Gram Positive and Negative Bacteria Flashcards

1
Q

Describe general properties of staphylococcus

A
  • Structure: Gram positive (purple), cocci 0.5-1.5 um diameter, singly and in pairs, tetrad, short chains and irregular grape like clusters, nonmotile, non-spore forming, catalase positive, enterotoxin A and B
  • Physical Requirements: Facultative anaerobes, grow in the presence or absence of air, prefer air (except S. saccharolyticus, S. aureus subsp. anaerobius)
  • Species: 35 species and 17 subspecies
  • Clinical Significance: Commensal on human skin, also occurs in nose frequently and throat less commonly, sometimes in gut
  • Emergence of multiple antibiotic resistant strains (MRSA to superbugs)
  • Methicillin: Form of penicillin to treat staph, organisms are MRSA (resistance to front line drugs)
  • Infections: Bacteraemia, pneumonia, food poisoning, acute myocarditis, pericarditis, abaecess of muscle, urogenital tract and CNS
  • Categorisation: Weak or striking lysis of RBC, due to release of exotoxins which target RBC and WBC, in attempt to obtain nutrients (iron), cream / yellow pigment, variation in zones of lysis
  • Mannitol Salt: Selective and differential, high salt (7.5%), halo tolerant organisms, unique sugar (mannitol), ferment mannitol (yellow), cannot ferment mannitol (pink)
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2
Q

Describe properties of staphylococcus aureus

A
  • Beta haemolytic on blood plate leads to production of exotoxins, production of coagulase (free coagulase, clots), sodium chloride tolerance (7.5%), mannitol fermentation on MSA plate
  • Presence of clumping factor (cell-bound coagulase), protection mechanism against immune recognition, covers itself with RBC and hence not recognised as foreign,
  • Hyaluronidase production (positive decapsulation test with S.equi
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3
Q

Describe properties of staphylococcus epidermis

A
  • Forms white non haemolytic colonies on blood agar, facultative anaerobe, part of the normal human skin flora (not usually pathogenic), cannot lyse RBC, rely on nutrients in agar
  • Opportunisticinfections, generally hospital-acquired (immunocompromised patients)
  • Catalase-positive, coagulase negative (no clumping / clotting) and oxidase-negative
  • Concern for people with catheters / implants, known to form biofilms that grow on these devices.
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4
Q

Describe general properties of streptococcus

A
  • Structure: Gram positive cocci, occur singly, pairs and short / long chains (characteristic), nonmotile, non-spore forming, catalase negative, some produce haemolysins (lyse RBC, ranges in ZoI)
  • Classification: Alpha (green, capsule / quellung test, bile solubility test, ), beta (clear, group A / B / C or bacitracin / antibiotic susceptibility test) or gamma haemolytic
  • Location: Transient colonisers of skin, resident colonisers of mucous membranes, normal flora in alimentary, respiratory and genital tract
  • Physical Requirements: Facultative anaerobes
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5
Q

What is lancefield typing and the CAMP test

A
  • Lancefield Typing: A serologic classification of bacteria / haemolytic streptococci into groups based on specific carbohydrate antigen, groups A-O (group A = pathogenic to man), visual, simple, quick
  • Antigenic cell wall carbohydrates, use of strain specific antibodies that differentiate cell wall CHOs
  • CAMP Test: Identify group B β-haemolytic streptococci based on their formation of a substance that enlarges area of haemolysis formed by the β-haemolysin, beta-haemolytic streptococci often cause disease
  • Production of CAMP factor reacts and causing increased haemolysis (arrow shaped)
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6
Q

Describe properties of staphylococcus group A / B

A

Group A:
- Streptococci pyogenes, found in humans and primates
- Beta haemolytic, large colony forming unit, gray-whitish, glisten, lancefield group A antigen, numerous virulence factors allow S pyogenes to cause a wide array of serious infections
- Gram positive encapsulated diplococcus, prevented by conjugated vaccine, cause of pneumonia and otitis media (most life threatening in children and elderly)
- Positive PVR test is useful for preliminary identification of isolated strains (with negative catalase test)
- Identification can be confirmed by the latex agglutination test (serotyping test)
Group B:
- Colony morphology, gram stain, catalase reaction, lancefield, CAMP test, hippurate hydrolysis

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7
Q

Describe 3 streptococcal skin infections

A
  • Erysipelas: S. pyogenes infects the dermal layer of the skin, causes local tissue destruction and sepsis
  • Necrotising Fasciitis: “Flesh-eating” disease, exotoxin A produced by S. pyogenes acts as a super antigen
  • Streptococcal toxic shock syndrome: Similar to staphylococcal TSS
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8
Q

