Microbio Lec 11 - Ecoli, Klebsiella Proteus, Citrobacter An

MICROBIOLOGY LECTURE 11 – Escherichia Coli, KlebsiellaEnterobacter Serratia Group Notes from Lecture USTMED ’07 Sec C AsM ESCHERICHIA COLI

Important Properties • most abundant facultative anaerobe in the colon • ferments lactose • has 3 antigens 1. 0 – 150 2. H – 50 result in more than 1000 3. K – 90 antigenic types Virulence Factors • Pili • Capsule • Endotoxin • exotoxin (enterotoxin) -

high molecular weight (heat labile) low molecular weight (heat stable)

Pathogenesis of Diseases A. Intestinal Tract Infection • adherence of bacteria to the epithelial cells of jejunum and ileum by means of pili o bacteria synthesize enterotoxin o (no inflammation nor invasion) o watery, non-bloody diarrhea (cells of the colon are not susceptible probably because they lack receptor for the toxin • Enterotoxigenic E. coli is the most common cause of traveler’s diarrhea • Enteropathogenic (enteroinvasive) strains cause disease not by enterotoxin formation but by invasion of the epithelium of the large intestine causing bloody diarrhea (dysentery) accompanied by inflammatory cells (nuetrophils) in the stools • Enterohemorrhagic strains (O157:H7) produces verotoxin or Shiga-like toxin causing bloody diarrhea but does not cause inflammation, so neutrophils are not found in the stool • Associated with outbreaks of diarrhea following ingestion of undercooked hamburgers at fast food restaurants and direct contact with animals (visit to farms and petting zoos) • Some strain cause hemolytic-uremic syndrome (nonimmune hemolytic anemia, thrombocytopenia, and acute renal failure B. Systemic Infections • Structures responsible for systemic disease are the capsule and endotoxin o Capsule – prevents phagocytosis, enhancing the organism ability to cause infection in various organs (neonatal meningitis) o Endotoxin – a lipopolysaccharide which cause features of gram negative sepsis (fever, hypotension, disseminated intravascular coagulation) C. Urinary Tract Infections • Factors favoring uropathic strains of E. coli to produce infection o pili with adhesion protein or adhesin that binds to specific receptors (dimers of galactose) in the urinary tract epithelium o motility aids in the ability to ascend the urethra into the bladder à urether à kidney • E. coli is the leading cause of community acquired UTI (occurs primarily in women) • Reasons why it is more common in women: o short urethra o proximity of the urethra to the anus o colonization of the vagina by members of the fecal flora • also the most frequent cause of nosocomial (hospital – acquired) UTI • occurs equally in both men and women • associated with indwelling catheters Clinical Presentation • Cystitis – if only the bladder is involved (present with dysuria and frequency)

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Pyelonephritis – characterized by fever, chills and flank pains Laboratory Diagnosis • lactose fermenters forming pink colonies in MacConkey agar • greenish sheen on EMB agar • produces indole from tryptophan decarboxylates lysine • uses acetate as its only source of carbon • motile

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ferments sorbitol (except E. coli 0.157:H7)

Treatment: • Uncomplicated UTI – oral cotrimoxazole • Complicated UTI and sepsis – parenteral antibiotics (3rd generation cephalosphorin with or without aminoglycosides) • Toxigenic/traveller’s diarrhea o self-limited (no antibiotic, only fluid and electrolyte replacement) KLEBSIELLA-ENTEROBACTER SERRATIA GROUP

Important Properties • Frequently found in the large intestine but are also present in soil and water • Group has very similar properties and are usually disintiguished on the basis of biochemical reactions and motility • Klebsiella pneumoniae has a very large capsule (giving the colonies striking mucoid appearance) • Serratia marcescens produces red pigmented colonies Pathogenesis and Epidemiology A. Klebsiella pneumoniae • Most likely to be a primary non-opportunistic pathogen (related to its antiphagocytic capsule) • Predisposing factors o advanced age o chronic respiratory disease o diabetes o alcoholism • 10% of healthy people are carriers B. Enterobacter /Serratia • associated with hospital acquired infections sec to invasive procedures o intravenous catheterization o respiratory intubation o urinary tract manipulation • outbreaks of Serratia pnuemonia have been associated with contamination of the water in respiratory therapy devices Clinical Findings/Disease • UTI

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Bacteremiaà sepsis Meningitis Pneumonia

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if due to Klebsiella, patient produces thick, bloody sputum (current-jelly) and can progress to necrosis and abscess formation

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Laboratory Diagnosis • Lactose fermenting colonies on differential agar (MacConkey’s or EMB • Serratia – late lactose fermenter and can produce a negative reaction • Differentiated by the use of biochemical test Treatment • Frequently resistant to multiple antibiotics especially if hospital acquired • Empicic treatment with cephalosporin plus an aminoglycosides pending result of sensitivity testing Prevention • Changing site of intravenous catheters • Removing urinary catheters when they are no longer

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needed Proper care of respiratory therapy devices

