Species distribution and antifungal susceptibility of clinical Aspergillus isolates: A multicentre study in Taiwan, 2016-2020.

BACKGROUND: Epidemiological knowledge is important to guide antifungal therapy. OBJECTIVE: This multicentre study aimed to investigate the species distribution and antifungal susceptibility of Aspergillus isolates in Taiwan. METHOD: Four hundred and ninety-two clinical Aspergillus isolates, collected during 2016-2020, were identified by calmodulin sequencing and tested for antifungal susceptibility using CLSI M38-A3. The Cyp51A sequences of azole-resistant Aspergillus fumigatus and Aspergillus flavus isolates were analysed. RESULTS: This collection comprised 30 species from eight Aspergillus sections-Flavi (33.5%), Nigri (26.0%), Fumigati (24.2%), Terrei (10.0%), Nidulantes (5.1%), Circumdati (0.8%), Restricti (0.2%) and Aspergillus (0.2%). Sections Fumigati, Flavi and Terrei were primarily represented by A. fumigatus (99.2%), A. flavus (95.8%) and A. terreus (100%), respectively. Section Nigri comprised nine species, mostly A. welwitschiae (60.2%), A. niger (12.5%), A. brunneoviolaceus (10.9%) and A. tubingensis (10.2%). A. fumigatus (39.6%) and A. flavus (26.4%) predominated among 53 isolates from lower respiratory samples, whereas section Nigri species (46.2%) and A. terreus (29.2%) predominated among 65 isolates from ear samples. Reduced susceptibility to amphotericin B (minimal inhibitory concentration (MIC) > 1 µg/mL) was noted in A. flavus (7.0%), A. terreus (6.1%), A. nidulans and section Circumdati (A. flocculosus, A. subramanianii and A. westerdijkiae) isolates. Acquired azole resistance was observed in seven A. fumigatus (5.9%), all of which carried TR34 /L98H or TR34 /L98H/S297T/F495I mutation, and three A. flavus (1.9%), one of which carried G441S mutation. Reduced susceptibility to itraconazole (MIC >1 µg/mL) was noted in 55.5% of section Nigri isolates, mainly in A. welwitschiae, A. niger and A. tubingensis, whereas A. brunneoviolaceus, A. aculeatinus and A. japonicus were hypersusceptible to azoles. Anidulafungin was active against all isolates except for one isolate. CONCLUSIONS: This study depicted the molecular epidemiology and species-specific characteristics of Aspergillus in Taiwan, which aids in appropriate antifungal therapy and underlines the need of speciation and susceptibility testing of disease-causing Aspergillus.

Multicenter Study of Azole-Resistant Aspergillus fumigatus Clinical Isolates, Taiwan1.

In a multicenter study, we determined a prevalence rate of 4% for azole-resistant Aspergillus fumigatus in Taiwan. Resistance emerged mainly from the environment (TR34/L98H, TR34/L98H/S297T/F495I, and TR46/Y121F/T289A mutations) but occasionally during azole treatment. A high mortality rate observed for azole-resistant aspergillosis necessitates diagnostic stewardship in healthcare and antifungal stewardship in the environment.

Azole resistance in Aspergillus species in Southern Taiwan: An epidemiological surveillance study.

Poor clinical outcomes for invasive aspergillosis are associated with antifungal resistance. Performing antifungal susceptibility tests on clinically relevant Aspergillus isolates from patients and environmental regions with known azole resistance is recommended. The aim of the study was to assess the presence of azole resistance in clinical Aspergillus spp. isolates and those from hospital environments and farmlands within a 40 km radius of the hospital. Clinical Aspergillus spp. isolates were cultured, as well as environmental Aspergillus spp. isolates obtained from air samples. Samples were subcultured in azole-containing agar plates. Isolates with a positive screening test were subjected to YeastOne methods to determine their minimum inhibitory concentrations of antifungals. Resistance mechanisms were investigated in the azole-resistant Aspergillus spp. isolates. No azole-resistant clinical or environmental A flavus, A oryaze, A niger or A terreus isolates were found in the present study. All A fumigatus clinical isolates were azole-susceptible. Seven A fumigatus environmental isolates were associated with cyp51A mutations, including two that harboured TR34 /L98H mutations with S297T/F495I substitutions, two with TR34 /L98H mutations and three with TR46 /Y121F/T289A mutations. One of these isolates was collected from farmland, one was from A ward and five were from B ward. The proportion of azole-resistant A fumigatus was 10.2% (6/59) and 3.2% (1/31) in the hospital environments and the farmlands near the hospital, respectively. The results showed that azole-resistant A fumigatus existed within hospital environments. This emphasises the importance of periodic surveillance in hospital environments and monitoring for the emergence of azole-resistant A fumigatus clinical isolates.

