Quiz #4

Identify an organism as Streptococcus pneumoniae and state the reasons why when it is seen growing on a Blood agar plate with a Taxo P® disc containing optochin.

1. Isolation on Blood agar Pneumococci frequently require enriched media and increased CO2 tension for initial isolation. They are usually isolated on Blood agar and incubated in a candle jar (a closed container in which a lit candle is placed to remove O2 and increase CO2 ) at 37C. On Blood agar, colonies appear small, shiny, and translucent. They are surrounded by a zone of alpha hemolysis (see Fig. 5B). Due to autolysis with age, the colonies may show a depressed center with an elevated rim. 2. Optochin sensitivity Pneumococci are the only streptococci that are sensitive to the drug optochin (ethylhydrocupreine hydrochloride). This can be detected by a zone of inhibition around a Taxo P® disc (see Fig. 10), a paper disc containing the drug optochin, which is placed on the Blood agar plate prior to incubation. 3. Bile solubility test Most colonies of S. pneumoniae will dissolve within a few minutes when a drop of bile is placed upon them. 4. Gram stain of sputum Streptococcus pneumoniae will usually appear as encapsulated, Gram-positive, lancet-shaped diplococci.

Identify an organism as an Enterococcus and state the reasons why when it is seen growing in SF broth and on Bile Esculin agar.

1. SF broth SF broth contains sodium azide, which inhibits most bacteria other than enterococci. The enterococci will grow in SF broth and ferment the dextrose, turning the pH indicator from violet to a yellow-brown color. 2. Bile Esculin agar Unlike most bacteria, the enterococci will grow in the presence of the bile salts in the medium. They hydrolyze the esculin, producing esculetin which reacts with the iron salts in the medium turning the agar black. On blood agar, most strains of Enterococcus faecalis show gamma reaction on sheep blood agar, however some strains exhibit beta hemolysis. Colonies are usually 1-2 millimeters in diameter. Enterococci are also being identified using chemiluminescent labelled DNA probes complementary to species-specific bacterial ribosomal RNA (rRNA) sequences.

Identify an organism as a group A beta streptococcus (or Streptococcus pyogenes) and state the reasons why when it is seen growing on a Blood agar plate with a Taxo A® disc containing bacitracin.

1. Very small, white to grey colonies approximately 1mm in diameter. 2. A zone of beta hemolysis around 2-3mm in diameter surrounding each colony. There are two streptococcal hemolysins, streptolysin S and streptolysin O. Streptolysin O can be inactivated by oxygen so more distinct hemolysis can be seen by stabbing the agar several times. In this way, some of the organisms form subsurface colonies growing away from oxygen. Since both streptolysin S and streptolysin O are active in the stabbed area, a more clear zone of beta hemolysis can be seen. 3. Sensitivity to the antibiotic bacitracin found in a Taxo A® disc. Only the group A beta streptococci are sensitive to bacitracin, as shown by a zone of inhibition around a Taxo A® disc, a paper disc containing low levels of bacitracin. Other serologic groups of streptococci are resistant to bacitracin and show no inhibition around the disc.

Describe the appearance of a positive GC smear and indicate its significance in the diagnosis of gonorrhea.

A GC smear (gonococcus smear) is a Gram stain of urethral exudates in men and endocervical secretions in women and can be part of a presumptive diagnosis of gonorrhea. One looks for Gram-negative diplococci with flattened adjacent walls that are seen both inside and outside of polymorphonuclear leukocytes (see Fig. 1).This test is quite sensitive in symptomatic males but only 40-60% sensitive in symptomatic females. In asymptomatic males and females the Gram stain has a lower predictive value.

