A Four-Hour Carbapenem Inactivation Method (CIM B.S ) Using Bacillus stearothermophilus as Indicator Strain.

Objectives: There is an urgent need for accurate and fast diagnostic tests to identify carbapenemase-producing bacteria. Here we used Bacillus stearothermophilus as an indicator strain in the format of the carbapenem inactivation method (CIM) procedure to develop a rapid carbapenemase phenotype detection method: CIMB.S. Methods: The CIMB.S test was derived from the mCIM, where B. stearothermophilus replaced Escherichia coli as the indicator strain. The test bacteria were incubated in the presence of imipenem for 30 min, and then, aliquots were placed on colorimetric plates, and incubation was continued for 3.5 h at 60°C. We examined 134 clinical strains to evaluate the CIMB.S performance. Results: The CIMB.S can be completed in 4 h, and we successfully identified 38/39 (97.4%) carbapenemase-producing Enterobacteriaceae, including 17/18 (94.4%) carbapenemase-producing Pseudomonas aeruginosa and 18/19 (94.7%) carbapenemase-producing Acinetobacter baumannii. All non-carbapenemase producers we tested were negative and included Enterobacteriaceae (n = 36), P. aeruginosa (n = 17), and A. baumannii (n = 5). Conclusions: The CIMB.S test is a rapid carbapenemase phenotype detection method requiring only 4 h of total work time and displays high sensitivity and specificity.

Rapid detection of plasmid-mediated high-level tigecycline resistance in Escherichia coli and Acinetobacter spp.

OBJECTIVES: The emergence and spread of plasmid-encoded tet(X3/X4) genes that confer high-level tigecycline and eravacycline resistance in Escherichia coli and Acinetobacter spp. pose serious threats to human and animal health. We developed a rapid and robust assay to detect Tet(X3/X4) in Gram-negative bacteria based on eravacycline degradation by the presence of the Tet(X) enzyme in the test strain. METHODS: This tetracycline inactivation method (TIM) is based on the degradation of eravacycline by the Tet(X3/X4)-producing strain, which results in reduced eravacycline activity against an acid-producing thermophile Bacillus stearothermophilus indicator strain. For Tet(X)-negative strains, eravacycline retains its antimicrobial activity. Coupled with a pH-sensitive dye (bromocresol purple), the reduced colorimetric inhibition zone can be measured to determine the production of Tet(X3/X4). One hundred and eighteen isolates, including 30 tet(X4)-positive E. coli, 30 tet(X3)-positive Acinetobacter spp. and 58 tet(X)-negative E. coli and Acinetobacter spp., were examined to evaluate the performance of this TIM. RESULTS: The sensitivity and specificity for E. coli carrying tet(X4) was 96.7% and 100%, respectively, and for Acinetobacter spp. carrying tet(X3) both were 100%. The TIM assay can be completed within 6.5 h. CONCLUSIONS: The TIM is a simple, rapid and cost-effective method for the detection of plasmid-mediated high-level tigecycline resistance in E. coli and Acinetobacter spp.

Nitrofurantoin Combined With Amikacin: A Promising Alternative Strategy for Combating MDR Uropathogenic Escherichia coli.

Urinary tract infections (UTI) are common infections that can be mild to life threatening. However, increased bacterial resistance and poor patient compliance rates have limited the effectiveness of conventional antibiotic therapies. Here, we investigated the relationship between nitrofurantoin and amikacin against 12 clinical MDR uropathogenic Escherichia coli (UPEC) strains both in vitro and in an experimental Galleria mellonella model. In vitro synergistic effects were observed in all 12 test strains by standard checkerboard and time-kill assays. Importantly, amikacin or nitrofurantoin at half of the clinical doses were not effective in the treatment of UPEC infections in the G. mellonella model but the combination therapy significantly increased G. mellonella survival from infections caused by all 12 study UPEC strains. Taken together, these results demonstrated synergy effects between nitrofurantoin and amikacin against MDR UPEC.