Gram Positive Bacteria Lecture Notes PDF

Pathogenic Gram-Positive Bacteria Outline Facultatively anaerobic Gram-positive cocci Staphylococcus spp. Streptococcus spp. Enterococcus spp. Facultatively anaerobic Gram-positive bacilli Bacillus spp. Listeria spp. Corynebacterium spp. Nocardia and...

Pathogenic Gram-Positive Bacteria Outline Facultatively anaerobic Gram-positive cocci Staphylococcus spp. Streptococcus spp. Enterococcus spp. Facultatively anaerobic Gram-positive bacilli Bacillus spp. Listeria spp. Corynebacterium spp. Nocardia and Actinomyces spp. Lecture Summary Staphylococcus Bacteria in the genus Staphylococcus live and reproduce on of human skin as normal members of the microbiota. However, they can be opportunistic pathogens, causing minor to life- threatening disease. Structure and Physiology Staphylococcus is a genus of Gram-positive, facultatively anaerobic prokaryotes whose spherical cells are typically clustered in grapelike arrangements. Staphylococcal cells are salt tolerant; thus, they tolerate the salt deposited on human skin by sweat glands. They also tolerate desic- cation, radiation, and heat. Further, they synthesize catalase. The most virulent species is Staphylococcus aureus which can colonize the skin and anterior nares of 10-30% of healthy indi- viduals. Staphylococcus aureus is the only human staphylococci that produces coagulase en- zyme. Therefore, staphylococci other than S. aureus is referred to as coagulase negative staphylococci (CNS). Staphylococcus epidermidis and other coagulase negative staphylococci are normal microbiota members of the skin and are important opportunistic pathogens. Deniz Sertel, PhD. Pathogenicity Staph infections result when staphylococci breach the body’s physical barriers. The virulence fac- tors aid in disease formation is given below. Structural Defenses Against Phagocytosis S. aureus cells are coated with protein A that interferes with antibody immune responses and the complement cascade by binding to the stem of IgG. The outer surfaces of most pathogenic strains of S. aureus contain bound coagulase (clumping factor: CF), an enzyme that converts fibrinogen into fibrin, producing clots that hide the bacteria from phagocytes. Both S. aureus and S. epidermidis (and certain other coagulase negative staph) also synthesize polysaccharide slime layers that inhibit chemotaxis of, and phagocytosis by, leukocytes and facilitate attachment to biotic and abiotic surfaces. Cells of S. aureus can be covered by a polysaccharide capsule which inhibits phagocytosis. Enzymes Staphylococci produce a number of enzymes that contribute to their pathogenicity. S. aureus produces cell-free coagulase in addition to the bound form. Other enzymes produced include hyaluronidase and staphylokinase, which enable the bacteria to spread within the body; lipases, which allow growth in sebaceous glands; and a -lactamase, which allows S. aureus to break down beta-lactam antimicrobial drugs. Toxins S. aureus, and sometimes S. epidermidis, produce cytolytic toxins that lyse cells and exfoliative toxins that cause sloughing of the skin. Toxic shock syndrome toxin and enterotoxins cause toxic shock syndrome and food poisoning, respectively. Epidemiology As noted, staphylococci are found on human skin, as well as in the upper respiratory, gastrointes- tinal, and urogenital tracts. They are transmitted through direct contact and indirect contact via fomites, and proper handwashing and aseptic techniques are essential in preventing their transfer in health care settings. Staphylococcal Diseases Staphylococcus aureus cause a variety of medical problems that can be categorized as toxin mediated diseases, suppurative and systemic infections. Staphylococcus epidermidis and other CNS are important opportunists in healthcare settings. They can also be isolated as contaminants in blood culture. Staphylococcus saprophyticus is a common pathogen causing acute non complicated urinary tract infections in young women. Toxin mediated diseases Food poisoning is one noninvasive disease caused by Staphylococcus. The food must remain at room temperature or warmer for several hours for the bacteria to grow and secrete enterotox- in, which produces the signs and symptoms of the disease. Signs and symptoms include vomit- Deniz Sertel, PhD.  ing, diarrhea, headache, and abdominal pain, and they usually appear within four (1-5) hours of ingestion. The disease is self-limiting, usually resolving within about 