GENERAL CHARACTERISTICS

The genus Streptobacillus is a member of the Fusobacteriaceae family. The Streptobacillus genus has only one species, S. moniliformis, a facultative, nonmotile anaerobe that tends to be highly pleomorphic.

EPIDEMIOLOGY AND PATHOGENESIS

The natural habitat of S. moniliformis is the upper respiratory tract (nasopharynx, larynx, upper trachea, and middle ear) of wild and laboratory rats (mice, gerbils, squirrels, ferrets, weasels); in addition, this organism occasionally has been isolated from other animals, such as cats and dogs that have fed on rodents. S. moniliformis is pathogenic for humans and is transmitted by two routes:

• Rat bite, or possibly through direct contact with rat feces or saliva

• Ingestion of contaminated food, such as unpasteurized milk or milk products and, less frequently, water

The incidence of S. moniliformis infections is unknown, but human infections appear to occur worldwide.

The pathogenic mechanisms of S. moniliformis are unknown. The organism is known to spontaneously develop L forms (bacteria without cell walls), which may allow its persistence in some sites.

SPECTRUM OF DISEASE

Despite the different modes of transmission, the clinical manifestations of S. moniliformis infection are similar. When S. moniliformis is acquired by ingestion, the disease is called Haverhill fever.

Patients with rat-bite or Haverhill fever develop acute onset of chills, fever, headache, vomiting, and often severe joint pains. Febrile episodes may persist for weeks or months. In the first few days of illness, patients develop a rash on the palms, soles of the feet, and other extremities. Complications can occur, including endocarditis, septic arthritis, pneumonia, pericarditis, brain abscess, amnionitis, prostatitis, and pancreatitis.

LABORATORY DIAGNOSIS

 Specimen Collection, Transport, and Processing

Unfortunately, the diagnosis of rat-bite fever caused by S. moniliformis is often delayed because of lack of expo sure history, an atypical clinical presentation, and the unusual microbiologic characteristics of the organism. Organisms may be cultured from blood or aspirates from infected joints, lymph nodes, or lesions. No special requirements have been established for the collection, transport, and processing of these specimens except for blood. Because recovering S. moniliformis from blood cultures is impeded by concentrations of sodium polyanethol sulfonate (SPS) used in blood culture bottles, an alternative to most commercially available bottles must be used. After collection by routine procedures (described in Chapter 68), blood and joint fluids are mixed with equal volumes of 2.5% citrate to prevent clotting and are then inoculated to brain-heart infusion cysteine broth supplemented with heated horse serum and yeast extract, commercially available fastidious anaerobe broth without SPS, or thiol broth.

Direct Detection Methods

Pus or exudates should be smeared, stained with Gram or Giemsa stain, and examined microscopically (Figure 1). S. moniliformis is a pleomorphic, gram-negative rod. Cells may appear straight of variable size or as long tangled chains and filaments with bulbar swellings. The cells may also appear spiral shaped and resemble a string of pearls. Direct detection of the 16sRNA gene sequence for S. moniliformis using polymerase chain reaction (PCF) analysis has been described.

Fig1. Gram stain of Streptobacillus moniliformis from growth  in thioglycollate broth with 20% serum. (Courtesy Robert E. Weaver,  Centers for Disease Control and Prevention, Atlanta, Ga.)

Cultivation

 As previously mentioned, S. moniliformis requires the presence of blood, ascitic fluid, or serum for growth. Growth occurs on blood agar, incubated in a very moist environment with 5% to 10% carbon dioxide (CO₂), usually after 48 hours of incubation at 37°C. Colonies are nonhemolytic. The addition of 10% to 30% ascitic fluid (available commercially from some media suppliers) or 20% horse serum should facilitate recovery of the organ ism. In broth cultures, the organism grows as “fluff balls” or “bread crumbs” near the bottom of the tube of broth or on the surface of the sedimented red blood cell layer in blood culture media. Colonies grown on brain-heart infusion agar supplemented with 20% horse serum are small, smooth, glistening, colorless or grayish and have irregular edges.

