Microbiology Quiz on Mollicutes and Actinomycetes

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Questions and Answers

What is a distinguishing feature of the mollicutes group?

Lack of a definite cell wall (correct)

Presence of a rigid cell wall

Resistance to osmotic lysis

Sensitivity to penicillin

Which mycoplasma is most commonly associated with atypical pneumonia in humans?

Mycoplasma hominis

Mycoplasma genitalium

Mycoplasma pneumoniae (correct)

Mycoplasma mycoides

What potential complication is associated with the use of an IUCD for more than one year?

Chronic pelvic pain

Endometritis (correct)

Uterine cancer

Ectopic pregnancy

What is the appearance of colonies developed by mollicutes on solid culture media?

Nipped or 'fried-egg' shape Signup and view all the answers

What is the recommended initial treatment approach for infections caused by mollicutes, given their resistance profile?

Empirical penicillin therapy Signup and view all the answers

What is a characteristic feature of Actinomycetes?

Branching, elongated G+ rods Signup and view all the answers

Which disease is primarily associated with Actinomyces israelii?

Chronic cellulitis Signup and view all the answers

What is the standard treatment for Actinomycosis?

Penicillin G Signup and view all the answers

Which of the following is an incorrect statement about Nocardia species?

Most cases of Nocardia infection are documented as outbreaks. Signup and view all the answers

How does Nocardia typically infect humans?

Through skin breaches due to environmental exposure Signup and view all the answers

What type of bacteria is Mycoplasma pneumoniae classified as?

Gram-positive, wall-deficient bacterium Signup and view all the answers

What is the primary ecological niche for Nocardia species?

Soil and organic matter Signup and view all the answers

Which of the following is NOT a characteristic of aerobic actinomycetes?

They are G- cocci. Signup and view all the answers

What is the primary mechanism by which Mycoplasma pneumoniae attaches to the respiratory epithelium?

Through an attachment factor called P1 Signup and view all the answers

Which of the following clinical manifestations is least associated with Mycoplasma infections?

Rigors and severe sweating Signup and view all the answers

What best describes the growth characteristics of Mycoplasma pneumoniae?

Aerobic and very slow-growing Signup and view all the answers

During Mycoplasma pneumoniae infection, what is the role of CARDS toxin?

To interfere with ciliary action and induce inflammation Signup and view all the answers

Which age group is most commonly affected by Mycoplasma pneumoniae infections?

Children aged 5 to 15 years Signup and view all the answers

What type of pneumonia is primarily caused by Mycoplasma pneumoniae?

Atypical pneumonia Signup and view all the answers

How is Mycoplasma pneumoniae commonly transmitted between individuals?

By droplet infection of nasopharyngeal secretions Signup and view all the answers

In what condition is the Mycoplasma pneumoniae infection underestimated due to its similarity to other illnesses?

Viral respiratory infections Signup and view all the answers

Which of the following is a consequence of M.pneumonia infection affecting epithelial cells?

Desquamation of the mucosal surface Signup and view all the answers

What is the duration of pathogen harboring in individuals recovered from Mycoplasma infection?

2 months or more Signup and view all the answers

What is the primary method used to conclusively identify Mycoplasma pneumoniae?

Staining colonies with a fluorescent probe Signup and view all the answers

Which statement accurately describes L-forms of bacteria?

L-forms result from impaired cell wall synthesis due to antibiotics. Signup and view all the answers

What distinguishes pleuropneumonia-like organisms (PPLO) from other bacteria?

Production of extremely small colonies on agar Signup and view all the answers

What is a significant characteristic of Mycoplasma and L-forms regarding their cellular structure?

They lack traditional cell wall components. Signup and view all the answers

In what way does multiplication of bacteria without a rigid cell wall differ from typical bacteria?

It does not involve the formation of a septum. Signup and view all the answers

What is the key feature of T-strains in mycoplasmas?

They form very tiny colonies on agar plates. Signup and view all the answers

What is a common environmental condition that can lead to the formation of L-forms?