24 hours. Staphylococcal scalded skin syndrome is caused by strains that produce exfoliative toxins and produces reddening of the skin that typically begins near the mouth, spreads over the entire body. Within two days, the affected skin peels off in sheets. It is mostly seen in infants and young children. In older children and adults, a localized form called bullous impetigo which is character- ized by large blisters that contain clear fluid lacking bacteria or white blood cells can be seen. Toxic shock syndrome, non-streptococcal (TSS), which is characterized by fever, vomiting, red rash, low blood pressure, and loss of sheets of skin in response to production of TSS toxin. The toxin can pass mucosal barriers, therefore systemic signs and symptoms occur even though bacteria does not invade the bloodstream. Suppurative and systemic infections Staphylococcus aureus causes localized pyogenic lesions. Impetigo is a skin disorder in children in which small, flattened, red patches appear on the face and limbs, and develop into pus-filled vesicles that eventually crust over. Folliculitis is an infection of a hair follicle, and when it occurs at the base of an eyelid, it is called a sty. A furuncle, or boil, is a large, painful, raised nodular extension of folliculitis into surrounding tissue. When several furuncles fuse, they form a carbun- cle, which extends deeper into the tissues. S. aureus is a common cause of bacteremia, the presence of bacteria in the blood. It may attack the lining of the heart, producing a condition called endocarditis, or it may invade the lungs, causing pneumonia. In 10% of patients with staphylococcal pneumonia, the fluid filling the alveoli is pus; this condition is called empyema. When Staphylococcus invades bone, it causes osteo- myelitis, inflammation of the bone marrow and surrounding bone. S. aureus is the primary cause of septic arthritis in young children and in adults who are receiving intraarticular injections or who have mechanically abnormal joints. Staphylococcus epidermidis can cause a variety of opportunistic infections (endocarditis, catheter and shunt infections, prosthetic joint infections) and is the most common coagulase negative staphylococci isolated from clinical specimens. S. saprophyticus has a predilection for causing non complicated urinary tract infections in young, sexually active women. Diagnosis, Treatment, and Prevention Culture is the gold standard. In direct microscopic examination done from pus, blood, or other flu- ids Gram-positive cocci in grapelike arrangements is detected. Staphylococci can be distin- guished from streptococci and enterococci by catalase test. Coagulase-positive S. aureus can be easily differentiated from other staphylococci. Deniz Sertel, PhD.  In 1945, 90% of staphylococci were susceptible to penicillin, but only 5% are susceptible today. For this reason, penicillins or other beta lactam antibiotics that are resistant to beta lactamase en- zymes (one of which is methicillin) became the drug of choice for staph infections; however, methi- cillin-resistant Staphylococcus aureus (MRSA) has emerged as a major problem, initially in health care settings but now in places such as day care centers, schools, and prisons. MRSA is re- sistant to a variety of antimicrobial agents; vancomycin became the treatment of choice. Now there is an increasing prevalence of vancomycin-resistant Staphylococcus aureus (VRSA) strains. Scrupulous attention to infection control measures can prevent transmission of Staphylococcus. Streptococcus The genus Streptococcus is a diverse assemblage of Gram-positive cocci arranged in pairs or chains. They are catalase negative and facultatively anaerobic. They are differentiated by vari- ous schemes, including the Lancefield groups A through H and K through V, which does not in- clude all species and hemolytic properties. Group A Streptococcus: Streptococcus pyogenes Group A Streptococcus, or S. pyogenes, is a beta-hemolytic coccus. Pathogenic strains often have capsules. M protein (>100 types) is the major type-specific protein associated with virulent strains. Pathogenicity S. pyogenes has a variety of structures, enzymes, and toxins that contribute to its pathogenicity. Virulence determined by ability to avoid phagocytosis (mediated primarily by capsule, M and M- like proteins, C5a peptidase), adhere to and invade host cells (M protein, lipoteichoic acid, F pro- tein), and produce toxins (streptococcal pyrogenic