Descriptions of Selected Pathogens

Lecture 18 [Notes] The following information relates causal organism, mode of transmission, manner of production of disease symptoms, immunization procedures, chemotherapy, and epidemiology. It is presented independent of organ or system in which the organism may be found.

Streptococcal Diseases (Streptococcus)

pathogens of humans and animals, producers of lactic acid - play a role in the production of buttermilk, silage, and other fermented products

Pathogens induce HEMOLYSIS on blood agar due to formation of toxins (streptolysins S & O); organisms are divided into immunological groups, known as Lancefield groups, based on the presence of a specific antigen (A-O); hemolytic streptococci are found primarily in Group A - pyogenic; diseases of humans

Group A is classified into antigenic TYPES based on the nature of a cell wall family of proteins (M); this M protein is associated with a resistance of the organism to phagocytosis; there are presently more than 55 antigenic types; e.g. Group A, type M12 is the cause of glomerular nephritis


mastitis (inflammation of breast tissue)
peritonitis (inflammation of lining of abdominal cavity)
streptococcal sore throat
purpural sepsis (disease of the uterus following childbirth)
erysipelas (St. Anthony's Fire) - skin level attack which spreads
to lymph nodes, may become septicemic; high mortality rate
glomerular nephritis
rheumatic fever (Ab against streptococci attach to heart valve)

Organisms in this group are transmitted through the air; starts in the upper respiratory tract with potential spread to other parts of the body; many people are symptomless carriers of Group A; these organisms are sensitive to penicillin and other antibiotics which are normally effective against Gram + bacteria; resistant strains are rarely seen

Extracellular Products of Group A Streptococci

erythrogenic toxin			Scarlet fever rash
streptolysins S & O			hemolysins
streptokinase				dissolve blood clots
deoxyribonuclease			decomposes DNA
ribonuclease				decomposes RNA
hyaluronidase				breaks down hyaluronic acid
proteinase				nonspecific protease
amylase					breaks down amylose starch