Recognize an organism as Staphylococcus aureus and state the reasons why after seeing the results of the following: a. a Blood agar plate with a novobiocin disc b. a Mannitol Salt agar plate c. a DNase agar plate d. a tube of citrated rabbit plasma e. a Staphyloslide® test

A. Staphylococci produce round, raised, opaque colonies 1-2mm in diameter. The novobiocin disc is used to detect sensitivity or resistance to the antibiotic novobiocin. Hemolysis - usually beta. Pigment - often creamy gold. B. Staphylococci are able to tolerate the high salt concentration found in Mannitol Salt agar and thus grow readily. If mannitol is fermented, the acid produced turns the phenol red pH indicator from red (alkaline) to yellow (acid). C. DNase agar contains 0.2% DNA. To detect DNase production, the plate is inoculated and incubated. After growth, the plate is flooded with 1N hydrochloric acid (HCl). DNase positive cultures show a distinct clear zone around the streak (see Fig. 1) where the DNA in the agar was broken down by the bacterial DNase. DNase negative cultures appear cloudy around the growth where the acid caused the DNA in the agar to precipitate out of solution. D. The staphylococcal enzyme coagulase will cause inoculated citrated rabbit plasma to gel or coagulate. The coagulase converts soluble fibrinogen in the plasma into insoluble fibrin. E. The Staphyloslide® Latex Test is an agglutination test that detects cell-bound coagulase (clumping factor) and/or Protein A. Approximately 97% of human strains of S. aureus possess both bound coagulase and extracellular coagulase. Approximately 95% of human strains of S. aureus possess Protein A on their cell surface (see Fig. 7). This test uses blue latex particles coated with human fibrinogen and the human antibody IgG. Mixing of the latex reagent with colonies of the suspected S. aureus having coagulase and/or Protein A bound to their surface causes agglutination of the latex particles.

State the results of N. gonorrhoeae and N. meningitidis for the oxidase test and for acid production from oxidation of the sugars glucose, maltose, sucrose, and lactose.

All Neisseria are oxidase positive. The oxidase test can be performed as in Lab 13 using a Taxo N® disc. A moistened Taxo N® disc can be placed on a growing culture and a blackening of the colonies surrounding the disc indicates a positive oxidase test (see Fig. 2). All oxidase-positive cultures would be Gram stained to confirm Gram-negative diplococci. The various species of Neisseria can be differentiated according to carbohydrate utilization patterns. Neisseria species do not produce acid from carbohydrate fermentation but rather by an oxidative pathway. These tests are done using a media with single carbohydrates ( glucose, maltose, sucrose, or lactose) and a pH indicator to detect acid. The medium seen today uses phenol red as a pH indicator. If the sugar is utilized, acid end products cause the phenol red pH indicator to turn yellow. N. gonorrhoeae produces acid from only glucose (see Fig. 5) whereas N. meningitidis produces acid from glucose and maltose

Define antibody and state where they are primarily found in the body.

Antibodies or immunoglobulins are specific protein configurations produced by B-lymphocytes and plasma cells in response to a specific antigen and capable of reacting with that antigen. Antibodies are produced in the lymphoid tissue and once produced, are found mainly in the plasma portion of the blood (the liquid fraction of the blood before clotting). Serum is the liquid fraction of the blood after clotting.

Name the most common obligate anaerobe to cause wound infections in humans, state its normal habitat, and name the most common type of infections it causes.

Bacteroides fragilis is the most common cause of anaerobic infections in humans. It is also a predominant organism of the normal human intestinal tract. It mainly causes wound infections. B. fragilis is a Gram-negative bacillus

Name the types of infections most commonly caused by coagulase-negative staphylococci other than Staphylococcus saprophyticus.

Clinically common species of staphylococci other than S. aureus are often referred to as coagulase-negative staphylococci. These staphylococci are normal flora of the skin and, as such, frequently act as opportunistic pathogens, especially in the compromised host. S. saprophyticus is a relatively common cause of urinary tract infections, especially in healthy young women, but is seldom isolated from other sources. The great majority of infections caused by other coagulase-negative staphylococci, including S. epidermidis, S. haemolyticus, and S. hominis, are associated with intravascular devices (prosthetic heart valves and intra-arterial or intravenous lines) and shunts. Also quite common are infections of prosthetic joints, wound infections, osteomyelitis associated with foreign bodies, and endocarditis.

