Important human pathogens of Gram-positive and Gram-negative cocci

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Important human pathogensof Gram-positive and
Gram-negative cocci

• SBM 2044
• Medical Microbiology

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Staphylococci
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Staphylococci

• Normal flora of the skin, nose, throat, and
  mucous membranes cause suppuration, abscess,
  pyogenic infections, fatal septicaemia.
• Haemolyse blood, coagulate plasma and produce a
  variety of extracellular enzymes and toxins
• At least 30 species S aureus, S epidermidis, S
  saprophyticus-UTI in young women
• Staphylococci are non-motile aerobic or
  microaerophilic and relatively resistant to
  drying and heat
• S aureus is catalase , coagulase form grey to
  golden yellow colonies, ferment mannitol.

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Staphylococci

• Staphylococci are resistant to drugs
• 1. ß-lactamase production makes them resistant to
  penicillins (inc ampicillin)
• 2. Independent ß-lactamase production in
  resistant to nafcillin. mecA gene in chromosome.
• 3. Resistant to vancomycin. Due to increased cell
  wall synthesis or alterations of cell wall, or
  the resistant vanA.
• 4. Plasmid mediated resistance to tetracyclines,
  aminoglycosides.

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Staphylococci - Antigenic Structure

• Antigenic peptidoglycans (polysaccharides)
  stimulate production of interleukin-1 and opsonic
  antibodies chemoattractant endotoxin-like and
  activate complement.
• Teichoic acids elicit anti-teichoic acid
  antibodies in endocarditis patients.
• Protein A binds to the Fc portion of IgG
  molecules, agglutinate bacteria.
• Capsules inhibit phagocytosis
• Coagulase is a clumping factor on cell wall
  surface, binds to fibrinogen and yield bacterial
  aggregation.

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Enzymes and toxins

• 1. catalase
• 2. coagulase and clumping factor clots oxalated
  or citrated plasma. Coagulase binds to
  prothrombin, polymerize fibrin.
• Hyaluronidase spreading factor staphylokinase
  fibrinolysis lipase.
• Toxic shock syndrome toxin TSST-1 is the
  superantigen binds to MHC class II.

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Regulations of vir determinants

• Protein expressions depend on the bacterial
  growth phase.
• Accessory global regulon gene, agr has 2 operons
  1st encodes RNA III that induces up-regulation of
  the secreted proteins and down-regulation of
  surface proteins.

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Pathology

• Furuncle or other localized abscess
• Accumulation in a hair follicle?tissue necrosis.
  Coagulase coagulates fibrin, resulting in fibrous
  tissue. Center of the lesion turns to
  liquefaction of the necrotic tissue?granulation
  tissue?healing.
• Suppuration via lymphatics or veins
• Spreading of toxins, eg. TSST-1.

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Clinical findings

• Localised staph infection appears as pimple
  hair follicle infection, or abscess.
• Dissemination of S. aureus?endocarditis,
  meningitis, pulmonary infection. 2 infection
  symptoms like organ dysfunction or intense focal
  suppuration
• Food poisoning due to staph enterotoxin presented
  with short incubation (1-8 hr) violent nausea,
  vomiting, diarrohea, rapid convalescence, no
  fever.
• TSS manifested by abrupt onset of high fever,
  vomiting, diarrhoea, scarlatiniform rash,
  cardiac/renal failures. Women with tampons, or
  men and children with injured wounds. Virtually
  never in bloodstream.

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• MRSA multiple resistant S aureus, because the
  organisms rapidly develop resistance to many
  antimicrobial drugs, drugs cannot act in the
  central necrotic part of a suppurative lesion.
• Emergence resistant to erythromycin group not
  used singly for treatment of chronic infection.

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The Streptococci

• Heterogenous group of bacteria, characterised by
  colony growth characteristics, haemolysis
  patterns on blood agar, antigenic composition of
  group-specific cell wall.
• Spherical cocci in chains, Gram .
• Most group A, B and C produce hyaluronic acid
  capsules.
• Cell wall contains proteins (M, T antigens),
  carbohydrates and peptidoglycans, . M-protein is
  hairl-like fimbriae.

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• Streptococci

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Streptococci

• Grow in blood or tissue fluids, 5 CO2 at 37C.
  Group D enterococci grow well at 15C and 45C.
• Classification is based on group-specific cell
  wall Ag M-protein T-antigen and nucleoproteins.
• -cell wall Ag by Lancefield grouping, by
  extraction of centrifuged culture with hot HCl,
  nitrous acid or formamide by enzymatic lysis of
  strep cells (eg. Pepsin or trypsin).chemical
  structure of cell wall rhamnose
  acetylglucosamine.
• - M-protein virulent factor, able to resist
  phagocytosis by polymorphs. There are more than
  100 serotypes of M proteins. M protein molecule
  rod-like coiled-coil structure.
• -T antigen not virulent, acid-labile and
  heat-labile.

