Gram-negative bacterial infections, especially multidrug-resistant (MDR) bacterial infection, are becoming a serious threat to public health. Although it is widely accepted that both appropriate initial empirical therapy and targeted therapy are important, but for patients needing therapy adjustment, few studies have explored whether adjustment strategy based on microbiologic susceptibility test (MST) brings better outcome compared with empirical adjustment.A total of 320 patients with gram-negative bacterial infection (airway, blood, or pleural effusion) were selected and a prospective cohort study was conducted. Baseline characteristics and outcomes (microbiologic, clinical, and economic) were documented during follow-up.MDR and nosocomial infections were common among subjects. Initial therapies consistent with MST could result in reduced in-hospital mortality, treatment failure rate, infection-related death, percentages of patients needing therapy adjustment, and daily hospitalization cost with increased successful treatment rate compared with inconsistent with MST, and microbiologic outcomes were also better with appropriate therapies.For patients needing therapy adjustment, relying on MST gained no significant benefit on mortality, clinical, or microbiologic outcomes compared with depending on clinical experience. But for patients with MDR infection, adjustment relying on MST gained more benefit than non-MDR infection.Appropriate initial therapy significantly improved the prognosis of patients with gram-negative bacterial infections, but improvement was not that obvious for patients needing therapy adjustment which was based on MST compared with clinical experience, and more beneficial effects of adjustment relying on MST were obtained for patients with MDR bacterial infection.