1. NON-ENTERIC GRAM NEGATIVE RODS
Legionella and Bacteroides

2. I. Legionella pneumophila
LEGIONAIRES’ DISEASE AND PONTIAC FEVER

3. 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%).

4. 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

5. 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.

6. 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

7. 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)

8. 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).

9. 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

10. 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.

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

12. 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.

13. 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

14. 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

15. 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.

16. 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.

17. 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. .

18. 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).

19. 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.

20. 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.

21. IV. FUSOBACTERIUM
Gram negative, anaerobic rods with fusiform morphology

22. 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.

23. 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