Presence of high salt concentrations Signup and view all the answers

Which statement is FALSE regarding Mycoplasma pneumoniae compared to L-forms?

L-forms are restricted to specific bacterial species. Signup and view all the answers

What are the conditions that can lead to bacteria becoming L-forms?

Antibiotic treatment and high salt concentration Signup and view all the answers

What is a distinguishing factor of the cell membranes in mycoplasmas?

They have high concentrations of sterols. Signup and view all the answers

What structural feature distinguishes mycoplasmas from typical bacteria?

Absence of a cell wall Signup and view all the answers

Which staining method would be ineffective in identifying mycoplasmas due to their cell wall structure?

Gram stain Signup and view all the answers

What is the typical diameter range of mycoplasmas?

0.15 u to 0.30 u Signup and view all the answers

Which antibiotic is ineffective against mycoplasmas due to their lack of a cell wall?

Vancomycin Signup and view all the answers

What type of environment do most mycoplasmas require for growth?

Facultatively anaerobic Signup and view all the answers

Which unique characteristic is associated with Mycoplasma pneumoniae's mode of movement?

Gliding motility Signup and view all the answers

What component is crucial for the growth and survival of mycoplasmas?

Sterols Signup and view all the answers

Which toxin is produced by Mycoplasma pneumoniae that is associated with respiratory diseases?

CARDS toxin Signup and view all the answers

How does the plasma membrane of mycoplasmas compare to that of animal cells?

It contains cholesterol Signup and view all the answers

Which of the following statements is true regarding the genetic material of mycoplasmas?

They have unique DNA sequences distinct from known prokaryotes Signup and view all the answers

Study Notes

Microbiology Lecture 13: Actinomycetes, Mycoplasma, and Cell Wall-Defective Bacteria

Lecture covers Actinomycetes, norcardiosis, actinomycetoma, Mycoplasma, and cell wall-defective bacteria.

Actinomycetes

Elongated Gram-positive rods
Branching morphology
Slow growth (4-10 days)
Microaerophilic or strictly anaerobic
Source: oral/intestinal endogenous flora
Disease: chronic cellulitis, draining sinuses
Lesion: composed of inflammatory sinuses that discharge to the surface
Major cause: Actinomyces israelii

Actinomycosis

Part of normal intestinal microflora
Endogenous infection; growth requires displacement into tissue (surgery, trauma, etc.)
Sinus tracts contain pus and sulfur granules
Little evidence of immunity
Treatment: Penicillin G

Aerobic Actinomycetes (Genus)

Aerobic Gram-positive branching filamentous bacteria
Slow growth (2-3 days)
Poorly stained
Subgroups:
- Nocardia
- Actinomadura
- Streptomyces
- Rhodococcus
- Gordonia
- Tsukamurella
- Tropheryma whipplei

Nocardia: History

Edmond Nocard, 1888
Aerobic actinomycetes isolated from cattle with bovine farcy

Nocardia: Growth on Blood Agar

(Image of bacterial growth on blood agar)

Nocardia: Species and Human Infections

At least 13 species cause human infections
7 most important species:
- Nocardia asteroides complex: 80% of noncutaneous; most systemic & CNS nocardiosis
- Nocardia farcinica: Less common, more virulent, more antibiotic-resistant
- Nocardia nova
- Nocardia brasiliensis: Skin, cutaneous, lymphocutaneous
- Nocardia pseudobrasiliensis: Systemic infections, CNS
- Nocardia otitidiscaviarum
- Nocardia transvalensis

Nocardia: Ecology & Epidemiology

Ubiquitous environmental saprophyte
Soil, organic matter, water
Tropical and subtropical regions (Mexico, Central and South America, Africa, India)
Nearly all cases are sporadic
Human-to-human transmission not documented
Animal-to-human transmission not documented
Outbreaks: Contamination of the hospital environment, solutions, or drug injection equipment
Occurrence in immunocompromised patients is increased
Transmission by: Inhalation and Skin
Risk of pulmonary or disseminated disease is associated with deficient cell-mediated immunity, such as in the following conditions: Alcoholism, Diabetes, Lymphoma, Transplantation, Glucocorticoid therapy, AIDS

