Amphotericin B-resistant Strains Research Articles

Analysis of Antimicrobial Susceptibility in Bacterial Pathogens Associated with Urinary Tract Infections from Beijing Teaching Hospital in China, 2009-2017.

Since a urinary tract infection (UTI) is easy to relapse and difficult to treat, the antibiotic resistance rate has increased year by year in recent years. This study was to analyze the characteristics of the common pathogenic bacteria and the changes of antibiotic resistance in urinary system infection, so as to guide the standard use of antibiotics in a clinical urinary tract infection and control nosocomial infection effectively. A total of 5,669 strains of a urinary tract infection in the hospital from January 2009 to December 2017 were retrospectively analyzed. Bacterial identification and the antibiotic sensitivity test (AST) were analyzed by using a VITEK-2 Compact system. Of the 5669 pathogens, 3,256 (57.44%) of the strains were Gram-negative bacteria (GNB), 1,474 (26%) were Gram-positive bacteria (GPB), and 939 (16.56%) were fungi. Resistant rates of ESBL-producing strains were all significantly different from non-ESBL-producing strains in Escherichia coli (p < 0.05). The resistance rate of ESBL-producing strains to β-lactam antibiotics was all higher than that of non-ESBL-producing strains in Klebsiella pneumoniae (p < 0.05). The detection rate of vancomycin-resistantEnterococcus faecium and Enterococcus faecalis was 37.3% and 3.1%, respectively, and the detection rate of linezolid-resistantEnterococcus faecium and Enterococcus faecalis was 0.68% and 0%, respectively. The drug resistance rate of candida sp. to fluconazole, itraconazole, and voriconazole was 1.7%, 8.5%, and 3.4%, respectively. No amphotericin B-resistant strains were detected in the research. Among the 5669 strains isolated from urinary tract infection patients, GNB were the main pathogens. Escherichia coli was the major pathogen. The resistance rate of ESBLs-producingEscherichia coli was higher than that of non-ESBLs-producingEscherichia coli in general; meanwhile, β-lactam/β-lactamase inhibitors and carbapenems maintained good antimicrobial activity against Escherichia coli. The resistance rate of non-ESBLs-producingKlebsiella pneumoniae strains was significantly higher than that of ESBLs-producingKlebsiella pneumoniae strains, and drug resistance was more prominent; most of the antibiotic resistance rates were over 50%. The antimicrobial resistance rate of Enterococcus faecium was significantly higher than that of Enterococcus faecalis. There were rare linezolid-resistant strains. The antimicrobial resistance rate of imidazole to fungi was controlled less than 10%.

Comparative Genome Sequence Analyses of Geographic Samples of Aspergillus fumigatus-Relevance for Amphotericin B Resistance.

Amphotericin B (AMB) is a major fungicidal polyene agent that has a broad spectrum of action against invasive fungal infections. AMB is typically used as the last-line drug against serious and life-threatening infections when other drugs have failed to eliminate the fungal pathogens. Recently, AMB resistance in Aspergillus fumigatus has become more evident. For example, a high rate of AMB resistance (96%) was noted in the A. fumigatus population in Hamilton, Ontario, Canada. AMB-resistant strains have also been found in other countries. However, the mechanism of AMB resistance remains largely unknown. Here, we investigated the potential genes and mutations associated with AMB resistance using whole-genome sequences and examined AMB resistance distribution among genetic populations. A total of 196 whole-genome sequences representing strains from 11 countries were examined. Analyses of single nucleotide polymorphisms (SNPs) at the whole-genome level revealed that these strains belonged to three divergent genetic clusters, with the majority (90%) of AMB resistant strains located in one of the three clusters, Cluster 2. Our analyses identified over 60 SNPs significantly associated with AMB resistance. Together, these SNPs represent promising candidates from which to investigate the putative molecular mechanisms of AMB resistance and for their potential use in developing rapid diagnostic markers for clinical screening of AMB resistance in A. fumigatus.

Cell Wall Changes in Amphotericin B-Resistant Strains from Candida tropicalis and Relationship with the Immune Responses Elicited by the Host.

