OBJECTIVE: To compare the efficacy and safety of intravenous colistin sulfate combined with nebulized inhalation versus intravenous monotherapy for pulmonary infections caused by carbapenem-resistant organism (CRO). METHODS: A multicenter retrospective cohort study was conducted. Clinical data were collected from patients admitted to the intensive care unit (ICU) of 10 tertiary class-A hospitals in Henan Province between July 2021 and May 2023, who received colistin sulfate for CRO pulmonary infections. Data included baseline characteristics, inflammatory markers [white blood cell count (WBC), neutrophil count (NEU), procalcitonin (PCT), C-reactive protein (CRP)], renal function indicators [serum creatinine (SCr), blood urea nitrogen (BUN)], life support measures, anti-infection regimens, clinical efficacy, microbiological clearance rate, and prognostic outcomes. Patients were divided into two groups: intravenous group (colistin sulfate monotherapy via intravenous infusion) and combination group ((intravenous infusion combined with nebulized inhalation of colistin sulfate). Changes in parameters before and after treatment were analyzed. RESULTS: A total of 137 patients with CRO pulmonary infections were enrolled, including 89 in the intravenous group and 48 in the combination group. Baseline characteristics, life support measures, daily colistin dose, and combination regimens (most commonly colistin sulfate plus carbapenems in both groups) showed no significant differences between two groups. The combination group exhibited higher clinical efficacy [77.1% (37/48) vs. 59.6% (52/89)] and microbiological clearance rate [60.4% (29/48) vs. 39.3% (35/89)], both P < 0.05. Pre-treatment inflammatory and renal parameters showed no significant differences between two groups. Post-treatment, the combination group showed significantly lower WBC and CRP [WBC (×10⁹/L): 8.2±0.5 vs. 10.9±0.6, CRP (mg/L): 14.0 (5.7, 26.6) vs. 52.1 (24.4, 109.6), both P < 0.05], whereas NEU, PCT, SCr, and BUN levels showed no significant between two groups. ICU length of stay was shorter in the combination group [days: 16 (10, 25) vs. 21 (14, 29), P < 0.05], although mechanical ventilation duration and total hospitalization showed no significant differences between two groups. CONCLUSIONS Intravenous colistin sulfate combined with nebulized inhalation improved clinical efficacy and microbiological clearance in CRO pulmonary infections with an acceptable safety profile.
Humans ; Colistin/therapeutic use* ; Retrospective Studies ; Administration, Inhalation ; Anti-Bacterial Agents/therapeutic use* ; Carbapenems/pharmacology* ; Male ; Female ; Middle Aged ; Gram-Negative Bacteria/drug effects* ; Aged ; Treatment Outcome ; Respiratory Tract Infections/drug therapy*

BACKGROUND: Acinetobacter baumannii infections are difficult to treat owing to the emergence of various antibiotic resistant isolates. Because treatment options are limited for multidrug-resistant (MDR) A. baumannii infection, the discovery of new therapies, including combination therapy, is required. We evaluated the synergistic activity of colistin, doripenem, and tigecycline combinations against extensively drug-resistant (XDR) A. baumannii and MDR A. baumannii. METHODS: Time-kill assays were performed for 41 XDR and 28 MDR clinical isolates of A. baumannii by using colistin, doripenem, and tigecycline combinations. Concentrations representative of clinically achievable levels (colistin 2 microg/mL, doripenem 8 microg/mL) and achievable tissue levels (tigecycline 2 microg/mL) for each antibiotic were used in this study. RESULTS: The colistin-doripenem combination displayed the highest rate of synergy (53.6%) and bactericidal activity (75.4%) in 69 clinical isolates of A. baumannii. Among them, thedoripenem-tigecycline combination showed the lowest rate of synergy (14.5%) and bacteri-cidal activity (24.6%). The doripenem-tigecycline combination showed a higher antagonistic interaction (5.8%) compared with the colistin-tigecycline (1.4%) combination. No antagonism was observed for the colistin-doripenem combination. CONCLUSIONS: The colistin-doripenem combination is supported in vitro by the high rate of synergy and bactericidal activity and lack of antagonistic reaction in XDR and MDR A. baumannii. It seems to be necessary to perform synergy tests to determine the appropri-ate combination therapy considering the antagonistic reaction found in several isolates against the doripenem-tigecycline and colistin-tigecycline combinations. These findings should be further examined in clinical studies.
Acinetobacter Infections/drug therapy/microbiology ; Acinetobacter baumannii/*drug effects/genetics/isolation & purification ; Anti-Bacterial Agents/*pharmacology/therapeutic use ; Bacterial Proteins/genetics ; Carbapenems/*pharmacology/therapeutic use ; Colistin/*pharmacology/therapeutic use ; Drug Resistance, Multiple, Bacterial/*drug effects ; Drug Synergism ; Drug Therapy, Combination ; Humans ; Microbial Sensitivity Tests ; Minocycline/*analogs & derivatives/pharmacology/therapeutic use ; Multilocus Sequence Typing ; beta-Lactamases/genetics

PURPOSE: Colistin resistance in Acinetobacter baumannii (A. baumannii) is mediated by a complete loss of lipopolysaccharide production via mutations in lpxA, lpxC, and lpxD gene or lipid A modifications via mutations in the pmrA and pmrB genes. However, the exact mechanism of therapy-induced colistin resistance in A. baumannii is not well understood. MATERIALS AND METHODS: We investigated the genotypic and phenotypic changes that underlie pan-drug resistance mechanisms by determining differences between the alterations in extensively drug-resistant (XDR) A. baumannii (AB001 and AB002) isolates and a pan-drug resistant (PDR) counterpart (AB003) recovered from one patient before and after antibiotic treatment, respectively. RESULTS: All three clinical isolates shared an identical sequence type (ST138), belonging to the global epidemic clone, clonal complex 92, and all produced OXA-23 carbapenemase. The PDR AB003 showed two genetic differences, acquisition of armA gene and an amino acid substitution (Glu229Asp) in pmrB gene, relative to XDR isolates. No mutations were detected in the pmrA, pmrC, lpxA, lpxC, or lpxD genes in all three isolates. In matrix-assisted laser desorption ionization-time of flight analysis, the three isolates commonly showed two major peaks at 1728 m/z and 1912 m/z, but peaks at 2034 m/z, 2157 m/z, 2261 m/z, and 2384 m/z were detected only in the PDR A. baumannii AB003 isolate. CONCLUSION: Our results show that changes in lipid A structure via a mutation in the pmrB gene and acquisition of armA gene might confer resistance to colistin and aminoglycosides to XDR A. baumannii strains, resulting in appearance of a PDR A. baumannii strain of ST138.
Acinetobacter Infections/*drug therapy/microbiology ; Acinetobacter baumannii/*drug effects/*genetics/isolation & purification ; Aged ; Anti-Bacterial Agents/*pharmacology/therapeutic use ; Bacterial Proteins/*genetics ; Colistin/*pharmacology/therapeutic use ; *Drug Resistance, Bacterial ; Electrophoresis, Gel, Pulsed-Field ; Genotype ; Humans ; Male ; Microbial Sensitivity Tests ; Molecular Typing ; Mutation ; Polymerase Chain Reaction ; Transcription Factors ; beta-Lactamases