UK Study Reveals Bleach Ineffective in Killing Clostridioides difficile Spores in Hospital Scrubs/Soft Surfaces

A bottle of bleach

(Adobe Stock 413542793 by FARBAI)

NOTE: This study was conducted in the UK. For the United States, the EPA does not have a test method for C difficile for soft surfaces. The study also did not use EPA-registered disinfectant.

To read the author’s discussion of the study, what she hopes IPs and other IPC personnel can take from it, and her lifelong research, click here.

One of the ongoing challenges for medical institutions is the prevention of fungal and bacterial infections and transmission within these facilities. Proper cleaning mechanisms have been set in place to help decrease in-facility transmissions.

Specifically, when patients are dealing with a health care-associated infection (HAI) such as Clostridioides difficile infection (CDI), hospitals use disinfectants such as chlorine-releasing agents (CRAs) and hydrogen peroxide to decontaminate surfaces including beds, bathrooms, and other areas within patient areas. In addition, hospital staff scrubs and patient gowns must be cleaned with strong agents.

A new study looked at sodium hypochlorite (NaOCl), otherwise known as bleach and the effect of the spore response to clinical in-use concentrations of the cleaner as applied to hospital scrubs. What investigators found was that the cleaner does not kill off the C difficile spores.¹

What You Need to Know

The study reveals that sodium hypochlorite, commonly used as a disinfectant in healthcare settings, is ineffective in killing C difficile spores.

The findings emphasize the need for disinfectants and guidelines specifically designed to combat evolving bacterial strains, considering the rising incidence of antimicrobial resistance.

The study prompts further questions about biocide tolerance within C difficile and raises the issue of whether the tolerance to disinfectants is influenced by antibiotic co-tolerance.

"With incidence of anti-microbial resistance on the rise, the threat posed by superbugs to human health is increasing,” Tina Joshi, PhD, associate professor in molecular microbiology at the University of Plymouth, carried out the study with Humaira Ahmed, a fourth-year medicine student from the University’s Peninsula Medical School, said in a statement. “This study highlights the ability of C difficile spores to tolerate disinfection at in-use and recommended active chlorine concentrations. It shows we need disinfectants, and guidelines, that are fit for purpose and work in line with bacterial evolution, and the research should have significant impact on current disinfection protocols in the medical field globally.”¹

Study Specifics
The new study examined the spore response of 3 different strains of C difficile to 3 clinical in-use concentrations of sodium hypochlorite.

“Spores from strains R20291, DS1813, and CD630 [C difficile strains] at a concentration of 1×108 spores ml–1 were independently exposed to 1000, 5000, and 10,000 ppm,” the investigators wrote. “NaOCl in liquid form for 10 min (recommended contact time) and biocide activity was neutralized with an equal volume of 5 g l–1 sodium thiosulphate for 10 min contact time to remove any residual chlorine biocide activity.”²

The spores were then spiked onto surgical scrubs and patient gowns and examined using scanning electron microscopes to establish if there were any morphological changes to the outer spore coat.¹

The research was conducted by investigators from the University of Plymouth in England, and they reported the C difficile spores were completely unaffected despite being treated with high concentrations of bleach used in many hospitals. In fact, the investigators said the chlorine chemicals are no more effective at damaging the spores when used as a surface disinfectant than when used with water with no additives.¹

“This study highlights the ability of C difficile spores to tolerate NaOCl disinfection at in-use recommended active chlorine concentrations,” the investigators wrote. “Understanding the molecular basis of these interactions is integral to practical management of CDI and reducing the burden of infection in health care settings.”²

The investigators point out another important consideration. Specifically, there is a need to answer questions around biocide tolerance within C difficile and whether biocide tolerance is affected by antibiotic co-tolerance.²

Reference

1. Chlorine Disinfectant is no More Effective Thank Water at Killing off Hospital Superbug, Study Shows. Microbiology Society. November 22, 2023. Accessed December 14, 2023. https://microbiologysociety.org/news/press-releases/chlorine-disinfectant-is-no-more-effective-than-water-at-killing-off-hospital-superbug-study-shows.html

2. Ahmed H, Joshi LT. Clostridioides difficile spores tolerate disinfection with sodium hypochlorite disinfectant and remain viable within surgical scrubs and gown fabrics. Microbiology (Reading). 2023;169(11):001418. doi:10.1099/mic.0.001418 https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.001418