We have morphologically characterizedCandida tropicalisisolates resistant to amphotericin B (AmB). These isolates present an enlarged cell wall compared to isolates of regular susceptibility. This correlated with higher levels of β-1,3-glucan in the cell wall but not with detectable changes in chitin content. In line with this, AmB-resistant strains showed reduced susceptibility to Congo red. Moreover, mitogen-activated protein kinases (MAPKs) involved in cell integrity were already activated during regular growth in these strains. Finally, we investigated the response elicited by human blood cells and found that AmB-resistant strains induced a stronger proinflammatory response than susceptible strains. In agreement, AmB-resistant strains also induced stronger melanization ofGalleria mellonellalarvae, indicating that the effect of alterations of the cell wall on the immune response is conserved in different types of hosts. Our results suggest that resistance to AmB is associated with pleiotropic mechanisms that might have important consequences, not only for the efficacy of the treatment but also for the immune response elicited by the host.

Theonellamide G, a Potent Antifungal and Cytotoxic Bicyclic Glycopeptide from the Red Sea Marine Sponge Theonella swinhoei

In our search for bioactive metabolites from marine organisms, we have investigated the polar fraction of the organic extract of the Red Sea sponge Theonella swinhoei. Successive chromatographic separations and final HPLC purification of the potent antifungal fraction afforded a new bicyclic glycopeptide, theonellamide G (1). The structure of the peptide was determined using extensive 1D and 2D NMR and high-resolution mass spectral determinations. The absolute configuration of theonellamide G was determined by chemical degradation and 2D NMR spectroscopy. Theonellamide G showed potent antifungal activity towards wild and amphotericin B-resistant strains of Candida albicans with IC50 of 4.49 and 2.0 μM, respectively. Additionally, it displayed cytotoxic activity against the human colon adenocarcinoma cell line (HCT-16) with IC50 of 6.0 μM. These findings provide further insight into the chemical diversity and biological activities of this class of compounds.

Fluconazole and amphotericin-B resistance are associated with increased catalase and superoxide dismutase activity in Candida albicans and Candida dubliniensis

Candida dubliniensis, a new species of Candida that has been recovered from several sites in healthy people, has been associated with recurrent episodes of oral candidiasis in AIDS and HIV-positive patients. This species is closely related to C. albicans. The enzymatic activity of C. dubliniensis in response to oxidative stress is of interest for the development of drugs to combat C. dubliniensis. Fluconazole- and amphotericin B-resistant strains were generated as described by Fekete-Forgács et al. (2000). Superoxide dismutase (SOD) and catalase assays were performed as described by McCord and Fridovich (1969) and Aebi (1984), respectively. We demonstrated that superoxide dismutase (SOD) and catalase activities were significantly higher (p<0.05) in the fluconazole- and amphotericin B-resistant strains of C. dubliniensis and C. albicans than in the sensitive strains. The catalase and SOD activities were also significantly (p<0.01) higher in the sensitive and resistant C. albicans strains than in the respective C. dubliniensis strains. These data suggest that C. albicans is better protected from oxidative stress than C. dubliniensis and that fluconazole, like amphotericin B, can induce oxidative stress in Candida; oxidative stress induces an adaptive response that results in a coordinated increase in catalase and SOD activities.

