Candida albicans, an opportunistic pathogen, has the ability to form biofilms in the host or within medical devices in the body. Biofilms have been associated with disseminated/invasive disease with increased severity of infection by disrupting the host immune response and prolonging antifungal treatment. In this study, the in vivo virulence of three strains with different biofilm formation strengths, that is, non-, weak-, and strong biofilm formers, was evaluated using the zebrafish model. The survival assay and fungal tissue burden were measured. Biofilm-related gene expressions were also investigated. The survival of zebrafish, inoculated with strong biofilms forming C. albicans,, was significantly shorter than strains without biofilms forming C. albicans. However, there were no statistical differences in the burden of viable colonogenic cell number between the groups of the three strains tested. We observed that the stronger the biofilm formation, the higher up-regulation of biofilm-associated genes. The biofilm-forming strain (140 and 57), injected into zebrafish larvae, possessed a higher level of expression of genes associated with adhesion, attachment, filamentation, and cell proliferation, including eap1, als3, hwp1, bcr1, and mkc1 at 8 h. The results suggested that, despite the difference in genetic background, biofilm formation is an important virulence factor for the pathogenesis of C. albicans. However, the association between biofilm formation strength and in vivo virulence is controversial and needs to be further studied.

Introduction: Mycobacterium tuberculosis (MTB), the causative agent of tuberculosis, has been a global threat to human beings for several decades. Treating tuberculosis has become more difficult as the prevalence of drug-resistant tuberculosis has increased globally. Evidence suggests that the comprehensive landscape of resistance mechanisms in MTB is ambiguous. More importantly, little is known regarding the series of events connected to resistance mechanisms in MTB before exposure to anti-TB drugs, during exposure to the drugs, and finally, when the MTB becomes resistant after exposure, upon analyses of its genome.Methods: We used the wild-type strain of MTB (H37Rv) in an in vitro model for generating induced resistance using a sub-inhibitory concentration of isoniazid, and the generated resistance-associated variants (RAVs) were identified using the whole genome sequencing method.Results: The detection of an inhA promoter mutation (fabG1−15C>T), which results in increased production of InhA protein, was found to be a major mechanism for developing resistance to isoniazid in the first place. We observed adaptation of MTB resistance mechanisms in high isoniazid stress by alteration and abolishment of KatG due to the detection of katG S315N, the common region of mutation that confers isoniazid resistance, along with katG K414N, katG N138S, and katG A162E. Furthermore, we detected the ahpC−72C>T and ahpC 21C>A mutations, but further investigation is needed to determine their role in compensating for the loss of KatG activity.Discussion: This suggests that increased InhA production is the main mechanism where there are low levels of isoniazid, whereas the alteration of KatG was found to be utilized in mycobacterium with a high concentration of isoniazid. Our work demonstrates that this in vitro approach of generating induced resistance could provide clinically relevant information after the fabG1−15C>T mutation, which is the common mutation found in clinical isolates. Moreover, other mutations detected in this work can also be found in clinical isolates. These findings may shed light on the impact of isoniazid in generating RAV and the resistance mechanism scenario that mycobacterium used under various isoniazid-pressuring conditions. More research is needed to understand better the role of RAV and mechanical resistance events within the mycobacterium genome in promoting a promising drug prediction platform that could lead to the right treatment for patients with MDR-TB and XDR-TB.

In recent decades, an epidemiological shift has been observed from Candida infections to non-albicans species and resistance to azoles. We investigated the associated factors and molecular mechanisms of azole-resistant blood isolates of C. tropicalis. Full-length sequencing of the ERG11 gene and quantitative real-time RT-PCR for the ERG11, MDR1, and CDR1 genes were performed. Male sex (odds ratio, 0.38), leukemia (odds ratio 3.15), and recent administration of azole (odds ratio 10.56) were associated with isolates resistant to azole. ERG11 mutations were found in 83% of resistant isolates, with A395T as the most common mutation (53%). There were no statistically significant differences in the expression of the ERG11, MDR1, and CDR1 genes between the groups resistant and susceptible to azole. The prevalence of azole-resistant isolates was higher than the usage of antifungal drugs, suggesting the possibility of environmental transmission in the healthcare setting. The unknown mechanism of the other 17% of the resistant isolates remains to be further investigated.