GROUP SPECIES SIGNIFICANCE A S. pyogenes important human diseases; infection S. pneumoniae by beta, hemolytic strep initiates S. scarlatinae acute rheumatic fever; group is sensitive to penicillin -- all major and classical diseases B S. agalactiae bovine mastitis C S. equi animal infections; mild respiratory S. zooepidemicus infections in humans; endocarditis S. equisimitis S. dysagalactiae D S. faecalis enterococci; urogenital tract S. durans infections; endocarditis; wound S. zymogenes infections in humans; found in S. liquefaciens dairy products S. bovis E disease of swine, found in normal milk F found in human respiratory tract G S. anginosus mild respiratory infections in humans; canine genital infections H S. sanguis found in human respiratory tract; endocarditis; dental caries K S. salivarius found in human respiratory tract; endocarditis; dental caries L canine genital infections M canine genital infections N S. lactis lactic acid group; found in S. cremoris dairy products S. thermophilus O S. viridans Viridans group; subacute bacterial endocarditis; found in upper res- piratory tract of humans Anaerobic streptococci - 13 species Not grouped S. mitis endocarditis and dental caries S. mutans
Staphylococcus parasites of humans and animals, occasionally cause serious infections; non-motile, non sporulating, Gram + cocci; division occurs in several planes causing clumped arrangement relatively resistant to drying; easily dispersed in the air; can grow in high salt concentration (6.5 - 7.5 %) Staphylococcus epidermidis - non pigmented, non pathogenic; found on skin and mucous membranes Staphylococcus aureus - golden yellow pigment on blood agar (not all strains are yellow); commonly associated with boils,pimples, impetigo, pneumonia, osteomyelitis, carditis, meningitis, arthritis
Human disease strains form a number of extracellular toxins and enzymes, including at least four different hemolysins coagulase cause fibrin to coagulate leukocidin destroys white blood cells fibrinolysin breaks down fibrin clots lipase nonspecific lipid destroyer hyaluronidase ribonuclease deoxyribonuclease common habitat is the upper respiratory tract, especially the nasopharyngeal passages; many people are symptomless carriers serious staph infections occur when resistance is low due to hormonal changes, illness, steroid or anti-inflammatory drug treatment; many antibiotic resistant strains exist food poisoning is due to an enterotoxin producing strain; symptoms occurs usually 2-4 hours after ingestion; death wish common; about 95-99 % of all food poisoning due to staph Neisseria Gram - cocci that live in humans; nutritionally highly specialized; grow well near or at body temperature; extremely sensitive to inhibitory materials and conditions Neisseria gonorrhoeae (gonococcus) - "diarrhea of the gonads"; sexually transmitted disease, rarely results in serious complications or death; mild vaginitis may spread to uterus where inflammation could lead to sterility; painful infection in urethral canal of males - in conjunction with Herpes II virus is implicated in uterine cancer; eye infections in newborns and adults fastidious, difficult to culture on initial media - requires 2-10 % carbon dioxide atmosphere; grows only between 30 - 38.5° C killed rapidly by drying, sunlight, and ultra violet radiation toxicity is due to ENDOTOXIN, no significant extracellular products produced; penicillin effective except against PPNG Incidence of infection remains high because: 1. acquired immunity does not occur; reinfection possible 2. symptoms in female may go undetected; she may serve as a reservoir of infection Incidence of gonorrhoeae correlates closely with sexual activity of society; elimination difficult because it continues to be viewed as a social rather than a medical problem Neisseria meningitidis (meningococcus) parasite of humans only; nasopharynx is natural habitat; fastidious; sensitive to adverse environmental factors; many carriers in human population may invade bloodstream and set up a generalized body infection by way of the lymphatics; may invade the CNS and become established in the meninges; symptoms include: severe headache, muscular spasm, stiff neck, exaggerated reflexes - leading to convulsions, coma, death pathogenicity results from ANTIPHAGOCYTIC CAPSULE and production of a characteristic ENDOTOXIN; sensitive to sulfonamides, penicillin, and most other antibiotics; sulfonamides are useful because they can penetrate the meninges Virtually impossible to control because of inapparent infections; common in crowded areas such as military barracks; serum of carriers contains Ab bactericidal to N. meningitidis. This may prevent the spread of the organisms from the nasopharynx to the bloodstream and CNS. Bacillus aerobic, sporeforming, Gram + rods; easy to isolate from soil or air; most common organisms to appear from soil samples Major human disease to be caused by a Bacillus is anthrax caused by Bacillus anthracis; some food poisoning has been associated with Bacillus cereus. Anthrax was the first disease shown conclusively to be caused by a bacterium. primarily a disease of farm animals, occasionally transmitted to humans; organism is large (1-1.5 - 4-8 µ); has a capsule, resistant to phagocytosis; highly invasive, grows throughout body - gets into bloodstream and releases an EXOTOXIN responsible for most symptoms: shock, electrolytic imbalance, swelling, hemoconcentration, acute renal failure Human beings become infected when they come into contact with diseased animals, their hides or products. Susceptible animals include cattle, sheep, horses, goats, pigs, minks, dogs, deer, birds, frogs, and fish. Animals usually ingest bacilli or spores from infected carcasses; spores may persist for several years. Human infection is usually an occupational hazard in the meat packing and tanning industries. The organism