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Flashcards in Clinical Bacteriology: Gram Negative Bacteria Deck (28):

What are the lactose-fermenting enteric bacteria?

Citrobacter, Klebsiella, E. coli, Enterobacter, and Serratia.


Lactose is KEE

Test with MacConKEE'S agar - lactose fermenters make pink colonies.

Eosin methylene blue (EMB) agar: Lactose fermenters grow as purple/black colonies. E. coli grows purple colonies with a green sheen.


What lactose-fermenting enzyme does E. coli produce?

β-galactosidase, cleaves lactose into glucose and galactose.


What are the gram negative diplococci?

What is an easy lab test to differentiate?

Neisseria meningitidis and Neisseria gonorrhoeae. Both ferment glucose.

N. meningitidis ferments maltose

N. gonorrhoeae does not ferment maltose.


MeninGococci ferment Maltose and Glucose

Gonococci ferment Glucose.


For gonococcus (N. gonorrhoeae), describe...

1. Capsule?

2. Maltose fermentation?

3. Vaccine?

4. Transmission?


Often intracellular (inside neutrophils)

1. No polysaccharide capsule

2. No maltose fermentation

3. No vaccine (pilus proteins have fast antigenic variation)

4. Sexually tansmitted.


For gonococcus (N. gonorrhoeae), describe...

1. Diseases caused by this bacteria?

2. Prevention?

3. Treatment for infection?

1. Gonorrhea, septic arthritis, neonatal conjunctivitis, pelvic inflammatory disease (PID), and Fitz-Hugh-Curtis syndrome (peritonitis + perihepatitis as a complication of PID?).

2. Condoms for sexual transmission. Erythromycin ointment for neonates

3. Ceftriaxone + (azithromycin or doxycycline) for possible chlamydia coinfection.


For Meningococci (N. meningitidis) describe...

1. Capsule?

2. Maltose fermentation?

3. Vaccine?

4. Transmission?

1. Polysaccharide capsule

2. Maltose fermentation

3. Vaccine available (none for type B)

4. Transmitted via respiratory and oral secretions


For meningococci (N. meningitidis) describe...

1. Diseases caused by this bacteria?

2. Prevention?

3. Treatment for infection?

1. Meningococcemia (DIC with petechial rash) and meningitis. Waterhouse-Friederichsen syndrome (hemorrhagic necrosis of adrenal glands).

2. Rifampin, ciprofloxacin, or ceftriaxone prophylaxis in close contacts

3. Ceftriaxone or penicillin G for treatment.


How is Haemophilus Influenzae identified on gram stain?

What is the most invasive subtype causing disease?

What types of disease does it cause?

Small, gram-negative coccobacillary rod.

Most invasive disease caused by capsular type B.


Nontypeable strains: Mucosal infections (otitis media, conjunctivitis, bronchitis)

HaEMOPhilus causes Epiglottitis (cherry red in children), Meningitis, Otitis media, and Pneumonia.


What are virulence factors for Haemophilus Influenzae?

What is required for culture?

Capsule, IgA protease

Chocolate agar with factors V (NAD+) and X (hematin) for culture. S. aureus can also be grown with it (provides factor V).


When a child has "flu", mom goes to five (V) and dime (X) store to buy some chocolate.


How do you treat mucosal infection with haemophilus influenzae?
How about meningitis?


Treat mucosal infection with amoxicillin +/- clavulanate

Treat meningitis with ceftriaxone. Rifampin prophylaxis in close contacts.


Prevent with vaccine - contains type B capsular polysaccharide (polyribosylribitol phosphate) conjugated to diphtheria toxoid or another protein. Given between 2-18 months of age.


Patient presents with pneumonia, fever, GI, and CNS symptoms. He works as a domestic hot-water system mechanic.

A poorly staining gram-negative rod is found.

What is this organism?
What is a better stain to visualize it?

What is required for culture?

Legionella pneumophilia, causing Legionnaires' disease

Transmitted via aerosols from environmental water source habitat (air conditioning systems, hot water tanks).

Use silver stain to visualize.

Culture requires charcoal yeast extract with iron and cysteine.


"Think of a French legionnaire (soldier) with his silver helmet, sitting around a campfire (charcoal) with his iron dagger - he is no sissy (cysteine).


What is a characteristic lab finding for infection with Legionella?

How is legionella detected clinically?

What is the name for a mild flu-like syndrome caused by legionella?

How do you treat legionella?


Labs show hyponatremia

Clinical detection by urine antigen

Pontiac fever is a mild form of disease

Give macrolide or quinolone for treatment.


A burn victim presents with sepsis. It is an aerobic gram-negative rod that is non-lactose fermenting and it is oxidase positive.

Culture shows that it produces a blue-green pigment.

What is that organism?

Q image thumb

Pseudomonas aeruginosa.

Produces procyanin (blue-green pigment); has a grape-like odor.

Produces endotoxin (fever, shock) and exotoxin A (inactivates EF-2)


Aeruginosa = Aerobic. Think water connection and blue-green pigment.


What types of infections does pseudomonas aeruginosa cause?

PSEUDOmonas is associated with wound and burn infections, Pneumonia (especially cystic fibrosis), Sepsis, External otitis (swimmer's ear), UTI, Drug use, and Diabetic Osteomyelitis, and hot tub folliculitis. Malignant otitis externa in diabetics.


