It is unknown as to whether other beta-lactams can be used for bloodstream infections (BSI) resulting from Pseudomonas aeruginosa (PA) which are non-susceptible to one or more carbapenem. We conducted a retrospective cohort study at the Assaf Harofeh Medical Center (AHMC) from January 2010 to August 2014. Adult patients with PA-BSI non-susceptible to a group 2 carbapenem but susceptible to ceftazidime or piperacillin (with or without tazobactam), were enrolled. We compared the outcomes of patients who received an appropriate beta-lactam antibiotic (“cases”) to those who received an appropriate non-beta-lactam antibiotic (“controls”). Whole genome sequencing was performed for one of the isolates. Twenty-six patients with PA-BSI met inclusion criteria: 18 received a beta-lactam and 8 a non-beta-lactam (three a fluoroquinolone, two colistin, one a fluoroquinolone and an aminoglycoside, one a fluoroquinolone and colistin, and one colistin and an aminoglycoside). All clinical outcomes were similar between the groups. There were large variations in the phenotypic susceptibilities of the strains. A detailed molecular investigation of one isolate revealed a strain that belonged to MLST-137, with the presence of multiple efflux pumps, OXA-50, and a chromosomally mediated Pseudomonas-derived cephalosporinase (PDC). The oprD gene was intact. Non-carbapenem-β-lactams may still be effective alternatives for short duration therapy (up to 14 days) for BSI caused by a carbapenem non-susceptible (but susceptible to ceftazidime, piperacillin, and/or piperacillin-tazobactam) PA strain. This observation requires further confirmatory analyses. Future molecular investigations should be performed, in order to further analyze additional potential mechanisms for this prevalent phenotype.

Case 1. Radiograph and photograph of the feet. Case 2-A 40-year-old housewife had developed systemic lupus erythematosus at the age of 28 with arthritis, pericarditis, pleurisy, and focal proliferative glomerulonephritis. Over the past five years her hands had become progressively deformed with pronounced ulnar deviation and flexion contractures, and for two years she had had severe clawing of the toes. Radiography of the feet showed subluxation of the right third, fourth, and fifth metatarsophalangeal joints; the left third and fourth metatarsophalangeal joints; and the third left proximal interphalangeal joint. Case 3-A 29-year-old girl had systemic lupus erythematosus for 16 years which had presented with thrombocytopenic purpura, fever, pleurisy, rash, and symmetrical arthritis affecting her hands, knees, and ankles. During the previous 13 years of her disease she had remained clinically and serologically active, with average DNA binding values of 75 ,' (upper limit 30 % in the Farr technique), and the main feature of her disease had been widespread arthralgias. Her hands had become grossly deformed with severe flexion contractures, and over the past two years she had developed similar changes in her feet. Radiography of the feet showed bilateral subluxation of the interphalangeal joints of the fourth and fifth toes and the interphalangeal joint of the right hallux.

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