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Two strains of Raoultella planticola and one of Raoultella ornithinolytica showing carbapenem resistance were recovered from patients hospitalized in New Jersey and Ohio. All patients had received previous antimicrobial treatment, including carbapenems. These strains harbored blaKPC-2 and blaKPC-3. Carbapenemase genes were embedded in isoforms of Tn4401 and were plasmidic and chromosomal in location.
Raoultella species are gram-negative aerobic bacilli belonging to the Enterobacteriaceae family that are closely related to Klebsiella spp. (7). These environmental organisms, infrequently causing human infections, appear to have pathogenicity similar to that of Klebsiella pneumoniae (8). The first human Raoultella spp. invasive infection was described in 1984, and bloodstream infections have been reported, though rarely (1). Studies have shown that 0.2 to 19.0% of isolates initially identified as Klebsiella spp. were Raoultella spp. by 16S rRNA analysis and that the prevalence of these organisms in clinical settings can vary geographically (8).
(This work was presented at the 19th European Conference of Clinical Microbiology and Infectious Diseases, Helsinki, Finland, 2009.)
A total of 7,248 Enterobacteriaceae isolates collected in medical centers from North America, Latin America, and Europe during 2008 were susceptibility tested by the reference broth microdilution method and interpretation criteria (3, 4). Isolates displaying imipenem and/or meropenem MICs of ≥2 μg/ml were tested with the modified Hodge test (MHT) using imipenem and meropenem disks (4) and multiplex PCRs for the detection of carbapenemase-encoding genes, including blaIMP, blaVIM, blaKPC, blaSME, and blaGES variants and blaIMI, blaNMC-A, and blaOXA-48.
Among 134 (1.8% overall) isolates that were nonsusceptible to carbapenems, three (2.2%) Raoultella isolates from bloodstream infections were observed. MHT was positive for all three strains, and PCRs were positive for blaKPC. Sequencing of 16S rRNA revealed that two isolates were R. planticola (from Ohio and New Jersey) and one was R. ornithinolytica (from New Jersey). The isolates from New Jersey were detected in the same hospital and harbored blaKPC-3, whereas the strain from Ohio carried blaKPC-2. The clinical histories of the patients presenting infections with KPC-producing Raoultella spp. are summarized below.
An 83-year-old female patient was admitted to a hospital (Ohio) with a diagnosis of community-acquired bacterial pneumonia in May 2008. Sputum, paracentesis, and blood cultures were negative. Urine culture grew Escherichia coli, and the patient received courses of moxifloxacin, ceftriaxone, azithromycin, and meropenem. The patient was discharged and returned after 3 weeks with respiratory complaints. A tracheal-aspirate specimen grew a multidrug-resistant A. baumannii strain, and blood culture grew an enteric-like gram-negative bacillus (R. planticola). The patient subsequently died.
The patient was a 64-year-old man admitted to a hospital (New Jersey) in September 2008 with a diagnosis of preacute B-lymphoblastic leukemia. After induction chemotherapy, he became neutropenic, febrile, and hypotensive and was transferred to the intensive care unit. Blood cultures grew E. coli that was treated with 14 days of meropenem. The patient developed a perirectal abscess that was debrided, and cultures grew mixed bacteria, including vancomycin-resistant enterococci, for which the patient was started on daptomycin. Fever, hypotension, and bradycardia followed, but three sets of blood cultures were negative, including from central lines. Antimicrobial therapy included daptomycin, fluconazole, and rifampin (rifampicin); imipenem was added, and the patient was also given one dose of amikacin. Two blood cultures subsequently grew R. planticola which was resistant to imipenem and susceptible to gentamicin, levofloxacin, and tetracycline. The patient was switched from imipenem to doxycycline. Repeat blood cultures on the following day were negative, but the patient died.
A 51-year-old male presented with hypertension and peripheral vascular and mitral valve disease and underwent surgery for valve replacement in November 2007 (New Jersey). Postoperatively, the patient developed respiratory and renal failure requiring mechanical ventilation and dialysis. The patient was febrile despite empirical treatment with piperacillin-tazobactam. Changes in antimicrobial therapy were performed due to thrombocytopenia, ischemic extremities, persistent leukocytosis, and lower-gastrointestinal bleeding. The patient received courses of imipenem alone and with vancomycin, linezolid with and without aztreonam, levofloxacin, and anidulafungin. The patient became afebrile, but after 1 month he was restarted on vancomycin (orally and intravenously), aztreonam, and metronidazole due to leukocytosis and fever. In February 2008, the therapy was changed to daptomycin, aztreonam, and metronidazole and blood cultures grew gram-positive and -negative bacilli, identified as Bacillus spp. and Klebsiella spp., respectively. Klebsiella spp. also grew moderately in culture of a respiratory tract specimen. The Klebsiella isolate from blood was later identified as R. ornithinolytica which was susceptible only to gentamicin and amikacin. The patient died.
The KPC-producing Raoultella strains were analyzed for the presence of β-lactamase-encoding genes, including extended-spectrum β-lactamases (2) and plasmidic AmpC genes (10). All strains harbored blaTEM-1, and both Raoultella spp. from New Jersey also carried blaSHV-7. Additionally, the R. planticola isolate from New Jersey harbored blaPSE-1 and blaFOX-5. Isolates were screened for qnr, aac(6′)-lb-cr, and qepA due to elevated fluoroquinolone MICs and the recent association of these acquired quinolone-resistance determinants and blaKPC (5, 6), but all PCRs yielded negative results.
Genes encoding blaKPC are carried in isoforms of a transposon structure named Tn4401 (9). Primers annealing to different regions of this transposon element were used for amplification, and amplicons were digested with EagI. blaKPC-2 (Ohio) was carried on Tn4401b, and blaKPC-3 (New Jersey) was carried on Tn4401c, containing a 200-bp deletion upstream of blaKPC (9).
Plasmid and ICeuI preparations were resolved in agarose gels that were hybridized with a blaKPC-specific probe. The strains carried multiple plasmids, ranging from 7.2 to 75 kb (data not shown). The R. planticola strain from Ohio showed hybridization on the ICeuI preparation, indicating a chromosomal location. The isolates from New Jersey carried blaKPC-3 in plasmids with different sizes. Conjugation experiments of KPC-carrying strains with a J53-derivative E. coli strain yielded colonies for one isolate (R. planticola from New Jersey) in sodium azide and ceftazidime selection plates. The transconjugant E. coli was confirmed to harbor blaKPC in an 11-kb plasmid and showed elevated MICs for several β-lactam agents, including carbapenems (Table (Table1).1). A positive MHT result was obtained for the blaKPC-carrying transconjugant E. coli.
In this report, we describe three blaKPC-carrying Raoultella isolates associated with fatal infections in patients in the United States. These organisms can be recovered from various environments, including estuarine waters and fish, and show similarities to Klebsiella species (7), which could facilitate the transfer of genetic material among these organisms. Notably, all patients that had infections due to KPC-producing Raoultella infections received antimicrobial therapy with carbapenems that could have facilitated selection of strains resistant to these agents.
Published ahead of print on 7 October 2009.