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EnterobacteriaceaeAman UllahCommon characteristicsGram-negativeShort rodsFacultative anaerobeFerments glucose and a wide range of carbohydratesOxidase negative

Escherichia coliPathogenesis/Clinical SignificanceE. coli is part of the normal flora in the colon of humans and other animals,Pathogenic both within and outside the gastrointestinal tract. E.coli species possess three types of antigens: O, K, and H. Pili facilitate the attachment of the bacterium to human epithelial surfacesPathogenic E. coli virotypes differ from the normal flora E. coli by the acquisition of genes that encode new virulence factors allowing for toxin production and attachment to or invasion of host cells.Pathogenesis/Clinical SignificanceUrinary tract infections (UTI)E. coli is the most common cause of UTIs, especially in womenSymptoms include dysuria, urinary frequency, hematuria, and pyuriaMeningitis in infantsE. coli and group B streptococci are the leading causes of neonatal meningitisE. coli strains that cause meningitis express the K1 capsule, which is chemically identical to the capsule produced by serogroup B meningococciPathogenesis/Clinical SignificanceDiarrheaSeveral categories of diarrhea are caused by different strains of E. coli

Lab diagnosisSpecimens: depend on the site of infectionDiagnose on the base of culture and sensitivity

SalmonellaSalmonella enterica serovar TyphiSalmonella enterica serovar Typhimurium

Salmonella enterica serovar TyphiPathogenesis/Clinical SignificanceS. enterica serovar Typhi is transmitted between humans, without animal or fowl reservoirsInfection is via the oralfecal route, generally through food or water contaminated by human fecesYoung children and older adults are particularly susceptible to Salmonella infections, as are individuals in crowded institutions or living conditionsS. enterica serovar Typhi causes disease by attaching to and invading macrophages of the intestinal lymphoid tissue (Peyer's patches)The bacteria replicate rapidly within these cells, and eventually spread to the reticuloendothelial system (including both liver and spleen, which become enlarged) and potentially to the gallbladder.Pathogenesis/Clinical SignificanceEnteric (typhoid) feverThis is a severe, life-threatening systemic illness, characterized by fever and, frequently, by abdominal symptomsAbout 30 percent of patients have a faint, maculopapular rash on the trunk (termed "rose spots")After 1 to 3 weeks of incubation, S. serovar Typhi can enter the blood, with the resulting bacteremia causing fever, headache, malaise, and bloody diarrheaPerforations of the intestine can lead to hemorrhageSome infected individuals may become chronic carriers for periods as long as years due to persistent residual infection of the gallbladderSalmonella enterica serovar TyphimuriumPathogenesis/Clinical SignificanceS. enterica serovar Typhimurium (and other Salmonella species that cause enterocolitis) reside in the gastrointestinal tracts of humans, other animals, and fowlThey are transmitted through contaminated food products, or via the oral/fecal routeEnterocolitis (gastroenteritis, foodborne infection)Contaminated poultry products including eggs are the primary vehicles for infection of humans by serovar Typhimurium, although raw milk and pets such as turtles also transmit the diseaseSalmonella adhere to and invade enterocytes of both the small and large intestine, causing a profound inflammatory response. Within 10 to 48 hours after ingestion, nausea, vomiting, abdominal cramps, and diarrhea ensueDiarrhea usually ends spontaneously within a week.Lab diagnosisBlood, urine and blood for culture and sensitivitySerologic tests for antibodies against O antigen in patient's serum also aid in the diagnosisShigellaMed. Imp. Species: Shigella sonnei and dysenteriaePathogenesis/Clinical SignificanceShigella species are spread from person to person, with contaminated stools serving as a major source of organismsFlies and contaminated food and water can also transmit the diseaseS. sonnei invades and destroys the mucosa of the large intestine but rarely penetrates to the deeper intestinal layersS. dysenteriae also invades the colonic mucosa but, in addition, produces an exotoxin (Shiga toxin) with enterotoxic and cytotoxic propertiesShigellaBacillary dysentery (shigellosis)This disease is characterized by diarrhea with blood, mucus, and painful abdominal crampingThe disease is generally most severe in the young and in older adults, and among malnourished individuals, in whom shigellosis may lead to severe dehydration and even deathLab diagnosisStool for C/SYersinia pestisPathogenesis/Clinical SignificanceY. pestis is endemic in a variety of mammals, both urban and sylvatic, and is distributed worldwide.Infection is transmitted by fleas, which serve to maintain the infection within the animal reservoirThe organism can also be transmitted by ingestion of contaminated animal tissues and via the respiratory route.Organisms are carried by the lymphatic system from the site of inoculation to regional lymph nodes, where they are ingested by phagocytesY. pestis multiplies in these cells. Hematogenous spread of bacteria to other organs and tissues may occur, resulting in hemorrhagic lesions at these sitesBubonic (septicemic) plagueThe incubation period (from flea bite to development of symptoms) is generally 2 to 8 days. Onset of nonspecific symptoms, such as high fever, chills, headache, myalgia, and weakness that proceeds to prostration, is characteristically sudden. Within a short time, the characteristic, painful buboes develop, typically in the groin, but they may also occur in axillae or on the neckBlood pressure drops, potentially leading to septic shock and death.Pneumonic plagueIf plague bacilli reach the lungs, they cause a purulent pneumonia that is highly contagious, and, if untreated, is rapidly fatal.Lab diagnosisLaboratory identification can be made by a gram stained smear, and culture of an aspirate from a bubo (or sputum in the case of pneumonic plague)OTHER ENTEROBACTERIACEAEOther genera of Enterobacteriaceae, such as Klebsiella, Enterobacter, Proteus, and Serratia, which can be found as normal inhabitants of the large intestine, include organisms that are primarily opportunistic and often nosocomial pathogensWidespread antibiotic resistance among these organisms necessitates sensitivity testing to determine the appropriate antibiotic treatmentEnterobacterThey rarely cause primary disease in humans but frequently colonize hospitalized patients, especially in association with antibiotic treatment, indwelling catheters, and invasive proceduresThese organisms may infect burns, wounds, and the respiratory (causing pneumonia) and urinary tractsKlebsiellaKlebsiellae are large, nonmotile bacilli that possess a luxurious capsuleKlebsiella pneumoniae and Klebsiella oxytoca cause necrotizing lobar pneumonia in individuals compromised by alcoholism, diabetes, or chronic obstructive pulmonary disease. K. pneumoniae also causes UTI and bacteremia, particularly in hospitalized patientsSerratiaThe species of Serratia that most frequently causes human infection is Serratia marcescensSerratia can cause extraintestinal infections such as those of the lower respiratory and urinary tracts, especially among hospitalized patientsProteus, Providencia, and MorganellaMembers of these genera are agents of urinary tract and other extraintestinal infectionsProteus species are relatively common causes of uncomplicated as well as nosocomial UTIOther extraintestinal infections, such as wound infections, pneumonias, and septicemias, are associated with compromised patientsProteus organisms produce urease, which catalyzes the hydrolysis of urea to ammonia. The resulting alkaline environment promotes the precipitation of struvite stones containing insoluble phosphates of magnesium and phosphate.