Shigella flexnerii infection leads to shigellosis, an acute gastrointestinal disease. Shigellosis affects socioeconomically disadvantaged and densely populated communities that have unsafe water, poor sanitation, and poor hygiene (1). Shigella spp. bacteria are major contributors to acute bloody diarrhea worldwide, adding to disease numbers and death in children under 5 years of age (2). The emergence of multidrug-resistant Shigella strains is a concerning trend. Multidrug-resistant strains resist multiple first-line oral antimicrobials (i.e., ampicillin, trimethoprim/sulfamethoxazole, and ciprofloxacin). The situation is further complicated by enzyme-mediated β-lactam resistance in Shigella bacteria, further impacting empiric therapy and making the isolates extensively drug-resistant (2). Although extensively drug-resistant isolates have remained susceptible to carbapenem therapy, carbapenem resistance in Shigella spp. through imipenemase-type metallo-β-lactamase, New Delhi metallo-β-Lactamase, and Verona integron-encoded metallo-β-lactamase has been reported (3,4).

We report a case of OXA-181–producing S. flexneri bacteria recovered from the stool of an immunocompromised patient with B-cell acute lymphoblastic leukemia (B-ALL). OXA-181 is a subtype of the OXA-48–like carbapenemase enzymes, classified as an Ambler class D β-lactamase, that primarily hydrolyzes penicillins and carbapenems. Those enzymes are usually transmitted on plasmids and are typically associated with Enterobacterales such as Klebsiella pneumoniae and Escherichia coli bacteria (5).

A 2-year-old girl, born in a rural area near Hyderabad, India, was diagnosed with standard-risk B-ALL. Her chemotherapy treatment was complicated by 2 episodes of culture-negative febrile neutropenia and acute gastroenteritis. Her diarrhea was presumed to be allopurinol-induced and was managed with supportive care. Her care team discovered evidence of a B-ALL relapse. The patient recovered from the fever and diarrhea, and her family immigrated to Canada, where the patient was admitted to a hospital to establish care for her relapsed B-ALL.

The patient was afebrile and did not have diarrhea until day 3 in the hospital, when she had onset of febrile neutropenia, nonbloody diarrhea, and abdominal pain. In accordance with the hospital’s infection prevention protocol, we collected a stool sample for carbapenemase-producing Enterobacterales (CPE) screening. It exhibited growth of non–lactose fermenting colonies on the OXA side of a Chromid Carba Smart plate (bioMérieux, http://www.biomerieux.com), which we confirmed to be S. flexneri bacteria type 2a by using a biochemical panel and serotyping. We performed a stool PCR by using Seegene Allplex GI-EB gastrointestinal multiplex assay (SeeGene Inc., https://www.seegene.com) that showed the presence of Shigella spp. bacteria and astrovirus. We also isolated S. flexneri bacteria from a stool culture by using molecular detection (Appendix).

We began treatment for febrile neutropenia with piperacillin/tazobactam and vancomycin, in addition to azithromycin because of the detection of S. flexneri bacteria from the patient stool samples. Both isolates from the CPE screen and stool culture demonstrated a similar susceptibility profile (Table 1). Although the meropenem MIC was susceptible according to Clinical and Laboratory Standards Institute breakpoints, it was higher than 0.12 mg/L, the CPE screening cutoff in our laboratory protocol (6). We used the CARBA-5 assay (NG Biotech, https://www.ngbiotech.com) to further evaluate the antibiotic susceptibility, and the results indicated the presence of an OXA-48–like enzyme. The Public Health Ontario Laboratory verified the presence of OXA-48–like gene by using multiplex PCR (7). Because of the azithromycin resistance, we modified the treatment to trimethoprim/sulfamethoxazole. After treatment, the patient experienced rapid defervescence and resolution of the diarrhea. We repeated the stool culture after 2 weeks of treatment, and the culture resulted in no growth of S. flexneri bacteria.

We conducted whole-genome sequencing (Appendix). We extracted DNA from the bacterial isolate by using easyMag (bioMérieux) and sequenced on a GridION system with a R10.4.1 flow cell (Oxford Nanopore Technologies, https://nanoporetech.com). We analyzed data with MinKNOW 23.04.5 (Oxford Nanopore Technologies) to construct a consensus genome. We analyzed the isolate’s genome and plasmid with the Comprehensive Antibiotic Resistance Database (CARD) (http://arpcard.mcmaster.ca), identifying 5 resistance genes on the plasmid (Table 2), including OXA-181 with >95% identity and length within the plasmid. The plasmid has a size of 91,956 bp and carries all the genes for the resistance profile (Appendix). We deposited the plasmid gene sequence into GenBank (accession no. PP417752).

Given the low-hydrolytic activity of OXA-48–like enzymes, microbiology laboratories face difficult challenges in accurately detecting these enzymes in Enterobacterales. The Clinical and Laboratory Standards Institute breakpoints for meropenem are not suited for CPE surveillance, potentially missing OXA-48–like producers (8). Our laboratory has adopted a meropenem MIC breakpoint of >0.12 mg/L for CPE screening, in line with European Committee on Antimicrobial Susceptibility Testing recommendations (9). This approach is crucial for identifying isolates that require further CPE investigation, especially considering the reduced activity of OXA-48–like enzymes against cephalosporins.

Identification of an OXA-181 carbapenemase in a plasmid carried by S. flexneri bacteria is an alarming finding and concerning for the spread of this resistance profile in densely populated low- and middle-income communities. The detection of OXA-181 in Shigella spp. bacteria increases concerns about the broad dissemination of carbapenem resistance among other Enterobacterales (10). This finding emphasizes the need for vigilant and targeted surveillance for CPE in at-risk patients.

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