Mutualism: Both members of the association living together benefit from the relationship Parasitism: One organism, the parasite, benefits from the relationship, whereas the other organism, the host, is harmed by it (e.g. bacteria, viruses, protozoa, fungi, helminths) Commensalism: Two species live together in a relationship such that one benefits and the other one neither benefits nor is harmed
Contamination: presence of microorganismInfection: refers to the multiplication of any parasitic organism within or on the host’s body - a condition in which pathogenic microbes penetrate host defenses, enter tissues & multiply
Disease: any deviation from health, disruption of a tissue or organ caused by microbes or their products - A disturbance in the state of health wherein the body cannot carry out all its normal functionsPathogenicity: the capacity of the organism to produce diseaseVirulence: refers to the intensity of the disease produced by pathogens, and it varies among different microbial species
Two categories of organisms can be distinguished:f Resident microflora: comprise microbes that are always present on or in the human body 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 & tissues & fluids are microbe-free bacterial flora benefit host by preventing overgrowth of harmful microbes
B. Transient microflora: microbes that can be present under certain conditions in any of the locations where resident microflora are found- Acquired from mother’s womb- Flora of the human skin- Flora of the gastro-intestinal tract- Flora of the respiratory tract- Flora of the Genito-urinary tract
- aerobic and anaerobic diphtheroid bacilli (Corynebacterium, Propionebacterium) - nonhemolytic aerobic and anaerobic staphylococci (S. epidermidis and other coagulase –negative staphylococci, occasionally S. aureus and Peptostreptococcus species) - Gram positive , aerobic sporeforming bacilli - α-hemolytic strptococci (S. viridans) - enterococci (Enterococcus species) - gram negative coliform bacilli and Acinetobacter - Fungi, yeasts in skin folds - nonpathogenic mycobacteria in sebaceous secretions (genetalia, external ear)* AEROBES AND ANAEROBIC bacteria often join tor form synergistic infections (gangrene, necrotizing fasciitis, cellulitis)
lactic acid streptococci and lactobacilli Bifidobacterium species Enterobacteriaceae (Klebsiella, Citrobacter, Enterobacter) Anaerobes: - Bacteriodes species (Bacteroides fragilis, Fusobsacterium species Anaerobic lactobacilli – bifidobacteria, clostridia (Clostridium perfringens) Anaerobic gram positive cocci – (Peptostreptococcus species) Facultative aerobes – gram negative coliform bacteria, enterococci, small number of protei, psuedomonads, lactobacilli, candidae)
( Protection - inhibit potential pathogens indirectly by competing for nutrients and receptors of production of antimicrobial factros (bacteriocins, lactic acid)a Development of mucosal immune system (induce secretion of IgA, helps develop intestinal humoral immune system, modulate local T-cell repsonses)o Metabolic functions – produces short chain fatty acid that control intestinal epithelial cell differentiation, Synthesize Vit K, biotin, folate and enhance absorption
- same microorganism as found in the skin andperinium- Group B streptococci – women and childbearingstage- α-hemolytic streptococci, anaerobic streptococci,Prevotella species, clostridia, Gardnerella vaginalis,Ureaplasma urealyticum)- diphtheroids, S epidermidis, nonhemolyticstrptococci- Neisseria and gram negative bacilli – checked byflow of tears which contain antimicrobial lysozymes
Microbial Antagonism: Normal flora inhibits overgrowth of harmful microbes. Mechanisms include competition for nutrients and affecting environmental factors such as pH, toxic substances, and oxygen availability. Vaginal flora maintains pH of 3.5-4.5 which inhibits overgrowth of Candida albicans. In mouth streptococci produce compounds that inhibit growth of many other cocci. In intestine E. coli produce bacteriocins, which inhibit growth of closely related bacteria. C. dificile is inhibited by normal intestinal flora.
