Medical Microbiology Exam 3

This reagent is used to demonstrate a positive tryptophan deaminase test

10% ferric chloride

The two reagents used in the Voges-Proskauer test

40% KOH and α-naphthol

What disease produced by a Salmonella spp. is a severe form of enteric fever?

Typhoid fever

A physician has requested a stool culture for Yersinia, which of the following would be the most appropriate medium to use

Colistin-irgasan-novobiocin

A fecal isolate identified as E. coli produces clear colonies on MacConkey agar with sorbitol. You should suspect

Enterohemorrhagic E. coli.

most common cause of UTIs

Escherichia coli.

What are the primary antigens used in serologic grouping of salmonellae?

Flagellar H antigen and somatic O antigen

A microbiologist is reading the plates from a sputum culture. On the sheep blood agar (SBA), the microbiologist sees flat spreading colonies with a metallic sheen. On cetrimide agar, a fluorescent green color is seen in the medium with clear colonies. On MacConkey, medium clear colonies are seen that have a fruity or grapelike odor. What is the most likely organism

P. aeruginosa

What organism is a common cause of pulmonary disease among individuals with cystic fibrosis?

P. aeruginosa

P. aeruginosa virulence factors

P. aeruginosa may produce a variety of factors that lend to its pathogenicity, such as endotoxin (lipopolysaccharides), motility, pili, capsule, and several exotoxins: proteases, hemolysins, lecithinase, elastase, and DNase. Despite a number of virulence factors, this bacterium is still considered an opportunistic pathogen.

What bacterium produces swarming colonies on nonselective media, such as sheep blood agar (SBA)?

P. mirabilis

What is the definitive method for collecting uncontaminated urine specimens?

Suprapubic aspirate

The EHEC strain serotype O157:H7 has been associated with

The EHEC strain serotype O157:H7 has been associated with hemorrhagic diarrhea, colitis, and HUS. HUS is characterized by low platelet count, hemolytic anemia, and kidney failure.

Why can direct microscopy not be used to provide a presumptive identification of the enteric bacteria

The microscopic characteristics are indistinguishable from other gram-negative bacteria.

The principle of the citrate test includes all the following, except: The pH indicator changes from red to bright yellow. The alkaline pH that results from use of the ammonium salts changes the pH indicator. The pH indicator changes from green to blue. Bacteria able to use citrate will use the ammonium salts releasing ammonia.

The pH indicator changes from red to bright yellow.

The three nonfermenters that make up the majority of isolates routinely seen in clinical laboratories include

Three species of nonfermenters make up the majority of isolates routinely seen in clinical laboratories are P. aeruginosa, Acinetobacter spp., and S. maltophilia.

When performing the O/F test, one tube is covered with mineral oil and one tube is left uncovered. Why is one tube covered with mineral oil?

To create an anaerobic (fermentative) environment

What bacterium is the causative agent of the plague?

Yersinia pestis

A technician is reading the biochemical tests for identifying a particular gram-negative rod. The organism has produced acid, indicated by a color change, in the closed tube only. This indicates that the organism is

a fermenter

If a bacterium utilizes lactose and produces H2S, what will the KIA reaction look like?

acid/acid black butt

If an organism fermented glucose only and utilized peptones, what would the KIA reaction be?

alkaline/acid

Oxidative/fermentative (O/F) basal medium is a medium that will test the oxidative and fermentative capabilities of a microbe. The pH indicator is _____.

bromothymol blue

Escherichia coli strains have all the following properties, except methyl red (MR) positive, Voges-Proskauer (VP) negative. can use citrate as a sole carbon source. indole production. fermentation of glucose and lactose.

can use citrate as sole carbon source

What substances do nonfermenters fail to ferment in traditional media

carbohydrates

A microbiologist is reading stool culture plates. She is looking for enteric pathogens on the MAC plate. What do they look like?

clear, colorless colonies

Amino acids can be metabolized by these substances that remove an amine group. What is this substance

deaminase

What is the most common cause of death among patients with diarrhea

dehydration

Some bacteria are asaccharolytic. This means that these bacteria

do not utilize any carbohydrate; instead they use other organic molecules for energy.

