SURVIVAL OUTSIDE HOST: The bacterium can survive on a dry surface for 3 days to 6.5 months (22). It has been found to survive in ice cream (18 days), raw and pasteurized milk at 15-37 ºC (96 hrs), room temperature butter (48 hrs), and neutralized butter (12-17 days) (17). GAS has been found to last several days in cold salads at room temperature (18).

Overall mortality remains high (20% to 34% in larger series)

Some resistance to er ythromycin, the agentof choice for penicillin-allergic patients with streptococ-cal phar yngitis, has been reported

High-dose penicillin G remains the antibiotic ofchoice for treatment of GAS, with no resistancerecorded.

Proteinases and other enzymes might con-tribute to tissue destruction

Streptococcal toxic shock syndrome (STSS) canbe associated with invasive infections secondar y toGAS infection

MODE OF TRANSMISSION: Transmission via respiratory droplets, hand contact with nasal discharge and skin contact with impetigo lesions are the most important modes of transmission (5, 9, 13). The pathogen can be found in its carrier state in the anus, vagina, skin and pharynx and contact with these surfaces can spread the infection (5, 14, 15) The bacterium can be spread to cattle and then back to humans through raw milk as well as through contaminated food sources (salads, milk, eggs); however, cattle do not contract the disease (16-18). Necrotizing fasciitis is usually because of contamination of skin lesions or wounds with the infectious agent (12).

Staphylococcus and Streptococcus species:

whereas Streptococcus and Enterococcus spp. are catalase negative.

whereas Streptococcus species and many other organisms are inhibited by high concentrations of NaCl.

Numerous epidemiological studies have identified high rates of invasive S. pyogenes infection in men rather than women, a pattern that can be observed for many other invasive bacterial infections and one that is not fully understood. Age-specific incidence rates show a typical J-shaped distribution, with highest rates in the elderly, followed by infants. Assessment of rates of disease according to patient ethnicity show generally higher rates of disease in individuals of non-white European descent. These observations have been made in a diverse range of populations, including indigenous populations of Australia, New Zealand, the Pacific Islands, and circumpolar regions of the northern hemisphere. The reasons behind these excesses in risk are poorly understood and could reflect differential access to healthcare or general living conditions—but could also encompass some genetic predisposing factors.

Carriage and transmission of group A streptococci

Numerous epidemiological studies have identified high rates of invasive S. pyogenes infection in men rather than women, a pattern that can be observed for many other invasive bacterial infections and one that is not fully understood. Age-specific incidence rates show a typical J-shaped distribution, with highest rates in the elderly, followed by infants. Assessment of rates of disease according to patient ethnicity show generally higher rates of disease in individuals of non-white European descent. These observations have been made in a diverse range of populations, including indigenous populations of Australia, New Zealand, the Pacific Islands, and circumpolar regions of the northern hemisphere. The reasons behind these excesses in risk are poorly understood and could reflect differential access to healthcare or general living conditions—but could also encompass some genetic predisposing factors. Future studies will assist in identifying potential strategies to mitigate this risk.

Vancomycin

Necrotizing Fasciitis (Streptococcal Gangrene): GAS necrotizing fasciitis is a rapidly progressing infection of the deep subcutaneous tissues and fascia with extensive and rapidly spreading necrosis. Infections often spare the skin, but 50% of patients may have associated myonecrosis. Necrotizing fasciitis is often associated with severe systemic involvement and an associated high mortality rate (7,80,87). As in other invasive streptococcal and staphylococcal skin infections, the site of inoculation is usually at area of minor trauma or the skin lesions of varicella. Like streptococcal bacteremia, there is a clear association between varicella and necrotizing fasciitis. Varicella is characterized by full-thickness dermal lesions that may induce selective immunosuppression to GAS, though this has not been substantiated (7). Necrotizing fasciitis caused by mixed infections, involving both aerobic and anaerobic Gram negative bacteria, is more likely to occur in the abdominal wall, following abdominal surgery or in diabetic patients.

Early and aggressive surgical debridement of the site of infection as well as appropriate antimicrobial therapy is required. Due to the "inoculum effect," penicillin may be less effective in the treatment of necrotizing fasciitis (83). Appropriate antibiotics include nafcillin and clindamycin (7,83).  

Puerperal Sepsis: Puerperal sepsis occurs during pregnancy or during an abortion, when group A streptococcus colonizing the patient invades the endometrium and surrounding structures as well as the lymphatics and bloodstream. Endometritis and septicemia result and can be complicated by pelvic cellulitis, thrombophlebitis, peritonitis, or pelvic abscess. Therapy consists of aggressive surgical exploration and parenterally administered penicillin or clindamycin (see section on myositis/myonecrosis). Patients allergic to penicillin can be treated with a first generation cephalosporin, clindamycin, or vancomycin (8).  

antibiotic

S. pyogenes isolates showed complete sensitivity to teicoplanin, vancomycin, and levofloxacin.

only five are known to commonly cause disease in immune-competent human beings: Group A, Group B, both members of Group D, and two groups that lack the Lancefield carbohydrate antigen: Streptococcus pneumoniae and Viridans streptococci.[5]

If the mixture produces bubbles or froth, the organism is said to be 'catalase-positive'

The reagent is a dark-blue to maroon color when oxidized, and colorless when reduced.

Dose-dependentinhibitionofgrowthofS43/192/

Penicillins and other antibiotics in the beta-lactam family contain a characteristic four-membered beta-lactam ring. Penicillin kills bacteria through binding of the beta-lactam ring to DD-transpeptidase, inhibiting its cross-linking activity and preventing new cell wall formation.

