Pseudomonas aeruginosa is a frequent pathogen isolated from bacterial bloodstream infection (BSI) and can be problematic to treat due to the rising incidence of multi-drug resistance. Resistance to serum-killing by complement is a vital trait for Gram-negative bacteria like P. aeruginosa to survive in the bloodstream. Despite this, serum sensitive bacteria are commonly isolated from patients with active infection. Antibody-mediated protection from serum killing by ‘cloaking antibodies (cAb)’ has been described for multiple Gram-negative bacteria, however no studies have investigated the relevance of these in P. aeruginosa BSI. In this study, a cohort of 100 P. aeruginosa BSI patients in Brisbane, Australia was investigated for clinical relevance of cAb. Overall, 36% of patients produced high titres of cAbs specific for their cognate isolates. These cAbs are only clinically relevant if the patients isolate is sensitive to healthy control serum (HCS) killing. We found that 34% of patients had bacterial blood isolates that were sensitive to HCS with 41% (n=14) of these patients having cAbs that could inhibit the HCS-killing of their cognate isolate. Therefore, cAbs can protect almost half of HCS-sensitive P. aeruginosa isolates and allow these strains to survive in the bloodstream. Patients with cAb were significantly associated with non-neutropenic patients with no comorbidities. Whether induction of cAbs during hospital-stay is a risk factor for development of BSI is yet to be determined.