Describe general properties of enterococcus

A
  • Structure: Occurs singly, in pairs and in short chains, catalase negative, group D antigen positive
  • Physical Requirements: Facultative anaerobes, optimum growth at 35ºC, growth in broth of 6.5% NaCl
  • Species: 19 species (common in humans are E faecalis and E faecium), superbug (antibiotic resistance)
  • Clinical Significance: 10% of all UTI’s, 16% of nosocomial UTI’s, intrabdominal or pelvic wounds (poly microbic), increasing rate in wound infection, leading cause of nosocomial bacteraemia
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9
Q

Describe properties of enterococcus faecalis

A
  • Gram-positive coccus, commensal bacterium inhabits the GI tracts of humans and other animals, ability to grow in the presence of high concentrations of bile salts and sodium chloride
  • Can cause life-threatening infections in humans, especially in the nosocomial (hospital) environment, where the naturally high levels of antibiotic resistance found in E. faecalis contribute to its pathogenicity
  • Severe virulence factors, colonies show beta haemolysis on blood agar plates, a plasmid-encoded haemolysin (cytolysin)
  • High-level gentamicin resistance is associated with a five-fold increase in risk of death in human bacteremia patients, resistant to vancomycin (last resort antibiotic)
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10
Q

List a number of gram positive aerobic and anaerobic bacteria

A
  • Aerobic: Bacilli - listeria, erysipelothrix, nocardia, mycobacterium
  • Anaerobic: Bacilli - clostridium, actinomyces, porphyromonas, lactobacillus, propionibacterium
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11
Q

Describe general properties of listeria

A
  • Structure: Non branching short gram positive rods (0.5-2 um by 0.4-0.5 um), occurs singly or in short chains, colonies 1-2mm, smooth, catalase positive, coccobacilli
  • Physical Requirements: Facultatively anaerobic, active growth at 4ºC, motile at 28ºC
  • Species: 7 species, including L. monocytogenes (pathogenic to humans) and L. ivanovii (frequent cause of abortions in animals)
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12
Q

Describe properties of listeria monocytogenes

A
  • Commonly found in soil, stream water, sewage, plants, and food, gram-positive non-sporing rod-shaped, pleomorphic (coccoid appearance), increased virulence
  • Reproduces in phagocytes, reorganises actin filaments which allows ‘jumping’ to other cells, adapted itself to human cells
  • Able to grow in temperatures ranging from 4°C (fridge) to 37°C (body’s internal temperature)
  • Listeriosis: A rare but potentially lethal food-borne infection, virulence is attributed to listeria’s ability to spread to the nervous system (meningitis), infects pregnant women via placenta (stillbirth),
  • Usually food borne and asymptomatic, meningitis more common in the immunocompromised, can invade the bloodstream (sepsis)
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13
Q

Describe general properties of bacillus anthracis

A
  • Structure: Gram positive rod (cause of anthrax), forms long chains, forms endospores, ‘biological weapon’ (spores, long-lasting, protection from environment)
  • Physical Requirements: Aerobe, found in soils
  • Clinical Significance: Severe and lethal respiratory infection (inhale spores), lethal infection of pneumonia
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14
Q

Describe general properties of clostridium

A
  • Structure: Gram positive rod shaped cells, form endospores that distend the shape of the cell, endospores are resistant to heat and chemicals (form in the absence of nutrients), tennis racket shape
  • Physical Requirements: Obligate anaerobes
  • Pathogen: C. tetani (tetanus), C. botulinum (botulism), C. perfringens (gas gangrene)
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15
Q

What is tetanus

A
  • Production of neurotoxin tetanospasmin, acts in CNS, binds to nerves that control contraction of skeletal muscles, blocks inhibiting pathway to prevent random contractions
  • Causing convulsive symptoms
    Infants are vaccinated against tetanus toxoid
  • Toxoid is a modified protein that retains immunogenicity but loses toxicity, denatured toxin (safe but generate innate immunity), ubiquitous
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16
Q

What is gas gangrene

A
  • Food poisoning, meat or meat stews that have come into contact with intestinal contents during slaughter, endospores remain dormant but can survive heating
  • Generation time less than 20 minutes
  • Symptoms appear 8-12 hours after ingestion, bacteria grows in intestinal tract, produces exotoxins
  • Travel from surface of skin to embedding in muscles (anaerobic environment), use of virulence factors
17
Q

Describe general properties of lactobacillus

A
  • Structure: Rod shaped cells, industrially important bacterial spp, L acidophilus naturally occurs in GI tract
  • Physical Requirements: Obligate anaerobe (cells are aerotolerant, grow poorly in oxygen), grows readily at low pH (<5)
18
Q

