The GramPositive Bacteria

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The Gram-Positive Bacteria
Chapter 19
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The Gram-Positive Bacilli of Medical Importance
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Bacillus anthracis With central endospores
Clostridium perfringens With subterminal
endospores
Clostridium tetani With terminal endospores
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Bacillus

• gram-positive, endospore-forming, motile rods
• mostly saprobic
• aerobic catalase positive
• versatile in degrading complex macromolecules
• source of antibiotics
• primary habitat is soil
• 2 species of medical importance
• Bacillus anthracis
• Bacillus cereus

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Bacillus anthracis

• large, block shaped rods
• central spores that develop under all conditions
  except in the living body
• virulence factors capsule exotoxins
• 3 types of anthrax
• Cutaneous spores enter through skin, black
  sore- eschar least dangerous
• Pulmonary inhalation of spores
• Gastrointestinal ingested spores
• treated with penicillin or tetracycline
• vaccine toxoid 6X over 1.5 years annual
  boosters
• dead livestock burned/chemically decontaminated
  before burial to prevent soil contamination

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Bacillus anthracis

• Biological warfare threat.
• Letter attacks of 2001
• Resulted in only 22 cases of anthrax and five
  deaths
• Great disruption and concern
• More than 32,000 people who may have come into
  contact with the letters were given prophylactic
  antibiotics.

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Anthrax- Domestic Bioterrorism

• Starting one week after the 9/11/2001 attack
  letters containing weaponized anhtrax were sent
  to media offices and to Democratic Senators Tom
  Daschle and Patrick Leahy -- the two individuals
  expected to resist passage of the USA PATRIOT
  ACT.

• The attacks came in two waves of letters with
  Trenton, New Jersey postmarks
• the first, with postmarks of Sepmtember 18, were
  sent to ABC, NBC, CBS, the New York Post, and the
  National Equiror at American Media Inc.
• the second, with postmarks of October 9, were
  sent to Senators Daschle and Leahy.

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Cutaneous anthrax showing the eschar
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Bacillus cereus

• common airborne dustborne
• grows in foods, spores survive cooking
  reheating
• ingestion of toxin-containing food causes nausea,
  vomiting, abdominal cramps diarrhea 24 hour
  duration
• no treatment
• spores abundant in the environment

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Clostridium

• gram-positive, spore-forming rods
• anaerobic catalase negative
• over 120 species
• oval or spherical spores produced only under
  anaerobic conditions
• synthesize organic acids alcohols (useful for
  some biotechnology application) exotoxins
• cause wound tissue infections food
  intoxications

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Clostridium perfringens

• causes gas gangrene in damaged or dead tissues
• 2nd most common cause of food poisoning,
  worldwide
• virulence factors
• toxins alpha toxin causes RBC rupture, edema
  tissue destruction
• collagenase
• hyaluronidase
• DNase

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C. perfringens infection
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C. perfringens wound infection
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Clostridium perfringens

• treatment of gangrene
• debridement of diseased tissue
• large doses of cephalosporin or penicillin
• hyperbaric oxygen

Hyperbaric treatment chamber Exposure to
increased oxygen levels inhibits anaerobes and
speeds healing
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Clostridium difficile

• normal resident of colon, in low numbers
• causes antibiotic-associated colitis
• treatment with broad-spectrum antibiotics kills
  the other bacteria, allowing C. difficile to
  overgrow
• produces entertoxins that damage intestine
• major cause of diarrhea in hospitals

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C. difficile infection. Lining of the colon
as seen via a sigmoidoscope
Mild
Severe pseudomembranous colitis
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Clostridium tetani

• common resident of soil GI tracts of animals
• causes tetanus or lockjaw, a neuromuscular
  disease
• spores usually enter through accidental puncture
  wounds, burns, umbilical stumps, frostbite,
  crushed body parts
• tetanospasmin neurotoxin causes paralysis
• vaccine booster needed every 10 years

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Tetanospasmin (a potent neurotoxin). Toxin
inhibits release of neurotransmitter from neurons
controlling inhibition of skeletal muscle
contraction
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Patient with Tetanus
Figure 19.17
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Neonatal tetanus
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Clostridium botulinum

• Causes 3 diseases
• food poisoning (an intoxication) spores are in
  soil, may contaminate vegetables improper
  canning does not kill spores they germinate in
  the can producing botulinum toxin
• toxin causes paralysis by preventing release of
  acetylcholine
• infant botulism caused by ingested spores that
  germinate in the body release toxin
• wound botulism spores enter wound cause food
  poisoning symptoms

