Abstract
Myroides odoratimimus is an aerobic, non-fermenting Gram-negative multidrug-resistant bacterium widely distributed in nature that rarely causes infections in immunocompromised patients. We recently described in a diabetic patient a case of recurrent calcaneal ulcer infection caused by a M. odoratimimus strain showing potential for biofilm formation. For the first time, we therefore evaluated the ability of M. odoratimimus to form biofilm under different pH values and glucose concentrations using an in vitro “skin-like” model, and its susceptibility to levofloxacin, meropenem, and tigecycline. The expression of some antibiotic-resistance related genes was also monitored by RT-PCR during planktonic-to-biofilm transition. Our results indicated that M. odoratimimus can produce relevant amounts of biofilm biomass, in a time-dependent manner, especially at acidic pH and regardless of glucose concentration tested. The comparative analysis of MIC and MBC values between planktonic and sessile cells showed that resistance to antibiotics increased during the planktonic-to-biofilm transition. Viable cell count indicated that none of the tested antibiotics were able to completely eradicate preformed biofilms, although meropenem and levofloxacin were the most active causing a significant, dose-independent, reduction of biofilm's viability, as also confirmed by microscopic analysis. RT-PCR showed that antibiotic-resistance related gyrA and acrB genes are over-expressed during the transition from planktonic to sessile (biofilm) lifestyle. Overall, our findings showed that M. odoratimimus can form relevant amounts of inherently antibiotic-resistant biofilm under conditions relevant to wound site, therefore suggesting a role in the pathogenesis of chronic ulcer infections.
Highlights
Myroides odoratimimus is a non-motile, non-fermentative, strictly aerobic, Gram-negative rod with a characteristic fruity odor and yellow pigmentation due to the flexirubin pigment (Vancanneyt et al, 1996)
The strain resulted in being a strong biofilm producer, according to criteria proposed by Stepanovicet al. (2007), and biofilm biomass increased over time (Figures 1A–D)
At the same pH value no significant differences were observed among glucose concentrations (Figure 2A), whereas at the same glucose concentration the cellularity of M. odoratimimus biofilm significantly changed depending on pH value considered (Figure 2B)
Summary
Myroides odoratimimus is a non-motile, non-fermentative, strictly aerobic, Gram-negative rod with a characteristic fruity odor and yellow pigmentation due to the flexirubin pigment (Vancanneyt et al, 1996). Considered as a low-grade opportunistic pathogen, M. odoratimimus is rarely isolated in the clinical setting causing life-threatening infections, mainly in the immunocompromised host (Benedetti et al, 2011). Myroides odoratimimus is widely distributed in the environment, especially in water. Only eight cases of M. odoratimimus infection have been reported in the literature. For the first time, a case of a recurrent post-traumatic calcaneal ulcer infection caused by M. odoratimimus, in a diabetic male (Pompilio et al, 2017). The recurrent nature of the infection together with the evidence that in vitro the strain formed relevant amount of biofilm, led us to hypothesize that M. odoratimimus could be able to form biofilm under experimental conditions relevant to wound infections. A growing body of published works, indicated that in chronic wounds antibiotic-resistant biofilm formation contributes to a delay in healing (Percival et al, 2012; Rahim et al, 2017)
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