Incidence and Antibiotic Susceptibility of Gram-Negative Bacteria Associated With Chest Infections in Intensive Care Unit Patients From a Selected Hospital in the Kingdom of Saudi Arabia.

Background: Hospital-acquired pneumonia (HAP), including ventilator-associated pneumonia (VAP), is a leading cause of morbidity and mortality in intensive care units (ICUs). Local, organism-specific antimicrobial resistance data are critical to guide empiric therapy and strengthen antimicrobial stewardship efforts. Objective: The aim of this study is to describe the spectrum of Gram-negative bacilli (GNB) responsible for ICU-acquired lower respiratory tract infections (LRTIs) in a Saudi general hospital and to characterize their antimicrobial resistance profiles, including multidrug-resistant (MDR), extensively drug-resistant (XDR), and pandrug-resistant (PDR) patterns. Methods: We retrospectively analyzed 271 nonduplicate GNB isolates recovered from ICU respiratory specimens (sputum, tracheal aspirates, and throat swabs) collected between 2020 and 2022. Demographic characteristics, specimen distribution, bacterial species, and antimicrobial susceptibility patterns were summarized. MDR, XDR, and PDR classifications were determined according to standard phenotypic criteria. Results: Of the 271 specimens, 126 (46%) were sputum, 108 (40%) were tracheal aspirates, and 37 (14%) were throat swabs. Patients were 52% male (141/271) and 48% female (130/271), with 56% aged > 65 years. Twenty-three GNB species were identified; the predominant pathogens were Klebsiella spp. (92/271, 34.0%), Pseudomonas spp. (73/271, 27.0%), and Acinetobacter spp. (32/271, 12%). Enterobacteriaceae accounted for 130 isolates (48.0%), while non-Enterobacteriaceae comprised 141 (52.0%). There were statistically significant (p = 0.016) differences between the three most common organisms (Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii complex). Antimicrobial susceptibility testing revealed extensive resistance patterns across the major isolates. Pseudomonas spp. demonstrated very high resistance to cephalosporins (> 95%), with lower resistance observed to amikacin (43%). Acinetobacter spp. showed the most alarming profile, with nearly universal resistance to β-lactams and carbapenems (> 90%), although colistin retained complete activity (0% resistance). In contrast, Klebsiella spp. exhibited high resistance to third-generation cephalosporins (86%-93%) and carbapenems (70%-77%) while maintaining moderate susceptibility to amikacin (45%) and tigecycline (36%). These findings demonstrate a substantial burden of MDR among ICU GNB isolates, with colistin emerging as the only consistently effective therapeutic option. Conclusions: ICU cohort is dominated by a limited number of highly resistant GNB led by K. pneumoniae, P. aeruginosa, and A. baumannii. The cohort predominantly affects older adults (> 60 years), and the breadth of MDR/XDR/PDR underscores the urgency of rigorous antimicrobial stewardship, infection prevention, and rapid diagnostics to optimize empiric therapy.