Prevalence, mechanisms and genetic relatedness of the human pathogenic fungus Aspergillus fumigatus exhibiting resistance to medical azoles in the environment of Taiwan.

Emerging azole resistance in Aspergillus fumigatus poses a serious threat to human health. This nationwide surveillance study investigated the prevalence and molecular characteristics of azole-resistant A. fumigatus environmental isolates in Taiwan, an island country with increasing use of azole fungicides. Of the 2760 air and soil samples screened from 2014 to 2016, 451 A. fumigatus isolates were recovered from 266 samples and 34 isolates from 29 samples displayed resistance to medical azoles (itraconazole, voriconazole or posaconazole). The resistance prevalence was 10.9% and 7.5% in A. fumigatus-positive samples and isolates respectively. Most (29, 85.3%) azole-resistant isolates harboured TR34 /L98H mutations, which were widely distributed, clustered genetically with clinical isolates, and had growth rates that were similar to those of the wild-type isolates. Microsatellite genotyping revealed both the global spread of the TR34 /L98H isolates and the occurrence of TR34 /L98H/S297T/F495I isolates belonging to local microsatellite genotypes. AfuMDR3 and atrF, two efflux transporter genes, were constitutively upregulated in two individual resistant isolates without cyp51A mutations, highlighting their potential roles in azole resistance. These results emphasize the need for periodic environmental surveillance at the molecular level in regions in which azole fungicides are applied, and agricultural fungicide management strategies that generate less selective pressure should be investigated.

Comparison of the Sensititre YeastOne and CLSI M38-A2 Microdilution Methods in Determining the Activity of Amphotericin B, Itraconazole, Voriconazole, and Posaconazole against Aspergillus Species.

This study compared the YeastOne and reference CLSI M38-A2 broth microdilution methods for antifungal susceptibility testing of Aspergillus species. The MICs of antifungal agents were determined for 100 Aspergillus isolates, including 54 Aspergillus fumigatus (24 TR34/L98H isolates), 23 A. flavus, 13 A. terreus, and 10 A. niger isolates. The overall agreement (within 2 2-fold dilutions) between the two methods was 100%, 95%, 92%, and 90% for voriconazole, posaconazole, itraconazole, and amphotericin B, respectively. The voriconazole geometric mean (GM) MICs were nearly identical for all isolates using both methods, whereas the itraconazole and posaconazole GM MICs obtained using the YeastOne method were approximately 1 dilution lower than those obtained using the reference method. In contrast, the amphotericin B GM MIC obtained using the YeastOne method was 3.3-fold higher than that observed using the reference method. For the 24 A. fumigatus TR34/L98H isolates assayed, the categorical agreement (classified according to the CLSI epidemiological cutoff values) was 100%, 87.5%, and 83.3% for itraconazole, voriconazole, and posaconazole, respectively. For four A. niger isolates, the itraconazole MICs were >8 µg/ml using the M38-A2 method due to trailing growth, whereas the corresponding itraconazole MICs obtained using the YeastOne method were all ≤0.25 µg/ml without trailing growth. These data suggest that the YeastOne method can be used as an alternative for azole susceptibility testing of Aspergillus species and for detecting the A. fumigatus TR34/L98H isolates but that this method fails to detect A. niger isolates exhibiting trailing growth with itraconazole. Additionally, for isolates with azole MICs that approach or that are at susceptibility breakpoints or with high amphotericin B MICs detected using the YeastOne method, further MIC confirmation using the reference CLSI method is needed.

Azole-resistant Aspergillus fumigatus isolates carrying TR34/L98H mutations in Taiwan.

