Enterobacteriaceae Flashcards
General characteristics of Enterobacteriaceae
- ferment glucose
- reduce nitrate to nitrites
- oxidase negative
- motile at body temperature
oxidase positive Enterobacteriaceae
Plesiomonas
Enterobacteriaceae that are non-motile at body temperature
Klebsiella, Shigella, Yersinia
Enterobacteriaceae colony morphology
Gram-negative rods, facultatively anaerobic, large moist gray colonies, some mucoid colonies
grow throughout thioglycolate broth tube
facultatively anaerobic Enterobacteriaceae
Enterobacteriaceae grow well on which agars?
MacConkey, EMB agar, HE agar, XLD agar
- selective and differential media
- bile salts and crystal violet to inhibit gram +
- differential for lactose fermentation
MacConkey agar
- peptone base with lactose and sucrose
- eosin and methylene blue indicators
- for the isolation and differentiation of lactose-fermenting and non-lactose-fermenting enteric bacilli
EMB agar
Sign of lactose fermentation on EMB agar
purple color change
No sign of lactose fermentation on EMB agar
colorless colonies
- bile salts to inhibit gram + and some gram -
- differential for lactose and sucrose fermentation
HE agar
non-pathogen growth on HE agar
most ferment lactose and sucrose; orange color (low pH)
pathogen growth on HE agar
green to blue color; black precipitate due to H2S gas production
- sodium desoxycholate to inhibit gram + and some gram -
- sucrose, lactose and xylose(with phenol red indicator)
- lysine to detect lysine decarboxylation
- thiosulfate to detect H2S
XLD agar
Yellow colonies on XLD agar
- fermenters or those not producing lysine decarboxylase
- E. coli, Citrobacter
Colorless or red colonies on XLD agar
likely Shigella
Red colonies with black centers on XLD agar
- were yellow then became red when lysine is decarboxylated
- Salmonella
Virulence factors of Enterbacteriaceae
adherence, toxins, invasive enzymes, O, H, K antigens
heat stable antigen located in LPS of cell wall
O antigen
flagellar antigen; heat stable
H antigen
capsular antigen; heat labile; present in E. coli and Salmonella typhi
K antigen
Opportunistic Enterobacteriaceae
- normal flora (E. coli)
- septicemia, wounds, UTI, meningitis
Pathogenic Enterobacteriaceae
Salmonella, Shigella, Yersinia enterocolitica
- pink on MacConkey agar, beta hemolytic on SBA
- motile, sex pili, fimbriae
- posses O, H, K antigens
Escherichia coli (morphology)
- ferments glucose, lactose, trehalose, and xylose
- indole positive, methyl red positive (glucose fermentation via mixed acid pathway)
- H2S, DNase, urease, PAD, and citrate negative
- IMVC (+ + - -)
E. coli (biochemical reactions)
Types of E. coli gastrointestinal infections
Enteropathogenic (EPEC), Enterotoxigenic (ETEC), Enteroinvasive (EIEC), Enterohemorrhagic (EHEC), and Enteroadherent
- infantile diarrhea, associated with nurseries and daycare
- adhesive, stool contain mucus but no blood
Enteropathogenic (EPEC) E. coli
- Traveler’s diarrhea (tropics and subtropics)
- requires large inoculum; contaminated food/water, poor hygiene and sanitation
- binds to intestinal microvilli (adhesive)
- releases toxins (heat-labile toxin and heat-stable toxin)
Enterotoxigenic (ETEC) E. coli
Enterotoxigenic E. coli toxins
- heat-labile toxin (LT): A and B units, leads to hypersecretion of fluids
- heat-stable toxin (ST): leads to hypersecretion
- dysentery with direct penetration, invasion and destruction of intestinal mucosa
- similar to Shigella but requires more inoculum
- watery diarrhea with blood, mucus, WBCs
- non-motile and don’t ferment lactose
Enteroinvasive (EIEC) E. coli
- hemorrhagic diarrhea, colitis
- hemolytic-uremic syndrome (HUS)
- watery to bloody diarrhea (no WBCs)
- E. coli O157:H7
Enterohemorrhagic (EHEC) E. coli
low platelets, hemolytic anemia, kidney failure
hemolytic-uremic syndrome
- watery to bloody diarrhea can be fatal
- associated with undercooked meat, unpasteurized milk, apple cider, bean sprouts, spinach
Enterohemorrhagic E. coli
- toxins produced by Shiga toxigenic E. coli (STEC)
- include Verotoxin I cytotoxin and Verotoxin II
- can be screened for on SMAC plate; does not ferment sorbitol
E. coli O157:H7
- phage mediated cytotoxin
- attacks vero cells, also called Shiga-like toxin
- neutralized by Shiga toxin antibodies
Verotoxin I
E. coli O157:H7 toxin not neutralized by Shiga toxin antibodies
Verotoxin II
Diagnosing E. coli O157:H7
- stool culture on differential medium with serotyping
- screens for toxin
- demonstrates a fourfold increase in toxin neutralizing antibody titer
Enteroadherent E. coli
includes diffusely adherent (DAEC) and enteroaggregative (EAEC)
- causes UTI’s and diarrheal disease
- cystitis in kids, acute pyelonephritis in pregnant women, recurring UTI’s, pediatric diarrheal disease (in developing countries)
Diffusely adherent (DAEC) E. coli
- adheres to small intestine; more than 2 weeks
- causes “stacked brick” pattern on cells
- watery diarrhea, vomiting, dehydration, abdominal pain
- mostly in children
Enteroaggregative (EAEC) E. coli
Extraintestinal infections of E. coli
UTI’s, meningitis, septicemia
Unpathogenic E. coli
most common cause of UTI’s (catheters, etc.)
