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Medical Microbiology II > Week 6 > Flashcards

Week 6 Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

GENERAL CHARACTERISTICS Bacillus

A
  • Gram-positive or gram-variable, straight, round- or square-ended
    rods, occur singly or in chains (range from few to many cells in
    length)
  • motile via peritrichous flagella with exceptions of Bacillus anthracisand Bacillus mycoides
  • produce endospores, 1 per mother cell (sporangium) in presence of oxygen
  • depending on species endospores may be: −cylindrical, oval, round or kidney-shaped
    −centrally, subterminally or terminally placed
    −characteristically swelling or not swelling sporangium
  • aerobic or facultatively anaerobic
  • diversity of metabolic types and nutritional requirements: − psychrophiles, mesophiles (majority), thermophiles −alkalophilic, neutrophilic, acidophilic
  • some species are producers of antibiotics
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2
Q

ENDOSPORES Bacillus

A
  • spore - dormant structure capable of surviving for prolonged
    periods
  • endowed with capacity to re-establish vegetative stage of growth under appropriate environmental conditions
  • at some point in vegetative cell cycle of spore-forming organisms growth arrested
  • cell undergoes progressive changes that results in formation of
    endospore
  • endospore formation occurs during stationary phase of growth after depletion of certain nutrients in culture medium or environment
  • single spore produced within vegetative cell
  • differs from parent cell in its:
    − morphology
    −composition
    −increased resistance to adverse environments −absence of detectable metabolic activity
  • resistance to radiation, drying, toxic chemicals depends on cystinerich, keratin-like spore coat proteins
  • thermal resistance attributed to very low water content of
    protoplast, which renders proteins and nucleic acids more resistant to denaturation
  • process of spore germination consists of 3 sequential phases:
    −activation stage - conditions spore to germinate in suitable
    environment
    − germination stage - characteristic properties of dormant
    spore lost
    − outgrowth stage - spore converted into new vegetative cell
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3
Q

SPORULATION Bacillus

A
  1. Spore septum begins to isolate newly replicated DNA and a small portion of cytoplasm
  2. Plasma membrane starts to surround DNA, cytoplasm, and membrane isolated in step 1
  3. Spore septum surrounds isolated portion, forming forespores
  4. peptidoglycan layer forms between membranes
  5. Spore coat forms
  6. endospore is freed from cell
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4
Q

NATURAL HABITAT Bacillus

A
  • widely distributed in nature; saprophytes in soil, dust, water, on materials of plant and animal origins
  • part of normal intestinal microbiota of humans and animals
  • majority of Bacillus spp. have little or no pathogenic potential,
    rarely associated with disease
  • some species (e.g., Bacillus anthracis, Bacillus cereus, Bacillus subtilis) may cause human and animal infections
  • world-wide in distribution
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5
Q

VIRULENCE FACTORS - BACILLUS ANTHRACIS

A
  • capsular polypeptide
    − D-glutamic acid
    −interferes with phagocytosis
  • anthrax toxin
    −complex exotoxin consisting of 3 protein components:
  • protective antigen - PA
  • lethal factor - LF
  • oedema factor - EF
    − none have any toxic activities by themselves, acting
    synergistically produce systemic effects of anthrax
    −inhibit phagocytosis and intracellular signal transduction
    resulting in inactivation of transcriptional factors in cell
    nucleus
  • production of both virulence factors enhanced by CO2
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6
Q

CLINICAL SIGNIFICANCE - BACILLUS ANTHRACIS

A
  • causative agent of anthrax
  • exploited and developed as agent of biological warfare by
    several countries
  • biological agent associated with bioterrorism
  • anthrax primarily disease of herbivorous animals
  • humans accidentally encounter disease by direct contact with
    certain animal products (hair, wool, bones)

Anthrax in animals
* severe, usually takes form of septicaemia
* infected animal remains free of symptoms until few hours before death
* mortality rate about 80%

Anthrax in humans
* humans can become infected via one of 3 possible routes:
− Cutaneous route
−Inhalation
−Ingestion

Cutaneous anthrax (malignant pustule)
* most common form (95% to 99% of all cases world-wide)
* organisms gain access through small abrasions or cuts, multiply locally
* incubation period 2 to 3 days
* at site of inoculation small, pruritic, non-painful papule, develops into haemorrhagic vesicle
* vesicle ruptures, leading to slow healing painless ulcer covered with black eschar surrounded by oedema
* may spread to lymphatics, may be regional adenopathy
* 20% mortality rate in untreated cases

Pulmonary anthrax (wool-sorter’s disease)
* acquired by inhalation of spores
* symptoms those of respiratory infection, fever, malaise, myalgia, unproductive cough
* rapidly progresses to very severe infection with marked respiratory distress, cyanosis, haemorrhagic necrosis of mediastinum* 80% to 90% mortality rate in untreated cases

