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The efficacy of ozone-based automated room disinfection by STERISAFE PRO was tested in complex room conditions against different surfaces contaminated with the bacterium Acinetobacter baumanii. The technology successfully reached an average kill-rate above 5-log reduction under complex room conditions, but A. baumanii exhibited different survival capacities depending on the tested surfaces, and some individual targets displayed reduction under the 5-log threshold. Those results suggest the need for further validation experiments under varying conditions.

The genus Acinetobacter comprises species typically found in soil and water, which are occasionally human pathogens. Amongst them, Acinetobacter baumanii represents the most clinically significant. A. baumanii is considered an opportunistic pathogen, which makes it dangerous in healthcare settings, particularly for immunocompromised individuals and patients under prolonged hospitalization. As such, it is considered a pathogen relevant to healthcare-associated infections (HAI). In the early days, infection by this microorganism commonly lead to pneumonia; but recently, A. baumanii has been linked to infections of the central nervous system, bones, skin and soft tissues.

But its most problematic feature is its ability to adapt and acquire resistance traits. While it is now known to exhibit high survivability rates against most antibiotics, in the 70s A. baumanii was considered a sensitive organism, relatively easy to treat. Nowadays, some A. baumanii strains are known to be resistant even to the higher classes of antibiotics such as carbapenem. As such, it is currently considered amongst the six most common and serious multidrug-resistant (MDR) pathogens, a group which is collectively known as the acronym “ESKAPE” (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.). More recently, A. baumanii has receive attention for its emergence in conflict zones hospitals, and due to its prominence during the Iraq war it came to receive the surname “Iraquibacter”.

Considering those traits, A. baumanii is a choice target for disinfection experiments in hospital settings. Knobloch et al. from the University Medical Center Hamburg-Eppendorf (UKE) investigated the efficacy of the ozone-based, automated room disinfection instrument STERISAFE PRO on A. baumanii, following existing experimental setups made with E. faecium and C. auris. As for the C. auris experiment, the tested microorganism was placed in different surface materials (ceramic tile, stainless steel, solid core furniture board) (see Figure 1). The strain used for this experiment was a carbapenem-resistant A. baumanii strain. Similarly to the previous experiments, the different surfaces were scattered in a hospital patient room, including its adjacent bathroom and vestibule. After verifying the samples could survive on inanimate surfaces after drying for 24h, a standard STERISAFE PRO ozonation cycle was launched and the survival rate of the A. baumanii samples was assessed.

The tested A. baumanii strain shown higher resilience to ozonation treatment on the furniture plates, irrespective of the plate position in the room. While for the two other type of surfaces, the number of colony forming units (CFUs) was under the limit of detection after treatment, some single cells on furniture plates were able to survive the ozonation cycle. This is reflected in the average log-reduction rate, which goes from 5.00 on the furniture plate to a higher 5.78 on the ceramic tile (see Figure 2). It is worth to note that the initial cell counts after the drying pre-step was the highest in the furniture plates, underlining the higher survival rate of A. baumanii on this surface, compared to ceramic and stainless steel. Nonetheless, if the mean reduction is sufficient to claim compliance with the 5-log reduction threshold required for bacteria in the NF T 72-281 standard, it is important to note that some individual samples on furniture plates were found under the 5-log limit.

Those results determine the efficacy of the STERISAFE PRO instrument is sufficient to comply with the highest quality standard of airborne disinfection systems for the tested carbapenem-resistant A. baumanii strain. However, different survival behaviour of A. baumanii on different surface materials suggest the need for further validation under other conditions.

Figure 1. Inanimate surface materials used for contamination before survival and disinfection experiments (reproduced with courtesy of Knobloch et al.,2019)

Figure 2. Boxplot for the disinfection experiment. The NF T 72-281 threshold of 5-log reduction is marked by the dotted blue line. (reproduced with courtesy of Knobloch et al.,2019)


  1. Knobloch J.K., Franke G., Belmar Campos C.E., Klupp E.M. & Knobling B. (2019). Disinfection of surfaces contaminated with Carbapenemase producing Acinetobacter baumannii using ozone under complex room conditions. UKE, Institute for Medical Microbiology, Virology and Hygiene, Department for Hospital Epidemiology and Infection Control.
  2. Peleg A.Y., Seifert H., Paterson D.L. (2008). Acinetobacter baumanii: Emergence of a Successful Pathogen. Clinical Microbiology Reviews 21 (3): 538-582.