General Bacteriology

Question 1

Name the two mechanisms by which bacteria produce disease.

Answer 1

Invasiveness and toxigenicity.

Question 2

Define virulence.

Answer 2

The degree of pathogenicity of a microorganism.

Question 3

Name several bacterial virulence factors.

Answer 3

Capsules, toxins, enzymes, cell wall receptors, and pili.

Question 4

How do capsules contribute to the virulence of certain bacteria?

Answer 4

They enable the organism to resist phagocytosis.

Question 5

Compare endotoxins and exotoxins.

Answer 5

Picture

Question 6

What is toxoid?

Answer 6

A toxin treated to decrease its toxicity but retain its antigenicity. It is given to stimulate anti-toxin production. The tetanus toxoid is an example.

Question 7

What is an antitoxin?

Answer 7

An antibody against a toxin. Antitoxins are used to treat diseases caused by toxins, for example, botulism.

Question 8

What kind of immunization results when a person is injected with a toxoid?

Answer 8

Artificially acquired active immunity.

Question 9

What is an opportunistic pathogen?

Answer 9

An organism that does not cause harm in a healthy host, but which can cause disease in a debilitated or immunocompromised host.

Question 10

What are some factors that can render an individual susceptible to opportunistic infections?

Answer 10

Very young or very old age, immune deficiencies, burns, dialysis, diabetes, chronic diseases, alcoholism, radiation, chemotherapy, organ transplants, invasive medical techniques, and antibiotics.

Question 11

What is a commercial organism?

Answer 11

One that lives on or in the host without causing harm, for example, the normal flora of the skin, mouth, and GI tract.

Question 12

What is a nosocomial infection?

Answer 12

An infection acquired while in the hospital.

Question 13

Define zoonosis.

Answer 13

An infectious disease contracted from direct or indirect animal contact.

Question 14

How do bacteria reproduce?

Answer 14

By binary fission. The cell divides into two genetically identical cells.

Question 15

What is generation time?

Answer 15

The time it takes for a population to double. This varies from approximately 15 minutes for E. coli to 24 hours for Mycobacterium tuberculosis.

Question 16

What is a facultative anaerobe?

Answer 16

An organism that can grow with or without oxygen. Most pathogen are facultative anaerobes.

Question 17

What is an obligate anaerobe?

Answer 17

An organism that can not grow in the presence of oxygen, for example, Clostridium and Bacteroides. Moderately obligate anaerobes can tolerate some expose to oxygen but require an oxygen-free environment for growth. Strict obligate anaerobes are killed by even a few minutes of exposure to oxygen, so they require special handling to protect them from oxygen.

Question 18

What is the optimum atmosphere for strict anaerobes?

Answer 18

80-85% nitrogen, 10% hydrogen, 5-10% carbon dioxide, and less than 1% oxygen.

Question 19

What is a capnophilic organism?

Answer 19

An organism that requires increased carbon dioxide, for example, pathogenic Neisseria.

Question 20

What concentration of CO2 is achieved with a candle jar?

Answer 20

Approximately 3%. This concentration is not sufficient for some capnophilic organisms such as Campylobacter. A CO2 incubator can be used to provide a concentration of 5-10% and commercial bio-bags are available for incubation of small numbers of plates.

Question 21

What quality control is required for the CO2 incubator?

Answer 21

The CO2 concentration and temperature should be checked daily.

Question 22

What types of candles should be used in a candle jar and why?

Answer 22

White unscented. Others may emit substances toxic to bacteria.

Question 23

Which type of organisms will grow in a candle jar?

Answer 23

Aerobes, facultative anaerobes, and capnophilic organisms. The candle jar is not oxygen free.

Question 24

What is a microaerophilic (microaerobic) organism?

Answer 24

An organism that requires a reduced level of oxygen in order to grow, for example, Campylobacter.

Question 25

What is the usual temperature of incubation for bacterial cultures?

Answer 25

35-37C. Most human pathogens are mesophiles and grow best close to body temperature.

Question 26

Name two organisms that grow at 42C?

Answer 26

Campylobacter and Pseudomonas aeruginosa.

Question 27

Name two bacteria that can grow below 35C?

Answer 27

Listeria monocytogenes and Yersinia enterocolitica can grow from 0-40C. Cold enrichment may be used to enhance the recovery of these organisms.

Question 28

What is the usual incubation time for bacterial cultures?

Answer 28

Most bacteria routinely encountered grow in 24-48 hours. Mycobacteria and some anaerobes require longer incubation.

Question 29

What are molecular diagnostic techniques?

Answer 29

Techniques in which specific sequences of DNA or RNA are targeted for analysis. These methods allow for detection of microorganisms directly in the clinical specimen.

Question 30

What are nucleic acid probes?

Answer 30

Probes are labeled single-strand sequence of DNA or RNA that are complementary to the nucleic acid sequence to be detected.

Question 31

What is polymerase chain reaction (PCR)?

Answer 31

A nucleic acid amplification technique in which a target sequence of DNA or RNA is identified & amplified enough so that it can be detected by gene probe technology.

Question 32

What is a major cause of false-positive results with PCR?

Answer 32

Contamination with nucleic acids. Scrupulous technique is required.