Domestic laundering machines commonly used by health care workers to clean their uniforms may be insufficient for decontamination, according to new research.
"The inability of [DLMs] and household detergents to effectively disinfect health care workers' uniforms poses significant infection control challenges and raises concerns about the potential emergence of antimicrobial resistance," noted study researchers.
They assessed the performance of six domestic laundering machines (DLM) and found that only 50% achieved sufficient decontamination (≥ 5 log₁₀ colony-forming unit [CFU] reduction) at 60°C during full-length cycles, whereas rapid cycles performed inconsistently.
"DLMs are preprogrammed and, except for the temperature and the spinning speed, users cannot control or validate the washing cycle parameters. Users rely on the manufacturer programmes without being able to check if it meets the recommendations for the thermal disinfection," the study authors noted.
The microbiome analysis revealed the presence of potentially pathogenic bacteria, including Mycobacterium, Pseudomonas, and Acinetobacter species, along with antibiotic resistance genes in the machines. Detergent tolerance assays demonstrated increased bacterial tolerance to detergents, with cross-resistance to antibiotics observed in Staphylococcus aureus (S. aureus) and Klebsiella pneumoniae (K. pneumoniae), including resistance to carbapenem and beta-lactam antibiotics.
Decontamination Efficacy Varies
The researchers used Enterococcus faecium (E. faecium) bioindicators to assess decontamination efficacy, finding that five of the six machines tested at 60°C for a full-length wash had peak temperatures ranging from 57.05°C to 58.14°C, held for between 5 and 39 minutes. However, only four of these machines achieved a 5 log₁₀ CFU reduction or greater.
The researchers found that rapid wash cycles were particularly problematic: "Of the rapid wash cycles, 50% of the six machines did not reach the stated 60°C ± 4°C (measured temperature, 19.72°C [to] 44.5°C), and failed to decontaminate E. faecium (< 5 log₁₀ CFU reduction)."
Pathogens and Resistance Genes
The researchers conducted shotgun metagenomic sequencing on 12 samples (from 8 different DLMs) to analyze their microbiome. Three main classes of bacteria represented more than 60% of the bacteria detected: Actinomycetes, Gammaproteobacteria, and Alphaproteobacteria.
"The presence of genera containing known pathogenic bacteria species was detected in all the samples," the study authors reported, with Acinetobacter (9% to 28%), Mycobacterium (1% to 49%), and Pseudomonas (1% to 61%) showing relative abundance greater than 1% of the total bacteria.
Antibiotic resistance genes were detected in all samples, with five genes encoding for efflux pumps (adeF, qacG, rsmA, abaQ, and abeS), three genes encoding for altered variants of antibiotic targets (vanYB, vanWI, and vanG), and one gene encoding an antibiotic inhibitor (ANT(3")-IIC).
Detergent Tolerance and Antibiotic Cross-Resistance
The researchers demonstrated that exposure to domestic detergents led to bacterial tolerance and antibiotic cross-resistance, with liquid detergents showing higher tolerance development compared with powder detergents.
"S. aureus increased from 0.000675 µl/ml to 0.60 µl/ml (an 89,000% increase), K. pneumoniae increased from 0.000675 µl/ml to 10.36 µl/ml (an increase of more than 1.5 million percent), and Pseudomonas aeruginosa from 0.00675 µl/ml to 2.05 µl/ml (a 30,000% increase)," the study authors reported for liquid detergent tolerance.
Whole-genome sequencing identified mutations in genes encoding efflux pumps in S. aureus (MgrA) and K. pneumoniae (AcrB) following detergent exposure, which could impact efflux pump function and explain the observed antibiotic resistance.
"K. pneumoniae exposure to powder detergent induced cross-resistance to ertapenem 10 μg (a ZOI reduction of 10.38 mm) and meropenem 10 μg (a ZOI reduction of 14.12 mm)," the study authors found. "This combination of resistances suggests K. pneumoniae has become a carbapenem-resistant Enterobacteriaceae (CRE)," they added.
Recommendations for Health Care Uniform Laundering
The researchers recommended revising current guidelines for laundering health care worker uniforms. Key recommendations included avoiding short wash cycles, ensuring cycle temperatures reach at least 70°C so that a minimum of 60°C is maintained for 10 minutes, regularly disinfecting and cleaning DLMs to reduce biofilm formation, and renewing DLMs every 4 years.
For health care employers, the researchers suggested establishing lists of approved detergents with proven disinfection efficacy, offering servicing and performance checks of workers' DLMs, providing on-premise laundering with controlled laundering machines, or outsourcing to industrial laundries accredited to BS EN 14065:2016 standards.
Source: PLOS ONE
