Which strep species is seen primarily in pairs

Among S. By contrast, the strains of H. Rather than direct tissue damage by these pathogens, bacterial components such as lipopolysaccharide LPS in gram-negative pathogens induce an inflammatory response that causes swelling, pus, and tissue damage within the middle ear Figure 3. Figure 3. Any blockage of the eustachian tubes, with or without infection, can cause fluid to become trapped and accumulate in the middle ear. This is referred to as otitis media with effusion OME.

The accumulated fluid offers an excellent reservoir for microbial growth and, consequently, secondary bacterial infections often ensue. This can lead to recurring and chronic earaches, which are especially common in young children. The higher incidence in children can be attributed to many factors. Children have more upper respiratory infections, in general, and their eustachian tubes are also shorter and drain at a shallower angle.

Young children also tend to spend more time lying down than adults, which facilitates drainage from the nasopharynx through the eustachian tube and into the middle ear. Bottle feeding while lying down enhances this risk because the sucking action on the bottle causes negative pressure to build up within the eustachian tube, promoting the movement of fluid and bacteria from the nasopharynx.

Diagnosis is typically made based on clinical signs and symptoms, without laboratory testing to determine the specific causative agent. Antibiotics are frequently prescribed for the treatment of AOM. High-dose amoxicillin is the first-line drug, but with increasing resistance concerns, macrolides and cephalosporin s may also be used.

Vaccination against influenza has also been shown to decrease the risk for AOM, likely because viral infections like influenza predispose patients to secondary infections with S.

Although there is a conjugate vaccine available for the invasive serotype B of H. Because unencapsulated strains of H. The microbial community of the nasopharynx is extremely diverse and harbors many opportunistic pathogens, so it is perhaps not surprising that infections leading to rhinitis and sinusitis have many possible causes. These conditions often occur as secondary infections after a viral infection, which effectively compromises the immune defenses and allows the opportunistic bacteria to establish themselves.

Bacterial sinusitis involves infection and inflammation within the paranasal sinuses. Because bacterial sinusitis rarely occurs without rhinitis, the preferred term is rhinosinusitis.

The most common causes of bacterial rhinosinusitis are similar to those for AOM, including S. Figure 4. The pseudomembrane in a patient with diphtheria presents as a leathery gray patch consisting of dead cells, pus, fibrin, red blood cells, and infectious microbes. The causative agent of diphtheria , Corynebacterium diphtheriae , is a club-shaped, gram-positive rod that belongs to the phylum Actinobacteria. Diphtheroids are common members of the normal nasopharyngeal microbiota.

However, some strains of C. Diphtheria is typically a respiratory infection of the oropharynx but can also cause impetigo-like lesions on the skin. Although the disease can affect people of all ages, it tends to be most severe in those younger than 5 years or older than 40 years. Like strep throat, diphtheria is commonly transmitted in the droplets and aerosols produced by coughing. After colonizing the throat, the bacterium remains in the oral cavity and begins producing the diphtheria toxin.

An accumulation of grayish exudate consisting of dead host cells, pus, red blood cells, fibrin, and infectious bacteria results in the formation of a pseudomembrane. The pseudomembrane can cover mucous membranes of the nasal cavity, tonsils, pharynx, and larynx Figure 4.

This is a classic sign of diphtheria. As the disease progresses, the pseudomembrane can enlarge to obstruct the fauces of the pharynx or trachea and can lead to suffocation and death. Sometimes, intubation , the placement of a breathing tube in the trachea, is required in advanced infections.

If the diphtheria toxin spreads throughout the body, it can damage other tissues as well. This can include myocarditis heart damage and nerve damage that may impair breathing. The presumptive diagnosis of diphtheria is primarily based on the clinical symptoms i. Broad-spectrum antibiotics like penicillin and erythromycin tend to effectively control C. Regrettably, they have no effect against preformed toxins.

If toxin production has already occurred in the patient, antitoxins preformed antibodies against the toxin are administered. Although this is effective in neutralizing the toxin, the antitoxins may lead to serum sickness because they are produced in horses see Hypersensitivities. Widespread vaccination efforts have reduced the occurrence of diphtheria worldwide.

There are currently four combination toxoid vaccines available that provide protection against diphtheria and other diseases: DTaP, Tdap, DT, and Td. If capitalized, the letters indicate a full-strength dose; lowercase letters indicate reduced dosages.

According to current recommendations, children should receive five doses of the DTaP vaccine in their youth and a Td booster every 10 years. Children with adverse reactions to the pertussis vaccine may be given the DT vaccine in place of the DTaP. Pneumonia is a general term for infections of the lungs that lead to inflammation and accumulation of fluids and white blood cells in the alveoli.