Oropharyngeal anthrax and Gastrointestinal anthrax
* acquired by ingestion of organism
* infections associated with cervical and oral pain and oedema,
and nausea, vomiting and diarrhoea, respectively
* occasionally there is loss of blood (either through
haematemesis or in stools)
* like pulmonary form, there is a high mortality rate if untreated* in all forms, there may be invasion of bloodstream and
localisation in meninges
* anthrax infection in humans provides permanent immunity

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7
Q

CLINICAL SIGNIFICANCE - BACILLUS CEREUS

A

Emetic or vomiting syndrome
* short incubation period of 1 to 6 hours
* characterised by severe nausea, vomiting, abdominal cramping* frequently mistaken for staphylococcal food poisoning
* patients recover after 10 to 24 hours after onset
* associated with fried Oriental rice dishes, cream and milk products, pastas, reconstituted infant formula

Diarrhoeal syndrome
* longer incubation period of 8 to 16 hours
* characterised by nausea, abdominal cramping, profuse watery diarrhoea, tenesmus
* commonly confused with clostridial food poisoning
* patients recover after 12 to 36 hours after onset
* associated with meat, vegetable dishes, cakes, sauces, dairy products

  • in patients with underlying diseases or immunosupressed patients causes:
    − bacteraemia
    − meningitis
    −endocarditis
    − necrotising pneumonia
    − peritonitis
    − osteomyelitis
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8
Q

COLLECTION, TRANSPORT, AND STORAGE OF SPECIMENS Bacillus

A

Anthrax
* specimens in cutaneous infections:
−swab samples of serous fluid of vesicles
− material beneath edge of black eschar
−3 sets of blood cultures
* specimens in pulmonary infections:
−sputum sample
−3 sets of blood cultures
* specimens in gastrointestinal infections:
− gastric aspirates
−faeces
−food
−3 sets of blood cultures

Bacillus cereus food poisoning
* isolation and identification of organism from stools insufficient
evidence as bacterium may be present in stools of healthy persons
* epidemiologically implicated food should be collected

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9
Q

CULTURE MEDIA Bacillus

A

Selective media
* Polymyxin-Lysozyme-EDTA-Thallous acetate (PLET) agar medium− best selective medium for Bacillus anthracis
* Phenylethyl alcohol (PEA) blood agar medium

Non-selective media
* 5% sheep blood agar medium
* Nutrient agar medium

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10
Q

INCUBATION CONDITIONS Bacillus

A
  • 35oC to 37oC
  • for 18 to 24 hours
  • in ambient air
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11
Q

ISOLATION PROCEDURES Bacillus

A

Bacillus anthracis
* colonies non-haemolytic, white to grey, large (4mm to 5mm in
diameter), with ground-glass appearance
* usually rough, flat with many comma-shaped outgrowths of long filamentous chains of bacilli (“Medusa head” appearance)
* when lifted with inoculating needle edge of colony stands up
like egg white - “tenacity”
* poor filiform growth followed by outgrowth of delicate lateral
extensions

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12
Q

DIRECT EXAMINATION Bacillus

A
  • Gram-stained smears
    − of infected tissue or fluid
  • Fluorescent antibody stain
    −for encapsulated strains of Bacillus anthracis
  • M’Fadyean-stained smears − of infected tissue, blood, fluid
    − polychrome methylene blue stain used to reveal capsules
  • PCR assay
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13
Q

IDENTIFICATION Bacillus

A
  • Gram stain and Spore stain of colony
  • Catalase production (positive)
  • Motility Test (Motile)
  • Lecithinase Test (positive)
  • Colony morphology
  • MALDI-TOF MS
  • Growth on PEA
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14
Q

SEROLOGIC TESTS Bacillus anthracis

A

Bacillus anthracis
* Indirect Haemagglutination (IHA) Test
* Enzyme-Linked Immunosorbent Assay (ELISA)

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15
Q

ANTIBIOTIC SUSCEPTIBILITIES Bacillus

A

Bacillus anthracis
* drug of choice is penicillin
* alternative drugs for penicillin-sensitive patients are ciprofloxacin, gentamicin, erythromycin

Bacillus cereus
* because of β-lactamase production, it is resistant to penicillin,
ampicillin, cephalosporins
* drug of choice is clindamycin

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16
Q

IMMUNISATION - BACILLUS ANTHRACIS

A
  • active immunisation only known method of preventing anthrax in
    herbivorous animals −living spore vaccine − derived from non-encapsulated strain of Bacillus anthracis(Sterne strain)
  • for protection of humans in high-risk work situations
    − non-living vaccine
    −consisting of aluminum hydroxide-adsorbed supernatant material from fermentor cultures of toxigenic but non-encapsulated strain of Bacillus anthracis
17
Q

