Microbiology- Clinical Bacteriology (Gram -)

Question 1

Gram-negative lab algorithm

Answer 1

pag. 141

Question 2

Neisseria Characteristics

Answer 2

Gram ⊝ diplococci. Metabolize glucose and produce IgA proteases. Contain lipooligosaccharides (LOS) with strong
endotoxin activity. N gonorrhoeae is often intracellular (within neutrophils).

Question 3

Gonococci Characteristics, Clinical features, treatment

Answer 3

No polysaccharide capsule, Maltose not fermented, No vaccine due to antigenic variation of pilus proteins, Sexually or perinatally transmitted.

Causes gonorrhea, septic arthritis, neonatal conjunctivitis (2–5 days after birth), pelvic inflammatory disease (PID), and Fitz-Hugh– Curtis syndrome.

Treatment: ceftriaxone (+ azithromycin or doxycycline, for possible chlamydial coinfection).

Question 4

Meningococci Characteristics, Clinical features, treatment

Answer 4

Polysaccharide capsule, Maltose fermentation, Vaccine (type B vaccine not widely available), Transmitted via respiratory and oral secretions.

Causes meningococcemia with petechial hemorrhages and gangrene of toes, meningitis, Waterhouse-Friderichsen syndrome (adrenal insufficiency, fever, DIC,
shock).

Treatment: ceftriaxone or penicillin G

Question 5

Haemophilus influenzae Clinical features and treatment

Answer 5

HaEMOPhilus causes Epiglottitis (endoscopic appearance, can be “cherry red” in children; “thumb sign” on lateral neck x-ray), Meningitis, Otitis media, and Pneumonia.

Treatment: amoxicillin +/− clavulanate for mucosal infections; ceftriaxone for meningitis; rifampin prophylaxis for close contacts.

Question 6

Haemophilus influenzae Characteristics, transmission, nontypeable strains, vaccine

Answer 6

Small gram ⊝ (coccobacillary) rod. Aerosol transmission. Nontypeable (unencapsulated) strains are the most common cause of mucosal infections (otitis media, conjunctivitis, bronchitis) as well as invasive infections since the vaccine for capsular type b was introduced.

Produces IgA protease.

Vaccine contains type b capsular polysaccharide (polyribosylribitol phosphate) conjugated to diphtheria toxoid or other protein. Given between 2 and 18 months of age.

Question 7

Bordetella pertussis Clinical features

Answer 7

ƒƒCatarrhal—low-grade fevers, Coryza.

ƒParoxysmal—paroxysms of intense cough followed by inspiratory “whooP” (“whooping cough”), posttussive vomiting.

ƒConvalescent—gradual recovery of chronic cough.

Prevented by Tdap, DTaP vaccines. May be mistaken as viral infection due to lymphocytic infiltrate resulting from immune response.

Question 8

Legionella pneumophila Characteristics, Transmission, Treatment

Answer 8

Gram stains poorly—use silver stain. Grow on charcoal yeast extract medium with iron and cysteine. Detected by
presence of antigen in urine. Labs may show hyponatremia.

Aerosol transmission from environmental water source habitat.

Treatment: macrolide or quinolone.

Question 9

Legionnaires’ disease

Pontiac fever

Answer 9

severe pneumonia (often unilateral and lobar A ), fever, GI and CNS symptoms. Common in smokers and in
chronic lung disease.

mild flu-like syndrome.

Question 10

Treatments Pseudomonas aeruginosa

Answer 10

Include “CAMPFIRE” drugs:
ƒƒCarbapenems
ƒƒ Aminoglycosides
ƒƒMonobactams
ƒƒ Polymyxins (eg, polymyxin B, colistin)
ƒƒ Fluoroquinolones (eg, ciprofloxacin, levofloxacin)
ƒƒThIRd- and fourth-generation cephalosporins (eg, ceftazidime, cefepime).
ƒƒ Extended-spectrum penicillins (eg, piperacillin, ticarcillin)

Question 11

PSEUDOMONAS is associated with:

Answer 11

Pneumonia, Sepsis, Ecthyma gangrenosum, UTIs, Diabetes, Osteomyelitis, Mucoid polysaccharide capsule, Otitis externa (swimmer’s ear), Nosocomial infections (eg,
catheters, equipment), Addicts (drug abusers), Skin infections (eg, hot tub folliculitis, wound infection in burn victims).

