法月 千尋

The number and type of metallo-β-lactamase (MΒL) are increasing over time. Carbapenem resistance conferred by MΒL is a significant threat to our antibiotic regimen, and the development of MΒL inhibitors is urgently required to restore carbapenem efficacy. Microbial natural products have served as important sources for developing antimicrobial agents targeting pathogenic bacteria since the discovery of antibiotics in the mid-20th century. MΒL inhibitors derived from microbial natural products are still rare compared to those derived from chemical compound libraries. Hydroxyhexylitaconic acids (HHIAs) produced by members of the genus Aspergillus have potent inhibitory activity against clinically relevant IMP-type MBL. HHIAs may be good lead compounds for the development of MBL inhibitors applicable for controlling carbapenem resistance in IMP-type MBL-producing Enterobacterales .

OBJECTIVES: We aimed to elucidate the relationship among blaCTX-M-carrying plasmids and their transmission between humans and domestic animals. METHODS: Phylogenetic relationship of 90 I1 plasmids harboring blaCTX-M genes encoding extended-spectrum β-lactamase (ESBL) was analyzed using the ORF-based binarized structure network analysis of plasmids (OSNAp). RESULTS: The majority of plasmids carrying blaCTX-M-1 or blaCTX-M-8 belonged to a single lineage, respectively, and were primarily associated with domestic animals especially chickens. On the other hand, plasmids carrying blaCTX-M-14 or blaCTX-M-15, identified from both humans and domestic animals, were distributed in two or more lineages. CONCLUSION: OSNAp has revealed the phylogenetic relationships and diversity of plasmids carrying blaCTX-M more distinctly than pMLST. The findings suggest that circulation of I1 plasmids between humans and animals may contribute to their diversity.

The worldwide distribution of carbapenemase-producing Enterobacterales (CPE) is a serious public health concern as they exhibit carbapenem resistance, thus limiting the choice of antimicrobials for treating CPE infections. Combination treatment with a β-lactam and one of the newly approved β-lactamase inhibitors, such as avibactam, relebactam, or vaborbactam, provides a valuable tool to cope with CPE; however, these inhibitors are active only against serine-type carbapenemases and not against metallo-β-lactamases (MβLs). Therefore, it is important to readily differentiate carbapenemases produced by CPE by using simple and reliable methods in order to choose an appropriate treatment. Here, we developed three practical agar-based disk diffusion tests (double-disk synergy test [DDST], disk potentiation test, and modified carbapenem inactivation method [mCIM]) to discriminate the production of subclass B1 MβLs, such as IMP-, NDM-, and VIM-type MβLs, from the other carbapenemases, especially serine-type carbapenemases. This was accomplished using B1 MβL-specific sulfamoyl heteroarylcarboxylic acid inhibitors, 2,5-dimethyl-4-sulfamoylfuran-3-carboxylic acid (SFC) and 2,5-diethyl-1-methyl-4-sulfamoylpyrrole-3-carboxylic acid (SPC), originally developed by us. The DDST and mCIM using SFC and SPC revealed high sensitivity (95.3%) and specificity (100%) in detecting B1 MβL-producing Enterobacterales. In the disk potentiation test, the sensitivities using SFC and SPC were 89.1% and 93.8%, respectively, whereas the specificities for both were 100%. These methods are simple and inexpensive and have a high accuracy rate. These methods would therefore be of immense assistance in the specific detection and discrimination of B1 MβL-producing Enterobacterales in clinical microbiology laboratories and would lead to better prevention against infection with such multidrug-resistant bacteria in clinical settings.

Measles encephalitis rarely affects young adults and has no established treatment strategy. This brief report described the rare case of an immunocompetent 30-year-old man with severe measles pneumonia and encephalitis, following the autoimmune disease acute disseminated encephalomyelitis, during a large measles outbreak in 2018 in Japan. With multidisciplinary treatments, including corticosteroids, intravenous immunoglobulins, vitamin A, and therapeutic plasma exchange, the patient was successfully treated. This case provides a new strategy for treating measles encephalitis and its complications during measles outbreak.

