Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

microbiology > gram-negative bacteria > Flashcards

gram-negative bacteria Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards
1
Q

what are the main gram-negative bacteria which we look at in clinic?

A
  • rods
  • cocci
  • spirochaetes
  • obligate intracellular bacteria
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are the gram-negative rod family group names?

A

anearobic:
- bacteroridies

aerobic:
- choliform / enterobacteria
- pseudomonas
- vibro
- haemophilus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are the gram negative cocci groups?

A

anaerobic:
- veilloella

aerobic:
- neisseria

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are the gram-negative spirochates groups?

A
  • leptospira
  • treponema
  • borrelia
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what are the gram-negative obligate intracellular bacteria that we consider?

A
  • rickettsia
  • chlamydia
  • coxiella
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

outline the characteristics of coliforms / enterobacteria

A

Enterobacteriaceae or Enterobacteria

Rod-shaped
Motile (most)
Peritrichous flagella

Facultatively anaerobic

Colonise the intestinal tract
Advantageously or disadvantageously

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what tests do we use to distinguish what species the gram-negative bacillus bacteria is?

A

assess phenotypes of different agar:

MacConkey-lactose agar
- lactose fementers turn red eg e.coli, non-lactose fermenters stay yellow eg salmonella
- it turns red because the acid produced by fermentation turns natural red dye in plate red

xylose lysine deoxycholate
- lactose fermenters turn phenol red in media yellow
- isolated salmonella and shingella
- shingella remaind red
- salmonella cannot ferment lactose but redue thiosulphate to produce hydrogen sulphide so appears black

further discrimination between species by serology based on virulence factors

antigen variation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Escherichia coli

A

Commensals
Most abundant facultative anaerobe (107-108/g faeces)

Pathogenicity determined by acquisition of ‘pathogenicity islands’
Blocs of genes causing which cause varying disease
Several biotypes (pathovars) with distinct strategies

Principal infections caused by pathogenic E. coli
Wound infections (surgical)
UTIs
Cystitis
75-80% of female UTIs –faecal source or sexual activity
Catheterisation – most common type of nosocomial infection

Gastroenteritis
Travellers’ diarrhoea
Bacteraemia (potentially sepsis syndrome)
Meningitis (infants) – rare in UK

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Shigella

A

Closely related to Escherichia - + virulence plasmid
Four species
S. dysenteriae S. flexneri S. boydii S. sonnei

Acid-tolerant (low infective dose, ~102)
Person-to-person, or contaminated water & food – low infective dose

Shigellosis: severe bloody diarrhoea (bacillary dysentery)
S. dysenteriae most severe form S. sonnei most prevalent in developed world

Endemic in developing countries where sanitation is poor – often children

Symptoms and pathology:
Frequent stools (>30/day) - small volume, pus and blood, prostrating cramps, fever
Self-limiting (in adults)

Shiga toxin inhibits protein synthesis  cell death
Systemic absorption of Shiga toxin
Targets kidneys  haemolytic uraemic syndrome  kidney failure

Also occurs in Shiga-toxin producing EHEC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Salmonella

A

Two species:
S. enterica - responsible for salmonellosis
>2,500 serovars
Originally thought to be distinct species, such as ‘Salmonella typhi’ but now recognised as serovars of S. enterica
i.e. Salmonella typhi is now Salmonella enterica serovar Typhi.

S. bongori - rare (contact with reptiles)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Infections caused by S. enterica (salmonella)

A

Ingestion of contaminated food/water - high I.D. (~106) (‘faecal-oral route’)
Three forms of salmonellosis caused by S. enterica:
1. Gastroenteritis/enterocolitis (serovars Enteritidis and Typhimurium)
Frequent cause of food poisoning (milk, poultry meat & eggs)
Second highest no. of food-related hospitalisations/deaths (UK)
6-36 hr incubation period, resolves (~7 days)
Localised infection, inflammation and necrosis of gut mucosa
Only occasionally systemic
Does not produce toxins

  1. Enteric fever - typhoid/paratyphoid fever (serovars Typhi and Paratyphi)
    Poor quality drinking water/poor sanitation
    Systemic disease – dissemination of macrophages
    ~20 million cases, ~200,000 deaths/year (globally)
    Produces typhoid toxin (DNase activity = a genotoxin)
  2. Bacteraemia (serovars Cholerasuis and Dublin)
    Uncommon
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Other pathogenic Enterobacteria