A Welcome Chink in Drug Resistance

Given the alarming news about drug-resistant super bugs, it's a relief to know that at least one drug still works even after 50 years of clinical use. Even better, researchers think they finally know why. The drug is amphotericin B and it kills the fungus Candida albicans, a common hospital-acquired infection that can be life-threatening. In this issue of PLOS Biology, Lindquist and colleagues show that amphotericin B-resistant Candida strains have a hard time surviving on their own, let alone against the defenses of a mammalian host. Normal Candida (left) forms filaments when stimulated, but amphotericin B-resistant erg2 mutants (right) are “impotent.” Amphotericin B binds a cholesterol-like component of fungal cell membranes called ergosterol, thereby punching holes in the membrane and killing the cell. The drug is no longer the go-to treatment for Candida because it can have nasty side-effects, including fever, tremors, and kidney failure. However, because Candida infections often resist modern antifungals, amphotericin B remains a common treatment today. While extremely rare, a few strains of Candida resist amphotericin B. Previous work linked this resistance to mutations in genes (ERG3 and ERG11) for enzymes required to make ergosterol. In the new study, genomic analysis of two resistant strains from patients confirmed the involvement of ERG3 and ERG11, and also added a third gene (ERG2) for an enzyme in the ergosterol pathway. To find more mutations that cause amphotericin B resistance, Lindquist and colleagues used rapid evolution techniques to make a new Candida strain that survives this drug. In keeping with the resistant strains from patients, this laboratory-developed resistant strain has a mutation in yet another gene (ERG6) involved in making ergosterol. To solve the mystery of amphotericin B's effectiveness after so many years of clinical use, the researchers investigated Hsp90, a protein that that helps other proteins keep their shapes. Previous experiments have suggested critical roles for Hsp90 in the acquisition of novel traits in species ranging from yeast and plants to fruit flies and humans with tumors. Hsp90 inhibitors block many routes by which pathogenic fungi evolve resistance to triazoles and echinocandins, the current drugs of choice for Candida, and likewise overcome resistance in strains that have lost sensitivity to these drugs. The authors found that the same is true for amphotericin B resistance. But to their surprise, Lindquist and colleagues found that Hsp90 inhibitors also devastate the amphotericin B-resistant strains — even in the absence of treatment with the drug. Because Hsp90 helps stress-response proteins fold properly, the researchers thought stress pathways might be involved. Indeed, while normally activated only during duress, several stress pathways were on all the time in the amphotericin B-resistant strains. These pathways included iron starvation and oxidative stress, both of which are linked to the integrity of fungal membranes. The next step was to confirm that amphotericin B-resistant Candida strains need Hsp90 to stabilize their stress-response proteins. Several fungal stress-response proteins are known to depend on Hsp90 and, as expected, inhibiting these proteins kept the amphotericin B-resistant strains from growing. After showing that amphotericin B resistance goes hand-in-hand with constant stress response, the researchers asked if this internal stress rendered mutant Candida strains helpless to external stresses that come from their host, including fever and attacks to the immune system.. Again, as expected, the amphotericin B-resistant strains hardly grew at elevated temperatures and were hypersensitive to neutrophil attacks. But that's not all. Amphotericin B resistance also comes with a fungal analog of impotence. While Candida normally invades its hosts with long, slender hyphae, the resistant strains hardly made these filaments and could barely penetrate a layer of cultured human skin cells. On top of these findings, mice that were particularly susceptible to Candida quickly succumbed to a wild-type strain, yet survived the amphotericin B-resistant strains. This work offers a solution to the long-standing evolutionary puzzle of why Candida has yet to develop resistance to amphotericin B. The results also suggest that new analogs of amphotericin with fewer side effects to patients would have long-lasting therapeutic value. Further, these findings could help anticipate and sidestep the resistance that currently seems inevitable with new antibiotics. For example, we can now design enzyme inhibitors to withstand point mutations, and microbes that become resistant to these designer compounds may, like amphotericin B-resistant Candida, find that the cost is too high. As the case of Candida and amphotericin B shows, what doesn't kill you won't necessarily make you stronger. Vincent BM, Lancaster AK, Scherz-Shouval R, Whitesell L, Lindquist S (2013) Fitness Trade-offs Restrict the Evolution of Resistance to Amphotericin B. doi:10.1371/journal.pbio.1001692 http://www.plosbiology.org/article/info:doi/10.1371/journal.pmed.1001692

Celebesides A-C and theopapuamides B-D, depsipeptides from an Indonesian sponge that inhibit HIV-1 entry.

Six new depsipeptides belonging to two different structural classes, termed celebesides A-C and theopapuamides B-D, have been isolated from the marine sponge Siliquariaspongia mirabilis. Their structures were determined using extensive 2D NMR and ESI-MS/MS techniques. Celebesides are unusual cyclic depsipeptides that comprise a polyketide moiety and five amino acid residues, including an uncommon 3-carbamoyl threonine, and a phosphoserine residue in celebesides A and B. Theopapuamides B-D are undecapeptides with an N-terminal fatty acid moiety containing two previously unreported amino acids, 3-acetamido-2-aminopropanoic acid and 4-amino-2,3-dihydroxy-5-methylhexanoic acid. The relative configuration of the polyketide moiety in celebesides was resolved by J-based analysis and quantum mechanical calculations, the results of which were self-consistent. Celebeside A neutralized HIV-1 in a single-round infectivity assay with an IC(50) value of 1.9 +/- 0.4 microg/mL while the nonphosphorylated analog celebeside C was inactive at concentrations as high as 50 microg/mL. Theopapuamides A-C showed cytotoxicity against human colon carcinoma (HCT-116) cells with IC(50) values between 2.1 and 4.0 microg/mL and exhibited strong antifungal activity against wildtype and amphotericin B-resistant strains of Candida albicans at loads of 1-5 microg/disk.

