Medical Microbiology: unit 11

Comprehensive review flashcards covering morphology, transmission, pathogenesis, clinical features, and laboratory diagnosis of clinically important Gram-negative and fastidious bacteria.

What is the Gram-stain morphology of Vibrio cholerae?

Gram-negative, comma-shaped curved rod.

What disease does Vibrio cholerae cause?

Cholera.

How is Vibrio cholerae transmitted?

Fecal–oral route through contaminated food or water.

What is the source of Vibrio cholerae?

Human feces; infected people and carriers shed the organism.

How does cholera toxin cause symptoms?

Causes massive intestinal fluid and electrolyte loss, producing watery diarrhea.

What are the characteristic stools in cholera?

Rice-water stools.

How can cholera cause hypovolemic shock?

Severe fluid loss decreases blood volume and blood pressure.

How can cholera cause metabolic acidosis?

Diarrhea causes bicarbonate loss, reducing blood buffering capacity.

What is the priority treatment for cholera?

Rapid fluid and electrolyte replacement (rehydration).

How can cholera transmission be prevented?

Safe water, sanitation, hygiene, and vaccination.

What is the morphology of Campylobacter jejuni?

Curved or S-shaped Gram-negative rods; often described as gull-wing shaped.

What is the main source of Campylobacter jejuni?

Undercooked poultry, unpasteurized milk, and contaminated water.

What disease does Campylobacter jejuni cause?

Gastroenteritis with abdominal cramps and often bloody diarrhea.

What is a characteristic growth requirement of Campylobacter jejuni?

Microaerophilic conditions; grows well at $42\,^{\circ}\text{C}$.

What is a serious complication of Campylobacter jejuni infection?

Guillain-Barré syndrome.

What is the morphology of Helicobacter pylori?

Curved or spiral-shaped Gram-negative rod with flagella.

What enzyme is characteristic of Helicobacter pylori?

Urease.

What diseases are associated with Helicobacter pylori?

Chronic gastritis and peptic ulcers; increased risk of gastric cancer.

How is active Helicobacter pylori infection diagnosed?

Urea breath test, stool antigen test, or gastric biopsy.

How does Helicobacter pylori survive stomach acidity?

Urease produces ammonia from urea, helping neutralize nearby acid.

What is the Gram-stain morphology of Pseudomonas aeruginosa?

Gram-negative rod.

Does Pseudomonas aeruginosa ferment carbohydrates?

No; it is a nonfermenter.

How can Pseudomonas aeruginosa be differentiated from Enterobacteriaceae?

It is a nonfermenter; use carbohydrate fermentation media such as TSI to distinguish patterns.

What pigment gives Pseudomonas aeruginosa its blue-green color?

Pyocyanin.

What fluorescent pigment can Pseudomonas aeruginosa produce?

Pyoverdine (fluorescein), a yellow-green fluorescent pigment.

What enzyme test is usually positive for Pseudomonas aeruginosa?

Oxidase.

What infections can Pseudomonas aeruginosa cause?

Opportunistic wound and burn infections, pneumonia, UTIs, bacteremia, and swimmer’s ear.

Which patients are especially susceptible to Pseudomonas aeruginosa?

Burn patients, people with cystic fibrosis, immunocompromised patients, and hospitalized patients.

Why is Pseudomonas aeruginosa difficult to treat?

It has intrinsic resistance and can acquire resistance to many antibiotics.

What is a major host defense against Pseudomonas aeruginosa?

Intact skin and mucosal barriers, supported by neutrophils and other innate immune defenses.

What disease is associated with Burkholderia pseudomallei?

Melioidosis.

How is Burkholderia pseudomallei usually acquired?

Contact with contaminated soil or water, especially through skin wounds or inhalation.

What is the Gram-stain morphology of Haemophilus?

Small, pleomorphic Gram-negative coccobacilli.

What is X factor?

Hemin; required for heme-dependent enzymes.

What is V factor?

NAD (nicotinamide adenine dinucleotide).

Which growth factors does Haemophilus influenzae require?

Both X factor and V factor.

Which medium supports Haemophilus influenzae growth?

Chocolate agar, which supplies X and V factors.

What serious diseases can Haemophilus influenzae cause?

Meningitis, epiglottitis, pneumonia, and other invasive infections.

How does Haemophilus influenzae meningitis differ epidemiologically from meningococcal meningitis?

Haemophilus influenzae classically causes sporadic, nonepidemic cases; Neisseria meningitidis can cause outbreaks or epidemics.

How is Haemophilus influenzae transmitted?

