lectures 5-6 Flashcards
Bacterial pathogens
Infectious disease
• Bacteria are responsible for the majority of
infectious diseases in human
• Some bacteria are associated with a specific
disease
• Ex) Tetanus is caused by the bacteria Clostridium tetani
• Ex) Malaria is caused by bacteria from the genus
Plasmodium
• However, most bacteria can cause MULTIPLE
types of infectious diseases, depending on the
location of the infection
• Ex) Streptococcus bacteria can cause skin infections,
lung infections, GI infections, CNS infections, etc.
• There are many different pathogenic bacteria in
humans
• Many pathogenic bacteria can be treated with
antibiotics
Bacterial pathogens
Normal bacterial flora
• The human body contains trillions of bacteria
with thousands of different species
• Many of these bacteria do not cause any
problems when found in their “normal” habitat
in the body
• Some of these bacteria are actually beneficial to
the human host
• Ex) Bacteria in the gut that synthesize Vitamin K
• Pathogenic bacteria cause infections under
certain conditions:
• By being inoculated into the human body from the
environment via blood transfer, skin penetration,
ingestion in the GIT, inhalation in the RT, etc.
• When bacteria living in one part of the body are
“relocated” to another part of the body causing an
infection
− Ex) Gut bacteria entering the bloodstream and
hematogenously spread to other organ systems
Microbial flora in humans is affected by a
number of different factors:
• Age • Diet • Hormones • State of health • Personal hygiene From birth to death, the microbial flora of an individual is subject to change
After an individual is exposed to a bacterial
species, one of 3 things will occur
- Transient colonization
- Permanent colonization
- Initiate an infectious disease
Because virulence varies between bacteria,
the disease process and outcome will vary
depending on the virulence of the
microorganism
• Ex) The severity of a lung infection with
Streptococcus pneumoniae can be significantly
different than a lung infection with Pseudomonas
aeruginosa
Trillions of bacteria occupy the human body • Skin • Eyes & ears • Mouth & nasopharyngeal tract • Gastrointestinal tract • Vaginal tract Knowledge of the normal bacteria that occupies these sections of the body is important in predicting infectious diseases
• Humna Microbiome Project is studying the
human microflora and categorizing the bacteria
Virulence
degree of pathogenicity of a
microorganism
Normal flora
Upper Respiratory Tract (URT) Aerobes:
Aerobes:
• Streptococci spp
• Hemophilus spp
• Neisseria spp
Normal flora
Upper Respiratory Tract (URT) Anaerobes
Peptostreptococci
• Veillonella
• Actinomyces
• Fusobacteria
Normal flora
Upper Respiratory Tract (URT)
• Common pathogens
- Streptococcus pyogenes
- Streptococcus pneumoniae
- Staphylococcus aureus
- Neisseria meningitidis
- Haemophilus influenzae
- Moraxella catarrhalis
- Gram negative Enterobacteriaceae family
Normal flora
Outer ear
Coagulase negative Staphylococci (S. epidermidis)
• Streptococcus pneumoniae
• Pseudomonas aeruginosa
• Enterobacteriaceae family
Normal flora
Eyes
Colonized by coagulase negative Staphylococci (S. epidermidis) • Pathogenic bacteria: • Streptococcus pneumoniae • Staphylococcus aureus • Haemophilus influenzae • Neisseria gonorrhoeae • Chlamydia trachomatis • Pseudomonas aeruginosa • Bacillus cereus
Normal flora
Lower Respiratory Tract (LRI)
Typically sterile
• Upper respiratory tract may be colonized
• Flora from the upper respiratory tract or mouth
may be aspirated into the lungs (aspiration
pneumonia)
• Typical pathogens
• S. pneumoniae
• S. aureus
• Enterobacteriaceae
• Fungi (C. albicans) infections are less common
• Chronic aspiration may lead to anaerobic infections
