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Dr. Richard Bloß, Christiane Ostermeyer
Dr. Richard Bloß, Christiane Ostermeyer

Expert Interview on biofilm-developing Gram-negative pathogens

Gram-negative bacteria that develop biofilms play a major role in the contamination of wipes dispensers used with surface disinfectants based on surface-active substances without aldehyde. DESINFACTS asked experts Christiane Ostermeyer, Head of Microbiology at BODE Chemie, and Dr. Richard Bloß, Head of Development Surfaces/Instruments in BODE Chemie’s Research and Development department, how biofilm develops and whether it is primarily a problem attributed to Gram-negative microorganisms.

DESINFACTS: Your investigations have showed that some pathogens in wipes dispensers have reduced susceptibility to surface disinfection solutions based on surface-active substances without aldehyde and may proliferate in them. What happens there?

Christiane Ostermeyer: The microorganisms were detected in dispensers that had been in use for a long time. In these cases, we could also often reproduce that the dispensers had not been reprocessed properly. Consequently, adaptation occurred. Adaptation means that, under certain conditions, bacteria are able to adapt to the environment and thus also to disinfection solutions to have the best chances of survival.

DESINFACTS: You also observed this phenomenon in wipes dispensers that were used in combination with correctly dosed disinfection solutions. Shouldn’t these actually kill the microorganisms?

Christiane Ostermeyer: For the isolates we examined, the development of biofilm most likely prevented the attack of the active substances in the disinfectants. Biofilms develop when microorganisms colonise interfaces between aqueous systems and solid phases. After attaching to a suitable surface, a protective slime matrix (extracellular polymeric substance, EPS) forms around the cells. By being able to form EPS, these bacterial communities are protected against sufficient efficacy of the disinfectant’s active substances. The pathogens adapt and become temporarily insusceptible to these disinfectants, even if these are dosed correctly. Once adapted, bacteria may proliferate strongly.

DESINFACTS: How long does it take for biofilms to develop?

Dr. Richard Bloß: The accumulation of microorganisms and development of slime can occur within a very short time. Bacteria irreversibly attach to the surfaces (particularly well to plastics surfaces) within a few minutes. Then, growth and proliferation of bacteria and production of extracellular polymeric substance (EPS) sets in. A few hours later, the biofilm development may be complete already, providing bacteria perfect protection to proliferate. After complete formation of a biofilm layer, individual biofilm fragments release and the microorganisms in the protective matrix contaminate the disinfection solution.

DESINFACTS: How do the bacteria get into the wipes dispenser and the disinfection solution respectively?

Dr. Richard Bloß: At this point in time, we can only speculate about this. One possible source is tap water, which is not sterile. According to the Drinking Water Ordinance, the total microorganism count may be 100 colony-forming units per millilitre, which may also include Gram-negative bacteria belonging to the Alcaligenes species. These microorganisms may then get into the wipes dispenser when preparing the use-solution. After our examinations, we – just as the Association for Applied Hygiene (VAH) in its current recommendation on wipes dispensers (1) – additionally assume that the manual reprocessing of the wipes dispensers often is deficient. Thus, bacteria may colonise the surface of dispenser systems and, subsequently, develop a biofilm. It has to be taken into account that biofilms that are not removed during reprocessing are a good basis for further development on the surfaces. Due to the effect of the disinfectant, the outer layers consist of dead biomass, which is an ideal culture medium for the bacteria further inside. Biofilm is a bacterial community that also lives on organic degradation products.

DESINFACTS: But what is it that the users do wrong during reprocessing?

Christiane Ostermeyer: According to our current knowledge, manual reprocessing is afflicted with many uncertainties and possible faults. Wiping out the dispenser with the last wipe of the roll is certainly not enough. In case residual moisture remains in the dispenser after a rinse with water, this might as well lead to contamination and development of biofilm.

What should users of wipes dispensers observe?

Dr. Richard Bloß: Our studies show that – with products based on surface-active substances without aldehyde – chemothermal reprocessing of the dispensers is the safest method to remove possible contamination and biofilms. Only effective reprocessing can prevent bacteria from adapting again within the recommended standing time. Effective reprocessing before refilling is of particular importance when the wipes dispenser is continued to be used in combination with disinfection solutions based on surface-active substances without aldehyde. To our knowledge, aldehyde and alcohol-based surface disinfectants, however, are not affected by such distinctive adaptation. Apart from this, safe reprocessing of the dispensers is imperative also when these disinfectants are applied.

DESINFACTS: Final question: Does the problem of biofilm development and adaptation primarily affect Gram-negative microorganisms?

Christiane Ostermeyer: In our examinations, we solely isolated Gram-negative bacteria. It is known that Gram-negative pathogens such as Alcaligenes, Serratia, pseudomonads, etc. possess higher ability of developing biofilms, although this phenomenon also occurs among Gram-positive bacteria.

Ms Ostermeyer and Dr. Bloß, thank you very much for this interview.

1 “Empfehlung zur Kontrolle kritischer Punkte bei der Anwendung von Tuchspendersystemen im Vortränksystem für die Flächendesinfektion” (Recommendations for monitoring critical points when using dispenser systems for pre-soaked surface disinfection wipes)
Current notice of the Disinfectant Commission in the Association for Applied Hygiene (VAH). Published in Hygiene & Medizin 2012: 468-470.