LECTURE 5 (Spore and non-spore forming bacteria)

Question 1

What are Clostridia?

Answer 1

Anaerobic, spore-forming, non-motile, gram-positive rods

Question 2

What are the four medically important species of Clostridia?

Answer 2

• Clostridium tetani (tetanus)
• Clostridium botulinum (botulism)
• Clostridium perfringens (gas gangrene)
• Clostridium difficile (diarrhoea)

Question 3

What are the most important exotoxins?

Answer 3

• alpha toxin = a phospholipase that hydrolyses lecithin and sphingomyelin which disrupts the cell membranes of various host cells (including erythrocytes, leukocytes and muscle cells)
• ϴ-toxin = alters capillary permeability + toxic to heart muscle
• enterotoxin = inserts into enterocyte membranes to form pores leading to alterations in intracellular calcium and membrane permeability -> loss of cellular fluid + macromolecules

Question 4

What is Clostridium perfringes?

Answer 4

A large, gram-positive, non-motile rod with square ends

Question 5

What is Gas gangrene?

Answer 5

A lethal infection of Clostridium perfringens that is associated with war wounds, car and motorcycle accidents and septic abortions (endometritis).

TRANSMISSION:
- spores located in soil
- vegetative cells in normal flora of coli and vagina
- significant delay in injury + surgical management -> bacterial multiplication + toxin production

PATHOGENESIS:
organisms grow in traumatised tissue + produce toxins -> alpha toxin damages cell membranes including erythrocytes -> degradative enzymes produce gas in tissues

MANIFESTATIONS: (1-4 days after injury or after 10 hours)
- severe pain at wound site
- sense of heaviness/pressure
- edema
- tenderness
- pallor
- discolouration/haemorrhagic bull
SEVERE MANIFESTATIONS:
- shock with intravascular hemolysis
- hypotension
- renal failure leading to coma and death

LAB FINDINGS:
- clostridium perfringens on sample
- detection of lecithinase activity of alpha toxin
- opalescence produced around colonies due to breakdown of lipoprotein complex

TREATMENT:
wound debridement + penicillin G

PREVENTION:
- no vaccine
- clean + debrided wounds
- penicillin for prophylaxis (prevention)

Question 6

What is Food poisoning caused by C. Perfringens?

Answer 6

People with C. perfringens food poisoning have diarrhea and stomach cramps but no vomiting. Symptoms usually begin 6 to 24 hours after swallowing the bacteria.

TRANSMISSION:
- enterotoxin-producing strain spores are located in soil and can contaminate food
- heat-resistant spores survive cooking and germinate
- organisms grow to large numbers in reheated foods

PATHOGENESIS:
C.perfringens is a member of the normal flora in the colon but not in the small bowel where enterotoxin acts to cause diarrhoea

SYMPTOMS:
- nausea
- abdominal pain
- diarrhoea
- no fever or vomiting

TREATMENT:
symptomatic treatment + no antimicrobial drugs given

PREVENTION:
food should be adequately cooked to kill organism

Question 7

What is Clostridium botulinum?

Answer 7

A large, gram-positive rod whose spores resist boiling for long periods, thus needs 121 degrees for destruction

PROPERTIES:
- classified into types (A-G) based on antigenic specificity of neurotoxins
- resistant to enzymes of GI tract
- ingested unheated toxin is readily absorbed + distributed in bloodstream

EPIDEMIOLOGY:
- found in soil, pond and lake sediments
- if contaminate food, may convert to vegetative state, multiply and produce toxins + food has no change in food taste, colour or odour
- alkaline conditions of vegetables support growth

Question 8

What is Botulinum toxin?

Answer 8

• One of the most potent toxins in nature
• An enzyme (metalloproteinase) that acts at neuromuscular junctions
• MOA: cleaves attachment protein receptors which block the release of acetylcholine from vesicles at presynaptic membrane -> flaccid paralysis of motor system

also called “Botox” it blocks acetylcholine release, muscle contractions and thus wrinkles

Question 9

What are the three ways that Clostridium botulinum cause disease?

Answer 9

• FOOD POISONING = botulinum toxin is ingested with food in which spores have germinated + organism has grown
• WOUND BOTULISM = grows in necrotic tissue of wound
• INFANT BOTULISM = spores enter body + vegetate, cells replicate and cause toxin which pass into bloodstream -> toxin binds to neuromuscular junctions of parasympathetic nerves + interferes with acetylcholine release causing flaccid muscle paralysis

Question 10

Why shouldn’t you give babies honey until 12 months old?

