Microbial Ecology PDF

Microbial Ecology Dr. Lorina Badger-Emeka COM-KFU  Learning outcome  Students should be able to:  Know the difference between colonization and infection  Know the distribution of organisms in our bodies  Know how the microbial population colonizing...

Microbial Ecology Dr. Lorina Badger-Emeka COM-KFU  Learning outcome  Students should be able to:  Know the difference between colonization and infection  Know the distribution of organisms in our bodies  Know how the microbial population colonizing our body is regulated  Differentiate between strictly pathogenic and opportunistic pathogenic microorganisms.  Know the most common microorganisms in the different body sites  Introduction  The microbial flora is determined by a variety of factors, such as:  age, diet,  hormonal state,  health, and personal hygiene.  human foetus lives in a protected, sterile environment,  At birth, is exposed to microbes from the mother and the environment.  The skin is colonized first, followed by the oropharynx, gastrointestinal tract,  Introduction cont’d  Changes in health can drastically disrupt the microbial balance  E.g., hospitalisation can lead to the replacement of normally avirulent organisms  Clostridium difficile is controlled in the gut. Treatment with antibiotic can alter this pattern  and C. difficile can proliferate and produce diarrheal disease and colitis.  Colonisation and Infection  Organisms that colonize  Infection leads to a pathologic humans process characterized by  (whether for a short period,  damage to the human host. such as hours or days  Damage can result from [transient], microbial factors e.g.,  or permanently)  damage to organs caused by  do not interfere with normal the proliferation of the body functions. microbe  or the production of toxins  or the host’s immune response to the organism Distribution of microorganism in our bodies (Google Image)  Normal flora of upper respiratory tract  1. non-haemolytic streptococci  2. Alpha- non-haemolytic streptococci  3. Neisseria species  4. Streptococcus pneumoniae  5. Streptococcus pyogenes  6. Haemophilus influenzae  7. Neisseria meningitidis  See complete list in Ch. 2 pg. 7  Ear and eye  most common organism colonizing the outer ear is coagulase-negative Staphylococcus.  Other organism colonizing the skin may also be found as well as potential pathogens such as:  S. pneumoniae, Pseudomonas aeruginosa, and members of the Enterobacteriaceae family.  surface of the eye is colonized with coagulase-negative staphylococci, as well as rare numbers of organisms (e.g., Haemophilus spp., Neisseria spp., viridans streptococci).  Disease is caused by S. pneumoniae, S. aureus, H. influenzae, N. gonorrhoeae, P. aeruginosa,  Nose  The human nose is home to the infamous Gram-positive bacterium Staphylococcus aureus,  known for its role in hospitals where it is a major cause of surgical wound and systemic infection.  where it is often referred to as MRSA, standing for Methicillin Resistant Staphylococcus aureus.  Mouth  500-600 different kinds of bacteria thrive on mucus and food remnants in the mouth.  A predominant member of this community is the Gram-positive bacterium Streptococcus mutans.  It grows on biofilms on the surface of teeth (plaque) where it consumes sugar and converts it to lactic acid.  Streptococcus pneumoniae is a much more threatening bacteria that can colonize the mouth.  It’s an opportunistic pathogen that resides in the mouth and throat awaiting an opportunity to infect the lungs when defence systems are low Micro-organism in the GI Tract (pp 7-8)  The Gastro-intestinal tract 1  Helicobacter pylori thrives in the gastric acid environment of the stomach. (ulcer)  the small intestine is colonized with many different bacteria, fungi, and parasites.  Most of these organisms are anaerobes, such as Peptostreptococcus,  Common causes of gastroenteritis (e.g., Salmonella and Campylobacter spp.) can be present in small numbers as asymptomatic residents;  The Gastro-intestinal tract 2  Various yeasts and non-pathogenic parasites can also establish residence in the large intestine.  The most common bacteria include Bifidobacterium, Eubacterium, Bacteroides, Enterococcus,  and the Enterobacteriaceae family.  E. coli is present in virtually all humans from birth until death. A Colonic Habitant. Microbial flora within the colon are able to digest polysaccharides that float by, which would otherwise be indigestible. Common Microbes That Colonize the Genitourinary Tract  Anterior Urethra  commensal population of the urethra consists of a variety of organisms,  lactobacilli, streptococci, and coagulase-negative staphylococci the most numerous.  In contrast, the urethra can be colonized transiently with faecal organisms, such as  Enterococcus, Enterobacteriaceae, and Candida—  all of which can invade the urinary tract, multiply in urine, and lead to significant disease.  Lactobacilli (6months) Maternal oestrogen declines, flora changes to include At birth Staphylococcus, Enterobacteriaceae and Streptococcus. Oestrogen production is initiated; lactobacilli re-emerges + streptococci (including group B Streptococcus), Enterococcus, Gardnerella, Mycoplasma, Ureaplasma, Enterobacteriaceae, and a puberty variety of anaerobic bacteria. oestrogen declines S. epidermidis, streptococcus, Enterococcus, Enterobacteriaceae MENOPAUSE + Gardnerella, Mycoplasma, Ureaplasma, candida etc.  Cervix  the cervix is not normally colonized with bacteria,  Neisseria gonorrhoeae and Chlamydia trachomatis are important causes of cervicitis (inflammation of the cervix).  Actinomyces can also produce disease at this site.  The Skin  Human skin is not a particularly rich place for microbes to live.  It is relatively dry,  slightly acidic and the primary source of nutrition is dead cells.  Thus preventing the growth of most organisms except for:  1. Propionibacterium acnes, a Gram positive bacterium that inhabits the skin.  P. acnes are anaerobes, so they lives in pores and glands  2. Another prominent member of the skin flora is Staphylococcus epidermidis.  How microbial population can be regulated  Factors that determine the population of organisms that colonize humans are complex  and include:  age,  diet,  hormonal state,  health, and personal hygiene. Strictly pathogenic and opportunistic pathogenic microorganism Strictly pathogenic Opportunistic pathogenic  Organisms always associated with  organisms that are typically members disease of the patient’s normal microbial flora  Mycobacterium  (e.g., Staphylococcus aureus, tuberculosis (tuberculosis), Escherichia coli, Candida albicans)  Neisseria gonorrhoeae (gonorrhoea),  They do not produce disease in their  Plasmodium spp. (malaria), normal setting  and rabies virus (rabies).  Disease results when introduced into unprotected sites (e.g., blood, tissues).  Question 1  Which of the following areas of the body do not have a resident microbial flora?  A. upper respiratory tract  B. eyes  C. bladder  D. ear  Question 2  Which one of the following would greatly influence the presence and numbers of the resident flora?  A. Occupational exposure  B. Humidity of the skin  C. Hygiene  D. Use of sterilant  References  MEDICAL MICROBIOLOGY  BY  MURRAY ROSENTHAL PFALLER  7TH & 8th ED.  Ch. 2.