Outline of Lectures 18 Review of the work on contagious disease by Koch. 19 Epidemiology and Public Health. 20 Microbial interactions with higher animals. Examination of the normal flora of animals. 21 Entry of the pathogen into the host. Colonisation and growth. 22 Transmission of pathogens. Bacterial respiratory infections and sexually transmitted bacterial diseases. 23 Insect transmitted diseases. 24 Food-borne and water-borne bacterial diseases.

BS104 Lecture 20 Microbial interactions with higher animals. Examination of the “normal flora” of animals. Human tongue bacterial flora

Microorganisms and Humans Normal microbial flora: Microbes that are usually found growing on or within the body of humans. Everyday the human body is constantly being exposed to new microbes. Colonisation: growth of microorganisms after accessing the host cells/tissues. Humans are colonised by bacteria at birth. The human gut has been described as a bacterial culture vessel. Normal microbial flora is important for general well- being. Most microbes are benign (cause no problems) and some even contribute to health. However, bacteria sometimes do invade (pathogens).

A host is an organism that harbours a parasite, another organism that lives in or on the host and causes disease. A microbial parasite is called a pathogen. Pathogens Outcome of a human:microbe interaction Pathogenicity - Ability of a parasite to inflict damage on the host -Pathogenicity varies amongst different pathogens. -As does the host resistance or susceptibility. –Virulence is a measure of pathogenicity. –Changing conditions in the pathogen, host and the environment make the host-microbe interaction dynamic.

Infection and Disease Infection is any situation leading to the establishment of microbial growth with or without causing damage to the host. Microorganisms cause disease when their existence in the host leads to damage or injury to the host resulting in host function impairment. However, not all infections result in disease. Thus infection with the normal flora does not usually cause disease.

Infection and Disease Disease might occur if the individual is unhealthy e.g. an immuno-compromised individual (e.g. Acquired immunodeficiency syndrome [AIDS] patient or cancer patient) An opportunistic pathogen causes disease in the absence of the normal host resistance. MRSA patient

Animals as microbial hosts Rich in nutrients Constant suitable temperature pH Osmotic pressure Various environments (skin, gut, nose) Dry conditions (skin): Staphylococcus aureus. Highly oxygenated (lung): Mycobacterium tuberculosis (an obligate aerobe). Anaerobic (colon): Clostridium genus (obligate anaerobes) Therefore, animals provide a favourable environment for the growth of many microbes.

Microbial infections Mucous membranes (mouth, pharynx, urogenital, gastrointestinal etc). Epithelial cells and mucus (soluble glycoproteins) layer. Main steps of infection (a) – association, (b) adhesion, (c) invasion into submucosal epithelial cells. Brock: Figure 28.1 Microbial cells Epithelial cell Mucus

Beneficial Microbial Interactions with Humans From birth onwards exposure of humans to microbes is constant. Normal flora: billions of microorganisms grow within or on us.

Normal flora of skin Adult human has ~2m 2 of skin Skin surface not generally favourable for bacterial growth as it is too dry. Sweat glands are favourable. Most skin microorganisms are associated with apocrine sweat glands (under arms, genital regions, the umbilicus). Hair follicles are also an attractive environment for microorganisms. Brock: Figure 28.2

Over 180 species of bacteria and several species of fungi have been found to inhabit the skin. Gram-positive bacteria including species of Streptococcus, Staphylococcus, Corynebacterium and Propionibacterium (Propionibacterium acnes – causal agent of acne) are the most common and stable microorganisms that reside on the skin. Skin can be also be contaminated with gram-negative bacteria e.g. enterics by faecal contamination but they will not grow. However, the gram-negative rod Acinetobacter is an exception. Malassezia spp., Pityrosporum ovale and Candida are some of the fungal species that inhabit the skin. The weather, the age of the host and personal hygiene influence the variety and the density of the microflora. Normal flora of skin

Some common skin microbes Mainly gram positive as cell walls are stronger and less prone to drying. Common microbes include: –Staphylococcus species. –Corynebacterium. –Propionibacterium acnes (acne). –Yeast. Cell walls C.M. = cell membrane

Flora of the Oral Cavity Saliva contains very few nutrients in low concentrations Contains antibacterial compounds such as: –lysozyme (breaks down peptidoglycan in bacterial cell wall, weakening the wall and causing cell lysis) and, –Lactoperoxidase, an enzyme found in both milk and saliva (kills bacteria and generates antibacterial singlet oxygen in the process). The problem is food (rich in nutrients) - especially refined food with a high sugar content.

Flora of teeth (Formation of dental plaque) Acidic glycoproteins from saliva form a thin organic film. Bacterial microcolonies attach to this film on tooth surface. Mainly Streptococcus species (S. sanguis, S. sobrinus, S. mutans and S. mitis) colonise the glycoprotein film. Dental plaque forms upon extensive growth of these bacteria, leading to further colonization (Fusobacterium species, Borrelia species). Build up of plaque leads to anaerobic environment. Brock: Figure 28.3

Microbial microcolonies Bacterial growth on a model tooth – note arrows showing matrix that glue bacteria together and to surface. Brock – Figure 28.4.

Dental Caries (cavities) Accumulation of dental plaque leads to production of organic acids that cause decalcification of enamel, resulting in dental caries (tooth decay) – an infectious disease. As sugars in diets high in sucrose are fermented to lactic acid (S. mutans and S. sobrinus), proteolysis of enamel matrix then occurs and dental caries are promoted. Decalcification prevented by fluoride treatment.