Opportunistic Pathogens: Organisms that normally do not cause disease in their natural habitat in a healthy person but may cause disease if the host is weakened or if they enter a different part of the body.3. Failure of the host’s normal defenses (immunocompromised)4. Introduction of the organisms into unusual body sites5. Disturbances in the normal microflora (microbial antagonism)
Pneumocystis carinii pneumonia in AIDS patients. Tooth decay and gum disease caused by mouth flora. Neisseria meningitidis is usually harmless in respiratory tract, but can cause meningitis. E. coli can cause urinary tract infections, meningitis, pneumonia, and abscesses.True pathogens – capable of causing disease in healthy persons with normal immune defenses Influenza virus, plague bacillus, malarial protozoan
The effect of two microbes acting together, is greater than the effect of either acting alone. AIDS and mycoplasma infection: Cells infected with mycoplasma and HIV die more readily than those infected with mycoplasma alone. AIDS and Oncogenic Viruses: Women with HIV infections develop very aggressive cervical cancers which are caused by papillomavirus. Individuals with HIV and Human Herpes Virus 8 infections, are more likely to develop Kaposi’s sarcoma. Oral streptococci and pathogens that cause gingivitis and periodontal disease, the oathogens bind to streptococci instead of host tissue.
Primary Infection: Acute infection that causes initial illness. Example: Common cold Secondary Infection: Caused by opportunistic pathogen after primary infection has weakened host immune system. Example: Pneumonia or bronchitis may develop after the common cold. Subclinical Infection: Does not cause any noticeable illness in host. Example: Over 90% of polio infections are asymptomatic.
Reservoirs of Infection Human Reservoirs: Infected individuals who may or may not present disease. Carriers are infected individuals without any signs or symptoms of disease (AIDS, polio, gonorrhea). Animal Reservoirs: Zoonoses are diseases that occur primarily in wild and domestic animals. About 150 different zoonoses are known (rabies, anthrax, and Lyme disease). Nonliving Reservoirs: Two major sources are soil and water. Soil: Clostridium tetani and botulinum. Water: Vibrio cholerae and Salmonella typhi.
skin gastrointestinal tract respiratory tract urogenital tract. Respiratory trace. Urogenital tractPathogens during pregnancy and birth
I. Contact Transmission: Spread by direct contact, indirect contact, or droplet transmission. f Direct Contact Transmission: Person-to-person transmission. No intermediate object is involved. Examples: Touching, kissing, sexual intercourse. B. Indirect Contact Transmission: Agent is transferred via a nonliving object (fomite). Examples: Towels, eating utensils, thermometers, stethoscopes, bedding, clothes, money, and syringes. C. Droplet Transmission: Microbes are spread in mucus droplets that travel short distances (less than 1 meter). Examples: Sneezing, coughing, talking, and laughing.
II. Vehicle Transmission: Transmission of disease via medium such as water, food, air, blood, body fluids, and intravenous fluids. Waterborne Transmission: Usually caused by water contaminated with sewage. Airborne Transmission: Spread of agents by droplets in dust that travel more than 1 m to host.III. Vectors: Animals that carry disease from one host to another. Arthropods (insects) are most important animal vectors. Mechanical Transmission: Passive transport of pathogens on insect’s body. Biological Transmission: Pathogen spends part of its life cycle in the vector.
Portals of Exit Site at which microbes leave body. Most common exit portals are respiratory and gastrointestinal tracts. Respiratory Tract: Exit in discharges (mucus droplets) from nose and mouth. Transmission by coughing, sneezing, spitting, etc. Examples: Tuberculosis, influenza, pneumonia, common cold, measles, mumps, scarlet fever, and meningococcal meningitis. Gastrointestinal Tract: Exit in feces or saliva. Feces: Amoebas, poliovirus, cholera, typhoid fever, salmonella, shigella, and many helminths. Saliva: Rabies virus, herpes simplex 1.
Urogenital Tract: Exit in secretions or urine. Penis and vagina: Sexually transmitted diseases. Chlamydia, herpes simplex 2, HIV, gonorrhea, and syphilis. Urine: Brucellosis and typhoid fever. Skin and Wound Infections: Spread through direct contact or through fomites. Example: S. aureus, P. aeruginosa, scabies, ringworm. Blood: Transmission through insects, needles, and syringes. Insects: Malaria, yellow fever, and Lyme disease. Needles: AIDS and hepatitis B.