Distribution of Aspergillus species and prevalence of azole resistance in clinical and environmental samples from a Spanish hospital during a three-year study period

BACKGROUND

Surveillance studies are crucial for updating trends in Aspergillus species and antifungal susceptibility information.

OBJECTIVES

Determine the Aspergillus species distribution and azole resistance prevalence during this 3-year prospective surveillance study in a Spanish hospital.

MATERIALS AND METHODS

Three hundred thirty-five Aspergillus spp. clinical and environmental isolates were collected during a 3-year study. All isolates were screened for azole resistance using an agar-based screening method and resistance was confirmed by EUCAST antifungal susceptibility testing. The azole resistance mechanism was confirmed by sequencing the cyp51A gene and its promoter. All Aspergillus fumigatus strains were genotyped using TRESPERG analysis.

RESULTS

Aspergillus fumigatus was the predominant species recovered with a total of 174 strains (51.94%). The rest of Aspergillus spp. were less frequent: Aspergillus niger (14.93%), Aspergillus terreus (9.55%), Aspergillus flavus (8.36%), Aspergillus nidulans (5.37%) and Aspergillus lentulus (3.28%), among other Aspergillus species (6.57%). TRESPERG analysis showed 99 different genotypes, with 72.73% of the strains being represented as a single genotype. Some genotypes were common among clinical and environmental A. fumigatus azole-susceptible strains, even when isolated months apart. We describe the occurrence of two azole-resistant A. fumigatus strains, one clinical and another environmental, that were genotypically different and did not share genotypes with any of the azole-susceptible strains.

CONCLUSIONS

Aspergillus fumigatus strains showed a very diverse population although several genotypes were shared among clinical and environmental strains. The isolation of azole-resistant strains from both settings suggest that an efficient analysis of clinical and environmental sources must be done to detect azole resistance in A. fumigatus.

An expanded agar-based screening method for azole-resistant Aspergillus fumigatus

Antifungal susceptibility testing is an essential tool for guiding antifungal therapy. Reference methods are complex and usually only available in specialised laboratories. We have designed an expanded agar-based screening method for the detection of azole-resistant Aspergillus fumigatus isolates. Normally, identification of resistance mechanisms is obtained only after sequencing the cyp51A gene and promoter. However, our screening method provides azole resistance detection and presumptive resistance mechanisms identification. A previous agar-based method consisting of four wells containing voriconazole, itraconazole, posaconazole and a growth control, detected azole resistance to clinical azoles. Here, we have modified the concentrations of voriconazole and posaconazole to adapt to the updated EUCAST breakpoints against A. fumigatus. We have also expanded the method to include environmental azoles to assess azole resistance and the azole resistance mechanism involved. We used a collection of A. fumigatus including 54 azole-resistant isolates with Cyp51A modifications (G54, M220, G448S, TR₅₃ , TR₃₄ /L98H, TR₄₆ /Y121F/T289A, TR₃₄ /L98H/S297T/F495I), and 50 azole susceptible isolates with wild-type Cyp51A. The screening method detects azole-resistant A. fumigatus isolates when there is growth in any of the azole-containing wells after 48h. The growth pattern in the seven azoles tested helps determine the underlying azole resistance mechanism. This approach is designed for surveillance screening of A. fumigatus azole-resistant isolates and can be useful for the clinical management of patients prior to antifungal susceptibility testing confirmation.

Are Point Mutations in HMG-CoA Reductases (Hmg1 and Hmg2) a Step towards Azole Resistance in Aspergillus fumigatus?

Invasive aspergillosis, mainly caused by Aspergillus fumigatus, can lead to severe clinical outcomes in immunocompromised individuals. Antifungal treatment, based on the use of azoles, is crucial to increase survival rates. However, the recent emergence of azole-resistant A. fumigatus isolates is affecting the efficacy of the clinical therapy and lowering the success rate of azole strategies against aspergillosis. Azole resistance mechanisms described to date are mainly associated with mutations in the azole target gene cyp51A that entail structural changes in Cyp51A or overexpression of the gene. However, strains lacking cyp51A modifications but resistant to clinical azoles have recently been detected. Some genes have been proposed as new players in azole resistance. In this study, the gene hmg1, recently related to azole resistance, and its paralogue hmg2 were studied in a collection of fifteen azole-resistant strains without cyp51A modifications. Both genes encode HMG-CoA reductases and are involved in the ergosterol biosynthesis. Several mutations located in the sterol sensing domain (SSD) of Hmg1 (D242Y, G307D/S, P309L, K319Q, Y368H, F390L and I412T) and Hmg2 (I235S, V303A, I312S, I360F and V397C) were detected. The role of these mutations in conferring azole resistance is discussed in this work.