A

Proteus mirabilis
Differentiate into an hyperflagellated form  surface motility (‘swarming’)
Causes catheter-associated UTIs (~30% cases)  pyelonephritis
Produces urease (causes urine pH )  calcium phosphate precipitation  formation of bladder/kidney stones, catheter blockage

Klebsiella pneumoniae
Environmental
Opportunistic, nosocomial infections (neonates, elderly, compromised)
Colonisation of gastrointestinal tract (normal) and oropharynx (less frequently) is benign but can lead to:
UTI
Pneumonia (aspiration from oropharynx)
Surgical wound infections
Bacteraemia  sepsis (high mortality)

Multi-drug resistant (resistant to carbapenems)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

name the species of gram-negative - rod - aerobic - choliform.

A
  • salmonella
  • shigella
  • E.coli
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

name the species of gram-negative - rod - aerobic - pseudomonads.

A

Pseudomonas aeruginosa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Pseudomonas aeruginosa

A

Ubiquitous, free-living
Motile (single polar flagellum)
Rod-shaped

Opportunistic (serious cause of nosocomial infections)

Resistant to multiple antibiotics (& disinfectants) - very difficult to treat

Acute infections (due to multiple toxins):
Localised
Burn/surgical wounds

Systemic (bacteraemic  sepsis)
neutropenic patients (leukaemia, chemotherapy, AIDS)

ICU patients (ventilator acquired pneumonia)
leading cause of nosocomial pneumonia
Chronic infections:
Cystic fibrosis (CF) patients

Common denominator to all infections - compromised host defences

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

P. aeruginosa and cystic fibrosis

A

CF, most common inherited lethal disorder among Caucasians

Defective CFTR  thick mucus produced in lungs.

Lungs prone to microbial infection.

P. aeruginosa most problematic.
P. aeruginosa ‘wild-type’ (non-mucoid).
P. aeruginosa ‘CF’ phenotype (mucoid)
Isolates that secrete a thick coating of exopolysaccharide: provides additional protection against host defences in the lung

Chronic inflammation leading to progressive lung damage and deterioration of lung function
Occurs following infection of the CF lung by P. aeruginosa
Mainly due to host immune system trying to clear the infection.

16
Q

name the species of gram-negative - rod - aerobic - vibro

A
  • vibrio cholerae
  • Campylobacter
  • Helicobacter pylori
17
Q

Vibrio cholerae

A

Facultative anaerobe
Saline environments: commensal to planktonic crustaceans
Ingestion by shellfish
Contamination of drinking water due to flooding or poor sanitation (faecal contamination) – high infective dose
Incubation, few hours to 5 days (multiplies in small intestine)

Cholera
Most severe diarrhoeal disease
Characterised by pandemics (7 recorded since 1817)
Most in Indian subcontinent
1.4-4.0 million cases/year, 20,000-140,000 associated deaths

Voluminous watery stools (‘secretory’ diarrhoea)

Can lose 20 litres fluid/day plus electrolytes
Dehydration/death (hypovolaemic shock)  50-60% mortality
Non-invasive  no blood, pus or fever (i.e. not dysenteric)
Release of cholera toxin causes pathogenesis

Most cases can be treated with ORT

18
Q

Campylobacter

A

C. jejuni
C. coli

Spiral rods
Unipolar (monotrichous) or bipolar (amphitrichous) flagella

Most common cause of food poisoning in UK & US
Undercooked poultry
Cattle (unpasteurised milk)

Infectious dose 500-800 (low)

Mild to severe diarrhoea, often with blood
Usually self-limiting (≤ 1 week)

Campylobacter shed in faeces for ~3 weeks

19
Q

Helicobacter pylori

A

Spiral shaped
Tuft of polar flagella

Discovered in gastric mucus, 1982 (stomach previously thought to be sterile)

Present in ~50% global population, but only a fraction develop disease

Major role in gastritis and peptic ulcer disease (80-90% of ulcers)

Oncogenic microbe - ~10% cases of gastric adenocarcinoma & mucosa-associated lymphoid tissue lymphoma