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Listeria monocytogenes

• non-spore-forming gram-positive
• primary reservoir is soil water
• can contaminate foods grow during refrigeration
• Most cases are from contaminated dairy products,
  poultry and meat
• Disease is often mild/subclinical may have
  fever, diarrhea
• Listerosis in immunocompromised patients, fetuses
  neonates affects brain meninges
• 20 death rate
• ampicillin trimethoprimsulfamethoxazole
• Prevention pasteurization cooking

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Listeria monocytogenes

• Pathogen isolated from
• 12 of ground beef
• 25-30 of chicken/turkey carcasses
• 6 of luncheon meats
• also in dairy products

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Erysipelothrix rhusiopathiae

• gram-positive rod widely distributed in animals
  the environment
• primary reservoir tonsils of healthy pigs
• enters through skin abrasion, multiples to
  produce erysipeloid, dark red lesions
• penicillin or erythromycin
• vaccine for pigs

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Erysipeloid lesion on hand of animal handler
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Corynbacterium diptheriae

• gram-positive irregular bacilli (pleiomorphic)
• produce catalase
• possess mycolic acids a unique type of
  peptidoglycan
• 2 stages of disease
• local infection upper respiratory tract
• diptherotoxin production toxemia
• pseudomembrane formation can cause asphyxiation

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Corynebacterium diptheriae
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United States
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pseudomembrane
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Diptheria

• 1990s epidemic in former Soviet Union countries.
• Reduced vaccination programs resulted in greatly
  reduced herd immunity
• Multitude of susceptible persons allowed spread
  in the community.
• Most cases are in children aged 1-10 in crowded
  settings.

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Propionibacterium acnes

• gram-positive rods
• aerotolerant or anaerobic
• nontoxigenic
• common resident of sebaceous glands
• causes acne

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Mycobacteria

• gram-positive irregular bacilli
• acid-fast staining
• strict aerobes
• produce catalase
• possess mycolic acids a unique type of
  peptidoglycan
• do not form capsules, flagella or spores
• grow slowly
• Mycobacterium tuberculosis
• Mycobacterium leprae

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Mycobacterium tuberculosis

• produces no exotoxins or enzymes that contribute
  to infectiousness
• contain complex waxes other substances that
  prevent destruction by lysosomes of macrophages
• transmitted by airborne respiratory droplets
• only 5 infected people develop clinical disease

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Primary TB

• infectious dose 10 cells
• phagocytosed by alveolar macrophages multiply
  intracellularly
• after 3-4 weeks immune system attacks, forming
  tubercles, granulomas consisting of a central
  core containing bacilli surrounded by WBCs

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Granulomatous infection by M. tuberculosis
Tubercule formation
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Primary Tuberculosis
Figure 19.22a
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Secondary TB

• reactivation of bacilli
• tubercles expand drain into the bronchial tubes
  upper respiratory tract
• gradually patient experiences more severe
  symptoms
• violent coughing, greenish or bloody sputum,
  fever, anorexia, weight loss, fatigue
• untreated 60 mortality rate
• Extrapulmonary TB
• during secondary TB, bacilli disseminate to
  regional lymph nodes, kidneys, long bones,
  genital tract, brain, meninges Bad News

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Secondary Tuberculosis
Figure 19.22b
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Diagnosis

• tuberculin testing (Mantoux test)
• X rays
• direct identification of acid-fast bacilli in
  specimen
• cultural isolation and biochemical testing

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Tuberculin skin test. Tests for hypersensitivity
Vaccination causes a positive test resultso test
is only useful in countries that do employ
widespread vaccination
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Colorized X-ray
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Treatment of TB

• 6-24 months of at least 2 drugs from a list of 11
• one pill regimen called Rifater (isoniazid,
  rifampin, pyrazinamide)
• vaccine based on attenuated bacilli Calmet-Guerin
  (BCG) strain of M. bovis used in other countries
  (not U.S.)
• Success rate of vaccination 80 in children and
  20-50 in adults.

