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Infection of catheterised patients: bacterial colonisation of encrusted Foley catheters shown by scanning electron
A J Cox1, D W Hukins, T M Sutton
1Department of Medical Biophysics, University of Manchester, United Kingdom.
Abstract:
The surfaces of 32 encrusted urinary catheters were examined by scanning electron microscopy to investigate the association of bacteria with the encrusting deposits. Deposits consisted of struvite crystals surrounded by aggregates of very small crystallites of hydroxyapatite. Underneath these minerals there was a layer of closely packed bacteria. Impressions of bacteria were also observed in hydroxyapatite. Crystals were often engulfed by the bacterial layer, which thus appeared to bind the crystals to each other and to the catheter surface. This thick layer of bacteria associated with crystals may protect both the bacteria from antibiotics and the crystals from acidic bladder washout solutions intended to dissolve them. Furthermore, the existence of this sessile population explains why urease-producing bacteria are not invariably detected in the urine of patients with encrusted catheters. The observation of this bacterial layer (or "biofilm") by scanning electron microscopy provided direct evidence for infection being implicated in catheter encrustation.
Insights
Scanning electron microscopy revealed a dense bacterial biofilm beneath mineral deposits on encrusted urinary catheters. This biofilm likely protects bacteria from antibiotics and encrustations from dissolution, explaining infection persistence.
Area of Science:
- Urology
- Microbiology
- Materials Science
Background:
- Urinary catheter encrustation is a common complication.
- The role of bacteria in the formation of these encrustations is not fully understood.
Purpose of the Study:
- To investigate the association between bacteria and mineral deposits on encrusted urinary catheters.
- To provide direct evidence of bacterial involvement in catheter encrustation.
Main Methods:
- Scanning electron microscopy (SEM) was used to examine the surfaces of 32 encrusted urinary catheters.
- Detailed analysis of the mineral composition and bacterial presence within the deposits.
Main Results:
- Encrustations comprised struvite and hydroxyapatite crystals.
- A thick layer of closely packed bacteria (biofilm) was consistently found underneath the mineral deposits.
- Bacteria were observed embedded within the hydroxyapatite crystallites, suggesting direct interaction.
Conclusions:
- The study provides direct evidence that bacterial biofilms are implicated in urinary catheter encrustation.
- This biofilm may shield bacteria from antibiotics and protect encrustations from dissolution therapies.
- The findings explain the presence of sessile bacterial populations not always detected in urine samples.