Name the infection caused by Clostridium difficile, state its significance in health care-associated infections, and the significance of the overusage of antibiotics to its cause.

Clostridium difficile causes severe antibiotic-associated colitis and is an opportunistic Gram-positive, endospore-producing bacillus transmitted by the fecal-oral route. C. difficile is a common healthcare-associated infection (HAIs) and is the most frequent cause of health-care-associated diarrhea. C. difficile infection often recurs and can progress to sepsis and death. CDC has estimated that there are about 500,000 C. difficile infections (CDI) in health-care associated patients each year and is linked to 15,000 American deaths each year. Antibiotic-associated colitis is especially common in older adults. It is thought that C. difficile survives the exposure to the antibiotic by sporulation. After the antibiotic is no longer in the body, the endospores germinate and C. difficile overgrows the intestinal tract and secretes toxin A and toxin B that have a cytotoxic effect on the epithelial cells of the colon. C.difficile has become increasingly resistant to antibiotics in recent years making treatment often difficult. There has been a great deal of success in treating the infection with fecal transplants, still primarily an experimental procedure. Polymerase chain reaction (PCRs) assays, which test for the bacterial gene encoding toxin B, are highly sensitive and specific for the presence of a toxin-producing Clostridium difficile organism. The most successful technique in restricting C. difficile infections has been the restriction of the use of antimicrobial agents.

State the normal habitat of Clostridium perfringens and name an infection it may cause.

Clostridium perfringens, as well as other clostridial species, are normal flora of the intestinal tract of various animals and may cause gas gangrene. C. perfringens is a Gram-positive bacillus

Name four infections commonly caused by Enterococcus faecalis.

E. faecalis is normal flora of the intestinal tract in humans and is regularly isolated from infections within the peritoneal cavity (especially following penetrating trauma), urinary tract infections, kidney infections, prostate infections, and infections of damaged or compromised skin such as diabetic or decubitus ulcers, burns and surgical wounds. Other opportunistic enterococcal species include E. faecium and E. durans. The enterococci have become the second most common bacterium isolated from nosocomial urinary and wound infections, and the third most common cause of nosocomial bacteremia. Each year in the U.S., in fact, enterococci account for approximately 110,000 urinary tract infections, 40,000 wound infections, 25,000 cases of nosocomial bacteremia, and 1100 cases of endocarditis. Furthermore, the enterococci are among the most antibiotic resistant of all bacteria, with some isolates resistant to all known antibiotics.

State the Gram reaction and morphology of the enterococci.

Enterococci are Gram-positive streptococci that are normal flora of the intestinal tract. They typically occur singly, in pairs, short chains, and clusters, especially when taken off an agar culture for staining. Â Like the genus Streptococcus, the genus Enterococcus is catalase-negative. Enterococci responsible for a variety of opportunistic infections in humans, and serologically belong to Lancefield group D streptococci.

State the significance of Staphylococcus aureus enterotoxin, the exotoxin TSST-1, and the exotoxin exfoliatin.

Finally, S. aureus is frequently introduced into food by way of abscesses or the nasal cavity of food handlers. If it is allowed to grow and produces an enterotoxin, it can cause staphylococcal food poisoning. Virulence factors for S. aureus include exotoxins such as leukocidin (kills leukocytes), alpha and delta toxins (damage tissue membranes), microcapsules (resist phagocytic engulfment and destruction), coagulase and protein A (both help resist phagocytic engulfment). Some strains also produce TSST-1 (toxic shock syndrome toxin-1) and cause toxic shock syndrome, usually associated with wounds. Approximately 25% of all S. aureus strains are toxigenic and approximately 6000 gases of toxic shock syndrome occur each year in the U.S. Some strains also produce exfoliatin, an exotoxin that causes scalded skin syndrome, an infection usually seen in infants and young children.

Identify an organism as N. gonorrhoeae or N. meningitidis and state the reasons why when it is seen growing on MTM Chocolate agar with a Taxo N® (oxidase) disc and in in carbohydrate utilization tubes containing the sugars glucose, maltose, sucrose, and lactose.

