Mutation detection and minimum inhibitory concentration determination against linezolid and clofazimine in confirmed XDR-TB clinical isolates

Diagnostic accuracy of direct drug susceptibility testing of second-line antitubercular drugs

It is well-established that direct drug susceptibility testing (DST) of Mycobacterium tuberculosis using a liquid medium for first-line drugs provides accurate and time-saving results. The purpose of this study was to determine whether DST for second-line drugs could be successfully performed using processed smear-positive specimens (direct DST) and whether this method is accurate and may result in a significant reduction in time. The accuracy and shorter turnaround time of this approach were established by comparing the results acquired through direct DST with those obtained through indirect DST. Of the 150 acid-fast bacteria smear-positive sputum specimens that were set up for direct DST, 130 (86.67%) produced results that could be reported. Direct DST reporting took an average of 10 days (range: 9-11 days). The time savings from direct DST to indirect DST, which took into account the time needed to isolate a culture and conduct DST, was 7 days on average (range: 6-9 days). When the direct and indirect DST results were compared, the concordance with levofloxacin (LFX), moxifloxacin (MOX), linezolid (LNZ), and clofazimine (CFZ) were 96.33%, 96.16%, 100%, and 99.24%, respectively. The sensitivity and specificity of the test result were 93.75%, 83.33%, 100%, and 100%, and 98.0, 99.10, 100, and 99.19% with an accuracy of 98%, 98%, 100%, and 99% for LFX, MOX, LNZ, and CFZ, respectively. Direct DST is a fast and accurate diagnostic technique for detecting second-line drug resistance in tuberculosis.

IMPORTANCE

The significance of this work is that it assesses whether direct drug susceptibility could be used in routine testing to save significant time, which is critical for early diagnosis of resistance and successful treatment.

Agreement between Phenotypically Detected Linezolid Resistance and Mutations in rrl and rplC Genes of Mycobacterium tuberculosis Isolates Using Nanopore Sequencing

BACKGROUND

Phenotypic drug susceptibility testing (DST) is considered the gold standard for detecting linezolid (LZD) resistance in Mycobacterium tuberculosis (MTB), but it is time-consuming. Nanopore sequencing offers a potentially faster alternative approach. This study evaluated the agreement between phenotypically detected LZD resistance and mutations in the rrl and rplC genes of MTB isolates using nanopore sequencing.

METHODS

Consecutive drug-resistant MTB isolates from pulmonary samples collected in 2021 underwent liquid culture (LC) DST for LZD. All resistant isolates and an equal number of susceptible isolates were subjected to targeted sequencing of the rrl and rplC genes using nanopore technology.

RESULTS

Sequencing identified a C154R mutation in the rplC gene in only one LZD-resistant isolate. No mutations were detected in the rrl gene. The agreement between sequencing and LC-DST for detecting LZD resistance was poor (Cohen's kappa: 0.03571, 95% confidence interval [CI]: -0.034-0.105). Additionally, no significant association was found between LZD resistance and clinical or microbiological outcomes at 6-month follow-up.

CONCLUSION

This study revealed a considerable discrepancy between phenotypic and genotypic detection of LZD resistance in MTB. Further research is needed to better understand the genetic mechanisms underlying LZD resistance and to develop reliable molecular diagnostics for rapid resistance detection.

Facile green synthesis of silver nanoparticles derived from the medicinal plant Clerodendrum serratum and its biological activity against Mycobacterium species

The emergence of multidrug-resistant mycobacterial strains is a significant crisis that has led to higher treatment failure rates and more toxic and expensive medications for tuberculosis (TB). The urgent need to develop novel therapeutics has galvanized research interest towards developing alternative antimicrobials such as silver nanoparticles (AgNPs). The current study focused on the anti-mycobacterial activity of green-synthesized AgNPs and its polyethylene glycol encapsulated derivative (PEG-AgNPs) with improved stability using the leaves extract of Clerodendrum serratum. Different characterization methods were used to analyze them. DLS analysis revealed a lower polydispersity index of PEG-AgNPs, suggesting a more uniform size distribution than that of AgNPs. The HR-TEM results revealed that the AgNPs and PEG-AgNPs have predominantly spherical shapes in the size range of 9-35 nm and 15-60 nm, respectively, while positive values of Zeta potential indicate their stability. FTIR-ATR analysis confirmed the presence of functional groups responsible for reducing and capping the bio-reduced AgNPs, whereas the XRD data established its crystalline nature. Impressively, the PEG-AgNPs exhibited maximum inhibitory activity against different Tubercular and Non-Tuberculous Mycobacterium species i.e., Mycobacterium smegmatis, Mycobacterium fortuitum and Mycobacterium marinum, relative to those of AgNPs and Linezolid. The flow cytometry assay showed that the anti-mycobacterial action was mediated by an increase in cell wall permeability. Notably, the results of AFM confirm their ability to inhibit mycobacterial biofilm significantly. We demonstrated the nontoxic nature of these AgNPs, explicated by the absence of hemolytic activity against human RBCs. Overall, the results suggest that PEG-AgNPs could offer a novel therapeutic approach with potential anti-mycobacterial activity and can overcome the limitations of existing TB therapies.

