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MBIO 360 > Module 1 > Flashcards

Module 1 Flashcards

1
Q

What types of nonselective media are there?

A

Chocolate agar- RBCs are lysed and release nutrients, supplements are added (supplement B, Iso-Vitatex)

Selective Neisseria media but with out antimicrobials (specific for Neisseria)

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2
Q

What is the purpose of selective media?

A

Prevents the overgrowth of contaminating normal flora

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3
Q

What types of selective media are there?

A

Modified Thayer Martin (MTM)

New York City (NYC)

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4
Q

What does MTM agar contain? What does each do?

A

Vancomycin- inhibits G+

Colistin- inhibits G- and no pathogenic Neisseria

Nystatin- inhibits yeast

Trimethoprim lactate- inhibits Proteus spread

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5
Q

What does NYC agar contain?

A

Vancomycin

Colistin

Amphotericin B- inhibits yeast

Trimethoprim lactate

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6
Q

What type of media is ideal for isolation of vancomycin resistant strains of Neisseria?

A

Combo of selective and nonselective media

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7
Q

What types of transport media are there?

A

Non nutrient holding media- without growth, Amie’s transport medium, up to 6hrs

Growing transport media- used when there’s a delay, container with CO2 generating system, more recovery of N. gonorrhoea, vancomycin resistant strains may not be isolated

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8
Q

What is the genus test for Neisseria and Moraxella? How does the test work?

A

Oxidase positive

Amine turns positive when oxidized by enzyme

Reagent- dimethyl or tetramethyl-para-phenylenedianire (Kovac’s oxidase reagent ~1%)

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9
Q

Why can oxidase reagent only stand for a few hours after prep? How can it be stabilized?

A

Readily oxidized by oxygen

Ascorbic acid- reduces sensitivity

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10
Q

What are the methods for performing the oxidase test?

A

Filter paper method- reagent on paper, rub colonies on

Alternate procedure- drop of reagent on colonies

Positive- purple

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11
Q

What can cause false positives or negatives in oxidase testing?

A

False neg- old colonies, inhibitory/selective media, carb utilization media

False pos- nichrome wire, MAC

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12
Q

What is the QC for the oxidase test?

A

PC- Neisseria or Moraxella catarrhalis

NC- Staph, Strep, Enterobacteriaceae

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13
Q

What are the cellular characteristics of N. gonorrhoea?

A

G- cocci, kidney beans in pairs, 0.8-1.0um

Intracellular G- cocci

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14
Q

What are the growth requirements for N. gonorrhoea?

A

Obligate aerobes

Capnophiles (3-7%)

35°C

Moist environment required

Enriched media required (chocolate agar)

72hrs of incubation

Colonies- 0.5-3mm, grey, translucent, entire, gummy, older colonies tend to stick

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15
Q

What tests are used for Neisseria species ID?

A

Carb utilization- determines what carbs bacteria use, phenol red detects acid produced by oxidative mech

Chromogenic substrate test- detects specific enzymes, Gonochek II

Ag-Ab tests- confirmatory, coagglutination, direct fluorescent Ab, test for Protein I

Gene probes- detects unique NA sequences, ssDNA probe, positive = high RLU

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16
Q

What are the ID results for N. gonorrhoea?

A

Carb utilization- glucose +

Chromogenic substrate test- no colour change, reagent added, red-pink colour (proline aminopeptidase enzyme)

Coagglutination with Protein I antisera (N. gonorrhoea)

17
Q

What causes false negatives in carb utilization tests?

A

Extended incubation can cause reversion and loss of acid pH

Utilization of peptone in the presence of O2

18
Q

What sugars are used for reference in carb utilization testing?

A

CTA sugars

19
Q

What rapid carb utilization test kits are there?

A

QuadFerm+kit

API NH

20
Q

What colours indicate what antibiotics in chromogenic substrate tests?

