Micro Elsevier questions/answers Flashcards
1
Q
What is the MIC
A
The lowest drug level that is bacteriostatic
Determined from serieal two-fold dilutions of each antibiotic
2
Q
- Recommended therapy for S pneumonia
- Is a urinary antigen test available for S pneumonia?
- Most virulent capsule type
- Who is vaccine recommended for
A
- penicillin G or 2nd or 3rd gen cephalosporin (must do susc because resistance is common)
- Yes
- Type 3
- 23-polyvalent vaccine is available for patients > 65 and patients with chronic pulmonary, cardiac, liver, or renal disease, asplenia, sickle cell disease, diabetes, and immunocompromised
3
Q
What antibiotic is used to treat ESBL-producing bacteria
A
Carbapenems
4
Q
Empiric therapy for G+ cocci in clusters
A
Vancomycin
5
Q
serovars for lymphogranuloma venereum
A
L1, L2, L3 of C trachomatis
6
Q
virulence factors and treatment for listeria
A
- Actins, hemolysins, and membrane proteins called internalins
- Ampicillin (resistance is not common)
7
Q
Quadrivalent menigococcal vaccine covers?
Recommended for?
A
A, C, Y, and W135 (C and W-135 are more common in industrialized countries); does not cover B because of poor immunogenicity
Recommended for military recruits, college freshmen, asplenic patients, children over 2 years, prisoners, and lab workers
8
Q
Diagnosis of B henselae
Spectrum of diseases in people
Disease in cats
A
- serology is best because it takes weeks to culture if it ever grows
- cat scratch disease, endocarditis, bacillary angiomatosis, and neuroretinitis
- intraRBC bacteremia in cats
9
Q
Shigella food born illness comes from what food
A
Contaminated water, vegetables
10
Q
Brucella
- growth
- oxidase result
- urease result
A
- no growth on MAC
- takes 2 days to grow on BAP and chocolate
- oxidase positive
- urease positive
(also catalase positive)
11
Q
V vulnificus
- lactose and sucrose fermentation
- treatment
- virulence factors
A
- lactose fermenter; sucrose non-fermenter
- tetracyclines or aminoglycosides
- capsule, elastolytic protease, cytolysins, and collagenase
12
Q
gram-negative organisms contain large amounts of ____ which is degraded by acetone alcohol decolorization step in gram stain
A
lipopolysaccharide
13
Q
Indole and ornithine decarboxylase positivity in Proteus species
Beta lactamase produced by which proteus species
A
P vulgaris is indole positive
P mirabilis is ODC positive
P vulgaris is intrinsically resistant to ampicillin due to chromosomal beta lactamase
14
Q
treatment for C diff
A
vancomycin or metronidazole
15
Q
Site of infection for whooping cough
A
nasopharynx
16
Q
How does salmonella appear on XLD media
- other agars used for salmonella
- motility of salmonella
- when to treat salmonella with abx
A
Black due to H2S
- brillant green agar, HE agar
- motile
- treat with abx if infection spread beyond GI tract, if it is severe, or if patient is immunocompromised
17
Q
Staph lug
PYR and ODC status
methicillin resistance?
S schleiferi
A
- PYR positive (unlike S aureus) and ODC positive (unlike other coagulase negative staph)
- methicillin resistance is rare
- S schleiferi is positive for PYR and negative for ODC
18
Q
Acinetobacter baumanii
A
- gram negative coccobacillus
- non motile (although some research shows that they actually can be motile)
- non lactose fermenter
- oxidase negative
- highly resistant to antimicrobial agents (multidrug resistance)
- possible to treat with amikacin or tobramycin; polymyxin reserved for highly resistant isolates
19
Q
Molecular strain typing methods in a hospital setting
A
(not MALDI-TOF; this only subtypes species)
- used to determine if a cluster of infections in a unit is caused by the same strain
- Methods:
- pulsed-field gel electrophoresis with DNA fragments
- random amplification of polymoprhic DNA
- multilocus sequence typing
- restriction fragment length polymorphisms
- amplified fragment length polymorphism
20
Q
NAAT method
A
Uses PCR or transcription mediated amplification
21
Q
Potential sequelae of bacterial vaginosis
A
Sequelae:
- PID
- cervicitis
- endometritis
- increased risk of HIV
Clinical diagnosis (need 3 of 4 of Amsel’s criteria):
- clue cells
- positive KOH amine testing
- pH > 4.5
- watery, fishy vaginal discharge
Shift in flora from mainly lactobacilli to bacteroides, prevotella,mobiluncus, gardnerella
Nugent gram stain is gold standard
22
Q
Biochemical differences between bacteroides, prevotella, and porphyromonas
A
Bacteroides is bile resistant
Prevotella is bile sensitive, pigmented, and saccharolytic
Porphyromonas is pigmented and asaccharolytic
23
Q
Burkholderia cepacia complex
- gram stain
- biochemicals
A
slow growing nonlactose fermenting, gram negative bacillus
weakly positive oxidase
24
Q
List of PYR positive staph
A
S haemolyticus
S lugdunensis
S saprophyticus
S schleiferi
25
Amp C
SPACE
Serratia
Proteus
Acinetobacter
Citrobacter
Enterobacter
Resistant to all beta lactam abx except carbapenems and cefepime (includes resistance to cefoxitin)
26
ESBL
Resistant to cephalosporins, but not cephamycins
E coli, Klebsiella, Proteus mirabilis
Clav acid inhibits ESBL
27
Strep dysgalactiae subspecies equisimilis
Common cause of pharyngitis in teens and young adults, as well as necrotizing fasciitis, cellulitis, and abscesses
