. Despite the critical importance of colistin as a last-resort antibiotic, limited studies have investigated colistin resistance in human infections in Cambodia. This study aimed to investigate the colistin resistance and its molecular determinants among Extended-spectrum beta-lactamase (ESBL)- and carbapenemase-producing (CP) Klebsiella pneumoniae (KP) and Escherichia coli (EC) isolated in Cambodia between 2016 and 2020. . EC (n=223) and KP (n=39) were tested for colistin minimum inhibitory concentration (MIC) by broth microdilution. Resistant isolates were subjected to PCR for detection of mobile colistin resistance genes (mcr) and chromosomal mutations in the two-component system (TCS). . Eighteen isolates (10 KP, 8 EC) revealed colistin resistance with a rate of 5.9% in EC and 34.8% in KP among ESBL isolates, and 1% in EC and 12.5% in KP among CP isolates. The resistance was associated with mcr variants (13/18 isolates, mcr-1, mcr-3 and mcr-8.2) and TCS mutations within EC and KP, with the first detection of mcr-8.2 in Cambodia, the discovery of new mutations potentially associated to colistin resistance in the TCS of EC (PhoP I47V, PhoQ N352K, PmrB G19R, PmrD G85R) and the co-occurrence of mcr genes and colistin resistance conferring TCS mutations in 11/18 isolates. The findings highlight the presence of colistin resistance in ESBL- and CP- Enterobacteriaceae involved in human infections in Cambodia as well as chromosomal mutations in TCS and the emergence of mcr-8.2 in EC and KP. It underscores the need for continuous surveillance, antimicrobial stewardship, and control measures to mitigate the spread of colistin resistance.

Clostridium perfringens (C. perfringens) is an anaerobic, spore-forming Gram-positive rod responsible for necrotizing gangrene, bacteremia in patients with cancer or gastrointestinal tract infection. C. perfringens virulence is due in large part to toxin production. In 2014, a new enterotoxin, BEC (binary enterotoxin of Clostridium perfringens) encoded by becA and becB genes, distinct from enterotoxin (CPE) encoded by the cpe gene, has been described. BEC-producing strains can be causative agents of acute gastroenteritis in humans. We present herein the case of a 64-year-old man who presented to the emergency department of Toulouse University Hospital with pneumonia and septic shock, without digestive symptoms. Blood cultures showed C. perfringens bacteremia and despite appropriate antibiotic treatment the patient passed away 7 h after admission. The characterization of the strain by whole genome sequencing revealed the presence of typical genes of C. perfringens: plc gene (alpha-toxin, phospholipase C) and pfoA (theta-toxin, perfringolysine). Surprisingly, this strain also harbored becA and becB genes encoding the recently described BEC toxin. Interestingly, alpha-toxin typing of our isolate and other published BEC isolates showed that they belonged to different PLC subtypes, confirming the high genetic diversity of these strains. To our knowledge, it is the first clinical case reporting bacteremia due to a BEC-producing C. perfringens isolate.

Despite the threat of antimicrobial resistance (AMR) worldwide, limited studies describe the situation in human infections in Cambodia. Our study aims to evaluate the current state of AMR and describe the resistance mechanisms of the main Enterobacterales responsible for various infections in Cambodia. Between January and April 2020, 222 clinical Enterobacterales isolates were collected from routine diagnostics at the Medical Biology Laboratory of the Institut Pasteur du Cambodge, Phnom Penh. Antimicrobial susceptibility testing and resistance phenotype analysis were performed. Beta-lactamase genes bla_CTX-M, bla_SHV, bla_TEM and bla_OXA-1 were screened in isolates resistant to third generation cephalosporin (3 GC). Carbapenem-resistant isolates were tested for carbapenemase production using a rapid immunochromatographic assay and confirmed by gene detection. Isolates harboring bla_CTX-M and carbapenemase genes were further characterized by sequencing. Overall, 39.2 % of isolates were resistant to at least one 3 GC, with 30.2 % confirmed as extended-spectrum beta-lactamase (ESBL) producers. The corresponding ESBL genes pertain to the KLUB/CTX-M-1 and KLUY/CTX-M-9 classes. Carbapenemase genes bla_NDM and bla_OXA–48 were detected in 4.1 % of isolates. Notably, 6.5 % of ESBL-producing Escherichia coli and Klebsiella pneumoniae also exhibited colistin resistance. The prevalence and molecular characterization of 3 GC-resistant and ESBL-producing Enterobacterales in our study is consistent with recent reports. Our findings further confirm the high rate of carbapenemase producing Enterobacterales (NDM and OXA-48), including in community-acquired infections. Additionally, we report notable colistin resistance among ESBL producing E. coli and K. pneumoniae isolates. These results highlight the urgent need for AMR strengthened surveillance and antimicrobial stewardship programs in Cambodia.