Barry Marshall ingested H. pylori → gastritis → Nobel prize 2005

20
Q

name the species in the gram-negative - rod - aerobic - parvobacteria

A
  • Haemophilus influenzae
  • Bordetella pertussis
  • Legionella pneumophila
21
Q

Haemophilus influenzae

A

Exclusively human reservoir
Nasopharyngeal carriage in 25-80% population (non-capsulate strains)
Transient carriage of capsulate strains occurs in 5-10%

Opportunistic infections seen mainly in young children and smokers:
Capsulated – 6 different capsule types (a-f) – rare in adults
Meningitis (age <5 yrs), 5-10% of adult cases  Hi b vaccine reduced incidence
Bacteraemia (often associated with pharyngitis)
Epiglottitis

Non-capsulated  Non-typeable H. influenzae (NTHi) – incidence increasing
Bronchopneumonia
Sinusitis, otitis media
Pneumonia in CF, COPD, HIV patients

Diagnostics
Fastidious
Requires ‘factor X’ (haem) and ‘factor Y’ (NAD)
Cultured on chocolate agar
Non-motile

22
Q

Bordetella pertussis

A

Short (sometimes oval) rods (‘coccobacilli’)
Fastidious
Humans - only known reservoir (obligate human pathogen)

Pertussis (whooping cough)
B. parapertussis causes mild pharyngitis

Highly contagious (low I.D.) - aerosol transmission
Non-specific flu-like symptoms (~7 d), followed by paroxysmal coughing

Non-invasive
Produces two major toxins
Pertussis toxin
CyaA

23
Q

Legionella pneumophila

A

Discovered 1976
Legionnaires’ disease - severe inflammatory pneumonia (1-3% of all pneumonias)
Immunocompromised (elderly, alcoholics, smokers)

Severe (15-20% mortality)
Infection from man-made aquatic environments
Air-conditioning cooling towers, shower heads, nebulisers, humidifiers…

Replicate within freshwater protozoa - intracellular parasite of amoeba

Can survive and replicate within alveolar macrophages
Upregulates pro-inflammatory genes in alveolar macrophages
Excessive influx of neutrophils into lungs → inflammation

24
Q

what species are involved in gram-negative - rod - anaerobic?

A

bacteriodes

25
Q

Bacteroides

A

Non-motile rods
Strict (obligate) anaerobes

Commensal flora (large intestine) - most abundant (30-40% of the total)
>1010/g faeces (outnumbers E. coli 20:1)

Opportunistic - tissue injury (surgery, perforated appendix or ulcer)
Predominantly peritoneal cavity infections (peritonitis, intraabdominal abscesses are most common) can lead to bacteraemia

Most frequent cause of anaerobic infections, usually B. fragilis (although it is only 0.5-1.0% of total commensal Bacteroides)

Often present in polymicrobial infections with enterobacteria
Presence of facultative anaerobes depletes O2, allowing anaerobes such as Bacteroides to proliferate

Treatment requires specific anti-anaerobe antibiotics e.g. metronidazole

26
Q

name the gram-negative - cocci - aerobic.

A
  • Neisseria
  • Neisseria meningitidis
  • Neisseria gonorrhoeae
27
Q

Neisseria gonorrhoeae

A

Gonorrhoea - second most common STD worldwide
82.4 million (2020)
Cases doubled in the UK last year

Person-to-person only
Infection can be asymptomatic (~10% men, ~50% women)
Usually characterised by urethritis with additional infection of female genitalia
Serious complications in women - can lead to salpingitis and/or PID if infection ascends

Proctitis, gingivitis, pharyngitis depending on sexual preference

Multi-drug resistance arising

Non-capsulated

28
Q

Neisseria meningitidis

A

Nasopharyngeal carriage in 5-10% population (asymptomatic)
Person-to-person (aerosol) transmission (universities)

Pathogenesis:
Low level bacteraemia (asymptomatic) or septicaemia (sepsis)
Meningitis: invasion of the meninges - bacteria enter CSF of subarachnoid space

Very high mortality from septicaemia if not treated
Requires rapid diagnosis!