A

Blue- N. lactamica (beta galactosidase)

Yellow- N. meningitidis (glutamylaminopeptidase)

No colour, reagent, red-pink- N. gonorrhoea (proline aminopeptidase enzyme)

21
Q

What can cause false negatives in Ag-Ab testing?

A

Some strains lack Protein I

22
Q

What is the antimicrobial susceptibility of N. gonorrhoea?

A

Originally all isolates were sensitive to penicillin

B lactamase resistant cephalosporins are effective (ceftizoxime and ciprofloxacin)

23
Q

How is penicillin resistance caused in N. gonorrhoea?

A

Plasmid- codes for B lactamase, PPNG

Genetic info on chromosome- changes the structure of PBPs and outer membrane permeability (resistance without B lactamase)

24
Q

What is the pathogenicity of N. gonorrhoea?

A

STI- urethral inflammation, dysuria, purulent discharge, prostatitis and epididymitis, salpingitis, endometriosis, peritonitis, infertility

Rectal infection

Purulent conjunctivitis

Occasionally spreads to bloodstream- DGI

25
Q

What are the growth requirements of N. meningitidis?

A

Aerobic

Capnophilic (3-7%)

50% humidity

35°C

Nutrient media not recommended, good growth on MTM and NYC

SPS anticoagulant is inhibitory to some strains

26
Q

What are the colonial characteristics of N. meningitidis?

A

Moist

Smooth

May be mucoid

No hemolysis

Translucent

Older colonies tend to autolyse

27
Q

What are the species ID results for N. meningitidis?

A

Oxidase +

Carb- glucose + and maltose +

Coagglutination and latex reagents

Polyvalent meningococcal antisera

28
Q

What is the antimicrobial susceptibility of N. meningitidis?

A

Most strains are susceptible to penicillin

Resistance due to plasmid induced B lactamase

29
Q

What is the pathogenicity of N. meningitidis?

A

Nasopharynx of ~5% of healthy individuals

Children and young adults are most susceptible

Petechial rash

Elevated WBC in spinal fluid

Fulminate form AKA Waterhouse Friderichsen syndrome

Endocarditis, pneumonia, arthritis, conjunctivitis

30
Q

What are the characteristics of other Neisseria species?

A

G- cocci in pairs, not usually intracellular

O2 required, but not increased CO2

Grows well on nutrient agar without enrichment, don’t grow on selective media

Dry, hard, wrinkled colonies

31
Q

What is the species ID for other Neisseria species?

A

Oxidase +

N. lactamica- glucose + maltose + lactose +

N. species- may be positive for sucrose, negative for all others

32
Q

What are the cellular characteristics of Moraxella catarrhalis (M. cat)?

A

G- cocci in pairs, resist decolourizing

Found intra and extracellularly

33
Q

What are the growth conditions of M. cat?

A

Aerobe, doesn’t require increased CO2

35°C

Grows on nutrient agar without enrichment (optimum growth on blood and chocolate agar)

34
Q

What are the species ID results of M. cat?

A

Strongly oxidase and catalase positive

Carb utilization- doesn’t produce any acid

Lipase pos

DNase pos (Neisseria are neg)

Butyrate esterase test- pos (most Neisseria neg)

35
Q

What is the antimicrobial susceptibility of M. cat?

A

Most strains are resistant to vancomycin, colistin, trimethoprim and clindamycin

Suitable antimicrobials- amoxicillin with clavlanate, cotrimoxazole, erythromycin, tetracycline, second gen cephalosporins

~80% produce B lactamase

36
Q

What is the pathogenicity of M. cat?

A

Normal respiratory flora

Otitis media and maxillary sinus infection

Conjunctivitis, pneumonia, bronchitis, tonsillitis, endocarditis, meningitis, septicaemia

37
Q

Why generas belong to the family Neisseriaceae?

A

Acinetobacter- G- rods

Kingella- G- coccobacilli

Neisseria- G- cocci

Moraxella- G- cocci and coccobacilli

MBIO 360 (14 decks)

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