Bacteriology 4: Gram-negative Anaerobes, Mycoplasma

Fusobacterium necrophorum

Gram-negative obligate anaerobe that normally inhabits the gastrointestinal tract and causes necrobacillosis

Necrobacillosis

Disease caused by Fusobacterium necrophorum characterized by tissue necrosis, abscess formation, and putrid odor

Four characteristics of necrobacillosis

1.) Focal coagulative necrosis

2.) Ischemia

3.) Abscess formation

4.) Putrid odor

Focal coagulative necrosis

Localized tissue death in which the basic tissue architecture is initially preserved

Fusobacterium infections frequently involve ______ infections

Synergistic

Synergistic infection

Infection in which multiple bacterial species work together to produce more severe disease

Five major diseases associated with Fusobacterium necrophorum

1.) Bovine rumenitis-liver abscess complex

2.) Bovine foot rot

3.) Bovine and ovine contagious interdigital dermatitis

4.) Ovine infective bulbar necrosis

5.) Bovine diphtheria

Bovine rumenitis-liver abscess complex

Infection in which Fusobacterium enters through damaged ruminal mucosa and spreads to the liver, producing abscesses

Pathogenesis of bovine rumenitis-liver abscess complex

1.) Injury to ruminal mucosa

2.) Fusobacterium invades through ulcers

3.) Bacteria travel through the portal vein

4.) Liver abscesses develop

Primary and secondary sites of infection in bovine rumenitis-liver abscess complex

Primary = rumen

Secondary = liver

Bovine foot rot

Synergistic infection between Fusobacterium necrophorum and Bacteroides melaninogenicus causing severe tissue destruction and putrid odor

Bacterial species associated with Fusobacterium in bovine foot rot

Bacteroides melaninogenicus

Bovine and ovine contagious interdigital dermatitis

Synergistic infection between Fusobacterium necrophorum and Dichelobacter nodosus causing inflammation and tissue damage between the digits

Bacterial species associated with Fusobacterium in contagious interdigital dermatitis

Dichelobacter (Bacteroides) nodosus

Ovine infective bulbar necrosis

Heel abscess caused by synergistic infection involving Fusobacterium necrophorum and Actinomyces pyogenes

Bacterial species associated with Fusobacterium in ovine infective bulbar necrosis

Actinomyces pyogenes

Bovine diphtheria

Synergistic infection involving Histophilus somni and Fusobacterium necrophorum that produces necrotic laryngeal lesions and pseudomembrane formation

Pathogenesis of bovine diphtheria

1.) Histophilus somni damages the laryngeal mucosa

2.) Fusobacterium necrophorum invades damaged tissue

3.) Pseudomembrane forms

Bacterial species that predisposes cattle to Fusobacterium infection in bovine diphtheria

Histophilus somni

Characteristic lesion of bovine diphtheria

Pseudomembrane (diphtherioid membrane)

Pseudomembrane

Adherent layer of bacteria, fibrin, dead cells, and leukocytes covering damaged mucosal tissue

Bovine diphtheria can cause ______ in severe cases because...

Airway obstruction; the pseudomembrane can enlarge and obstruct the airway

Three major virulence factors of Fusobacterium necrophorum

1.) Endotoxin

2.) Hemolysin

3.) Leukocidin

Endotoxin of Fusobacterium

Activates macrophages and induces inflammation

Hemolysin of Fusobacterium

Damages red blood cells

Leukocidin of Fusobacterium

Damages leukocytes and contributes to pus formation

Three major predisposing factors for necrobacillosis

1.) Filthy environments

2.) Oxygen insufficiency

3.) Coinfection with other bacteria

Fusobacterium is ubiquitous in the gastrointestinal tract, but not all animals develop necrobacillosis because...

It requires predisposing conditions that create an anaerobic environment and allow tissue invasion

Filthy environments predispose animals to necrobacillosis because...