exotoxins, streptolysin S, streptolysin O, strep- tokinase, DNases). Deniz Sertel, PhD. Epidemiology Transient colonization in upper respiratory tract and skin surface occur. Person-to-person spread by respiratory droplets (pharyngitis) or through breaks in skin after direct contact with infected person or fomite is possible. In general, S. pyogenes disease is caused by recently acquired strains that can establish an infection of the pharynx or skin before specific antibodies are pro- duce or competitive organisms are able to proliferate or depleted, or when a large inoculum ena- bles them to get a foothold. Group A strep is sensitive to most antimicrobial agents but remains a significant pathogen. Group A Streptococcal Diseases Diseases caused by group A streptococci include the following: Pharyngitis. A sore throat caused by streptococci, commonly called “strep throat,” is a type of pharyngitis, or inflammation of the pharynx. Rheumatic fever is a complication of untreated streptococcal pharyngitis in which inflamma- tion leads to damage of heart valves and muscle. The damage may be due to cross-reactive immune responses. Scarlet fever (scarlatina) often accompanies streptococcal pharyngitis when the infection in- volves a lysogenized strain. It is characterized by a diffuse rash followed by sloughing of the skin. Pyoderma and Erysipelas. A pyoderma is any confined, pus-producing lesion that usually occurs on the exposed skin of the face, arms, or legs, similar to impetigo. When infection also involves lymph nodes and triggers pain and inflammation, the condition is called erysipelas. Streptococcal toxic-shock syndrome (STSS) is a rare but severe bacteremia followed by in- tense pain and organ failure, and over 40% of patients die. Necrotizing Fasciitis. Another serious disease caused by S. pyogenes is necrotizing fasciit- is, sensationalized by the news media as “flesh-eating bacteria.” It results in loss of muscle and fat tissues, toxemia, organ failure, and death in about 20% of patients. Glomerulonephritis can result from accumulation of immune complexes in the glomeruli fol- lowing infection with S. pyogenes. Kidney function declines and permanent damage may oc- cur. Diagnosis, Treatment, and Prevention Microscopy is useful in soft-tissue infections but not pharyngitis or nonsuppurative complications. Direct tests for the group A antigen are useful for the diagnosis of streptococcal pharyngitis, but negative results must be confirmed by culture or molecular assays. After isolating the pathogen in culture, isolates identified by catalase (negative), positive PYR (L-pyrrolidonyl arylamidase) re- action, susceptibility to bacitracin, and presence of group-specific antigen (group A antigen). Antistreptolysin O (ASO) test is useful for confirming rheumatic fever or glomerulonephritis as- sociated with streptococcal pharyngitis; anti-DNase B test should be performed for glomerulone- phritis associated with pharyngitis or soft-tissue infections. Penicillin and many other antimicrobial agents are effective against S. pyogenes. Necrotizing fasciitis must be treated with aggressive removal of infected tissues in addition to intravenous an- timicrobial agents. Active immunity against one strain does not confer resistance to other strains, which explains why an individual can develop strep throat more than once. Deniz Sertel, PhD. Group B Streptococcus: Streptococcus agalactiae Group B Streptococcus, or S. agalactiae, is a Gram-positive coccus that divides to form chains, is beta-hemolytic, and bacitracin resistant. Pathogenicity S. agalactiae forms capsules and produce multiple enzymes (proteases, hemolysins, deoxyribo- nuclease, and hyaluronidase) that probably play a role in pathogenesis. Epidemiology Group B Streptococcus can colonize the lower gastrointestinal, urinary, and genital tracts of humans. However, they can cause serious disease in newborns who may be inoculated during passage through the birth canal or by health care workers. These infections do not cause disease when maternal antibodies have crossed the placenta but can be fatal in children of uninfected mothers. Infections in newborns less than one week produces early-onset disease. Infection oc- curring between one week and three months results in late-onset disease. Diseases In current times, S. agalactiae is most often associated with neonatal bacteremia, meningitis, and pneumonia. Group B streptococcal infections also occur in pregnant women and