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Directly Observed Therapy (DOT)to assure that
medication is actually taken
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Mycobacterium leprae

• Hansens bacillus
• strict parasite has not been grown on
  artificial media or tissue culture
• slowest growing of all species
• multiplies within host cells in large packets
  called globi
• causes leprosy, a chronic disease that begins in
  the skin mucous membranes progresses into
  nerves

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leprosy

• endemic regions throughout the world
• spread through direct inoculation from leprotics
• 2 forms
• tuberculoid superficial infection without skin
  disfigurement which damages nerves and causes
  loss of pain perception
• lepromatous a deeply nodular infection that
  causes severe disfigurement of the face
  extremities
• treatment by long-term combined therapy

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Leprosy
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Leprosy
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Feather test for leprosy. Tickling to determine
sensitivity to touch
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Actinomycetes

• Genera Actinomyces Nocardia are nonmotile
  filamentous bacteria related to mycobacteria
• may cause chronic infection of skin and soft
  tissues
• Actinomyces sp responsible for diseases of the
  oral cavity intestines
• Nocardia brasiliensis causes pulmonary disease
  similar to TB

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Actinomycosis
Periodontal infection. Infection works its way to
the surface of the face to rupture and drain
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Nocardiosis
Pulmonary infection that has disseminated to the
skin
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Gram Positive Cocci
Oral streptococci on agar plate
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General characteristics of the Staphylococci

• Spherical cells arranged in irregular clusters
• Gram positive
• Common inhabitant of the skin mucous membranes
• Lack spores and flagella
• May have capsules
• numerous species

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Staphylococcus aureus

• grows in large, round, opaque colonies
• optimum temperature of 37oC
• facultative anaerobe
• withstands high salt, extremes in pH, high
  temperatures
• produces many virulence factors

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S. aureus
SEM showing grape-like clusters
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Enzymes of S. aureus

• coagulase coagulates plasma and blood produced
  by 97 of human isolates diagnostic
• hyaluronidase
• staphylokinase
• DNase
• lipases
• penicillinase

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Toxins of S. aureus

• hemolysins lyse RBCs a, b, g
• leukocidin
• enterotoxins
• exfoliative toxin
• toxic shock syndrome toxin

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S. aureus

• Present in most environments frequented by humans
• Readily isolated from fomites
• Carriage rate for healthy adults is 20-60
• Carriage is mostly in anterior nares, skin,
  nasopharynx, intestine

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S. aureus diseases

• Ranges from localized to systemic
• localized -abscess, folliculitis, furuncle,
  carbuncle, impetigo
• systemic osteomyelitis, bacteremia
• toxigenic disease food intoxication, scalded
  skin syndrome, toxic shock syndrome

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S. aureus
Skin Lesions
Boil or Furuncle
Carbuncle
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S. aureus
Osteomyelitis
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S. aureus
Staphylococcal scalded skin syndrome (SSSS)
Exfoliative toxin
Epidermal shedding/separation
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Staphylococcus aureus

• Food Poisoning
• Food contaminated by handling with bare hands.
  Bacteria grow and produce toxin.
• Refrigerate food to prevent growth. Heating
  doesnt always destroy toxin.
• Symptoms usually start within 1-6 hours after
  eating contaminated food (usually gone in a day)
• Symptoms include diarrhea, vomiting, nausea,
  cramps

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Staphylococcus aureus

• Toxic Shock Syndrome (TSS)
• First linked to use of ultra-absorbent tampons
  that bound Mg ions and created a favorable
  environment for increased colonization and growth
  of vaginal S. aureus and increased TSS toxin
  production.
• Toxin enters bloodstream and causes fever,
  vomiting organ damage and potential fatality.
• Height of problem 1980-198415,000 affected/yr
  with 15 mortality.

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SuperBug ?

• MRSA Methicillin Resistant Staphylococcus aureus
• A strain of staph that is highly resistant to
  broad-spectrum antibiotics.
• Once found almost exclusively in hospital
  settings the bacteria is now showing up in the
  wider community
• People can be colonized by the bacteria (skin and
  nose primarily) and be healthy but act as
  carriers to spread the microbe.
• It is thought that perhaps 25-30 of people may
  harbor S.aureus.