Molecular mechanisms of resistance and treatment efficacy of clofazimine and bedaquiline against Mycobacterium tuberculosis

Clofazimine (CFZ) and bedaquiline (BDQ) are currently used for the treatment of multidrug-resistant (MDR) Mycobacterium tuberculosis (Mtb) strains. In recent years, adding CFZ and BDQ to tuberculosis (TB) drug regimens against MDR Mtb strains has significantly improved treatment results, but these improvements are threatened by the emergence of MDR and extensively drug-resistant (XDR) Mtb strains. Recently, CFZ and BDQ have attracted much attention for their strong clinical efficacy, although very little is known about the mechanisms of action, drug susceptibility test (DST), resistance mechanisms, cross-resistance, and pharmacokinetics of these two drugs. In this current review, we provide recent updates on the mechanisms of action, DST, associated mutations with individual resistance and cross-resistance, clinical efficacy, and pharmacokinetics of CFZ and BDQ against Mtb strains. Presently, known mechanisms of resistance for CFZ and/or BDQ include mutations within the Rv0678, pepQ, Rv1979c, and atpE genes. The cross-resistance between CFZ and BDQ may reduce available MDR-/XDR-TB treatment options. The use of CFZ and BDQ for treatment in the setting of limited DST could allow further spread of drug resistance. The DST and resistance knowledge are urgently needed where CFZ and BDQ resistance do emerge. Therefore, an in-depth understanding of clinical efficacy, DST, cross-resistance, and pharmacokinetics for CFZ and BDQ against Mtb can provide new ideas for improving treatment outcomes, reducing mortality, preventing drug resistance, and TB transmission. Along with this, it will also help to develop rapid molecular diagnostic tools as well as novel therapeutic drugs for TB.

Alarming Increase of Azole-Resistant Candida Causing Blood Stream Infections in Oncology Patients in Egypt

Candidemia is a life-threatening invasive fungal infection in immunocompromised patients. The widespread use of azoles and the shift toward non-albicans Candida (NAC) species remarkably increase azole resistance in developing countries. We aimed to study candidemia trends and associated risk factors in oncology patients since they vary geographically, and rapid and appropriate treatment improves outcomes. Vitek 2 was used to identify the Candida species, and the E-test determined their susceptibility to azoles. Candida was the cause of 3.1% (n = 53/1701) of bloodstream infections (BSIs) during a 1-year study. Candida tropicalis was the most predominant species among the 30 candidemia episodes studied (36.7%), followed by C. albicans (33.3%). However, C. krusei, C. guilliermondii, C. pelliculosa, C. parapsilosis, C. famata, and C. inconspicua accounted for 30.0% of the isolates. An increased risk of NAC BSI was significantly associated with chemotherapy and leucopenia (P = 0.036 and 0.016, respectively). However, the multivariable analysis revealed that leucopenia was the only independent risk factor (P = 0.048). Fluconazole and voriconazole resistance were 58.3% and 16.7%, with NAC species showing higher resistance rates than C. albicans. Both fluconazole and voriconazole minimum inhibitory concentration (MIC) median values were higher in NAC than in C. albicans, but only voriconazole was significantly higher (0.220 versus 0.048 μg/ml, P = 0.047). In conclusion, the increased prevalence of NAC BSIs and incredibly high fluconazole resistance rates in cancer patients emphasize the necessity of antifungal stewardship to preserve voriconazole effectiveness, continued surveillance of candidemia, and future studies into azole resistance molecular mechanisms.