A Cyp51B Mutation Contributes to Azole Resistance in Aspergillus fumigatus

The emergence and spread of Aspergillus fumigatus azole resistance has been acknowledged worldwide. The main problem of azole resistance is the limited therapeutic options for patients suffering aspergillosis. Azole resistance mechanisms have been mostly linked to the enzyme Cyp51A, a target of azole drugs, with a wide variety of modifications responsible for the different resistance mechanisms described to date. However, there are increasing reports of A. fumigatus strains showing azole resistance without Cyp51A modifications, and thus, novel resistance mechanisms are being explored. Here, we characterized two isogenic A. fumigatus clinical strains isolated two years apart from the same patient. Both strains were resistant to clinical azoles but showed different azole resistance mechanisms. One strain (CM8940) harbored a previously described G54A mutation in Cyp51A while the other strain (CM9640) had a novel G457S mutation in Cyp51B, the other target of azoles. In addition, this second strain had a F390L mutation in Hmg1. CM9640 showed higher levels of gene expression of cyp51A, cyp51B and hmg1 than the CM8940 strain. The role of the novel mutation found in Cyp51B together with the contribution of a mutation in Hmg1 in azole resistance is discussed.

Point Mutations in the 14-α Sterol Demethylase Cyp51A or Cyp51C Could Contribute to Azole Resistance in Aspergillus flavus

Infections caused by Aspergillus species are being increasingly reported. Aspergillus flavus is the second most common species within this genus causing invasive infections in humans, and isolates showing azole resistance have been recently described. A. flavus has three cyp51-related genes (cyp51A, cyp51B, and cyp51C) encoding 14-α sterol demethylase-like enzymes which are the target of azole drugs. In order to study triazole drug resistance in A. flavus, three strains showing reduced azole susceptibility and 17 azole susceptible isolates were compared. The three cyp51-related genes were amplified and sequenced. A comparison of the deduced Cyp51A, Cyp51B, and Cyp51C protein sequences with other protein sequences from orthologous genes in different filamentous fungi led to a protein identity that ranged from 50% to 80%. Cyp51A and Cyp51C presented several synonymous and non-synonymous point mutations among both susceptible and non-susceptible strains. However, two amino acid mutations were present only in two resistant isolates: one strain harbored a P214L substitution in Cyp51A, and another a H349R in Cyp51C that also showed an increase of cyp51A and cyp51C gene expression compared to the susceptible strain ATCC2004304. Isolates that showed reduced in vitro susceptibility to clinical azoles exhibited a different susceptibility profile to demethylation inhibitors (DMIs). Although P214L substitution might contribute to azole resistance, the role of H349R substitution together with changes in gene expression remains unclear.

Biofilm production is not associated with poor clinical outcome in 485 patients with Staphylococcus aureus bacteraemia

OBJECTIVES

Staphylococcus aureus biofilm may constitute a major cause of virulence. Our main objective was to analyse whether there was an association between biofilm production and poor outcome in patients with S. aureus bacteraemia.

METHODS

We studied 485 S. aureus strains isolated from the blood of patients with bacteraemia from 2012 to 2015. We assessed in vitro biomass production using crystal violet assay and metabolic activity using tetrazolium salt assay. Strains were classified in tertile ranks as follows: low biomass producers, moderate biomass producers, high biomass producers, low metabolic activity, moderate metabolic activity and high metabolic activity. We excluded from analysis strains with moderate crystal violet and tetrazolium salt values. We defined poor outcome as fulfillment of one or more of the following conditions: 30-day attributable mortality, infective endocarditis, persistent bacteraemia and recurrent bacteraemia.

RESULTS

Outcome was poor in 199 (41.0%) of 485 S. aureus bacteraemia episodes. The distribution of poor outcome with respect to biomass production and metabolic activity was as follows: low biomass producers, 36.6% vs. high biomass producers, 43.2% (p 0.26); and low metabolic activity, 43.5% vs. high metabolic activity, 36.2% (p 0.91). The presence of methicillin-resistant S. aureus was the only characteristic that was more likely to be present in the high metabolic activity group (17.4% vs. 39.3%, p < 0.001).

CONCLUSIONS

Biofilm production, as determined by any of the methods used in the present study, is not associated with poor outcome in patients with S. aureus bacteraemia.

