Evaluation of Performance With an Adaptive Digital Remote Microphone System and a Digital Remote Microphone Audio-Streaming Accessory System

2015 ◽  
Vol 24 (3) ◽  
pp. 440-450 ◽  
Author(s):  
Jace Wolfe ◽  
Mila Morais Duke ◽  
Erin Schafer ◽  
Christine Jones ◽  
Hans E. Mülder ◽  
...  
Keyword(s):  
Speech Recognition ◽  
Hearing Aids ◽  
Good Predictor ◽  
Adaptive System ◽  
Noise Levels ◽  
Sentence Recognition ◽  
Evaluation Of Performance ◽  
High Level

Purpose One purpose of this study was to evaluate the improvement in speech recognition obtained with use of 2 different remote microphone technologies. Another purpose of this study was to determine whether a battery of audiometric measures could predict benefit from use of these technologies. Method Sentence recognition was evaluated while 17 adults used each of 2 different hearing aids. Performance was evaluated with and without 2 different remote microphone systems. A variety of audiologic measures were administered to determine whether prefitting assessment may predict benefit from remote microphone technology. Results Use of both remote microphone systems resulted in improvement in speech recognition in quiet and in noise. There were no differences in performance obtained with the 2 different remote microphone technologies in quiet and at low competing noise levels, but use of the digital adaptive remote microphone system provided better speech recognition in the presence of moderate- to high-level noise. The Listening in Spatialized Noise–Sentence Test Prescribed Gain Amplifier (Cameron & Dillon, 2010) measure served as a good predictor of benefit from remote microphone technology. Conclusions Each remote microphone system improved sentence recognition in noise, but greater improvement was obtained with the digital adaptive system. The Listening in Spatialized Noise–Sentence Test Prescribed Gain Amplifier may serve as a good indicator of benefit from remote microphone technology.

scholarly journals Multitasking with typical use of hearing aid noise reduction in older listeners

2018 ◽  
Author(s):  
Tim Schoof ◽  
Pamela Souza
Keyword(s):  
Speech Recognition ◽  
Noise Reduction ◽  
Hearing Aids ◽  
Recognition Task ◽  
Hearing Impaired ◽  
Improve Performance ◽  
Sentence Recognition ◽  
Monitoring Task ◽  
Speech In Noise ◽  
Dual Task Paradigm

Objective: Older hearing-impaired adults typically experience difficulties understanding speech in noise. Most hearing aids address this issue using digital noise reduction. While noise reduction does not necessarily improve speech recognition, it may reduce the resources required to process the speech signal. Those available resources may, in turn, aid the ability to perform another task while listening to speech (i.e., multitasking). This study examined to what extent changing the strength of digital noise reduction in hearing aids affects the ability to multitask. Design: Multitasking was measured using a dual-task paradigm, combining a speech recognition task and a visual monitoring task. The speech recognition task involved sentence recognition in the presence of six-talker babble at signal-to-noise ratios (SNRs) of 2 and 7 dB. Participants were fit with commercially-available hearing aids programmed under three noise reduction settings: off, mild, strong. Study sample: 18 hearing-impaired older adults. Results: There were no effects of noise reduction on the ability to multitask, or on the ability to recognize speech in noise. Conclusions: Adjustment of noise reduction settings in the clinic may not invariably improve performance for some tasks.

scholarly journals Differences in Word and Phoneme Recognition in Quiet, Sentence Recognition in Noise, and Subjective Outcomes between Manufacturer First-Fit and Hearing Aids Programmed to NAL-NL2 Using Real-Ear Measures

2018 ◽  
Vol 29 (08) ◽  
pp. 706-721 ◽  
Author(s):  
Michael Valente ◽  
Kristi Oeding ◽  
Alison Brockmeyer ◽  
Steven Smith ◽  
Dorina Kallogjeri
Keyword(s):  
Speech Recognition ◽  
Hearing Aids ◽  
Best Practice ◽  
Hearing Aid ◽  
Monosyllabic Word ◽  
Phoneme Recognition ◽  
Double Blind ◽  
Sentence Recognition ◽  
Subjective Outcomes ◽  
Fitting Hearing Aids

