Objective To understand the infection characteristics and drug resistance of carbapenem-resistant Serratia marcescens (CRSM) in a general hospital in Shanghai, and to provide a theoretical basis for clinical anti-infective treatment and prevention of drug-resistant bacteria.

Methods Clinical data on cases with CRSM infections detected in clinical specimens at a gradeⅢ level A general hospital in Shanghai from June 2022 to June 2024 were retrospectively collected, and their clinical distributions, factors of hospital-acquired infections, prognosis, and drug-resistant situation were analyzed simultaneously.

Results A total of 38 cases with CRSM were detected from June 2022 to June 2024, and the number of CRSM strains accounted for 25.00% (38/152) of the number of SM strains. The 38 CRSM infection samples were all derived from sputum. CRSM were distributed in 9 clinical departments, and the top 3 departments having the highest percentages of CRSM among SM strains, were intensive care unit (ICU) (78.79%, 26/33), gastrointestinal surgery department (57.14%, 4/7), and thyroid hernia surgery department (50.00%, 1/2). Among the 38 patients with CRSM infections, 8 cases were identified as hospital-acquired infection, resulting in a hospital-acquired infection rate of 21.05. The mortality rate of the 38 cases of CRSM infected patients within 30 days after detection of CRSM was 23.68% (9/38). The results of multivariate logistic regression analysis showed that sequential organ failure assessment (SOFA) score $\ge$6.5 points (OR=15.33, P<0.001), septic shock (OR=4.85, P=0.032), and suffering from neoplastic diseases (OR=0.12, P=0.018) were the related factors for death within 30 days after the detection of CRSM in patients with CRSM infection. The results of drug sensitivity test showed that the 38 cases of CRSM exhibited 100.00% (38/38) sensitivity to trimethoprim/sulfamethoxazole, tigecycline, or ceftazidime/avibactam; demonstrated high resistance to β-lactams except for ceftazidime (18.42%, 7/38), the latter of which was one of the third-generation of cephalosporins; showed elevated resistance to fluoroquinolones levofloxacin (89.47%, 35/38), ciprofloxacin (94.74%, 36/38); maintained good tetracycline sensitivity doxycycline (97.37%, 37/38), minocycline (76.32%, 29/38); and displayed high susceptibility to the aminoglycoside gentamicin (94.74%, 36/38) and elevated resistance to tobramycin (86.84%, 34/38). The detection rate of serine carbapenemase in the 38 strains of CRSM was 100.00%, while all strains tested negative for metallo-β-lactamases.

Conclusion From June 2022 to June 2024, the detection rate of CRSM in a gradeⅢ level A general hospital in Shanghai was relatively high, especially in the ICU. CRSM has a high resistance rate to commonly used antibacterial drugs such as the first and second-generation cephalosporins, quinolones, and polypeptide antibacterial drugs. Therefore the dynamics of drug-resistant bacteria should be tracked in a timely manner to guide the rational clinical application of antibacterial drugs.