MTM Chocolate agar is selective for Neisseria. The medium contains enrichment factors to promote the growth of Neisseria. In addition, it contains antibiotics to inhibit normal body flora: vancomycin to inhibit Gram-positive bacteria; colistin to inhibit Gram-negative bacteria; trimethoprim to suppress Proteus; and nystatin to inhibit yeast. The "chocolate" color is due to the hemoglobin enrichment added to the medium. Plates are then incubated under increased carbon dioxide tension as mentioned above. (Transgrow Medium is a convenient flask containing MTM Chocolate agar and CO2.) N. gonorrhoeae forms small, convex, grayish-white to colorless, mucoid colonies in 48 hours at 35-37°C. The various species of Neisseria can be differentiated according to carbohydrate utilization patterns. Neisseria species do not produce acid from carbohydrate fermentation but rather by an oxidative pathway. These tests are done using a media with single carbohydrates ( glucose, maltose, sucrose, or lactose) and a pH indicator to detect acid. The medium seen today uses phenol red as a pH indicator. If the sugar is utilized, acid end products cause the phenol red pH indicator to turn yellow. N. gonorrhoeae produces acid from only glucose whereas N. meningitidis produces acid from glucose and maltose

State the Lancefield group of streptococcus that is the most common cause of acute streptococcal infections in humans and name five other Lancefield groups that frequently cause human infections.

Many of the streptococci can also be classified under the Lancefield system. In this case, they are divided into 19 different serologic groups on the basis of carbohydrate antigens in their cell wall. These antigenic groups are designated by the letters A to H, K to M, and O to V. Lancefield serologic groups A, B, C, D, F, and G are the ones that normally infect humans, however, not all pathogenic streptococci can be identified by Lancefield typing (e.g., Streptococcus pneumoniae). Lancefield serologic groups A, B, C, D, F, and G are all streptococci that may show beta hemolysis on Blood agar. However, some group B streptococci are non-hemolytic and group D streptococci (discussed below) usually show alpha hemolysis or are non-hemolytic.

State the correct scientific names for the gonococcus and the meningococcus and indicate what disease each causes.

Neisseria gonorrhoeae (the gonococcus), causes gonorrhea. Neisseria meningitidis (the meningococcus) is the causative organism of meningococcal (epidemic) meningitis.

Name three infections the group B streptococci may cause in adults.

Other infections associated with group B streptococci include urinary tract infections, skin and soft tissue infections, osteomyelitis, endometritis, and infected ulcers (decubitus ulcers and ulcers associated with diabetes). In the immunocompromised patient it sometimes causes pneumonia and meningitis.

State the natural habitat of Streptococcus pneumoniae and name four infections it may cause in humans.

Pneumococci are frequently found as normal flora of the nasopharynx of healthy carriers. Pharyngeal colonization occurs in 40%-50% of healthy children and 20%-30% of healthy adults. Worldwide, as well as in the U.S., S. pneumoniae remains the most common cause of community-acquired pneumonia, otitis media, bacteremia, and bacterial meningitis. In the U.S., pneumococci are the most common cause of community-acquired pneumonia requiring hospitalization, causing an estimated 500,000 cases per year and usually occuring as a secondary infection in the debilitated or immunocompromised host. The pneumococci also cause between 6 and 7 million cases of otitis media per year, are the leading cause of sinusitis in people of all ages, are responsible for 55,000 cases of bacteremia, and 3000 cases of meningitis, being the most common cause of meningitis in adults and children over 4 years of age. The capsule serves as the major virulence factor, enabling the pneumococcus to resist phagocytic engulfment, and glycopeptides from its Gram-positive cell wall can lead to excessive cytokine production and a massive inflammatory response.

Describe 1 way of producing known antiserum.