AbstractThe American Speech-Language-Hearing Association (ASHA) and American Academy of Audiology (AAA) have created Best Practice Guidelines for fitting hearing aids to adult patients. These guidelines recommend using real-ear measures (REM) to verify that measured output/gain of hearing aid(s) match a validated prescriptive target. Unfortunately, approximately 70–80% of audiologists do not routinely use REM when fitting hearing aids, instead relying on a manufacturer default “first-fit” setting. This is problematic because numerous studies report significant differences in REM between manufacturer first-fit and the same hearing aids using a REM or programmed-fit. These studies reported decreased prescribed gain/output in the higher frequencies for the first-fit compared with the programmed fit, which are important for recognizing speech. Currently, there is little research in peer-reviewed journals reporting if differences between hearing aids fitted using a manufacturer first-fit versus a programmed-fit result in significant differences in speech recognition in quiet, noise, and subjective outcomes.To examine if significant differences were present in monosyllabic word and phoneme recognition (consonant-nucleus-consonant; CNC) in quiet, sentence recognition in noise (Hearing in Noise Test; HINT), and subjective outcomes using the Abbreviated Profile of Hearing Aid Benefit (APHAB) and the Speech, Spatial and Qualities of Hearing (SSQ) questionnaires between hearing aids fit using one manufacturer’s first-fit and the same hearing aids with a programmed-fit using REM to National Acoustic Laboratories Nonlinear Version 2 (NAL-NL2) prescriptive target.A double-blind randomized crossover design was used. Throughout the study, one investigator performed all REM whereas a second investigator measured speech recognition in quiet, noise, and scored subjective outcome measures.Twenty-four adults with bilateral normal sloping to moderately severe sensorineural hearing loss with no prior experience with amplification.The hearing aids were fit using the proprietary manufacturer default first-fit and a programmed-fit to NAL-NL2 using real-ear insertion gain measures. The order of the two fittings was randomly assigned and counterbalanced. Participants acclimatized to each setting for four weeks and returned for assessment of performance via the revised CNC word lists, HINT, APHAB, and SSQ for the respective fitting.(1) A significant median advantage of 15% (p < 0.001; 95% CI: 9.7–24.3%) for words and 7.7% (p < 0.001; 95% CI: 5.9–10.9%) for phonemes for the programmed-fit compared with first-fit at 50 dB sound pressure level (SPL) and 4% (p < 0.01; 95% CI: 1.7–6.3%) for words at 65 dB SPL; (2) No significant differences for the HINT reception threshold for sentences (RTS); (3) A significant median advantage of 4.2% [p < 0.04; 95% confidence interval (CI): −0.6–13.2%] for the programmed-fit compared with the first-fit for the background noise subscale problem score for the APHAB; (4) No significant differences on the SSQ.Improved word and phoneme recognition for soft and words for average speech in quiet were reported for the programmed-fit. Seventy-nine percent of the participants preferred the programmed-fitting versus first-fit. Hearing aids, therefore, should be verified and programmed using REM to a prescriptive target versus no verification using a first-fit.

scholarly journals An Evaluation of Hearing Aid Beamforming Microphone Arrays in a Noisy Laboratory Setting

2019 ◽  
Vol 30 (02) ◽  
pp. 131-144 ◽  
Author(s):  
Erin M. Picou ◽  
Todd A. Ricketts
Keyword(s):  
Hearing Loss ◽  
Speech Recognition ◽  
Hearing Aids ◽  
Linear Models ◽  
Hearing Aid ◽  
Recognition Performance ◽  
Microphone Arrays ◽  
Laboratory Setting ◽  
Subjective Ratings ◽  
Sentence Recognition