Question 12

Pseudomonas aeruginosa Produces PEEP:

Answer 12

Phospholipase C (degrades cell membranes); Endotoxin (fever, shock); Exotoxin A (inactivates EF-2); Pigments:
pyoverdine and pyocyanin

Question 13

Ecthyma gangrenosum

Answer 13

Rapidly progressive, necrotic cutaneous lesion caused by

Pseudomonas bacteremia. Typically seen in immunocompromised patients.

Question 14

Pseudomonas aeruginosa Characteristics

Answer 14

Aeruginosa—aerobic; motile, gram ⊝ rod. Nonlactose

fermenting. Oxidase ⊕. Frequently found in water. Has a grape-like odor.

Question 15

Salmonella vs Shigella

Answer 15

pag. 144

Question 16

typhoid fever

Answer 16

(rose spots on abdomen, constipation, abdominal

pain, fever); treat with ceftriaxone or fluoroquinolone

Question 17

Yersinia enterocolitica

Answer 17

Gram ⊝ rod. Usually transmitted from pet feces (eg, puppies), contaminated milk, or pork.

Causes acute diarrhea or pseudoappendicitis (right lower abdominal pain due to mesenteric adenitis and/ or terminal ileitis).

Question 18

Lactose-fermenting enteric bacteria

Answer 18

Lactose is key. Test with MacConKEE’S agar.

Fermentation of lactose Ž pink colonies on MacConkey agar. Examples include Citrobacter, Klebsiella, E coli, Enterobacter, and Serratia (weak fermenter).

Question 19

Escherichia coli virulence factors

Answer 19

Gram ⊝ rod.

E coli virulence factors: fimbriae—cystitis and pyelonephritis (P-pili); K capsule— pneumonia, neonatal meningitis; LPS endotoxin—septic shock.

Question 20

Escherichia coli:

Enteroinvasive

Answer 20

EIEC is Invasive; dysentery. Clinical manifestations similar to Shigella.

Question 21

Escherichia coli:

Enterotoxigenic

Answer 21

ETEC; Traveler’s diarrhea (watery).

Question 22

Escherichia coli:

Enteropathogenic

Answer 22

Diarrhea, usually in children (think EPEC and Pediatrics).

Question 23

Escherichia coli:

Enterohemorrhagic

Answer 23

O157:H7
Dysentery (toxin alone causes necrosis and
inflammation).

Does not ferment sorbitol (vs other E coli).

Hemorrhagic, Hamburgers, Hemolytic-uremic syndrome.

Question 24

hemolytic-uremic syndrome:

Answer 24

triad of anemia, thrombocytopenia, and acute renal failure due to microthrombi forming on damaged endothelium.

Question 25

Klebsiella Clinical features

Answer 25

5 A’s of KlebsiellA:
Aspiration pneumonia
Abscess in lungs and liver
Alcoholics
DiAbetics
“CurrAnt jelly” sputum

Question 26

Campylobacter jejuni Clinical features

Answer 26

Major cause of bloody diarrhea, especially in children.

Fecal-oral transmission through person-to-person contact or via ingestion of undercooked contaminated poultry or meat, unpasteurized milk. Contact with infected animals (dogs, cats, pigs) is also a risk factor.

Common antecedent to Guillain-Barré syndrome and reactive arthritis.

Question 27

Vibrio cholerae Clinical features

Answer 27

Produces profuse rice-water diarrhea via enterotoxin that permanently activates Gs,  cAMP.

Sensitive to stomach acid (acid labile); requires large inoculum (high ID50) unless host has gastric acidity.

Transmitted via ingestion of contaminated water or uncooked food (eg, raw shellfish). Treat promptly with oral rehydration solution.

Question 28

Helicobacter pylori Characteristics, Clinical features, Treatment

Answer 28

Curved, flagellated (motile), gram ⊝ rod that is triple ⊕: catalase ⊕, oxidase ⊕, and urease ⊕ (can use urea breath test or fecal antigen test for diagnosis).

Colonizes mainly antrum of stomach; causes gastritis and peptic ulcers (especially duodenal). Risk factor for peptic ulcer disease, gastric adenocarcinoma, and MALT lymphoma.

Most common initial treatment is triple therapy: Amoxicillin (metronidazole if penicillin allergy) + Clarithromycin + Proton pump inhibitor; Antibiotics Cure Pylori.