WEEK 14: GRAM POSITIVE RODS Flashcards by ZACHARIE JAEDIEL GONZAGA

What are the tests used to differentiate Corynebacterium (-) to Listeria(+)?

Motility (22C)
Bile esculin Hydrolysis

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Found as free-living saprophytes
Water, soil, air
Resistant to drying
80 species, of which 50 are clinically significant
Members of the usual flora of humans and animals
Closely related to Mycobacteria and Nocardia
Clinically significant isolates
Catalase positive and nonmotile

Corynebacterium

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Facultatively anaerobic
Gram-positive, non–spore-
forming rods
Arranged in palisades
Club-shaped
Babes-Ernst granules
Polymerized phosphates

Corynebacterium

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is the most significant pathogen.
Causes diphtheria
Difficult to speciate other species
Other species may cause infections in immunocompromised hosts.
Generally thought of as contaminants

Corynebacterium diphtheriae

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Worldwide distribution
Rare in places where vaccination programs exist
Exotoxin is a major virulence factor.
Diphtheria toxin
Toxin is produced by certain strains.
Lysogenized by bacteriophage with toxin gene (tox+)
Only toxin-producing bacteria can cause diphtheria.
Toxin production is inversely proportional to iron availability.
Toxin is antigenic.
Thus can use immunoglobulin G (IgG) to block toxin effects

Toxigenic Corynebacterium diphtheriae

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What is the major virulence factor of Corynebacterium diphtheriae?

Exotoxin

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Inhibits protein synthesis
NAD+ + EF-2 → ADPR-EF-2 + Nicotinamide + H+
Catalyzes transfer of ADPR to link with EF2 ADPR.EF (inactive)
Leads to cell/tissue death

A: active fragment

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Mediates entry of fragment A
binds to specific cell membrane receptors

Fragment B

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Respiratory
Acquired by droplet spray
Aerosol or hand-to-mouth contact
Unimmunized individuals are susceptibleb

Clinical Infections of Diphtheria

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More prevalent in the tropics
Infections occur at the site of minor abrasions.
Nonhealing ulcers with a dirty gray membrane

Cutaneous form of C. diphtheriae

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Used to demonstrate
pleomorphism and
metachromatic granules
Babes-Ernst granules

Loeffler’s serum agar

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Modified Tinsdale medium
Selective and differential
Black colonies with brown
halos around the colonies

Cystine-tellurite blood
agar (CTBA)

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Common on skin and most frequently recovered species
Opportunistic infections
Prosthetic joint infections, sepsis, and endocarditis
In nosocomial or immunocompromised patients

C. amycolatum

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Mastitis in cattle
Contact with animals or unpasteurized milk

C. ulcerans

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Infections from catheters or prosthetic devices
Prosthetic valve endocarditis

C. jeikeium

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Urinary pathogen
Highly urease positive (within minutes)

C. urealyticum

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Opportunistic infection
Often endocarditis

C. pseudodiphtheriticum

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Contact with sheep
Dermonecrotic toxin

C. pseudotuberculosis

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Rare infections
Normal flora

C. striatum

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Gram-positive non–spore-forming coccobacillary

L. monocytogenes

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Induces phagocytosis

Surface protein p60

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Cold enrichment
Grows at 4°C
Catalase positive
Rules out Streptococcus
Negative for hippurate hydrolysis
Motility
Motile at 25°C
“Umbrella” type motility
Tumbling motility in hanging drop method

L. monocytogenes

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Likely develop disease from penetration of the intestine
and systemic spread
Septicemia/meningitis in the compromised/elderly
Also endocarditis
Mild flulike syndrome in pregnant women could be fatal to fetus
Premature labor, spontaneous abortion

Listeriosis

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Gram-positive, nonsporulating forming rods
Coccobacillus that often appears like cocci
Widespread in nature
Primarily infect animals
Human exposure is limited.
Generally dairy products because it grows at low temperature
Processed meats can also contain this bacteria

Listeria monocytogenes

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* Normal oral flora * Endocarditis

