Enterobacteriaceae Practice Flashcards

Comprehensive vocabulary flashcards covering the characteristics, identification, and clinical significance of the Enterobacteriaceae family.

Enterobacteriaceae

A large family of Gram-negative bacilli and coccobacilli with 100 recognized species that are frequent and diverse opportunistic and true pathogens.

True Pathogen

An organism that is always pathogenic in a host, regardless of the host's health status.

Cytochrome oxidase

An enzyme that members of Enterobacteriaceae are generally negative for, with the exception of Plesiomonas.

Glucose fermentation

A defining biochemical characteristic of all members of the Enterobacteriaceae family.

Nitrate reduction

The biochemical process where most Enterobacteriaceae reduce nitrates to nitrites.

Facultative anaerobes

Organisms that can grow well on blood agar and are able to survive in both the presence and absence of oxygen.

Nonmotile Enterobacteriaceae

Includes the genera Klebsiella, Shigella, and Yersinia (the latter being nonmotile specifically at $37\,\text{°C}$).

Somatic antigen (O)

A heat-stable antigen located in the cell wall (LPS or endotoxin) used to identify a serogroup.

Envelope antigen (K)

A heat-labile capsular antigen that surrounds the bacterial cell.

Flagellar antigen (H)

A protein antigen located on the flagellum that defines a serotype when paired with the O antigen.

Swarming motility

A characteristic growth pattern of the genus Proteus where the bacteria grow into the agar in waves or swarms.

Mucoid morphology

The appearance of Klebsiella pneumoniae colonies on agar, caused by its large polysaccharide capsule.

Sorbitol MacConkey (SMAC)

A differential medium used to identify verotoxic E. coli, which appear as sorbitol-negative colonies.

CIN Agar

A selective and differential medium (Cefsulodin-irgasan-novobiocin) used for the recovery of Yersinia enterocolitica.

XLD or HE Agar

Selective media used to differentiate and isolate Shigella and Salmonella from stool specimens.

Campy BAP

A specialized blood agar plate used for the isolation of C. jejuni.

EMB Agar

Eosin Methylene Blue agar, where E. coli typically produces a characteristic green metallic sheen.

Hektoen Enteric (HE) Agar

A medium where nonfermenters that produce hydrogen sulfide, like Salmonella, show green growth with black centers.

Phenol red

A pH indicator used in carbohydrate fermentation tests that becomes yellow at a pH of $6.8$ or less.

TSI (Triple Sugar Iron) Agar

A two-reaction chamber (slant and deep) used to determine carbohydrate fermentation and hydrogen sulfide production.

TSI K/A reaction

Alkaline slant (Red) over Acid deep (Yellow), indicating that only glucose was fermented.

TSI A/A reaction

Acid slant (Yellow) over Acid deep (Yellow), indicating fermentation of glucose, lactose, and/or sucrose.

Indole test

Detects the enzyme tryptophanase, which converts tryptophan to indole, resulting in a red color with Kovach’s reagent.

Methyl Red (MR)

Part of the IMViC reactions; it detects the production of mixed acids from glucose metabolism.

Voges-Proskauer (VP)

Part of the IMViC reactions; it detects the production of the neutral end-product acetoin.

Citrate test

Determines if an organism can use citrate as its sole carbon source, indicated by growth and a blue color change.

Lysine Decarboxylase (LDC)

An enzyme that removes the carboxyl group from lysine to form the alkaline amine cadaverine.

Ornithine Decarboxylase (ODC)

An enzyme that removes the carboxyl group from ornithine to form the alkaline amine putrescine.

Arginine Dihydrolase (ADH)

An enzyme that removes the carboxyl group from arginine to form the alkaline amine citrulline.

Deaminase

An enzyme that performs the removal of an amino group from lysine, tryptophan, or phenylalanine, characteristic of Proteus and Providencia.

Lysine Iron Agar (LIA)

A differential medium used to detect deamination and decarboxylation of lysine, as well as H2S production.