older indi- viduals who are immunocompromised. Diagnosis, Treatment, and Prevention Isolating and identifying the organism in culture is the gold standard. Beta hemolytic Gram- positive cocci, catalase negative, resistant to bacitracin and co-trimoxazole (SXT) is con- sidered as S. agalactiae. CAMP test and hippurat hydrolysis is also positive. Polymerase chain reaction–based assays to detect vaginal carriage in pregnant women are commercially available, as sensitive as culture and rapid. Penicillin or ampicillin is used to treat group B Streptococcus infections. The Centers for Disease Control and Prevention (CDC) recommends prophylactic administration of penicillin at birth to children whose mothers’ urinary tracts are colonized with group B streptococci. Other Beta-Hemolytic Streptococci S. equisimilis and S. anginosus are the only other pathogenic beta-hemolytic streptococci. The former causes pharyngitis, and the latter produces abscesses. Penicillin is effective against both. Streptococcus pneumoniae S. pneumoniae is a Gram-positive coccus that commonly forms pairs (diplococci-candle flame/lancet appearance) and short chains. Ninety-two different strains of pneumococci are known to infect humans. They are alpha-hemolytic under aerobic conditions and are not part of a Lancefield group. Pathogenicity and Epidemiology S. pneumoniae is a normal member of the pharyngeal microbiota. Virulent strains of S. pneu- moniae are protected by polysaccharide capsules and phosphorylcholine in their cell walls, which together allow the bacteria to enter cells and “hide.” These bacteria secrete protein adhe- Deniz Sertel, PhD.  sin, which facilitates binding of the bacteria to epithelial cells of the pharynx. Additionally, secreto- ry IgA protease destroys IgA and pneumolysin causes lysis of cells in the lungs. S. pneumoniae grows in the mouths and pharynges in 75% of humans, but do not typically cause disease until they gain access to the lungs (nonencapsulated strains are avirulent). Pneumococcal Diseases Most infections are caused by endogenous spread from the colonized nasopharynx or oropharynx. Person-to-person spread through infectious droplets is rare. Pneumococcal pneumonia is the most prevalent disease caused by S. pneumoniae infection, which constitutes about 85% of all cases pneumonia and results following viral infections or other damage to the lungs. Sinusitis and Otitis Media. Viral infections of the upper respiratory tract also allow S. pneu- moniae to invade the sinuses and middle ear, producing sinusitis and otitis media (inflamma- tion of the middle ear). Pus production and inflammation in these cavities creates the characteristic pressure and pain. Bacteremia and Endocarditis. S. pneumoniae can also enter the blood through lacerations or damage in the lungs, producing bacteremia, and can colonize the lining of the heart, causing endocarditis. Pneumococcal Meningitis. Pneumococci can spread to the meninges from the blood, result- ing in pneumococcal meningitis, which can be fatal. Diagnosis, Treatment, and Prevention Gram stains of sputum smears, the Quellung reaction, and agglutination tests may be used to di- agnose infection with S. pneumoniae. Culture requires use of enriched-nutrient media (e.g., sheep blood agar). The bacteria are alpha-hemolytic and susceptible to optochin and soluble in bile. Penicillin resistance has developed in recent years, and cephalosporin, erythromycin, or chloramphenicol may be used. Prevention may be possible with pneumococcal vaccine. Viridans Streptococci The viridans streptococci are not part of a Lancefield group. Most are alpha-hemolytic and pro- duce a green pigment when grown on blood media. Some members of the viridans streptococci (e.g., S. anginosus group) can have β-hemolytic strains with the group-specific cell wall polysac- charides. These microbes normally inhabit the human mouth; pharynx; and gastrointestinal, urinary, and genital tracts. They are opportunists that produce pus-filled abdominal lesions, and they are one cause of dental caries (cavities). The bacteria produce a biofilm known as dental plaque on the surface of teeth. Viridians streptococci are not invasive but enter the blood through small and large cuts to cause meningitis and endocarditis. Alpha hemolytic viridans streptococci can be differentiated from S. pneumoniae by their re- sistance to optochin and bile Good oral hygiene and using prophylactic antibiotics when invasive dental procedures are