During this process, glucose enters the glycolysis pathway, resulting in the formation of pyruvic acid, which is further oxidized to other acids. What is this process called?

fermentation

What organ is colonized in a patient that carries Salmonella typhi

gallbladder

Nucleic acid assays are based on the _____ of the organism and are believed to be more accurate.

genotype

What do specimens with multiple uropathogens (i.e., three or more) indicate?

probable contamination

The primary pathogens of the Enterobacteriaceae include all the following, except Shigella spp. Salmonella enterica. Proteus mirabilis. Yersinia spp.

proteus mirabilis The primary pathogens, which include S. enterica, Shigella spp., and Yersinia spp., are considered true pathogens—i.e., they are not present as commensal microbiota in the gastrointestinal tract of humans. These organisms produce infections resulting from ingestion of contaminated food or water, or from other sources.

what kind of medium is used in the motility test

semi-solid

Bacillary dysentery caused by this organism is marked by penetration of intestinal epithelial cells following attachment of the organisms to mucosal surfaces, local inflammation, shedding of the intestinal lining, and formation of ulcers that follow the epithelial penetration. What is this organism?

shigella

positive mobility test

shows hazy appearance throughout or movement away from a stab.

What additive can maintain urine sample integrity for up to 48 hours at room temperature?

sodium borate

To inoculate Kligler iron agar (KIA), the laboratory scientist should pick a well-isolated colony with an inoculating needle and

stab the butt almost all the way to the bottom of the tube, then move the needle back and forth over the surface of the slant all the way to the top of the tube.

What amino acid is the substrate in indole test broth

tryptophan

Decarboxylase tests exist for all the following amino acids, except arginine. tyrosine. lysine. ornithine.

tyrosine

Commercial identification systems fall into all of the following categories, except pH-based reactions. enzyme-based reactions. visual detection of bacterial growtth use of nitrogen and sulfur sources.

use of nitrogen and sulfur sources

The chemical reaction for the ONPG test is

β-galactosidase hydrolyzes ONPG into galactose and o-nitrophenol (a yellow compound)

Bacteria gain access to the urinary tract by

Bacteria gain access to the urinary tract by three different routes; ascending, hematogenous, and lymphatic pathways.

All of the following are categories of diarrhea-causing Escherichia coli, except EMEC. ETEC. EIEC. EPEC.

EMEC Based on definitive virulence factors, clinical manifestation, epidemiology, and different O and H serotypes, there are five major categories of diarrheogenic E. coli: enterotoxigenic (ETEC), enteroinvasive (EIEC), enteropathogenic (EPEC), and enterohemorrhagic (EHEC), which includes the diffusely adherent (DAEC) and the enteroaggregative (EaggEC) strains.

A microbiologist is reading stool culture plates. She sees an organism that has a large, mucoid pink colony on MAC. What is a good presumptive identification of this organism?

Klebsiella/Enterobacter-like organism

All of the following are characteristics of pseudomonads, except -resistance to a variety of antimicrobials, such as aminoglycosides, third-generation cephalosporins, penicillins, and fluoroquinolones. - indole-positive. -oxidase-positive. -thin gram-negative bacilli or coccobacilli.

indole positive Some characteristics or initial clues can indicate the presence of pseudomonads in the clinical laboratory include thin gram-negative bacilli or coccobacilli on Gram stain; oxidase-positive reaction, although reaction can be weak and variable; nonreactivity in 24 hours in commercial kit systems for the identification of Enterobacteriaceae; no acid production in the slant or butt of triple sugar iron or Kligler's iron agar; and resistance to a variety of classes of antimicrobial agents, such as aminoglycosides, third-generation cephalosporins, penicillins, and fluoroquinolones.

The initial screening of gram-negative rods is done by testing for the use of this carbohydrate

lactose

All the following are biochemical features of Salmonella, except indole negative. hydrogen sulfide positive. lactose positive. VP negative.

lactose positive The biochemical features for the genus include the following: (1) in almost every case, they do not ferment lactose; (2) they are negative for indole, the VP test, phenylalanine, and urease; (3) most produce hydrogen sulfide; (4) they do not grow in medium containing potassium cyanide.

What characteristic of urine inhibits growth of many pathogens

low Ph

The methyl red test detects metabolic by-products from what pathway

mixed-acid fermentation pathway

These bacteria are unable to ferment either lactose or glucose, but they can degrade the peptones present in the TSI agar or KIA aerobically or anaerobically, resulting in the production of alkaline by-products in the slant or deep, respectively, changing the indicator to a deep red color. What kind of bacteria cannot ferment lactose or glucose?

nonfermenting bacilli

Presence of red colonies with black centers on xylose-lysine-decarboxylase medium is indicative of

nonlactose fermenter and H2S positive.

In what single setting does Stenotrophomonas maltophilia typically produce disease?

nonsocomial

What biochemical test will differentiate nonfermenters from Enterobacteriaceae (except Plesiomonas)?

oxidase Most nonfermentative gram-negative bacilli are oxidase-positive, a feature that differentiates them from the Enterobacteriaceae (except Plesiomonas, which is oxidase-positive)

Biochemical tests are based on the _____ of microorganisms.

phenotype