MLS 2212 - Unit 3A Final Examination
with All Solved Questions 2025-2026
Updated.
List the four major groups of Gram negative rods, and the percentages of each that are isolated
in clinical labs. - Answer 70-80% Enteric GNR
10-15% Non-fermentative GNR
10-15% Fastidious GNR
1% Misc and infrequently encountered GNR
List and explain the common characteristics, including common laboratory characteristics of the
Enterobacteriaceae. - Answer Facultative anaerobes (however they prefer aerobic
conditions)
Non-fastidious
Most are normal flora (human fecal)
Ubiquitous in nature (except for intestinal pathogens)
All reduce nitrate to nitrite
Oxidase negative
Glucose Fermenter (THIO - yellow at the bottom)
G. neg. pleomorphic rods -> do not report cellular arrangement
Colony morphology: SBA: large gray mucoid, generally larger than Staph or Strep
Divided into lac. pos. and lac. neg
Explain why Enterobacteriaceae are also referred to as coliforms or enterics - Answer
Enterobacteriaceae is a large family of Gram negative bacteria. Coliforms are a group of Gram
negative bacteria which are lactose fermenting. Coliforms belong to Enterobacteriaceae. Hence,
all coliforms are members of Enterobacteriaceae.
,List the three pathogenic categories of enteric pathogens and explain the basis for the groups. -
Answer Opportunistic pathogens
Urinary tract infections
Wounds of all types
Septicemia
Lower respiratory tract infections
Meningitis
Intestinal pathogens
Salmonella, Shigella
E. Coli -> strains that cause diarrheal illness
Yersinia enterocolitica
Non-intestinal pathogen
Yersinia pestis
Explain the difference between identifying the Enterobacteriaceae using manual vs. automated
systems. List two examples of automated instruments. Explain the term "best fit" as it is used to
identify the enterics using manual testing. - Answer Manual approach:
Gram stain
Selective and differential plating media
Biochemical test
Spot tests
Tubed or plating media
Automated instruments and ID kits:
20-30 biochemical tests
Involve large databases
Instruments:
Microscan walkaway
Vitec
Kits: Crystal ID system
, Some are referred to State Health Labs for serological ID
List the three broad classifications that are used from the results of MAC plates to initially
identify Enterobacteriaceae. - Answer Lactose fermenter
Non-lactose fermenter
Delayed lactose fermenter
Outline the overall plan for identifying GNRs. - Answer Plating, SBA(except stools), MAC,
HEA(only GI sources), SMAC(only GI sources)
Growth characteristics
Colony morphology
Spot tests, biochemical tests
Presumptive or definitive ID (list of 3-4 key terms)
Biochemical tests (only used on isolated colonies)
TSI( Triple Sugar Iron)
ONPG
Indole
Decarboxylase (ornithine)
Citrate
Urease
Deaminase (PAD)
Motility
MR-VP
DNase
List the ingredients (and percentages) of a TSI tube and the function of each, the inoculation
and incubation conditions and precautions. Define the terms monosaccharide and disaccharide.
For the disaccharides in a TSI tube, list the enzymes used to break them down and the
monosaccharide products. List four ways that a TSI tube is used to differentiate groups of
common GNR's. Explain in detail, the TSI reactions. - Answer 1)Glucose 0.1%
2)Lactose 1.0%. (3 carbohydrates)
3)Sucrose 1.0%.
with All Solved Questions 2025-2026
Updated.
List the four major groups of Gram negative rods, and the percentages of each that are isolated
in clinical labs. - Answer 70-80% Enteric GNR
10-15% Non-fermentative GNR
10-15% Fastidious GNR
1% Misc and infrequently encountered GNR
List and explain the common characteristics, including common laboratory characteristics of the
Enterobacteriaceae. - Answer Facultative anaerobes (however they prefer aerobic
conditions)
Non-fastidious
Most are normal flora (human fecal)
Ubiquitous in nature (except for intestinal pathogens)
All reduce nitrate to nitrite
Oxidase negative
Glucose Fermenter (THIO - yellow at the bottom)
G. neg. pleomorphic rods -> do not report cellular arrangement
Colony morphology: SBA: large gray mucoid, generally larger than Staph or Strep
Divided into lac. pos. and lac. neg
Explain why Enterobacteriaceae are also referred to as coliforms or enterics - Answer
Enterobacteriaceae is a large family of Gram negative bacteria. Coliforms are a group of Gram
negative bacteria which are lactose fermenting. Coliforms belong to Enterobacteriaceae. Hence,
all coliforms are members of Enterobacteriaceae.
,List the three pathogenic categories of enteric pathogens and explain the basis for the groups. -
Answer Opportunistic pathogens
Urinary tract infections
Wounds of all types
Septicemia
Lower respiratory tract infections
Meningitis
Intestinal pathogens
Salmonella, Shigella
E. Coli -> strains that cause diarrheal illness
Yersinia enterocolitica
Non-intestinal pathogen
Yersinia pestis
Explain the difference between identifying the Enterobacteriaceae using manual vs. automated
systems. List two examples of automated instruments. Explain the term "best fit" as it is used to
identify the enterics using manual testing. - Answer Manual approach:
Gram stain
Selective and differential plating media
Biochemical test
Spot tests
Tubed or plating media
Automated instruments and ID kits:
20-30 biochemical tests
Involve large databases
Instruments:
Microscan walkaway
Vitec
Kits: Crystal ID system
, Some are referred to State Health Labs for serological ID
List the three broad classifications that are used from the results of MAC plates to initially
identify Enterobacteriaceae. - Answer Lactose fermenter
Non-lactose fermenter
Delayed lactose fermenter
Outline the overall plan for identifying GNRs. - Answer Plating, SBA(except stools), MAC,
HEA(only GI sources), SMAC(only GI sources)
Growth characteristics
Colony morphology
Spot tests, biochemical tests
Presumptive or definitive ID (list of 3-4 key terms)
Biochemical tests (only used on isolated colonies)
TSI( Triple Sugar Iron)
ONPG
Indole
Decarboxylase (ornithine)
Citrate
Urease
Deaminase (PAD)
Motility
MR-VP
DNase
List the ingredients (and percentages) of a TSI tube and the function of each, the inoculation
and incubation conditions and precautions. Define the terms monosaccharide and disaccharide.
For the disaccharides in a TSI tube, list the enzymes used to break them down and the
monosaccharide products. List four ways that a TSI tube is used to differentiate groups of
common GNR's. Explain in detail, the TSI reactions. - Answer 1)Glucose 0.1%
2)Lactose 1.0%. (3 carbohydrates)
3)Sucrose 1.0%.