Describe general properties of propionibacterium

A
  • Function: Produce lactic acid, propionic acid and acetic acid from glucose
  • Physical Requirements: Slow growing anaerobic bacteria
  • Species: P. freudenreichii (important infermentation of swiss cheese) and P. acnes (commonly found on skin, primary cause of acne, grows well at low pH ~4)
19
Q

Describe general properties of nocardia

A
  • Structure: Extensive branched hyphae that fragment into rod-shaped to coccoid nonmotile elements, early cultures have smooth appearance, more commonly chalky white reflecting aerial hyphae
  • Characteristic gram stain, bacteria not fungi
  • Species: 11 described species, most infections caused by N asteroides complex and N brasiliens
20
Q

List a number of examples where bacterial toxins are used safely

A
  • C botulimum used in botox in the beauty industry
  • V cholera, cholera toxin used in mucosal vaccines
  • S aureus, both SEA and SEB mitogens for polyclonal stimulation of T cells, protein A (protein purification)
21
Q

What are opportunistic diseases

A
  • Enterobacteriaceae: Members are a frequent cause of gastrointestinal and UTI infections in humans as well as septicemia, pneumonia and meningitis
  • Species Include: Citrobacter, Enterobacter, Escherichia, Hafnia, Morganella, Providencia, Serratia
22
Q

Describe general properties of enterobacteriaceae

A
  • Gastrointestinal Diseases: Escherichia coli, salmonella, shigella, yersinia entercoliticia
  • Structure: Gram negative (pink) rod shaped cells, do not form spores, motile by peritrichous flagella or nonmotile, catalase positive, oxidase negative
  • Media Growth: Grow well on macconkey agar, grow on peptone or meat extract media without addition of NaCl or other supplements
  • Physical Requirements: Facultative anaerobic, can grow both aerobically and anaerobically, active biochemically (ferment glucose and other sugars)
  • Faeces: E coli (lactose positive, peritrichous flagella, not usually identified, lactose positive sp. common, healthy intestine) and shigella, salmonella, and yersinia (lactose negative, identified
23
Q

What are serotypes

A
  • Serotype: A serologically distinguishable strain of a microorganism, classification of a microbe based on their antigenic structure or their ability to react with specific antibodies
  • Antigens: K (capsular), H (flagellar, motility) and O (lipopolysaccharide, gram negative cell wall, carbohydrate modifications on N terminus)
24
Q

Describe general properties of shigella and shigellosis

A
  • Structure: Gram negative rod shaped cells, non-spore forming, non motile, lactose negative,
  • Physical Requirements: Facultative aerobic
  • Serogroups: S. dysenteriae (group A), S. flexneri (group B), S. boydi (group C) and S. sonnei (group D)
  • Shiga Toxin: Enterotoxin, cytotoxic, inhibits protein synthesis
  • Enter epithelial cell and multiply, shigella invade neighbouring epithelial cells avoiding immune defences via breaking of tight junctions, mucosal abscesses form as cells are killed
  • Symptoms of Shigellosis: Bacillary dysentery, bloody faeces, intestinal pain / cramping, puss (increased mucous secretion / death of cells), within 2-3 days causes epithelial cell damage, infects gut in particular
  • Transmission: Man only ‘reservoir’, mostly young children (faecal to oral contact, children to adults), transmitted by adult food handlers (unwashed hands)
25
Q

Describe general properties of salmonella

A
  • Structure: Gram negative rod shaped cells, non-spore forming, motile (peritrichous flagella)
  • Physical Requirements: Facultative aerobic
  • Species: Genetically single species is S enterica, huge diversity
  • Disease Category: S. enteritidis (many serotypes), S. cholerae-suis, S. typhi
  • Infection of Cells: Salmonella enters epithelial cell, multiplies within vesicle inside the cell, multiples in mucosal cells and there is an inflammatory response results in diarrhoea, occasionally bacteria cross epithelial cell membrane and enter lymphatic system and blood stream
26
Q

Describe general properties of yersinia (plague) bacteria

A
  • Structure: Gram negative, variable rod shaped or coccoibacillus (pleomorphic), non-spore forming, 0.5-0.8 um in width and 1-3 um in length, motile (except Y pestis) at 22-30°C (non-motile at 37°C)
  • Physical Requirements: Facultative anaerobes, however grow aerobically and anaerobically, optimum growth at 25-28°C (lower than internal body temp)
27
Q

Describe general properties of vibrionaceae

A
  • Structure: Gram negative, curved or straight rods, 0.5-0.8 um in diameter and 1.2-2.4 um in length, motile, single sheathed polar flagellum
  • Physical Requirements: Facultative anaerobes
  • Species: More than 35 species, approximately 1/3 are pathogenic for humans
28
Q