ap- plied can prevent disease. Deniz Sertel, PhD. Enterococcus Enterococci are Gram-positive, catalase-negative cocci that are normal members of the intesti- nal microbiota. The enterococci (“enteric cocci”) were previously classified as group D strepto- cocci because they share the group D cell wall antigen, a glycerol teichoic acid, with other streptococci. Structure and Physiology Enterococci are spherical and form short chains and pairs. They are unencapsulated, able to grow at temperatures up to 45°C, in alkaline conditions, and are salt and bile salt tolerant. En- terococci produce often non-hemolytic or alpha hemolytic colonies. Rare beta hemolytic strains are present. Two species that are significant pathogens of humans include E. faecalis and E. faecium. Pathogenesis, Epidemiology, and Diseases E. faecalis is ubiquitous in the human colon, E. faecium is less common. They have few virulence factors but can adhere to epithelial cells and form biofilms. Both cause disease when introduced into other parts of the body, such as the urinary tract and bloodstream, and account for about 10% of healthcare-associated infections (HAIs). Enterococci either are inherently resistant to many commonly used antibiotics (e.g., oxacillin, cephalosporins) or have acquired resistance genes (e.g., to aminoglycosides, vancomycin). Diagnosis, Treatment, and Prevention Enterococcal infection is diagnosed by isolating and identifying the pathogen from clinical speci- mens. Grows readily on common, nonselective media; differentiated from related organisms by simple tests (catalase negative, L-pyrrolidonyl arylamidase [PYR]–positive, bile-esculine posi- tive, and tolerant to salt). Strains resistant to frequently used antimicrobial agents are common. Preventing enterococcal in- fections is difficult when patients’ immune systems are compromised. Good hygiene and asep- tic techniques are essential in health care settings. Deniz Sertel, PhD. Bacillus Bacteria in the genus Bacillus are Gram-positive endospore-forming bacilli. The member of this genus can form endospores. The tough external coat and the internal chemicals of their endo- spores enable the microbe to resist harsh environmental conditions. Bacillus anthracis, the organism responsible for anthrax, is the most important member of this genus. The other clinically important species in this genus is Bacillus cereus, an organism responsible for gastroenteritis, traumatic eye infections, catheter-associated sepsis. Structure, Physiology, and Pathogenicity B. anthracis and B. cereus are large, endospore-forming, rod-shaped, facultatively anaerobic bacteria that normally present in soil. B. anthracis is non-motile, and the vegetative cells produce an antiphagocytic capsule (poly-D- glutamic acid: protein). Pathogenic strains contain copies of a plasmid coding for anthrax toxins, three distinct polypeptide components (protective antigen, lethal factor, edema factor) that in combination cause edema and are lethal to cells. B. cereus is motile and do not possess a capsule. This bacterium can produce exotoxins (heat- stable and heat-labile enterotoxin) and cytotoxic enzymes (cereolysin-beta hemolysin- and phospholipase C). Deniz Sertel, PhD. Epidemiology Anthrax is primarily a disease of herbivores; humans normally contract the disease from in- fected animals (zoonosis). The endospores can invade three ways: inhalation, inoculation of wounds, and ingestion. B. cereus and other Bacillus species are ubiquitous organisms, present in virtually all environ- ments. Virtually all infections originate from an environmental source (e.g., contaminated soil). Humans can be infected via ingestion of contaminated food or trauma/invasive procedure. Disease Anthrax can have three clinical manifestations: 1. Gastrointestinal anthrax is very rare in humans. It results in intestinal hemorrhaging and even- tually death. 2. Inhalation anthrax (wool sorters disease) requires the inhalation of airborne endospores. After the endospores germinate in the lungs, they secrete toxins that are absorbed into the blood- stream, producing toxemia. Victims develop a high fever and labored breathing and then go in- to shock. Even with aggressive treatment, inhalation anthrax is fatal in about 50% of cases. 