SURVIVABILITY OF HIGH RISK, MULTIRESISTANT BACTERIA ON COTTON TREATED WITH COMMERCIALLY AVAILABLE ANTIMICROBIAL AGENTS Adrienn Hanczvikkel 1, András Vígh 2, Ákos Tóth 3,4 1 Óbuda University, Budapest, Hungary 2 Department of Organic Chemistry and Technology, BUTE, Budapest, Hungary 3 National Center for Epidemiology, Budapest, Hungary 4 European Program for Public Health Microbiology Training (EUPHEM), European Centre for Disease Prevention and Control, (ECDC), Stockholm, Sweden Corresponding author: Adrienn Hanczvikkel; hanczvikkel.a@gmail.com Introduction Healthcare Associated Infections (HAIs) present a global public health problem. [1] HAIs are often caused by high risk bacteria, which are adapted to the extreme environment of health institutions. Abiotic surfaces contaminated with such strains can contribute to the transmission of hospital pathogens and can be the sources of nosocomial infections and outbreaks. [2, 3] Fabrics in contact with patients can be important sources of pathogens. Surfaces finished with antimicrobial agents may help in the elimination of microorganisms. [4, 5] Our goal was to examine the survival capability of the most important aerobic, multidrug resistant, nosocomial bacteria on 100% cotton sheet separately treated with two commercially available antimicrobial agents. We chose four bacterial species, which are important and frequent pathogens in Hungarian hospitals, and also cause public health concern worldwide. Materials and methods We examined 10 representative strains each of VRE (i.e., vancomycin-resistant Enterococcus faecium), MRSA (i.e., methicillin-resistant Staphylococcus aureus), MACI (i.e., multidrug-resistant Acinetobacter baumannii), and MRKP (i.e., multidrugresistant Klebsiella pneumoniae). We used 100% cotton sheet treated with Sanitized T99-19 (50 m/m% dimethyltetradecyl (3-(trimethoxysilyl)propyl)ammonium-chloride) or Sanitized T27-22 Silver liquid (2 m/m% AgCl and 8 m/m% TiO2), according to the manufacturer s (Sanitized AG) instructions. 105-106 CFU (colony forming unit) were inoculated onto surfaces of untreated and two kinds of treated swatches. The samples were incubated at 25 C, and 52% RH. 3 strains of each species were examined in the detailed surviving study. The surviving capability (CFU of surviving bacteria) were established immediately after inoculation, drying, one hour and one day. Based on these results, we chose incubation times for additional 7 strains of each species (MRKP: one hour; MRSA, VRE, MACI: one hour, one day).
Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values were determined for Sanitized liquids by broth microdilution method. We used IBM SPSS Statistics Data Editor, One-Way ANOVA model and dependent t- test for paired samples to perform the statistical tests. Results and discussion The surviving capabilities were compared on untreated fabric for 10 strains of each species. The mean CFUs showed an increasing trend in the following order: MRKP < MRSA < VRE MACI. After one day MACI and VRE retained their viability significantly better than MRSA strains (P<0.01 and P=0.012, respectively). This is consistent with other literature data. [6, 7] Both antibacterial agents proved to be bactericide regarding all 40 examined pathogens, but Gram-negative species (MRKP, MACI) can tolerate significantly higher concentration of T99-19 and also of Silver liquid (P<0.01) than Gram-positive ones (MRSA, VRE). Figure 1 shows the results of the detailed surviving study with 3 strains of each species on untreated and on treated textiles. The Silver agent reduced the CFU of Gram-positive strains even during drying. After one hour only 1 VRE isolate was recoverable. T99-19 also reduced the CFU of Gram-positive bacteria, but 2 MRSA and 3 VRE strains were recoverable even after one day incubation. The antibacterial agents were less effective against the Gram-negative isolates. Figure 1. The surviving ability with standard deviation rate of the three strains per species. X-axis shows the CFU of surviving bacteria, y-axis shows the incubation times. Figure 2 shows the results of comprehensive surviving test with 10 strains of each species on untreated and on treated textiles. The Silver liquid treated fabric reduced the CFU of Gram-positive strains significantly (P<0.01). The T99-19 agent also
reduced the CFU of VRE and MRSA bacteria, but 9 VRE and 6 MRSA strains were recoverable even after one day incubation. Regarding Gram-negative bacteria antibacterial coatings proved to be effective only against MACI isolates (after one hour P<0.01), but despite of this all MACI strains were recoverable. No correlation was found between MIC or MBC values and the survival capability on textiles finished with antimicrobial agents. According to our results surviving capability of the strains on antimicrobial surfaces is not predictable based on MIC and MBC values. Figure 2. The surviving ability of 10 strains per species on untreated and on treated textiles after one hour incubation time. Statistical tests: dependent t-test for paired samples. Conclusion Silver liquid proved to be effective against Gram-positive bacteria. 18 strains from the examined 20 were destroyed on the sheet finished with Silver agent after one hour. Although T99-19 liquid also reduced the number of surviving bacteria significantly, 15 strains preserved their viability after one day incubation time. None of the antimicrobial agents were able to destroy the Gram-negative strains on the swatches. MRKP strains are well-known for their ability to accumulate and transfer drug-resistance determinants, and to cause epidemics, so despite being less viable on dry surfaces, these microorganisms can pose health risk in hospitals. The tolerance of MACI isolates against desiccation and antibacterial agents may contribute to their recently observed success in HAIs. REFERENCES 1. ECDC, Annual epidemiological report 2014. Antimicrobial resistance and healthcare-associated infections. 2015 Stockholm.
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