Respiratory droplets or secretions from infected people or carriers.

How can invasive Hib disease be prevented?

Hib vaccination.

What disease is classically associated with Haemophilus aegyptius?

Acute contagious conjunctivitis (pink eye).

What disease does Haemophilus ducreyi cause?

Chancroid, a sexually transmitted infection.

What is the characteristic lesion of chancroid?

A painful genital ulcer, often with tender swollen lymph nodes.

What are clue cells?

Vaginal epithelial cells coated with bacteria, giving fuzzy or stippled borders.

What condition is associated with clue cells?

Bacterial vaginosis, commonly associated with Gardnerella vaginalis.

What is the Gram-stain morphology of Bordetella pertussis?

Small Gram-negative coccobacillus.

What disease does Bordetella pertussis cause?

Pertussis (whooping cough).

What medium is used to culture Bordetella pertussis?

Bordet–Gengou medium, a potato-blood-glycerol medium.

What is the alternative medium used for Bordetella pertussis?

Regan–Lowe charcoal-blood agar.

How is pertussis transmitted?

Respiratory droplets.

What are the three clinical stages of pertussis?

Catarrhal, paroxysmal, and convalescent.

What is the characteristic symptom of pertussis?

Repeated coughing fits followed by an inspiratory “whoop.”

What is a major complication of pertussis?

Pneumonia; infants may develop apnea or other severe complications.

What does the pertussis toxin do?

Disrupts cell signaling, contributing to disease and lymphocytosis.

What type of immunity does the DTP/DTaP vaccine provide?

Artificially acquired active immunity.

What is the Gram-stain morphology of Brucella?

Small Gram-negative coccobacilli.

What is the disease caused by Brucella called?

Brucellosis, also called undulant fever.

What is the main source of human brucellosis?

Infected livestock and unpasteurized dairy products.

How is Brucella transmitted?

Ingestion of unpasteurized dairy, direct animal contact, or inhalation of aerosols.

What are common symptoms of brucellosis?

Recurrent or undulating fever, night sweats, fatigue, malaise, and joint or muscle pain.

What is the febrile agglutination test for brucellosis detecting?

Patient antibodies that agglutinate Brucella antigens.

Why must the Brucella agglutination test be interpreted carefully?

Cross-reacting antibodies can cause false-positive results; results must fit clinical and exposure history.

What disease does Francisella tularensis cause?

Tularemia, also called rabbit fever.

What is the Gram-stain morphology of Francisella tularensis?

Tiny, faintly staining Gram-negative coccobacillus.

What are common sources of Francisella tularensis?

Rabbits, rodents, other wild animals, and ticks.

How is tularemia transmitted?

Tick or deer-fly bites, handling infected animals, inhalation, or ingestion.

What are common symptoms of tularemia?

Fever, chills, headache, fatigue, and sometimes an ulcer with enlarged lymph nodes.

What is ulceroglandular tularemia?

Skin ulcer at the entry site with regional swollen lymph nodes.

What is glandular tularemia?

Enlarged regional lymph nodes without an obvious skin ulcer.

What is oculoglandular tularemia?

Eye infection with nearby lymph-node swelling.

What is pneumonic tularemia?

Lung infection following inhalation or spread through the bloodstream.

Why are suspected Francisella tularensis cultures sent to reference laboratories?

The organism is highly infectious by aerosol; special containment and expertise are needed.

What is the Gram-stain morphology of Pasteurella multocida?

Small Gram-negative coccobacillus, often showing bipolar staining.

What is the source of Pasteurella multocida?

Animal oral flora, especially cats and dogs.

How is Pasteurella multocida transmitted?

Animal bites, scratches, or contact of animal saliva with broken skin.

What is the major manifestation of Pasteurella multocida infection?

Rapid-onset cellulitis around a bite or scratch; deeper infections can occur.

What is the Gram-stain morphology of Legionella pneumophila?

Slender, faintly staining Gram-negative rod.

What is the source of Legionella pneumophila?

Water systems, including cooling towers, plumbing, and hot tubs.

How is Legionella transmitted?

Inhalation of contaminated water aerosols; person-to-person spread is uncommon.

What disease does Legionella pneumophila cause?

Legionnaires’ disease, a severe atypical pneumonia.

What is Pontiac fever?

A milder, flu-like Legionella illness without pneumonia.

What laboratory medium is used to culture Legionella?

Buffered charcoal yeast extract (BCYE) agar, supplemented with L-cysteine and iron.

What is an important diagnostic test for Legionnaires’ disease?

Urinary antigen testing; respiratory PCR or culture may also be used.