PATHOGENIC BACTERIOLOGY –
Bacterial mass in each body site
Each gram of feces contains ~10^8 facultative anaerobes and 10 obligate anaerobes.
There are more bugs in your gut than people on the planet.
Babies don’t have many associated microbes but they quickly develop a microbiota, and
everyone has a very specific microbiota.
Associated microbiota ~200g (wet weight).
Arms and legs are like deserts for microbiota, because they’re very dry.
- Head: many sebaceous and sudoriferous glands -> high population density.
- Axillae: high moisture, high temperature, high pH -> high microbial density.
- Perineum: high moisture, high temperature -> high microbial density.
- Toe webs: high moisture, high temperature -> high microbial density.
- Arms and legs: few sebaceous glands, no sudoriferous glands, relatively dry – low
- Hands: no sebaceous glands, exposed area, low water content -> low microbial
Lungs are not sterile, and the respiratory tract has many opportunist pathogens.
Many residents of the RT include: Viridans spreptococci, Strep. Pyogenes, Strep. Pneumonia,
Neisseria spp. Haemophilus spp., Moraxella spp. And Staph. Aureus
Mostly in the nose and throat.
How would you ensure that a lung microbiota sample from bronchoscopy was not contaminated
with oral flora? You don’t know.
Droplets are a very effective way of spread diseases
The environment of the vagina changes during the menstrual cycle (hormone levels, pH, host-
derived antimicrobial compounds) and during various stages of sexual maturity (oestrogen level,
pH, glycogen content, redox potential) Lactobacillus spp. Are the main residents form a polysaccharide-encased biofilm on epithelial
More than 200 species have been culturing the human mouth. These are marked differences
between species resident on the tongue, palate, tooth surface, and gingival crevices.
On average, we sallow 8x10 bacteria every day!
Grouping together: eyes, eyelids, eyelashes and lacrimal apparatus.
Generally the same as the organisms present on the skin.
Different relative numbers.
Affected by contact lens wear, sleep. The tears have a lot of antimicrobial components.
Virulence (pathogenicity) – the ability of a microorganism to cause disease.
Symbiosis – close association between 2 different species
Parasite – an organism that grows, feeds, and is sheltered on or in a different organism while
contributing nothing to the survival of its host.
Pathogen – an organism that causes disease.
Virulence determinants – characteristics of a pathogen that are involved with disease
Step 1 – adherence
Step 2 – immune system evasion (invasion, secretion of bacterial products)
Step 3 – damage to host cell
Host factors: age, sex, nutritional status, genetic make-up, immune system status.
Pathogen factors: ability to invade, to secrete products detrimental to host health, ability to
survive and multiply, antibiotic resistance.
Immunosenescence Influences microbiota at all sites
Decreased mucociliary clearance Increased microbial colonization of RT Malnutrition Affects composition of host secretions which
affects microflora colonization
Decreased stomach acid production Increased colonization of the stomach
Urinary tract changes Increased colonization of the urinary tract
Lack of oestrogen (females) Decreased vaginal pH leading to increased
Decreased intestinal mobility Increased colonization of small intestine
- Males have a significantly higher risk of colonization by Helicobacter pylori
- Males have a higher density of bacteria and females a higher diversity of species on
- Females have a higher risk of urinary tract infections than males.
- The carriage of Staph. aureus in the nose is higher in males than in females.
Host genetic issues
- Everyone’s microflora is different and unique to them
- However, the e.g. fecal and nasal microflora of monozygotic twins can share a high
degree of similarity points to host genetis playing a role in selecting microbial
1. The microorganism must be found in abundance in all organisms suffering from the
disease, but not in healthy organisms.
2. The microorganism must be isolated from a diseased organism and grow in pure culture.
3. The culture microorganism should cause disease when introduced into a healthy
4. The microorganism must be re-isolated from the inoculated, diseased experimental host
and identified as being identical to the original specific causative agent.
It is a human specific organism, there are no know reservoirs.
It’s hard to culture and does not survive long out of its host.
Its mode of transmission is not understood. Likely to be maternal transfer as well as transfer
Types of symbiotic relationships
Both species benefit and depe