Preparation of known antiserum in animals involves inoculating animals with specific known antigens such as a specific strain of a bacterium. After the animal's immune responses have had time to produce antibodies against that antigen, the animal is bled and the blood is allowed to clot. The resulting liquid portion of the blood is the serum and it will contain antibodies specific for the injected antigen. However, one of the problems of using antibodies prepared in animals (by injecting the animal with a specific antigen and collecting the serum after antibodies are produced) is that up to 90% of the antibodies in the animal's serum may be antibodies the animal has made "on its own" against environmental antigens, rather than those made against the injected antigen. The development of monoclonal antibody technique has largely solved that problem.

Name and describe three types of abscesses caused by Staphylococcus aureus.

S. aureus causes pus-filled inflammatory lesions known as abscesses. Depending on the location and extent of tissue involvement, the abscess may be called: 1. a pustule A pustule is an infected hair follicle where the base of the hair follicle appears red and raised with an accumulation of pus just under the epidermis. Infected hair follicles are also referred to as folliculitis. 2. a furuncle or boil Furuncles appear as large, raised, pus-filled, painful nodules having an accumulation of dead, necrotic tissue at the base. The bacteria spread from the hair follicle to adjacent subcutaneous tissue. 3. a carbuncle Carbuncles occur when furuncles coalesce and spread into surrounding subcutaneous and deeper connective tissue. Superficial skin perforates, sloughs off, and discharges pus.

Define direct serologic testing and indirect serologic testing.

Serologic testing may be used in the clinical laboratory in two distinct ways: a. To identify unknown antigens (such as microorganisms). This is called direct serologic testing. Direct serologic testing uses a preparation known antibodies, called antiserum, to identify an unknown antigen such as a microorganism. b. To detect antibodies being made against a specific antigen in the patient's serum. This is called indirect serologic testing. Indirect serologic testing is the procedure by which antibodies in a person's serum being made by that individual against an antigen associated with a particular disease are detected using a known antigen.

Define serology.

Serology refers to using antigen-antibody reactions in the laboratory for diagnostic purposes. Its name comes from the fact that serum, the liquid portion of the blood where antibodies are found is used in testing. Serologic testing may be used in the clinical laboratory in two distinct ways

State the Gram reaction and morphology of all staphylococci.

Staphylococci (see Fig. 6) are often found in the human nasal cavity (and on other mucous membranes) as well as on the skin. They are Gram-positive cocci 0.5-1.0 µm in diameter and occur singly, in pairs, in short chains, and most commonly, in irregular grape-like clusters. The staphylococci are strongly catalase positive and generally tolerate relatively high concentrations of sodium chloride (7.5-10%). This ability is often employed in preparing media selective for staphylococci. Staphylococcal capsules play a major role in the ability of the bacteria to adhere to and colonize biomaterials.

State the genus and species of the pneumococcus.

Streptococcus pneumoniae, or the pneumococcus, is a lancet-shaped (pointed like a lance) Gram-positive coccus 0.6-1.2 µm in diameter.

State the Gram reaction and morphology of Streptococcus pneumoniae.

Streptococcus pneumoniae, or the pneumococcus, is a lancet-shaped (pointed like a lance) Gram-positive coccus 0.6-1.2 µm in diameter. They typically appear as a diplococcus, but occasionally appear singularly or in short chains.

State what the term "group A beta" means when referring to streptococci.

Streptococcus pyogenes, often referred to as group A beta streptococci or GAS because they belong to Lancefield serologic group A and show beta hemolysis on blood agar, are responsible for most acute human streptococcal infections.

State the genus and species of the group A beta streptococci.

Streptococcus pyogenes. S. pyogenes isolates are Gram-positive cocci 0.5-1.0 µm in diameter that typically form short chains in clinical specimens and longer chains in laboratory media.

Define antigen

Technically, an antigen is defined as a substance that reacts with antibody molecules and antigen receptors on lymphocytes. An immunogen is an antigen that is recognized by the body as nonself and stimulates an adaptive immune response. For simplicity, both antigens and immunogens are usually referred to as antigens. Chemically, antigens are large molecular weight proteins (including conjugated proteins such as glycoproteins, lipoproteins, and nucleoproteins) and polysaccharides (including lipopolysaccharides). These protein and polysaccharide antigens are found on the surfaces of viruses and cells, including microbial cells (bacteria, fungi, protozoans) and human cells

State the normal habitat of the viridans streptococci and name three infections they may cause in humans.