Pneumonia can be caused by bacteria, viruses, fungi, and other organisms, although the vast majority of pneumonias are bacterial in origin. Bacterial pneumonia is a prevalent, potentially serious infection; it caused more 50, deaths in the United States in In addition, pneumonia can lead to pleurisy , an infection of the pleural membrane surrounding the lungs, which can make breathing very painful. Although many different bacteria can cause pneumonia under the right circumstances, three bacterial species cause most clinical cases: Streptococcus pneumoniae , H.

In addition to these, we will also examine some of the less common causes of pneumonia. Figure 5. A chest radiograph of a patient with pneumonia shows the consolidations lesions present as opaque patches. The most common cause of community-acquired bacterial pneumonia is Streptococcus pneumoniae.

This gram-positive, alpha hemolytic streptococcus is commonly found as part of the normal microbiota of the human respiratory tract. The cells tend to be somewhat lancet-shaped and typically appear as pairs Figure 6. The pneumococci initially colonize the bronchioles of the lungs. Other virulence factors include autolysin s like Lyt A, which degrade the microbial cell wall, resulting in cell lysis and the release of cytoplasmic virulence factors.

One of these factors, pneumolysin O , is important in disease progression; this pore-forming protein damages host cells, promotes bacterial adherence, and enhances pro-inflammatory cytokine production. The resulting inflammatory response causes the alveoli to fill with exudate rich in neutrophils and red blood cells. As a consequence, infected individuals develop a productive cough with bloody sputum.

Figure 6. Pneumococci can be presumptively identified by their distinctive gram-positive, lancet-shaped cell morphology and diplococcal arrangement. In blood agar cultures, the organism demonstrates alpha hemolytic colonies that are autolytic after 24 to 48 hours.

In addition, S. All clinical pneumococcal isolates are serotyped using the quellung reaction with typing antisera produced by the CDC. Positive quellung reactions are considered definitive identification of pneumococci.

Antibiotics remain the mainstay treatment for pneumococci. However, S. There are currently two pneumococcal vaccines available: pneumococcal conjugate vaccine PCV13 and pneumococcal polysaccharide vaccine PPSV These are generally given to the most vulnerable populations of individuals: children younger than 2 years and adults older than 65 years. Figure 7. Culture of Haemophilus influenzae on a chocolate agar plate. Encapsulated strains of Haemophilus influenzae are known for causing meningitis, but nonencapsulated strains are important causes of pneumonia.

This small, gram-negative coccobacillus is found in the pharynx of the majority of healthy children; however, Haemophilus pneumonia is primarily seen in the elderly. Like other pathogens that cause pneumonia, H. A fastidious organism, H. Serotyping must be performed to confirm identity of H. Infections of the alveoli by H. Resistance to the fluoroquinolones is rare among isolates of H. As discussed for AOM, a vaccine directed against nonencapsulated H. Elizabeth is a 6-year old who developed a serious cough that would not seem to go away.

After 2 weeks, her parents became concerned and took her to the pediatrician, who suspected a case of bacterial pneumonia. Tests confirmed that the cause was Haemophilus influenzae. Quality Control Quality controls, positive and negative reactions are determined each day the test is determined.

AccuProbe- Pneumococcus Test Principle The AccuProbe- Pneumococcus test is used to aid in the identification of atypical pneumococci and to help differentiate between viridans Streptococcus strains. Acid Formation in Carbohydrate Broths Principle The ability of bacteria to form acid in some carbohydrate broths and not in others can be used in identification schemes.

If the bacteria acidify the carbohydrate, the pH will change and the indicator brom cresol purple will turn yellow. Most of the carbohydrate broths are commercially available Remel. An asterisk indicates those that are made by CDC media lab. Pipet Procedure Inoculate carbohydrate broth tube with drops of inoculum. Fastidious organisms may be held up to 14d. Reading and Interpretation A positive reaction is recorded when the broth turns yellow. A negative reaction is when no color change occurs.

A definite color change that is not quite yellow may be interpreted as a weak positive reaction. Limitations Do not incubate in CO 2 as this may alter the pH. Quality Control Each lot and shipment of carbohydrate broth medium is tested for positive and negative reactions upon receipt in the laboratory.

The strains and reactions for each broth are listed below. This hydrolysis results in an alkaline change in the media results in a color change in the media. This test can be used for differentiated different bacteria. Inoculum A drop of Todd Hewitt broth culture grown overnight is the preferred inoculum. Alternatively a suspension in Todd Hewitt broth from growth on a plate or a tiny amount of growth from a plate may be used as the inoculum. The medium is commercially available.

Some fastidious organism may be held up to 14d. Reading and Interpretation A positive reaction is recorded with the broth turns a deep purple color indicating an alkaline reaction, NH 3 is released. The development of a yellow color or no change in color of the broth indicates a negative reaction. Quality Control Each new lot and shipment of medium is tested for positive and negative reactions.

