Introduction to Microbiology

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Foundations in MicrobiologySeventh Edition
13.1 We Are Not Alone
The human body exists in a state of dynamic equilibrium
Many interactions between human body and microorganisms involve the development of biofilms Colonization of the body involves a constant “give and take” Contact, Colonization, Infection, Disease

Microbes that engage in mutual or commensal associations – normal (resident) flora , indigenous flora, microbiota Infection – a condition in which pathogenic microbes penetrate host defenses, enter tissues, and multiply Pathogen – infectious agent

Infectious disease – an infection that causes damage or disruption to tissues and organs Resident Flora
Most areas of the body in contact with the outside environment harbor resident microbes Internal organs, tissues, and fluids are microbe-free
Transients – microbes that occupy the body for only short periods Residents – microbes that become established

Resident Flora
Bacterial flora benefit host by preventing overgrowth of harmful microbes – microbial antagonism Endogenous infections – occur when normal flora is introduced to a site that was previously sterile

Initial Colonization of the Newborn
Uterus and 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 Flora of the Human Skin

Skin is the largest and most accessible organ
Two cutaneous populations
Transients: influenced by hygiene
Resident: stable, predictable, less influenced by hygiene

Flora of the Gastrointestinal Tract
GI tract is a long hollow tube, bounded by mucous membranes
Tube is exposed to the environment
Variations in flora distribution due to shifting conditions (pH, oxygen tension, anatomy) Oral cavity, large intestine, and rectum harbor appreciable flora Flora of the Mouth
Most diverse and unique flora of the body
Numerous adaptive niches
Bacterial count of saliva (5 x 109 cells per milliliter)
Flora of the Large Intestine
Has complex and profound interactions with host
108-1011 microbes per gram of feces
Intestinal environment favors anaerobic bacteria
Intestinal bacteria contribute to intestinal odor

Flora of the Respiratory Tract
Oral streptococci, first organisms to colonize
Nasal entrance, nasal vestibule, anterior nasopharynx – S. aureus Mucous membranes of nasopharynx – Neisseria
Tonsils and lower pharynx – Haemophilus
Flora of the Genitourinary Tract
Sites that harbor microflora
Females – Vagina and outer opening of urethra
Males – Anterior urethra
Changes in physiology influence the composition of the normal flora Vagina (estrogen, glycogen, pH)

Maintenance of the Normal Resident Flora
Normal flora is essential to the health of humans
Flora create an environment that may prevent infections and can enhance host defenses Antibiotics, dietary changes, and disease may alter flora
Probiotics – introducing known microbes back into the body 13.2 Major Factors in the Development of an Infection
13.2 Major Factors in the Development of an Infection
True pathogens – capable of causing disease in healthy persons with normal immune defenses Influenza virus, plague bacillus, malarial protozoan
Opportunistic pathogens – cause disease when the host’s defenses are compromised or when they grow in part of the body that is not natural to them Pseudomonas sp & Candida albicans
Severity of the disease depends on the virulence of the pathogen; characteristic or structure that contributes to the ability of a microbe to cause disease is a virulence factor.

Becoming Established
Portals of entry – characteristic route a microbe follows to enter the tissues of the body Skin – nicks, abrasions, punctures, incisions
Gastrointestinal tract – food, drink, and other ingested materials Respiratory tract – oral and nasal cavities
Urogenital tract – sexual, displaced organisms...
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