Medical Microbiology - Borders Unit 4 Pathogenic and Non-pathogenic Microbes

2 Essential or beneficial flora: These bacteria are referred to as our indigenous friendly bacteria. The main members of this group are: Bifidobacteria (Bifidobacterium bifidum), Lactobacteria (Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus rhamnosus), Propionobacteria, Peptostreptococci and Enterococci. Beneficial flora is made up of beneficial or good bacteria also called probiotic. They are the housekeepers of the gut, without them your gut cannot be healthy. These bacteria fulfill a myriad of vital functions in the body. The whole surface of the digestive system in a healthy gut flora is covered and dominated by beneficial bacteria. In a healthy body these beneficial bacteria predominate and control all other microbes. The beneficial bacteria provide a natural barrier and protects us against all sorts of invaders, bacteria, parasites, fungi, viruses, toxins etc. that are in our food and drink that we ingest every day. Apart from providing us with a physical barrier the beneficial bacteria produce antibiotic like substances that are anti fungal, anti viral that dissolve viruses and 'bad' bacteria. They also reduce pH near the wall of the gut making it uninhabitable for the 'bad' bacteria to colonize.

3 In a healthy animal, the internal tissues, e.g. blood, brain, muscle, etc., are normally free of microorganisms. However, the surface tissues, i.e., skin and mucous membranes, are constantly in contact with environmental organisms and become readily colonized by various microbial species. The mixture of organisms regularly found at any anatomical site is referred to as the normal flora. The normal flora of humans consists of a few eucaryotic fungi and protists, but bacteria are the most numerous and obvious microbial components of the normal flora. Gram stain of a species of Micrococcus, commonly isolated from the skin and nasal membranes of humans.

4 Bifidobacteria are Gram-positive, non- sporeforming, lactic acid bacteria. They have been described as "friendly" bacteria in the intestine of humans. Bifidobacterium bifidum is the predominant bacterial species in the intestine of breast-fed infants, where it presumably prevents colonization by potential pathogens. These bacteria are sometimes used in the manufacture of yogurts and are frequently incorporated into probiotics. Bifidobacterium bifidum. Gram stain

5 Forms of symbiotic relationships- species “Living Together”  Mutualism ▪Association in which both partners benefit ▪Synthesis of vitamins K and B  Commensalism ▪Association in which one partner benefits and other is unharmed ▪Flora living on skin  Parasitism ▪Association in which the microbe benefits at the expense of the host - pathogenic infection

 Normal flora are the ~harmless microorganisms found on your body  Normal flora are found on every part of your body that normally comes in contact with outside world (deep lungs and stomach are exceptions)  Normal flora can be transient or permanent (“transient” vs. “resident”)  Note that not all normal flora is always harmless – normal flora includes opportunistic pathogens such as E. coli which can cause urinary tract infections Normal Flora

7 Physical barriers Chemical barriers Normal flora

Normal Flora

 Includes bacteria, fungi, protozoa, viruses and arthropods  Most areas of the body in contact with the outside environment harbor resident microbes; large intestine has the highest numbers of bacteria.  Internal organs and tissues and fluids are microbe-free.  Bacterial flora benefit host by preventing overgrowth of harmful microbes – microbial antagonism. 9

10

11 Normal flora defined as populations of microorganisms routinely found growing on the body of a healthy individual Resident flora Transient flora

 Digestion  Production of vitamins  Mucosal maturation  Stimulate Immune System  Attachment  Intestinal transit  Colonization resistance

13

Dynamic nature of normal flora  Normal flora established during birth process  Once established, composition of flora is dynamic ▪Changes result from physiological variation within the host ▪Each member of flora ecosystem is influenced by presence and condition of other members Composition is Dynamic

Normal flora can help the you) by synthesizing vitamins (such as vitamin K) Normal flora can help the host by metabolizing materials into useful nutrients such as cellulose digestion in termites, ungulates, and even primates Normal flora can help the host by effecting Microbial Competition or Microbial Antagonism

 Uterus and its contents are normally sterile and remain so until just before birth.  Breaking of fetal membrane exposes the infant; all subsequent handling and feeding continue to introduce what will be normal flora. 16

Protective role of normal flora Contributions include ▪Protection against potentially harmful organisms ▪Stimulate immune system If normal flora are killed or growth suppressed pathogens may colonize and cause disease Protective Role

Protection against potentially harmful organisms Normal flora competitively exclude pathogens by: ▪Covering binding sites used for pathogenic attachment ▪Consuming available nutrients ▪Producing toxic compounds such as antibiotics Competitively Excluding Pathogens

Stimulate immune system Response mounted against normal flora that occasionally breaches body’s anatomical barriers ▪Response to normal flora may enable the immune system to cross-react with a future pathogen ▪Priming the immune system without causing illness in the host Stimulating immune system

Stomach Gram+ aerobes, Lactobacillus & Streptococcus

Small intestine: Proximal ileum ( cfu/ml) aerobic Gram+ Distal ileum ( cfu/ml) Gram- anaerobes Colon ( cfu/ml): Bacteroides, Eubacteria, Peptostreptococci, E. coli, Bifidobacterium, Fusobacteria

22

Kidneys: sterile Bladder: sterile Urethra: E. coli

 Avg. adult has 2 m 2 of skin surface.  Skin is not favorable to microbial growth since it is subject to drying. Most microbes are associated with the sweat glands.  The flora of the skin consists of resident and transient populations of microbes. Resident microbes live and multiply on the skin, whereas transient flora almost always are unable to multiple and usually die.  Resident flora remains fairly constant, although it can be affected by several factors.

 Saliva contains antibacterial enzymes: lysozyme and lactoperoxidase (also present in milk).  Saliva (pervasive, although not the best nutrient source), food particles, and epithelial debris provide nutrients for microbes.  Microbes colonize many surfaces in the mouth, including teeth and gingival crevices. The flora of the mouth changes with stages of growth, ex. acquisition of teeth.  A thin organic film forms on the tooth surface, to which acidic glycoproteins from the saliva attach, enabling only a few species of Streptococcus (ex. S. mutans) to adhere.  Dental caries = tooth decay = infectious disease caused by microbes. High sugar diets promote tooth decay because lactic acid bacteria ferment the sugars to lactic acid  decalcification of the enamel  proteolysis of the matrix of tooth enamel  further infection/decay. Fluoride prevents the decalcification step.  Microorganisms in the mouth can also cause other infections.

 Upper respiratory tract = nasopharynx, oral cavity, and throat.  Staphylococci, streptococci, diphtheroid bacillia, and gram-neg. cocci, as well as potentially harmful bacteria (ex. Staph. aureus and Strep. Pneumoniae) are often part of the normal flora of the nasopharynx of healthy individuals.  Lower respiratory tract = trachea, bronchi, and lungs. The lower respiratory tract is essentially sterile. Ciliated epithelium beat contaminants upward.

 Humans are unable to synthesize vitamin K.  It must either be acquired from dietary sources, or as metabolic by-products of intestinal bacteria. 27 Vitamin K Synthesis

 Bring you completed notes to class on Oct 18, for they will count as part of your quiz grade.  Study the notes, for you will have a quiz over the information in the notes.(you will not be able to use your notes on the quiz) 28