Top of Page Bacitracin Test Principle The bacitracin disk is sensitivity test used to differentiate the beta- hemolytic Streptococcus. Tap disk lightly to ensure that it adheres to the agar. Reading and Interpretation Any zone of inhibition is considered a positive test or sensitive test.

Growth to the edge of the disk is interpreted as a negative test or resistant test. Limitations Quality Control Quality Control is performed on each shipment and lot of bacitracin disk.

Streptococcus pyogenes is the positive sensitive control and Enterococcus faecalis SS is the resistant or negative control. Results are recorded in the QC log book. Bile Esculin Test Principle A selective and differential medium used in the identification of catalase-negative bacteria. The selective agent bile, inhibits most gram positive bacteria.

The enterococci and Streptococcus bovis will grow. Esculin in the medium is hydrolyzed to esculetin and dextrose. The esculetin reacts with ferric chloride in the media to form a black-brown color. An inoculating loopful of culture may also be used. Reagents and Materials Bile esculin slant Remel Procedure Inoculate tube with 1 drop of inoculum allowing drop to run down slant. Alternatively, the slant may be inoculated with a loopful of growth from a blood agar plate.

Reading and Interpretation The bile esculin test is positive when a black color forms over one-half or more of the slant. If no blackening occurs the test is negative. Limitations Do not incubate medium in a carbon dioxide atmosphere.

The increase in C0 2 will cause the viridans streptococci to grow better and increase the likelihood of a positive BE reaction. Streptococcus bovis and enterococci do not require C0 2 for good growth.

Quality Control Positive and negative reactions are determined on each new lot and shipment of media. Enterococcus faecalis strain SS is used for positive control reactions and Streptococcus sanguinis strain SS is used for negative control reactions.

A turbidity equal to that of 1. After a satisfactory density is achieved, divide the suspension into 2 tubes with approximately 0. Add 0. Mix by vigorous shaking. Reading and Interpretation Examine for clearing of the turbidity periodically. A clearing of the turbidity in the bile tube but not in the saline control tube indicates a positive test, i. If the tube containing the cells and bile have not cleared the test is negative. On occasion some strains of pneumococci are only partially soluble in the bile salts, that is, a partial clearing occurs.

These strains must have the proper zone of inhibition around the optochin test to be called pneumococci. Partially soluble strains with zones of inhibition of less than 14 mm are not considered pneumococci. Limitations The turbidity must be sufficient to detect a difference in the saline control tube. Quality Control Each new lot of deoxycholate is tested for positive and negative reactions with S. Results are recorded in QC log book.

Top of Page Camp Test Principle Some bacteria produce CAMP factor a diffusible extracelluar protein that synergistically acts with the beta-lysin of Staphylococcus aureus and enhances the lysis of red blood cells.

Inoculum Growth from a blood agar plate or any solid media. Strain SS Strep. A single colony of the unknown strain beta hemolytic streptococci is picked up with an inoculating loop and used to make a single streak perpendicular but not touching the S. A mm space should remain between the streaks. Reading and Interpretation This enhanced activity is in the shape of an arrowhead at the juncture of the two streaks, with the widest portion of the arrowhead on the group B side.

Limitations Do not incubate in an anaerobic environment or under CO 2. Some S. Therefore it is necessary to test a known group B streptococcus for CAMP reaction as a positive control on each test plate.

Group B streptococcus strain SS should be used as a positive control on each test plate. Inoculum Cultures that are grown on a blood free media or a colony grown on a blood agar plate that is carefully transferred to a slide without carry-over of any of the erythrocytes. Reagents and Materials Three percent hydrogen peroxide is obtained from a commercial drug store.

Pipet Slides Procedure The catalase test is best performed by flooding the growth of the bacteria usually on an agar slant but blood free agar plates can be used in question with 1.

The bacteria must be grown on blood free medium. Modifications of the catalase test may be performed by very carefully removing a colony of growth from a blood agar plate with a plastic needle or wooden applicator stick and transferring the colony to a glass slide.

Reading and Interpretation Any sign of bubbling is interpreted as a positive test. The absence of bubbling is interpreted as negative. Limitations False positive results will result if any red bloods cell are transferred. Weak positive results should be repeated on a blood free medium.

The catalase test gives the majority of differentiations very efficiently, however, there will be occasions when the catalase test and colony morphology will be misleading. Quality Control The catalase quality control is performed once per lot and shipment. For positive reaction use a blood-free culture of Staphylococcus aureus : i. Record in QC manual. This resistance is useful in differentiating the Lactococcus species. Reading and Interpretation Any zone of inhibition around the disk is considered sensitive.

