Bacterial Growth in an In-Use Hospital-Grade Quaternary Ammonium-Based Disinfectant

Background: Monitoring of disinfection practices revealed that cultures obtained from high-touch surfaces after terminal cleaning of a patient’s room yielded heavy growth of Gram-negative organisms not present on the same surfaces sampled before cleaning, suggesting bacterial growth in the disinfectant used. 

Objective: Investigate the factors associated with contamination of an in-use quaternary ammonium-based disinfectant (Quat) and characterization of the contaminating organisms.  

Methods:  An epidemiologic investigation included interviewing the housekeeper who cleaned/disinfected the room and establishing practices for dilution and use of disinfectant solution.  Microbiological studies included cultures of the in-use Quat solution, bucket and wipes used by the implicated housekeeper, and the hoses, water and concentrated Quat from the dispensing station. Identification and susceptibility testing of the isolates from the contaminated Quat and from the patient’s room were performed with the MicroScan System. Comparison of the isolates was performed using PFGE with spe1 restriction enzyme and CHEF DR III System. Bactericidal activity of the contaminated Quat was verified by placing 50 ul of it onto a Mueller-Hinton agar plate inoculated with a 0.5 McFarland concentration of a control strain of Serratia marcescens (Smarc). The colony forming units (CFU) of organisms in the contaminated Quat were determined.  The relative activity of in-use concentration of the Quat against the contaminating Smarc and Smarc ATCC 13880 was established using a quantitative carrier test (ASTM E-2197) method. 

Results: The housekeeper who cleaned the implicated room was seldom responsible for terminal cleaning of patient rooms and had not used her bucket of Quat in many weeks.  The bucket containing the contaminated Quat had been used repeatedly for months, without being emptied and dried appropriately between uses.  Cultures of the contaminated in-use solution of Quat obtained from the housekeeper’s bucket, the bucket lid, and wipes from the bucket yielded two strains of Smarc and one strain of Achromobacter xylosoxidans.  PFGE verified the organisms from the patient rooms were the same as those in the Quat. The contaminated Quat solution inhibited the growth of the control strain of Smarc, demonstrating the presence of continued bactericidal activity.  The contaminated Quat contained 9.3 x10⁴ CFU/ml of organisms.  Cultures of the concentrated Quat, hoses and water from the dispensing station were negative for the bacteria.  Based on the carrier tests, the contaminating strains of Smarc were >100-fold more resistant to the in-use concentrations of Quat than the control strain.  

Conclusions: Failure to adhere to recommended practices for use and cleaning of buckets with disinfectants resulted in the selection and growth of disinfectant-resistant bacteria, which contaminated patient rooms during routine decontamination.