Distribution and antimicrobial resistance of Acinetobacter spp. isolated from different types of infections from hospitalized patients and outpatients in Poland

Background: Acinetobacter baumannii (AB) is the most frequently isolated nosocomial pathogen, but severe infections by A. pittii , A. ursingii , and A. bereziniae are increasing. This study investigated the distribution and antibiotic resistance of Acinetobacter spp. strains from various infections. Methods: Data were collected between 2021–2023 from clinical samples of hospitalized and outpatient individuals in southern Poland. Strains were identified using MALDI-TOF Biotyper, and antibiotic susceptibility was tested with the MIDITECH-Analyzer system. Statistical analyses were conducted using IBM SPSS Statistics. Results: Among 1507 isolated Acinetobacter strains, 951 (63.1%) were AB, while 556 (36.9%) represented 27 non-AB species. Most isolates (73.6%) came from outpatients, while 26.4% were from hospitalized patients. A. ursingii (30.2%), A. pittii (20.6%), and A. junii (13%) were the most common non-AB species. A. bereziniae , A. calcoaceticus , and A. proteolyticus were more frequently found in hospitalized patients. Non-AB species dominated in/among genital tract infections (87%), whereas AB was more common in invasive infections. Nearly all strains were non-susceptible to ciprofloxacin (98.4%), with lower resistance rates to ampicillin/sulbactam (11.1%), trimethoprim/sulfamethoxazole (5.8%), gentamicin (2.9%), amikacin (2.5%), meropenem (1.6%), and colistin (1.6%). A. bereziniae showed frequently resistance to carbapenems, aminoglycosides, and trimethoprim/sulfamethoxazole. Colistin resistance was observed in A. ursingii and A. pittii . Conclusions: While AB accounted for 63.1% of isolates, non-AB species were common, particularly in genitourinary and skin infections. Emerging hospital-acquired infections by species like A. pittii underline the need for vigilant monitoring. The high resistance to ciprofloxacin and low but noticeable resistance to carbapenems and colistin highlights the importance of early detection and resistance surveillance to prevent the spread of resistant strains.