3. Cutaneous anthrax is the most common form in humans. Infection results in the formation of a nodule, which progresses to a black crusty ulcer called an eschar. B. anthracis growing in the eschar release anthrax toxins into the blood. Left untreated, it is fatal in 20% of cases. B. cereus can cause food poisoning (emetic form or diarrheal form) and foreign body infections. Diagnosis, Treatment, and Prevention B. anthracis, is present in high concentrations in clinical specimens (microscopy typically positive) and grows readily in culture. Preliminary identification is based on microscopic (gram-positive, nonmotile rods) and colonial (nonhemolytic, adherent colonies resembling Medusa head) mor- phology; confirmed by demonstrating capsule and either lysis with gamma phage, a positive di- rect fluorescent antibody test for the specific cell wall polysaccharide, or positive nucleic acid amplification assay. Penicillin, doxycycline, and quinolones are used to treat B. anthracis. Preventive measures in- clude vaccination of livestock. A vaccine for humans has been developed but requires multiple doses and has limited usefulness. B. cereus infections can be confirmed by isolating and identifying the organism in implicated food product or nonfecal specimens (e.g., eye, wound). Gastrointestinal disease is prevented by prop- er preparation of food (e.g., foods should be consumed immediately after preparation or refriger- ated). Listeria The genus Listeria consists of 10 species, with Listeria monocytogenes is the only recognized human pathogen. L. monocytogenes is a short, gram-positive, facultatively anaerobic rod capable of growth at a broad temperature range (1° C to 45° C) and in a high concentration of salt. The organisms are motile at room temperature but less so at 37° C. L. monocytogenes is isolated from a variety of environmental sources and from the feces of mammals, birds, fish, and other an- imals Deniz Sertel, PhD.  Listeria monocytogenes enters the body in contaminated food or drink and causes listeriosis. However, human to human transmission can occur primarily from mother to child in utero or at birth. L. monocytogenes is a facultative intracellular pathogen. Listeria monocytogenes binds to the surface of cells, and triggers phagocytosis. After penetration into the cells, the acid pH of the phagolysosome that surrounds the bacteria activates a bacterial pore-forming exotoxin, listerioly- sin O and two different phospholipase C enzymes, leading to release of the bacteria into the cell cytosol After exiting the phagosome, it grows and reproduces inside the cytosol. The bacteria can move within the cell and can pass to the adjacent cell by forming a filopod. A neighboring cell en- docytizes the bacterium, and the cycle begins again. Listeria is widespread in the environment. Listeria is rarely symptomatic in healthy adults, but infection in fetuses, newborns, the elderly, and immunocompromised patients can be se- vere, resulting in meningitis and even death. Listeria infection of pregnant women can cause premature birth, miscarriage, or meningitis in the newborn. In the newborn two forms of disease is described: (1) early-onset disease (granulomatosis infantiseptica), acquired transplacentally in utero, and (2) late-onset disease (meningitis, meningoencephalitis), acquired at or soon after birth. Listeria infection is diagnosed by isolating and identfying the pathogen from clinical specimen. At room temperature the bacterium will exhibit characteristic end-over-end “tumbling.” Listeriosis is treated with ampicillin and an aminoglycoside. Individuals at risk should avoid undercooked meat and vegetables, soft cheeses, and unpasteurized milk products. Corynebacterium Corynebacterium is a genus of high G + C, pleomorphic, non-endospore-forming bacteria that are ubiquitous on plants and in animals and humans. They divide via snapping division, producing V- shapes (sometimes referred to as Chinese letters) and palisades. These bacteria contain meta- chromatic granules (Babe-Ernst granules), which may stain differently from the cell. The cell wall of Corynebacterium species contain short chained mycolic acids, but these bacteria do not stain acid-fast. The most important species in this genus is Corynebacterium diphtheriae Pathogenesis, Epidemiology, and Disease Corynebacterium diphtheriae can colonize human oropharynx and skin and is transmitted via respiratory droplets or skin contact. Diphtheria toxin is directly responsible for the signs and symptoms of diphtheria. Toxin inhibits eukaryotic protein synthesis by binding elongation factor 2 and causes cell death. The receptor for the toxin is heparin-binding epidermal growth