Virulence determinants of N. meningitidis
Capsule is major virulence determinant (serogroup B - 90% cases in UK)
LPS (membrane ‘blebs’)
Cytokine cascade
Sepsis

29
Q

Neisseria

A

Non-flagellated diplococci

Fastidious – humans only known reservoir

Two species of medical importance:
N. meningitidis
N. gonorrhoeae

30
Q

name the gram-negative - spirochates.

A
  • Borrelia burgdorferi
  • Leptospira interrogans
  • Treponema pallidum
31
Q

Spirochaetes

A

Long, slender, helical, highly flexible
Most are free-living and non-pathogenic
Pathogenic varieties difficult to culture

Modified outer membrane (“outer sheath”)
Treponema and Borrelia lack LPS, replaced by a different glycolipid

Endoflagella (‘axial filaments’ = periplasmic flagella)
Located between peptidoglycan and outer membrane
Fixed at each end of the bacterium and confers shape

Overlap in the centre of the bacterium

Propels bacterium in a corkscrew motion
Swim faster in high viscosity medium
“Hides” antigenic flagellum

Three medically important genera

32
Q

Borrelia burgdorferi

A

Lyme disease (zoonosis) (~300 cases in UK)
Infects small mammals (rodents)
Acquired by tick larvae feeding on infected animal

Transmitted to humans by tick nymphs (adults easier to spot!)
Bull’s eye rash, flu-like symptoms (fever, fatigue, headache)

Dissemination via lymphatics/blood to other organs
Neurological problems in 10-15% patients, joints → arthritis

Most symptoms arise due to immune response

33
Q

Leptospira interrogans

A

Leptospirosis (zoonosis)
Rare in UK

Common infection of rats
Systemic infection of the rat, excreted in faeces and urine
Proximity of rats to water often means water sources are colonised
Rivers, streams country parks, lakes

Contact of infected animal urine with mucous membrane or abraded skin
Flu-like symptoms
Severe form (Weil’s disease) in 10-15% infected individuals
2-4 week incubation period, clinical multi-organ infection occurs
Liver infection leads to cell destruction and jaundice
Acute renal and hepatic failure
Pulmonary distress
Haemorrhage

34
Q

Treponema pallidum

A

Syphilis (STD)
2,800 cases in UK – increasing again

Primary stage
Localised genital infection (ulcer (“chancre”))
Days-weeks post-infection
Highly transmissible phase

Secondary stage (~50% cases)
Systemic
Skin (rash), swollen lymph nodes, joint pains, muscle aches, headache, fever
1-3 months post-infection
Still highly transmissible

Tertiary stage (~30% cases)
‘Gummas’ (granulomas) in bone and soft tissue
Cardiovascular syphilis (aorta)
Neurosyphilis (brain and spinal cord)
Occurs several years post-infection
Non-infectious form

35
Q

gram-negative - obligate intracellular bacteria which are clinically relevant

A

Chlamydia

36
Q

Chlamydia

A

Very small, non-motile

Obligate intracellular parasites

Many species live asymptomatically as endosymbionts in amoebae, invertebrates and vertebrates

Cannot culture in bacteriological media - detect by serum Abs or PCR
Detects presence of anti-Chlamydia antibodies in serum
May be the result of a previous infection
Test must not be used to detect a current infection without an alternative confirmatory test

Also referred to as NAA (nucleic acid amplification) or NAAT (nucleic acid amplification test)

37
Q

Medically important members of Chlamydia

A

C. trachomatis (3 biovars):
Trachoma biovar (serotypes A-C) → trachoma → blindness
Eye-to-eye transmission via hands, fomites or flies

Genital tract biovar (serotypes D-K)
Most common STD - infects epithelial cells of urethra (both sexes) and vagina
Can ascend to uterus and ovaries (PID, infertility)
Usually asymptomatic (i.e. 70-80% cases in women)

Conjunctivitis (STD), hand-to-eye transmission

Lympho granuloma venereum (LGV) biovar (serotypes L1-L3)
Causes LGV (an STD) - invasive urogenital or anorectal infection
Endemic to the tropics, cases rising in Europe/N. America

C. pneumoniae
Respiratory tract (mild or “walking” pneumonia)
~10% community acquired pneumonias

C. psittaci
Mainly birds
Psittacosis (zoonotic infection), severe pneumonia

microbiology (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions