The effect of intestinal microbiota dysbiosis on growth and detection of carbapenemase-producing Enterobacterales within an in vitro gut model

BACKGROUND

Carbapenemase-producing Enterobacterales (CPE) can colonize the gut and are of major clinical concern. Identification of CPE colonization is problematic; there is no gold-standard detection method, and the effects of antibiotic exposure and microbiota dysbiosis on detection are unknown.

AIM

Based on a national survey we selected four CPE screening assays in common use. We used a clinically reflective in vitro model of human gut microbiota to investigate the performance of each test to detect three different CPE strains under different, clinically relevant antibiotic exposures.

METHODS

Twelve gut models were seeded with a pooled faecal slurry and exposed to CPE either before, after, concomitant with, or in the absence of piperacillin-tazobactam (358 mg/L, 3 × daily, seven days). Total Enterobacterales and CPE populations were enumerated daily. Regular screening for CPE was performed using Cepheid Xpert® Carba-R molecular test, and with Brilliance™ CRE, Colorex™ mSuperCARBA and CHROMID® CARBA SMART agars.

FINDINGS

Detection of CPE when the microbiota are intact is problematic. Antibiotic exposure disrupts microbiota populations and allows CPE proliferation, increasing detection. The performances of assays varied, particularly with respect to different CPE strains. The Cepheid assay performed better than the three agar methods for detecting a low level of CPE within an intact microbiota, although performance of all screening methods was comparable when CPE populations increased in a disrupted microbiota.

CONCLUSION

CPE strains differed in their dynamics of colonization in an in vitro gut model and in their subsequent response to antibiotic exposure. This affected detection by molecular and screening methods, which has implications for the sensitivity of CPE screening in healthcare settings.

The effect of tendon compliance on in vitro/in vivo estimations of sarcomere length

The errors likely to result from using excised rigor muscles to determine in vivo sarcomere length ranges were calculated for mouse extensor digitorum longus muscle (EDL). This muscle was chosen because its very long tendon makes it particularly susceptible to errors arising from tendon compliance. By placing dissected limbs into different locomotory stances, and allowing them to go into rigor, the range of sarcomere lengths over which muscles operate in vivo can be determined, but it is subject to errors due to tendon compliance. A tendon compliance of 0.24 GPa and a muscle rigor stress of 35 kPa were determined, and these were used to correct the estimates of in vivo sarcomere length, under worst case conditions. The error introduced was very small: a reduction in sarcomere length of less than 0.5 %.

Tuning in to fish swimming waves: body form, swimming mode and muscle function

Most fish species swim with lateral body undulations running from head to tail. These waves run more slowly than the waves of muscle activation causing them, reflecting the effect of the interaction between the fish's body and the reactive forces from the water. The coupling between both waves depends on the lateral body shape and on the mechanical properties of the tail. During steady swimming, the length of each myotomal muscle fibre varies cyclically. The phase relationship between the strain (muscle length change) cycle and the active period (when force is generated) determines the work output of the muscle. The muscle power is converted to thrust either directly by the bending body or almost exclusively by the tail, depending upon the body shape of the species and the swimming kinematics. We have compared the kinematics and muscle activity patterns from seven species of fish with different body forms and swimming modes and propose a model which yields a consistent pattern, with at least three extremes. Subtle tuning of the phase relationship between muscle strain and activation cycles can lead to major changes in the way muscles function in different swimming modes.