Background: Medical devices face the challenge of microbial biofilm attached to the surface. Ultimately, this may jeopardize the function of the device and increase the patient's risk of infection. However, reliable methods to prevent biofilm are lacking. Aim: To investigate the effect of silicone oil-coated polypropylene plastic, used in a new automatic urinometer, on biofilm formation; furthermore, to explore the impact of silicone oil viscosity and compare polypropylene with polystyrene, another common medical plastic. Methods: Common pathogens, including extended-spectrum beta lactamase (ESBL) -producing and multi-drug-resistant bacteria, as well as Candida albicans, were investigated. Isogenic Escherichia coli strains deficient in the important biofilm forming factors curli, cellulose and type 1 fimbriae (fim D) were used to determine the possible mode of action by silicone oil. Clear flat-bottomed polypropylene or polystyrene wells were pretreated with either low-or medium-viscosity silicone oil and microbes were added. After 72 h, biofilm formation was quantified using crystal violet assay. Findings: Silicone oil-coated polypropylene plastic surfaces, regardless of the oil viscosity, significantly inhibited biofilm formation of all tested Gram-negative and Gram-positive bacteria, including ESBL-producing and multi-drug resistant strains, as well as C. albicans. Silicone oil did not affect bacterial or candida growth and curli fimbriae were found to be the main target of silicone oil. Polypropylene plastic itself without oil had a better effect in preventing biofilm formation than polystyrene. Conclusion: These findings suggest a new strategy to decrease microbial biofilm formation, which may reduce hospital-acquired infections and prevent dysfunction of medical devices.

IntroductionIn the intensive care setting, most physiologic parameters are monitored automatically. However, urine output (UO) is still monitored hourly by manually handled urinometers. In this study, we evaluated an automatic urinometer (AU) and compared it with a manual urinometer (MU).MethodsThis prospective study was carried out in the intensive care unit of a cardiothoracic surgical clinic. In postoperative patients (n = 34) with indwelling urinary catheters and an expected stay of 24 hours or more, hourly UO samples were measured with an AU (Sippi, n = 220; Observe Medical, Gothenburg, Sweden) or an MU (UnoMeter™ 500, n = 188; Unomedical, Birkerød, Denmark) and thereafter validated by cylinder measurements. Malposition of the instrument at the time of reading excluded measurement. Data were analyzed with the Bland-Altman method. The performance of the MU was used as the minimum criterion of acceptance when the AU was evaluated. The loss of precision with the MU due to temporal deviation from fixed hourly measurements was recorded (n = 108). A questionnaire filled out by the ward staff (n = 28) was used to evaluate the ease of use of the AU compared with the MU.ResultsBland-Altman analysis showed a smaller mean bias for the AU (+1.9 ml) compared with the MU (+5.3 ml) (P <0.0001). There was no statistical difference in measurement precision between the two urinometers, as defined by their limits of agreement (±15.2 ml vs. ±16.6 ml, P = 0.11). The mean temporal variation with the MU was ±7.4 minutes (±12.4%), and the limits of agreement were ±23.9 minutes (±39.8%), compared with no temporal variation with the AU (P <0.0001). The ward staff considered the AU easy to learn to use and rated it higher than the MU (P <0.0001).ConclusionsThe AU was not inferior to the MU and was significantly better in terms of bias, temporal deviation and staff opinion, although the clinical relevance of these findings may be open to discussion.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-015-0899-4) contains supplementary material, which is available to authorized users.

Capacitance-based automatic urine measurement is a validated technique already implemented in clinical practice. However, albuminuria and free hemoglobinuria cause progressive biofilm buildup on the capacitance sensors of the urinometers. The aim of this experimental study is to investigate the influence of albumin and free hemoglobin on the capacitance signal of an automatic urinometer with and without the addition of silicone oil. A solution of Ringer’s acetate mixed with either albumin or free hemoglobin was run through an automatic urinometer containing either a water-soluble capsule with silicone oil or not. In total, around 500 capacitance measurements were retrieved from the albumin and free hemoglobin group, respectively. The mean increase in capacitance in the albumin 3 g/L group was 257 ± 100 pF without and 105 ± 30 pF with silicone oil, respectively, during 24 h. After ten hours of recording, differences between the two albumin groups reached statistical significance. For the free hemoglobin groups (0.01 g/L), the mean increase in capacitance was 190 ± 170 pF with silicone oil, and 324 ± 80 pF without, with a significant difference between the groups after 20 h and onwards. Coating of the capacitance measurement membrane of the automatic urinometer by albumin or free hemoglobin was significantly decreased by silicone oil, prolonging the functionality of the device.