Gram negative bacilli

Brief description of a few gram negative bacilli, their characteristic features, pathological lesions caused by them and biochemical properties

1. By- Sneha A (MBBS UG) GRAM NEGATIVE BACILLI

2. Classes Bacteroides ( most common ) Prevotella Porphyromonas Fusobacterium Leptotrichia All gram negative bacilli are non motile

3. BACTEROIDS Commensals in IT, RT and female genital tract. Morphology Gram negative, non-sporing, non-motile Pleomorphic slender rods Seen singly, in pairs in short chains or as branching forms, Culture characters Obligate anaerobes capnophilic (10%) Media: Brain heart infusion agar Colonies: Non hemolytic, semi opaque, grey colony with concentric whorls inside

4. Virulence factors- Capsular polysaccharides Protect from host immune response Antigenic Species B. fragilis (most common) B. thetaiotaomicron B. melaninogenicus etc Resistance Susceptible to Metranidazole, Clindamycin, Penicilline(species variation) Specimen collection sites Blood, pleura and peritoneal fluids, CSF and cervical swabs

5. PREVOTELLA Previously placed under bacteroids Sacchrolytic Pigment producing- brown to black Culture- Brown to black colonies on BA Brick-red fluorescence (UV)-P. melaninogenica Biochemical reactions Indol +ve Glucose fermentors Species P. melaninogenica (pigment-brown black colonies on BA, hemin derivative, earlier melanin) P. buccalis P. denticola , etc

6. Pathogenesis Liver abscess, mastoiditis , intestinal lesions and lesions of mouth and gums

7. PORPHYROMONAS Previously classified under bacteroids Asaccharolytic Pigment producing- brown-black pigment Sensitive to vancomycin Species P. gingivalis (periodontal diseases) P. endodontalis (dental root canal infections) etc

8. FUSOBACTERIUM Morphology- long, thin or spindle shaped with pointy ends Species F. nucleatum F. necrophorum

9. Property F. nucleatum F. necrophorum Feature Commensal in mouth Produce exotoxins Major lesions Oral infection and pleuropulmonary sepsis Liver abscess and other abdominal infections (mostly in animals, less in humans) Maltose fermentation - - Lactose fermentation - - Sucrose fermentation - - Growth in Bile - - Indol test + + Resistance to refampacin - -

10. Leptotrochia L. buccalis (Vincent’s fusiform bacilli/ Fusobacterium fusiforme) Commensal in oral cavity Morphology- long straight or slightly curved rods with pointed ends (fusiform or spiral bacilli) Pathogenesis Acute necrotizing lesion Vincent’s angina (resemble diphtheria, inflamed pharyngeal mucosa, grayish membrane which peels easily)

11. What did we learn ? The current genus name of a saccharolytic group of Bacteroides is A. Porphyromonas B. Bacteroides C. Prevotella D. None of these Which of the following bacterial colonies fluoresce brick-red in UV light? A. P gingivalis B. P melaninogenicus C. Bacteroides fragilis D. B levii The commonest species of Bacteroides group , which causes human infection, is A. B vulgatus B. B fragilis C. B ovatus D. B merdae