The nature and role of microbial biofilm in infections associated with prosthetic devices

The concomitant development of poly(vinyl chloride)-related biofilm and antimicrobial resistance in relation to ventilator-associated pneumonia

Ventilator-associated pneumonia is a major cause of death in intensive care patients and the endotracheal tube, commonly fabricated from poly(vinyl chloride) (PVC), is acknowledged as a significant factor in this. Bacteria colonise the biomaterial, thereby adopting a sessile mode of growth that progresses to the establishment of an antibiotic-resistant biofilm by the accretion of a protective glycocalyx. This study examined the sequential steps involved in the formation of biofilm on PVC by atomic force microscopy and the concomitant development of resistance to an antibiotic (ceftazidime) and to a non-antibiotic antimicrobial agent (hexetidine). Staphylococcus aureus and Pseudomonas aeruginosa isolated from ET tube biofilm were employed. The surface microrugosity of bacteria growing in sessile mode on PVC decreased significantly (p < 0.05) over the period 4, 24, 48 h and 5 d. The progressive accretion of bacterial glycocalyx was readily visualised in micrographs leading to a smoother surface topography with time. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) for ceftazidime and hexetidine against planktonic (suspension) S. aureus were lower than for Ps. aeruginosa. Furthermore, sessile populations of S. aureus and Ps. aeruginosa on PVC exhibited greater resistance to both ceftazidime and hexetidine when compared to planktonic bacterial growth. The efficacy of the agents, determined by kill kinetics, against sessile bacteria was dependent on age, with established biofilms (> or = 24 h) significantly more resistant (p < 0.05) than early sessile populations (< or = 4 h). Importantly, for practice, even newly colonised bacteria (1 h) were significantly more resistant to antibiotic than planktonic bacteria. Hexetidine was significantly more active (p < 0.05) than ceftazidime on biofilms of both isolates, irrespective of age, with total kill within 24 h treatment. Hexetidine may offer promise in the resolution of infection associated with PVC endotracheal tubes.

Incidence and nature of peritoneal catheter biofilm determined by electron and confocal laser scanning microscopy

Thirty-two Tenckhoff catheters retrieved from continuous ambulatory peritoneal dialysis patients with a history of peritonitis were examined for microbial biofilm. Confocal laser scanning microscopy was successfully employed to visualize bacteria in biofilm occluded from view by scanning electron microscopy. Occluded but viable microbial biofilm was associated with 17 (81%) catheters from patients free from infection following renal transplant. Mixed isolate biofilm with two or more isolates of coagulase-negative staphylococci or Staphylococcus aureus was found on 41% of these catheters. Clearly visible viable biofilm consisting exclusively of Pseudomonas aeruginosa occurred on all four catheters removed due to recurrent peritonitis. Five (71%) catheters retrieved from patients transferred to haemodialysis had viable biofilm. Antibiotic sensitivities of the biofilm isolates were similar in profile to those reported for non-biofilm isolates from infected dialysate. Persistence of catheter biofilm despite direct contact with therapeutic levels of antibiotics in peritoneal dialysate requires that attention be directed towards improving antibiotic efficacy against peritonitis-causing bacteria in biofilm form.

Characterization of biofilm and encrustation on ureteric stents in vivo

OBJECTIVE

To examine the relationship between encrustation and microbial biofilm formation on indwelling ureteric stents.

PATIENTS AND METHODS

Ureteric stents from 40 patients were examined for the presence of a microbial biofilm and encrustations. Bacteria in stent biofilms were isolated and identified.

RESULTS

A profuse biofilm (> 10(4) c.f.u. cm-3) was identified on 11 (28%) stents. Enterococcus faecalis was the most common biofilm organism identified and Proteus spp. were not present. Encrustation was seen in 23 (58%) of stents and was not associated with the level of urinary calcium. The major risk factor for stent encrustation was the presence of urolithiasis. Importantly, there was no causative link between stent biofilm formation and encrustation. Both biofilm formation and encrustation increased with the duration of stenting.

CONCLUSION

The results indicate that polyurethane is readily encrusted and colonized by bacteria in vivo despite antibiotic prophylaxis. Newer materials must be sought if effective long-term stenting is to be achieved.