Answer 10

Due to Infant Botulism

Explanation: Honey can be used for transmission to cause it. It is a food borne illness causing symptoms of constipation, weakness and paralysis which can lead to death

Question 11

What is Foodbourne botulism?

Answer 11

The botulinum toxin is ingested with food in which spores have germinated and the organism has grown

SYMPTOMS: start 12-36 hours after ingestion
- nausea, dry mouth + diarrhoea
- blurred vision, pupillary dilation, nystagmus
- symmetric paralysis: ocular, laryngeal, respiratory muscles and trunk + extremities

Question 12

What is Infant Botulism?

Answer 12

An illness that occurs when infants ingest Clostridium botulinum. It occurs between the ages of 3 weeks and 8 months.

SYMPTOMS:
- constipation
- poor muscle tone
- lethargy
- feeding problems
- ophthalmic and other paralysis

Question 13

What is the diagnosis, treatment and prevention of Clostridium botulinum?

Answer 13

DIAGNOSIS:
- detection of toxin (in food serum, faeces and rectal wash)
- detection of toxin genes A, B, E and F -> real time PCR
- culture and isolation of C. botulinum

TREATMENT:
Trivalent antitoxin is given along with respiratory support. Antitoxin is made in horses.

PREVENTION:
- proper sterilisation of all canned and vacuum-packed food
- food must be adequately cooked to inactivate the toxin
- swollen cans must be discarded (clostridial proteolytic enzymes from gas swells cans)

Question 14

What is Clostridium tetani?

Answer 14

A slim, gram-positie rod which forms spores readily in nature and requires anaerobic conditions. Spores stay in soil for many years and are resistant to disinfectant and boiling for several minutes.

TRANSMISSION:
- through a wound
- spores introduced during “skin-popping” (technique drug addicts use)
- germination favoured by necrotic tissue + poor blood supply

PATHOGENESIS:
C. tetani remains localised at the site of local infection and produces tetani toxin -> absorbed + ascends to CNS via motor nerves -> effect of toxin produces an increased reflex excitation of motor centres -> muscular spasms

SYMPTOMS: (4 days to several weeks)
- strong muscle spasms
- lockjaw (due to rigid contraction of jaw muscles)
- risus sardonicus (fixed sarcastic grimace expression)
- exaggerated reflexes
- opisthotonos (arching of back due to spasm of strong extensor muscles of back)
- respiratory failure
- high mortality rate

LAB FINDINGS:
- no microbiologic/serologic diagnosis (since organisms rarely isolated from wound site)
- terminal spores, “tennis racket” appearance”

TREATMENT:
- tetanus immune globulin (used to neutralise toxin)
- adequate airway + respiratory support
- benzodiazepines (to prevent spasms)

PREVENTION:
- immunisation with tetanus toxoid (formaldehyde-treated toxin) in childhood (alongside DTaP vaccine)
- trauma -> cleaned + derided wound + tetanus toxoid booster should be given
- grossly contaminated wound: tetanus immune globulin + toxoid booster + penicillin

Question 15

Describe the product of Clostridium tetani

Answer 15

A neurotoxic exotoxin called “tetanospasmin” or “tetanus toxin”

PROPERTIES:
- degrades a protein required for neurotransmitter release from vesicles on presynaptic membranes
- neurotransmitters (glycine + gamma-aminobutyric acid) affect INHIBITORY NEURONS -> unopposed firing of active motor neurons, generating spasms and spastic paralysis
- heat-labile, antigenic, readily neutralised by antitoxin and rapidly destroyed by intestinal proteases
- formaldehyde stimulates production of antitoxin

Question 16

Describe Clostridium difficile

Answer 16

A gram-positive rod that readily forms spores.

TOXINS
- Toxin A (TcdA) and Toxin B (TcdB) which both act in the cytoplasm by disrupting G proteins (especially those in the actin skeleton)
- Transferase (CDT) = exerts an ADP-ribosylating action which inhibits actin polymerisation within the enterocyte

Question 17

What is Clostridium difficile?

Answer 17

A bacteria that causes diarrhoea and inflammation of the colon

TRANSMISSION:
- carried in the GI tract
- transmitted by fecal-oral route
- hands of hospital personnel are important intermediaries
- associated with antibiotic-associated diarrhoea

PATHOGENESIS:
- antibiotics suppress drug-sensitive members of the normal flora, allowing C-diff to multiply and produce exotoxins A and B (glucosyltransferases)
- exotoxin B causes depolymerisation of actin, resulting in a loss of cytoskeletal integrity, apoptosis and death of enterocytes

SYMPTOMS:
- pseudomembranes (yellow-white plaques) on colonic mucosa
- diarrhoea (not bloody)
- neutrophils found in stool
- fever
- abdominal pain

LAB FINDINGS
- stool culturing
- presence of toxin in stool
- cytotoxicity test (human cells in culture are exposed to exotoxin in stool filtrate + death of cells observed)
- PCR

TREATMENT:
- oral metronidazole or vancomycin and fluids replaced
- fecal bacteriotherapy (administer bowel flora from a normal individual by enema/nasoduodenal tube to pt with pseudomembranous colitis
- surgical resection of colon may be necessary

PREVENTION:
no prevention

Question 18

What is Anthrax?

