Terms Used in Medical Bacteriology
Pathogenic |
organism that can cause disease |
Opportunistic pathogen |
microbes that generally do not cause harm --> ex:// HIV, AIDS, chemo patients, long-term antibiotics |
Normal microbiota |
microbes that generally do not cause harm --> ex:// Lactobacillus spp., E. coli (gut) |
Virulence |
severity of disease/degree of harm --> quantitave measure of the ability to cause disease |
Toxicity/toxigenicity |
ability to produce toxins |
Invasiveness |
ability to enter into host tissues, multiply and spread |
LD_50 |
Measure of virulence --> number of organisms or number of ug toxin needed to kill 50% of animals |
Virulence factor |
properties of bacteria that can contribute to the ability of the bacteria to cause disease --> ex:// toxins, lipopolysaccharide (LPS), flagella |
Infection |
colonization of bacteria (microbe has entered host and replicated) |
Disease |
follows infection, occurs when host cells are damaged |
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Overview of Steps to Infection and Disease
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1.) How do pathogens enter human host? respiratory tract, GI tract, bloodstream (through broken skin), sexually transmitted, transplacental, eyes
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2.) Pathogens penetrate host defenses and multiply sd
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3.) Some basic host defense mechanisms - Resistance of host depends on age, immune system health, antibiotic/drug use, and lifestyle of host
- normal flora --> takes up space, compete w/ pathogens for space and nutrients, some secrete inhibitory compounds that prevent growth of pathogens
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Factors that Influence Potential Risk of Infection
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1.) Host immune system and host defenses - strong vs. compromised
- infects --> weak, poorly developed immune systems
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2.) Ability of pathogen to adhere to, colonize and replicate - can it remain in host?
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3.) Ability of organism to cause disease |
Factors That Influence Potential Risk of Infection
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1.) Host immune system and host defenses - strong vs. compromised - infects --> weak, poorly developed immune systems
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2.) Ability of pathogen to adhere to, colonize and replicate - can it remain in host?
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3.) Ability of organism to cause disease - are the appropriate virulence factors expressed?
- ex:// Corynebacterium diphtheriae causes diptheria when it has a gene encoding DT (diphtheria toxin)
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4.) Number of pathogens - highly virulent pathogen vs. avirulent pathogen
- ex:// Salmonella needs 1000s of cells to cause disease vs. Shigella which only needs 10 cells
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Normally Sterile Areas of the Body
Central nervous system, bone/marrow, organs (brain, heart, spleen, liver, kidney, pancreas, ovary), fluids (joint, pericardial, peritoneal, pleural) muscle |
Urinary Tract
Vagina
- Lactobacillus spp. is part of the normal microbiota
- Lactobacillus produces lactic acid, which lowers pH
- it also produces hydrogen peroxide (H2O2) (decomposes into toxic oxygen radicals) |
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