Family Enterobacteriaceae often referred to as “enterics” Four major features: All ferment glucose (dextrose) All reduce nitrates to nitrites All are oxidase negative All except Klebsiella, Shigella and Yersinia are motile Prof.Dr.Ali H.Al-Kubaissy

Microscopic and Colony Morphology Gram negative bacilli or coccobacilli Non-spore forming Colony morphology on BAP or CA of little value, as they look the same, except for Klebsiella Selective and differential media are used for initial colony evaluation (ex. MacConkey, HE, XLD agars)

Escherichia coli Most significant species in the genus Important potential pathogen in humans Common isolate from colon flora

Escherichia coli (cont’d) Characteristics Dry, pink (lactose positive) colony with surrounding pink area on MacConkey

Escherichia coli (cont’d) Ferments glucose, lactose, trehalose, & xylose Positive indole and methyl red tests Does NOT produce H 2 S or phenylalanine deaminase Simmons citrate negative Usually motile Voges-Proskauer test negative

Escherichia coli (cont’d) Infections Wide range including meningitis, gastrointestinal, urinary tract, wound, and bacteremia Gastrointestinal Infections Enteropathogenic (EPEC) – primarily in infants and children; outbreaks in hospital nurseries and day care centers; stool has mucous but not blood; identified by serotyping

Escherichia coli (cont’d) Enterotoxigenic (ETEC) – “traveler’s diarrhea”; watery diarrhea without blood; self-limiting; usually not identified, other than patient history and lactose-positive organisms cultured on differential media Enteroinvasive (EIEC) – produce dysentery with bowel penetration, invasion and destruction of intestinal mucosa; watery diarrhea with blood; do NOT ferment lactose; identified via DNA probes

Escherichia coli (cont’d) Enterohemorrhagic (EHEC serotype 0157:H7) – associated with hemorrhagic diarrhea and hemolytic- uremic syndrome (HUS), which includes low platelet count, hemolytic anemia, and kidney failure; potentially fatal, especially in young children; undercooked hamburger, unpasteurized milk and apple cider have spread the infection; does NOT ferment sucrose; identified by serotyping

Escherichia coli (cont’d) Enteroaggregative (EaggEC) – cause diarrhea by adhering to the mucosal surface of the intestine; watery diarrhea; symptoms may persist for over two weeks Urinary Tract Infections E. coli is most common cause of UTI and kidney infection in humans Usually originate in the large instestine Able to adhere to epithelial cells in the urinary tract

Escherichia coli (cont’d) Septicemia & Meningitis E. coli is one of the most common causes of septicemia and meningitis among neonates; acquired in the birth canal before or during delivery E. coli also causes bacteremia in adults, primarily from a genitourinary tract infection or a gastrointestinal source Escherichia hermannii – yellow pigmented; isolated from CSF, wounds and blood Escherichia vulneris - wounds

Klebsiella, Enterobacter, Serratia & Hafnia sp. Usually found in intestinal tract Wide variety of infections, primarily pneumonia, wound, and UTI General characteristics: Some species are non-motile Simmons citrate positive H 2 S negative Phenylalanine deaminase negative Some weakly urease positive MR negative; VP positive

Klebsiella species Usually found in GI tract Four major species K. pneumoniae is mostly commonly isolated species Possesses a polysaccharide capsule, which protects against phagocytosis and antibiotics AND makes the colonies moist and mucoid Has a distinctive “yeasty” odor Frequent cause of nosocomial pneumonia

Klebsiella species (cont’d) Significant biochemical reactions Lactose positive Most are urease positive Non-motile

Enterobacter species Comprised of 12 species; E. cloacae and E. aerogenes are most common Isolated from wounds, urine, blood and CSF Major characteristics Colonies resemble Klebsiella Motile MR negative; VP positive

Enterobacter species (cont’d)

Serratia species Seven species, but S. marcescens is the only one clinically important Frequently found in nosocomial infections of urinary or respiratory tracts Implicated in bacteremic outbreaks in nurseries, cardiac surgery, and burn units Fairly resistant to antibiotics

Serratia species (cont’d) Major characteristics Ferments lactose slowly Produce characteristic pink pigment, especially when cultures are left at room temperature S. marscens on nutrient agar →

Hafnia species Hafnia alvei is only species Has been isolated from many anatomical sites in humans and the environment Occasionally isolated from stools Delayed citrate reaction is major characteristic

Proteus, Morganella & Providencia species All are normal intestinal flora Opportunistic pathogens Deaminate phenylalanine All are lactose negative

Proteus species P. mirabilis and P. vulgaris are widely recognized human pathogens Isolated from urine, wounds, and ear and bacteremic infections Both produce swarming colonies on non- selective media and have a distinctive “burned chocolate” odor Both are strongly urease positive Both are phenylalanine deaminase positive

Proteus species (cont’d) A exhibits characteristic “swarming” B shows urease positive on right

Morganella species Morganella morganii is only species Documented cause of UTI Isolated from other anatomical sites Urease positive Phenylalanine deaminase positive

Citrobacter species Citrobacter freundii associated with nosocomial infections (UTI, pneumonias, and intraabdominal abscesses) Ferments lactose and hydrolyzes urea slowly Resembles Salmonella sp.

Salmonella Produce significant infections in humans and certain animals On differential selective agar, produces clear, colorless, non- lactose fermenting colonies with black centers (if media contains indicator for hydrogen sulfide)

Salmonella (cont’d) Salmonella on MacConkey

Salmonella (cont’d) Lactose negative Negative for indole, VP, phenylalanine deaminase, and urease Most produce H 2 S Do not grow in potassium cyanide Large and complex group of organisms; grouped by O, H, and Vi (for virulence) antigens

Salmonella (cont’d) Typhoid and Other Enteric Fevers Prolonged fever Bacteremia Involvement of the RE system, particularly liver, spleen, intestines, and mesentery Dissemination to multiple organs Occurs more often in tropical and subtropical countries

Shigella (cont’d) Characteristics Non-motile Do not produce gas from glucose Do not hydrolyze urea Do not produce H 2 S on TSI Lysine decarboxylase negative ONPG positive (delayed lactose +) Fragile organisms Possess O and some have K antigens

Shigella (cont’d) Clinical Infections Cause dysentery (bloody stools, mucous, and numerous WBC) S. sonnei is most common, followed by S. flexneri (“gay bowel syndrome”) Humans are only known reservoir Oral-fecal transmission Fewer than 200 bacilli are needed for infection in health individuals