BACKGROUND: According to the Clinical Practice Guidelines for Clostridioides difficile, oral vancomycin is to be used in vancomycin tapered and pulsed regimen (VCM-TP) for recurrent Clostridium difficile infection (CDI). However, data on the efficacy of VCM-TP in Japanese patients with recurrent CDI are scarce. To address this gap, we investigated the efficacy of VCM-TP and performed a case-controlled study to assess the risk factors associated with treatment failure in these patients. FINDINGS: We conducted this study on all patients who were administered VCM-TP for recurrent episodes of CDI between January 2008 and December 2018 at Tosei General Hospital. All patients had documented follow-ups within 90 days after completion of the VCM-TP. Data were obtained for comparative analysis of treatment success or failure. Thirty-six patients were eligible for this study, and treatment success was documented in 23 patients (63.9%) following VCM-TP treatment. Treatment success was documented in 22 of 30 (73.3%) patients who received the recommended therapy according to the Clinical Practice Guidelines. The frequency of patients treated with the recommended therapy was higher in the treatment success group (95.7%) than in the treatment failure group (61.5%) (OR: 13.75, 95% CI: 1.39-136.39, p = 0.016). Vancomycin-resistant enterococci culture tests were performed in 20 patients (55.6%), and all results were negative. CONCLUSIONS: Our findings suggest that VCM-TP is a good therapeutic option for recurrent CDI in Japanese patients. Furthermore, administration of the recommended VCM-TP is important for achieving a high rate of treatment success. Hence, antimicrobial stewardship teams should support the implementation of recommended VCM-TPs.

We investigated the prevalence and characteristics of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli isolates from Japanese pigs. A total of 345 pig fecal specimens were collected from 30 farms in the Aichi prefecture of Japan between June 2015 and April 2016, and 22 unique ESBL-producing E. coli were isolated from 16 samples spanning 8 farms. The ESBL types included CTX-M-15 (54.5%), CTX-M-55 (27.2%), CTX-M-3 (0.9%), and CTX-M-14 (0.9%). The predominant plasmid replicon type was IncN, and the isolates carried blaCTX-M-55. Nine sequence type (ST)s, including ST117, ST1706, ST38, and ST10, were detected in the ESBL-producers, but no B2-O25-ST131 was found. ESBL producers were highly resistant to cefotaxime, ceftiofur, and tetracycline, but were susceptible to imipenem, amikacin, and fosfomycin (FOM), although 2 ST354 isolates showed resistance to ciprofloxacin. All 11 chloramphenicol-resistant isolates, including ST117 (n = 6) and ST38 (n = 3) isolates, harbored floR, and the 2 FOM-resistant ST38 isolates harbored fosA3. Our results suggest that pigs do not act as direct reservoirs in the transmission of ESBL genes to E. coli in humans. However, ST117 E. coli carrying IncN-type plasmids mediating blaCTX-M-55 were isolated from several different farms, suggesting the potential for future spread in Japan. Therefore, plasmid sequence analyses and continuous surveillance are necessary from an epidemiological point of view and are required to better protect against ESBL-producer transmission.

This study was performed to investigate the carriage rates of CTX-M-type extended-spectrum β-lactamase (ESBL)-producing Escherichia coli among ill companion animals in Japan. Among the 178 nonrepetitive E. coli isolates, including 131 from dogs and 47 from cats, collected between September and November 2015, 42 (23.6%) isolates from 29 dogs and 13 cats were identified as ESBL producers. The antimicrobial susceptibility, O serotype, phylogenetic group, β-lactamase genotype, plasmid replicon type, and sequence type (ST) of each isolate were analyzed. The major ESBL types were CTX-M-14 (26.8%), CTX-M-15 (24.4%), CTX-M-27 (19.5%), and CTX-M-55 (19.5%); predominant replicon types of blaCTX-M-carrying plasmid were IncF group and IncI1-Iγ. The most prevalent STs were ST131 (n = 15, 35.7%), followed by ST38, ST10, and ST410. The 15 isolates of ST131 belonged to B2-O25. E. coli B2-O25-ST131 isolates harboring blaCTX-M-15 or blaCTX-M-27 were resistant to ceftazidime and ciprofloxacin. In particular, CTX-M-15 producers showed multidrug resistance. Our results demonstrated that the CTX-M-producing pandemic E. coli clone B2-O25-ST131 has already spread in Japanese companion animals as well. Moreover, the similarity of genotypes, serotypes, phylogenetic groups, and STs of the isolates from companion animals to those from humans suggested probable transmission of resistant bacteria between pets and humans.

We investigated the genetic backbones of 14 blaCTX-M-8-positive Escherichia coli isolates recovered from human stool samples and chicken meat. All isolates carried IncI1 plasmids with blaCTX-M-8 (blaCTX-M-8/IncI1), and most (9/14) belonged to a specific genetic lineage, namely, plasmid sequence type 113 (pST113). The genetic contexts of the nine blaCTX-M-8/IncI1 pST113 plasmids were similar, regardless of the source. These results suggest the probable local transfer of blaCTX-M-8/IncI1 between humans and chickens with genetically diverse E. coli.