EMBARGOED UNTIL: Wednesday, September 11, 11:00 AM MDT
(Session 72, Paper C1-505)
Nottingham Trent Univ., Nottingham, -null-, United Kingdom
Although Acinetobacter spp. is a relatively harmless group of microorganisms for the average healthy person, it can cause life-threatening infections to hospitalized patients who have undergone surgical operations or have a weakened immune system. These infections are notoriously difficult to treat, since in most cases the infecting bacteria are Multi Drug Resistant (MDR) which makes the vast majority of the available antibiotics ineffective against MDR Acinetobacter. This research project provides evidence that extensive use of disinfectants, commonly used for cleaning in hospitals, could produce resistant Acinetobacter spp. to those disinfectants which are also cross-resistant to some antibiotics commonly used to treat Acinetobacter spp. infections like Polymyxin B. These results suggest that the emergence of a disinfectant-resistant Acinetobacter spp. could be the first step towards the emergence of a Multi Drug Resistant microorganism. This suggestion is underpinned by the finding that the mechanisms that confer resistance to the disinfectants for Acinetobacter spp. are the same with those mechanisms which confer resistance to antibiotics. In most cases resistance derives from over-expression of the same genes which produce a series of proteins, called efflux-pumps, which can recognize the disinfectant or antibiotic and prevent it from entering inside the bacterial cell. Learning more about the factors which can lead to the emergence of MDR Acinetobacters in hospitals can lead to the design of better hospital policies and tactics in order to prevent the emergence of MDR bacteria and minimize the in-hospital infections.
This project was carried out by Charalampos Tsoukalas and Dr. Michael Loughlin in the School of Science and Technology of Nottingham Trent University, Nottingham, UK and was funded by the same source.
In order to investigate the ability of Acinetobacter to become resistant to disinfectants and polymyxin B, we used 43 Acinetobacter strains that were isolated either from hospital environment or other sources namely; food, household items and soil. Initially the minimum inhibitory concentration (MIC) for the wild types was determined for two disinfectants (Trigene, Hycolin) and for Polymyxin B. After that, all 43 strains were cultured for a week in Tryptone Soya Broth (TSB) which contained half the concentration of Hycolin or Trigene or polymyxin B than the MIC that was determined before for each chemical. The liquid cultures that contained Hycolin or Trigene were cultured at 30oC without shaking. The medium was refreshed every second day. These culture conditions are closer to the conditions the microorganisms would face in a hospital environment. (Close to a room temperature, limited nutrient sources, natural oxygen provision). In contrast, the liquid cultures that contained polymyxin B were incubated at the 36oC by shaking and the medium was refreshed every day. These conditions are more similar to those of the human body (human body temperature, provision of plenty of nutrients and oxygen by the human blood). At the beginning of every week a sample of each bacterial culture was taken and the MIC of the disinfectants and Polymyxin B was measured respectively. The cultures were passaged in TSB that contained double the concentration of the disinfectants or Polymyxin B than the one used the previous week. If no growth was observed in a culture for two weeks it was removed from the experiment. After ten weeks of passaging the experiment was stopped.
Another aspect of this study is that there is evidence that the cross-resistant Acinetobacters have a genetic predisposition of becoming cross-resistant. When all the disinfectant-resistant bacteria were tested for genetic relationships, using a molecular technique called REP-PCR, it was found that there were disinfectant-resistant bacteria that were not genetically related. To the contrary, when the same method was applied for all the cross-resistant bacteria (the bacteria which were resistant to disinfectants and Polymyxin B at the same time) it was found that almost all of them, with only one exception, appear to be closely genetically related. This is an interesting result that may suggests that it can be possible to predict in the future the potential of a strain becoming cross-resistant to antibiotics just by genetically profiling it.