Chapter 34 Medical Microbiology

Chapter 34 Medical Microbiology
Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Pretest True or False Microbiology is the scientific study of microorganisms and their activities. A disease that can be spread from one person to another is known as an infectious disease. Droplet infection is the transfer of pathogens from a fine spray emitted from a person already infected with the disease. Streptococci are round bacteria that grow in pairs. Chickenpox is caused by a virus. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Pretest, cont. True or False
The course adjustment on a microscope is used to obtain precise focusing of an object. The purpose of transport media is to provide nutrients for the multiplication of the specimen. A throat specimen should be collected from the tonsillar area and posterior pharynx. A wet mount is used to examine microorganisms in the living state. A smear is material spread on a slide for microscopic examination. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Content Outline Introduction to Microbiology
Microbiology: the scientific study of microorganisms and their activities Microorganisms: tiny living plants or animals that cannot be viewed with the naked eye Anton van Leeuwenhoek ( ) Designed a magnifying glass strong enough for viewing microorganisms Precursor of modern microscope First to observe and describe protozoa and bacteria Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Introduction to Microbiology, cont.
Microbiology: deals with unicellular (one-celled) microscopic organisms All life processes of a microorganism are performed by one cell, including: Ingestion of food substances and their use for energy Growth Reproduction Excretion Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Only a small number of microorganisms are pathogenic (disease-producing) Pathogen infects host: produces symptoms of that disease Assists physician in diagnosing that disease Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Microbiologic tests: Also help physician identify pathogen causing disease Identification of pathogen: leads to proper treatment Most microbiologic tests: performed at outside laboratory Medical assistant often responsible for collecting the specimen Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Normal Flora Every individual has normal flora
Normal flora: harmless microorganisms that normally reside in many parts of the body but do not cause disease Examples of body areas with an abundant normal flora Surface of skin Mucous membranes of gastrointestinal (GI) tract Respiratory tract Genitourinary tract Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Normal Flora, cont. Normal flora may be beneficial Example:
Normal flora in intestinal tract: Feed on potentially harmful microorganisms Synthesize vitamin K (needed for blood clotting) From Mahon CR, Manuselis G, Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Normal Flora, cont. Sometimes normal flora can become pathogenic and cause disease May occur during lowered body resistance Courtesy Cathy Bissonette Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Infection Infection: invasion of the body by pathogenic microorganisms
If body conditions are favorable Pathogen grows and multiplies Results in an infectious disease Infectious disease: a disease caused by a pathogen that produces harmful effects on its host Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Infection, cont. Not all invading pathogens are able to cause disease
Body attempts to stop invasion Uses second line of defense mechanisms: Inflammation: a protective response of the body to the entrance of foreign matter The purpose of inflammation is to destroy invading microorganisms and to repair injured tissue Phagocytosis by white blood cells (WBCs) Production of antibodies Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Infection, cont. First line of defense: works to prevent entrance of pathogens into body Examples: Skin Mucous membranes Mucus and cilia in nose Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Infection, cont. Coughing and sneezing Tears and sweat
Acid nature of urine and vaginal secretions Hydrochloric acid secreted by stomach Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Infection, cont. If body defenses are successful: pathogens are destroyed Individual does not get infectious disease If body defenses are overcome by pathogen Individual gets infectious disease Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Infection, cont. Many infectious diseases are contagious
Contagious: capable of being transmitted directly or indirectly from one person to another Droplet infection: inhalation of pathogens from a fine spray emitted by person infected with disease When infected individual exhales (breathing, talking, coughing, sneezing) Pathogens are dispersed on minute liquid particles Infected individual: should cover mouth when coughing and sneezing Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Stages of an Infectious Disease
Infection: invasion and multiplication of pathogenic microorganisms in the body Incubation period: interval of time between invasion by a pathogen and appearance of first symptoms of disease May range from a few days to several months Pathogen is growing and multiplying during this time Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Stages of an Infectious Disease, cont.
Prodromal period: first symptoms appear Examples: Headache Feeling of illness From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Stages of an Infectious Disease, cont.
Acute period: disease is at its peak and symptoms fully developed Example: fever Decline period: symptoms begin to subside Convalescent period: patient regains strength and returns to good health Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Microorganisms and Disease
Groups of microorganisms known to contain species capable of causing human disease: Bacteria Viruses Protozoa Fungi (yeast) Animal parasites Courtesy Cathy Bissonette Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Bacteria Microscopic single-celled organisms
Of 1700 species known to dwell in humans: only about 100 produce human disease Antibiotics: help in controlling bacterial infections Not effective against viral infections Classified according to shape Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Classification of Bacteria by Shape

