Acinetobacter baumannii (Ab), a common opportunistic pathogen, forms biofilms that enhance antibiotic resistance and environmental tolerance, posing challenges for clinical treatment. Prodigiosin (PG), a natural red pigment with broad-spectrum antimicrobial activity, has unclear mechanisms against Ab and its biofilms. This study investigated PG (derived from Serratia marcescens CM01) for its antibacterial/antibiofilm effects on Ab and explored its molecular mechanisms through phenotypic and wholegenome transcriptomic analyses.

Seven clinical Ab strains and one reference strain were studied. Antimicrobial susceptibility was assessed by disk diffusion; PG's minimum inhibitory concentrations (MICs) were determined via microbroth dilution; antibiofilm activity (0.1 to 3.0 μg/mL PG) was quantified by crystal violet staining; synergistic effects of tigecycline were evaluated via checkerboard assay. Under minimum biofilm inhibitory concentration (MBIC), PG's impact on extracellular polymeric substances (EPS) was measured using phenol-sulfuric acid (exopolysaccharides) and bicinchoninic acid (extracellular proteins) assays. Hydrogen peroxide (H₂O₂) sensitivity and cell surface hydrophobicity (CSH) were assessed post-MBIC PG treatment. RNA sequencing (RNA-Seq) analyzed differentially expressed genes (DEGs) in Ab reference strain exposed to 1/2 MIC PG.

Six of seven clinical Ab strains exhibited multidrug resistance. Prodigiosin (PG) demonstrated minimum inhibitory concentrations (MICs) of 64 to 128 μg/mL against all eight strains. Biofilm formation was inhibited at PG concentrations of 0.1 to 1.0 μg/mL (inhibition rate >50%). Synergy testing with tigecycline yielded fractional inhibitory concentration indices (FICI) of 0.5 to 1.0, indicating additive effects. PG treatment at minimum biofilm inhibitory concentration (MBIC) significantly reduced exopolysaccharide content (from 28.77 μg/mL to 14.90 μg/mL; P<0.05), extracellular protein production (from 0.192 to 0.164; P<0.05), and cell surface hydrophobicity [from (41.31±6.51)% to (31.61±7.18), P<0.05]. Bacterial survival under hydrogen peroxide stress decreased from 6.7×10⁶ CFU/mL to 1.5×10⁴ CFU/mL (P<0.05). RNA sequencing revealed 1342 differentially expressed genes (|Log₂FC|>1, P<0.05) with 737 downregulated and 605 upregulated, showing significant enrichment in amino acid metabolism, peptidoglycan biosynthesis, and energy metabolism pathways. Key biofilm-associated genes were substantially downregulated.

PG inhibits Ab growth and biofilm formation by disrupting amino acid, peptidoglycan and energy metabolic pathways, downregulating biofilm-related genes, reducing EPS production, diminishing bacterial stress resistance, and ultimately impeding biofilm development.

The pathogenic characteristics of Escherichia coli (E. coli) in bacterial infections were analyzed using a combination of multiple molecular typing techniques in order to provide evidence for the management of clinical medication safety.

Samples from some bacterial infection-related cases in a district of Chongqing in 2021 were collected. A total of 30 E. coli strains were selected by a completely random method, and phoA gene PCR assay was performed for identification. Molecular typing of the strains was analyzed using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Antimicrobial susceptibility testing was conducted to determine the drug resistance of the strains, and four β-lactamase-encoding genes (blaCTX-M, blaTEM, blaSHV, blaZ) were selected to detect the carriage of resistance genes.

All 30 E. coli strains displayed the phoA gene target band. Their PFGE banding patterns, with a similarity of 50%~98%, could be classified into 8 clusters. Cluster C was the dominant group, accounting for 53.3%(16/30). C1 and C2 exhibited high genetic correlation, indicating a close phylogenetic relationship. One E. coli strain could not be assigned a sequence type (ST) by MLST, while the remaining 29 E. coli isolates were classified into 16 different STs, demonstrating a polymorphic distribution. Among them, 10 isolates belonged to ST131 (10/30, 33.33%). Evolutionary analysis of the 10 ST131 E. coli strains revealed their distribution across different branches, indicating varying degrees of genetic relatedness. Antimicrobial susceptibility testing revealed that all 30 E. coli strains exhibited varying degrees of resistance, with the highest resistance rate observed against the β-lactam antibiotic ampicillin (25/30,83.33%). Among them, 60.0% were multidrug-resistant bacteria (MDRB). These MDRB strains exhibited 16 distinct resistance profiles, displaying a scattered distribution without a dominant resistance pattern.50.0%(9/18) of the MDRB strains exhibited six-drug resistance, while the most drug-resistant strain showed eight-drug resistance. Furthermore, the blaCTX-M gene carriage rate among the 30 E. coli strains was 86.67%(26/30), while no blaZ gene was detected.

E. coli related to bacterial infections from a Chongqing district exhibited diverse PFGE/MLST patterns and significant drug resistance. The application of multiple molecular typing techniques can reveal the genetic diversity, evolutionary relationships, and antimicrobial resistance characteristics of pathogenic bacteria.

It is recommended to enhance the molecular typing and drug resistance surveillance network for pathogenic bacteria, establish an early warning mechanism, and implement hierarchical management of antibiotics, thereby improving targeted prevention and epidemic traceability capabilities for key drug-resistant bacteria such as ST131.