Ten species of streptococci are known as the viridans streptococci. They are the dominant normal flora in the upper respiratory tract. Species include S. mutans, S. sanguis, S. mitis, and S. salivarius. S. mutans is the primary cause of dental caries. Viridans streptococci are responsible for between 50% and 70% of the cases of bacterial endocarditis, especially in people with previously damaged heart valves. They are also frequently associated with bacteremia, deep wound infections, dental abscesses, and abscesses of internal organs. The viridans streptococci show alpha hemolysis or no hemolysis on Blood agar, do not possess Lancefield group antigens, and can be differentiated from other alpha streptococci by biochemical testing.

State the principle and the general procedure behind indirect serologic testing.

The concept and general procedure for indirect serologic testing. The concept and general procedure for this type of serological testing are as follows: •Concept: This type of testing is based on the fact that antibodies are only produced in response to a specific antigen. In other words, a person will not be producing antibodies against a disease antigen unless that antigen is in the body stimulating antibody production. •General Procedure: A sample of the patient's serum (the liquid portion of the blood after clotting and containing antibodies against the disease antigen if the person has or has had the disease) is mixed with the known antigen for that suspected disease. One then looks for an antigen-antibody reaction. Examples of serologic tests to diagnose disease by the detection of antibodies in the patient's serum include the various serological tests for syphilis or STS (such as the RPR, the VDRL, and the FTA-ABS tests), the tests for infectious mononucleosis, the tests for the Human Immunodeficiency Virus (HIV), the tests for systemic lupus erythematosus, and tests for variety of other viral infections.

Describe the concept and general procedure for using serologic testing to identify unknown antigens (direct serologic testing).

The concept and general procedure for using antigen-antibody reactions to identify unknown antigens are as follows: •Concept: This testing is based on the fact that antigen- antibody reactions are very specific. Antibodies usually react only with the antigen that stimulated their production in the first place, and are just as specific as an enzyme-substrate reaction. Because of this, one can use known antiserum (prepared by animal inoculation or monoclonal antibody technique as discussed above) to identify unknown antigens such as a microorganism. • General Procedure: A suspension of the unknown antigen to be identified is mixed with known antiserum for that antigen. One then looks for an antigen-antibody reaction.

Name four possible extragenital Neisseria gonorrhoeae infections.

The gonococcus may also cause extragenital infections such as pharyngitis (from oral-genital sex), ophthalmia (from inoculation of the eyes with contaminated fingers), and proctitis (from anal sex). In 1% - 3% of infected women and a lower percentage of infected males, the organism invades the blood and disseminates, causing a rash, septic arthritis, endocarditis, and/or meningitis. Dissemination occurs more frequently in females. Congenital gonorrhea is known as ophthalmia neonatorum and occurs as a result of the eyes of newborns becoming infected as the baby passes through the birth canal.

State the normal habitat of the group B streptococci, name three infections they may cause in newborns, and describe how the infants become colonized.

The group B streptococci (GBS or Streptococcus agalactiae) usually show a small zone of beta hemolysis on Blood agar, although some strains are non-hemolytic. S. agalactiae isolates are Gram-positive cocci 0.6-1.2 µm in diameter that typically form short chains in clinical specimens and longer chains in laboratory media. They are found in the gastrointestinal tract and genitourinary tract of 15%-45% healthy woman. This reservoir, along with nosocomial transmission, provides the inoculum by which many infants are colonized at birth. The transmission rate from a mother colonized with GBS to her baby is thought to be around 50%. Most colonized infants (and adults) remain asymptomatic, however, an estimated 1-2% of neonates colonized will develop invasive GBS diseases, including pneumonia, septicemia, and/or meningitis. Pregnant women should be tested to determine if they are GBS carriers and be given IV antibiotics if they are a carrier

State the most common infection caused by Streptococcus pyogenes and name six other infections it may cause.