Staphylococci Cocci: round shape Staphylococci
Round bacteria that grow in grapelike clusters From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Staphylococci, cont. Staphylococcus epidermidis: normally present on skin surface and mucous membranes of the mouth, nose, throat, intestines Usually nonpathogenic Break in the skin can allow invasion Example: cut Results in a mild infection Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Staphylococci, cont. Staphylococcus aureus: associated with pathologic conditions Boils Carbuncles Pimples Impetigo Abscesses Staphylococcal food poisoning Wound infections Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Staphylococci, cont. Staphylococcal infections usually cause pus formation (suppuration) Termed: pyogenic infections From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Philadelphia, 2000, Saunders
Streptococci Streptococci Round bacteria that grow in chains From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Streptococci, cont. Before antibiotics: major cause of human death
Diseases caused by streptococci: Streptococcal sore throat Scarlet fever Rheumatic fever Pneumonia Puerperal sepsis Erysipelas Carbuncles Impetigo From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Diplococci Diplococci Round bacteria that grow in pairs Diseases caused by diplococci: Pneumonia Gonorrhea Meningitis From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Courtesy Cathy Bissonette
Bacilli Bacilli: rod-shaped bacteria Found in soil and air Courtesy Cathy Bissonette Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Bacilli, cont. Some are able to form spores
Spore: a hard, thick-walled capsule formed by some bacteria that contains only the essential parts of the protoplasms of the bacterial cell Enables them to resist adverse conditions Heat Disinfectants Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Bacilli, cont. Diseases caused by bacilli: Botulism Tetanus Gas gangrene Gastroenteritis caused by Salmonella food poisoning Typhoid fever Pertussis Bacillary dysentery Diphtheria Tuberculosis Courtesy Cathy Bissonette Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Bacilli, cont. Escherichia coli (E. coli): a species of bacillus
Normal flora of the large intestine From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Bacilli, cont. Normally harmless May cause a urinary tract infection (UTI) if enters urinary tract due to: Lowered resistance Poor hygienic practices From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Spirilla Spirilla: spiral- or curved-shaped bacteria
a. Treponema pallidum Causative agent of syphilis Cannot be grown in culture media Diagnosis of syphilis made through serologic tests Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Spirilla, cont. d. Vibrio cholerae Causative agent of cholera
Immunization and proper sanitation: have eliminated cholera in United States Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Viruses Smallest living organisms
Electron microscope must be used to view them Can infect: plants, animals, humans Use nutrients inside host cells For metabolic and reproductive needs Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Viruses, cont. Diseases caused by viruses: Influenza Chickenpox
Rubeola (measles) Rubella (German measles) Mumps Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Viruses, cont. Poliomyelitis Smallpox Rabies Herpes simplex
Herpes zoster Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Viruses, cont. Yellow fever Hepatitis
Majority of diseases in upper respiratory tract Example: common cold Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

What Would You Do? What Would You Not Do?