AbstractPeople with hearing loss experience difficulty understanding speech in noisy environments. Beamforming microphone arrays in hearing aids can improve the signal-to-noise ratio (SNR) and thus also speech recognition and subjective ratings. Unilateral beamformer arrays, also known as directional microphones, accomplish this improvement using two microphones in one hearing aid. Bilateral beamformer arrays, which combine information across four microphones in a bilateral fitting, further improve the SNR. Early bilateral beamformers were static with fixed attenuation patterns. Recently adaptive, bilateral beamformers have been introduced in commercial hearing aids.The purpose of this article was to evaluate the potential benefits of adaptive unilateral and bilateral beamformers for improving sentence recognition and subjective ratings in a laboratory setting. A secondary purpose was to identify potential participant factors that explain some of the variability in beamformer benefit.Participants were fitted with study hearing aids equipped with commercially available adaptive unilateral and bilateral beamformers. Participants completed sentence recognition testing in background noise using three hearing aid settings (omnidirectional, unilateral beamformer, bilateral beamformer) and two noise source configurations (surround, side). After each condition, participants made subjective ratings of their perceived work, desire to control the situation, willingness to give up, and tiredness.Eighteen adults (50–80 yr, M = 66.2, σ = 8.6) with symmetrical mild sloping to severe hearing loss participated.Sentence recognition scores and subjective ratings were analyzed separately using generalized linear models with two within-subject factors (hearing aid microphone and noise configuration). Two benefit scores were calculated: (1) unilateral beamformer benefit (relative to performance with omnidirectional) and (2) additional bilateral beamformer benefit (relative to performance with unilateral beamformer). Hierarchical multiple linear regression was used to determine if beamformer benefit was associated with participant factors (age, degree of hearing loss, unaided speech in noise ability, spatial release from masking, and performance in omnidirectional).Sentence recognition and subjective ratings of work, control, and tiredness were better with both types of beamformers relative to the omnidirectional conditions. In addition, the bilateral beamformer offered small additional improvements relative to the unilateral beamformer in terms of sentence recognition and subjective ratings of tiredness. Speech recognition performance and subjective ratings were generally independent of noise configuration. Performance in the omnidirectional setting and pure-tone average were independently related to unilateral beamformer benefits. Those with the lowest performance or the largest degree of hearing loss benefited the most. No factors were significantly related to additional bilateral beamformer benefit.Adaptive bilateral beamformers offer additional advantages over adaptive unilateral beamformers in hearing aids. The small additional advantages with the adaptive beamformer are comparable to those reported in the literature with static beamformers. Although the additional benefits are small, they positively affected subjective ratings of tiredness. These data suggest that adaptive bilateral beamformers have the potential to improve listening in difficult situations for hearing aid users. In addition, patients who struggle the most without beamforming microphones may also benefit the most from the technology.

Evaluation of Wideband Frequency Responses and Nonlinear Frequency Compression for Children with Cookie-Bite Audiometric Configurations

2014 ◽  
Vol 25 (10) ◽  
pp. 1022-1033 ◽  
Author(s):  
Andrew John ◽  
Jace Wolfe ◽  
Susan Scollie ◽  
Erin Schafer ◽  
Mary Hudson ◽  
...  
Keyword(s):  
Hearing Loss ◽  
Speech Recognition ◽  
Hearing Aids ◽  
High Frequency ◽  
Repeated Measures ◽  
Nonsense Syllable ◽  
Nonlinear Frequency ◽  
Frequency Compression ◽  
Sentence Recognition ◽  
Phoneme Perception

Background: Previous research has suggested that use of nonlinear frequency compression (NLFC) can improve audibility for high-frequency sounds and speech recognition of children with moderate to profound high-frequency hearing loss. Furthermore, previous studies have generally found no detriment associated with the use of NLFC. However, there have been no published studies examining the effect of NLFC on the performance of children with cookie-bite audiometric configurations. For this configuration of hearing loss, frequency-lowering processing will likely move high-frequency sounds to a lower frequency range at which a greater degree of hearing loss exists. Purpose: The purpose of this study was to evaluate and compare the effects of wideband amplification and NLFC on high-frequency audibility and speech recognition of children with cookie-bite audiometric configurations. Research Design: This study consisted of a within-participant design with repeated measures across test conditions. Study Sample: Seven children, ages 6–13 yr, with cookie-bite audiometric configurations and normal hearing or mild hearing loss at 6000 and 8000 Hz, were recruited. Intervention: Participants were fitted with Phonak Nios S H2O III behind-the-ear hearing aids and Oticon Safari 300 behind-the-ear hearing aids. Data Collection: The participants were evaluated after three 4-to 6-wk intervals: (1) Phonak Nios S H2O III without NLFC, (2) Phonak Nios S H2O III with NLFC, and (3) Oticon Safari 300 with wideband frequency response extending to 8000 Hz. The order in which each technology was used was counterbalanced across participants. High-frequency audibility was evaluated by assessing aided thresholds (dB SPL) for warble tones and the high-frequency phonemes /sh/ and /s/. Speech recognition in quiet was measured with the University of Western Ontario (UWO) Plurals Test, the UWO Distinctive Features Difference (DFD) Test, and the Phoneme Perception Test vowel-consonant-vowel nonsense syllable test. Sentence recognition in noise was evaluated with the Bamford-Kowal-Bench Speech-In-Noise (BKB-SIN) Test. Analysis: Repeated-measures analyses of variance were used to analyze the data collected in this study. The results across the three different conditions were compared. Results: No difference in performance across conditions was observed for detection of high-frequency warble tones and the speech sounds /sh/ and /s/. No significant difference was seen across conditions for speech recognition in quiet when measured with the UWO Plurals Test, the UWO-DFD Test, and the Phoneme Perception Test vowel-consonant-vowel nonsense syllable test. Finally, there were also no differences across conditions on the BKB-SIN Test. Conclusions: These results suggest that NLFC does not degrade or improve audibility for and recognition of high-frequency speech sounds as well as sentence recognition in noise when compared with wideband amplification for children with cookie-bite audiometric configurations.