PROTEUS

Important Properties • Produce the enzymes phenylalanine deaminase (distinguish them from other members of Enterobacteriacea) • Produce the enzyme urease • Certain species are motile and produce swarming effect on blood agar • Cell wall O antigens (Ox-2, Ox-19, Ox-K) cross react with antigen of several species of rickettsiae in patient’s serum (Weil- Felix reaction) • Species of clinical importance- P. vulgaris, P. mirabilis, P. morganii (Morganella morganii) and P. rettgeri (Providencia rettgeri) Pathogenesis and Epidemiology • Organism present in human colon, soil and water

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their tendency to cause urinary tract infection is probably due to their presence in the colon and to colonization of the urethra, especially in women the vigorous motility of the organism may contribute to their ability to invade the urinary tract produces urease which hydrolysis urea in urine to form ammonia, which changes the pH and encourage stone formation (struvite calculi) which obstruct urine flow, damage urinary epithelium, and serve as nidus for recurrent infection by trapping bacteria within the stone

Clinical Infection • UTI • Pneumonia • Wound infection • Septicemia 

Proteus mirabilis is the species of Proteus that causes most community and hospital acquired infection.

Laboratory Diagnosis • Non-lactose fermenting colonies in MacConkeys or EMB agar • “Swarming” on blood agar/MacConkey • P. vulgaris and P. mirabilis produce H2S (blackers the butt of TSI agar) • All proteus are indole positive except P. mirabilis Treatment • For indole positive – cephalosporin (Cefotaxime) • Most strains are sensitive to Aminoglycoside and Cotrimoxazole • P. mirabilis is frequently sensitive to Ampicillin • P. rettgeri is frequently resistant to multiple antibiotics CITROBACTER

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gram negative rods related to Salmonella and Arizona Occur in the environment and in human colon Causes sepsis in immuno-compromised host

PSEUDOMONAS

Important Properties • gram-negative rods

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strict aerobes non-fermenters (do not ferment glucose) oxidase-positive able to grow in water containing only traces of nutrients e.g. tap water Some species (aeruginosa and cepacia) have a remarkable ability to withstand disinfectants (grows in exachlorophene- containing soap solution, in antiseptics, and in detergents.

Pseudomonas Aeruginosa • Produces 2 pigments 1. Pyocyanin – color the pus in a wound blue 2. Pyoverdin – a yellow-green pigment that fluoresces under ultraviolet light (can be used to detect early infection in burn patient) • strains of Pseudomonas with prominent shrine layer (glycocalyx) give colonies a very mucoid appearance • slime layer mediates adherence of the organism to mucous membrane of the respiratory tract and prevents antibody from binding to the organism Epidemiology of P. Aeruginosa • found chiefly in soil and water • approximately 10% of people carry • it in the normal flora of the colon • found in the skin of moist areas • can colonize the upper respiratory tract of hospitalized patients • grow in simple aqueous solutions (results in contamination of respiratory therapy and anesthesia equipment, intravenous fluids, and even distilled water) Primarily an opportunistic pathogen that causes infections in hospitalized patients • those with extensive burns • those with chronic respiratory disease • those who are immunocompromised (neutrophil count less than 500/uL) • those with indwelling catheters • 10-20% of hospital-acquired infection are due to Pseudomonas • most common cause of gram negative nosocomial pneumonia Pathogenesis of P. Aeruginosa • based on multiple virulence factors 1. Endotoxin – similar to those of other gram-negative bacteria causing symptom of sepsis and septic shock 2. Exotoxin A – causes tissue necrosis (inhibits eukaryotic protein synthesis) 3. Enzymes (elastase and proteases) – histotoxic and facilitates invasion of the organism into the bloodstream 4. Pyocyanin – damages cilia and mucosal cells of the respiratory tract • • •

Some strains with type III secretion system are significantly more virulent than those without this secretion system This secretion system transfer the exotoxin from the bacterium directly into the adjacent human cell, which allow the toxin to avoid neutralizing antibody This system is mediated by transport pumps in the bacterial cell membrane

Clinical Findings • can cause infection virtually anywhere in the body but urinary tract infections, pneumonia, and wound infections (burns) predominate • can enter the blood causing sepsis causes endocarditis in IV drug users, severe external otitis (malignant otitis externa), skin lesion (folliculitis) from inadequately chlorinated swimming pools and hot tubs, osteochondritis of the foot in those who sustain punctured wound through the soles of gym shoes, and corneal infection in contact lens users • When bacteria spread to the skin, they cause black necrotic lesions called ecthyma gangrenum

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Laboratory Diagnosis A. Presumptive • non- lactose fermenting (colorless) on MacConkey or EMB agar • typical metallic sheen of the growth on TSI agar • blue-green pigment on ordinary nutrient agar • fruity aroma B. Confirmatory • biochemical reactions Treatment • resistant to many antibiotics • treatment of choice – combination of anti-pseudomonal penicillin (ticarcillin or piperacillin) plus an aminoglycoside (gentamicin or amikacin)

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