Microbiology 2- Bacterial Diseases Flashcards
What are the sources and roots of human bacterial infection
Intrinsic
Extrinsic
Mythical- toilet seats, space, cold- misconceptions
What are the sources of intrinsic infection
Non-sterile sites in the body: Nasal cavity & sinuses Upper Respiratory tract Stomach Skin Mouth Small Intestine/biliary tract Large intestine Lower genital tract (vagina)
Which parts of the body are usually sterile
Stomach and small intestine- due to stomach acid.
List some of the bacteria found in the Nasal cavity and sinuses (Upper Respiratory Tract)
Staphylococcus spp.
S. pneumoniae
List some of the bacteria found on the skin
Staphylococcus epidermidis
Staphylococcus aureus
List some of the bacteria found in the mouth
Streptococcus spp
List some of the bacteria found in the small intestine/bilary tract
Escherichia coli
Bacteroides ap.
List some of the bacteria found in the large intestine
Enterococci
Strep group B
Anaerobes
List some of the bacteria found in the lower genital tract (vagina)
Lactobacillus
Strep group B
What are the two routes of infection (portals of entry)
Expected- e.g. normal (harmless) microbiota entering via an expected route
(newborn infant and maternal microbiota)
Unexpected- e.g. normal (harmless) microbiota entering unusual site OR
pathogenic microbiota entering any site
What is the portal of entry for pathogens of the upper respiratory tract
Mouth and nose
What are the characteristics of the pathogens that target the upper respiratory tract
Usually extrinsically-acquired from other people as respiratory tract droplets or airborne
Hand transmission can act as intermediate
List some of the bacterial diseases of the upper respiratory tract
Streptococcus spp (dental bacteria)
Streptococcus pneumoniae
Streptococcus pyogenes
Neisseria meningitidis
Staphylococcus aureus
(MSSA and MRSA
What is MRSA
A sub-set of S.Aureus
Antibiotic resistance S.Aureus
What are the disease consequences of bacterial pathogens acquired by the upper respiratory tract
Upper respiratory tract infection- Pharyngitis
Tonsillitis
Sinusitis
Spread to adjacent tissues
Middle ear infection
Brain abscess
Meningitis
Lower respiratory tract infection Bronchitis Pneumonia Pneumonitis Empyema
Spread to bloodstream
Bacteraemia eg pneumococcal bacteremia; meningococcal bacteremia
Why are upper respiratory tract bacterial pathogens able to cause diseases in the brain
Bones at the bottom of the skull are thin, hence bacteria in the sinus can spread to the brain easily, causing a brain abscess or meningitis.
What is Sepsis
Organ failure dysfunction in response to infection, variable with different bacteria.
What are the portals of entry for the urogenital tract
Extrinsic sources- urinary catheters to help pass urine- bypasses normal protection- extrinsic bacteria can infect the bladder by travelling up the catheter. Bladder Large intestine Intrinisic Sources
How is the bladder connected to the outside world
Urinary bladder connected to the outside world by urethra to the penis or vagina ( shorter in females).
Also connected to the rectum (exit of LI).
Describe the bacterial pathogens that usually infect the urinary tract
Usually intrinsic bacteria that infect the urinary tract - from the large intestine. (Escherichia coli
Bacteroides ap.
Proteus spp
Klebsiella)
Extrinisic bacteria can infect the urinary tract
Nosocomial transmission via catheters
Escherichia coli
Klebsiella spp
What are the pathogens that usually infect the genital tract
Intrinsic pathogens that infect the genital tract- usually from the large intestine (Streptococcus group B (pregnancy)
Candida/yeast)
Extrinisic infections that infect the genital tract
Sexually transmitted Neisseria gonorrhoeae Chlamydia trachomatis Treponema pallidum (syphilis) HIV, HSV (viruses)
What are the infectious disease consequences of urogenital tract infection
Urinary tract infection- Cystitis
Pyelonephritis
Spread to bloodstream
Bacteraemia
E.g. E. coli bacteremia
Genital tract infection
Gonococcal urethritis
Pelvic inflammatory disease
Tubo-ovarian abscess
Pregnancy-related infection
Neonatal group B strep infection
Neonatal gonococcal conjunctivitis
Which part of the body is cystitis limited to
The bladder
What is Pyelonephritis
bacteria travels from bladder to kidney via ureter- can spread to the bloodstream.