Comparison of Speech Recognition With Adaptive Digital and FM Remote Microphone Hearing Assistance Technology by Listeners Who Use Hearing Aids

2014 ◽  
Vol 23 (2) ◽  
pp. 201-210 ◽  
Author(s):  
Linda Thibodeau
Keyword(s):  
Speech Recognition ◽  
Hearing Aids ◽  
Real World ◽  
Digital Technology ◽  
Normal Hearing ◽  
Wireless Technology ◽  
Noisy Environment ◽  
Sentence Recognition ◽  
Wireless Signal ◽  
Speech Recognition In Noise

Purpose The purpose of this study was to compare the benefits of 3 types of remote microphone hearing assistance technology (HAT), adaptive digital broadband, adaptive frequency modulation (FM), and fixed FM, through objective and subjective measures of speech recognition in clinical and real-world settings. Method Participants included 11 adults, ages 16 to 78 years, with primarily moderate-to-severe bilateral hearing impairment (HI), who wore binaural behind-the-ear hearing aids; and 15 adults, ages 18 to 30 years, with normal hearing. Sentence recognition in quiet and in noise and subjective ratings were obtained in 3 conditions of wireless signal processing. Results Performance by the listeners with HI when using the adaptive digital technology was significantly better than that obtained with the FM technology, with the greatest benefits at the highest noise levels. The majority of listeners also preferred the digital technology when listening in a real-world noisy environment. The wireless technology allowed persons with HI to surpass persons with normal hearing in speech recognition in noise, with the greatest benefit occurring with adaptive digital technology. Conclusion The use of adaptive digital technology combined with speechreading cues would allow persons with HI to engage in communication in environments that would have otherwise not been possible with traditional wireless technology.

scholarly journals Evaluation of a Remote Microphone System with Tri-Microphone Beamformer

2020 ◽  
Vol 31 (01) ◽  
pp. 050-060 ◽  
Author(s):  
Jace Wolfe ◽  
Mila Duke ◽  
Erin Schafer ◽  
Christine Jones ◽  
Lori Rakita ◽  
...  
Keyword(s):  
Hearing Loss ◽  
Speech Recognition ◽  
Small Group ◽  
Hearing Aids ◽  
Hearing Aid ◽  
Group Learning ◽  
Learning Activities ◽  
Small Group Learning ◽  
Sentence Recognition ◽  
Percentage Points

AbstractChildren with hearing loss often experience difficulty understanding speech in noisy and reverberant classrooms. Traditional remote microphone use, in which the teacher wears a remote microphone that captures her speech and wirelessly delivers it to radio receivers coupled to a child’s hearing aids, is often ineffective for small-group listening and learning activities. A potential solution is to place a remote microphone in the middle of the desk used for small-group learning situations to capture the speech of the peers around the desk and wirelessly deliver the speech to the child’s hearing aids.The objective of this study was to compare speech recognition of children using hearing aids across three conditions: (1) hearing aid in an omnidirectional microphone mode (HA-O), (2) hearing aid with automatic activation of a directional microphone (HA-ADM) (i.e., the hearing aid automatically switches in noisy environments from omnidirectional mode to a directional mode with a cardioid polar plot pattern), and (3) HA-ADM with simultaneous use of a remote microphone (RM) in a “Small Group” mode (HA-ADM-RM). The Small Group mode is designed to pick up multiple near-field talkers. An additional objective of this study was to compare the subjective listening preferences of children between the HA-ADM and HA-ADM-RM conditions.A single-group, repeated measures design was used to evaluate performance differences obtained in the three technology conditions. Sentence recognition in noise was assessed in a classroom setting with each technology, while sentences were presented at a fixed level from three different loudspeakers surrounding a desk (0, 90, and 270° azimuth) at which the participant was seated. This arrangement was intended to simulate a small-group classroom learning activity.Fifteen children with moderate to moderately severe hearing loss.Speech recognition was evaluated in the three hearing technology conditions, and subjective auditory preference was evaluated in the HA-ADM and HA-ADM-RM conditions.The use of the remote microphone system in the Small Group mode resulted in a statistically significant improvement in sentence recognition in noise of 24 and 21 percentage points compared with the HA-O and HA-ADM conditions, respectively (individual benefit ranged from −8.6 to 61.1 and 3.4 to 44 percentage points, respectively). There was not a significant difference in sentence recognition in noise between the HA-O and HA-ADM conditions when the remote microphone system was not in use. Eleven of the 14 participants who completed the subjective rating scale reported at least a slight preference for the use of the remote microphone system in the Small Group mode.Objective and subjective measures of sentence recognition indicated that use of remote microphone technology with the Small Group mode may improve hearing performance in small-group learning activities. Sentence recognition in noise improved by 24 percentage points compared to the HA-O condition, and children expressed a preference for the use of the remote microphone Small Group technology regarding listening comfort, sound quality, speech intelligibility, background noise reduction, and overall listening experience.