Nocardia: Pathogenesis

Neutralization of oxidants
Prevention of phagosome-lysosome fusion
Prevention of phagosome acidification
Mycolic acid polymers associated with virulence

Nocardia: Clinical Manifestations

4 main forms:
- Lymphocutaneous syndrome
- Pulmonary nocardiosis (pneumonia)
- CNS nocardiosis (brain abscess)
- Disseminated disease (Eyes (retina), Skin, Subcutaneous tissue, Kidneys, Joints, Bone, Heart)

Lymphocutaneous Syndrome

Ubiquitous in soil; inoculation injuries or contaminated abrasions from insect and animal bites
N. brasiliensis is most common
N. asteroides is typically self-limited
Disease duration: Days to months
Common site: Distal limb

Pulmonary Disease

Subacute (more acute in immunocompromised); cough with small amounts of thick, purulent sputum; fever, anorexia, weight loss, malaise
Endobronchial inflammatory mass
Lung abscess
Cavitary disease
Inadequate therapy may lead to progressive fibrotic diseases
Cerebral imaging is recommended in all cases of pulmonary and disseminated nocardiosis.

CNS Nocardiosis (Brain Abscess)

Common presentations: insidious presentations mistaken for neoplasia; granulomas & abscesses, often affecting the cerebral cortex, basal ganglia, or midbrain.
Less commonly, spinal cord or meninges may be affected
Brain tissue diagnosis in pulmonary nocardiosis may NOT be needed
Cerebral biopsy: common in immunocompromised patients

Laboratory Diagnosis (Nocardia)

Gram-positive, beaded, and branching filaments
Standard blood culture may take 48-hours to several weeks
Colonies can be grown from sputum from patients with underlying lung disease
Deep-seated or disseminated disease that fails initial therapy and relapses after therapy warrants an alternative treatment based on susceptibility testing
Susceptibility to sulfonamide may be crucial in deciding on a treatment or treatment modification

Management (Nocardia): Medication

Sulfonamides: Mainstay of therapy (N. brasiliensis, N. asteroides complex)
Severely ill patients with CNS or disseminated infections/immunocompromised patients require additional drugs such as Amikacin and Carbapenem OR 3rd generation cephalosporin.

Mycoplasma (Mollicutes)

Smallest known free-living organisms
Lack a cell wall
Not stained by Gram stain; more pleomorphic/plastic than eubacteria
Staining: Giemsa stain (pleomorphic cocci, rods, spirals, and sometimes as hollow ring forms) ; diameter: 0.15 μ to 0.30 μ
Genera: Mycoplasma, Ureaplasma, Acholeplasma, Anaeroplasma, Spiroplasma

Mycoplasma: Structure

Enclosed by a limiting membrane similar to animal cells
Contain sterols; cytoplasm with ribosomes, but lack mesosomes
No nuclear membrane
Some strains have amorphous material on outer membrane, suggesting a capsule

Mycoplasma: Structure (Terminal Organelle)

Terminal organelle; mediates attachments and gliding motility
Proteins (P1, P30) responsible for attachment

Mycoplasma: Growth and Replication

Requires sterols for growth
Cultivation: Can be grown on laboratory media
Most are facultatively anaerobic; M. pneumoniae is an exception (aerobic)
Replication is controversial; replication time: 1-6 hours

Mycoplasma: Toxin Production

M. pneumoniae produces an ADP-ribosylating toxin: Commonly Associated Respiratory Disease Syndrome (CARDS) toxin
Lab: Colonies bind red blood cells to agar plate cultures (hemadsorption)

Mycoplasma: Clinical Features

Also known as Eaton's agent
Extracellular pathogen
Attaches to respiratory epithelium by an attachment factor: P1.
Interacts with glycoprotein receptors on epithelial cell surface
Ciliostasis is followed by epithelial cell destruction.