Streptococcus mutans Produces a dextran polysaccharide adhesive from sucrose (table sugar) % of the US and Western Europe population have S. mutans colonization. No sugar in diet: no plaque. Susceptibility varies amongst individuals. S. mutans is common in the US and Europe (teeth decay) but absent in plaque of Tanzanian children (no decay). Microorganisms can also infect and cause the inflammation of the gum tissues (gingivitis). Sticky dextran holds cells together

Flora of the Gastrointestinal Tract Human gastrointestinal (GI) tract consists of the stomach, small intestines and large intestines (see next slide). Responsible for digestion of food, absorption of nutrients and synthesis of nutrients by the residing microbial flora. About to microbial cells are present in the entire GI tract. Stomach fluids are highly acidic (pH 2) – therefore the stomach acts as a chemical barrier for GI tract. Studies using 16S rRNA sequences from human stomach biopsies have revealed that bacteria do populate this hostile environment, albeit at a lower number than the small and large intestines. Individuals have very different bacterial populations in their stomach, but all contain gram-positive bacteria (Proteobacteria, Bacteroidetes, Actinobacteria and Fusobacteria) Also, remember Helicobacter pylori and stomach ulcers - the work of Barry J. Marshall and J. Robin Warren).

Esophagus Major bacteria present Prevotella Streptococcus Veillonella Helicobacter Gram-positive bacteria Proteobacteria Bacteroidetes Actinobacteria Fusobacteria Enterococci Lactobacilli Bacteroides Bifidobacterium Clostridium Enterobacteria Enterococcus Escherichia Eubacterium Gram-positive bacteria Klebsiella Lactobacillus Methanobrevibacter Peptococcus Peptostreptococcus Proteus Ruminococcus Staphylococcus Streptococcus Organ Esophagus Stomach Small intestine Duodenum Jejunum Ileum Colon Large intestine Major physiological processes Secretion of acid (HCl) Digestion of macromolecules pH 2 Continued digestion Absorption of monosaccharides, amino acids, fatty acids, water pH 4–5 Absorption of bile acids, vitamin B 12 pH 7 Anus Brock: Figure 28.8 Flora of the Gastrointestinal Tract

Intestinal Tract Small intestine: Separated into two parts: the duodenum and the ileum connected with the jejunum. Duodenum is also acidic but pH increases towards ileum and bacterial numbers increase reaching cells/gram digestive material in the lower ileum. Large intestine: Enormous bacterial numbers of obligate anaerobes cells/gram. (See previous figure for flora). Some facultative aerobes such as E. coli are present (in smaller numbers than other bacteria). Oxygen is consumed by these and the result is a strictly anaerobic environment. This creates an environment for growth of obligate anaerobes, including species of Clostridium.

Normal Microbial GI Tract Flora Diet influences the microbial populations in the GI tract. Vegeterians show higher numbers of coliforms and lactic acid bacteria than do individuals with high consumption of meat. Many microorganisms cannot colonise the stomach and the duodenum due to the highly acidic (~pH 2) environment.

Functions and Products of Intestinal Flora –Various compounds are produced through biochemical/metabolic processes, by the intestinal microorganisms. –Diet and the composition of the intestinal flora are influencing factors in the production of the type and amount of the compounds. Compounds produced include –Vitamins B 12 and K (not synthesised by humans, but by intestinal microflora. They are then absorbed from the gut). –Gas (CO 2, CH 4 and H 2 ) Normal Microbial GI Tract Flora

Contributions of intestinal microbes

Oral antibiotics interfere with growth of normal flora – signalled by loose faeces or diarrhoea. Opportunistic bacteria such as antibiotic-resistant Staphylococcus, Clostridium difficile or the yeast Candida albicans can become established in the absence of normal flora. After antibiotic treatment, the normal intestinal flora is re-established relatively quickly. Probiotics also help with the re-establishment of the desired species of bacteria. Changing the normal flora

Respiratory Tract Microorganisms are inhaled but most get trapped in nasal cavity. Staphylococcus and Streptococcus are normal flora. Potential pathogens such as Staphylococcus. aureus and Streptococcus pneumoniae may also be present. Immune system and competition by other bacteria keep their growth in check. Lower respiratory tract is sterile. As breathed air velocity slows, bacteria stick to walls of airways. A lining of ciliated cells also help to eliminate bacteria from lower tract. Brock: Figure Sinuses Nasopharynx Pharynx Oral cavity Larynx Trachea Bronchi Lungs Upper respiratory tract Lower respiratory tract

Urogenital Tract Bladder itself is typically sterile (M&F). Urethra is colonized by Escherichia coli and Proteus mirabilis. Sometimes these are opportunistic pathogens (pH changes) and cause UTI, especially in women. Vagina (weakly acidic in adult) contains Lactobacillus acidophilus that ferments glycogen and lowers pH. Before puberty (and after menopause) glycogen is not present and so pH increases. Flora thus changes according to maturity. Lactobacillus acidophillus (Gram-stain) Brock: Figure

Points to consider Where in the body are bacteria found? What type of bacteria are they and how are they suited to that particular environment? What parts of the body must be sterile? Where in the body are bacterial numbers the highest?

EXPOSURE to pathogens ADHERENCE to skin or mucosa INVASION through epithelium COLONIZATION and GROWTH Production of virulence factors TOXICITY: toxin effects are local or systemic INVASIVENESS: further growth at original site and distant sites TISSUE DAMAGE, DISEASE Further exposure at local sites Further exposure Pathogenesis Mechanisms

Further reading Brock 12 th edition Chapter 28 Brock 11 th edition Chapter 21