Methylotroph Infections and Chronic Granulomatous Disease

E. Liana Falcone; Jennifer R. Petts; Mary Beth Fasano; Bradley Ford; William M. Nauseef; João Farela Neves; Maria João Simões; Millard L. Tierce IV; M. Teresa de la Morena; David E. Greenberg; Christa S. Zerbe; Adrian M. Zelazny; Steven M. Holland

Disclosures

Emerging Infectious Diseases. 2016;22(3):404-409. 

In This Article

Discussion

We have identified a total of 12 infections caused by 3 methylotroph bacteria in patients with CGD: 2 A. methanolica, 1 M. lusitanum, and 9 G. bethesdensis infections. Infections caused by A. methanolica and G. bethesdensis have been reported only for patients with CGD, whereas M. lusitanum in a patient without CGD undergoing chemotherapy for leukemia has been reported.[10] These observations suggest that Nox2-based complex activity (superoxide production) is critical for protection against methylotroph infections. Consistent with this hypothesis, previous studies have demonstrated that G. bethesdensis persists in Nox2-based complex-deficient myeloid cells and is largely resistant to oxygen-independent microbicidal activity.[11,12]

Methylotroph infections in CGD patients typically result in elevated inflammatory markers and lymphadenopathy, which may progress to necrotizing lymphadenitis with or without abscess formation. The clinical course may be protracted because of infection persistence, antimicrobial drug resistance, and relapse. Culturing these bacteria is difficult, requiring atypical media and prolonged incubation. These infections have not been fatal for patients in North and Central America, but G. bethesdensis infections in patients from Portugal and Spain[5] have caused fatal meningitis and bacteremia, respectively. The different clinical courses and outcomes for these patients compared with those in North and Central America suggest that the G. bethesdensis strain from Europe may be more virulent; animal studies are needed to explore this possibility. Furthermore, the strains isolated in Spain and Portugal showed only a 99.7% match with the 16S rRNA sequence of the type strain from North America, whereas most strains from North and Central America showed a 100% match with the type strain. Moreover, the strain from Europe displayed more in vitro resistance to antimicrobial agents and was resistant to colistin, most β-lactams, and quinolones.[5] Although the value and accuracy of in vitro susceptibility testing for G. bethesdensis are unknown and may lack predictive value, the clinical and laboratory differences between G. bethesdensis strains from the United States and Europe may have substantial implications for therapy.

The facultative methylotrophs we report were difficult to culture; their correct identification required non–culture-based techniques, such as 16S rRNA gene sequencing, and a high index of suspicion. Application of 16S rRNA sequencing and molecular probes to target tissues may identify previously unrecognized bacteria, which may accompany and possibly facilitate methylotroph infections.

G. bethesdensis is a gram-negative, aerobic, oxidase-negative, and catalase positive bacillus. Culture is facilitated by specimen centrifugation and plating on buffered charcoal yeast extract agar or solid mycobacterial media; incubation takes up to 2 weeks.[6]A. methanolica is a gram-negative, aerobic, acid-tolerant, catalase-positive, urease-positive, oxidase-positive, non–spore-forming, and nonmotile rod-shaped bacterium.[13] It forms tan colonies in <5 days on chocolate agar and grows well on potato dextrose agar. M. lusitanum is a vacuolated gram-negative aerobic rod that is positive for indophenol oxidase, catalase, and urease and produces a pink pigment. It also reduces nitrate and assimilates malate.[10] Methanol dehydrogenase serology is currently under investigation as a potential supportive diagnostic or prognostic tool for tracking methylotroph infections, particularly those caused by G. bethesdensis.[14]

Management of methylotroph infections is often prolonged and may require combination antimicrobial drug therapy and surgery. Drug susceptibilities are difficult to determine and interpret. In vitro, G. bethesdensis is typically resistant to most penicillins, cephalosporins, carbapenems, and quinolones, but it is sometimes susceptible in vitro to ceftriaxone, aminoglycosides, doxycycline, and trimethoprim/sulfamethoxazole; combinations of these drugs have helped achieve initial resolution.[6] Although antimicrobial drug susceptibilities for A. methanolica are not well defined, infections seemed to respond to combinations including meropenem, ciprofloxacin, gentamicin, doxycycline, and trimethoprim/sulfamethoxazole. M. lusitanum seems to be susceptible to aminoglycosides, cephalosporins, ciprofloxacin, piperacillin/tazobactam, and imipenem but not to meropenem, trimethoprim/sulfamethoxazole, or aztreonam. The role of surgery in treating methylotroph infections has not been defined, but its successful use in several cases is noteworthy.

In conclusion, methylotrophs are environmental organisms that can cause necrotizing infections in patients with CGD. Infectious prodromes and clinical courses may be prolonged. Diagnosis requires a high index of suspicion so that appropriate culture conditions and culture-independent techniques can be established for diagnosis. The difficulty of growing methylotrophs from infected lesions gives pause for the use of the label "sterile inflammation" with regard to CGD patients. Methylotrophs should be aggressively sought as the cause of chronic necrotizing infections in patients with CGD.

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