Microbiological and Clinical Features of Four Cases of Catheter-Related Infection by Methylobacterium radiotolerans

Abstract

Four cases of central venous catheter-related Methylobacterium radiotolerans infection are presented here. The patients were all long-term catheter carriers with an underlying diagnosis of leukemia, and they mostly manifested fevers. The isolated bacterial strains all showed far better growth on buffered charcoal yeast extract agar during the initial isolation and/or subcultures than they did on sheep blood or chocolate agar. This microbiological feature may improve the culture recovery of this fastidious pink Gram-negative bacillus that has rarely been isolated in clinical microbiology laboratories. Methylobacterium species are fastidious aerobic Gram-negative bacilli (1). They are of environmental origin and are rarely isolated in clinical microbiology laboratories (2, 3). Of these pink-colored organisms, Methylobacterium mesophilicum has occasionally been reported as an opportunistic pathogen that may infect immunocompromised hosts, such as patients with malignancy, organ transplant, HIV infection, renal failure, or alcoholism (4-7). Methylobacterium radiotolerans is less known, however, with only two series of infections reported thus far (2,8). In this study, we report four cases of central venous line-related M. radiotolerans infection in patients who had underlying leukemia. We paid attention to the culture features of the bacterial strains.These cases occurred from 2009 to 2014 in patients at The University of Texas M. D. Anderson Cancer Center, a comprehensive cancer center with 600 beds in Houston, TX. Anticancer chemotherapy often required the long-term use of indwelling venous catheters. Cultures of the blood samples from patients with suspected bloodstream infection were performed using the Bactec 9240 automated system with Plus Aerobic/F bottles (BD Diagnostic Systems, Sparks, MD) and Isolator tubes (Wampole Laboratories, Princeton, NJ) (9). Typically, a 20-ml blood sample was divided equally into a Bactec bottle and an Isolator tube for cultures. The bottle was incubated for 7 days at 35°C with aeration in the system. The Isolator tube was processed by centrifugation to pellet the lysed cellular sludge, which was evenly divided and spread onto four agar plates. Before October 2009, culture involved two sheep blood agar plates and two chocolate agar plates; after this time, one buffered charcoal yeast extract plate (BCYE) was included in exchange for one sheep blood agar plate. All the plates were from BBL (BD Microbiology Systems, Cockeysville, MD). The plates were incubated for 4 days at 35°C in 5% CO 2 to allow the bacterial or fungal colonies to be counted. About 30,000 blood cultures were performed annually at M. D. Anderson during the study period.The fastidious nature of the M. radiotolerans strains required 16S rRNA gene sequencing for the initial identification, using a previously published method (10). Briefly, bacterial genomic DNA was extracted from cultured colonies and amplified by PCR for a 594-bp amplicon in the mid-region of the gene using two universal bacterial primers (5=-TGCCAG...

Influence of Intratumor Microbiome on Clinical Outcome and Immune Processes in Prostate Cancer

“…Of the microbes we identified as negatively correlated with TNM staging, Methylobacterium species are opportunistic pathogens found to infect immunocompromised hosts, and M. radiotolerans infections are common in leukemia and neutropenic cancer patients [44]. Stenotrophomonas maltophilia is a multidrug-resistant global opportunistic pathogen and frequently co-colonizes with Pseudomonas aeruginosa.…”

“…While the remaining three strains have not previously been associated with cancer, they are often observed either in immunosuppressed patients or in patients with in-dwelling intravascular devices. Immunosuppression appears to be a major risk factor in the pathogenesis of Rhodococcus infections, and cases of Methylobacterium radiotolerans infection in cancer patients have mostly been associated with immunocompromised patients with long-indwelling central venous catheters [43,44]. Similarly, Stenotrophomonas maltophilia in patients with cancer are associated with infected in-dwelling intravascular devices [45][46][47].…”

Microbiological and Clinical Studies of Legionellosis in 33 Patients with Cancer

“…This case led us to include a BCYE agar plate in exchange for a sheep blood agar plate in our Isolator blood cultures starting in September 2009; so far, no Legionella organism has been isolated this way, but this medium has improved the recovery of Methylobacterium radiotolerans, another environmental Gram-negative bacillus (23).…”

First report of Methylobacterium radiotolerans bacteraemia identified by MALDI-TOF mass spectrometry

“…In this study, we present the first case of an initial identification at species level of M. radiotolerans by MALDI-TOF MS (an identification by this technology was attempted in the paper by Li et al. [14], in which two out of the four strains investigated, initially identified by molecular methods, were subsequently identified by the Vitek MS instrument from the colony as ‘unvalidated’ results, while two were not identified). The species identification was first obtained directly from the positive blood-culture bottle, after a quick extraction of the bacterial cells from the blood culture by a commercially available system, and later from the plate subcultures.…”

“…Methylobacterium radiotolerans [11] is much less known. At the time of writing, only three reports of M. radiotolerans bacteraemia have been described [12], [13], [14] (Table 1).…”