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 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.

Table1.  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.

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 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.

Table2. Antimicrobial Therapy and Susceptibility Testing

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 col lection and transport of the organisms discussed in this chapter.

SPECIMEN PROCESSING

No special considerations are required for processing of the organisms discussed in this chapter.

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. nonliquefaiens, 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.

Colonial Appearance

 Table 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 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.

Table3. Colonial Appearance and Characteristics

Table4. Key Biochemical and Physiologic Characteristics

APPROACH TO IDENTIFICATION

As previously mentioned, these organisms can be difficult to differentiate from 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.

Comments Regarding Specific Organisms

M. nonliquefaciens and M. osloensis, the two most frequently isolated species, can be differentiated by the ability of M. osloensis to utilize acetate. M. lacunata is able to liquefy serum, so depressions are formed on the surface of Loeffler’s serum agar slants. Most of the species considered in this chapter do not utilize glucose; Neisseria elongata subsp. glycolytica, which produces acid from glucose in the rapid sugar test used for Neisseria spp., is the only exception. Unlike Oligella spp., none of the organisms considered here are motile.

SERODIAGNOSIS

 Serodiagnostic techniques are not generally used for the laboratory diagnosis of infections caused by the organ isms discussed in this chapter.

PREVENTION

Because these organisms do not generally pose a threat to human health, there are no recommended vaccination or prophylaxis protocols.

اخر الاخبار

اخبار العتبة العباسية المقدسة

المجمَع العلمي يقيم دورة في أحكام التلاوة وفنون القراءة بقضاء الهندية

المجمع العلمي يحيي ذكرى شهادة الإمام الجواد (عليه السلام) في كربلاء

جمعية كشافة الكفيل تدعو للمشاركة في مجلس عزاء ذكرى استشهاد الإمام الجواد (عليه السلام)

عبر مجلس عزاء.. المجمع العلمي يحيي ذكرى شهادة الإمام الجواد (عليه السلام) في النجف الأشرف

المزيد

الآخبار الصحية

طريقة مبتكرة للكشف المبكر عن أمراض القلب والشرايين

منظمة الصحة تحذر من خطر إدمان الشباب لأكياس النيكوتين

خبراء يحذرون من عادة شائعة تهدد صحة الملايين

خبير يكشف 5 حقائق طبية صادمة وغير معروفة

المزيد

الآخبار التكنلوجية

الأولى في العالم.. الصين تجري تجربة رائدة في الفضاء باستخدام "جنين اصطناعي"

دراسة حديثة تفند ربط التستوستيرون بالمخاطرة لدى الرجال

ميتا تضيف وضع "المحادثة المخفية" إلى تطبيق "واتساب"

فوبيا المرتفعات ليست من الدماغ.. دراسة تكشف السبب

المزيد

مواضيع ذات صلة

Sphingomonas paucimobilis and Similar Organisms : Laboratory Diagnosis

Alcaligenes, Bordetella (Non-pertussis), Comamonas, and Similar Organisms : Pathogenesis and Spectrum of Disease

Chryseobacterium, Sphingobacterium, and Similar Organisms

Pseudomonas, Burkholderia, and Similar Organisms : Epidemiology

Acinetobacter, Stenotrophomonas, and Similar Organisms : Pathogenesis and Spectrum of Disease

Nocardia, Streptomyces, Rhodococcus, and Similar Organisms: Antimicrobial Susceptibility Testing and Therapy

Erysipelothrix, Lactobacillus, and Similar Organisms : Antimicrobial Susceptibility Testing and Therapy

Erysipelothrix, Lactobacillus, and Similar Organisms : Approach to Identification

Staphylococcus, Micrococcus, and Similar Organisms : Pathogenesis and Spectrum of Disease

Strategies to Control Bacteria at the Environmental Level

Definition and Measurement of Bacterial Death

Growth in Biofilms