Answer 18

A serious infectious disease caused by gram-positive, endospor-forming, rod-shaped bacteria known as “bacillus anthracis”

TRANSMISSION:
domestic and wild animals can become infected when they breathe in or ingest spores in contaminated soil, plants or water -> anthrax spores get into the body and become “activated” -> multiply, spread out and produce toxins

Question 19

Describe the pathogenesis of Anthrax

Answer 19

Anthrax toxins are made up of three proteins:
- Protective antigen (PA)
- Edema factor (EF)
- Lethal factor (LF)

MOA:
PA binds to specific cell receptors and after proteolytic activation forms a membrane channel that mediates entry of EF and LF into the cell -> EF (an adenylate cyclase) with PA forms a toxin known as oedema toxin -> LF with PA form a lethal toxin causing death of infected host

Question 20

What are the different forms of Anthrax?

Answer 20

• Inhalation anthrax (most common)
• Cutaneous anthrax
• Gastrointestinal (GI) anthrax

Question 21

What is Inhalation anthrax?

Answer 21

From breathing bacterial spores while handling infected animal products or making biological weapons
[incubation period may be as long as 6 weeks]

MANIFESTATIONS:
spores replicate in lymph nodes + hemorrhagic necrosis and oedema of mediastinum start -> bacterial toxins released result in mediastinal widening + pleural effusions (accumulation of fluid in the pleural space)

SYMPTOMS:
- similar to common cold
- breathing problems + shock
- fatal

COMPLICATIONS:
- cough (due to effects on the trachea)
- sepsis -> hematogenous spread to GI tract causing bowel ulceration or to meninges causing hemorrhagic meningitis

Question 22

What is Cutaneous anthrax?

Answer 22

Through cuts and abrasions resulting from contact with infected animals

MANIFESTATIONS:
a pruritic papule develops 1-7 days after entry of organisms/spores through a scratch (resembles insect bite) -> lesions 1-3cm in diameter + have central black eschar (fully developed after 7-10 days) -> may take many weeks for lesion to heal and oedema to subside

SYMPTOMS:
- skin infection (sometimes spreads to lymph nodes)
[if treated with antibiotics -> death is rare]
- fever
- malaise
- headache

COMPLICATIONS:
- sepsis (20%)
- meningitis
- death

Question 23

What is Gastrointestinal anthrax?

Answer 23

From eating infected meat

SYMPTOMS:
- inflammation of intestinal tract
- nausea
- vomiting
- fever
[25% to 60% of cases are fatal]

Question 24

Describe the Laboratory diagnosis of anthrax

Answer 24

• Large, gram-positive rods in chains
• Spores usually not seen in smears of exudate
  [spores form when nutrients are insufficient, but nutrients are plentiful in infected tissue]
• Non-hemoltyic colonies form aerobically
• Polymerase chain reaction (PCR)
• Direct fluorescent antibody test
• Serologic tests (e.g ELISA)

Question 25

What is the treatment and prevention of anthrax?

Answer 25

TREATMENT:
- Ciprofloxacin (drug of choice)
- Doxycycline

PREVENTION:
- Ciprofloxacin or doxycycline used as prophylaxis
- Vaccine (weakly immunogenic + six doses given over an 18-month period) for people with high occupational risk
- Disposal of animal carcasses by burning/deep burial in lime pits
- Decontamination of animal products

Question 26

If a bioterrorism attack were to happen, why would Bacillus anthracis be used?

Answer 26

• Anthrax spores are easily found in nature, can be produced in a lab and last a long time
• Small (you cannot see, smell or taste them)

Question 27

What is Bacillus cereus?