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Toxins and Enzymes

• Streptokinase (fibrinolysin) human
  plasma?plasmin (active proteolytic enzyme that
  digests fibrin and other proteins). Rx of
  pulmonary emboli.
• Hyaluronidase splits hyaluronic acid. Acts as a
  spreading factor
• Haemolysins streptolysin O (SLO)-inactivated in
  O2, anti-SLO level increases following infection
  (ASO serum titer of 160-200 units) and
  streptolysin S (SLS) zones around colonies,
  elaborated in the presence of serum

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Streptococcus species

• S pyogenes Group A ß-haemolytic human
  pathogen only diseases such as local
  tonsillitis, necrotizing fasciitis and
  post-streptococcal glomerulonephritis.
• S agalactiae- group B ß-haemolytic NF of female
  genital tract, neonatal sepsis and meningitis.
• Enterococcus faecalis normal enteric flora ?-
  or a-haemolytic.
• S pneumoniae a-haemolytic growth is inhibited
  by optochin and colonies are bile-soluble.
• Viridans streptococci - a-haemolytic typically
  growth not inhibited by optochin and colonies are
  not bile-soluble NF of the upper resp T
  Viridans such as S mutans synthesise large
  polysaccharides (dextrans) contribute to dental
  caries.

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Gram-negative bacilli

• Pseudomonads, vibrios, Helicobacter pylori,
  pasteurella and plague

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Pseudomonads

• Gram-negative bacilli motile
• aerobic occur widely in soil, water, plants
  and animals.
• P aeruginosa is an obligate aerobe, sometimes
  producing sweet or grape-like odour forms smooth
  round colonies with fluorescent greenish
  pyoverdin in agar bluish pigment pyocyanin.
• In cystic fibrosis, P aeruginosa produces
  alginate, an exopolysaccharide that forms mucoid
  colonies and provide the matrix for biofilm.
• Rx combination of penicillinaminoglycoside, not
  just a single-therapy because the bacteria can
  rapidly develop resistance with a single drug
  therapy.

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P aeruginosa - toxins

• Pili (fimbriae) promote attachment to epith.
• Exopolysaccharide for mucoid colonies.
• Lipopolysaccharide immunotypes endotoxic.
• Exotoxin A causes tissue necrosis by inhibiting
  protein synthesis (like diphtheria toxin).

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Clinical findings

• A nosocomial pathogen.
• P aeruginosa infection gives rise to blue-green
  pus, meningitis (lumbar puncture) and UTI.
• Organism is pathogenic only when introduced into
  areas devoid of normal defenses when intravenous
  or urinary catheters are used when neutropenia
  is present as in cancer chemo.
• In most cases, symptoms and signs are nonspecific
  and are related to organ involved.
• Ecthyma gangrenosum is haemorrhagic necrosis of
  the skin, where lesions are surrounded by
  erythema with no pus.

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Burkholderia pseudomallei

• Small, motile, aerobic G-, grows in 42C.
• Grows on standard media, colonies vary from
  mucoid and smooth to rough and wrinkled from
  cream to orange in colour.
• Causes melioidosis of humans, in Southeast Asia
  and N Australia.
• -Incubation period is short (2-3 days) localised
  infection may result in acute septicaemic and may
  involve many organs. Commonly pulmonary infection
  (1 pneumonia)

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Vibrio cholerae

• Vibrios are comma-shaped aerobic rods, motile and
  possess a polar flagellum oxidase .
• V cholerae produces enterotoxin that causes
  cholera (serogroups O1 and O139).
• The culture presented as convex, smooth, opaque
  round colonies and granular grow well at 37C on
  thiosulfate-citrate-bile-sucrose agar with yellow
  colonies against the dark-green b/ground.
  Colonies are rapidly killed by acid.

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Cholera

• The connection between cholera and faecal
  bacteria in drinking water was discovered in
  London by John Snow in 1854.
• Not an invasive infection. Organisms remain in
  intestinal tract. V cholerae attach to the
  microvilli of epith cells whereby they multiply
  and liberate cholera toxin.
• Incubation period 1-4 days, presented with sudden
  onset of nausea, vomiting and profuse diarrhoea
  with abdominal cramps. Stools (rice water)
  contain mucus, epith cells and a lot of vibrios.
• Rx water and electrolyte replacement

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Helicobacter pylori

• A spiral-shaped G- multiple flagella at one pole
  and highly motile grow at 37C pH 6-7 and killed
  in acidic oxidase and catalase .
• Cause gastritis, duodenal ulcer/peptic disease
  and gastric carcinoma. Urease producer.
• Identification H pylori grow in 3-6 days when
  incubated at 37C in a microaerophilic
  environment. Colonies are translucent 1-2mm in
  diameter.

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H pylori - pathogenesis

• H pylori ingested through food, retain in gastric
  mucus (physiological pH).
• Produces protease makes mucous impermeable to
  acid urease which yields ammonia production and
  buffers the acidic pH.
• Presence of H pylori correlates with duodenal
  ulcer disease.
• Lab tests gastric biopsies, blood for serum Abs.
• Immunity Infected patients will develop IgM Abs.
  later, IgG and IgA.
• Rx Antibiotics with metronidazole,
  acid-suppressing agent for healing ulcers, proton
  pump inhibitors to inhibit organism (as well as
  urease inhibitors).

