Characteristics of a Carbapenem-Resistant Strain Causing Community-Acquired Pneumonia in a Young Healthy Women.

Background: Multidrug-resistant rarely causes community-acquired pneumonia. Here, we report the clinical and genomic characteristics of a multidrug-resistant strain responsible for community-acquired pneumonia in a 31-year-old healthy young women.

Methods: strain W2LL was recovered from the alveolar lavage fluid sample of a hospitalized patient with pulmonary infection. Growth rate studies were conducted under various conditions, and virulence assessments were performed using larvae. Whole Genome Sequencing (WGS) was carried out using Oxford Nanopore MinIon and Illumina HiSeq. multilocus sequence typing (MLST), plasmid replicons, antimicrobial resistance genes, and virulence genes were determined using the BacWGSTdb webserver. Phylogenetic analysis between strain W2LL and other closely related genomes retrieved from NCBI database was performed.

Results: WGS identified strain W2LL as a rare sporadic lineage sequence type (ST) 1431. In addition to the detection of the β-lactamase gene () on the chromosome, was found on a 92,034 bp plasmid. Antimicrobial susceptibility testing revealed this strain was resistant to cephalosporins and carbapenems, with initial treatment using cefoxitin proving ineffective. Subsequent treatment with piperacillin-sulbactam combined with levofloxacin led to gradual improvement. Compared to ATCC 17978, W2LL exhibited similar growth rates at 37°C and 42°C, as well as in the presence of zinc. However, strain W2LL exhibited higher virulence phenotype compared to ATCC 17978 in model. The closest relative of W2LL was CAM180_1, another isolate recovered from Cambodia, which differed by 191 SNPs.

Conclusion: W2LL is a rare ST1431 carbapenem-resistant strain recovered from a patient with no prior hospitalization or typical risk factors. This underscores the growing menace posed by carbapenem-resistant , no longer limited to hospitalized patients, potentially impacting the broader, younger population.