Chronic pneumonia in CF patients associated with biofilm.


An immunocompromised person presents with rapidly progressive necrotic cutaneous lesions.

Disease? Organism?

Ecthyma gangrenosum - caused by Pseudomonas bacteremia.


How do you treat pseudomonas?

Aminoglycoside polus extended-spectrum penicillin (Piperacillin, ticarcillin, cefepime, imipenum, meropenem)


What are some of E. coli's virulence factors, and what infections do they mediate?

Fimbriae - cystitis and pyelonephritis

K capsule - pneumonia, neonatal meningitis

LPS endotoxin - septic shock


What is the presentation for enteroinvasive E. coli (EIEC)?

What is the mechanism of disease?

Presentation for EIEC: Invasive; dysentery

Microbe invades intestinal mucosa and causes necrosis and inflammation. Clinical manifestations similar to Shigella.


What is the presentation for enterotoxigenic E. coli (ETEC)?

What are its toxins and mechanism of disease?

ETEC presentation: Travelers' diarrhea (watery).

Produces heat-labile and heat-stable enteroToxins. No inflammation or invasion.


What is the presentation for enteropathogenic E. coli (EPEC)?

What are its toxins and mechanism of disease?

Presentation of EPEC: Diarrhea usually in children (Pediatrics)

No toxin produced. Adheres to apical surface, flattens villi, prevents absorption.


What is the presentation for enterohemorrhagic E. coli (EHEC)?

What are its toxins and mechanism of disease?

Presentation EHEC: Dysentery (toxin alone causes necrosis and inflammation). Additionally does not ferment sorbitol (distinguishing from other E. coli)


O157:H7 most common serotype. Produces Shiga-like toxin that causes Hemolytic-uremic syndrome (triad of anemia, thrombocytopenia, and acute renal failure). STEC another name (Shiga toxin-producing E. coli).

Microthrombi form on endothelium damaged by toxin -> mechanical hemolysis (schistocytes formed) and decreased renal blood flow; microthrombi consume platelets -> thrombocytopenia.


An older diabetic patient presents with lobar pneumonia and currant jelly sputum.

What is the organism?


Intestinal flora that causes lobar pneumonia in alcoholics and diabetics when aspirated. Very mucoid colonies caused by abundant polysaccharide capsules.

Also causes nosocomial UTIs.


4A's of Klebsiella:

Aspiration pneumonia

Abscess in lungs and liver




Salmonella vs. Shigella

Which has flagella?

Which can disseminate hematogenously and which is limited to cell-cell?

Which has only human and primate reservoirs?

Which produces hydrogen sulfide?

For which may antibitoics shorten fecal excretion?

Which causes a monocytic response with invasion of intestinal mucosa?

Which causes a PMN infiltration with invasion of intestinal mucosa?

Which causes bloody diarrhea?

Which ferments lactose?

Only Salmonella have flagella (salmon can swim)

Salmonella disseminates hematogenously, Shigella does not - only cell-cell.

Shigella has primate + human reservoir. Salmonella has many animal reservoirs.

Salmonella produces hydrogen sulfide

Antibiotics shorten fecal excretion of shigella; prolong salmonella

Salmonella = monocytic while Shigella = PMN.

Shigella often blood diarrhea. Salmonella can cause bloody diarrhea.

Neither ferments lactose.


Patient presents with rose spots on abdomen, fever, headache, and diarrhea.

A gram-negative non-lactose fermenting bacteria is found.


Salmonella typhi - Typhoid fever.

Can remain in gallbladder and cause a carrier state.


Child presents with bloody diarrhea.

Gram stain shows a gram-negative comma shaped bacteria that is Oxiase positive and grows at 42°C.


What is that bacteria?
What are some potential complications?

Campylobacter jejuni

Fecal-oral transmission through foods such as poultry, meat, unpasteurized milk.

Common antecedent to Guillain-Barre syndrome (autoimmine attack on nerves) and reactive arthritis.


"Campylobacter likes the hot campfire - grows at 42°C!"


Patient returning from a developing nation presents with profuse rice-water diarrhea.

The organism is a gram-negative, comma-shaped, oxidase positive organism that grows in an alkaline media.



Vibrio cholerae.

Produces cholera exotoxin that permanently activates Gs, leading to increased cAMP and Chloride secretion (water follows).


A patient with a new puppy presents with mesenteric adenitis.

Gram stain revels a gram-negative comma shaped bacteria.


Yersinia enterocolitica.

Transmitted from pet feces, contaminated milk, or pork.

Mesenteric adenitis - enlarged mesenteric lymph nodes. Can mimic Crohn disease or appendicitis.


Patient presents with abdominal pain that is relieved by eating and antacids.

The urea breath test is positive.

Diagnosis? Other lab characteristics?


Helicobacter pylori - causes gastric and peptic ulcers.

Risk factor for peptic ulcer, gastric adenocarcinoma and lymphoma.


Curved, gram-negative rod that is catalase, oxidase, and urease positive. Can do urea breath test or fecal antigen test for diagnosis. Creates alkaline environment.


Most common treatment: Triple therapy. Proton pump inhibitor + clarithromycin + amoxicillin or metronidazole.