Eurysterols A and B, Cytotoxic and Antifungal Steroidal Sulfates from a Marine Sponge of the Genus Euryspongia

Two new steroidal sulfates, eurysterols A (1) and B (2), were isolated from an undescribed marine sponge of the genus Euryspongia collected in Palau. The structures of the new compounds were assigned by NMR spectroscopic data interpretation. Compounds 1 and 2 showed cytotoxicity against human colon carcinoma (HCT-116) cells with IC50 values of 2.9 and 14.3 microg/mL, respectively, and exhibited antifungal activity against amphotericin B-resistant and wild-type strains of Candida albicans with MIC values, in turn, of 15.6 and 62.5 microg/mL.

Candida albicans mutations in the ergosterol biosynthetic pathway and resistance to several antifungal agents.

The role of sterol mutations in the resistance of Candida albicans to antifungal agents has not been thoroughly investigated. Previous work reported that clinical C. albicans strains resistant to both azole antifungals and amphotericin B were defective in ERG3, a gene encoding sterol Delta(5,6)-desaturase. It is also believed that a deletion of the lanosterol 14alpha-demethylase gene, ERG11, is possible only under aerobic conditions when ERG3 is not functional. We tested these hypotheses by creating mutants by targeted deletion of the ERG3 and ERG11 genes and subjecting those mutants to antifungal susceptibility testing and sterol analysis. The homozygous erg3/erg3 mutant created, DSY1751, was resistant to azole derivatives, as expected. This mutant was, however, slightly more susceptible to amphotericin B than the parent wild type. It was possible to generate erg11/erg11 mutants in the DSY1751 background but also, surprisingly, in the background of a wild-type isolate with functional ERG3 alleles under aerobic conditions. This mutant (DSY1769) was obtained by exposure of an ERG11/erg11 heterozygous strain in a medium containing 10 micro g of amphotericin B per ml. Amphotericin B-resistant strains were obtained only from ERG11/erg11 heterozygotes at a frequency of approximately 5 x 10(-5) to 7 x 10(-5), which was consistent with mitotic recombination between the first disrupted erg11 allele and the other remaining functional ERG11 allele. DSY1769 was also resistant to azole derivatives. The main sterol fraction in DSY1769 contained lanosterol and eburicol. These studies showed that erg11/erg11 mutants of a C. albicans strain harboring a defective erg11 allele can be obtained in vitro in the presence of amphotericin B. Amphotericin B-resistant strains could therefore be selected by similar mechanisms during antifungal therapy.

DEVELOPMENT OF RESISTANCE TO POLYENE ANTIBIOTICS IN CANDIDA ALBICANS.

Hebeka, Elias K. (Rutgers, The State University, New Brunswick, N.J.), and Morris Solotorovsky. Development of resistance to polyene antibiotics in Candida albicans. J. Bacteriol. 89:1533-1539. 1965.-Strains of Candida albicans resistant to the polyenes candidin and amphotericin B, but not to nystatin, were developed by sub-culturing the organism in gradually increasing concentrations of the antibiotic in broth on a shaker, or by repeated transfer on gradient plates. Demonstration of resistance on solid media was best observed when a purified agar, Ionagar no. 2 (Oxoid), was used in preparing the medium. Strains that were 150-fold resistant to candidin, and 4-, 16-, 45-, and 60-fold resistant to amphotericin B were developed. The degree of resistance depended on the strain, the type of medium, and, most importantly, on the antibiotic used. The polyenes candidin, amphotericin B, nystatin, and fungimycin and the nonpolyenes griseofulvin and eulicin were used to extend the scope of study of cross-resistance. Cells rendered resistant to candidin were also resistant to amphotericin B, but not to nystatin, fungimycin, or griseofulvin. Cells rendered resistant to amphotericin B showed cross-resistance to candidin, but not to nystatin, fungimycin, or griseofulvin. Candidinor amphotericin B-resistant strains were more sensitive to eulicin than their parent strains. Increased resistance to candidin or amphotericin B was accompanied by a decrease in virulence for mice, the rate of growth, the ability to reduce bismuth sulfite, and by an increased tendency for filamentation. No change in the ability to form chlamydospores was noticed.