- most common in neonates, gain infection just before or during birth, can involve amniotic fluid
- has capsule antigen K1
Meningitis (caused by E. coli)
Septicemia (caused by E. coli)
may result from urogenital tract infection or from GI source
Other E. coli
- Escherichia hermanii (clinical significance not established)
- Escherichia vulneris (wound infections)
Klebsiella, Enterobacter, Serratia, Pantoea, Cronobacter, and Hafnia (source/general infections)
- normal flora of GI tract, soil, water, on plants
- opportunistic and nosocomial infections
- UTI’s, wounds, pneumonia
Klebsiella, Enterobacter, Serratia, Pantoea, Cronobacter, and Hafnia (biochemical reactions)
- Simmon’s citrate +, Potassium cyanide broth +, no H2S production, no deamination of phenylalanine, urease -
- Indole -, methyl red -, Voges-Proskauer +, citrate + (all),
- IMVC - - + +
- most common Klebsiella isolate; affects lower resp. tract
- moist, gray mucoid colonies
- polysaccharide capsule (virulence)
Klebsiella pneumoniae
- similar to K. pneumoniae
- indole +
Klebsiella oxytoca
- isolated from nasal secretions and cerebral abscesses
- plasmid-mediated ESBL’s
Klebsiella ozaenea
- infection of the nasal cavity; intense swelling and malformation of entire face and neck
- Africa and South America
Klebsiella rhinoscleromatis (pneumoniae subspecies)
Two most commonly isolated Enterobacter species
E. cloacae and E. aerogenes
Enterobacter (biochemical reactions)
MR -, VP +, most produce lysine decarboxylase (not E. cloacae) and ornithine decarboxylase; infect wounds, urine, blood, CSF
Pantoea agglomerans
- similar to K. pneumoniae
- motile; lysine, ornithine, and arginine negative
- outbreak from contaminated IV fluids
- associated with neonate meningitis and bacteremia
- brain abscesses, respiratory and wound infections
Coronobacter sakazakii
- positive ONPG (slow lactose)
- DNase
- highly resistant to antimicrobials
Serratia
- prodigiosin (red at room temp)
- most clinically relevant Serratia species
- opportunistic: UTI’s, bacteremia, respiratory nosocomial infections
Serratia marcescens
Other Serratia species
- S. liquefaciens, S. ficaria, S. entomophila, S. fonticola
- S. rubidaea, S. plymuthica (red at room temp)
- S. odorifera (dirty musty odor)
Hafnia alvei
- linked to gastroenteritis, can be isolated from stool samples
- delayed citrate reaction, two biotypes
Hafnia Biotype 1
grows in beer wort of breweries; not clinically isolated
Hafnia Biotype 2
grown from environmental and human samples
- isolated from urine, wounds, ear and blood infections
- produce swarming on lab media, burnt chocolate odor
- positive phenylalanine deaminase, produce H2S
- lactose -, urease +
Proteus species
Proteus mirabilis
- most commonly isolated Proteus
- indole -, ornithine decarboxylase +, K/A with H2S on TSI
Proteus vulgaris
indole +, ornithine decarboxylase -, sucrose fermentation = A/A with H2S on TSI
UTI infections, possibly diarrhea, similar to Proteus
Morganella morganii
Providencia species
- high resistance to antimicrobials
- P. rettgeri, P. stuartii, P. alcalifaciens
urinary tract pathogen, nosocomial outbreaks
Providencia rettgeri
nosocomial burn unit outbreaks, no swarming, isolated from urine clutures
Providencia stuartii
- E. tarda is only pathogen
- urea -, lysine decarboxylase +, H2S +, indole +, no growth on citrate
- bacteremia and wound infections
Edwardsiella
Erwinia and Pectobacterium
plant pathogens
- weak urease activity, ferment lactose, grow on Simmon’s citrate, MR +, similar to Salmonella
- C. freundii hydrolyzes urea and doesn’t decarboxylate lysine
- Salmonella doesn’t hydrolyze urea and decarboxylates lysine
Citrobacter
- most common Citrobacter
- nosocomial UTI’s, pneumonia, endocarditis, intraabdomial abscesses
Citrobacter freundii
Citrobacter associated with neonatal meningitis and brain abscesses
Citrobacter koseri
Citrobacter braakii
nosocomial UTI’s
Primary Enterobacteriaceae Intestinal Pathogens
Salmonella, Shigella, Yersinia
- gram negative rods, facultative anaerobes
- clear, colorless, non lactose-fermenting colonies with black centers (K/A, H2S +)
- indole -, VP -, phenylalanine deaminase -, urease -, no growth in Potassium cyanide medium, produce H2S
Salmonella
most serious pathogens are Subgroup I (S. typhi, S. choleraesuis, S. paratyphi)
Salmonella enterica
