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

Phenotypical and molecular characterization of Rhodococcus equi isolated from foals in the Agreste region of Pernambuco - Brazil

Equine rhodococcosis is caused by Rhodococcus equi, an intracellular coccobacillus whose main virulence factor is a plasmid that harbors genes encoding proteins from the Vap family, with the vapA gene being the most important in equine isolates. Furthermore, other factors observed in R. equi strains, such as antimicrobial resistance and biofilm production, may represent significant challenges in the treatment of affected animals. The objective of this study was to characterize four isolates of R. equi from foals in the state of Pernambuco, Brazil. All isolates were identified as R. equi through biochemical tests, amplification of the choE gene, and sequencing of 16 S rRNA. PCR analysis revealed that three isolates were positive for the plasmid virulence genes (vapA, -C, -D, -E, -F, -H and traA), although vapD was absent in one of the three isolates. One isolate did not present any virulence genes, possibly due to the loss of the plasmid after repeated passages at 37ºC. In the antimicrobial susceptibility test, all isolates were susceptible to erythromycin, clarithromycin, azithromycin, rifampicin, gentamicin, and doxycycline. However, all isolates were capable of forming biofilms, with moderate biofilm formation in isolates Rhodo1 and Rhodo2, and weak biofilm formation in isolates Rhodo3 and Rhodo4, which may be associated with increased antimicrobial tolerance. This molecular characterization demonstrated, for the first time, the presence of the virulence plasmid in R. equi isolates from foals in Northeast Brazil, as well as their capacity for biofilm formation.

Characterization of Rhodococcus equi isolated from pyogranulomatous lesions in cats from Brazil

This study aimed to describe and provide a laboratory characterization of three cases of Rhodococcus equi isolates from pyogranulomatous lesions in domestic cats in Brazil, collected between 2015 and 2021. Swabs and aspirates from nodular skin lesions located in the abdominal region (Case 1) and thoracic limbs (Cases 1-3) were subjected to microbiological culture, biochemical and molecular analyses, evaluation of biofilm formation capacity, and antimicrobial sensitivity testing. Cats 1 and 2 were positive for FeLV p27 antigen on SNAP testing. Cat 1 died at home from complications of Rhodococcus infection, and Cat 2 was euthanized following failure of medical and surgical treatment of infection. The cat in Case 3, which was FeLV-negative, received treatment with oral erythromycin and topical rifampicin for 30 days. However, due to failure of antimicrobial therapy to resolve the lesions, the cat underwent amputation of the affected right hindlimb. R. equi, positive for the plasmid-encoded virulence-associated protein A, was identified on the microbiological cultures and PCR from all cases. Biofilm formation analysis categorized all three isolates as weak biofilm formers. Additionally, antimicrobial susceptibility testing revealed that all isolates were sensitive to azithromycin, clarithromycin, erythromycin, imipenem, and rifampicin in vitro. These findings underscore the clinical, epidemiological, and laboratory characteristics of R. equi infection in Brazilian cats, indicating that these microorganisms are phenotypically and molecularly similar to those isolated from horses.

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

In humans, Rhodococcus equi (R. equi) is a zoonotic infection usually involving immunocompromised subjects, only rarely affecting immunocompetent subjects. Herein, we describe an R. equi infection in a 50-year-old Russian man with acquired immune deficiency syndrome (AIDS) who presented with pulmonary cavitary lesions and clinical manifestation of colonic malakoplakia. A colonoscopy examination showed ulceration and mucosal erosion, and the histological findings confirmed the colonic malakoplakia. The patient recovered from pulmonary and gastrointestinal disease after four weeks of antibiotic treatment with intravenous ciprofloxacin and oral azithromycin and also underwent subsequent long-term oral antibiotic treatment to achieve clinical and immune restoration after antiretroviral therapy. Infectious disease pathology subspecialties should always consider R. equi chronic infection as a cause of malakoplakia in patients with AIDS. As only a few cases of colonic malakoplakia associated with R. equi are reported in the literature, these cases are important to describe, especially for clinical and treatment management.

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

Corynebacterium pseudotuberculosis is the etiological agent of caseous lymphadenitis in small ruminants, a chronic disease characterized by the development of granulomas in superficial and visceral lymph nodes as well as in several organs. An important characteristic of the infection with this bacterium is the formation of a biofilm and the absence of effective antibiotic therapy against the disease. From this scenario, the objective of this study was to evaluate the susceptibility of C. pseudotuberculosis to conventional antibiotics and to red, green, and brown propolis extracts obtained by the supercritical and ethanolic extraction methods as well as its activity in the bacterial biofilm. The results of the sensitivity test using antibiotics indicated a sensitivity of C. pseudotuberculosis strains to the antimicrobial agents. The ethanolic extract of green propolis and the supercritical red propolis extract showed the best antibacterial activities against planktonic C. pseudotuberculosis. A lower antimicrobial activity of the brown propolis extract was identified. Propolis extracts were effective in interfering with the formation of the C. pseudotuberculosis biofilm but had little activity on the consolidated biofilm. In conclusion, propolis extracts are more effective against C. pseudotuberculosis in the planktonic stage, being able to interfere with the formation of bacterial biofilm. However, the action of propolis extracts in a sessile and structured microbial biofilm is reduced.