Cumulative evidence described the emergence and geographical expansion of azole-resistant A. fumigatus associated with azole treatment failure. To investigate the status of azole resistance in A. fumigatus in Taiwan, we studied 38 A. fumigatus clinical isolates cultivated from 31 patients at two teaching hospitals from 2011 to 2014. Three isolates obtained from respiratory samples of two azole-naïve patients with pulmonary aspergillosis were found to display multi-azole resistance and cross resistance to agricultural azole fungicides, and all carried TR34/L98H mutations in cyp51A gene. The prevalence rates of azole resistance were 7.9% and 6.5% based on isolates and patients respectively. A phylogenetic analysis suggested genetic diversity of the TR34/L98H isolates in Taiwan, including a unique genotype distinct from strains outside Taiwan. The result underlines the emergence of such isolates in Taiwan as well, emphasising the importance of further surveillance for azole-resistant A. fumigatus and implementation of strategies that prevent fungicide-driven resistance selection.

Rapid identification of bacteria and Candida pathogens in peritoneal dialysis effluent from patients with peritoneal dialysis-related peritonitis by use of multilocus PCR coupled with electrospray ionization mass spectrometry.

PCR coupled with electrospray ionization mass spectrometry (PCR/ESI-MS) was compared with culture for pathogen detection in peritoneal dialysis (PD)-related peritonitis. Of 21 samples of PD effluent, PCR/ESI-MS identified microorganisms in 18 (86%) samples, including Mycobacterium tuberculosis in 1 culture-negative sample. Of 15 double-positive samples, PCR/ESI-MS and culture reached levels of agreement of 100% (15/15) and 87.5% (7/8) at the genus and species levels, respectively. PCR/ESI-MS can be used for rapid pathogen detection in PD-related peritonitis.

Emerging Aspergillus lentulus infections in Taiwan: clinical and environmental surveillance.

Objectives: This study aimed to investigate the prevalence and characteristics of Aspergillus lentulus clinical and environmental isolates in Taiwan. Methods: Aspergillus isolates obtained from patients at three hospitals and from 530 soil samples across Taiwan were screened. A. lentulus, confirmed by calmodulin sequencing, was subjected to antifungal susceptibility testing and cyp51A analyses. Soil samples yielding A. lentulus were analysed for residues of 25 azole fungicides. Results: Nine A. lentulus isolates were identified, which included seven (1.2%, 7/601) isolates from three antifungal-naïve patients out of 601 Aspergillus section Fumigati clinical isolates and two (0.3%, 2/659) isolates out of 659 Aspergillus soil isolates. All isolates developed white colonies and failed to grow at 48°C. They were susceptible to anidulafungin but showed reduced susceptibility to amphotericin B (AmB), voriconazole and azole fungicides. One heart transplant recipient with proven invasive pulmonary aspergillosis (IPA) initially showed suboptimal response to voriconazole monotherapy but was cured with a combination of voriconazole-caspofungin, liposomal AmB (LAmB)-caspofungin, along with surgery, followed by voriconazole maintenance therapy. Among two critically ill patients with probable IPA, one survived with micafungin, while the other died of aspergillosis despite sequential isavuconazole and LAmB monotherapy. Clinical and environmental isolates sharing identical Cyp51A sequence are identified, matching the Cyp51A sequence of A. lentulus NIID0096. Flusilazole (0.0009 mg/kg) was detected in one soil sample. Conclusions: This study raises concerns about health threat posed by human pathogenic A. lentulus originating from natural environments and underscores the need for increased clinical and laboratory vigilance regarding A. lentulus infections.

Phylogenetic characteristics of Non-SARS human coronavirus in southern Taiwan, 2012-2013.

This study characterizes the phylogenetic relatedness of non-SARS human coronaviruses (HCoVs) in southern Taiwan by sequencing the nucleocapsid (N), spike (S), and RNA-dependent RNA polymerase (RdRp) genes directly from ten HCoV PCR-positive respiratory samples collected during 2012-2013. In the N, S1, and RdRp phylogeny, HCoV-OC43 in one and three samples was clustered with genotypes F and G, respectively, and HCoV-OC43 in sample YC101/TWN/2013 represented a recombination event between genotypes F and G. Amino acid substitutions in the S1 protein of HCoV-OC43 were also identified. In the N phylogeny, HCoV-HKU1 in one and two samples clustered with genotypes A and B, respectively, and HCoV-229E in two samples was clustered with genogroup 6. The genotypes and genogroup detected here were in line with the prevalent phylogenetic lineages reported outside of Taiwan during the contemporary period. In summary, three species of non-SARS HCoVs with different genotypes cocirculated in the community, with genetic evolution observed in HCoV-OC43.