GENERAL CHARACTERISTICS Listeria

A
  • Gram-positive coccobacilli, occur singly, in short chains or in palisade arrangement; may be filamentous in older cultures* motile at room temperature by means of 1 to 5 peritrichous flagella, do not form spores
  • facultatively anaerobic, facultative intracellular organisms
  • oxidase negative, catalase and aesculin positive
  • Voges-Proskauer and methyl red positive
  • urease, indole, and H2S negative
18
Q

NATURAL HABITAT Listeria

A
  • widely distributed in environment, isolated from soil, decaying
    vegetable matter, silage, sewage, water, animal feed, meats, milk* part of normal microbiota of many mammals and birds
  • 1% to 15% of healthy humans are asymptomatic intestinal carriers
19
Q

VIRULENCE FACTORS - SOLUBLE PRODUCTS Listeria

A
  • Actin-assembly-inducing protein (ActA)
  • Phospholipases C (PLCs)
  • Zinc metalloproteinase (Mpl)
  • Listeriolysin O (LLO)
20
Q

VIRULENCE FACTORS - SURFACE
COMPONENTS Listeria

A
  • Internalin A and internalin B (InlA and InlB)
  • Endotoxin-like material
21
Q

CELL CYCLE OF LISTERIAMONOCYTOGENES

A
  • Listeria monocytogenes - facultative intracellular organism* invades and grows in variety of mammalian cells: macrophages, epithelial cells, fibroblasts
  • subsequent to internalisation, organism escapes from host vacuole* bacterium undergoes rapid division in cytoplasm of host cell
  • organism becomes encapsulated by short, host actin filaments* these filaments reorganise into long tail extending from only one end of bacterium
  • tail mediates movement of organism through cytoplasm to surface of host cell
  • at periphery, formed protrusions penetrate neighbouring cells
22
Q

CLINICAL SIGNIFICANCE Listeria

A
  • Listeria monocytogenes causes: spontaneous abortions in animals, basilar meningitis - “circling disease” in sheep
  • causative agent of human listeriosis
  • occur as sporadic cases or epidemics
  • contaminated foods primary vehicles of transmission (raw vegetables, dairy products, meats)
  • organism survives and multiplies:
    − at refrigerator temperature
    − in wide range of pHs
  • human-to-human transmission - infection of foetus
    transplacentally
  • exhibits striking tropism for: foetus, placenta, CNS
23
Q

ADULT INFECTIONS Listeria

A
  • meningitis
    − most common form of listeriosis (55% of cases)
  • septicaemia
    − affects patients under 50 years of age
    − 25% of cases
  • encephalitis
    − 6% of cases
  • focal infections
    − occur after episode of bacteraemia
24
Q

NEONATAL INFECTIONS Listeria

A

Early type - granulomatosis infantiseptica
* results from infection in utero
* appears within 2 days of birth
* symptoms of septicaemia followed by foetal distress, pneumonia, diarrhoea, seizures, maculopapular skin lesions
* very high mortality rate (54% to 90%)

Late type - meningitis
* infection acquired either during or after birth rather than in utero* appears after 5th day of life

25
Q

COLLECTION, TRANSPORT, AND STORAGE OF SPECIMENS Listeria

A
  • clinical specimens: CSF, blood, amniotic fluid, placenta, foetal tissue, genital tract specimen, stool
26
Q

CULTURE MEDIA Listeria

A
  • 2 types of enrichment:
    − cold enrichment technique
    − enrichment in primary selective enrichment broth

Selective media
* Columbia base Colistin-Nalidixic Acid (CNA) agar medium* PALCAM agar medium
* Lithium chloride-Phenylethanol-Moxalactam (LPM) agar mediumNon-selective media
* Tryptic soy agar containing 5% sheep, horse or rabbit blood* Conventional blood culture broth

27
Q

INCUBATION CONDITIONS Listeria

A
  • 30oC to 37oC
  • for 24 hours to 48 hours
  • in ambient air or under microaerobic conditions
28
Q

IDENTIFICATION Listeria

A

Genus identification
* Colony morphology
* Gram stain of colony
* Growth at 4oC
* Catalase Test
* Aesculin hydrolysis Test

Species identification
* β-haemolysis
* CAMP (Christie, Atkinson, Munch, Peterson) Test
* MALDI-TOF MS
* Serotyping (13 serotypes of L. monocytogenes)

29
Q

ANTIBIOTIC SUSCEPTIBILITIES - LISTERIA MONOCYTOGENES

A
  • susceptible to: penicillin, ampicillin, erythromycin,
    gentamicin, tetracycline, trimethoprim-sulfamethoxazole, chloramphenicol

Medical Microbiology II (10 decks)

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