Gram-Negative Bugs Flashcards
Gram negative, maltose-fermenting, kidney-bean-shaped diplococci
Neisseria meningitidis
- IgA protease
- Metabolizes maltose and glucose (vs gonorrhea)
- Selectively grows on Thayer-Martin media
- Tx: Pencillin, Ceftriaxone
- PPx: rifampin for close contacts
Gram negative, non-maltose-fermenting diplococci
Neisseria gonorrhoeae
- Attaches to mucosal cells via pili (antigenic variation prevents immunity, allowing recurrent infections)
- IgA protease
- Metabolizes glucose for not maltose (vs. meningitidis)
- Selectively grows on Thayer-Martin media
- Tx: Ceftriaxone and doxy
- PPx for neonates: erythromycin eye drops
Gram negative, oxidase positive diplococci
**Moraxella catarrhalis **
- Specialized pili allow attachment to mucosal surface, evasion from host defenses via antigenic variation, and prevent phagocytosis
- Hydrolyzes tributyrin, produces DNAse, reduces nitrites
- Common cause of pneumonia in pt with COPD (along with H. influenzae)
- Most produce beta-lactamase (tx: amox-clav)
Gram-negative, lactose-fermenting bacilli
-
Klebsiella (fast fermenter)
- Pneumoniae with “currant-jelly” sputum in alcoholics
- Nosocomial UTI (drug-resistant)
-
Escherichia coli (fast fermenter)
- K antigen (capsule), O antigen (component of LPS in outer membrane), H antigen (flagella), Endotoxin (lipid A component of LPS)
- ETEC (traveler’s diarrhea), EPEC (infant’s diarrhea), EHEC (dysentery, HUS), EIEC (dysentery with leukocytes in stool)
- Enterobacter (fast fermenter)
- Citrobacter (slow fermenter)
- Serratia (slow fermenter)
Gram negative, lactose-non-fermenting, oxidase negative, H2S-producing motile bacilli
- **Salmonella typhi **- Typhoid Fever, osteomyelitis in SCA
- Vi capsule allows survival in phagocytes of Peyer’s patches, where it spreads to gallbladder, spleen, liver and releases endotoxin
- Motile via flagella (H antigen) vs. nonmotile Shigella
- H2S-producing vs. Shigella
- Lactose-non-fermenting vs. E. coli
- Monocytic response to mucosal invasion
-
Salmonella enteritidis - gastroenteritis
- Fecal-oral transmission from turtles and uncooked chicken
- Abx may prolongs fecal excretion of organism
Gram negative, lactose-non-fermenting, oxidase negative, H2S-non-producing, non-motile bacilli
Shigella dystenteriae
- O antigen (polysaccharide in outer membrane)
- Shiga toxin (inactivates 60S ribosome) - further damages mucosa for not vital for disease
- Nonmotile, nonhematogenous spread vs motile Salmonella
- Does not produce H2S vs. Salmonella
- Does not ferment lactose vs. E. coli
- PMN response to mucosal infiltration
- Abx shortan duration of fecal excretion
Gram negative, lactose-non-fermenting, oxidase negative, urease positive bacilli
Proteus mirabilis
- Urease - splits urea to form ammonium hydroxide, which alkalinizes the urine pH and causes precipitation of ammonium magnesium phosphate (struvite) stones
- O antigen of proteus cross-reactions with serum Abs vs. Rickettsia (Weil-Felix reaction)
- Many flagella allow for great motility
Gram negative, lactose-non-fermenting, oxidase positive, glucose-fermenting “comma-shaped” bacilli
Vibrio cholerae
- Transmitted via water, food and shellfish
- Mucinase - digests protective mucous coat around intestinal cells
- Very acid-sensitive (achlorhydria increases susceptibility)
- Single flagellum
- Cholera toxin (AB toxin) ribosylates Gs, increasing cAMP, thus increasing Cl excretion by crypt cells and decreasing Na absorption by villous cells
- Vibrio parahaemolyticus presents similarly and is associated with raw seafood consumption
Gram negative, lactose-non-fermenting, oxidase positive, glucose-non-fermenting bacilli
Pseudomonas aeruginosa
- Blue-green colonies (pyocyanin pigment) with fruity odor
- Exotoxin A - ribosylates host EF2, inhibiting protein synthesis
- Phospholipase C - damages host cell membrane
- Elastase - permits dissemination
- Endotoxin - shock
Gram negative, lactose-non-fermenting bacilli that are motile at 25 C but not at 37 C
Yersinia enterocolitica
- Transmitted in raw milk or via fecal-oral route, localizes in terminal ileum, and secretes heat-stable enterotoxin (similar to E coli ST toxin), leading to dysentery and mesenteric adenitis
- Enterocolitis may be accompanied by appendicitis-like pain in children > 5 yo and arthritis in adults
Gram negative, lactose-non-fermenting, “safety-pin” bipolar staining bacilli
Yersinia pestis
- Capsular F-1 antigen - prevents phagocytosis and generates antibody response
- Cutaneous hemorrhagic necrosis (“Black Death”)
- Tx: streptomycin, tetracycline
Gram negative, urease-positive, catalase-positive, oxidase-positive, spiral-shaped bacilli with small growth on Campy agar
Helicobacter pylori
- Risk of duodenal ulcers (acid hypersecretion if gastritis is limited to antrum where it decreases somatostatin secretion by antral D cells)
- Risk of gastric ulcers and gastric adenocarcinoma/MALT (acid hyposeretion if gastritis extends throughout stomach)
- Urea breath test - labeled CO2 exhaled if urease present
- Tx: PPI + amoxicillin + clarithromycin
Gram negative, urease-negative, “S”-shaped bacilli with small growth on Campy agar
Campylobacter jejuni
- Grows best at 42 C, microaerophilic
- May lead to Guillain-Barre Syndrome
Gram negative, strict anaerobic bacilli
Bacteroides fragilis
- Normal GI flora that may cause GI or pelvic abscesses (“below the diaphragm”) following mucasal rupture
- Normally, makes Vitamin K for the host
- Survives oxygen environment via catalase and superoxide dismutase
- Capsule gives colonies a “mucoid appearance”
- Only Gram negative bus without LPS
Gram-negative coccobacilli, requiring X and V factors
Haemophilus influenzae
- Type B polysaccharide capsule (Quellung test +) - Hib vaccine is a capsular polysaccharide of type B strain conjugated to diphtheria toxin
- Requires factors V and X for growth (can also be grown with S aureus which provides factors V)
- IgA protease
- Tx: Ceftriaxone
- PPx: Rifampin
