severe asphyxia (2), pneumatothorax (2), severe pneumonia (1), scleredema neonatorum (1), inborn pulmonary hypoplasia (1) and recurrent apnea (1). Thirteen cases did not present symptoms and signs of lower respiratory infection before mechanical ventilation. However, during the mechanical ventilation process, symptoms and signs of lower respiratory infection presented and lasted until extubation. Nine of the above mentioned thirteen cases (70%) had the same duration of tube use as mechanical ventilation duration (mean: 3.6 days). Observation by SEM showed that colonization was time dependent and the incidence of microbial colonization increased when the duration of tube use exceeded one days (12/20). There were no obvious bacterial colonies except that some amorphous material was noted in 5 of 20 ETTs as early as one day of tube use. Up to 2 days of tube use (4/20), attached bacterial colonization was seen embedded in amorphous material (3/4). Up to 3 days (7/20), a layer of biofilm formation presented on ETTs (5/7). Furthermore, biofilm architecture became more mature and complex if the duration exceeded 3 days. Neither bacteria nor biofilm formation was seen on the control ETT. The results of aerobic/anaerobic cultures showed that there were 14 cultures from ETTs (normal flora grew in 4) and 7 pathogens were isolated; 13 cultures from the secretions of lower respiratory tract (normal flora grew in 1) and 10 pathogens were isolated. Seven samples had the same pathogen both on the surface of ETTs and in the secretions of lower respiratory tract, which accounted for 50% of the positive cultures from ETTs, including Xanthomonas maltophilia (2), Klebsiella pneumoniae (2), Acinetobacter lwoffii (1), Acinetobacter baumannii (1) and normal flora (1). The gram-negative bacteria isolated from the surface of ETTs and the secretions of lower respiratory tract presented multi-resistance to antibiotics.

CONCLUSIONSThe ETT-biofilm develops into mature and complex form with the duration of tube use increase. This study provides evidence that there is correlation between microbial colonization, biofilm formation on the surface of ETTs and the lower respiratory infection in neonates who were intubated and ventilated for a prolonged period. ETT-Biofilm could also be a possible source of the recurrent infection. Increased attention must be paid to modification of the ETT to prevent or substantially reduce biofilm formation.