Liquid bleach does not kill off a hospital superbug that can cause fatal infections, found British researchers, saying it is no more effective than water, and calling for new approaches to tackle care-setting disinfection.
Clostridium difficile, or C diff, is a type of bacteria found in the human gut, and while it can coexist with other bacteria without problem, a disruption to gut flora can allow it to thrive, leading to bowel problems including diarrhoea and colitis.
Severe infections can kill, with 1 910 people known to have died within 30 days of an infection in England during 2021-2022.
Those at greater risk of C diff infections include people over 65, hospital patients, anyone with a weakened immune system or who is taking antibiotics, with some people experiencing repeated infections.
UK Government guidance updated in 2019 recommended chlorine-containing cleaning agents with at least 1 000ppm available chlorine as a disinfectant to tackle C diff, reports The Guardian.
But the researchers say it is unlikely be sufficient, their experiments suggesting that even at high concentrations, sodium hypochlorite – a common type of bleach – is no better than water at doing the job.
“With antimicrobial resistance increasing, people need to recognise that overuse of biocides can cause tolerance in certain microbes, and we’re definitely seeing that with chlorine and C diff,” said Dr Tina Joshi, co-author of the research, from the University of Plymouth.
While chlorine-based chemicals used to be effective at killing such bacteria, that no longer appears to be the case, she said.
“The UK doesn’t seem to have any written new gold standard for C diff disinfection. And I think that needs to change immediately,” she said.
Writing in the journal Microbiology, Joshi and colleagues report how they exposed spores from three different strains of Clostridium difficile to three different concentrations of sodium hypochlorite bleach – ranging from 1 000 ppm to 10 000 ppm. The spores were left for 10 minutes before the bleach was neutralised.
The researchers then attempted to culture the spores on agar plates, and compared the results with the controls of spores exposed only to water or the neutralising substance.
The results reveal spores from all three strains of C diff survived all three concentrations of bleach, with no significant reduction in their ability to germinate, compared with the controls.
In fact, scrutiny of the spores with scanning electron microscopy showed they underwent no visible damage when exposed to the cleaning agent.
The researchers also applied spores of C diff to squares of fabric cut from new multiuse surgical scrubs and patient gowns and tested whether they would transfer when an agar plate was touched by the fabric.
They found the spores largely remained on the gowns and scrubs, with exposure of the spores to different concentrations of bleach making no tangible difference.
“It’s very clear the spores are sticking to the fibres,” said Joshi, noting that this finding suggests such items are reservoirs of transmission.
She said the new work has important implications. “Even if we’re trying to disinfect across different surfaces, the chlorine is not doing its job,” she added. “It’s not the right biocide.”
Study details
Clostridioides difficile spores tolerate disinfection with sodium hypochlorite disinfectant and remain viable within surgical scrubs and gown fabrics
Humaira Ahmed, Lovleen Tina Joshi.
Published in Microbiology on 21 November 2023
Abstract
Clostridioides difficile is the most common cause of antibiotic-associated diarrhoea globally. Its spores have been implicated in the prevalence of C. difficile infection due to their resistance and transmission ability between surfaces. Currently, disinfectants such as chlorine-releasing agents (CRAs) and hydrogen peroxide are used to decontaminate and reduce the incidence of infections in clinical environments. Our previous research demonstrated the ability of C. difficile spores to survive exposure to recommended concentrations of sodium dichloroisocyanurate in liquid form and within personal protective fabrics such as surgical gowns; however, the present study examined the spore response to clinical in-use concentrations of sodium hypochlorite. Spores were exposed to a 10 min contact time of 1000, 5000 and 10 000 p.p.m. sodium hypochlorite, and spore recovery was determined. To understand whether biocide-exposed spores transmitted across clinical surfaces in vitro, biocide-exposed spores were spiked onto surgical scrubs and patient gowns and recovery was determined by a plate transfer assay. Scanning electron microscopy was used to establish if there were any morphological changes to the outer spore coat. The results revealed that viable biocide-exposed C. difficile spores can be recovered from surgical scrubs and patient gowns, with no observable changes to spore morphology, highlighting the potential of these fabrics as vectors of spore transmission. This study demonstrates that alternative strategies should be urgently sought to disinfect C. difficile spores to break the chain of transmission in clinical environments.
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