Gram Negative Bacteria Flashcards
Lactose Fermenting Bacteria
Fast fermenter: Klebsiella, E. coli, Enterobacter
Slow fermenter: Citrobacter, Serratia, Others
Neissera Meningitidis Lab Algorithm, Transmission, Capsule Status, and Treatment
Gram negative diplococci that ferments maltose
Transmitted by respiratory and oral secretions
Has a polysaccharide capsule (vaccine available)
Treated with ceftriaxone or penicillin G (?)
Neissera gonorrhoeae Lab Algorithm, Transmission, Capsule Status, and Treatment
Gram negative diplococci that does not ferment maltose
Sexually transmitted
No capsule
Treated with ceftriaxone + azithromycin or doxycycline (for chlamydia)
Neissera Presentation
Gonorrhoeae: causes gonorrhea, septic arthritis, neonatal conjunctivitis, PID, and Fitz-Hugh-Curtis. Often intracellular
Meningitidis: causes meningococcemia (with petechial rash), meningitis, and Waterhouse-Friederichsen syndrome
Neissera 2 Unique Features
Both ferment glucose
Both produce IgA proteases
Haemophilus influenzae Lab Algorithm
Gram negative coccobacilli that grows on chocolate agar (requires factors V and X for growth)
Haemophilus influenzae Transmission, Capsule Status, Virulence Factor
Aerosol transmission
Type B polysaccharide capsule is most invasive type (vaccine available)
IgA Protease
Haemophilus influenzae Presentation and Treatment
Mucosal infections (nontypeable) Also epiglottitis (cherry red in children), meningitis, otitis media, and pneumonia
Treat mucosal infections with amoxicillin +/- clavulanate
Treat meningitis with ceftriaxone
Rifampin prophylaxis in close contacts
Legionella pneumophila Lab Algorithm
Gram negative rod. Gram stains poorly so use silver stain. Grow on charcoal yeast extract and culture with iron/cysteine
Clinically detected by presence of antigen in urine
Legionella pneumophila Transmission and Treatment
Aerosol transmission from environmental water source habitat (air conditioning, hot water tanks, ect.)
No person to person transmission
Treatment: macrolide or quinolone
Legionella pneumonphila Presentation
Legionnaries’ disease: severe pneumonia, fever, GI, and CNS symptoms
Pontiac fever: mild flu-like syndrome
Pseudomonas aeruginosa Lab Algorithm
Gram negative rod, lactose non-fermenter, oxidase positive
Obligate aerobe
Pseudomonas aeruginosa Presentation
Associated with wound and burn infections
Pneumonia, sepsis, external otitis (swimmer’s ear), UTI, drug use and diabetic osteomyelitis, hot tub follicultis
Can also cause ecthyma gangrenosum: rapidly progressive, necrotic cutaneous lesions caused by pseudomonas bacteremia typically seen in immunocompromised patients
Psuedomonas aeruginosa Pigment, Odor, Toxins, and Treatment
Blue-green pigment
Grape-like odor
Endotoxin and exotoxin A (inactivates EF-2)
Treatment: amingoglycoside + extended spectrum penicillin
E. coli Lab Algorithm, Virulence Factors, and Treatment
Gram negative rod, fast lactose fermenter
Fimbriae (cystitis and pyelonephritis), K capsule (pneumonia and neonatal meningitis), LPS endotoxin (septic shock)
TMP-SMX for UTI and Ceftriaxone for meningitis and sepsis
EIEC (Invasive) Mechanism and Presentation
Microbe invades intestinal mucosa and causes necrosis and inflammation
Presentation: dysentery
ETEC (Toxigenic) Mechanism and Presentation
Produces heat labile and heat stable enterotoxins (no inflammation or invasion)
Presentation: travelers’ diarrhea
EPEC (Pathogenic) Mechanism and Presentation
Adheres to apical surface and flattens villi, preventing absorption
Presentation: diarrhea usually in children
EHEC (Hemorrhagic) Mechanism, Presentation, and Differentiation
O157:H7 is the most common serotype. Produces shiga-like toxin that causes HUS (triad of anemia, thrombocytopenia, and acute renal failure)–microthrombi use up the platelets and cause the thrombocytopenia
Presents with dysentery
Does not ferment sorbitol (unlike the other E. coli)
Klebsiella Lab Algorithm
Gram negative rod, lactose fast fermenter
Klebsiella Presentation
An intestinal flora that causes lobar pneumonia in alcoholics and diabetics when aspirated
Also cause of UTIs
4 A’s: Aspiration pneumonia, Abscess in lungs and liver, Alcoholics, diAbetics
Kelbsiella Capsule Status, Sputum Finding, Treatment
Polysaccharide capsule (abundant mucoid colonies)
Red “currant jelly” sputum
Treat with 1st and 2nd gen Cephalosporins
Salmonella and Shigella Lab Algorithm
Gram negative rod, lactose non-fermenter, oxidase negative
Salmonella Information
Have flagella, can disseminate hematogenously, animal reservoirs (like turtles), produce H2S, antibiotics prolong fecal excretion, invades intestinal mucosa, can cause blood diarrhea
Shigella Information
No flagella, cell to cell transmission (no hematogenous spread), humans and primates reservoirs, does not produce H2S, antibiotics shorten duration of fecal excretion, invades mucosa and may cause PMN infiltration, often causes bloody diarrhea
Salmonella typhi Presentation
Typhoid fever: ROSE spots on the abdomen, fever, headache, and diarrhea
Can remain in GALLBLADDER and cause a carrier state
Campylobacter jejuni Lab Algorithm
Gram negative, comma shaped, oxidase +, grows in 42 degrees
Campylobacter jejuni Presentation
Major cause of bloody diarrhea, especially in children
Fecal-oral transmission through poultry, meat, unpasteurized milk
Common antecedent to Guillain Barre and reactive arthritis
Vibrio cholerae Lab Algorithm
Gram negative, comma shaped, oxidase +, grows in alkaline media
Vibrio cholerae Presentation, Epidemiology, and Treatment
Rice-water diarrhea via enterotoxin that permanently actives Gs
Endemic to developing countries
Prompt Oral Rehydration
Yersinia enterocolitica Lab Algorithm
Gram negative rod, lactose non-fermenter, oxidase negative
Yersinia enterocolitica Transmission and Presentation
Transmitted from pet feces, contaminated milk, or pork
Causes mesenteric adenitis that can mimic Crohn disease or appendicitis
Helicobacter pylori Lab Algorithm
Gram negative, comma shaped, oxidase +, produces urease
Helicobacter pylori Presentation and Treatment
Gastritis and peptic ulcers (especially duodenal)
Treatment: PPI + clarithromycin + amoxicillin or metronidzole
Pasteurella multocida Lab Algorithm and Presentation
Gram negative coccobacilli, oxidase +, catalase +
Cellulitis and osteomyelitis following cat/dog bites
Bartonella henselae
Gram negative coccobacilli (silver impregnation stains)
Causes cat scratch fever: fever, ocular involvement, hepatosplenomegaly
