Microbiology Lecture 10: Infection & Disease (Dr. Rafeik 2023)

Lecture 10 Infection & Disease Micro FIRST-TERM Infection & Disease Host–Microbe Relationship ▪ Microbes found on + in human body Microbiota ▪ (biota = life) ▪ pop...

Lecture 10 Infection & Disease Micro FIRST-TERM Infection & Disease Host–Microbe Relationship ▪ Microbes found on + in human body Microbiota ▪ (biota = life) ▪ population of mos inhabiting in body without cause disease Indigenous microbiota Transient microbiota permanent relationship with body Temporary, only for limited time. In large intestine In large intestine Escherichia coli + Candida albicans Streptococcus Symbiosis ▪ Is example of relationship between body + its microbiota (living together) Symbiosis Mutualism ▪ Beneficial to both host & microbe Commensalism ▪ Beneficial only to microbe ▪ host is unaffected Parasitism ▪ Beneficial only to microbe ▪ host is harmed Opportunistic ▪ caused by commensals. infections ▪ If indigenous microbiota is reduced or host’s immune system is weakened ✓ some commensals take “opportunity” to invade tissues + cause disease AIDS (acquired immunodeficiency HIV (Human targets WBC weakening immune immunodeficiency system. syndrome) Virus) treated by antiretroviral therapy (ART) “stop viral replication” 1 Micro FIRST-TERM ART is pill every day for rest of life or shot once every 1 or 2 months. no cure for HIV infection, but can reach undetectable levels of HIV. Untreated HIV can progress to AIDS AIDS Most severe stage of HIV (Stage 3) Ex) paralyzing of immune system so makes patient susceptible to opportunistic mos Example of opportunistic infections associated with AIDS Kaposi’s sarcoma ▪ caused by Kaposi’s sarcoma herpesvirus (KSHV) or human (KS) herpesvirus 8 (HHV-8). ▪ Causes abnormal small blood vessels + spread in body ▪ appears as firm pink or purple spots on skin ▪ life-threatening when affects organs inside body, as lung, lymph nodes, intestines Pneumonia ▪ infection in lungs. ▪ Caused by Many germs, as bacteria, viruses, fungi ▪ Symptoms : cough (with mucous), fever, chills, trouble breathing. ▪ In people with HIV, pneumonia with Streptococcus pneumoniae “Pneumococcus” is life-threatening ✓ So get vaccine to prevent infection with S. pneumoniae 2 Micro FIRST-TERM Infection Infection ▪ multiplication of microbe in host + competition for supremacy (domination) occur between (host + microbe). Host with Strong ▪ remains healthy resistance ▪ microbe is driven from host so benign relationship Host with weak ▪ Disease develope resistance ▪ Host lose competition Disease ▪ Any change from general state of good health ▪ disease & infection are not synonymous ✓ person may be infected without suffer disease Pathogenicity & virulence Pathogenicity ▪ ability of mos to enter to host’s tissues + bring physiological or anatomical change, lead to disease ▪ (Potential of pathogen to cause disease) = qualitative ‫فيه مرض او ل‬ Virulence ▪ Degree of pathogenicity (degree of damage caused by microbe) ▪ Quantitative Highly virulent ▪ organism regularly causing disease ✓ Typhoid bacillus ✓ Mycobacterium tuberculosis ( tuberculosis) ✓ Bacillus anthracis (anthrax). Moderately ▪ Sometimes cause disease virulent ✓ Candida albicans Avirulent ▪ not regarded as disease agents ✓ lactobacilli + streptococci in yogurt 3 Micro FIRST-TERM Pathogenicity ▪ clusters of genes responsible for virulence. (unstable islands) islands on (plasmid or chromosome) encode virulence factors absent in nonpathogenic strains. ▪ move by horizontal gene transfer. genes move from pathogens to avirulent mos, so become pathogen. So evolution of pathogenicity can make quick jumps ▪ So any mos able to change genetically & become virulent Virulence ▪ molecules or structures produced by pathogens + allow to invade factors host & cause disease Examples Adhesion ▪ capsules, slime layers, surface carbohydrates, factors proteins, flagella, pili] ▪ aid in attachment Enzymes ▪ enzymes enhance invasiveness enhance ▪ destroy body tissues + cells ▪ ex: hyaluronidase, collagenase Invasiveness Toxicity ▪ produce toxins (endotoxins + exotoxins) ▪ intoxication : disease by toxins Pathogen come in contact with body to cause disease, several outcomes are possible : 1. pathogen may be lost to environment 2. pathogen may colonize with normal microbiota ✓ remain as transient member. (Depend on nature of pathogen) 3. pathogen could become commensal 4 Micro FIRST-TERM ▪ Some pathogens don’t need to penetrate cells or tissues to cause disease ✓ cholera bacillus attaches to surface of intestine, where it produces toxins Invasiveness ▪ ability of pathogen to penetrate tissues & cause structural damage. 1) Colonization (adherence + multiplication) 2) Production extracellular substances “invasins” 3) Overcome host defense Group A ▪ found in throat + on skin. Streptococcus ▪ people carry it without disease. (GAS) or ▪ Most group A streptococcal diseases are mild : Streptococcus ✓ As Streptococcal pharyngitis ("strep throat"). pyogenes ▪ occasionally, cause life-threatening "invasive" infections. ✓ when group A Streptococci invade parts of body (where not normally present) ✓ blood + soft tissues as muscle. 5 Micro FIRST-TERM Neisseria ▪ Cause Invasive meningococcal disease meningitidis ✓ (acute & serious infection) ▪ Cause : ✓ sepsis (bloodstream infection) ✓ meningitis (inflammation of tissues that cover brain & spinal cord) Successful invasiveness requires “Virulence Factors (extracellular enzymes + toxins)” : Hemolysins ▪ Cause lysis of Erythrocytes ✓ release iron “in hemoglobin” that bacteria need for its metabolism ▪ Ex) Staphylococci & streptococci Leukocidins ▪ Destroy WBC + neutrophils + macrophage + phagocyte + lysosomal enzymes ▪ By streptococcus + staphylococcus + pneumococcus Hyaluronidase ▪ spreading factor ✓ As it enhances penetration of pathogen through tissues. ▪ Digests hyaluronic acid ✓ (polysaccharide binds cells together in tissue). ▪ Ex) Pneumococci + streptococci + staphylococci. 2 ways to develop Infections : primary infection ▪ occurs in healthy body secondary infection ▪ in individual weakened by primary infection 6 Micro FIRST-TERM Example ▪ In influenza pandemic 1918 ✓ influenza was primary infection ✓ pneumonia as secondary infection. Local diseases ▪ restricted to single area of body ▪ Ex) infected wound ✓ without treatment, cause serious problems, lead to systemic infection. ▪ Ex) staphylococcal skin boils (‫)دمامل‬ ✓ beginning as localized skin lesion ✓ may become more serious when staphylococci spread & cause systemic disease of bones, meninges, heart Systemic diseases ▪ spreading to deeper organs ▪ Ex) infection in bloodstream Bacteremia ▪ appearance of living bacteria in blood ▪ (not dangerous) Septicemia ▪ presence & multiplication of bacteria in blood ▪ life-threatening condition Bacteremia Septicemia ▪ presence of viable bacteria in blood ▪ blood poisoning by bacteria ▪ simple presence of bacteria ▪ presence + multiplication of bacteria (less number) in blood (higher number) ▪ not dangerous ▪ life threatening ▪ due to wound, surgery, injection ▪ due to infection throughout body (lung, abdomen, Urinary tract) ▪ no toxins ▪ produce toxins ▪ no symptoms ▪ symptoms : chills, fever, prostration, fast respiration and heart rate ▪ immune system clear it ▪ antibiotics treat it 7 Micro FIRST-TERM Establishment of Infection & Diseases Syndrome ▪ collection of signs & symptoms by which disease can be characterized Sign Symptoms ▪ Indicative condition or factors that ▪ Conditions + characters