scholarly journals Degree of Hearing Loss Affects Bilateral Hearing Aid Benefits in Ecologically Relevant Laboratory Conditions

2019 ◽  
Vol 62 (10) ◽  
pp. 3834-3850 ◽  
Author(s):  
Todd A. Ricketts ◽  
Erin M. Picou ◽  
James Shehorn ◽  
Andrew B. Dittberner
Keyword(s):  
Hearing Loss ◽  
Speech Recognition ◽  
Hearing Aids ◽  
Visual Cues ◽  
Hearing Aid ◽  
Recognition Performance ◽  
Listening Effort ◽  
Sentence Recognition ◽  
Predictive Variables ◽  
The Relationship

Purpose Previous evidence supports benefits of bilateral hearing aids, relative to unilateral hearing aid use, in laboratory environments using audio-only (AO) stimuli and relatively simple tasks. The purpose of this study was to evaluate bilateral hearing aid benefits in ecologically relevant laboratory settings, with and without visual cues. In addition, we evaluated the relationship between bilateral benefit and clinically viable predictive variables. Method Participants included 32 adult listeners with hearing loss ranging from mild–moderate to severe–profound. Test conditions varied by hearing aid fitting type (unilateral, bilateral) and modality (AO, audiovisual). We tested participants in complex environments that evaluated the following domains: sentence recognition, word recognition, behavioral listening effort, gross localization, and subjective ratings of spatialization. Signal-to-noise ratio was adjusted to provide similar unilateral speech recognition performance in both modalities and across procedures. Results Significant and similar bilateral benefits were measured for both modalities on all tasks except listening effort, where bilateral benefits were not identified in either modality. Predictive variables were related to bilateral benefits in some conditions. With audiovisual stimuli, increasing hearing loss, unaided speech recognition in noise, and unaided subjective spatial ability were significantly correlated with increased benefits for many outcomes. With AO stimuli, these same predictive variables were not significantly correlated with outcomes. No predictive variables were correlated with bilateral benefits for sentence recognition in either modality. Conclusions Hearing aid users can expect significant bilateral hearing aid advantages for ecologically relevant, complex laboratory tests. Although future confirmatory work is necessary, these data indicate the presence of vision strengthens the relationship between bilateral benefits and degree of hearing loss.

A Questionnaire Survey of Current Rehabilitation Practices for Adults With Normal Hearing Sensitivity Who Experience Auditory Difficulties

2020 ◽  
Vol 29 (4) ◽  
pp. 738-761
Author(s):  
Tess K. Koerner ◽  
Melissa A. Papesh ◽  
Frederick J. Gallun
Keyword(s):  
Hearing Aids ◽  
Questionnaire Survey ◽  
Patient Population ◽  
Clinical Care ◽  
Normal Hearing ◽  
Auditory Training ◽  
Training Methods ◽  
Hearing Sensitivity ◽  
Considerable Benefit ◽  
High Level

