An effective evidence-based cleaning method for the safe reuse of intermittent urinary catheters: In vitro testing

AIMS

To determine a safe bactericidal cleaning method that does not damage urethral catheters used for intermittent catheterization. In some countries, single-use catheters are the norm; in others, the reuse of catheters is common depending on health insurance, personal preference, or individual concerns about the environment. However, no recent study of cleaning methods has been published to provide evidence for the safe reuse of catheters.

METHODS

Using advanced microbiological methods, a laboratory study of eight cleaning methods was conducted. Sections of uncoated polyvinylchloride (PVC) catheters were exposed to bacterial uropathogens in physiologically correct artificial urine media then tested with a range of heat, chemical, and mechanical cleaning methods. Analysis of culturable and viable but nonculturable (VBNC) bacteria was done and direct microscopy was used. Descriptive statistics were used to compare values.

RESULTS

Heat treatments, although effective, resulted in catheter surface breakdown and damage. Ultrasonic cleaning and vinegar showed evidence of VBNC populations indicating the methods were bacteriostatic. Detergent and water wash followed by immersion in a commercially available 0.6% sodium hypochlorite solution and 16.5% sodium chloride (diluted Milton) gave consistent bactericidal results and no visible catheter damage.

CONCLUSIONS

Combined mechanical and chemical treatment of a detergent and water wash followed by immersion in diluted Milton (the "Milton Method") provided consistent and effective cleaning of uncoated PVC catheters, showing bactericidal action for all uropathogens tested after repeated exposure. If found safe in clinical testing, this method could increase the reuse of catheters, reduce plastic waste in the environment, reduce cost, and increase patient choice.

A Repeating Sulfated Galactan Motif Resuscitates Dormant Micrococcus luteus Bacteria

Only a small fraction of bacteria can autonomously initiate growth on agar plates. Nongrowing bacteria typically enter a metabolically inactive dormant state and require specific chemical trigger factors or signals to exit this state and to resume growth. Micrococcus luteus has become a model organism for this important yet poorly understood phenomenon. Only a few resuscitation signals have been described to date, and all of them are produced endogenously by bacterial species. We report the discovery of a novel type of resuscitation signal that allows M. luteus to grow on agar but not agarose plates. Fractionation of the agar polysaccharide complex and sulfation of agarose allowed us to identify the signal as highly sulfated saccharides found in agar or carrageenans. Purification of hydrolyzed κ-carrageenan ultimately led to the identification of the signal as a small fragment of a large linear polysaccharide, i.e., an oligosaccharide of five or more sugars with a repeating disaccharide motif containing d-galactose-4-sulfate (G4S) 1,4-linked to 3,6-anhydro-α-d-galactose (DA), G4S-(DA-G4S) _n≥2IMPORTANCE Most environmental bacteria cannot initiate growth on agar plates, but they can flourish on the same plates once growth is initiated. While there are a number of names for and manifestations of this phenomenon, the underlying cause appears to be the requirement for a molecular signal indicating safe growing conditions. Micrococcus luteus has become a model organism for studying this growth initiation process, often called resuscitation, because of its apparent connection with the persistent or dormant form of Mycobacterium tuberculosis, an important human pathogen. In this report, we identify a highly sulfated saccharide from agar or carrageenans that robustly resuscitates dormant M. luteus on agarose plates. We identified and characterized the signal as a small repeating disaccharide motif. Our results indicate that signals inherent in or absent from the polysaccharide composition of solid growth media can have major effects on bacterial growth.

Molecular Viability Testing of UV-Inactivated Bacteria

PCR is effective in detecting bacterial DNA in samples, but it is unable to differentiate viable bacteria from inactivated cells or free DNA fragments. New PCR-based analytical strategies have been developed to address this limitation. Molecular viability testing (MVT) correlates bacterial viability with the ability to rapidly synthesize species-specific rRNA precursors (pre-rRNA) in response to brief nutritional stimulation. Previous studies demonstrated that MVT can assess bacterial inactivation by chlorine, serum, and low-temperature pasteurization. Here, we demonstrate that MVT can detect inactivation of Escherichia coli, Aeromonas hydrophila, and Enterococcus faecalis cells by UV irradiation. Some UV-inactivated E. coli cells transiently retained the ability to synthesize pre-rRNA postirradiation (generating false-positive MVT results), but this activity ceased within 1 h following UV exposure. Viable but transiently undetectable (by culture) E. coli cells were consistently detected by MVT. An alternative viability testing method, viability PCR (vPCR), correlates viability with cell envelope integrity. This method did not distinguish viable bacteria from UV-inactivated bacteria under some conditions, indicating that the inactivated cells retained intact cell envelopes. MVT holds promise as a means to rapidly assess microbial inactivation by UV treatment.IMPORTANCE UV irradiation is increasingly being used to disinfect water, food, and other materials for human use. Confirming the effectiveness of UV disinfection remains a challenging task. In particular, microbiological methods that rely on rapid detection of microbial DNA can yield misleading results, due to the detection of remnant DNA associated with dead microbial cells. This report describes a novel method that rapidly distinguishes living microbial cells from dead microbial cells after UV disinfection.