Colonies are embedded in the agar and may also have a “fried egg” appearance, with a dark center and a flattened, lacy edge. These colonies are also referred to as L-phase colonies because they have undergone spontaneous transformation to the L form. Staining of L-form colonies yields coccobacillary or bipolar-staining coccoid forms (usually a special stain, such as the Dienes stain performed by pathologists), is required. Acridine orange stain also reveals the bacteria when Gram stain fails because of lack of cell wall constituents.

As previously stated, Gram-stained organisms from standard colonies show extreme pleomorphism, with long, looped, filamentous forms, chains, and swollen cells. The club-shaped cells can be 2 to 5 times the diameter of the filament. Carbolfuchsin counterstain or Giemsa stain may be necessary for visualization (see Figure 1).

Approach to Identification

 S. moniliformis does not produce indole and is catalase, oxidase, and nitrate negative, in contrast to organisms with which the Streptobacillus sp. may be confused, such as Actinobacillus spp., Haemophilus aphrophilus, and Cardiobacterium spp. In addition, S. moniliformis is nonmotile and urea and lysine decarboxylase negative; hydrogen sulfide (H2S) is not produced in triple sugar iron agar but can be detected using lead acetate paper.

Serodiagnosis

Serologic diagnosis of rat-bite fever is also useful; most patients develop agglutinating titers to the causative organism. The specialized serologic tests are performed only at national reference laboratories, because the disease is extremely rare in the United States. A titer of 1 : 80 is considered diagnostic unless a fourfold rise in titer is demonstrated.

ANTIMICROBIAL SUSCEPTIBILITY TESTING AND THERAPY

No standardized methods have been established for determining S. moniliformis susceptibility to various anti microbials. Different in vitro techniques, such as agar dilution and disk diffusion, have had similar results. Although S. moniliformis is susceptible to a broad spectrum of antibiotics, penicillin is regarded as the drug of choice for human rat-bite fever. An aminoglycoside or tetracycline can be used to eliminate L forms or for patients allergic to penicillin.

PREVENTION

There are no vaccines available to prevent rat-bite fever. Disease is best prevented by avoiding contact with animals known to harbor the organism. Individuals with frequent animal contact should wear gloves, practice regular handwashing and avoid hand-to-mouth contact when handling rats or cleaning rat cages.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الصيانة ينفذ أعمال إدامة لإحدى المدارس في محافظة النجف الأشرف

المجمع العلمي يستأنف الختمة القرآنية الأسبوعية في محافظة الديوانية

حملة تطوير وتأهيل تشهدها مدينة الفردوس الترفيهية استعدادًا لاستقبال العوائل

العتبة العباسية المقدسة تطلق فعاليات مهرجان (ترتيل الرأس) السنوي الثاني في بغداد

المزيد

الآخبار الصحية

لون أسنانك يتحدث عن صحتك.. إليك ما يقول

عادة يومية بسيطة تخفض الكوليسترول وتحمي القلب

الزنجبيل.. دواء سحري لحماية القلب

المشروبات شديدة السخونة.. "خطر خفي" يهدد صحتك

المزيد

الآخبار التكنلوجية

كيف يمكن لعادات القيادة السيئة أن تؤثر على قيمة سيارتك

في طوفان الذكاء الاصطناعي.. نصائح لحجز "تذكرة النجاة"

هكذا يسرق "قراصنة الذكاء الاصطناعي" المليارات بطرق بسيطة

فيديو لانفجار كرة نارية في سماء اليابان.. ما تفسير ذلك؟

المزيد

مواضيع ذات صلة

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Laboratory Diagnosis of Neisseria and Moraxella catarrhalis

Spirillum Minus

Myositis and Myonecrosis

Necrotizing Fasciitis

Cellulitis

Laboratory Diagnosis of Francisella

Laboratory Diagnosis of Bordetella pertussis, Bordetella parapertussis, and Related Species

Epidemiology and Pathogenesis of Bordetella pertussis, Bordetella parapertussis, and Related Species

Group B Streptococcal Disease

Streptococcal Toxic Shock Syndrome

Signs and Symptoms of Streptococcal Infections