Chapter 19 Micro

Gram Positive Bacilli can be categorized into three groups

-Endospore-formers

-Non-endospore-formers

-Irregular shaped and staining properties

Bacillus anthracis

• Infection occurs when spores

  get into the body

• Found naturally in soil and

  commonly affects domestic

  and wild animals around the

  world

Cutaneous (anthrax)

spores enter through skin, black sore- eschar; least dangerous

Pulmonary (anthrax)

inhalation of spores

Gastrointestinal (anthrax)

ingested spores

Injection

recently identified in heroine injecting users in Northern Europe

Clostridium perfringens

• Spores found in soil, intestine of humans and animals

• Common contaminant of raw meat and poultry that have not been cooked

  thoroughly enough to destroy spore

Food Poisoning

• 1 million cases of foodborne illness in USA annually

• Incubation period 6 - 24 hrs

Enterotoxins cause

diarrhea

What is the most frequent clostridia involved in soft tissue and wound infections causing Gas Gangrene?

Clostridium perfringens

Gas gangrene is typically _______

not highly invasive

Exotoxins released cause much of the damage of

gangrene

Prevention and Treatment: Food Poisioning

• Food thermometer

• Thoroughly cook meats andpoultry to a safe internaltemperature

• Refrigerate cold foods within 2hrs @ 40ᵒF or below

• Keep hot food @ 140ᵒF or above

• Leftovers should be divided into shallow containers and refrigerated immediately

Prevent and Treatment: Gas Gangrene

Immediate cleansing of dirty wounds, deep wounds, compound fractures, and infected incisions

Clostridium tetani: Tetanus

• Common resident of soil and GI tracts of animals

• Most commonly among geriatric patients and IV

  drug abusers; neonates in developing countries

Clostridium tetani can cause

Tetanus and lockjaw

Pathology: Clostridium tetani

Spores usually enter through accidental puncture wounds, burns, umbilical stumps,

frostbite, and crushed body parts

Tetanospasmin

neurotoxin causes paralysis by binding to motor nerve endings; blocking the release of neurotransmitter for muscular contraction inhibition; muscles contract uncontrollably

Death from tetanus is usually caused from the paralysis of ______ muscles

respiratory

The tetanus vaccine is usually needed every __ years

10

Tetanus can be treated with

penicillin or tetracycline; and muscle relaxants

Clostridium difficile usually resides in the ____

Colon, present in low numbers

Clostridium difficile can cause

• antibiotic-associated colitis

• Major cause of diarrhea in hospitals

• Increasingly common in community-

  acquired diarrhea

• Produces enterotoxins that damage

  intestines

Clostridium difficile is generally (invasive/non-invasive)

non-invasive

C. difficile infection can result from

gastrointestinal dysbiosis

Clostridium botulinum

• spore-forming anaerobe; commonly inhabits soil and water

• rare but severe intoxication usually from home canned food

Botulism

intoxication associated with inadequate food preservation

The potent toxin of botulism is

botulin

When botulin toxin is carried to neuromuscular junctions, it blocks the release of THIS neurotransmitter, essential for muscle contraction

acetylcholine

Symptoms of botulism

Double or blurred vision, difficulty swallowing, neuromuscular symptoms — flaccid paralysis

Death is usually caused from respiratory failure.

Infant botulism

caused by ingested spores that germinate and release toxin; flaccid paralysis

Wound botulism

spores enter wound and cause symptoms similar to food-borne botulism

Gram-Positive Regular Non-Spore-Forming Bacilli

stain uniformly and do not assume pleomorphic shapes

Listeria monocytogenes

• Non-spore-forming gram-positive

• Ranging from coccobacilli to long filaments

• 1-4 flagella and lack capsules

• Resistant to cold, heat, salt, pH extremes, and bile

• Virulence attributed to ability to replicate in the cytoplasm

of host cells after inducing phagocytosis; avoids humoral

immune system

The primary reservoir for Listeria monocytogenes

soil and water; animal intestines

Listeriosis

most cases associated with dairy products, poultry, and meat

Gram-Positive Irregular Non-Spore-Forming Bacilli

are pleomorphic, stain unevenly

Corynebacterium diptheriae

• Acquired via respiratory droplets from carriers or actively infected individuals

• Reservoir of healthy carriers; potential for diphtheria is always present

Most cases of Corynebacterium diptheriae occur in

non-immunized children living in crowded, unsanitary conditions

C. diptheriae - Stage 1: Local Infection

upper respiratory tract inflammation

Affects: Sore throat, nausea, vomiting, swollen lymph nodes

C. diptheriae - Stage 2: Diptherotoxin production and toxemia

• Toxin absorbed into blood from throat can target organs – primarily heart and nerves

• pseudomembrane (film) formation from inflammation and excess fluid across pharynx can cause asphyxiation

Mycobacteria: Acid-Fast Bacilli

• Gram-positive irregular bacilli

• Acid-fast staining

• Strict aerobes

• Produce catalase

• Possess mycolic acids and a unique type ofpeptidoglycan

• Do not form capsules, flagella, or spores

• Grow slowly

Mycobacterium tuberculosis is also known as

Tubercle bacillus

Mycobacterium tuberculosis

Produces no exotoxins or enzymes that contribute to infectiousness

Predisposing factors of tuberculosis include

inadequate nutrition, debilitation of the immune system, poor access to medical care, lung damage, and genetics

Estimate 1/3rd of world population and 15 million in U.S. carry this bacterium

tubercle bacillus

The infectious dose for Primary TB is

10 cells

Secondary TB is

the reactivation of bacilli from Primary TB

Symptoms of secondary TB

Violent coughing, greenish or bloody sputum, fever, anorexia, weight loss, fatigue

Extrapulmonary TB

bacilli disseminate to regional lymph nodes, kidneys, long bones, genital tract, brain, and meninges

Mantoux test

local intradermal injection of purified protein derivative (PPD); look for red wheal to form in 48-72 hours

Interferon-gamma release assays

• blood test for detection of TB, positive and negative for the presence of TB bacterial products

• Used when person has been vaccinated for TB and/or cannot make multiple appointments

Mycobacterium leprae

• Strict parasite – has not been grown on artificial media or tissue culture

• Slowest growing of all Mycobacterium species

• Multiplies within host cells in large packets called globi

Leprosy

a chronic disease that begins in the skin and mucous membranes and progresses into nerves

Two forms of mycobacterium leprae

– Tuberculoid

– Lepromatous

Tuberculoid (leprae)

asymmetrical, shallow lesions, damage nerves – results in local loss of pain reception

Lepromatous (Multibacillary)

a deeply nodular infection that causes severe disfigurement of the face and extremities, widespread dissemination

Ways to test TB

1. In vivo or tuberculin testing/blood test

2. X-ray

3. Direct identification of acid-fast bacilli in specimen

4. Cultural isolation and biochemical testing