We hypothesized that bacterial populations growing in the absence of antibiotics will accumulate more resistance gene mutations than bacterial populations growing in the presence of antibiotics. If this is so, the prevalence of dysfunctional resistance genes (resistance pseudogenes) could provide a measure of the level of antibiotic exposure present in a given environment. As a proof-of-concept test, we assayed field strains of Escherichia coli for their resistance genotypes using a resistance gene microarray and further characterized isolates that had resistance phenotype-genotype discrepancies. We found a small but significant association between the prevalence of isolates with resistance pseudogenes and the lower antibiotic use environment of a beef cow-calf operation versus a higher antibiotic use dairy calf ranch (Fisher's exact test, P ‫؍‬ 0.044). Other significant findings include a very strong association between the dairy calf ranch isolates and phenotypes unexplained by well-known resistance genes (Fisher's exact test, P < 0.0001). Two novel resistance genes were discovered in E. coli isolates from the dairy calf ranch, one associated with resistance to aminoglycosides and one associated with resistance to trimethoprim. In addition, isolates resistant to expanded-spectrum cephalosporins but negative for bla CMY-2 had mutations in the promoter regions of the chromosomal E. coli ampC gene consistent with reported overexpression of native AmpC beta-lactamase. Similar mutations in hospital E. coli isolates have been reported worldwide. Prevalence or rates of E. coli ampC promoter mutations may be used as a marker for high expanded-spectrum cephalosporin use environments.

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After anterior cruciate ligament (ACL) injury and reconstruction, biomechanical and neuromuscular control deficits persist and 25% of those who have experienced an ACL injury will experience a second ACL rupture in the first year after returning to sports. There remains a need for improved rehabilitation and the ability to detect an individual's risk of secondary ACL rupture. Nonlinear analysis metrics, such as the largest Lyapunov exponent (LyE) can provide new biomechanical insight in this population by identifying how movement patterns evolve over time. The purpose of this study was to determine how ACL injury, ACL reconstruction (ACLR), and participation in high‐performance athletics affect control strategies, evaluated through nonlinear analysis, produced during a novel task that simulates forces generated during cutting movements. Uninjured recreational athletes, those with ACL injury who have not undergone reconstruction (ACLD [ACL deficient]), those who have undergone ACL reconstruction, and high‐performance athletes completed a task that simulates cutting forces. The LyE calculated from forces generated during this novel task was greater (ie, force control was diminished) in the involved limb of ACLD and ACLR groups when compared with healthy uninjured controls and high‐performance athletes. These data suggest that those who have experienced an ACL injury and subsequent reconstructive surgery exhibit poor force control when compared with both uninjured controls and high‐performance athletes. Clinical significance: significantly larger LyE values after ACL injury and reconstruction when compared with healthy athletes suggest a continuing deficit in force control not addressed by current rehabilitation protocols and evaluation metrics that could contribute to secondary ACL rupture.

Purpose: The external knee adduction moment (KAM) has been demonstrated to be a risk factor for the progression of knee osteoarthritis. The KAM can be changed by the relative position of the knee center, the center of pressure (COP), and the center of the mass (COM) during walking. Few previous gait analysis studies have examined whether the distance from the COM to the knee center are variables that influence the KAM or its relationship with the kinematics of the trunk and lower limbs. Therefore, the objective of this study was to clarify the relationships among the KAM, COM and other kinematic variables. Methods: Nineteen subjects with knee osteoarthritis, eighteen females and one male, with an average age of 70.9 years (range: 50-79 years) were recruited from the university hospital. The study was approved by the institutional board, and all subjects gave their written informed consent for their participation. All subjects had a radiograph taken while standing on one foot. The femorotibial joint in all radiographs was evaluated using the Kellgren and Lawrence scale (K/L). Two subjects had a K/L score of 2, nine had a K/L of 3, five had a K/L of 4. The knees with more symptoms were investigated. The average femorotibial angle (FTA) was 178.9 (range: 174-187). Gait data were collected with a six camera motion analysis system and two force plates that were time synchronized and sampled at 120 Hz and 1200 Hz, respectively. Modified Helen Hays marker sets with 31 retroreflective markers were attached. The subjects were instructed to walk on a 10 m walkway at a selfselected speed. A total of three trials with clean, single force plate strikes from the study limb were collected. The external first peak knee adduction moment in the stance phase (1st KAM), COM, the distance from the COM to the center of the knee in the frontal plane (COM-K), lateral trunk tilt, lateral pelvic tilt, adduction angle at the hip joints, toeout angle of the foot, gait width and the gait speed were analyzed. The external moment was calculated with OrthoTrak. The kinetic data were calculated using the Matlab R2009b software program. All angles were reported during the stance phase of the gait for the affected limb at the first peak knee adduction moment. Values for each gait variable were obtained by averaging them across the trials. We used Pearson correlation coefficients to examine the relationships among the 1st KAM, FTA, COM-K, trunk tilt angle, pelvic tilt angle, hip adduction angle, leg heel angle, heel floor angle and toe-out angle. We used a multiple regression analysis to evaluate the amount of variance in the 1st KAM explained by FTA, COM-K, pelvic tilt angle and toe-out angle. Results: The 1st KAM was significantly correlated with the COM-K (r¼0.64, p¼0.014) and the pelvic tilt angle (r¼-0.458, p¼0.043). The COM-K was also significantly correlated with the trunk tilt angle (r¼-0.46, p¼0.040) and hip adductor angle (r¼-0.60, p¼0.005). In a multiple regression analysis, the COM-K and pelvic tilt angle were independently correlated w...

Control of shear ground reaction forces (sGRF) is important in performing running and cutting tasks as poor sGRF control has implications for those with knee injuries, such as anterior cruciate ligament (ACL) ruptures. The goal of this study was to develop a novel and safe task to evaluate control or accurate modulation of shear ground reaction forces related to those generated during cutting. Our approach utilized a force control task using real-time visual feedback of a subject’s force production and evaluated control capabilities through accuracy and divergence measurements. Ten healthy recreational athletes completed the force control task while force control via accuracy measures and divergence calculations was investigated. Participants were able to accurately control sGRF in multiple directions based on error measurements. Forces generated during the task were equal to or greater than those measured during a number of functional activities. We found no significant difference in the divergence of the force profiles using the Lyapunov Exponent of the sGRF trajectories. Participants using our approach produced high accuracy and low divergence force profiles and functional force magnitudes. Moving forward, we will utilize this task in at-risk populations who are unable to complete a cutting maneuver in early stages of rehabilitation, such as ACL deficient and newly reconstructed individuals, allowing insight into force control not obtainable otherwise.