Rothia dentocariosa

* Damages phagocytic membrane and prevents killing of the organism

Listeriolysin O

* Grows well on sheep blood agar (SBA) and chocolate agar * Prefers slightly increased carbon dioxide (CO2) * Colonies produce a narrow zone of hemolysis. * Similar to group B Streptococcus

L. monocytogenes

Produces a “block” type of hemolysis in contrast to “arrow” shape produced by group B Streptococcus

Christie Atkins Munch-Petersen (CAMP) test (L. monocytogenes)

* Gram positive, non–spore-forming, pleomorphic rods * Distributed in nature * Can cause disease in animals (swine, turkey, sheep) * Infection through occupational exposure * Erysipeloid * Heals within 3 to 4 weeks * Endocarditis

Erysipelothrix rhusiopathiae

* CO2 is required. * Grows on blood or chocolate agar * Colonies may appear gray or translucent with alpha hemolysis. * Pleomorphic, gram-positive thin rods that may form long filaments * Singly, in short chains, or in a V shape * Catalase negative * Production of hydrogen sulfide (H2S) on triple sugar iron (TSI)

Erysipelothrix rhusiopathiae

* SBA or chocolate agar * 5% to 7% CO2 at 35°to 37°C * Human blood bilayer Tween (HBT) agar * Medium of choice * Treatment * Metronidazole * Clindamycin

Gardnerella vaginalis

- Pharyngitis and pruritic scarlatiniform rash with desquamation of the skin of the hands and feet - Lipase and lecithinase positive - Exhibits a CAMP inhibition reaction

Arcanobacterium haemolyticum

Sepsis and wound infections in those with animal contact

A. pyogenes

* Catalase negative * Narrow zone β-hemolysis * Black dot on agar surface under the colony

Arcanobacterium

* Short, pleomorphic gram-positive rod or coccobacillus * Often stains gram-variable or gram-negative * Infections * Bacterial vaginosis (BV) * Malodorous discharge * Vaginal pH of greater than 4.5 * Wet mounts of vaginal fluid * Observe clue cells

Gardnerella vaginalis

Bacteriemia, wound infections, urinary tract infections (UTIs), and septic arthritis

A. bernardiae

* Aerobic * Gram-positive filamentous rods * Weakly acid-fast and may stain gram-variable * Sometimes resembling branched hyphae * Morphologically resemble fungi * In culture and in types of infections * Generally found in the environment and mostly affect immunocompromised individuals  Sulfur granules

Nocardia

* Slow growers, may take 3 to 6 days * Primarily affect immunocompromised * Rare but high mortality rate (40%) * Gram-positive branching filaments are seen in direct smears from sputum or aspirated material. * May show beading appearance

Nocardia

* Confluent bronchopneumonia * Necrosis with abscesses * No “sulfur granules”

N. cyriacigeorgica and N. farcinica

* Cutaneous infection termed actinomycotic mycetomas * Trauma to skin * Major destruction of the tissue and bone * “Sulfur granules” present

N. brasiliensis

* Large, square-ended gram-positive rods * Bamboo appearance * Nonhemolytic on 5% blood agar; raised, large, grayish-white, irregular, fingerlike edges * “Medusa head” or “beaten egg whites”

Bacillus anthracis

Nocardia can be identified using?

paraffin bait test

* Agent of anthrax, a disease in livestock * Humans acquire infection by contamination of wound or ingestion or inhalation of spores. * Morphology * Large, spore-forming, gram-positive bacilli * Spores viable for over 50 years (even restored from fossils) * Nonhemolytic on SBA

Bacillus anthracis

* Found in nature * Most are saprophytic and are isolated as contaminants * Gram-positive large rods with “empty” spaces * Endospores * Highly resistant to heat, drying, and chemicals * Catalase positive

Bacillus

* Acquired through inhalation of spores * Mild fever, fatigue, and malaise 2 to 5 days after exposure * Similar to flu or common cold, lasting 2 to 3 days * Sudden respiratory distress, disorientation, coma, and death * May last less than 24 hours from onset to death