The most common infection is pharyngitis(streptococcal sore throat) with the organism usually being limited to the mucous membranes and lymphatic tissue of the upper respiratory tract. From the pharynx, however, the streptococci sometimes spread to other areas of the respiratory tract resulting in laryngitis, bronchitis, pneumonia, and otitis media (ear infection). Occasionally, it may enter the lymphatic vessels or the blood and disseminate to other areas of the body, causing septicemia, osteomyelitis, endocarditis, septic arthritis, and meningitis. It may also infect the skin, causing erysipelas, impetigo, or cellulitis.

List two pathogenic species of Mycobacterium and name the infection that each causes.

The most common species of Mycobacterium to cause human infections are M. tuberculosis, M. leprae, M. avium complex, M. kansasii, M. fortuitum, M. chelonae, and M. abscessus. M. tuberculosis is the causative organism of tuberculosis, M. leprae causes leprosy. The other species of Mycobacterium occasionally cause tuberculosis-like infections, especially in the debilitated or immunosuppressed host.

Discuss one characteristic common to the genus Mycobacterium which allows us to distinguish this organism from most other genera of bacteria.

The mycobacteria are rod-shaped bacteria generally 0.4 by 3.0 µm in size that are said to be acid-fast. This means that because of their unique cell wall, when they are stained by the acid-fast procedure, they will resist decolorization with acid-alcohol and stain red, the color of the initial stain, carbol fuchsin. With the exception of a very few other acid-fast bacteria such as Nocardia, all other bacteria will be decolorized and stain blue (the color of the counterstain, methylene blue). The acid-fast stain is an important test for the genus Mycobacterium. Fluorescent microscopy staining may also be used to identify Mycobacterium.

State the Gram reaction and the morphology of the neisseriae.

The neisseriae are a group of Gram-negative diplococci 0.6-1.5 µm in diameter

Give the normal habitat for Neisseria meningitidis and briefly describe how it reaches the meninges.

There are between 2000 and 3000 cases of meningococcal meningitis per year in the U.S. Approximately 50% of the cases occur in children between 1 and 4 years old. N. meningitidis infects the nasopharynx of humans causing a usually mild or subclinical upper respiratory infection. Colonization of the nasopharynx may persist for months. However, in about 15% of these individuals, the organism invades the blood and disseminates, leading septicemia and from the there may cross the blood-brain barrier causing meningitis. A petechial skin rash, caused by endotoxin in the blood, appears in about 75 percent of the septic cases and fatality rates for meningococcal septicemia are as high as 30 percent as a result of the shock cascade. A fulminating form of the disease, called Waterhouse-Frederichsen syndrome, can be fatal within several hours due to massive intravascular coagulation and resulting shock, probably a result of massive endotoxin release. N. meningitidis is especially dangerous in young children.

Name three common clinically important species of Staphylococcus and state which species is most pathogenic.

There are five species of staphylococci commonly associated with clinical infections: Staphylococcus aureus, S. epidermidis, S. haemolyticus, S. hominis and S. saprophyticus. Staphylococcus aureus is the most pathogenic species and is implicated in a variety of infections. S. aureus is with some frequency found as normal human flora in the anterior nares (nostrils). It can also be found in the throat, axillae, and the inguinal and perineal areas. Approximately 30% of adults and most children are healthy periodic nasopharyngeal carriers of S. aureus. Around 15% of healthy adults are persistent nasopharyngeal carriers. The colonization rates among health care workers, patients on dialysis, and people with diabetes are higher than in the general population.

Define titer.

Titer indicates how far you can dilute the patient's serum and still have it contain enough antibodies to give a detectable antigen-antibody reaction.

State the Gram reaction and morphology of the streptococci.

Gram-positive cocci 0.5-1.0 µm in diameter, typically occurring in pairs and chains of varying length when grown in a liquid medium, and often occurring singly, in pairs, short chains, and clusters when taken from an agar culture. they are both catalase-negative. usually isolated on Blood agar.

Name two autoimmune diseases associated with the group A beta streptococci.

