week 8 Gram-Negative Bacteria Practice Flashcards

This set of vocabulary flashcards covers key characteristics, diagnostic tests, virulence factors, and clinical presentations of major Gram-negative bacteria including Haemophilus, Gardnerella, Bordetella, and Legionella species.

Haemophilus influenzae

An encapsulated, gram-negative rod that is a major cause of invasive disease, especially via capsular type b (Hib).

Factor X

Also known as hemin; a specific growth factor required by Haemophilus influenzae for growth on nutrient agar.

Factor V

Also known as nicotinamide adenine dinucleotide (NAD); a nutrient required for the growth of H. influenzae, often provided by Staphylococcus aureus or lysed red blood cells.

Satellite phenomenon

The growth of small H. influenzae colonies around Staphylococcus aureus on blood agar, because the staphylococci provide factor V.

Chocolate agar

A culture medium containing lysed red blood cells that release factors X and V, allowing for the optimal growth of Haemophilus species.

Polyribitol phosphate (PRP)

The polymer of ribosyl and ribitol phosphate that makes up the capsule of Haemophilus influenzae type b and is the specific component used in the Hib vaccine.

Quellung reaction

A biochemical reaction used for the serotyping of encapsulated H. influenzae isolates via capsule swelling.

IgA protease

A virulence factor produced by H. influenzae that breaks down secretory IgA to facilitate mucosal colonization.

Epiglottitis

A life-threatening airway obstruction caused by H. influenzae type b, characterized by a "cherry red" epiglottis, dysphagia, and drooling.

Hib Vaccine

A conjugate vaccine containing H. influenzae type b capsular polysaccharide linked to a carrier protein (such as tetanus or diphtheria toxoid) to induce a T-cell response.

Haemophilus ducreyi

The causative agent of chancroid, a sexually transmitted infection characterized by painful genital ulcers and regional lymphadenitis.

Syphylis: not painful

Gonorrhea: discharge

Soft chancre

A tender, painful genital ulcer with sharply defined margins caused by H. ducreyi, distinguished from the painless, indurated chancre of syphilis.

DsrA

An outer membrane protein produced by H. ducreyi that facilitates attachment to epithelial cells and provides resistance to complement-mediated killing.

Gardnerella vaginalis

A gram-variable rod and facultative anaerobe that causes bacterial vaginosis when the normal vaginal flora is disturbed.

Clue cells

Vaginal epithelial cells covered with Gardnerella vaginalis bacteria, used as a diagnostic indicator of bacterial vaginosis.

Whiff test

A diagnostic procedure for Gardnerella vaginalis where potassium hydroxide (KOH) is added to a vaginal sample to reassess for a "fishy" amine odor.

Bordetella pertussis

Small, gram-negative, aerobic coccobacilli that are the causative agent of whooping cough.

Filamentous hemagglutinin

A surface protein on B. pertussis that mediates attachment to ciliated epithelial cells of the nasopharynx.

Tracheal cytotoxin

A toxin produced by B. pertussis that damages ciliated epithelial cells and interferes with mucociliary clearance.

Pertussis toxin

An A-B toxin that acts via ADP-ribosylation of Gi proteins, leading to increased cAMP levels and impaired immune cell function.

Catarrhal stage

The initial stage of pertussis lasting $1$ to $2$ weeks, characterized by rhinorrhea, malaise, and sneezing.

Paroxysmal stage

The second stage of pertussis lasting $2$ to $4$ weeks, characterized by repetitive coughs with whoops, vomiting, and leukocytosis.

Regan-Lowe or Bordet-Gengou media

Specialized, nutrient-rich media used for the culture of the fastidious organism Bordetella pertussis.

Legionella pneumophila

A gram-negative rod that requires special silver stains to visualize and causes atypical pneumonia (Legionnaires' disease).

Buffered Charcoal Yeast Extract (BCYE) agar

A specialized culture medium supplemented with iron and cysteine required for the growth of Legionella.

Dieterle silver impregnation stain

A special staining method used to visualize Legionella in lung biopsy sections because the organism stains poorly with Gram stain.

Hyponatremia

A clinical laboratory finding (serum sodium $\le 130\,mEq/L$) that occurs more frequently in Legionella pneumonia than in other bacterial pneumonias.