factor, which is present on the surface of many eukaryotic cells, particularly heart and nerve cells. Respiratory diphtheria is characterized by sudden onset, with malaise, sore throat, exuda- tive pharyngitis and formation of a pseudomembrane, which adheres to the underlying tissues firmly (bleeds when dislodged). Paralysis of the soft palate may be seen which cause difficulty in speaking, eating and drinking. Bull neck appearance may be seen due to enlargement of cervical lymph nodes. Fever is absent or low grade. Complications (myocarditis, neuropathy, tubular ne- crosis, etc) may occur. Skin, or wound diphtheria occurs by transmission of C. diphtheriae via skin contact. A papule develops first and then evolves into a chronic, nonhealing ulcer, some- times covered with a grayish membrane. Due to active immunization program diphtheriae is un- common in Turkey Deniz Sertel, PhD. Diagnosis, Treatment, and Prevention Initial diagnosis is based on the clinical signs and symptoms (eg. presence of a pseudomem- brane). Culture is the gold standard in definitive diagnosis. Both nonselective (blood agar) and selective (cysteine-tellurite agar, Tinsdale medium, colistin-nalidixic agar) media should be used. An immunodiffusion assay called an Elek test, in which antibodies against the toxin react with toxin produced by the bacteria isolated from the patient confirms the diagnosis. Polymerase chain reaction (PCR) assays can also be used to demonstrate the presence of exotoxin. Administering an antitoxin is critical, as is treatment with penicillin or erythromycin. Surgery or a tracheostomy may be necessary if the airway is blocked due to pseudomembrane. A toxoid vaccine is availa- ble for prevention of diseases. Immunization is recommended at 2, 4, 6, 18, and 60 months of age, followed by booster immunizations every 10 years. Nocardia and Actinomyces Nocardia and Actinomyces have elongated filamentous cells that resemble fungal hyphae. Nocardia Nocardia species are strictly aerobic bacteria which contains mycolic acids in their cell wall and stains weakly (or partially) acid-fast. It is a common inhabitant of soils rich in organic matter. The most common pathogens in this genus are Nocardia asteroids and Nocardia brasiliensis. Pathogenesis, Epidemiology, and Disease Nocardia spp are opportunistic pathogens that infects numerous sites. The bacteria in the soil en- ters the human body via inhalation or inoculation (through skin). In the lungs, it causes pneumo- nia. Cutaneous infections may produce mycetoma, a painless, long-lasting infection characterized by swelling, pus, and draining sores. Diagnosis, Treatment, and Prevention The presence of partially acid-fast, hypha-like cells in a clinical sample is diagnostic of Nocardia infection and can usually be treated with an antimicrobial drug for six weeks. Immunocompro- mised patients with disseminated infection have a poor prognosis, so avoiding exposure to No- cardia is especially important in these individuals. Actinomyces Actinomyces is a non-acid-fast bacterium that grows in hyphae-like cells and colonies that form visible masses that resemble grains of sand. Actinomyces species are facultative anaerobe or anaerobic. Pathogenesis, Epidemiology, and Disease Actinomyces is a normal member of the microbiota of human mucous membranes and can cause dental caries. However, when Actinomyces enters through breaks in the mucous mem- branes resulting from trauma, surgery, or infection by other pathogens, it causes a disease called actinomycosis. This disease is an endogenous infection and characterized by the formation of multiple abscesses in the skin or mucous membranes. Most common species encountered in clinical specimens is Actinomyces israelli Deniz Sertel, PhD. Diagnosis, Treatment, and Prevention Actinomycosis can be difficult to diagnose since Actinomyces is normally found on the mucous membranes and other organisms cause similar symptoms. Observation of filamentous cells in “sulfur granules” can be useful in diagnosis. Treatment involves surgical removal of the infected tissue and administration of penicillin for several months. Actinomycosis can be prevented with good oral hygiene and the use of prophylactic antimicrobials if trauma occurs to the mu- cous membranes. References Bauman RW (ed). Microbiology with Diseases by Taxonomy, 5e, Global Edition. Pearson:2017 Murray P, Rosenthal K, Pfaller M (eds). Medical microbiology, 9th ed. 2020; Elseiver. Deniz Sertel, PhD.