Microscope Compound microscope: used most often in medical office
Consists of two-lens system Components: Support system Optical system Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System Frame Supports microscope Consists of:
Base: for support Arm For carrying it To support magnifying and adjusting systems Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. Stage Flat, horizontal platform
Slide is placed on stage Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. Has small, round opening in center
Permits light from below to pass through the object being viewed and up into lenses Standard microscope: has metal clips to hold slide in place Slide must be moved by hand Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. Mechanical stage: allows movement of slide in vertical or horizontal position using adjustment knobs Needed for: Differential WBC count Inspection of gram-stained smear Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. Light source Located at the base
Consists of: built-in illuminator Switch for turning on and off Light directed to condenser above Then through object to be viewed Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. Condenser
Compound microscopes have lens system between light source and object Known as substage condenser Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. Popular type: Abbe's condenser
Consists of two lenses Collects and concentrates light rays and directs them up Brings light rays to a focus on the object so that it is well-illuminated Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. Diaphragm
Controls the amount of light focused on an object Amount of light controlled by iris diaphragm Located beneath or inside condenser Consists of: Series of horizontally arranged interlocking plates With central opening (aperture) Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. Diaphragm lever: increases or decreases aperture
Increases or decreases light admitted Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. As magnification increases: more light is necessary Example: oil immersion requires increased light intensity Low-power objective Do not need as much light Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. Adjustment knobs
Degree of illumination: also influenced by density of the object Stained structures: require more light than unstained specimens Adjustment knobs Coarse adjustment: to obtain an approximate focus quickly Fine adjustment: to obtain precise focusing Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Support System, cont. Adjustment knobs:
May be mounted as two separate knobs May be placed together Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System Compound microscopes have two-lens magnification system
Magnification: the ratio of the apparent size of an object viewed through the microscope to the actual size of the object Eyepiece First lens system Also called ocular lens Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Located at top of body tube
Marked 10× (magnifies 10 times) Monocular microscope: has one eyepiece Binocular microscope: has two eyepieces Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Objective lenses Second lens system
Three objective lenses: located on a revolving nosepiece Each objective has a different degree of magnification: engraved on metal shaft Low-power objective: 10× High-power objective: 40× Oil-immersion objective: 100× Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. May have color-coded rings to identify objective
Example: Low-power objective: yellow ring High-power objective: blue ring Oil-immersion objective: white ring Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Metal shafts of objectives: differ in length
Low-power objective: shortest length High-power objective: length between low and oil objectives Oil-immersion objective: longest length Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Total magnification: multiply the ocular magnification by the objective magnification: Low-power total magnification: 100× (10 × 10) High-power total magnification: 400× (10 × 40) Oil-immersion magnification: 1000× (10 × 100) Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Focus
Barrel focus: body tube or barrel moves while stage remains stationary Stage focus: stage moves while body tube remains stationary Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Low and high power Low-power objective used for:
Initial focusing and light adjustment Initial observation and scanning requirements High-power objective used for: A more thorough study of the slide Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Working distance: distance between tip of lens and slide High-power objective: working distance is short Care must be taken when using high-power objective To prevent it from striking and breaking slide To prevent damaging the lens Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Most compound microscopes are parafocal
Parafocal: once focused on low power the nosepiece can be rotated to high power and focused with fine adjustment Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Oil immersion Provides highest magnification
Used to view very small structures or the detail of structures Microorganisms Blood cells Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Oil immersion has a very short working distance
Lens nearly rests on slide Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Must use immersion oil
Does not dry out when exposed to air for a long time Drop of oil placed on slide Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Oil resides between objective and slide
Provides path for light to travel between slide and lens Prevents scattering of light rays Permits clear viewing of small structures Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical System, cont. Oil immersion used for:
Differential white blood counts Examination of gram-stained smears Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Care of the Microscope Carry with two hands: one on arm and one under base Place down gently: prevents jarring it Could damage delicate parts Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Care of the Microscope, cont.
Do not touch the lenses: prevents fingerprints Avoid wearing mascara: difficult to remove from lens When not in use: keep covered with plastic dust cover Store in case or cupboard Rotate nosepiece to low objective Position as close as possible to stage Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Clean by washing enameled surfaces with soap and water Dry thoroughly with a soft cloth Clean stage after each use: Wipe stage with gauze or tissue If immersion oil gets on stage: Remove with gauze moistened with xylene Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Optical glass: softer than ordinary glass Do not use tissue or gauze to clean: scratches the lens If lenses are especially dirty Clean with commercial lens cleaner or xylene Dry and polish with lens paper Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Microscope that is malfunctioning Have repaired by qualified service person Do not try to fix yourself May result in further damage Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Microbiologic Specimen Collection
Purpose: To identify pathogen causing the disease Assists in the diagnosis Example: obtaining a urine specimen to assist in diagnosis of a UTI Specimen: a small sample or part taken from the body to show the nature of the whole Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Microbiologic Specimen Collection, cont.
MA often responsible for collecting microbiologic specimens Examples: throat, nose, and wound specimens MA may assist physician in collecting specimens Examples: vagina, cervix, urethra, rectum Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Sterile swab used to collect specimen Swab: small piece of cotton wrapped around the end of a slender wooden or plastic stick Passed across body surface or opening To obtain a specimen for microbiologic analysis Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