FORMULA Ingredients per liter of deionized water:* Pancreatic Digest of Casein 15.0gm Peptic Digest of Soybean Meal 5.0gm Sodium Chloride 5.0gm Sheep Blood 50.0ml Agar 12.0gm Final pH 7.3 +/- 0.2 at 25ºC.

SUPPORT PROTOCOLS FOR DIFFERENTIAL IDENTIFICATION OF S. PYOGENES (GAS) (adapted from microbelibrary.org)

NOTE: All steps should be performed using sterile technique. GAS will remain viable on plates for only 5–7 days after streaking if stored at room temperature. GAS does not survive at 4°C.

is a facultative anaerobe and is grown at 37°C in either ambient air or in 5–10% CO2. Like all streptococci, GAS is both catalase and oxidase negative. GAS lacks the necessary enzymes for a functional TCA cycle and oxidative-cytochromes for electron transport; therefore, relies completely on fermentation of sugars for growth and energy production. It is a member of the lactic acid bacteria and is homofermentative for lactic acid production from glucose fermentation. Specific components of a rich growth medium for GAS include neo peptone extracts, glucose as carbon source, and a complex mixture of nutrients from beef heart infusion as first described by Todd & Hewitt (Todd and Hewitt, 1932). GAS is considered a multiple amino acid auxotroph requiring nearly all amino acids to be present in its growth media. A Chemically Defined Medium has been developed for GAS containing all of the necessary amino acids for GAS growth (van de Rijn, 1980).

GAS grows best on complex “rich” medium such as Trypticase Soy Agar (TSA) supplemented with 5% Sheep Blood

Adjust the pH to 7.5.

Optimal growth of GAS is seen in 5% CO2; however, GAS will also grow in ambient air albeit a little slow.

S. pyogenes is a facultative anaerobe and is grown at 37°C in either ambient air or in 5–10% CO2

GAS is considered a multiple amino acid auxotroph requiring nearly all amino acids to be present in its growth media. A Chemically Defined Medium has been developed for GAS containing all of the necessary amino acids for GAS growth

For presumptive identification of S. pyogenes, cultures should be tested for bacitracin susceptibility and PYR activity (as described below). A definitive diagnosis should include a positive Lancefield group A antigen test. Negative results can be confirmed after a total culture time of 48 hours.

To identify S. pyogenes in clinical samples, blood agar plates are screened for the presence of β-hemolytic colonies. The typical appearance of S. pyogenes colonies after 24 hours of incubation at 35-37°C is dome-shaped with a smooth or moist surface and clear margins. They display a white-greyish color and have a diameter of > 0.5 mm, and are surrounded by a zone of β-hemolysis that is often two to four times as large as the colony diameter. Microscopically, S. pyogenes appears as Gram-positive cocci, arranged in chains (Figure 1).

The ability of bacterial species to hydrolyze the compound hippurate was classically tested using ferric chloride indicator to detect benzoic acid, the first byproduct in the hippurate hydrolysis pathway. However, a 2½ hour rapid method as opposed to the 48 hour classical method for detecting hippurate hydrolysis has since been developed. The rapid test employs ninhydrin as the indicator, which detects glycine, the second byproduct of hippurate hydrolysis. The rapid hippurate hydrolysis test has been shown to be as specific and as sensitive as the classical method that detects the benzoic acid byproduct. (4,5,8,9)

Superantigens are potent immunostimulators that cause clonal proliferation of T cells and watershed production of pro-inflammatory cytokines that mediate shock and organ failure.

The attachment of S. pyogenes to the pharyngeal and skin epithelial cell surfaces represents a critical first step in establishing such infections.

human infections that involve the upper respiratory tract and skin, including acute pharyngitis and impetigo.

Occasionally, however, these bacteria can cause much more severe and even life threatening diseases such as necrotizing fasciitis (occasionally described as "the flesh-eating bacteria") and streptococcal toxic shock syndrome (STSS).

The skin may be warm with red or purplish areas of swelling that spread rapidly. There may be ulcers, blisters, or black spots on the skin.

TheseresultsindicatethatthehyaluronicacidcapsuleofmucoidGASprotectstheorganismfromphagocytosisandenhancesvirulence.

Mproteinhasbeenconsideredtobethemajorsurfacecomponentrespon-sibleforresistanceofGAStophagocytosis(12)

OccasionalstrainsofGASisolatedfromclinicalsourcesgrowaslarge,spreading,wetcoloniesonsolidmedia;

Humans (neonates, elderly, immunocompromised, diabetic, alcoholic, and stroke and cancer patients have a higher risk of infection), cattle (mastitis), dogs, cats, rabbits, horses, guinea pigs, and goats have been shown to contain the infectious agent

Laboratory Photo Examples

Gram-positive

tetracycline, to which 26 strains were resistant

chronic conditions (diabetes, cancer), compromised immune systems (receiving chemotherapy, autoimmune disorders or HIV infection) or open wounds or sores that allow the bacteria to enter the tissue.

"Strep throat," – swollen tonsils possible covered with a grayish-white film, swollen lymph nodes, and fever with or without chills, painful swallowing and headache. Impetigo - mild skin infection accompanied by open, draining sores and other general symptoms of GAS infection such as fever, swollen lymph nodes and a sore throat. Scarlet fever - characterized by a fever, sore throat, red sandpaper-like rash and a red "strawberry" tongue. It is caused by several different strains of the streptococcal bacteria, all of which produce a toxin that cause the characteristic red rash.

culture of a single throat swab on a blood agar plate yields a sensitivity of 90-95% for the detection of group A streptococci (GAS) in the pharynx

Most laboratories inoculate throat swabs on 5% sheep blood agar containing trimethoprim-sulfamethoxazole

In patients with acute pharyngitis, group A beta-hemolytic streptococcal infection should be ruled out.

antibodies for the detection of group A carbohydrate antigen.

frozen section biopsy