Normal flora
Gastrointestinal tract
• Huge numbers of microorganisms can be found
in the GIT from birth to death
• Exposure to new organisms occurs frequently
through food ingestion
• Bacterial population remain relatively constant
unless the balance of microorganisms is
disrupted (an example would be broad-spectrum
antimicrobial use)
Colonized by: • Acinetobacter • Actinomyces • Bacteroides • Bifidobacterium • Campylobacter • Clostridium • Corynebacterium • Enterobacteriaceae • Enterococcus • Eubacterium • Fusobacterium • Haemophilus • Helicobacter • Lactobacillus • Mobiluncus • Peptostreptococcus • Porphyromonas • Prevotella • Propionibacterium • Pseudomonas • Staphylococcus • Streptococcus • Veilonella • Fungi • Candida • Parasites • Blastocystis • Chilomastix • Endolimax • Entamoeba • Iodamoeba • Trichomonas
Normal flora
Esophagus
Rarely becomes infected • May contain: • Oropharyngeal bacteria and yeasts • Bacteria that colonize the stomach • Fungi (C. albicans) or viruses (H. simplex or CMV) may cause infections
Normal flora
Stomach
• Caustic nature of the stomach kills off many
potential infectious pathogens
• HCl acid
• Pepsinogen / Pepsin
• Acid tolerant bacteria may survivie
• Lactobacillus
• Streptococcus
• Helicobacter pylori
• Antacids or H2 antagonists / PPIs may alter pH
significantly allowing for bacterial growth
Normal flora
Small intestine
- Large number of bacteria present
- Common anaerobes
- Peptostreptococcus
- Porphyromonas
- Prevotella
- Common organisms causing infectious diarrhea
- Salmonella
- Shigella
- Campylobacter
- E. coli
Normal flora
Large intestine
• Huge number of bacteria present (1011 bacteria/ gram of feces) • Anaerobes are very common • Common organisms • Bifidobacterium • Eubacterium • Bacteroides • Enterococcus • Enterbacteriaceae family
Enterobacteriaceae characteristics
• Family of bacteria are a large group of Gramnegative bacteria • Characteristics • Enteric bacteria (related to the gut) • Typically shaped as bacilli • Facultative anaerobes • Flagellated • May produce endotoxins • Many have developed significant resistance to antibiotics
Normal flora
Enterobacteriaceae
family (partial list)
- Aquamonas
- Citrobacter
- Edwardsiella
- Enterobacter
- Ewinia
- Escherichia
- Klebsiella
- Morganella
- Pleisiomonas
- Proteus
- Providencia
- Salmonella
- Serratia
- Shigella
- Yersinia
Genitourinary system
The only area that is routinely colonized with bacteria are: • Anterior urethra • Vaginal tract • Urine is typically sterile, but bacteria may be present on some of the urinary tract organs • Common organisms: • Lactobacilli • Streptococci • Coagulase negative Staphylococci • Lactobacilli • Streptococci • Coagulase negative Staphylococci • Neisseria • Chlamydia • Organisms present in feces may also inhabit the urethral areas: • Enterobacteriaceae • Enterococcus • Fungi (Candida)
Vaginal tract
• Multiple organisms colonize the vaginal tract, and this changes depending on the patient’s age and hormone levels • Newborns • Lactobacilli • Infants • Staphylococci • Streptococci • Enterobacteriaceae • At puberty • Lactobacilli • Coagulase negative Staphylococci • Streptococci • Enterococci • Mycoplasma • Ureaplasma • Enterobactericeae • Anaerobes • Adult females may develop disruption in normal flora (reduction in Lactobacilli) resulting in: • Mobiluncus • Gardnerella • Trichomonas • Fungi − Candida albicans − Candida glabrata
Normal flora
Skin
• Multiple microbes come into the contact with skin, but normal flora include: • Coagulase negative Staphylococci • Less common − Other Staphylococci − Corynebacteria − Proprionibacteria − Clostridium perfringens − Candida • Gram negative rods are not commonly found on the skin
Pharyngitis
S. pyogenes