that person doctor see feel ▪ Objective, visible, can be quantified, ▪ Subjective, not visible, cant be verified verified ▪ Ex) high temp, rapid pulse rate, low ▪ Ex) chills, shivering, nausea, shaking, blood pressure, wound dizziness, tiredness 5 Stages of Diseases 1. Incubation Time elapsing between entry of microbe & appearance of first period symptoms. Incubation period may be : ✓ short (2 to 4 days for flu) ✓ 1 to 2 weeks for measles (‫(الحصبة‬ ✓ 3 to 6 years for leprosy (‫)الجذام‬ Factors determine incubation period’s length : ✓ number of organisms ✓ generation time + virulence ✓ level of host resistance ✓ location of entry ▪ Ex) of entry location: incubation period for rabies may be : ✓ short as several days or long as year ✓ depend on how close to central nervous system viruses enter body 2. prodromal Is time of mild signs or symptoms. phase characterized by indistinct & general symptoms as ✓ nausea, headache, muscle pains ✓ indicate competition between host + microbe begin. 8 Micro FIRST-TERM 3. acute period or when signs & symptoms are of greatest intensity. climax ✓ In scarlet fever : skin rash ✓ In flu: high fever + chills, differences in temp between superficial & deep areas of body. ✓ headache, cough, body, joint pains, loss of appetite are common. length of this period variable, depend on : ✓ body’s response to pathogen ✓ virulence of pathogen. 4. Decline period signs & symptoms begin to decrease. Sweating ‫ العرق‬is common ✓ as body releases excessive heat 5. Convalescence sequence comes to end. (recovery) period Body return to normal. In flu severity or duration of disease acute ▪ develops rapidly, severe symptoms, comes to climax, then fades disease quickly ▪ ex. Flu, Covid 19 9 Micro FIRST-TERM chronic ▪ remains for long time. disease ▪ symptoms are slower to develop, ▪ acute period is rarely reached, recovery in several months. ▪ Ex. diabetes, cancer, high blood pressure + heart diseases. ▪ Sometimes acute disease become chronic when body is unable to rid itself completely of microbe. ✓ Ex) patient with parasitic disease, as giardiasis or amoebiasis, may has irregular symptoms for years Portals of Entry + Exit of Pathogen ▪ Pathogens must gain access to enter & leave host to spread disease portal of entry ▪ route by which exogenous pathogen enters host. ▪ can be : ✓ Abrasions or mechanical injury to skin ✓ respiratory droplets, contaminated food or milk ▪ Ex: tetanus occur if Clostridium tetani spores ✓ On (sharp object) in soil ✓ puncture skin, enter anaerobic tissue of wounds. Infectious dose ▪ (numbers of microbes taken into body). ▪ ability of pathogen to establish infection & disease depends on infectious dose Pathogens must leave host to spread disease through portals of exit 10 Micro FIRST-TERM Nosocomial infections ▪ Infections developed as result of being treated for another illness in hospitals ▪ occur when hygiene barriers are penetrated nosocomial infections involve 3 elements : 1. compromised host (hospital patient) 2. source of hospital pathogens 3. chain of transmission 1. Compromised Most hospital patients have physical injury, as wound, burn Host. hospital patients are immunocompromised ✓ so if pathogen enter body, patient’s immune system unable to attack + eliminate it 2. Hospital Hospital personnel attempt to maintain sanitary & clean Pathogens. hospital environment. Although some pathogens come from other patients or healthcare staff 3. Chain of The way agent can be transmitted Transmission. involve : ✓ direct contact between patients or ✓ between healthcare staff & patient. ✓ use of instruments that aren’t sterile as Intravenous catheters, respirators ▪ use of chemical disinfectants is essential. + sterilization methods ‫باقي صفحة هتكون مع المحاضرة القادمة‬ 11