Fecal contamination provides a source of bacteria and can help protect them from oxygen

Three conditions that produce oxygen insufficiency and predispose animals to necrobacillosis

1.) Aerobic bacterial infection

2.) Surgery or trauma

3.) Disruption of normal intestinal flora

Aerobic bacterial infections predispose animals to necrobacillosis because...

Aerobes consume oxygen, creating an anaerobic environment favorable for Fusobacterium growth

Surgery or trauma predisposes animals to necrobacillosis because...

Damage to blood vessels reduces oxygen delivery to tissues

Disruption of normal intestinal flora predisposes animals to necrobacillosis because...

It allows Fusobacterium to overgrow

Coinfection with other bacteria predisposes animals to necrobacillosis because...

Other bacteria damage tissues and create conditions favorable for Fusobacterium invasion and growth

Three bacteria associated with synergistic Fusobacterium infections

1.) Bacteroides

2.) Histophilus

3.) Actinomyces

Two major laboratory characteristics used to identify Fusobacterium

1.) Gram-negative fusiform rods

2.) Anaerobic fermentation producing a putrid odor

Fusiform

Elongated, spindle-shaped bacterium with tapered ends

Fusobacterium requires ______ conditions for culture

Anaerobic

Fermentation product primarily associated with Fusobacterium

Butyric acid

Fermentation product particularly associated with Bacteroides

Propionic acid

Fusobacterium and Bacteroides are both ______, but differ in their ______

Gram-negative obligate anaerobes; fermentation products

Two major challenges associated with antibiotic treatment of necrobacillosis

1.) Poor antibiotic penetration into infected tissues

2.) Antibiotic resistance

Reservoir of Fusobacterium necrophorum

Normal gastrointestinal flora

Fusobacterium cannot realistically be eradicated because...

It is a normal inhabitant of the gastrointestinal tract

Mycoplasma

Smallest self-replicating prokaryotes that lack a cell wall and primarily cause chronic pneumonia or arthritis

Four major characteristics of Mycoplasma

1.) Smallest self-replicating prokaryotes

2.) Lack a cell wall

3.) Extremely pleomorphic

4.) Obligate parasites of animal hosts

Pleomorphic

Variable in shape

Mycoplasma is extremely pleomorphic because...

It lacks a rigid cell wall

Mycoplasma can pass through some bacterial filters because...

It is extremely small

Mycoplasma is generally ______ specific

Host-species

Two major diseases caused by classical Mycoplasma

1.) Chronic pneumonia

2.) Arthritis

Mycoplasma pneumonia

Chronic respiratory disease primarily affecting the epithelium of the conducting airways rather than the alveoli

Mycoplasma primarily infects the ______ rather than the ______

Respiratory epithelium of conducting airways; alveoli

Mycoplasma pneumonia differs from pneumonia caused by Mycobacterium or Streptococcus because...

Mycoplasma primarily infects conducting airway epithelium, whereas Mycobacterium and Streptococcus can involve alveolar regions

Characteristic lesion associated with chronic Mycoplasma pneumonia

Bronchiectasis

Bronchiectasis

Abnormal, persistent dilation of the bronchi

Bronchiectasis develops during Mycoplasma infection because...

Chronic respiratory infection damages and enlarges the bronchi

Three major consequences of bronchiectasis

1.) Impaired air filtering

2.) Impaired warming and humidification of inhaled air

3.) Increased susceptibility to secondary respiratory infections

Bronchiectasis increases susceptibility to secondary respiratory infections because...

Impaired airway conditioning allows contaminants to reach and damage the alveoli

Mycoplasma arthritis

Joint inflammation caused by Mycoplasma infection of the synovial membrane

Three major changes associated with Mycoplasma arthritis

1.) Inflammatory cell infiltration

2.) Swelling of synovial villi

3.) Painful joint movement

Mycoplasma arthritis causes painful joint movement because...