ONPG

A test used to detect slow or late lactose fermenters by demonstrating the presence of the $\beta$-galactosidase enzyme.

Hydrogen Sulfide (H2S) production

Detected in media like TSI or LIA through a blackening caused by the reaction of H2S with an iron salt indicator.

Urease

An enzyme that degrades urea into alkaline end products, causing a red or pink color change.

MALDI-TOF MS

An automated system used for the rapid identification of bacterial species.

Uropathogenic E. coli (UPEC)

A specific strain of E. coli that is a frequent isolate in clinical laboratories causing urinary tract infections.

Neonatal meningitis E. coli (NMEC)

A strain of E. coli that is a major cause of meningitis in newborns.

ETEC

Enterotoxigenic E. coli, the causative agent of 'Traveler’s Diarrhea,' characterized by watery diarrhea with mucus but no RBCs.

EIEC

Enteroinvasive E. coli, which invades the mucosa and causes severe abdominal cramps and bloody stools, similar to Shigella.

EPEC

Enteropathogenic E. coli, which causes nonbloody vomiting and chronic diarrhea in newborns and infants, particularly in daycares.

EHEC

Enterohemorrhagic E. coli, also known as Shiga toxin-producing E. coli (STEC) or verocytotoxic E. coli (VTEC).

O157:H7

The most common serotype of EHEC and the only strain that is sorbitol negative on SMAC agar.

Hemolytic Uremic Syndrome (HUS)

A potential progression of EHEC infection involving acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia.

CHROMagar O157

A specialized medium where EHEC colonies appear mauve-colored.

EAEC

Enteroaggregative E. coli, which causes watery, mucoid diarrhea without RBCs or WBCs.

Tribe Klebsielleae

A group of genera within Enterobacteriaceae including Klebsiella, Enterobacter, Serratia, and Pantoea that are typically VP and Citrate positive.

Klebsiella pneumoniae subsp. pneumoniae

A nonmotile, lactose-positive isolate that causes severe necrotizing pneumonia and various healthcare-associated infections.

Currant jelly sputum

A clinical characteristic of pneumonia caused by K. pneumoniae, resulting from lung abscess and hemorrhage.

Klebsiella oxytoca

A species that resembles K. pneumoniae but is biochemically distinguished by being indole positive.

Raoultella

A genus found in soil and water that serves as a Klebsiella look-alike and is indole positive.

Enterobacter

A genus of motile, ODC-positive rods that are part of the enteric flora and resemble Klebsiella.

Cronobacter sakazakii

Formerly E. sakazakii; produces a yellow pigment at $25\,\text{°C}$ and is associated with meningitis from contaminated powdered infant formula.

Serratia marcescens

An opportunistic pathogen that produces lipase, gelatinase, and DNase, and often exhibits a red pigment.

Prodigiosin

The red pigment produced by approximately half of Serratia marcescens strains at room temperature.

Hafnia alvei

A genus that resembles Enterobacter but does not ferment lactose, sucrose, or sorbitol and is an infrequent human pathogen.

Pantoea agglomerans

Commonly isolated from traumatic soil inoculations; it is triple decarboxylase (LDC, ODC, ADH) negative and produces yellow pigment.

Tribe Proteeae

A group including Proteus, Morganella, and Providencia, characterized by rapid urease activity and being deaminase positive.

Proteus mirabilis

The most frequent human isolate of its genus, indole negative, and susceptible to ampicillin.

Proteus vulgaris

A Proteus species found in immunocompromised patients that is indole positive and resistant to ampicillin.

Providencia rettgeri

The only species within the Providencia genus that is urease positive.

Morganella morganii

An opportunistic pathogen causing UTI and wound infections; it is urease and deaminase positive but citrate negative.

Citrobacter

A late lactose fermenter that resembles Salmonella but is distinguished by being ONPG positive and LDC negative.

Edwardsiella tarda

Found in reptiles and fish; it resembles E. coli but is lactose negative and produces abundant H2S in TSI.

