1. Identify the distinguishing characteristics of the species within the genera Moraxella and Neisseria. 2. Identify what species within this group of bacteria that are frequently isolated as pathogens and which are considered potential contaminants. 3. Explain the procedure the microbiologist can use to determine whether the bacteria in this grouping exist as true cocci and name these organisms. 4. Identify the species of Moraxella and Neisseria that may be isolated from human wounds resulting from a dog or cat bite. 5. Identify the species of Moraxella frequently isolated from cases of human conjunctivitis. 6. Explain the media used for culture for this group of organisms, including the chemical principle and composition. 7. List some of the conventional biochemical tests that can be used to distinguish these organisms from other bacteria, and explain the principle for each. 8. Correlate patient signs and symptoms with laboratory data, and identify the most likely etiologic agent. Infections caused by Moraxella spp. and Neisseria elongata most likely result when a breakdown of the patient’s mucosal or epidermal defensive barriers allows subsequent invasion of sterile sites by an organism that is part of the patient’s normal flora (i.e., an endogenous strain; Table 28-1). The fact that these organisms rarely cause infection indicates that they have low virulence. Whenever these organisms are encountered in clinical specimens, the possibility that they are contaminants should be seriously considered. This is especially the case when the specimen source may have come in contact with a mucosal surface. TABLE 28-1 Epidemiology, Pathogenesis, and Spectrum of Disease Moraxella catarrhalis is the species most commonly associated with human infections, primarily of the respiratory tract. However, because the cellular morphology of this species is more similar to that of Neisseria spp. than that of the other Moraxella spp., details of this organism’s characteristics are discussed in Chapter 40. The rarity with which these organisms are encountered as the cause of infection and the lack of validated in vitro susceptibility testing methods does not allow definitive treatment guidelines to be given (Table 28-2). Although many of these organisms may grow on the media and under the conditions recommended for testing other bacteria, this does not necessarily mean that interpretable and reliable results will be produced. Chapter 12 should be reviewed for preferable strategies that can be used to provide susceptibility information when validated testing methods do not exist for a clinically important bacterial isolate. TABLE 28-2 Antimicrobial Therapy and Susceptibility Testing *Validated testing methods include those standard methods recommended by the Clinical and Laboratory Standards Institute (CLSI) and those commercial methods approved by the Food and Drug Administration (FDA). No special considerations are required for specimen collection and transport of the organisms discussed in this chapter. Refer to Table 5-1 for general information on specimen collection and transport.
Moraxella and Related Organisms
Epidemiology, Spectrum of Disease, and Antimicrobial Therapy
Organism
Habitat (Reservoir)
Mode of Transmission
Virulence Factors
Spectrum of Disease and Infections
Moraxella nonliquefaciens, Moraxella lacunata, Moraxella osloensis, Moraxella lincolnii, Moraxella canis, and Moraxella atlantae
Normal human flora that inhabit mucous membranes covering the nose, throat, other parts of the upper respiratory tract, conjunctiva, and, for some species (i.e., M. osloensis), the urogenital tract; may also colonize the skin
Infections are rare; when they occur, they are probably caused by the patient’s endogenous strains; person-to-person transmission may be possible, but this has not been documented
Unknown; because they are rarely associated with infections, they are considered opportunistic organisms of low virulence
M. lacunata has historically been associated with eye infections, but these infections also may be caused by other Moraxella spp.; other infections include bacteremia, endocarditis, septic arthritis, and, possibly, respiratory infections
Neisseria elongate
Normal flora of upper respiratory tract
When infections occur, they are probably caused by the patient’s endogenous strains
Unknown; an opportunistic organism of low virulence
Rarely implicated in infections; has been documented as a cause of bacteremia, endocarditis, and osteomyelitis
Neisseria weaverii
Oral flora of dogs
Dog bite
Unknown
Infections of dog bite wounds
Organism
Therapeutic Options
Potential Resistance to Therapeutic Options
Validated Testing Methods*
Moraxella spp.
No definitive guidelines; generally susceptible to penicillins and cephalosporins
β-lactamase–mediated resistance to penicillins common
Not available
Exception: See CLSI document M45 for testing guidelines for M. catarrhalis (see Chapter 40)
Neisseria elongata and Neisseria weaverii
No definitive guidelines; generally susceptible to penicillins and cephalosporins
None known
Not available
Laboratory Diagnosis
Specimen Collection and Transport
Basicmedical Key
Fastest Basicmedical Insight Engine