Purpose A questionnaire survey was conducted to collect information from clinical audiologists about rehabilitation options for adult patients who report significant auditory difficulties despite having normal or near-normal hearing sensitivity. This work aimed to provide more information about what audiologists are currently doing in the clinic to manage auditory difficulties in this patient population and their views on the efficacy of recommended rehabilitation methods. Method A questionnaire survey containing multiple-choice and open-ended questions was developed and disseminated online. Invitations to participate were delivered via e-mail listservs and through business cards provided at annual audiology conferences. All responses were anonymous at the time of data collection. Results Responses were collected from 209 participants. The majority of participants reported seeing at least one normal-hearing patient per month who reported significant communication difficulties. However, few respondents indicated that their location had specific protocols for the treatment of these patients. Counseling was reported as the most frequent rehabilitation method, but results revealed that audiologists across various work settings are also successfully starting to fit patients with mild-gain hearing aids. Responses indicated that patient compliance with computer-based auditory training methods was regarded as low, with patients generally preferring device-based rehabilitation options. Conclusions Results from this questionnaire survey strongly suggest that audiologists frequently see normal-hearing patients who report auditory difficulties, but that few clinicians are equipped with established protocols for diagnosis and management. While many feel that mild-gain hearing aids provide considerable benefit for these patients, very little research has been conducted to date to support the use of hearing aids or other rehabilitation options for this unique patient population. This study reveals the critical need for additional research to establish evidence-based practice guidelines that will empower clinicians to provide a high level of clinical care and effective rehabilitation strategies to these patients.

scholarly journals Periods of Excess Energy in Extreme Weather Events

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Igor G. Zurbenko ◽  
Amy L. Potrzeba-Macrina
Keyword(s):  
Atmospheric Pressure ◽  
Original Data ◽  
Extreme Weather Events ◽  
Noise Levels ◽  
Tidal Waves ◽  
Numerical Reconstruction ◽  
Weather Events ◽  
Periodic Signals ◽  
High Level ◽  
The Waves

The reconstruction of periodic signals that are embedded in noise is a very important task in many applications. This already difficult task is even more complex when some observations are missed or some are presented irregularly in time. Kolmogorov-Zurbenko (KZ) filtration, a well-developed method, offers a solution to this problem. One section of this paper provides examples of very precise reconstructions of multiple periodic signals covered with high level noise, noise levels that make those signals invisible within the original data. The ability to reconstruct signals from noisy data is applied to the numerical reconstruction of tidal waves in atmospheric pressure. The existence of such waves was proved by well-known naturalist Chapman, but due to the high synoptic fluctuation in atmospheric pressure he was unable to numerically reproduce the waves. Reconstruction of the atmospheric tidal waves reveals a potential intensification on wind speed during hurricanes, which could increase the danger imposed by hurricanes. Due to the periodic structure of the atmospheric tidal wave, it is predictable in time and space, which is important information for the prediction of excess force in developing hurricanes.

Experimental Prediction of the Evolution of Cefepime Resistance From the CMY-2 AmpC β-Lactamase

Genetics ◽  
2003 ◽  
Vol 164 (1) ◽  
pp. 23-29
Author(s):  
Miriam Barlow ◽  
Barry G Hall
Keyword(s):  
Good Predictor ◽  
Evolutionary Potential ◽  
Biochemical Activity ◽  
Class A ◽  
Naturally Occurring ◽  
Experimental Prediction ◽  
Lactam Antibiotic ◽  
High Level ◽  
Level Resistance

Abstract Understanding of the evolutionary histories of many genes has not yet allowed us to predict the evolutionary potential of those genes. Intuition suggests that current biochemical activity of gene products should be a good predictor of the potential to evolve related activities; however, we have little evidence to support that intuition. Here we use our in vitro evolution method to evaluate biochemical activity as a predictor of future evolutionary potential. Neither the class C Citrobacter freundii CMY-2 AmpC β-lactamase nor the class A TEM-1 β-lactamase confer resistance to the β-lactam antibiotic cefepime, nor do any of the naturally occurring alleles descended from them. However, the CMY-2 AmpC enzyme and some alleles descended from TEM-1 confer high-level resistance to the structurally similar ceftazidime. On the basis of the comparison of TEM-1 and CMY-2, we asked whether biochemical activity is a good predictor of the evolutionary potential of an enzyme. If it is, then CMY-2 should be more able than the TEMs to evolve the ability to confer higher levels of cefepime resistance. Although we generated CMY-2 evolvants that conferred increased cefepime resistance, we did not recover any CMY-2 evolvants that conferred resistance levels as high as the best cefepime-resistant TEM alleles.

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