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Plague

• Plague infection of wild
  rodents, transmitted
  interspecies,
  occasionally
  from rodents to humans,
  by bites of fleas.
  Outbreak
  seen in India, Africa, North/South of
  America and S.E.Asia.
• Black death pandemic that killed 2/3 of
  Europeans (75mill people) in late 1340s.
• Caused by Yersinia pestis, G- rod exhibits
  striking bipolar staining with Wright-Giemsa
  stain non-motile.
• Antigenic structure all possess LPS, which gives
  endotoxin activity when released.

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Pathogenesis
1
Polymorphs? killed Monocytes? survive
By coagulase
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Clinical findings

• After 2-7 days of incubation, patients presented
  with high fever, painful lymphadenopathy,
  enlarged, tender nodes (buboes hence bubonic
  plague) in groin and axillae. Sometimes with
  vomiting and diarrhoea.
• Later disseminated intravascular coagulation
  leads to hypotension, altered mental status,
  renal cardiac failures.
• Diagnostic important to recognise early,
  confirms with lab.
• Specimens taken from blood, aspirates of enlarged
  lymph nodes and sputum.
• Control (1) streptomycin, alternatively
  tetracycline (2) destruction of plague-infected
  rodents, (3) vaccine (formalin-killed) for
  travellers.

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• Swollen nodes

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Pasteurella

• Gram - Non-motile coccobacilli, aerobes or
  facultative anaerobes.
• Pasteurella multocida worldwide in Resp T and
  GIT most common organisms in human wounds
  infected by bites from cats and dogs.
• History of animal bite followed within hours of
  acute onset of redness, swelling and pain.
• Rx antibiotics penicillin G.

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The Neisseriae

• Gram cocci usually in pairs, sometimes
  piliated. 2 major species gonococci and
  meningococci differentiated by the usual
  clinical presentations of the diseases they
  cause.
• Cultures after 48h on enriched media
  (Mueller-Hinton) form convex, glistering,
  elevated, mucoid colonies, 1-5mm non-haemolytic,
  transparent colonies.
• Produce oxidase. Test paper soaked with
  tetramethyl-paraphenylenediamine hydrochloride ?
  dark purple rapidly.
• Rapidly killed by drying, sunlight, moist, heat
  and many disinfectants.

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Neisseria gonorrhoeae

• Gonorrhoea "flow of seed" in ancient times it
  was thought that the pus discharge associated
  with the disease contained semen.
• Antigenic switching mechanism
  pilin ?Opa ? lipooligosaccharide (LOS)
• Rapid and occurs 1 in every 103 organisms
• Different mechanisms applied - Multiple genes
  encode for pilin,removal part of DNA for Opa.

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Neisseria gonorrhoeae

• Clinical specimens are looked for Opa protein
  colonies form transparent or opaque.
• Pathogenesis gonococci attack mucous membranes
  of GUT, eyes, rectum
• Acute suppuration?tissue invasion? chronic
  inflammation?fibrosis spread to other tissues.
• Gonococcal bacteriaemia leads to skin lesions,
  haemorrhagic papules and pustules.
• Newborn gonococcal ophthalmia neonatum.

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Neisseria gonorrhoeae

• Rx localised infection serum-sensitive (killed
  by Abs and c) bacteria whereas bacteriaemia
  serum-resistant.
• Diagnostic lab tests taken from pus secretions
  from urethra, cervix, throat, synovial fluid and
  smears from endocervix and urethral are stained.
• Disease worldwide, sexually, multiple sexual
  partners, asymptomatic infection.

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Meningococcus

• Piliated cocci meningococci pathogenic to human
  only.
• Symptoms with upper Resp T, high fever, sudden
  intense headache, vomiting, stiff neck, coma
  within hours. Meningococcemia thrombosis of
  many small blood vessels in multiple organs.
• Specimens blood, spinal fluid, nasopharyngeal
  swab all are tested with Gram staining and
  oxidase test. Further test Abs to meningococcal
  polysaccharides by latex agglutination or
  haemagglutination.

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Gram-positive Gram-negative
F anaer Aerobes Anaerobes F anaer Aerobes Anaerobes
Cocci - Bordatella Neisseria -
Bacilli Bacillus-S Clostridium -S Escherichia Klebsiella Salmonella Shigella Yersinia Vibrio Haemophilus Pasteurella Pseudomonas Bacteriodes
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• Pustules Pustules are well circumscribed
  elevations of the superficial layers of the
  epidermis. Like papules, they may be follicular
  or interfollicular in distribution. The most
  common cause is bacterial infection, where the
  pustules are filled with neutrophils, bacteria,
  debris, and possibly a few loose keratinocytes
  (acantholytic cells). It must be kept in mind
  that pustules, due to the thinness of the
  epidermis are usually transient. What is often
  observed is a transition from erythematous
  macules to papules to relatively few pustules to
  small crusts and scale.
• Papules P Papules are circumscribed, solid
  elevations of the skin, up to 1 cm in diameter.
  The elevation may be due to accumulation of
  cells, fluid, debris or metabolic deposits and
  may be follicular or interfollicular in
  orientation. Papules often begin as erythematous
  macules.