invades by way of skin cuts and abrasions. A primary lesion develops at the site as an inflamed pustule or blister - this can spread and become systemic, in which case it is often fatal. Inhalation of spores causes "woolsorter's disease" often leading to pneumonia and death. Initial work was done by Koch and formed the basis for his Postulates. Immunity is developed through production of Ab to toxins. Pasteur produced the first attenuated vaccine for sheep (immunity is relatively short-lived, lasting 9-12 months). There is still no anthrax vaccine considered safe for humans. can be treated effectively with penicillin, tetracyclines, or erythromycin if symptoms are detected before bacteremia develops Clostridium Gram +, sporeforming, usually rods; obligate anaerobes (with exceptions); main habitat is anaerobic pockets in the soil; most produce EXOTOXINS responsible for the symptoms Clostridium botulinum - botulism Clostridium tetani - tetanus Clostridium perfringens - gas gangrene Botulism is FOOD POISONING rather than a FOOD INFECTION since the microbes grow in the food and not the host; toxins are released into the food and are ingested if not heated to at least 60° C. Tetanus is generally fatal due to a toxin that acts on the nerves of the CNS causing spastic paralysis; infects dirty wounds; once toxin combines with nerves the action cannot be reversed; treat-ment is difficult, control is through immunization with TOXOID. Gas gangrene organism also infects wounds; more invasive due to a series of toxins that cause extensive tissue damage. Gangrene refers to dead tissue and gangrenous conditions may result from microbial or nonmicrobial causes. Dead tissue frequently contains gaseous products of the bacterium's activity. The infected region may become liquid or hollow. Toxins may spread and cause destruction of heart tissue and internal organs leading to death. Immunization against all toxins is not possible therefore control is by antibiotics and surgery (super oxygenation has been effective in some cases). Corynebacterium aerobic, nonsporulating, nonmotile, Gram + rods; may have swollen ends with club shaped appearance (koryne is Greek for "club"); widespread, common in soil; some cause plant diseases, others are pathogenic to humans and animals; Corynebacterium acnes (now called Propionibacterium acnes) is a common skin inhabitant and is implicated as a secondary invader in the skin condition - acne Corynebacterium diphtheriae first infectious disease whose symptoms were shown to be caused by an EXOTOXIN, also first disease to be controlled by immunization procedures; strictly an inhabitant of the respiratory tract - cannot invade other parts; transmitted by respiratory route; inflammatory response of throat tissue results in pseudomembrane which blocks the throat and leads to suffocation; death usually from toxemia as toxin spreads throughout the body organism is weakly invasive, powerful toxin makes it viru- lent; production of toxin requires presence of specific virus within the cell toxoids result in formation of antitoxin Ab which neutralize the toxin but fail to prevent the establishment of the organism in the upper respiratory tract; inapparent infections are common, as are carriers Schick test is used to determine if a person is immune; non-immune persons will show swelling and redness at injection site Mycobacterium rod-shaped, nonsporulating, aerobic, ACID-FAST, weakly Gram + Mycobacterium tuberculosis tuberculosis was first shown by Koch to be caused by a bacterium; simple nutritional requirements; able to resist chemical agents like alkali and phenol due to lipid content of cell walls; both primary and post primary (reinfection) infections possible tuberculin - protein fraction used in testing; positive test may be due to early inapparent infections; Streptomysin, INH (isonicotinic acid hydrazide) and PAS (para-aminosalicylic acid) are presently the most effective drugs BCG - live vaccine which may turn negative individuals positive; TB is serious in cattle, contaminated dairy products; site of infection becomes the lymph nodes and it localizes in the bones and joints; pasteurization has eradicated most of this type of TB Mycobacterium leprae (Hansen's disease - Leprosy) difficult to culture, grows in intracellular sites in lesions; intermediate hosts are armadillos in south cutaneous form - affects skin, causing extensive disfiguration neural form - infects peripheral nerves, causes loss of sensation patient may have both types; NOT contagious - requires prolonged and intimate contact such as crowding, poor sanitation; DDS (di-aminodiphenylsulfone) is effective but treatment is prolonged The Enteric Bacteria Most belong to the family Enterobacteriaceae. As a group they are Gram -, nonsporulating, stubby to short rods, facultative anaerobic, have simple nutritional requirement, show varying degrees of motility based on species. Quick Comparison of Some of the Enteric Group Use Produce Lactose Indole H2S Motile Gas from Glucose Esherichia + + - var/- + Shigella - + - - - Salmonella - - + + var/+ Proteus - var/+ + + + Enterobacter + - - var/+ +