Group A beta streptococcus infections can result in two autoimmune diseases, rheumatic fever and acute glomerulonephritis, where antibodies made against streptococcal antigens cross react with joint membranes and heart valve tissue in the case of rheumatic fever, or glomerular cells and basement membranes of the kidneys in the case of acute glomerulonephritis.

Describe alpha hemolysis, beta hemolysis, and gamma reaction on Blood agar plates.

Hemolysis refers to is the lysis of the red blood cells in the agar surrounding bacterial colonies and is a result of bacterial enzymes called hemolysins. Beta hemolysis refers to a clear, red blood cell-free zone surrounding the colony, where a complete lysis of the red blood cells by the bacterial hemolysins has occurred. This is best seen in subsurface colonies where the agar has been stabbed since some bacterial hemolysins, like streptolysin O, are inactivated by oxygen. Alpha hemolysis appears as a zone of partial hemolysis surrounding the colony, often accompanied by a greenish discoloration of the agar. This is also best seen in subsurface colonies where the agar has been stabbed. Gamma reaction refers to no hemolysis or discoloration of the agar surrounding the colony

Describe the appearance of C. perfringens when it is anaerobically-grown on Blood agar and in Litmus Milk.

In anaerobically-grown Litmus Milk cultures, enzymes of C. perfringens will attack the proteins and carbohydrates of the milk producing a "stormy fermentation" with acid production (litmus turns pink), clotting of milk proteins, and gas formation

State the sources and the portal of entry for most Staphylococcus aureus infections.

In the majority of S. aureus infections the source of the organism is either: • a healthy nasal carrier, or •contact with an abscess from an infected individual. The portal of entry is usually the skin.

State the difference between a qualitative serological test and a quantitative serological test.

Indirect serologic tests may be qualitative or quantitative. A qualitative test only detects the presence or absence of specific antibodies in the patient's serum and is often used for screening purposes. A quantitative test gives the titer or amount of that antibody in the serum. Titer indicates how far you can dilute the patient's serum and still have it contain enough antibodies to give a detectable antigen-antibody reaction. In other words, the more antibodies being produced by the body, the more you can dilute the person's serum and still see a reaction. Quantitative serological tests are often used to follow the progress of a disease by looking for a rise and subsequent drop in antibody titer.

Describe how symptoms of gonorrhea differ in the male and in the female.

It is estimated that there are approximately 2,000,000 cases of gonorrhea per year in the U.S. Infection usually occurs following sexual contact, with the incubation period averaging 2-7 days. In males, the gonococcus typically invades the anterior urethra, usually producing a purulent discharge, pain upon urination, and a frequency of urination. Approximately 5-10% of infected males are asymptomatic but will still be infectious. The infection may spread up the reproductive tract, infecting the prostate, vas deferens, epididymis, and testes, causing painful inflammation and scar tissue formation that can result in sterility. In females, 30-50 percent of those initially infected are asymptomatic or show mild symptoms. They are, however, still infectious. Initially, the organism invades the cervix, the urethra, and frequently the rectum. In about 15 percent of the cases, the organism spreads up the reproductive tract and infects the fallopian tubes causing pelvic inflammatory disease (PID). The resulting inflammation and scar tissue formation may result in sterility or abnormal (ectopic or tubal) pregnancies.

Name four systemic Staphylococcus aureus infections.

Less commonly, S. aureus may escape from the local lesion and spread through the blood to other body areas, causing a variety of systemic infections that may involve every system and organ. Such systemic infections include septicemia, septic arthritis, endocarditis, meningitis, and osteomyelitis, as well as abscesses in the lungs, spleen, liver, and kidneys. S. aureus pneumonia may also be a secondary respiratory complication of viral infections such as measles, and influenza and is a frequent cause of nosocomial pneumonia in patients who are debilitated.

State the significance of Mycobacterium avium complex (MAC).

M. avium complex (MAC) frequently causes systemic infections in people with HIV/AIDS

Define antiserum.

a preparation known antibodies, called antiserum