What are the consequences of gonorrhoea
Can spread to the fallopian tubes- abscess- infertility.
Describe how broken skin can act as a portal of entry.
Surgery/any wound
Skin diseases incl. varicella, eczema burns,athletes foot, pressure sores…..
IVDA- intravenous drug abuse
Insect bites- not directly- people scratch- skin breaks
Bites-human and animal
i.v. cannulae
(intravenous portal of entry)
Bacteria have virulence- wait for break in skin and infect the body.
List some of the bacteria that infect broken skin
Skin & mouth bacteria:
Staphylococcus aureus
Streptococcus pyogenes
Recent antibiotics/hospital
MRSA, Pseudomonas
Surgery/bowel flora exposure
All the above + Gram negatives
Describe some of the unusual pathogens that target broken skin
Pasteurella multocida from dog bites
Aeromonas hydrophilia from medicinal leeches
Clostridium perfringens from soil
What are the consequences of infection via broken skin
Superficial infection Cellulitis- red and inflamed skin Abscess- collection of pus Fasciitis Myositis Gangrene/necrotic infection Bacteremia
What is the portal of entry for bacteria of the GI tract
‘faeco-oral route’ Contaminated food & water Escherichia coli (travellers diarrhoea/EPEC/EHEC) Campylobacter jejuni (food poisoning) Shigella spp(dysentery) Vibrio cholerae (cholera) Salmonella enterica (food poisoning) Salmonella typhi (typhoid) Listeria monocytogenes Clostridium difficile
Describe the disease consequences of bacteria acquired by the GI tract
Diarrhoeal illnesses Vomiting only (eg toxins) ‘D & V’ Diarrhoea only Dysentery- bloody diarrhoea (suggests invasive infection) Bacteremic/systemic infections Typhoid (S. typhi) Listeriosis (L. monocytogenes) Salmonellosis and septic arthritis, aortitis
Toxin-mediated disease
D & V (eg S. aureus enterotoxin)
Neurological (eg botulism)
What is meant by pathogenic bacteria
Bacteria that cause disease
What are the two types of pathogenic bacteria, give examples of each
True
eg Staphylococcus aureus from skin causing large abscess and bacteremia
Opportunistic
Eg Staphylococcus epidermidis from skin causing prosthetic hip joint infection
What are commensal bacteria
Bacteria that do not cause disease- Eg Lactobacillus in vagina and GI
What is meant by pathogenicity
The ability to cause disease
What two factors affect pathogenicity
Infectivity and Virulence
What is meant by infectivity, what factors effect infectivity
General features favoring infection
Infectious dose
Transmission to host
Ability to colonise host
Tropism– Find unique niche (in or outside cells)
Replicate
Immune Evasion at site of colonisation or niche
What is meant by virulence, what factors effect virulence
Features that enhance disease causation Toxin production Enzymes that degrade host molecules Interruption of normal host processes Complete immune evasion
What is meant by infectious dose
The infectious dose is the number of bacteria required to initiate an infection
What is the infectious dose affected by
Route of transmission
Ability to colonise host-
Tropism and motility
Replication speed
Immune evasion at site
Describe how the route of transmission can affect infectious dose
Stomach acid means high doses often req. Use of antacid lowers infectious dose eg C. difficile, Vibrio cholerae easily killed by acid
Describe how the ability to colonise the host can affect infectious dose
Enteropathogenic E. coli “EPEC” type 3 secretion for adherence (pedestals
Describe how tropism and motility can affect infectious dose
Vibrio cholerae. High infective dose
But flagella motility may help reach gut epithelium
Describe how replication speed and immune evasion at site can affect infectious dose
Mycobacterium tuberculosis. Low infective dose. Very low replication rate. Able to survive inside macrophages and resist killing
What is a key characteristic of bacteria with low infectious dose
Ability to resist phagocytic killing.