To prevent inaccurate test results: Use good techniques of medical and surgical asepsis Do not contaminate with extraneous microorganisms Extraneous microorganisms: undesirable microorganisms that can enter the specimen in various ways. They grow and multiply Can obscure and prevent identification of pathogens that might be present Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

To prevent contamination of a specimen with extraneous microorganisms: Supplies used to collect specimen must be sterile Examples: swabs and specimen containers Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Do not allow swab to touch areas surrounding collection site Example: throat specimen—do not allow swab to touch inside of mouth Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Follow OSHA Bloodborne Pathogens Standard when performing microbiologic procedures: Wear gloves No eating, drinking, smoking, or applying makeup Pathogens can be transmitted through hand-to-mouth contact Do not lick labels for specimen containers Cover breaks in skin with a bandage Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

If accidentally touch specimen: Wash area immediately with soap and water If specimen comes in contact with worktable: Immediately clean with soap and water followed by disinfectant (e.g., phenol) At end of day: Clean worktable with disinfectant Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

After collection: place specimen in proper container Securely fasten lid Label with: Patient's name Date Source of specimen Initials Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Handling and Transporting Microbiologic Specimens
Delay in processing specimen: May cause death of pathogens Overgrowth of specimen by normal flora (usually collected along with pathogen) If specimen analyzed in office: Examine under microscope or culture immediately Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Handling and Transporting Microbiologic Specimens, cont.
If specimen transported to outside laboratory by courier Place in transport medium (e.g., Starswab II, Culturette) Prevents drying of specimen Preserves specimen in its original state b. Outside laboratory: provides instructions on care and handling of specimen Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Specimen must be accompanied by laboratory request, which includes: Physician's name and address Patient's name, age, and gender Date and time of collection Type of microbiologic examination requested Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Source of specimen Examples: throat, wound, urine Physician's clinical diagnosis Clinical diagnosis: a tentative diagnosis of a patient's condition obtained through the evaluation of the health history and the physical examination without the benefit of laboratory or diagnostic tests Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Wound specimens Must be collected from within wound (rather than from surface of wound) To obtain accurate and reliable test results Usually two swabs used Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Swab inserted into area of wound that contains the most drainage Swab gently rotated from side to side To completely absorb microorganisms present Swab placed in specimen container Process repeated with second swab Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Collection and Transport System
Types available Culturette Starswab II Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Collection and Transport System, cont.
Consist of sterile swab and plastic tube that contains a transport medium Comes packaged in peel-apart envelope Should be stored at room temperature Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Check expiration date Peel open envelope Remove cap from the collection tube Remove cap/swab unit from envelope Collect specimen using aseptic technique Do not allow swab to touch any other area Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

i. Insert swab into collection tube j. Push cap/swab as far as it will go to completely immerse in transport medium k. Remove gloves and sanitize hands Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