Pulmonary anthrax or "woolsorter's disease”

* Polypeptide capsule * Potent exotoxin * Edema factor (EF) * Protective antigen (PA) * Lethal factor (LF)

Virulence factors of Bacillus anthracis

* Acquired by ingestion of contaminated raw meat * Inoculates into a lesion on the intestinal mucosa * Abdominal pain, nausea, anorexia, vomiting, and sometimes bloody diarrhea * More likely to be fatal but less likely to occur than cutaneous form

Gastrointestinal anthrax

* Enter through cuts causing a localized infection * Malignant pustule or black eschar * Painless and non–pus-producing * Produces a permanent scar

cutaneous anthrax

* Acquired by direct injection of the endospores into tissue * Injection drug use * Does not form black eschar * Causes necrotizing fasciitis, organ failure, shock, coma, and meningitis

Injectional anthrax

* Caused by distinct enterotoxins * Diarrheal syndrome * Associated with meat, poultry, and soups * Incubation period of 8 to 16 hours * Fever uncommon * Resolves within 24 hours * Emetic form * Associated with fried rice * Abdominal cramps and vomiting * Incubation period of 1 to 5 hours * Resolves in 9 hours

B. cereus

* Infections in the immunosuppressed hosts * Opportunistic infections of the eye * Endophthalmitis, panophthalmitis, and keratitis * Forms abscesses * Meningitis, septicemia, and osteomyelitis

B. cereus

* Boxcar-shaped, gram-negative bacillus * Produces a double zone of hemolysis on Brucella blood agar or blood agar

Clostridium perfringens

Antibiotic-associated diarrhea and pseudomembranous colitis

Clostridium difficile

Heavily swarming with terminal spores

C. tetani

Heavily swarming with subterminal spores

C. septicum

* Enteritis necroticans * Acute onset of severe abdominal pain and diarrhea, which is often bloody, and may be accompanied by vomiting * Followed by necrotic inflammation of the small intestines, at times leading to bowel perforation * Without treatment it can be fatal

Type C Clostridium perfringens

* A through G, but only types A, B, and E are associated with human disease * Toxin A is now used in medical treatments, including Botox®

Botulinum toxins

* Causes flaccid paralysis * In contrast to tetanus

Clostridium botulinum

- Ingestion of enterotoxin causing diarrhea and cramps - Usually self-resolving

Type A Clostridium perfringens

* Home canning * Home-cured meats * 2 hours to 8 days later * Infant botulism * Ingestion of spores in contaminated honey * Colonize the colon and produce toxins

Botulism

* Also known as gas gangrene * Contaminated wounds from trauma or surgery

Myonecrosis

* Develops from tetanospasmin neurotoxin * Inhibits neurons by inhibiting neurotransmitters * Symptoms: * Begin about 7 days after inoculation * Muscular rigidity of the jaw, neck, and lumbar region * Difficulty in swallowing * Sometimes involves limbs as well

Tetanus

most common cause of Myonecrosis

C. perfringens

Most common isolate from blood cultures

C. perfringens

* Grow, multiply, and produce toxin * Alpha toxin causes tissue necrosis and deeper invasion * Causes death of tissue that can require amputation * Symptoms * Pain and swelling with obvious tissue necrosis * Treatment * Antibiotic and surgical débridement of necrotic tissue * Hyperbaric oxygen can help destroy anaerobes

Myonecrosis

Marker organism for malignancy of GI tract

C. septicum

Both isolated from patients with underlying disease

C. tertium

* Most common isolate in antibiotic-associated diarrhea * Can cause pseudomembranous colitis * Necrosis of colon tissue and bloody diarrhea

C. difficile

* Commonly transmitted as a nosocomial infection * Transferred among patients * Hands of hospital personnel

Antibiotic-Associated Diarrhea

Chronic, granulomatous disease characterized by sinus tracts and fistulae that erupt to the surface and drain pus that contains “sulfur granules"

Actinomycosis

WEEK 14: GRAM POSITIVE RODS Flashcards

(70 cards)