Mycoplasma Pneumonia: Clinical Features

Low infectious dose
Walking pneumonia
Frequently confused with virus infection (primary atypical clinical manifestations)
Tracheobronchitis
Pharyngitis (use differential diagnosis from strep throat)

Mycoplasma Infections: Spread

Worldwide; all ages
Transmission by droplets of nasopharyngeal secretions
Important in military personnel
Epidemics: Intervals of 4-6 years
Retained by pathogens in recovered patients; common in 5-15-year-old adolescents/teenagers more than in older groups of patients
Infections in children under 6 months are uncommon
No seasonal incidence

Mycoplasma: Clinical Manifestations

Generalized aches and pains
Fever (usually 102°F)
Cough (frequently, non-productive)
Sore throat (nonexudative pharyngitis)
Headache/myalgias
Chills, but not rigors
Nasal congestion with coryza
Earache
General malaise

Mycoplasma: Pathogenesis

Infection involves the trachea, bronchi, and bronchioles (peribronchiolar tissues)
M. pneumoniae initially attaches to cilia and microvilli of cells lining bronchial epithelium
Attachment mediated by protrusion associated proteins (e.g., P1, P30); other proteins bind to extracellular matrix (e.g., fibronectin)
CARDS toxin interferes with ciliary action, leading to nuclear vacuolization and fragmentation of tracheal epithelial cells
Inflammation and desquamation of affected mucosa

Radiological Presentation

Variable presentation on CXR; commonly presents as bilateral lower lobe consolidation with small pleural effusions
Initially, as partly mottled, partly node-like peribronchial opacities with gradual development to involve whole segments or lobes

Mycoplasma: Immunity

Incomplete immunity
Re-infection may occur
Clinical presentation appears more severe in older children
Many clinical manifestations likely caused by immune response; not due to organism invasion

Urethritis

Half of urethral infections are not caused by Chlamydia or N. gonorrhoeae
Causes: Mycoplasma hominis and Ureaplasma
Diagnosis through culturing (fried egg colonies on medium containing sterols), serology (complement fixation tests, hemagglutination)

Laboratory Diagnosis (Mycoplasma)

Culture techniques: Mycoplasma from specimen (sputum, mucous membrane) inoculated in liquid/solid media with serum, yeast extract, and penicillin to inhibit contaminating bacteria
Cultural Characteristics: Lack a cell wall, but grow on solid media as small, transparent colonies (fried-egg appearance). Growth period; 2 days-several weeks

Serology Diagnosis (Mycoplasma)

Complement fixation
Hemagglutination (cold agglutinin test, positive for M. pneumoniae (Primary Atypical) Pneumonia; agglutination of human O group erythrocytes at 4°C, reversible at 37°C.
Hemabsorption & B-hemolysis of guinea pig red blood cells

Identification (Mycoplasma)

Conclusive identification through staining colonies with fluorescein-labeled antibody

Mycoplasma Nucleic Acid Probes

Specific recombinants to oligonucleotide sequences found exclusively in M. pneumoniae

L-forms

Some bacteria readily form variants that can replicate as filterable protoplasmic elements lacking a cell wall– called L-forms
L-forms formation may occur when cell wall synthesis is impaired by antibiotic treatment or high salt concentration.

L-Forms vs Mycoplasma

L-Forms: Contain a rigid cell wall at least at one stage in life cycle; lack sterols in cytoplasmic membrane
Mycoplasma: No cell wall; contain sterols in cytoplasm membrane

Pleuropneumonia-like organisms (PPLO)

Many organisms with similar morphological characteristics and cultural properties
Common reference: As PPLO.
A group of Mycoplasmas create extremely small colonies (T-strains) on agar plates

Multiplication (Mycoplasma)

Replication pattern differs due to the absence of a rigid cell wall; replication of typical bacteria starts with formation of a well-defined septum

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Description

Test your knowledge on the unique features of mollicutes and actinomycetes in this microbiology quiz. Explore characteristics, infections, and treatment approaches associated with these bacterial groups. Perfect for students and professionals interested in microbial pathogens.