Phenotypic Characterization of Rhodococcus equi Biofilm Grown In Vitro and Inhibiting and Dissolving Activity of Azithromycin/Rifampicin Treatment

Abstract

Microbial biofilm has been implicated in a wide range of chronic infections. In spite of the fact that Rhodococcus equi is a recognized cause of chronic disease in animals and humans, few studies have focused on the sessile phenotype of R. equi. The aim of this research was to phenotypically characterize the biofilm development of R. equi and its answerability for hypo-responsiveness to macrolides and rifampicin. Biofilm formation is initiated by bacterial adhesion to the surface. In this work, the ability of R. equi to adhere to the surface of human lung epithelial cells was detected by a fluorometric adhesion test performed on 40 clinical isolates. Subsequently, the capability of R. equi to produce biofilm was investigated by colorimetric, fluorescence and scanning electron microscopy analysis, revealing a general slow growth of rhodococcal biofilm and different sessile phenotypes among field isolates, some also including filamented bacteria. Azithromycin treatment produced a higher long-term inhibition and dissolution of R. equi biofilms than rifampicin, while the two antibiotics combined boosted the anti-biofilm effect in a statistically significant manner, although this was not equally effective for all R. equi isolates. Increasing the MIC concentrations of drugs tenfold alone and in combination did not completely eradicate pre-formed R. equi biofilms, while a rifampicin-resistant isolate produced an exceptionally abundant extracellular matrix. These results have strengthened the hypothesis that biofilm production may occur as an antibiotic tolerance system in R. equi, potentially determining persistence and, eventually, chronic infection.

Activity of Ethanolic and Supercritical Propolis Extracts in Corynebacterium pseudotuberculosis and Its Associated Biofilm

“…In any case, our results are promising because there is recent progress in the research on natural products with the objective to face resistance and tolerance to antibiotics, which are current global problems ( 42 ). This becomes more evident when recent studies, as described by Rampacci et al ( 64 ), experimentally demonstrate that increasing MIC concentrations (10x) of azithromycin and rifampicin alone and combined did not eradicate the preformed biofilm of Rhodococcus equi although a rifampicin-resistant isolate produced an exceptionally abundant extracellular matrix. Regarding Corynebacterium diphtheriae biofilm, all tested strains showed increased biofilm formation over a glass support after treatment with sub MIC concentrations of erythromycin.…”

Intestinal Lesions Due to Rhodococcus equi in a Patient With Advanced Retroviral Disease and Pulmonary Infection: A Case of Colonic Malakoplakia

“…The emergence of resistant strains of R. equi could complicate the clearance of this pathogen both in localized and disseminated infections, especially in immunocompromised subjects or subjects with chronic disorders such as diabetes [ 26 ]. In addition, R. equi infections can be challenging due to their tendency to form biofilms and have antibiotic resistance [ 26 , 27 ]. Clinical isolates in the United States (US) are usually susceptible to trimethoprim/ sulfamethoxazole, whereas more than half of the isolates in Europe are resistant [ 28 ].…”

Effects of Aromatic Compounds Degradation on Bacterial Cell Morphology

“…Regulation of processes in one direction or another may illustrate different strategies for bacterial survival. Thus, in the presence of antimicrobial agents or under oxidative stress, bacterial populations can respond with the appearance of filamentous forms together with other cell types [23,55].…”