Answer 27

An endospore-forming, aerobic, gram-positive, catalase-positive, B-hemolytic & motile bacteria found in soil that causes food poisoning
[it is resistant to PENICILLIN]

2 TYPES OF ENTEROTOXINS:
- a heat-labile toxin = causes nausea, abdominal pain and diarrhoea, lasting 12-24 hours
- a heat-stable toxin = short incubation period followed by severe nausea and vomiting with limited diarrhoea

CLINICAL FINDINGS:
- one syndrome: short incubation period (4 hours) and consists primarily of nausea and vomiting
- other: long incubation period (18 hours) and features watery, non-bloody diarrhoea

LAB DIAGNOSIS:
none

TREATMENT:
symptomatic treatment given

Question 28

Describe C. diphtheria

Answer 28

• Gram-positive rods that appear club-shaped and arranged in V or L shaped formations
• Granules stain metachromatically
• Non-capsulated
• Non-sporing
• Non-motile
• Aerobic
• Optimum temp is 37 degrees

Question 29

Describe the appearance of C. diphtheriae colonies on blood air and agar containing potassium tellurite

Answer 29

Blood agar = colonies are small, granular, gray with irregular edges and have small zones of haemolysis

Potassium tellurite agar = colonies are brown to black with a brown-black halo

Question 30

Describe the mechanism of action of Diphtheria toxin

Answer 30

Diphtheria toxin is a lethal, heat-labile, single-chain, three domain polypeptide encoded by LYSOGENIC PHAGE -> DT production is controlled by a repressor protein which responds to iron concentrations + regulates other toxin-related functions -> DT is an A-B toxin that acts in the cytoplasm to inhibit protein synthesis

Question 31

What is Corynebacterium Diphtheriae

Answer 31

A gram-positive bacteria that causes diphtheria

PATHOGENESIS:
has little invasive capacity and is due to local and systemic effects of DIPHTHERIA TOXIN (DT) -> locally, action on epithelial cells causes necrosis and inflammation forming a PSEUDOMEMBRANE composed of fibrin, leukocytes and cellular debris -> systemically, causes myocarditis, demyelination often resulting in paralysis of the soft palate, eye muscles or extremities

MANIFESTATIONS: (incubation of 2-4 days)
- thick, gray pseudomembrane over tonsils and throat
- malaise
- sore throat
- fever
- patch of exudate/membrane develops on tonsils, uvula, soft palate or pharyngeal wall
- lesions might form pustule or non-healing ulcer

COMPLICATIONS:
- extension of membrane into larynx and trachea, causing airway obstruction
- myocarditis accompanied by arrhythmia and circulatory collapse
- nerve weakness/paralysis
- cutaneous diphtheria

DIAGNOSIS:
- swabs from nose, throat or other lesions before antimicrobial drugs administered (swabs cultured on Loeffler’s medium, tellurite plate and a blood agar plate)
- PCR

TREATMENT:
- antitoxin (should be given immediately bc once bound to cells it cannot be neutralised anymore)
- antimicrobials (e.g penicillin, cephalosporins, erythromycin and tetracycline

Question 32

What is the Transmission and prevention of C. Diphtheriae?

Answer 32

TRANSMISSION:
(humans are the only natural host - resides in upper respiratory tract)
- airborne droplets
- site of pre-existing skin lesion

PREVENTION:
immunisation

Question 33

What is Listeria Monocytogenes?

Answer 33

L. monocytogenes causes meningitis and sepsis in newborns, pregnant women and immunosuppressed adults as well as febrile gastroenteritis.

EPIDEMIOLOGY:
- widespread in soil, ground water, decaying vegetation, intestinal tract of animals
- can be transmitted transplacentally to foetus and to newborns during birth

PATHOGENESIS:
Invasion of cells mediated by INTERNALIN (surface protein) made by Listeria and E-CADHERIN on surface of human epithelial cells -> enters cell, produces LISTERIOLYSIN which allows it to escape from the phagosome into the cytoplasm (escaping destruction in phagosome) -> move from cell to cell via ACTIN ROCKETS (filaments of actin polymerise and propel bacteria through membrane of one cell to another)

MANIFESTATIONS:
- Infection during pregnancy: abortion, premature delivery, sepsis
- Newborns infected during delivery can have acute meningitis 1 to 4 weeks later
(infected mother is asymptomatic/has influenza like illness)
- Gastroenteritis: watery diarrhoea, fever, headache, myalgias, abdominal cramps, little vomiting

DIAGNOSIS:
- culture of blood, cerebrospinal fluid (CSF) or focal lesions
- motile organisms

TREATMENT:
- trimethoprim-sulfamethoxazole (treatment of invasive disease e.g meningitis)
- combinations of ampicillin and gentamicin or ampicillin and trimethoprim-sulfamethoxazole
- Listeria gastroenteritis typically doesn’t require treatment

Question 34

Describe Listeria Monocytogenes

Answer 34

• Small gram-positive rods arranged in V or L shaped formations
• Catalase positive
• Beta hemolysis + aerobic
• Able to grow slowly in cold so can survive at refrigerator temp (due to RNA helices induced at low temperatures)