Escherichia - rarely pathogenic, primarily opportunistic causing problems when host's resistance is lowered or defenses have been breached; has been implicated in infant diarrhea in epidemics in nurseries; may cause urinary tract infections in older persons (_ and _) or surgical patients; streptomycin, chloramphenicol, and tetracyclines are all effective Salmonella and Escherichia are closely related; Salmonella are usually pathogenic, either to humans or warm blooded animals; most common diseases in humans are TYPHOID FEVER and GASTROENTERITIS Salmonella typhi organism resists digestion after phagocytosis; can live and reproduce intracellularly in macrophages and other phagocytic cells; transmitted in food and water contaminated from fecal sources. Organisms replicate in intestinal tract, enter the lymphatic vessels that drain the intestine, travel to the bloodstream and spread throughout the body; organism grows in the bile duct, spleen and lymph nodes. Once the organism is established a characteristic FEVER develops as the result of the release of EXOTOXIN; diarrhea is NOT a common symptom; ROSE SPOTS appear on the trunk of the body; the intestinal phase is treated with antibiotics active against Gram - bacteria; organisms may still be shed from the bile duct and appear in the feces (carrier state) intracellular phase is treated with chloramphenicol - antibiotic therapy must be continued Controlled by pasteurization, sewage treatment, water purification, and elimination of chronic carriers as food handlers. A killed bacteria vaccine is available and used in areas where epidemics are still common. Gastroenteritis - often called food poisoning but is not since the symptoms develop as the result of the multipli- cation of the microbe in the intestinal tract of the host. rarely spreads from the intestine and thus is self limiting; symptoms develop 8-48 hours after ingestion and include headache, chills, vomiting, diarrhea, followed by fever Shigella differs from Escherichia in being UNABLE to utilize lactose or produce gas during fermentation of sugars; shigellas are non flagellated and nonmotile commonly pathogenic to humans causing a severe gastroenteritis called "bacterial dysentery" - pathogenicity seems related to its ability to produce a powerful ENDOTOXIN almost exclusively in humans and other primates affects communities with poor sanitation, e.g.military troops in combat zones; does not invade bloodstream, usually self limiting, rarely fatal, unless patient is debilitated initially, spontaneous cure within a few days Yersinia pestis - causative agent of bubonic plague; epidemic in Middle Ages associated with severe HEMOLYSIS, producing dark skin in dying person - hence the name "black death"; this symptom is usually not seen in cases today; still ENDEMIC in parts of Asia, Africa, and U.S. (sylvatic plague in rodents and ground squirrels of the West - sylvatic vs. urban plague); carried by flea on surface of rodent, etc. as a result of the bite of an infected flea, bacteria get into the lymphatic system, multiply in the lymph nodes and cause the nodes to enlarge (enlarged nodes are called BUBOES) thus the name "Bubonic Plague"; in the latter stages the bacteria spread throughout the body; in untreated cases mortality reaches 100 %; death results from release of an ENDOTOXIN; invasiveness is determined at least in part by a capsule; optimum growth temperature is 28° C rather than 37° C; at 28° C virulence factors are not produced; bacteria can also reproduce in fleas; can become established in the lungs and is known as PNEUMONIC PLAGUE, highly contagious by droplet infection recovery involves formation of OPSONIZING ANTIBODIES that seem to confer lifelong immunity; control in urban areas is affected by the elimination of rats; sylvan plague cannot be eliminated because the vectors are wild animals Franciscella tularensis - causes tularemia, primarily a disease of wild animals; microbe is small enough to get through breaks in the skin; humans acquire organism by handling infected carcasses; organisms concentrate in lymph glands and cause headache, body pain, fever, and sometimes death; symptoms probably due to ENDOTOXIN; Streptomysin useful; sometimes called rabbit fever Hemophilus influenzae - mistakenly thought to cause flu; nonmotile, aerobic, nonsporeforming, Gram - with varying shapes (pleomorphic); virulence seems related to capsule; six antigenic types; requires growth factors found in lysed red blood cells (X and V factors); drug of choice is combination of ampicillin and chloramphenicol primarily a secondary invader implicated in generalized inflammatory responses such as meningitis and nasopharyngitis, also in pneumonia; implicated as cause of meningitis in about 15 % of cases in children under 4 years of age - Hib vaccine has nearly eliminated this as a problem; Hemophilus aegypticus implicated in conjunctivitis Bordetella pertussis - Gram -, nonmotile, coccobacillary shape; virulent strains form capsule; causative agent of whooping cough; organism is weakly invasive; growth induces mucus secretion which induces coughing; ENDOTOXIN and EXOTOXIN released upon death of organism; highly infectious through droplet transmission; erythromycin, tetracyclines or chloramphenicol render patient noninfectious; recovery confers immunity; DPT vaccine regularly used to prevent Brucella abortus - small Gram - , nonspore forming rods, pathogenic to humans and animals; enters body through cuts and abrasions; ingested by fixed macrophages; travels via lymphatics to various lymphatic organs; grows intracellularly thus making eradication difficult; streptomycin in combination with tetracycline may be effective, but not long term; causes infectious abortions in cattle and UNDULANT FEVER; disease may last for several years and spread by infected dairy products; symptoms include intermittent fever, chills, and body aches Vibrio cholerae - Gram -, polar flagellated, comma shaped rods, waterborne, aerobic; virtually absent from Western world since advent of water purification; produces two substances that affect intestinal mucosa - enzyme like hyaluronidase and an EXOTOXIN (ENTEROTOXIN) that affects the permeability of the intestinal walls and causes water loss and electrolyte imbalance; "rice-water stools"; may lose 10-15 liters of fluid a day leading to shock, dehydration, death; streptomycin, tetracyclines, chloramphenicol sometimes effective in early stages of disease; fluid replacement and electrolyte balance most critical factors to control; humans are only natural host of organism
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