HOST PATHOGENS INTERACTION…….

Origen of microbial flora

The fetus is in a sterile environment during first few days of life

New born……. Many micro organisms

Once established onto or into a particular body site……..

Symbiosis, commensalism, parasitism.

Characteristics of indigenous flora

• Indigenous flora• Body sites …same or different flora• Resident microbial flora• Transient flora

• Carriers• Carrier state• Carrier state may be acute or chronic • Colonizing….host resistance….microbial flora

provide protection

Factors that determine the composition of the usual microbial flora

• Presence of organisms …. Influenced by nutritional and environmental fectors.

Composition of the microbial flora at different body sites

• Human host…colonized by….app. 100 microbs• Effectiveness of host…..low incidence of

infection• Clinical microbiologist must be able to

recognize and identify the types of microbs …at diff body sites

Usual flora of the skin

• Skin has numbr of mechanisms...prevent infections

• Skin…..vide veriety of microbs• Reduce but not eliminated by scrubbing and

washing

• Composition of flora….depends…• Concentrate….. Moist areas• Aerobic diptheroids…moist areas• staphylococcus …hair follicles• Inhibit pathogenic bacteria• P.acnes colonize deep sebaceous glands

Usual flora of the mouth

• Contain larg number of bacteria• Many bind… buccal mucosa & tooth surface• Bacterial plaques..1011

streptococci• Plaque…..low oxidation potential at tooth

surface…growth of anarobes

Usual flora of the Respiratory tract

• Upper….lower tracts• Upper….mouth,nasopharynx,oropharynx,larynx• Lower….tracea,bronchi,lungs…protected by cilia• Usual flora of the mouth….streptocococci• Upper….mouth,nasopharynx,oropharynx…

microbs show some diff• Staphylococcus….30% of normal individuals

colonize anterior nares

• Individuals ….hospitalized…upper r.t…..by gram negative bacteria.

• Orophyarynx….streptococci• A number of species…...s.mutans, s.milleri,

s.sanguis,• Hospitalizwd patients…..gram negative rods

Usual flora of the gastrointestinal tract

• Comprisis….esophagus,stomach,s.intestine,colon

• Equiped…defenses & antimicrobial fectors• Ingesting organisms• Don’t multiply ….esophagus, stomach• In ingested food…as transient flora.• Most mirobs susceptible...acid ph…destroy….

Exception sper forming becteria,cysts

• Stomach acidty….reduce• Smal intestine….few microbs• In the colon….108 -1011

• Anarobs…90% large intestine• Gram positive cocci, yeasts, pseudomonas• Population….antibiotics• In some cases …microbs supressed….othr able

to proliferate…enterocolititis

Role of the microbial flora in the pathogenesis of infectious disease

• Microbial flora….provide some benefits… symbiotic relationship

• Some opportunists….when damage..disturbed or change…or immune system

• Trauma….accidentalor surgical….not part of microbial flora…

• Host immune response….reduces…due to ….drugs…

• Lymphoma, leukemia….reduce immune response

• Microbial flora…initiat an infection….in patients with chronic illnesses

Role of the microbial flora in the host defense against infectious disease

• Beneficial effects• Immunological competence• Immune system developed or undeveloped• Newborn….not developed

• Micobial flora…block colonization by extragenious pathogens

• Indigenous flora altered• gastroenteritis• Pathogenic species • C. albcans

Microbial flora…

• Important role in health and diseases• Eradication….negative effects• Knowledge in…clinical samples

Microbial factors contributing to pathogenesis and virulence

Pathogenesis

• Ability to produce disease • True pathogens… health immuno competent• Yersinia pestis &bacillus anthracis

• Pt population changed• Long life…more susceptible to ……• Normal flora….increase frequency in infections• Haemophilus influenzae…sometime life

threating infection• Staphylococcus epidermidis….somtimes

infectious• Both are called upertunistics

• So…the definition of a pathogen must be expended to apply ….when conditions for infection are met.

• Healthy 20 year old student……short pathogen than healthy 90 year old person, a transplant patient

• Iatrogenic infection……result of medical treatment

Virulence

• Ability of a micro organism to cause disease or is the degree of pathogenicity

• Measured by number of micro organisms to cause infection in the host

• Low infective dose….more virulent

1st lab Diagnostics of infectious diseasesUrine specimen collection1. Urine specimens will obtained from patients by clean-catch midstream

collection; samples will transported without delay to the microbiology laboratory

2. Urine samples for culture will collected into a container the specimen will stored at 4°C (in a fridge). Low temperature serves to inhibit bacterial replication in the specimen, until the specimen is processed in the laboratory. This is important because the number of bacteria in the urine specimen is important in determining if there is clinically significant bacteriuria. If the specimen is not properly stored small numbers of contaminating bacteria may multiply to large numbers and create a false impression of significant bacteriuria.

• The urine sample will routinely processed for culture. MacConkey agar and nutrient agar will used for culturing E.coli.

Sample Processing in Laboratory

• Growth on MacConkey agar • Laboratory procedure that will carried out

includes growth on MacConkey agar plates. • These MacConkey agar plates will prepared by

dissolving 5.1 gram of MacConkey agar in 100ml of distilled water.

• This mixture will autoclaved at 121ºC for 45 minute.

• After cooling the media, it will poured in petri dishes.

• These plates will kept at room temperature till the media in these plates get solidify.

• When media will solidified, it will kept in incubator for 24 hrs at 37ºC.

• Now the plates will ready for culture growth and collected urine samples will spread on MacConkey agar plates with the help of sterile loop.

• The procedure will carried out near flame under aseptic conditions.

• These MacConkey plates will again kept in incubator at 37 ºC for 24 hours.

• After 24 hours when the plates will examined for bacterial growth, a mixed culture will seen with different colours and types of colonies.