Genome sequence of a novel human pathogen, Aeromonas aquariorum.

Aeromonas aquariorum, a recently described species, is associated with a variety of human diseases. We present here the first genome sequence of A. aquariorum strain AAk1, which was isolated as the sole pathogen from the blood of a patient with septicemia and necrotizing fasciitis.

Characterization of glycan binding specificities of influenza B viruses with correlation with hemagglutinin genotypes and clinical features.

The carbohydrate binding specificities are different among avian and human influenza A viruses and may affect the tissue tropism and transmission of these viruses. The glycan binding biology for influenza B, however, has not been systematically characterized. Glycan binding specificities of influenza B viral isolates were analyzed and correlated to hemagglutinin (HA) genotypes and clinical manifestations. A newly developed solution glycan array was applied to characterize the receptor binding specificities of influenza B virus clinical isolates from 2001 to 2007 in Taiwan. Thirty oligosaccharides which include α-2,3 and α-2,6 linkage glycans were subjected to analysis. The glycan binding patterns of 53 influenza B isolates could be categorized into three groups and were well correlated to their HA genotypes. The Yamagata-like strains predominantly bound to α-2,6-linkage glycan (24:29, 83%) while Victoria-like strains preferentially bound to both α-2,3- and α-2,6-linkage glycans (13:24, 54%). A third group of viruses bound to sulfated glycans and these all belonged to Victoria-like strains. Based on the HA sequences, Asn-163, Glu-198, Ala-202, and Lys-203 were conserved among Victoria-like strains which may influence their carbohydrate recognition. The viruses bound to dual type glycans were more likely to be associated with the development of bronchopneumonia and gastrointestinal illness than those bound only to α-2,6 sialyl glycans (P < 0.05). Glycan binding analyses provide additional information to monitor the antigenic shift, tissue tropism, and transmission capability of influenza B viruses, and will contribute to virus surveillance and vaccine strain selection.

Clinical and Microbiological Characteristics of Culture-Positive, Influenza-Associated Pulmonary Aspergillosis: A Single-Center Study in Southern Taiwan, 2016-2019.

This study delineated the characteristics of 24 (11.2%) culture-positive, influenza-associated pulmonary aspergillosis (IAPA) patients out of 215 patients with severe influenza during 2016-2019 in a medical center in southern Taiwan. Twenty (83.3%) patients did not have EORTC/MSG-defined host factors. The mean time from influenza diagnosis to Aspergillus growth was 4.4 days, and 20 (83.3%) developed IAPA within seven days after influenza diagnosis. All patients were treated in intensive care units and all but one (95.8%) received mechanical ventilation. Aspergillus tracheobronchitis was evident in 6 (31.6%) of 19 patients undergoing bronchoscopy. Positive galactomannan testing of either serum or bronchoalveolar lavage was noted in all patients. On computed tomography imaging, IAPA was characterized by peribronchial infiltrates, multiple nodules, and cavities superimposed on ground-glass opacities. Pure Aspergillus growth without bacterial co-isolation in culture was found in 17 (70.8%) patients. A. fumigatus (15, 62.5%), A. flavus (6, 25.0%), and A. terreus (4, 16.7%) were the major causative species. Three patients had mixed Aspergillus infections due to two species, and two had mixed azole-susceptible and azole-resistant A. fumigatus infection. All patients received voriconazole with an all-cause mortality of 41.6%. Of 14 survivors, the mean duration of antifungal use was 40.5 days. In conclusion, IAPA is an early and rapidly deteriorating complication following influenza that necessitates clinical vigilance and prompt diagnostic workup.

Appearance of intratypic recombination of enterovirus 71 in Taiwan from 2002 to 2005.

Genetic recombination is a well-known phenomenon for enteroviruses. In this study, we determined the phylogenetic relationships of five distinct regions of the EV71 genome for 73 EV71 isolates from 1986 and from 1998 to 2005 in Taiwan. Phylogenetic analyses showed that the 5'-UTR, VP4-VP2, VP1, and 3D regions of EV71 isolated in 2004 and 2005 were grouped into genotype C. However, the 2B region of these isolates differed in that it grouped with genotype B, indicating recombination within EV71 had occurred. This intratypic recombination was first seen in 2002 and became predominant in 2004 and 2005. The simplot and bootscan analyses identified two recombination points located at the 3'-termini of the 2A and 3C regions. This intratypic recombination was identified among naturally circulating EV71 isolates in Taiwan, therefore, it suggests that nonstructural genes may recombine to produce new EV71 variants.