l. Label tube m. Place in biohazard specimen transport bag Place laboratory request in outside pocket n. Chart procedure o. Transport to laboratory within 24 hours Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Streptococcus Testing
Streptococcal sore throat (streptococcal pharyngitis) Primarily affects children and young adults Causative agent: group A beta-hemolytic streptococcus Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Streptococcus Testing, cont.
Potentially serious condition Small percentage of patients develop a poststreptococcal sequela Sequela: a morbid secondary condition that occurs as a result of a less serious primary infection Example: rheumatic fever Early diagnosis and treatment of “strep throat” with antibiotics is important Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Rapid Streptococcus Tests
Detects group A streptococci from a throat swab Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Rapid Streptococcus Tests, cont.
Requires only 4-10 minutes to process Diagnosis can be made while patient is at office If streptococci present: antibiotics prescribed Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Direct antigen identification test: most frequently used Particles sensitized to streptococcal antibody are combined with specimen (antigen) Produces a color change if streptococcal is present (through antigen-antibody reaction) Test includes a control To ensure results are accurate and reliable Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Sensitivity Testing Determines susceptibility of pathogenic bacteria to antibiotics Allows physician to determine best antibiotic to use to treat patient's condition Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Sensitivity Testing, cont.
Disk-diffusion method Most common method Use disks impregnated with various antibiotics Dropped on surface of solid culture medium in Petri plate inoculated with pathogen Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Culture is incubated Allows antibiotics to diffuse into culture medium If pathogen is susceptible to an antibiotic: Clear zone without bacterial growth around disk Indicates antibiotic is effective against pathogen Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Microscopic Examination of Microorganisms
Can be examined in fixed or living state Examining microorganisms in a fixed state Most microorganisms are examined this way Preparation of a smear through heat fixation: followed by staining Example: Gram staining Easier to examine when stained Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Microscopic Examination of Microorganisms, cont.
Examining microorganisms in a living state Allows visualization of movement Helpful in identification of certain motile microorganisms Example: Trichomonas vaginalis Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Microscopic Examination of Microorganisms, cont.
Microorganisms suspended in liquid medium Microorganisms are free to move about Wet mount: most common method used Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Wet Mount Method MA prepares slide
Drop of fluid containing organism: placed on glass slide Covered with coverslip Coverslip ringed with petroleum jelly Provides seal Reduces rate of evaporation Evaporation could lead to drying out of slide and death of specimen Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Wet Mount Method, cont. Slide placed under microscope
Examined under high power by physician Slide discarded in biohazard sharps container Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Smears Smear: material spread on a slide for microscopic examination

Smears, cont. Prepared: Directly from specimen swab Specimen first grown on culture medium Most smears must be stained before viewing under microscope Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Smears, cont. Smears can be prepared and examined immediately
Helpful when time is a factor Provides a preliminary clue While more time-consuming tests are being performed Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Gram Stain Used in combination with other tests: to diagnose and treat infectious diseases Bacteria in a smear are colorless Makes them difficult to identify Staining allows for direct viewing of bacteria Size Shape Growth patterns Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Gram Stain, cont. Discovered by Christian Gram in 1883
Differentiates bacteria on basis of their color reactions to various stains Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Gram Stain, cont. Gram-positive bacteria: exhibit a purple color When treated with purple crystal violet dye: gram-positive bacteria permanently retain this dye Courtesy Cathy Bissonette Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Gram Stain, cont. Gram-negative bacteria: exhibit pink or red color Gram-negative bacteria are unable to retain purple dye: are counterstained with a red dye Staining characteristics of bacteria: Caused by differences in the chemical composition of bacterial cell walls From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Gram Stain, cont. Infectious diseases caused by gram-positive bacteria: Streptococcal sore throat Scarlet fever Rheumatic fever Diphtheria Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Gram Stain, cont. Infectious diseases caused by gram-negative bacteria: Whooping cough Gonorrhea Meningitis From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Gram Stain, cont. Bacillary dysentery Cholera Typhoid fever Plague From Mahon CR, Manuselis G Jr: Textbook of diagnostic microbiology, ed 2, Philadelphia, 2000, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Gram Stain, cont. Categories of gram-stained bacteria
Gram-positive rods Gram-negative rods Gram-positive cocci Gram-negative cocci Example: gonorrhea caused by a gram-negative diplococcus Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Prevention and Control of Infectious Diseases
Practice good techniques of medical asepsis Obtain proper nutrition and rest Use good hygienic measures Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Prevention and Control of Infectious Diseases, cont.
Infected individuals should contact their physicians to ensure early diagnosis and treatment MA responsible for educating community members Practices that reduce transmission of pathogens Practices that control and prevent infectious diseases Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Posttest True or False Microorganisms that reside in the body but do not cause disease are known as transient flora. The invasion of the body by a pathogenic microorganism is known as infection. The interval of time between the invasion by a pathogen and the first symptoms of disease is known as the prodromal period. Staphylococcal infections usually result in pus formation. E. coli normally reside in the urinary tract. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

Posttest, cont. True or False
The high-power objective has a magnification of 40×. Examination of urine sediment requires the use of the oil immersion objective. A sequela to streptococcal sore throat is rheumatic fever. The purpose of sensitivity testing is to identify the type of microorganism present. When viewed under a microscope, gram-positive bacteria appear pink or red in color. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.

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