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MRSA has become a subject for some intensive
public education efforts
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MRSA-2

• A CDC survey completed recently suggests that in
  2005 there were 94,000 cases of MRSA in the US
  and that perhaps 19,000 people died. (A higher
  rate than AIDS in the US)
• 85 of the cases were in hospitals, nursing homes
  etc. But many are concerned about the large
  number of infections acquired in normal community
  environments.
• Spread may be by hands (direct contact) or from
  contaminated surfaces.
• Infections range from an inconsequential skin
  lesion to a fatal septicemia or pneumonia

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S. aureus
Coagulase Test
Catalase Test
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Other Staphylococci

• S. epidermidis lives on skin mucous
  membranes endocarditis, bacteremia, UTI
• S. hominis lives around apocrine sweat glands
• S. capitis live on scalp, face, external ear
• All 3 may cause wound infections
• S. saprophyticus infrequently lives on skin,
  intestine, vagina UTI

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Streptococci

• Gram-positive spherical/ovoid cocci arranged in
  long chains
• Non-spore-forming, nonmotile
• Can form capsules slime layers
• Facultative anaerobes
• Do not form catalase
• Most parasitic forms are fastidious require
  enriched media
• Small, nonpigmented colonies
• numerous species

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Streptococcus
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Streptococci

• Lancefield classification system based on cell
  wall Ag 14 groups (A,B,C,.)
• Another classification system is based on
  hemolysis reactions
• b-hemolysis A,B,C,G some D strains
• a hemolysis S. pneumoniae others
  collectively called viridans

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Human streptococcal pathogens

• S. pyogenes
• S. agalactiae
• viridans streptococci
• S. pneumoniae
• Enterococcus faecalis

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b-hemolytic S. pyogenes

• Group A
• Most serious streptococcal pathogen
• Strict parasiteInhabits throat, nasopharynx,
  occasionally skin
• Produces C-carbohydrates, M-protein (fimbrae),
  streptokinase, hyaluronidase, DNase, hemolysins
  (streptolysin O (SLO), streptolysin S (SLS)),
  pyogenic (erythrogenic) toxin

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S. pyogenes

• Humans only reservoir
• Transmission contact, droplets, food, fomites
• Skin infections pyoderma, impetigo, erysipelas
• Systemic infections strep throat, pharyngitis,
  scarlet fever
• Sequelae -rheumatic fever, glomerulonephritis

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Pharyngitis and Tonsilitis Strep Throat
Note white pus patches on tonsils
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Toxic sequelae to Strep throat
http//www.cnn.com/video//video/health/2008/10/22
/tessman.strep.throat.kare
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Impetigo lesions
Streptococcal skin infections
Erysipelas
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FLESH-EATING BacteriaNecrotizing fasciitis
Streptococcus pyogenes
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Rheumatic fever is a possible sequelae to S.
pyogenes infection. Antibodies against the
bacteria may cross-react with host tissue leading
to damage of heart valves
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Group B S. agalactiae

• Regularly resides in human vagina, pharynx
  large intestine
• can be transferred to infant during delivery
  cause severe infection
• Most prevalent cause of neonatal pneumonia,
  sepsis, meningitis
• 15,000 infections 5,000 deaths in US
• Pregnant women should be screened treated
• wound and skin infections endocarditis in
  debilitated people

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Enterococcus faecalis, E. faecium

• Normal colonists of human large intestine
• Cause opportunistic urinary, wound, and skin
  infections, particularly in debilitated persons
• Enterococcus Genus related to streptococci and
  so studied together

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Viridans group

• a-hemolytic
• Large complex group
• Most numerous widespread residents of the oral
  cavity also found in nasopharynx, genital
  tract, skin
• Not very invasive butdental or surgical
  procedures facilitate entrance

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Viridans group

• Bacteremia, meningitis, abdominal infection,
  tooth abscesses
• Most serious infection subacute endocarditis
  blood-borne bacteria settle grow on heart
  lining or valves
• Persons with preexisting heart disease are at
  high risk receive prophylactic antibiotics
  before surgery or dental procedures

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Subacute bacterial endocarditis. Colonization of
heart valve surfaces lead to layers of fibrin and
bacteria called vegetations
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Viridans group

• S. mutans produces slime layers that adhere to
  teeth, basis for plaque
• involved in dental caries

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S. pneumoniae

• Causes 60-70 of all bacterial pneumonias
• arranged in pairs and short chains
• All pathogenic strains form large capsules
  major virulence factor
• Causes pneumonia otitis media
• Vaccine available for high risk people

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Gram stain of sputum from pneumonia patient
showing diplococci
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S. pneumoniae

• 5-50 of all people carry it as normal flora in
  pharynx
• Very delicate, does not survive long outside of
  its habitat
• Pneumonia occurs when cells are aspirated into
  the lungs of susceptible individuals
• Pneumococci multiply induce an overwhelming
  inflammatory response
• Treated with penicillin

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S. pneumoniae
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S. pneumoniae
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S. pneumoniae
Buldging eardrum (otitis media)
Normal eardrum