Oxidant/antioxidant balance in isolated glomeruli and cultured mesangial cells

The mechanisms responsible for age-related glomerular sclerosis (GS) have not been clearly identified. The present experiments were aimed at assessing the importance of the oxidant/antioxidant balance in the early stages of this process. For this purpose, the renal function (biochemical and clearance studies), some characteristics of isolated glomeruli, and reactive oxygen production (superoxide anion, hydrogen peroxide) as well as the antioxidant ability (superoxide dismutase, catalase, glutathione peroxidase) of glomeruli and cultured mesangial cells were studied in 3- and 18-month-old Fischer 344 rats (YOUNG and OLD rats, respectively). OLD animals show a normal renal function, increased urine protein excretion, and augmented protein glomerular content, an indirect index of GS. Isolated glomeruli from these rats produced increased amounts of superoxide anion and hydrogen peroxide, and catalase activity was increased. The glomerular thiobarbituric acid-reactive substances (TBARS) content was higher in OLD than in YOUNG animals. Similar results were obtained in cultured mesangial cells. In summary, the present results demonstrate, at an early stage of rat GS development, an association between the functional and structural changes of this process and an increased TBARS content (likely indicative of lipid oxidative damage) at the glomerular structures as well as in cultured mesangial cells. More extensive studies are needed to confirm the nature of this association.

Heterogeneity of allergic airway responses in sheep: differences in signal transduction?

In preliminary studies we have observed that inhaled heparin blocks antigen-induced airway responses in sheep that develop only acute responses to inhaled antigen (acute responders), but not in sheep that develop both acute and later responses (dual responders). Because heparin is an antagonist of inositol triphosphate (IP3) (one of the pathways involved in stimulus-secretion-coupling in mast cells), the differential effect of inhaled heparin in acute responders and dual responders might indicate the involvement of different signaling pathways during IgE-mediated mast cell reactions. Therefore, in this study we compared the effects of heparin on antigen-induced bronchconstriction, allergic cutaneous reaction, and histamine release into bronchoalveolar lavage fluid (BAL) in sheep that develop only acute responses or dual responses to inhaled Ascaris suum antigen. Specific lung resistance (SRL) was measured in 21 sheep (eight acute responders; 13 dual responders) before and after inhalation challenge with antigen, without and after pretreatment with inhaled heparin (1,000 units/kg). Histamine in BAL was measured by RIA before and after segmental antigen challenge, without and after pretreatment with inhaled heparin (eight acute responders; eight dual responders). In acute responders, mean +/- SE SRL increased by 197 +/- 21% with antigen; this was prevented by inhaled heparin (deltaSRL = 15 +/- 7%; p < 0.05). In dual responders, inhaled heparin had no effect on antigen-induced early (deltaSRL = 328 +/- 51% versus 305 +/- 76%) or late (deltaSRL = 201 +/- 33% versus 163 +/- 15%) responses. After segmental antigen challenge, BAL mean +/- SE histamine increased from 2.09 +/- 0.8 nM to 75.4 +/- 21.1 nM in acute responders and 1.58 +/- 0.7 nM to 66.8 +/- 27.3 nM in dual responders (p < 0.01). Inhaled heparin inhibited the increase in BAL histamine by 81% in acute responders (p < 0.05) and by only 19% in dual responders (p = NS). As was seen in the airways, heparin attenuated the allergic cutaneous reaction in acute responders by 46% (p < 0.05), but it was ineffective in dual responders. In contrast, H-7, a nonspecific protein kinase C inhibitor, attenuated the cutaneous reaction in dual responders by 28% (p < 0.05), but it was ineffective in acute responders. These data suggest that heterogeneity of allergic airway response is related to difference in mast cell signal transduction; IP3 is the predominant second messenger in acute responders, whereas non-IP3 pathways may be involved in dual responders.

Inhalation of nitrous oxide expands epidural air bubbles

BACKGROUND AND OBJECTIVES

Epidural air bubbles are known to persist for more than 24 hours after injection. Nitrous oxide may cause expansion of these bubbles.

METHODS

Nine dogs were anesthetized. Ten mL air and 9 mL of iophendylate were injected into the lumbar epidural space. Control animals (n = 3) breathed halothane in 100% oxygen. Experimental animals (n = 6) breathed halothane in 70/30 nitrous oxide/oxygen. Lateral radiographs were taken before and just after injection, and again 3 hours after breathing either 70% nitrous oxide or 100% oxygen. Epidural space pressure was monitored and recorded during these 3 hours.

RESULTS

In all experimental animals, an increase in bubble size was observed. In the control animals, bubble size either remained the same or decreased. Epidural space pressure did not change in any animal.

