Current Name	Previous Name
Moraxella atlantae
Moraxella canis
Moraxella lacunata
Moraxella lincolnii
Moraxella nonliquefaciens
Moraxella osloensis
Neisseria elongata subspecies elongata	CDC group M6
Neisseria elongata subspecies glycolytica
Neisseria elongata subspecies nitroreducens
Neisseria weaverii	CDC group M5

General Characteristics

The organisms discussed in this chapter are either coccobacilli or short to medium-sized, gram-negative rods. This group of bacteria consists of several species within the genera Moraxella and Neisseria, other than the three frequently isolated pathogens, Moraxella catarrhalis, Neisseria. gonorrhoeae, and Neisseria meningitidis. Most of these organisms rarely cause infection and should be considered as potential contaminants. Many Moraxella spp. are considered to be normal mucosal flora with low virulence. Two of these species, N. weaverii and M. canis, are oropharyngeal flora in dogs and cats and are sometimes seen in humans as a result of a bite wound. Subinhibitory concentrations of penicillin, such as occurs in the presence of a 10-unit penicillin disk, cause the coccoid forms of these bacteria to elongate to bacilli morphology. In contrast, true cocci, such as most Neisseria spp. and Moraxella (Branhamella) catarrhalis, with which these organisms may be confused, maintain their original cocci shape in the presence of penicillin. In addition, the organisms discussed in this chapter do not use glucose and most do not grow on MacConkey agar but will grow well on blood and chocolate agar, as well as in commercial blood culture systems. Specific morphologic and physiologic features are presented later in this chapter in the discussion of laboratory diagnosis.

Epidemiology, Spectrum of Disease, and Antimicrobial Therapy

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

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

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.

Data collected from the Centers for Disease Control and Prevention (CDC) show that these rare isolates may also be a cause of infection. In a study of the bacteria, Neisseria elongate subsp. nitroreducens, one fourth of the isolates received at the CDC for analysis were from cases of bacterial endocarditis. Data collected during a 16-year period found that most of these isolates were from blood, but they were also recovered from wounds, respiratory secretions, and peritoneal fluid. Individuals at risk had preexisting heart damage or had undergone dental manipulations.

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

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

^*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).

In general, β-lactam antibiotics are thought to be effective against these species. However, some evidence suggests that β-lactamase–mediated resistance may be capable of spreading among Moraxella spp.

Laboratory Diagnosis

Specimen Collection and Transport

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.

Specimen Processing

No special considerations are required for processing of the organisms discussed in this chapter. Refer to Table 5-1 for general information on specimen processing.

Direct Detection Methods

Other than a Gram stain of patient specimens, there are no specific procedures for the direct detection of these organisms in clinical material. M. atlantae, M. nonliquefaciens, and M. osloensis may appear as either coccobacilli or as short, broad rods that tend to resist decolorization and may appear gram-variable. This is also true for M. canis, which appears as cocci in pairs or short chains. M. lacunata is a coccobacilli or medium-sized rod, and M. lincolnii is a coccobacilli that may appear in chains. All subspecies of Neisseria elongata are either coccobacilli or short, straight rods, and N. weaverii is a medium-length, straight bacillus.

Cultivation

Media of Choice

Moraxella spp. and the elongated Neisseria spp. grow well on 5% sheep blood and chocolate agars. Most strains grow slowly on MacConkey agar and resemble the non-lactose-fermenting Enterobacteriaceae. Both genera also grow well in the broth of commercial blood culture systems and in common nutrient broths, such as thioglycollate and brain-heart infusion.

Incubation Conditions and Duration

Five percent sheep blood and chocolate agars should be incubated at 35° C in carbon dioxide or ambient air for a minimum of 48 hours. For those species that may grow on MacConkey agar, the medium should be incubated at 35° C in ambient air.

Table 28-3 describes the colonial appearance and other distinguishing characteristics (e.g., pitting) of each species on 5% sheep blood and MacConkey agars. The ability of most commercial identification systems to accurately identify the organisms discussed in this chapter is limited or uncertain. Table 28-4 lists some conventional biochemical tests that can be used to presumptively differentiate the species in this chapter. This is a simplified scheme; clinically important isolates should be sent to a reference laboratory for definitive identification.

TABLE 28-3

Colonial Appearance and Characteristics

Organism	Medium	Appearance
Moraxella atlantae	BAP	Small, pitting and spreading
Moraxella atlantae	Mac	NLF
M. lacunata	BAP	Small colonies that pit the agar
M. lacunata	Mac	No growth
M. lincolnii	BAP	Smooth, translucent to semiopaque
M. lincolnii	Mac	No growth
M. nonliquefaciens	BAP	Smooth, translucent to semiopaque; occasionally, colonies spread and pit agar
M. nonliquefaciens	Mac	NLF, if growth
M. osloensis	BAP	Smooth, translucent to semiopaque
M. osloensis	Mac	NLF, if growth
M. canis	BAP	Resemble colonies of Enterobacteriaceae
M. canis	Mac	NLF
Neisseria elongata (all subspecies)	BAP	Gray, translucent, smooth, glistening; may have dry, claylike consistency
Neisseria elongata (all subspecies)	Mac	NLF, if growth
N. weaverii	BAP	Small, smooth, semiopaque
N. weaverii	Mac	NLF, if growth

BAP, 5% sheep blood agar; Mac, MacConkey agar; NLF, non-lactose-fermenter.

TABLE 28-4

Key Biochemical and Physiologic Characteristics

Organism	Growth on MacConkey	Catalase	Nitrate Reduction	Nitrite Reduction	DNase	Digests Loeffler’s Slant	Sodium Acetate Utilization	Growth in Nutrient Broth
Moraxella atlantae	+	+	−	−	−	−	ND	−
M. lacunata	−	+	+	−	−	+	−	−
M. lincolnii	−	+	−	−*	−	−	−	−
M. nonliquefaciens	−	+	+	−	−	−	−	v
M. osloensis	v	+	v	−	−	−	+	+
M. canis	+	+	+	v	+	−	+	+
Neisseria elongata subsp. elongata	v	−	−	+	ND	ND	v	+
Neisseria elongata subsp. glycolytica	+	+	−	v	ND	ND	+	+
Neisseria elongata subsp. nitroreducens	v	−	+	+	ND	ND	v	v
N. weaverii	v	+	−	+	ND	ND	−	v

ND, No data; v, variable; +, >90% of strains positive; −, >90% of strains negative.

Note: Organisms listed are generally indole-negative.

^*Nitrite-positive strains have been reported.

Approach to Identification

As previously mentioned, these organisms can be difficult to differentiate from gram-negative diplococci (see Chapter 40 for more information about gram-negative diplococci). In addition, these organisms are relatively biochemically inert. Elongation in the presence of penicillin is a useful criterion for differentiating them from true cocci. The effect of penicillin is determined by streaking a blood agar plate, placing a 10-unit penicillin disk in the first quadrant and overnight incubation at 35° C. A Gram stain of the growth taken from around the edge of the zone of inhibition readily demonstrates whether the isolate in question is a true cocci or has elongated.