Chapter 16: Aerobic Gram-Positive Bacilli Identification

from quizlet

What are the three main genera of aerobic Gram-positive bacilli?

Bacillus, Corynebacterium, and Nocardia.

What is the characteristic shape of Bacillus bacteria?

Large rods in long chains.

Describe the arrangement of Corynebacterium cells.

They appear in palisades and V shapes, resembling Chinese letters.

What type of pathogens are most Corynebacterium species?

They are animal and human pathogens, as well as saprophytes and plant pathogens.

Which Corynebacterium species is the most significant pathogen?

Corynebacterium diphtheriae.

What is a diphtheroid?

Any rod that resembles Corynebacterium diphtheriae, especially in shape.

What medium enhances the growth of C. diphtheriae?

Loeffler serum medium.

What is the primary cause of respiratory diphtheria?

The diphtheria toxin produced by lysogenized strains of C. diphtheriae.

How is respiratory diphtheria transmitted?

By droplets or hand-to-mouth contact.

What are the symptoms of respiratory diphtheria?

Low-grade fever, malaise, mild sore throat, and a tough white to gray pseudomembrane.

What is the treatment for diphtheria?

Antitoxin plus IM penicillin or oral erythromycin for 7 to 10 days.

What is the significance of the Elek plate in diphtheria diagnosis?

It tests for the presence of diphtheria toxin by showing precipitin lines.

What are the key characteristics of Listeria monocytogenes?

Short gram-positive, non-spore-forming rods that can appear as cocci.

At what temperature can Listeria monocytogenes grow?

At 4°C, allowing it to thrive in refrigerated foods.

What virulence factor does Listeria monocytogenes produce?

Listeriolysin O, which damages phagocytic membranes.

What is the CAMP test used for?

To identify Listeria monocytogenes by observing enhanced lysis in an arrowhead zone.

What are the common sources of Listeria infection?

Refrigerated dairy products and processed meats.

What is a distinguishing feature of Listeria monocytogenes in culture?

It shows narrow zones of beta hemolysis on blood agar.

What is the motility characteristic of Listeria monocytogenes?

It exhibits tumbling motility at room temperature.

What test differentiates Listeria monocytogenes from group B streptococci?

The catalase test; Listeria is catalase positive.

What is the appearance of Listeria monocytogenes in direct smears?

Short gram-positive rods.

What is the incubation period for respiratory diphtheria?

2 to 4 days.

What is the role of the tox gene in C. diphtheriae?

It is responsible for the production of diphtheria toxin.

What type of agar is used to selectively culture C. diphtheriae?

Cystine-tellurite blood agar.

What does a brown halo indicate on cystine-tellurite blood agar?

It indicates the presence of C. diphtheriae.

What are the symptoms of cutaneous diphtheria?

Nonhealing ulcers covered by a dirty gray membrane.

What is the significance of urease testing in identifying Corynebacteria?

It helps differentiate C. diphtheriae (urease negative) from C. ulcerans and C. pseudotuberculosis (urease positive).

What is Erysipelothrix rhusiopathiae commonly associated with?

Occupational exposure in fish handlers, meat packers, and others who handle animal products.

What is the clinical form of Erysipelothrix rhusiopathiae characterized by a painful, red, swollen skin infection?

Erysipeloid.

What is the treatment of choice for Erysipelothrix infections?

Penicillin.

What are the microscopic characteristics of Erysipelothrix rhusiopathiae?

Thin gram-positive rods that may stain gram-variable and can form long filaments.

How does Erysipelothrix rhusiopathiae grow in culture?

Needs CO2, grows on SBA or chocolate agar, with pinpoint colonies at 24 hours.

What key test is positive for Erysipelothrix rhusiopathiae?

H2S positive on TSI.

What is the reverse CAMP test associated with?

Arcanobacterium haemolyticum, which inhibits the S. aureus beta-lysin zone.

What is the primary clinical manifestation of Arcanobacterium haemolyticum?

Pharyngitis in patients aged 10 to 20 years.

What type of colonies does Arcanobacterium haemolyticum produce on SBA?

Small colonies with a narrow zone of beta hemolysis.

What is Gardnerella vaginalis associated with?

Bacterial vaginosis, characterized by malodorous discharge and elevated vaginal pH.

What are clue cells in the context of Gardnerella vaginalis infection?

Epithelial cells with coccobacilli clustered on their edges.

What is the medium of choice for culturing Gardnerella vaginalis?

Human blood bilayer Tween (HBT) agar.

What are the general characteristics of Nocardia?

Aerobic, thin, branching filaments that are gram-positive and beaded.

What is the mortality rate associated with nocardiosis?

About 40 percent, mostly in immunocompromised hosts.

What distinguishes Bacillus anthracis from other Bacillus species?

It has a capsule of poly-D-glutamic acid and three toxin proteins.

What are the four ways Bacillus anthracis can enter the body?

Cutaneous, inhalation, injection, and gastrointestinal routes.

What is the appearance of Bacillus anthracis colonies on sheep blood agar?

Large, raised, grayish-white colonies with irregular, fingerlike edges (medusa head).

What is the primary treatment for Bacillus anthracis infection?

IV ciprofloxacin or doxycycline until susceptibilities are known.

What are the two syndromes associated with Bacillus cereus food poisoning?

Emetic syndrome (nausea and vomiting) and diarrheal syndrome (cramps and diarrhea).

What type of colonies does Bacillus cereus produce?

Beta-hemolytic, frosted glass colonies.

What is the significance of the Nugent scoring system?

It is used to diagnose bacterial vaginosis based on the presence of clue cells.

What is the common laboratory characteristic of Nocardia?

Chalky, matte colonies with aerial hyphae.

What distinguishes Listeria monocytogenes from group B Streptococcus?

Listeria is catalase positive, esculin positive, and motile, while group B strep is catalase negative.

What is the typical source of Listeria monocytogenes infection in pregnant women?

Soft cheese and deli meats.

What is the significance of the modified acid-fast stain for Nocardia?

It helps identify partially acid-fast filaments that are characteristic of Nocardia.

What is the treatment for Nocardiosis?

Drainage or surgery plus antimicrobials; resistant to penicillin, susceptible to sulfonamides.

What is the appearance of Erysipelothrix rhusiopathiae in culture after 48 hours?

Small, smooth, glistening colonies or larger, rough, flat, matte colonies with irregular edges.

What is a common complication of Listeria monocytogenes infection during pregnancy?

Septic abortion or early-onset neonatal sepsis.

What type of infections can Trueperella species cause?

Bacteremia, wound infections, UTIs, and septic arthritis.

What is the primary laboratory characteristic that separates Arcanobacterium from other bacteria?

It is catalase negative and exhibits reverse CAMP reaction.