Clinical features of children infected with different strains of influenza B in southern Taiwan.

BACKGROUND: This study was designed to determine the clinical characteristics of children infected with different strains of influenza B viruses isolated in southern Taiwan. The clinical features were compared with influenza A infection occurring in the same period. METHODS: All children enrolled in the study had laboratory-confirmed infection with influenza A or B viruses. Influenza B speciation was performed by RNA extraction, cDNA synthesis, and amplification by polymerase chain reaction and sequencing. Demographic data, clinical findings, diagnoses, and outcomes were obtained. RESULTS: During the study period, 163 strains of influenza A and 118 strains of influenza B were isolated. The Yamagata-like strains were most prevalent in 2001. New reassortant strains were identified since 2002 and became predominant in 2005 and 2006. Children with influenza B were more likely than those with influenza A to be diagnosed as upper respiratory tract infection, myositis, and gastroenteritis (P < 0.05). Children infected with Yamagata-like strains were more likely to develop lower respiratory tract infection (P < 0.05) and accounted for all cases of invasive disease. Children infected with the Victoria-like group had the longest hospital stays associated with severe bacterial superinfection. CONCLUSIONS: Currently new reassortant influenza B viruses are the predominant strains circulating in southern Taiwan. There is considerable similarity of clinical features between influenza A and B in children. The Yamagata-like strains were associated with more invasive infections. Continuous influenza virus surveillance is essential particularly in Taiwan where pandemic strains tend to appear earlier than in other countries.

Co-circulating genetically divergent A2 human metapneumovirus strains among children in southern Taiwan.

An outbreak of human metapneumovirus (hMPV) among children in southern Taiwan in 2004 prompted the investigation of the molecular epidemiology of hMPV from September 2003 to August 2005. Respiratory specimens that were culture negative for a panel of respiratory viruses were examined for the presence of hMPV by RT-PCR. The results indicated that 59 out of 546 (10.8%) children were hMPV-positive. The majority of these hMPV-positive children were less than 2 years old (59.4%), females (61%), and inpatients (67.8%). Infections occurred throughout the year, but peaked during the spring and/or summer months. Sequence analysis of the fusion gene from the isolates revealed two phylogenetic groups with five possible lineages (A1, A2a/A2b, B1, and B2). Among these co-circulating strains, A2 strains were most frequently observed and demonstrated the greatest divergence. Deduced amino acid sequence analysis identified several variant amino acids specific to the A2 lineage. Lineage-specific amino acid substitutions were noted at aa233, aa286, aa312, aa348, and aa296. This study indicated that genetically divergent strains of hMPV which caused respiratory disease and hospitalization were circulating among children in Taiwan.

Genome Sequences of Three Helicobacter pylori Strains from Patients with Gastric Mucosa-Associated Lymphoid Tissue Lymphoma.

Most of the published complete genome sequences of Helicobacter pylori strains are limited to clinical isolates associated with gastritis, peptic ulcers, or gastric cancer. The genome sequences of three H. pylori strains isolated from patients with gastric mucosa-associated lymphoid tissue (MALT) lymphoma are presented here to facilitate studies of H. pylori-associated MALT lymphomagenesis.

Viral Respiratory Tract Infections in Adult Patients Attending Outpatient and Emergency Departments, Taiwan, 2012-2013: A PCR/Electrospray Ionization Mass Spectrometry Study.