Describe general properties of cholera

A
  • Structure: Slightly curved (banana), gram negative rod with single polar flagellum (vibrio),
  • Physical Requirements: Associated with salty waters,
  • Cholera Toxin: Exotoxin that causes host cells to secrete electrolytes (chlorides, bicarbonates and water) causing ‘rich water’ stools and loss of up to 12-20 litres of fluid per day
  • Causes shock, collapse, organ failure and death
  • Treatment includes IV fluid replacement (salt, sugar and water)
  • Tetracycline is used for treatment, chemotherapy is not a effective as replacing fluid loss and electrolytes
  • Mortality rate of cholera without treatment = 50%, with rehydration ± antibiotics < 1%
  • Infection: increases when sanitation and sewage disposal systems are compromised, ultimate solution is proper sanitation, water storage and hand washing and stockpiling vaccines
29
Q

Describe general properties of pseudomonas

A
  • Structure: Gram negative straight or slightly curved rods, non-spore forming, mobile (presence of one or more polar flagella), oxidase positive
  • Physical Requirements: Strictly aerobic, optimal growth between 30-37°C
  • Problematic: In hospital environment (disinfectants, soaps, ointments), rate of colonisation increases with patients who have been hospitalised for extended periods / received broad spectrum antimicrobial therapy
  • Resistant to soaps, growth on soap bars and sinks
30
Q

Describe general properties of haemophilus

A
  • Structure: Gram negative bacilli, oxidase positive, pleomorphic, fastidious organism
  • Physical Requirements: Optimum growth at 33-37°C in 5-7% CO2, requires precursor of haeme to grow
  • Growth Medium: Requires complex medium with performed growth factors that are present in blood X factor (haemin) and V factor NAD, NADP), grows on chocolate agar
31
Q

Describe general properties of campylobacter

A
  • Structure: Gram negative, curled, motile rod
  • Physical Requirements: Grows best in low oxygen (<5%)
  • Infection: Produce silica acid on cell surface to avoid hosts immune response, causes more diseases per year than shigella and salmonella, exposure through contaminated water, milk or undercooked meat
  • C jejuni: Causes campylobacteriosis and gastroenteritis, produces gut mucosa destroying toxins, fever, cramping, abdominal pain, diarrhoea, dysentery, 1 in 1000 cases lead to gullian-barre syndrome
32
Q

Describe general properties of helicobacter

A
  • Structure: Gram negative, spiral shaped motile rod, produces urease enzyme that helps it survive in acidic pH conditions through cloud of ammonia (stomach and duodenum)
  • Infection: Avoids host immune system by living in acidic environment of stomach, produces urease, diagnostic test requires a biopsy, culture and urea breath test
  • Species: H pylori is an important cause of stomach ulcers
33
Q

Describe general properties of bacteroids

A
  • Structure: Gram negative anaerobic rod shaped bacteria, polymicrobial nature
  • Beneficial: Colonises the human intestine, establishes symbiotic relationship with host, assist in breaking down food and producing valuable nutrients for host
  • Anaerobic Respiration: By products include acetic acid, isovaleric acid and succinic acid
  • Example: Polysaccharides from plant fibres, such as cellulose, xylan, arabinogalactan, and pectin, and vegetable starches such as amylose and amylopectin, are prevalent in the colon
  • Infection: If they escape the gut problems arise, huge problem as source of infection during gastrointestinal surgeries, pathogenistic
  • Antibiotic Resistance: Bacteroides fragilis, which occurs with the most in clinical infections, B. distasonis, B. ovalus, B. thetaiotaomicron (ability to survive as humans), and B. vulgatus are almost universally resistant to penicillins
  • Diagnosis: Complicated due to the slow growth of bacteroids, hence difficult to treat
34
Q

List gram positive bacteria

A
  • Staphylococcus
  • Streptococcus
  • Enterococcus
  • Listeria
  • Bacillus anthracis
  • Clostridium
  • Lactobacillus
  • Propionibacterium
  • Nocardia
35
Q

List gram negative bacteria

A
  • Enterobacteriaceae
  • Shigella
  • Salmonella
  • Yersinia
  • Vibrionaceae
  • Cholera
  • Pseudomonas
  • Haemophilus
  • Campylobacter
  • Helicobacter
  • Bacteroids
36
Q

What is Klebsiella pneumoniae

A
  • Short gram negative, capsule, pink (weak lactose fermenter) otherwise healthy people
  • Respiratory diseases, prominent capsule, urease (degrades urea) is a virulence factor, alkaline urine