CONCLUSIONS

Inhalation of nitrous oxide results in expansion of epidural air bubbles. This may cause displacement of epidural local anesthetics it large volumes of air are present in the epidural space.

Inhibition of antigen-induced airway and cutaneous responses by heparin: a pharmacodynamic study

We have previously shown that heparin attenuates the acute bronchoconstrictor response and immediate cutaneous reaction (ICR) to antigen in allergic sheep. In the present investigation, we studied the pharmacodynamics of the antiallergic action of heparin. Specific lung resistance (sRL) was measured in eight sheep, allergic to Ascaris suum antigen, before and 5 min after inhalation challenge with the antigen. On different experiment days, antigen challenge was repeated after pretreatment with 1) aerosol heparin (1,000 U/kg) administered < or = 20 min, 6 h, 12 h, and 24 h and 2) intravenous heparin (1,000 U/kg) administered < or = 20 min, 1 h, 6 h, and 12 h before antigen challenge. sRL increased by 374 +/- 116% (SE) above baseline with antigen alone. Both aerosol and intravenous heparin attenuated the antigen effects on sRL in a time-dependent fashion. Prolonging the lag time between pretreatment and antigen challenge decreased the inhibitory effect of aerosol heparin; delta sRL was 31 +/- 29, 99 +/- 38, 142 +/- 40, and 306 +/- 60% for < or = 20-min, 6-h, 12-h, and 24-h pretreatment protocols, respectively. In contrast, prolonging the lag time increased the inhibitory effect of intravenous heparin: delta sRL was 246 +/- 64, 66 +/- 26, and 76 +/- 32% for < or = 20 min, 1 h, and 6 h, respectively. In seven additional sheep pretreatment with intravenous heparin (1,000 U/kg) attenuated the ICR also in a time-dependent manner; the inhibitory effect of heparin on ICR to antigen was enhanced 60% by increasing the heparin pretreatment interval from 20 to 60 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunologic mast cell-mediated responses and histamine release are attenuated by heparin

Heparin has been shown to act as a competitive inhibitor of inositol 1,4,5-triphosphate (InsP3) receptors in various cell types. Because InsP3 is one of the second messengers involved in stimulus-secretion coupling in mast cells, it is possible that heparin may inhibit mast cell-mediated reactions. Therefore, in allergic sheep, we tested this hypothesis in two mast cell-mediated reactions induced by immunologic and nonimmunologic stimuli: immediate cutaneous reaction (ICR) and acute bronchoconstrictor response (ABR). In 12 sheep allergic to Ascaris suum antigen, the surface area of the skin wheal was determined 20 min after intradermal injection (0.05 ml) of increasing concentrations of specific antigen, compound 48/80, and histamine, without and after pretreatment with heparin (100, 300, or 1,000 U/kg i.v.). Antigen, compound 48/80, and histamine produced concentration-dependent increases in ICR. Heparin "partially" inhibited the ICR to antigen and compound 48/80 in a dose-dependent manner without modifying the ICR to histamine. The heparin preservative benzyl alcohol was ineffective. In 11 additional sheep, specific lung resistance was measured before and after inhalation challenges with antigen, compound 48/80, and histamine without and with aerosol heparin pretreatment (1,000 U/kg). Heparin blocked the antigen- and compound 48/80-induced bronchoconstriction without modifying the airway effects of histamine. In isolated human uterine mast cells, heparin inhibited the anti-immunoglobulin E- but not the calcium ionophore- (A23187) induced histamine release. These data suggest that heparin inhibits the ICR and ABR induced by stimuli that produce immunologic and nonimmunologic mast cell degranulation without attenuating the effects of histamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellulose acetate membrane improves some aspects of red blood cell function in haemodialysis patients

The present study was designed to evaluate the influence of two haemodialysis membranes of different biocompatibility on red blood cell function. Twelve patients were studied in two consecutive dialyses, with cuprophan and cellulose acetate. Blood was extracted at 0, 20 and 180 min after the beginning of the haemodialysis session and general haematological parameters, osmotic fragility, deformability, methaemoglobin concentration and malonyldialdehyde (MDA) red blood cell content were determined. Osmotic fragility improved with both membranes, but this improvement was more marked with cellulose acetate. MDA red blood cell content showed a tendency to increase after 3 h with cuprophan (114 +/- 11% of the basal value), whereas it tended to decrease with cellulose acetate (92 +/- 12%), the differences between the two groups being statistically significant. These results suggest that red cell function may improve by changing the characteristics of haemodialysis membranes. This phenomenon could be related to a better biocompatibility.