NON-ENTERIC GRAM NEGATIVE RODS Legionella and Bacteroides

I. Legionella pneumophila LEGIONAIRES’ DISEASE AND PONTIAC FEVER

In August of 1976 at an American Legion Convention Philadelphia more than 200 members were stricken with an unknown respiratory illness with an abrupt onset of fever, chills, headache, cough, and progressive multi-lobar pneumonia. Many became confused and comatose with multi-organ failure (especially GI, CNS, liver and kidneys). Thirty four (34) individuals died from this outbreak (17%).

CHARCTERISTIC PROPERTIES OF Legionella pneumophila A difficult organism to visualize in clinical material (A). It does not stain well with the Gram stain. In culture, L. pneumophila is a thin, pleomorphic Gram negative rod (B). A B

2-4. Legionellae are visualized best using modified Giemsa, silver impregnation, or immunofluorescent staining (below). Since they are facultative intracellular pathogens, legionellae are typically seen in macrophages.

5. Legionella pneumophila grown on a charcoal buffered yeast extract agar with L-cysteine (BCYE). 6. Incubated for 5 days at 37OC aerobically with 5% CO2

Characteristics (Cont.) 7. Legionella are strictly aerobic, catalase positive, and weakly oxidase positive. 8. There are at least 4 serogroups. (most human infections are caused by Serogroup I)

B. EPIDEMIOLOGY: Legionella pneumophila Environmental Isolates mostly from aquatic sources such as air conditioning systems, rivers, lakes, ponds, and tap water (including samples of distilled water). These organisms are not found normally in animals ( NOT ZOONOTIC AGENTS). Causes Legionaires’ Disease as an endemic, sporadic, point source outbreak: Also causes Pontiac Fever. Incubation period for Legionaires’ Disease is 2-10 Days. Low attack rate of 0.1 to 4% of those exposed. In contrast, Pontiac Fever has a high attack rate > 95% of those exposed with a short incubation period of 6 hours to 2 days. (NO PNEUMONIA) Worldwide incidence More prevalent in summer Affects middle aged to elderly males most frequently. Spread by airborne transmission (not Human to Human).

C. CLINICAL MANIFESTATIONS: 2 FORMS OF DISEASE LEGIONAIRES’ DISEASE AND PONTIAC FEVER LEGIONAIRES’ DISEASE Portal of entry is respiratory Acute fibrinopurulent bronchopneumonia May have Bacteremia May vary from mild to severe fulminant systemic disease and death PONTIAC FEVER Acute, self limited, febrile NOT FATAL Abrupt onset, myalgia, malaise, headache NO PNEUMONIA May be asymptomatic Recover in 2 to 5 days

D. DIAGNOSIS 1. Diagnosis can be problematic, since definitive diagnosis depends upon isolation and identification of L. pneumophila from the appropriate clinical material. 2. Serology is a quick way to make a tentative diagnosis, utilizing increasing antibody titers (> 4 fold), however immunofluorescent staining, hemagglutination, hemagglutination inhibition, micro-agglutination and ELISA may all be used to augment diagnosis.

E. THERAPY Erythromycin and Rifampin are the drugs of choice; DO NOT USE Cephalosporins, Tetracyclines, Clindamycin or Vancomycin

II. More that 39 species in the genus Legionella Many cause a pneumonia similar to Legionaires’ disease, e.g. L. micdadei and L. bozemaniae. In addition to Legionella, there are a large number of miscellaneous Gram negative rods that cause serious to fatal infections in Humans. These are too numerous to list here, but include important pathogens such as in the genus Bartonella.

III. BACTEROIDES (GRAM NEGATIVE RODS) AND RELATED ANAEROBIC BACTERIA Heterogeneous group of bacteria Strictly anaerobic, non-spore forming All are part of the normal flora in either the mouth or GI tract Taxonomy in flux

Many Genera and Species The following are encountered most frequently in human infections: Bacteroides fragilis Bacteroides thetaiotaomicron Prevotella melaninogenica Prevotella bivia Porphyromonas gingivalis Porphyromonas asaccharolytica Fusobacterium nucleatum Fusobacterium necrophorum

Fusobacterium spp. can be differentiated from all other Gram negative, strictly anaerobic rods by its ability to produce significant amounts of butyric acid from glucose. (Thus, Bacteroides, Prevotella, and Porphyromonas do not produce large amounts of Butyric acid from glucose.) Bacteroides has a defective LPS that has reduced toxicity whereas Fusobacterium has a typical LPS with enhanced toxicity.

BACTEROIDES FRAGILIS The most important pathogenic species of the Gram negative anaerobic rods Colonies are neither pigmented nor hemolytic on blood agar (It ferments carbohydrates, requires vitamin B12 and it is saccharolytic). Virulence depends on capsule and pili.

BACTEROIDES FRAGILIS It is present in the colon, but it is not the dominant Bacteroides species. It causes endogenous, mixed anaerobic infections Usually anaerobic abscesses (an opportunist) May be in lung abscesses (Usually Prevotella) Brain abscesses (Often Prevotella) Intra-abdominal infections (MOST COMMON) Gynecological abscess Bacteremia (often secondary to GI surgery or trauma) Anaerobic lesion in the foot of a diabetic patient. Bacteroides fragilis was the dominant organism. .

PREVOTELLA MELANINOGENICA This organism is part of the normal oral flora, fairly fastidious, needs hemin and vitamin K for growth, and produces a dark to black pigment when grown on blood agar. It is often involved in anaerobic abscesses in the lungs, mouth, and injuries associated with human bites (Often with Eikenella that may more frequently cause disease from bites).

Porphyromonas species are similar to Bacteroides species in the types of diseases that they cause. They are differentiated by being non-saccharolytic. All of these anaerobes are opportunistic pathogens causing mixed endogenous infections as part of the normal flora getting into the wrong place.

THERAPY Bacteroides fragilis is often resistant to many antimicrobials, and they produce beta lactamase. Clindamycin was the drug of choice, however Metronidazole is the current drug of choice. Therapy may also require surgical intervention. The other Gram negative anaerobes may be treated with Metronidazole combined with surgical procedures.

IV. FUSOBACTERIUM Gram negative, anaerobic rods with fusiform morphology

At least 4 species of Fusobacterium cause disease in humans, they have variable morphology and they are differentiated by specific phenotypic properties. All of them produce large amounts of butyric acid, giving the lesions a characteristic odor. Since many of them lack both SOD and Catalase, they are very sensitive to exposure to the air. Fusobacterium nucleatum is most frequently encountered Fusobacterium in human disease.

Fusobacterium nucleatum In association with spirochetes in the mouth, this species causes the fusospirochetal disease Vincent’s angina. (Trench mouth, which is a necrotizing ulcerative gingivitis) Penicillin is the drug of choice for fusobacterial infections