Plesiomonas shigelloides

The only oxidase-positive member of the Enterobacteriaceae; a straight, motile rod found in fresh water.

Salmonella enterica

The primary species of Salmonella containing six subspecies, with Subgroup I containing most human pathogens.

Kaufmann-White scheme

The classification system used to identify over 2,400 Salmonella serotypes based on somatic (O) and flagellar (H) antigens.

Vi antigen

A capsular or virulence antigen found specifically in Salmonella typhi.

Bismuth Sulfite Agar

A selective and differential medium where Salmonella colonies appear black due to H2S production.

Salmonella Typhi

The causative agent of typhoid fever, which may present with fever, multi-organ involvement, and a carrier state for up to 1 year.

Rose colored spots

A transient rash on the trunk associated with Salmonella serotype Paratyphi infection.

Widal test

A serological test for S. typhi antibodies that is no longer recommended due to a high false-positive rate.

Salmonella enterica subsp. arizonae

Found in reptiles and poultry; distinguished as ONPG positive and malonate positive.

Shigella

A nonmotile, lactose-negative, biochemically inert organism with a low infectious dose that causes bacillary dysentery.

Shigella Serogroup A

The classification for S. dysenteriae, the most virulent species which produces a neurotoxin leading to paralysis.

Shigella Serogroup B

The classification for S. flexneri.

Shigella Serogroup C

The classification for S. boydii.

Shigella Serogroup D

The classification for S. sonnei, which accounts for approximately $75\,$ of Shigella cases in the U.S.

Bacillary dysentery

A condition caused by Shigella characterized by abdominal pain, cramping, and stools containing blood and mucus.

Yersinia

Small coccobacilli that are catalase positive and oxidase negative, with optimal growth at $25\,\text{°C}$ to $32\,\text{°C}$.

Yersinia pestis

The nonmotile causative agent of the Bubonic, Pneumonic, and Septicemic plagues.

Black Death

A historical pandemic from 1347-1351 caused by Y. pestis that killed 17-28 million Europeans.

Bubo

A swollen lymph node, typically cervical, axillary, or inguinal, characteristic of the Bubonic plague.

Bi-polar staining

A 'safety pin' appearance of Yersinia pestis seen in Wright-stained blood smears.

Beaten copper

A description of the appearance of Yersinia pestis colonies when viewed under a stereoscope.

Yersinia enterocolitica

The most common Yersinia species isolated from humans, associated with contaminated meat and acute enterocolitis.

Bull's eye colonies

The characteristic appearance of Yersinia enterocolitica on CIN agar, appearing clear with a red center.

ESBL (Extended-spectrum beta-lactamase)

An enzyme produced by some Enterobacteriaceae that confers resistance to penicillins and cephalosporins.

MDR (Multidrug-resistant)

Bacteria that show resistance to more than 3 antibiotic classes.

Kovach’s reagent

A chemical used in the Indole test to detect the conversion of tryptophan, yielding a red color.

Acetoin

The neutral end-product detected by the Voges-Proskauer test in the identification of glucose metabolism pathways.

Bromthymol Blue

The pH indicator used in the Citrate utilization test.

Cadaverine

The alkaline amine end-product formed by the action of lysine decarboxylase.

Putrescine

The alkaline amine end-product formed by the action of ornithine decarboxylase.

Citrulline

The alkaline amine end-product formed by the action of arginine dihydrolase.

Lipase

One of the enzymes produced by Serratia marcescens to break down fats.

DNase

An enzyme produced by Serratia species that breaks down DNA.

Lactose-positive E. coli

Appears as pink colonies on MacConkey agar due to carbohydrate fermentation.

Verocytotoxic E. coli (VTEC)

Alternative name for EHEC/STEC, highlighting the production of Shiga-like toxins.

Atrophic rhinitis

A purulent nasal infection associated with K. pneumoniae subsp. ozaenae.

Enteric selective media

Used to recover EPEC from stool specimens, where colonies appear nonbloody.