Classification:
Large group C and G colonies have been reclassified as S dysgalactiae and the small group C and G colonies are classified as Strep anginosus, which can cause absesses
SDSE is VP negative, whereas the anginosus group is VP positive
28
Carbapenemases
Grouped as molecular classes A, B, and D
## Footnote
Class A: KPC (K pneumoniae and other enterobacteriaceae including serratia); demonstrated with Hidge (clover leaf test): streak plate with carbapenem suscepitble E coli, place ertapenem disk in center and test organisms are streaked out from the disk; if KPC is present it will distort the zone of inhibition of E coli
Class B: metallo-beta-lactamases such as IMP, VIM, and SPM produced by pseudomonas, acinetobacter, stenotrophomonas maltophilia, and enterobacteriaceae
OXA carbapenamases are made by acintobacter baumannii
29
Multiplex PCR assays detect what MRSA specific genetic regions
spa (Staphylococcal protein A)
SCCmec
mecA
30
Temperature at which P aeruginosa grows
42 degrees
31
CLSI requirements for susceptibility testing of bacteria
0.5 McFarland inoculum == 1-2 x 108 CFU/ml
Mueller Hinton agar
Ambient air incubation
If a new antibiotic is started, susc testing must be done for 20-30 days; if no more than 1/20 or 3/30 MICs for each antibiotic/organism is out of the acceptable range, then QC can be reduced to once per week
32
Fusobacterium nucleatum colonies
white, rough, bread-crumb like
33
Porphyromonas and prevotella colonies
black and fluoresce red
34
Atmosphere for anaerobic incubation
85% N2, 10% H2, and 5% CO2
Need selective, enrichment, and nonselective media
35
Anaerobes associated with brain abscesses
peptostreptococcus
fusobacterium
prevotella
porphyromonas
36
If sexual abuse is suspected, what tests should be done?
NAAT for C trachomatis and N gonorrhoeae and serology for HIV
37
Aerococcus viridans biochemicals
Can cause IE
alpha hemolytic
PYR positive
LAP negative
Susceptible to vanc
(other orgs in this group that are resistant to vanc include pediococcus, leuconostoc, globicatella)
38
Closely related and possibly related outbreak strains with PFGE testing
If 2-3 bands differ, the strains are closely related
If 4-6 bands differ, the strains are possibly related
39
MRSA can cause subcutaneous infections leading to necrotizing fasciitis with eschar
Community associated MRSA strains include USA300 and USA400
40
Tests for detecting AFB directly in specimens
NAAT
Fluorochrome stain
41
M marinum
chromogenicity
rate of growth
temperature of growth
Photochromogen, rapid grower at 30 degrees
42
M haemophilum
chromogenicity
rate of growth
temperature of growth
Nonchromogenic
Slow growing
30 degrees
Needs iron
43
M bovis and MAC
## Footnote
chromogenicity
rate of growth
temperature of growth
nonchromogenic
slow growing
37 degrees
44
In a BCG vaccinated person, what test can be done to show that she is infected with TB
interferon-gamma release assay
45
M Tb versus M bovis
M TB is niacin positive and bovis is negative
46
M fortuitum versus M chelonae
Fortuitum uptakes iron and chelonae does not
Chelonae uses citrate and fortuitum does not
47
Gold standard for molecular typing of M tuberculosis isolates
**IS6110 (a transposable genetic element varying in location and number of repeats: 0-25) restriction length polymorphism analysis**
(For strains with 6 or fewer copies of IS6110 spoligotyping can be done)
48
Most common mycobacteria causing cervical lymphadenitis in children
**MAC** \> **M** **scrofulaceum** (a **scrotochromogen** that is negative for niacin)
49
Processing of mycobacterial specimens
* All specimens must be procesed under a biologic safety cabinet (BSC) within a confined access facility
* UV light is not required for sterilization or decontamination
* There must be 6-12 negative air exchanges per hour
* The BSC is in a controlled access area with the capacity to draw 75-100 linear feet of air per minute across the entire front opening for proper functioning of the HEPA filter
* Annual fit testing for N95 or N100 mask
* Skin testing or IGRAs are performed annually on technicians
* Specimens must be centrifuged in aerosol-free safety cups with o-ring sealed closures for at least 15 minutes at 3000 g
50
M xenopi
transmitted from water source or infected people
Pigmented, grow at 42-45 degrees and is arylsulfatase positive
51
How is M avium transmitted
Inhalation or ingestion and NOT by person to person spread
52
Pathogenicity of M gordonae
Non pathogenic
53
M kansasii transmission and geographic distribution
Transmitted by inhaled aerosols, not person to person
Southern and Central US
2nd most common cause of non TB pulmonary disease (second to MAC)
Niacin negative
Nitrate positive
Catalase positive
54
* When can airborne isolation for possible TB patient be discontinued
* who should be on airborne isolation
* Another diagnosis is made that excludes TB and three sputum specimens are AFB smear negative and NAAT negative
* Patients at high risk for TB should be on airborne isolation (i.e., negative pressure room with at least 12 exchanges/hour) and people entering the room should wear and N-95 mask
55
When are DNA probe assays used on M TB?
