Lecture 5: Pathogen/Host interactions Mechanisms of Infections Disease Flashcards
What is a pathogen?
Always causes disease.
Example: Neisseria gonorrhoea, Ebola virus
Potential Pathogen
Does not always lead to disease, needs to be the right time and place
Example: Escherichia coli
Non-Pathogen
This one is difficult, most organisms can cause disease in the right setting. But non-pathogens generally don’t cause disease except in rare cases
Example: Lactobacillus (in yoghurt and cheese)
Virulence factors
Factors that help organisms cause disease or avoid immune responses
Example: Toxin production, capsule
Normal flora/Microbiota
Organisms that are typically found at a body site - may cause disease if in other sites
Mucus membranes
Mouth, nose, genital tract, GI tract all have bacteria that reside in those ecological niches
Normal Flora: Skin
- Staphylococcus is gram positive cocci in clusters
- In skin swab
- Corynebacteria will also be found on the skin
- Generally colonized by Gram positive bacteria, both bacilli (Corynebacteria AKA “diptheroids”) and cocci (Staphylococci)
- Below the best, likely have gram negatives
- Organisms that can cause infection colonies the skin including pathogens like Staphylococcus aureus (coagulase positive staphylococcus) but usually coagulase-negative staphylococci predminate
Normal Flora: Respiratory Tract
- All strep hang out in the mouth, can develop community pneumonia
- Obviously oral health plays a big role in bacterial populations of the oral flora
Normal Flora: Gastrointestinal (GI) Tract
- Flora is dependent on the site - upper vs. lower GI tract
- Upper GI - Facultative aerobes- grows anaerobically and aerobically
- Lower GI = anaerobes (grows only in the absence of O2)
- Few gram positive bacteria in the GI tract (although enterococci are present as they are resistant to bile)
- Bacteria can move using flagella that can transport them short distance
- Lactobacillus is very common in GI tract, common in women because it drops pH of genital tract, in pubescence women, prior to puberty has the same bacterial makeup as skin, post menopausal women have skin flora there, but 12 and 60 women get colonized by lactobacillus and it produces lactic acid, dropping pH by 1000 fold, not hospitable for most bacterial infections
- Entire defense system is mediated by this bacteria, that modules the entire pH of the environment
Normal Flora: Genitourinary Tract
- The urine washes organism from the urethra to maintain a sterile bladder
- Vaginal flora changes with age
- Prepubescent and postmenopausal women - flora similar to skin flora
- Women of childbearing age - many bacterial species with a predominance of lactobacillus
What are the parts of the microbiome
- Nose
- Mouth
- Vagina
- Skin
What organisms do we term “commensals” or “normal flora” at least in the GI tract help us with extracting nutrients from our food
Intestinal flora
- Bacteroides
- Lachnospiraceae
- Clostridium
- Bifidobacteria
- Lactobacillus
- Actinomycetales
- Streptococcus
What does normal flora do
- Provide a level of protection from potential pathogens from taking hold
- Ex: C.difficile - antibiotics wipes out the normal flora and allow the C.diff spores to colonize in the gut
- Can lead to death
- In genital flora, perturbations in the Microbiota of the Vaginal tract has been associated with bacterial vaginosis
- Normal flora of the GI tract prevents the colonization by pathogens
- Prevents onset of disease
Clinical Manifestations of altered immune flora - C.difficile
- Leading cause of antibiotic associated diarrhea
- Associated with changed to the GI flora
- Risk factors include using antibiotics, being in hospital, age
- Associated with ulcerative colitis and can lead to death or in some cases a colectomy
Non-specific host defences and examples
- Non-specific, non immune host defences
- Barriers include structural, enzymatic and pH of the environment
- Normal flora also prevent pathogens from taking a foothold and causing infection
Examples:
Resp Tract - Coughing, sneezing, mucus, ciliary action, phagocytes, lysozyme
GI - stomach acidity, normal flora, peristalsis, antimicrobial compounds
Skin - Structural barrier, lactic acid, propionic acid, lysozyme, normal flora
Urogenital Tract - Lavaging action of urine, acidity of urine, lysozyme, vaginal lactic acid
Eyes - Blinking, tears, lysozyme
