The family Moraxellaceae is a member of the order Pseudomonadales, consists of aerobic, Gram-negative, catalase positive, nonfermenting bacteria and is subdivided into three well-recognized genera, Moraxella, Acinetobacter, and Psychrobacter . The genus Moraxella includes seven species, the most common of which is Moraxella catarrhalis, a frequent cause of otitis media in children and of infectious exacerbations of chronic obstructive pulmonary disease in adults [15, 16].
M. nonliquefaciens is a usually non-pathogenic microorganism that exists as part of the upper respiratory tract flora . It has been reported as an occasional cause of localized invasive infections, including meningitis , endophthalmitis [3, 4], endocarditis [5,6,7], pneumonia , and septic arthritis . Immediately life-threating conditions in the form of bloodstream infections seem to be even more rare: Including the case presented here, only five cases of M. nonliquefaciens bacteremia have been reported in the literature to date [9,10,11,12] (Table 1). In all cases, underlying diseases may have acted as predisposing factors: three patients presented with hemato-oncological disorders and treatment-induced neutropenia, and the remaining two patients had significant comorbidities. This suggests that M. nonliquefaciens has a relevant pathogenicity potential in immunocrompromised and critically ill patients, while it is unlikely to cause disease in healthy hosts. Bloodstream-associated and catheter-associated infections with other Moraxella species have been reported in cancer patients in association with chemotherapy-related mucositis , which constitutes a plausible portal of entry also in our patient.
The ability to produce biofilms observed in M. nonliquefaciens and other Moraxella species  and the interaction with other microorganisms within this milieu can contribute to bacterial persistence and resistance against antibiotic treatment . In spite of the lack of specific susceptibility breakpoints for M. nonliquefaciens, an in vitro resistance pattern frequent in the genus Moraxella was observed, with resistance against penicillin, amoxicillin, ampicillin und piperacillin and susceptibility to piperacillin plus tazobactam that suggest the production of β-lactamases . Although not possible to prove, and based on the evidence regarding the pathogenicity of M. nonliquefaciens in immunocompromised patients, the clinical deterioration of our patient at day two of appropriate antibacterial therapy with prompt recovery after removal of the indwelling central venous catheter suggests a role of biofilm in the pathogenesis of the evolving sepsis. This supports the importance of immediate source control for successful management of bloodstream infections by M. nonliquefaciens.
Although very infrequently, Moraxella nonliquefaciens may cause bloodstream infections, especially in immunocompromised patients. A successful therapeutic approach should include prompt source control and administration of adequate antibiotic therapy.