Define virulence
Features that enhance disease causation
Using the example of S. pneumoniae- explain some features that enhance disease causation (virulence)
Toxin production eg Pneumolysin: cholesterol-dependent pore-forming toxin affecting lung architecture
Degradation of host molecules eg Hyaluronan lyase- degrades host hyaluronic acid matrix for nutrition and ? spread
Explain virulence using the example of
S. aureus
Interference with host cell function eg Superantigens made by S. aureus interfering with normal T cell function
Immune evasion eg S. aureus leukocidins leading to neutrophil death and abscesses
What are superantigens
T cell proliferation- tricks the body into thinking its a self cell
Cytokine Release- sepsis and organ failure
List some diseases spread by droplet infection via the mouth
Tonsillitis.
Streptococcus pyogenes
Meningococcal septicaemia
Neisseria meningitidis colonises nasopharynx asymptomatically before invading epithelial then endothelial cells
What is a disease spread by faecal-oral transmission
Cholera
Describe the pathogenicity of Vibrio Cholerae
Enormous infective dose 106- 1010
Flagella used to penetrate mucus
Then makes 2 component toxin A + B
Binds to GM gangliosides on gut
Triggers cAMP
Chloride efflux
Na and water follow
Profuse diarrhoea “Rice water stools”
Describe the transmission of pathogens from the GI tract to the UG tract and its consequences for neonates
Genital tract colonisation with group B strep (from GI tract)- Harmless 30-40% of women
leading to invasive group B strep infection in neonates: meningitis, septicaemia, death
What is S. aureus and how does it cause disease
S. aureus produces a family of Leukocidins
=toxins which destroy neutrophils, producing characteristic pus
List some pathogenic gram negative bacteria
Neisseria (meningitidis and gonorrhoeae)
Haemophilus influenzae
Escherichia coli (EPEC, EHEC, ETEC, UPEC)
Salmonella spp.,
Vibrio cholerae
Shigella
List some pathogenic gram positive bacteria
Staphylococcus aureus Streptococcus Group A= S. pyogenes Group B=S. agalactiae Viridans strep=dental bacteria Pneumococcus=S. pneumoniae
Clostridium (difficile, tetani, botulinum, pergringens)
Listeria spp.
Describe some opportunistic gram negative bacteria
Pseudomonas aeruginosa
eg indwelling long-term urinary catheters and multiple UTI’s previously treated with antibiotic
Acinetobacter baumanii
eg open battlefield trauma heavy prophylaxis with broad spectrum antibiotics followed by ICU stay and nosocomial transmission
Describe some opportunistic gram positive bacteira
Staphylococcus epidermidis
eg prosthetic joint and valve infections, metalwork, central line infections
Enterococcus faecalis
eg abnormal heart valves
What is meant by opportunistic pathogens
only cause disease when the conditions are permissive.
What usually causes vomiting
Swallowing the toxins, not the bacteria- C.Difficile.
Can soft tissue be infected
Yes, connective tissues such as skin as well as muscle can be infected. Results in pain and fever- difficult to see if its an infection.
Describe the growth of bacteria in acute disease
Rapid growth in tissues to produce the effect of disease before a protective immune response can be mounted.
Describe the growth of bacteria in chronic disease
Slow growth at all stages- leading to a reduced stimulation of the immune system.
What is meant by a carrier state
Resistant stationary phase
Which mineral is essential to bacteria
Iron
Describe the mucous surface interactions of bacteria
Rapid growth to overcome receptors that could block contact on the epithelial surfaces.
Describe the primary lodgement of bacteria in tissues
Rapid growth of a small number of bacterial invaders to replace loss inflicted by host defences in inflammatory response to bacterial invasion.