Limitations Quality Control The quality control is tested with each lot and shipment. Lactococcus lactis is used for the negative control Sensitive and L. Top of Page Esculin Hydrolysis Principle A differential medium used in the identification of catalase-negative bacteria.

An inoculating loopful of culture from a blood agar plate may also be used. Reagents and Materials Esculin slant Remel Procedure Inoculate slant tube with drops of inoculum allowing drop to run down slant. Reading and Interpretation The esculin test is positive when a black color forms over one-half or more of the slant.

The increase in C0 2 will cause the viridans streptococci to grow better and increase the likelihood of a positive reaction.

Enterococcus faecalis strain SS is used for positive control reactions and Streptococcus mitis strain SS is used for negative control reactions. Procedure The broth is inoculated with 2 or more colonies from a plate or with 1 to 2 drops of broth culture.

Reading and Interpretation Gas production is indicated by the gas formation between the broth and the petroleum jelly plug which pushes the wax plug toward the top of the tube. Small bubbles that may accumulate over the incubation period are not read as positive, only when the wax plug is separated from the broth is the test read positive.

Most leuconostoc strains are positive at 24 h but some strains may take longer. Results are recorded in the QC log. Top of Page Gram Stain Principle The gram stain is used to differentiate between gram-positive and gram-negative bacteria.

Cellular morphology can also be determined. The species A. Figure 1. Note the distinctive palisades. This micrograph shows a Pap smear from a woman with vaginosis. The genus Mycobacterium is represented by bacilli covered with a mycolic acid coat.

This waxy coat protects the bacteria from some antibiotics, prevents them from drying out, and blocks penetration by Gram stain reagents see Staining Microscopic Specimens.

Because of this, a special acid-fast staining procedure is used to visualize these bacteria. The genus Mycobacterium is an important cause of a diverse group of infectious diseases. Treatment of M. Complicating treatment even further is the development and spread of multidrug-resistant strains of this pathogen. Another pathogenic species, M. Loss of pain sensation and the presence of skin lesions increase susceptibility to secondary injuries and infections with other pathogens.

Bacteria in the genus Corynebacterium contain diaminopimelic acid in their cell walls, and microscopically often form palisades , or pairs of rod-shaped cells resembling the letter V.

Cells may contain metachromatic granules , intracellular storage of inorganic phosphates that are useful for identification of Corynebacterium. The vast majority of Corynebacterium spp. The genus Bifidobacterium consists of filamentous anaerobes, many of which are commonly found in the gastrointestinal tract, vagina, and mouth. In fact, Bifidobacterium spp. The genus Gardnerella , contains only one species, G.

Table 1 summarizes the characteristics of some important genera of Actinobacteria. Although less common in the United States, tuberculosis is still extremely common in many parts of the world, including Nigeria.

He also said that Sharnita had to take one semester off school. He prescribed isoniazid and rifampin, antibiotics used in a drug cocktail to treat tuberculosis, which Marsha was to take three times a day for at least three months.

The best studied genus of this class is Clostridium. These rod-shaped bacteria are generally obligate anaerobes that produce endospores and can be found in anaerobic habitats like soil and aquatic sediments rich in organic nutrients.

The endospores may survive for many years. Figure 2. Clostridium difficile , a gram-positive, rod-shaped bacterium, causes severe colitis and diarrhea, often after the normal gut microbiota is eradicated by antibiotics. Clostridium spp. Gas gangrene occurs when C. Botulinum toxin is responsible for rare but frequently fatal cases of botulism.

The toxin blocks the release of acetylcholine in neuromuscular junctions, causing flaccid paralysis. In very small concentrations, botulinum toxin has been used to treat muscle pathologies in humans and in a cosmetic procedure to eliminate wrinkles.

Infections often occur in patients who are immunosuppressed or undergoing antibiotic therapy that alters the normal microbiota of the gastrointestinal tract. Taxonomy of Clinically Relevant Microorganisms lists the genera, species, and related diseases for Clostridia.

Bacteria of the latter three genera typically are spherical or ovoid and often form chains. Streptococcus , the name of which comes from the Greek word for twisted chain , is responsible for many types of infectious diseases in humans. Species from this genus, often referred to as streptococci , are usually classified by serotypes called Lancefield groups, and by their ability to lyse red blood cells when grown on blood agar.

This species is considered a pyogenic pathogen because of the associated pus production observed with infections it causes Figure 3. Figure 3. This area appears transparent. This area appears dark and greenish. Streptococcus pneumoniae and a group of streptococci Streptococcus viridans or viridans streptococci found in oral flora display alpha hemolysis.

The agar under and around the colony is unchanged. No Other alpha strep. Regular size colony.