Differentiating Salmonella subgroup I members
- lysine decarboxylase rules out S. paratyphi
- ornithine decarboxylase rules out S. typhi
- trehalose fermentation rules out S. choleraesuis
Salmonella enterica virulence factors
- fimbriae required for adhesion to intestines
- invasion factor (able to transverse intestinal mucosa)
- enterotoxin involved in gastroenteritis
Antigenic structures of Salmonella
- O and H antigens
- Vi capsular antigen
- used in serologic typing
H antigen
- occur in phase I and II
- Phase I not always present but identify particular serotype
- Phase II are nonspecific
Capsular Vi antigen
similar to capsular K antigen, always present, prevents phagocytosis
Salmonella enterica (clinical infections)
- acute gastroenteritis or food poisoning caused by organism (not toxin); milk, poultry, eggs, pet handling
- carrier state in gallbladder
- nontyphoidal bacteremia, typhoid fever, other fevers
Typhoid fever disease course
- ingestion of organism; fever, malaise, anorexia, lethargy begin 9-14 days later (flu-like)
- invades and penetrates intestinal mucosa, constipation
- enters lymphatic system, sustained in mesenteric lymph nodes
- enters blood stream; goes to spleen, liver, bone marrow; engulfed by monocytes and grow intracellularly
- released into blood stream again (isolated from blood now); prolonged bacteremia, rose spots on abdomen
- invasion of gallbladder and Peyer’s patches, bacteria released into bowel (isolated from stool now), long-term infection/necrosis of gallbladder, hemorrhage and perforation of bowel
non-typhoidal bacteremia
- prolonged fever with intermittent bacteremia
- fever and gastroenteritis with brief bacteremia in kids
- transient bacteremia during gastroenteritis or septicemia without gastroenteritis in adults
Shigella species
S. dysenteriae (group A), S. flexneri (group B), S. boydii (group C), S. sonnei (group D)
- Shigella that causes the most serious infections
- primarily in developing countries
Shigella dysenteriae (group A)
Shigella flexneri (group B)
second most common Shigella in the United States; associated in men having sex with men pop. and young adults
Shigella boydii (group C)
most common in developing countries
most common Shigella isolate in the United States; causes short, self-limiting infections
Shigella sonnei (group D)
Shigella species (general characteristics)
- non-motile, non lactose-fermenting (K/A)
- don’t produce gas (except group B)
- urease -, no H2S on TSI, doesn’t decarboxylate lysine
- S. sonnei is ONPG and ornithine decarboxylase + (S. flexneri is -)
Shigella species (clinical infections)
- dysentery (S. dysenteriae)
- fever and watery diarrhea (S. sonnei)
- requires low inoculum (resistant to stomach acid, spread by fecal-oral route
- penetration of mucosal epithelium (Shiga toxin)
Dysentery (S. dysenteriae)
- most severe Shigella infection
- local inflammation, fever, chills, shedding of intestinal mucosa, mucus, blood, ulcers, tenesmus (prolapsed rectum)
- H2S - on TSI (K/A)
- isolated on CIN agar or CIN II agar with Aeromonas
Yersinia
- Class A Bioterrorism agent
- causes The Plague; transmitted through rodents (except pneumonic form-respiratory droplets)
- gram - coccobacilli resembling a safety pin
- negative for motility above 22C, ornithine decarboxylase -
Yersinia pestis
- contact with/ingestion of swine, cats, dogs, fecal material
- survives at cold temperatures, affects kids and ICP’s
- acute gastroenteritis, simulates apendicitis
- causes erythema nodosum (red nodules on lower legs - cause itching and burning)
- motility at 25C, non-motile at 37C
- grows at 4C, ornithine decarboxylase +
Yersinia enterocolita
- rodents, farm animals, birds, guinea pigs; ingestion of fecal material
- caseous swelling called pseudotubercles in mesenteric lymph nodes
- motile at 25C; ornithine decarboxylase -
Yersinia pseudotuberculosis
- peptone base with yeast extract, mannitol, bile salts, cefsulodin, igrasan, novobiocin, neutral red and crystal violet indicators
- selective for Yersinia and Aeromonas
CIN (Cefsulodin-Igrasan-Novobiocin) agar
Screen stool pathogens (HE, XLD, Mac, SMAC) for ______
Salmonella, Shigella, Campylobacter, E. coli O157:H7
Screen stool pathogens (CIN agar) for ____________
Yersinia
Serologic grouping for __________
- Salmonella (60 types of O antigens; agglutination)
- Shigella (A through D serotypes)