Ethidium bromide exposure unmasks an antibiotic efflux system in Rhodococcus equi

BACKGROUND

This study introduces a newly created strain (Rhodococcus equiEtBr25) by exposing R. equi ATCC 33701 to ethidium bromide (EtBr), a substrate for MDR transporters. Such an approach allowed us to investigate the resulting phenotype and genetic mechanisms underlying the efflux-mediated resistance in R. equi.

METHODS

R. equi ATCC 33701 was stimulated with increasing concentrations of EtBr. The antimicrobial susceptibility of the parental strain and R. equiEtBr25 was investigated in the presence/absence of efflux pump inhibitors (EPIs). EtBr efflux was evaluated by EtBr-agar method and flow cytometry. The presence of efflux pump genes was determined by conventional PCR before to quantify the expression of 30 genes coding for membrane transporters by qPCR. The presence of erm(46) and mutations in 23S rRNA, and gyrA/gyrB was assessed by PCR and DNA sequencing to exclude the occurrence of resistance mechanisms other than efflux.

RESULTS

R. equi EtBr25 showed an increased EtBr efflux. Against this strain, the activity of EtBr, azithromycin and ciprofloxacin was more affected than that of rifampicin and azithromycin/rifampicin combinations. Resistances were reversed by combining the antimicrobials with EPIs. Gene expression analysis detected a marked up-regulation of REQ_RS13460 encoding for a Major Facilitator Superfamily (MFS) transporter. G→A transition occurred in the transcriptional repressor tetR/acrR adjacent to REQ_RS13460.

CONCLUSIONS

Exposure of R. equi to EtBr unmasked an efflux-mediated defence against azithromycin and ciprofloxacin, which seemingly correlates with the overexpression of a specific MFS transporter. This genotype may mirror an insidious low-level resistance of clinically important isolates that could be countered by EPI-based therapies.

Biodegradation of crude oil by immobilized Exiguobacterium sp. AO-11 and shelf life evaluation

Exiguobacterium sp. AO-11 was immobilized on bio-cord at 10⁹ CFU g⁻¹ carrier for the removal of crude oil from marine environments. To prepare a ready-to-use bioremediation product, the shelf life of the immobilized cells was calculated. Approximately 90% of 0.25% (v/v) crude oil removal was achieved within 9 days when the starved state of immobilized cells was used. The oil removal activity of the immobilized cells was maintained in the presence of oil dispersant (89%) and at pH values of 7–9. Meanwhile, pH, oil concentration and salinity affected the oil removal efficacy. The immobilized cells could be reused for at least 5 cycles. The Arrhenius equation describing the relationship between the rate of reaction and temperature was validated as a useful model of the kinetics of retention of activity by an immobilized biocatalyst. It was estimated that the immobilized cells could be stored in a non-vacuum bag containing phosphate buffer (pH 7.0) at 30 °C for 39 days to retain the cells at 10⁷ CFU g⁻¹ carrier and more than 50% degradation activity. These results indicated the potential of using bio-cord-immobilized crude oil-degrading Exiguobacterium sp. AO-11 as a bioremediation product in a marine environment.

Quorum sensing: a new prospect for the management of antimicrobial-resistant infectious diseases

INTRODUCTION

Quorum-sensing (QS) is a microbial cell-to-cell communication system that utilizes small signaling molecules to mediates interactions between cross-kingdom microorganisms, including Gram-positive and -negative microbes. QS molecules include N-acyl-homoserine-lactones (AHLs), furanosyl borate, hydroxyl-palmitic acid methylester, and methyl-dodecanoic acid. These signaling molecules maintain the symbiotic relationship between a host and the healthy microbial flora and also control various microbial virulence factors. This manuscript has been developed based on published scientific papers.

AREAS COVERED

Furanones, glycosylated chemicals, heavy metals, and nanomaterials are considered QS inhibitors (QSIs) and are therefore capable of inhibiting the microbial QS system. QSIs are currently being considered as antimicrobial therapeutic options. Currently, the low speed at which new antimicrobial agents are being developed impairs the treatment of drug-resistant infections. Therefore, QSIs are currently being studied as potential interventions targeting QS-signaling molecules and quorum quenching (QQ) enzymes to reduce microbial virulence.

EXPERT OPINION

QSIs represent a novel opportunity to combat antimicrobial resistance (AMR). However, no clinical trials have been conducted thus far assessing their efficacy. With the recent advancements in technology and the development of well-designed clinical trials aimed at targeting various components of the, QS system, these agents will undoubtedly provide a useful alternative to treat infectious diseases.