Viral etiologies of respiratory tract infections (RTIs) have been less studied in adult than in pediatric populations. Furthermore, the ability of PCR/electrospray ionization mass spectrometry (PCR/ESI-MS) to detect enteroviruses and rhinoviruses in respiratory samples has not been well evaluated. We sought to use PCR/ESI-MS to comprehensively investigate the viral epidemiology of adult RTIs, including testing for rhinoviruses and enteroviruses. Nasopharyngeal or throat swabs from 267 adults with acute RTIs (212 upper RTIs and 55 lower RTIs) who visited a local clinic or the outpatient or emergency departments of a medical center in Taiwan between October 2012 and June 2013 were tested for respiratory viruses by both virus isolation and PCR/ESI-MS. Throat swabs from 15 patients with bacterial infections and 27 individuals without active infections were included as control samples. Respiratory viruses were found in 23.6%, 47.2%, and 47.9% of the 267 cases by virus isolation, PCR/ESI-MS, and both methods, respectively. When both methods were used, the influenza A virus (24.3%) and rhinoviruses (9.4%) were the most frequently identified viruses, whereas human coronaviruses, human metapneumovirus (hMPV), enteroviruses, adenoviruses, respiratory syncytial virus, and parainfluenza viruses were identified in small proportions of cases (<5% of cases for each type of virus). Coinfection was observed in 4.1% of cases. In the control group, only 1 (2.4%) sample tested positive for a respiratory virus by PCR/ESI-MS. Patients who were undergoing steroid treatment, had an active malignancy, or suffered from chronic obstructive pulmonary disease (COPD) were at risk for rhinovirus, hMPV, or parainfluenza infections, respectively. Overall, immunocompromised patients, patients with COPD, and patients receiving dialysis were at risk for noninfluenza respiratory virus infection. Rhinoviruses (12.7%), influenza A virus (10.9%), and parainfluenza viruses (7.3%) were the most common viruses involved in the 55 cases of lower RTIs. The factors of parainfluenza infection, old age, and immunosuppression were independently associated with lower RTIs. In conclusion, PCR/ESI-MS improved the diagnostic yield for viral RTIs. Non-influenza respiratory virus infections were associated with patients with comorbidities and with lower RTIs. Additional studies that delineate the clinical need for including non-influenza respiratory viruses in the diagnostic work-up in these populations are warranted.

Clinical implications of species identification in monomicrobial Aeromonas bacteremia.

BACKGROUND: Advances in Aeromonas taxonomy have led to the reclassification of aeromonads. Hereon, we aimed to re-evaluate the characteristics of Aeromonas bacteremia, including those of a novel species, Aeromonas dhakensis. METHODOLOGY/PRINCIPAL FINDINGS: A retrospective study of monomicrobial Aeromonas bacteremia at a medical center in southern Taiwan from 2004-2011 was conducted. Species identification was based on rpoB sequencing. Of bacteremia of 153 eligible patients, A. veronii (50 isolates, 32.7%), A. dhakensis (48, 31.4%), A. caviae (43, 28.1%), and A. hydrophila (10, 6.5%) were the principal causative species. A. dhakensis and A. veronii bacteremia were mainly community-acquired and presented as primary bacteremia, spontaneous bacterial peritonitis, or skin and soft-tissue infection, whereas A. caviae was associated with hospital-onset bacteremia. The distribution of the AmpC ß-lactamase and metallo-ß-lactamase genes was species-specific: bla(AQU-1), bla(MOX), or bla(CepH) was present in A. dhakensis, A. caviae, or A. hydrophila, respectively, and bla(CphA) was present in A. veronii, A. dhakensis, and A. hydrophila. The cefotaxime resistance rates of the A. caviae, A. dhakensis, and A. hydrophila isolates were higher than that of A. veronii (39.5%%, 25.0%, and 30% vs. 2%, respectively). A. dhakensis bacteremia was linked to the highest 14-day sepsis-related mortality rate, followed by A. hydrophila, A. veronii, and A. caviae bacteremia (25.5%, 22.2%, 14.0%, and 4.7%, respectively; P = 0.048). Multivariate analysis revealed that A. dhakensis bacteremia, active malignancies, and a Pitt bacteremia score ≥ 4 was an independent mortality risk factor. CONCLUSIONS/SIGNIFICANCE: Characteristics of Aeromonas bacteremia vary between species. A. dhakensis prevalence and its associated poor outcomes suggest it an important human pathogen.

Genome Sequence of Aeromonas taiwanensis LMG 24683T, a Clinical Wound Isolate from Taiwan.

Aeromonas taiwanensis was first described in 2010 on the basis of one clinical wound isolate (strain LMG 24683(T) = A2-50(T) = CECT 7403(T)) from Taiwan. We present here the genome sequence of A. taiwanensis LMG 24683(T), which carries several genes encoding virulence determinants and Ambler class C and D ß-lactamases.