Inflamed and swollen synovial villi become compressed between bones during movement

Four important classical Mycoplasma species

1.) M. gallisepticum

2.) M. synoviae

3.) M. hyorhinis

4.) M. hyopneumoniae

M. gallisepticum

Causes chronic respiratory disease, airsacculitis, and infectious sinusitis in poultry

M. synoviae

Causes infectious synovitis in chickens and turkeys

M. hyorhinis

Causes polyserositis and polyarthritis in young pigs

M. hyopneumoniae

Causes enzootic pneumonia in swine

Two important avian Mycoplasma species

1.) M. gallisepticum

2.) M. synoviae

Two important swine Mycoplasma species

1.) M. hyorhinis

2.) M. hyopneumoniae

Erythrocyte-tropic Mycoplasma

Mycoplasma species that attach to erythrocytes and cause anemia rather than pneumonia or arthritis

Erythrocyte-tropic Mycoplasma were formerly classified as ______ or ______

Haemobartonella; Eperythrozoon

Three important erythrocyte-tropic Mycoplasma species

1.) M. haemosuis

2.) M. wenyonii

3.) M. haemofelis

M. haemosuis

Erythrocyte-tropic Mycoplasma of pigs

M. wenyonii

Erythrocyte-tropic Mycoplasma of cattle

M. haemofelis

Erythrocyte-tropic Mycoplasma of cats

Two major clinical manifestations of erythrocyte-tropic Mycoplasma infections

1.) Anemia

2.) Jaundice

Erythrocyte-tropic Mycoplasma causes anemia because...

Bacteria attach to erythrocytes and promote their destruction

Severe erythrocyte-tropic Mycoplasma infection may cause ______ due to...

Jaundice; increased erythrocyte destruction

Four major virulence mechanisms of Mycoplasma

1.) Adherence

2.) Immune evasion

3.) Immune-mediated host cell destruction

4.) Endonuclease production

Major virulence factor of Mycoplasma

Adherence

Attachment organelles

Specialized membrane structures that allow Mycoplasma to tightly adhere to host cell surfaces

Mycoplasma adheres to host cells using...

Attachment organelles

Gliding motility

Movement that allows Mycoplasma to spread along host cell and tissue surfaces

Mycoplasma evades host immune recognition by...

Acquiring host cell surface antigens that help conceal bacterial antigens

Mycoplasma can cause immune-mediated destruction of host cells because...

Host cells acquire Mycoplasma antigens and may be attacked by antibodies directed against the bacteria

Two consequences of surface antigen exchange between Mycoplasma and host cells

1.) Immune evasion

2.) Immune-mediated destruction of host cells

Endonuclease

Enzyme that breaks down DNA and RNA

Mycoplasma produces endonucleases because...

It cannot synthesize purine and pyrimidine bases and must obtain them from host nucleic acids

Mycoplasma cannot synthesize ______ and ______

Purines; pyrimidines

Two additional inflammatory virulence factors produced by some Mycoplasma species

1.) ADP-ribosylating toxins

2.) Superantigens

ADP-ribosylating toxins and superantigens contribute to Mycoplasma disease by...

Stimulating excessive inflammatory responses

Three major characteristics of classical Mycoplasma culture

1.) Aerobic growth

2.) Requirement for serum-containing media

3.) Fried-egg colonies

Classical Mycoplasma requires ______ conditions for growth

Aerobic

Mycoplasma requires rich culture media containing serum because...

It depends on cholesterol for membrane stability and growth

Mycoplasma depends on host-derived ______ for membrane function

Cholesterol

Characteristic colony morphology of Mycoplasma

Fried-egg colonies

Fried-egg colony

Colony with a dense central region surrounded by a thinner peripheral region

Two major diagnostic methods for erythrocyte-tropic Mycoplasma

1.) Giemsa-stained blood smear

2.) PCR

Giemsa-stained blood smear for erythrocyte-tropic Mycoplasma

Allows visualization of small organisms attached to erythrocytes

Mycoplasma cannot be diagnosed using conventional ______ _______

Culture methods