Environmental persistence of Enterococcus spp.: what dry surface biofilms mean for IPC

My interest in dry surface biofilms (DSB) started almost 10 years when working with Dr Issy Centeleghe and Prof Jean Yves Maillard, examining the ability of Klebsiella to from dry surface biofilms. In the last decade various species of bacteria have been shown to produce DSB including; Salmonella, Candida auris and more recently* Enterococcus spp.* I am a firm believer that DSB is one of the survival mechanisms which enables prolonged surival on inanimate surfaces. I’ve take a look at a recent paper on DSB formation by Enterococcus spp. and the implications for infection prevention and control (IPC).

Why dry surface biofilms matter

Dry surface biofilms differ from conventional hydrated biofilms in both structure and behaviour. They form through repeated cycles of wetting and drying, a process that closely mirrors real‑world conditions in healthcare environments where surfaces are intermittently cleaned, used, and allowed to dry.

DSBs are difficult to detect through conventional means and more tolerant to environmental stressors, including desiccation and disinfection. Previous studies have demonstrated that DSBs can harbour clinically important organisms and facilitate transfer via hands, gloves, and shared equipment. However, until now, the ability of Enterococcus spp. to form persistent DSBs had not been fully characterised.

Overview of the study

Harsent et al. investigated the capacity of multiple Enterococcus species and clinical isolates, including epidemic and vancomycin‑resistant strains (VRE) to form DSBs on materials commonly found in healthcare settings. Using a standardised laboratory DSB model, biofilms were grown on a range of surfaces including stainless steel, PVC, ceramic, and several textiles. Viability was assessed through culture‑based methods, while biofilm structure and heterogeneity were examined using scanning electron microscopy, confocal microscopy, and flow cytometry. Crucially, the study also evaluated long‑term persistence, incubating mature DSBs under controlled ambient conditions for up to 84 weeks.

Key findings

The study produced several findings of direct relevance to IPC:

• All Enterococcus strains tested were capable of forming dry surface biofilms on stainless steel and other healthcare‑relevant materials. This included both E. faecium and E. faecalis, as well as epidemic and non‑epidemic strains.
• Second, high levels of viable, culturable bacteria were recovered from mature DSBs, typically around 5–6 log₁₀. Importantly, these levels were maintained over extended periods. Most strains remained viable for the full 84‑week incubation period, demonstrating exceptional environmental persistence.
• Surface characteristics did not reliably predict DSB formation or survival. Neither surface roughness nor hydrophobicity was associated with reduced bacterial recovery. DSBs formed on smooth, non‑porous materials as well as on porous textiles and furnishings.
• Vancomycin‑resistant strains retained phenotypic resistance following prolonged survival within DSBs. Although VRE strains showed slightly lower culturability than non‑VRE strains, resistance was maintained, reinforcing concerns about environmental reservoirs of antimicrobial resistance.

Implications for IPC practice

The findings from this study reinforce several important messages for IPC programmes.

The ability of Enterococcus spp. to persist for months and even years in a dry state highlights the limitations of visual cleanliness as a marker of safety. The study underscores the critical role of mechanical cleaning. The authors conclude that chemical disinfection alone is unlikely to reliably control established DSBs. Instead, effective mechanical removal followed by application of an appropriate disinfectant currently represents the most robust strategy for DSB control on hard surfaces. The results emphasise the need to broaden attention beyond traditional high‑touch surfaces. Shared medical equipment, furnishings, and non‑obvious surfaces may all act as long‑term reservoirs if cleaning practices are inconsistent or incomplete. Finally, the work highlights gaps in current surveillance and detection methods. Standard swabbing techniques may underestimate environmental contamination when DSBs are present, which has implications for audit, assurance, and outbreak investigations.

Conclusions

This study adds to a growing body of evidence demonstrating that dry surface biofilms are a clinically relevant and persistent feature of the healthcare environment. The ability of Enterococcus spp., including VRE, to survive for prolonged periods within DSBs strengthens the case for sustained investment in environmental hygiene, staff training, and compliance monitoring. For IPC teams, the message is clear: enhanced cleaning, with appropriate mechanical action, remains fundamental to reducing environmental reservoirs of healthcare‑associated pathogens. As our understanding of DSBs continues to evolve, translating this evidence into practical cleaning and disinfection strategies will be essential for patient safety.