NAAT testing in TB?
Probes are only used on cultured specimens and can identify to the species level
NAATs are never used to exclude TB as the definitive test; NAAT does not distinguish among the TB complex
56
Agar that grows C gatii
canavanine glycine bromothymol blue agar turns blue
57
Endothrix versus ectothrix hair invasion by fungi
**Endothrix**
T tonsurans; arthroconidia within hair shaft; does not fluoresce with wood lamp
**Ectothrix**
M canis and M gypseum; arthroconidia on hair shaft; does fluoresce with wood lamp
58
Syncephalastrum racemosum
saprophytic fungus
45 degree dichotomous branching, but is pauciseptate and do not have phialides
59
Use of a BSC is necessary for processing molds, not yeast
Tape or shrink seals are needed when using plated agar media; however, petri plates should not be used if C immitis is suspected
Negative pressure is not necessary for processing fungi
Do not do slide culture if dimorphic fundi is suspected
60
Blood cultures are rarely positive in invasive aspergillosis infections
61
A niger - otomycosis
62
Risk factors for Malassezia infection
total parenteral nutrition (high in lipids)
skin diseases
63
Most common dermatophyte in feet and nails
T rubrum
64
testing for candida that can be performed directly on blood culture
PNA (peptide nucleic acid) FISH assay - targets 26S rRNA sequences
65
HAART should be given to
HIV load of \> 100,000 and should be tested 2-8 weeks following therapy, then 3-4 months after that
66
P marnefii is inhibited by
cyclohexamide
67
Liver injury in HBV is immune mediated (not from virus particles themselves)
68
HIV **qualitative** PCR
used to diagnose, not follow HIV patient
used if ELISA is positive and Western blot is negative
69
DFA is one method for detecting HSV (turn around is 2 hours)
70
High-risk infants can get monthyl RSV prophylaxis via injected palivizumab
71
Influenza treatment
Should start within 2 days of infection
Oseltamivir and zanamivir treat A and B (neuraminidase inhibitors)
Amantadine treats A only
72
Differences in Influenza A and B
A and B differ by matrix (M) and nucleoprotein (NP)
A viruses are further classified by H and N proteins
A infects animals and humans whereas B only infects humans
73
VZV vaccine
Live, attenuated
given at 1 year if not immunocompromised
given for adults \> 50 yo
74
Roseola rash
Starts on trunk and spread to extremities and face
75
Norwalk virus is highly infectious and survives on fomites
76
HPV cannot be cultured in vitro and transmission occurs through epithelium-epithelium contact (not fluids)
77
Rapid antigen detection tests are available for C diff, Giardia, Cryptosporidium, E histolytica, rotavirus, adenovirus 40/41
78
Amblyomma tick anal groove versus Ixodes
Amblyomma has posterior anal grove, and Ixodes has anterior anal groove
79
EDTA tube used for specimen preservation in malariae diagnosis
80
Acanthamoeba does not have a flagellated form, whereas naegleria does
81
Symptoms of trichinella:
- first GI
- after 2 weeks: muscle pain, fever, facial swelling (e.g., periorbital edema)
All stages of T spiralis development occur in a single host
Ingest larvae that invade small bowel wall where they become adults that release more larvae a week later. The larvae then migrate to striated muscle and encyst.
82
Malaria positive blood donors have to wait three years before they can donate again
83
Oral chloroquine is a treatment for P falciparum in regions where it is not resistant
Resistant regions are in Africa, South America, and South East Asia
84
Cysticercosis occurs with ingestion of T solium eggs
(T solium has 7-13 uterine branches, whereas T saginata has 15-20)
85
Stool preservatives for permanent micro exam:
* Polyvinyl alcohol
* Refrigeration for up to 3 hours
* Sodium acetate-acetic acid formalin (SAF)
* merthiolate iodine formalin (MIF)
Do not use ethanol (this is used for DNA extraction and not for morphological exam)
Should examine three stools (one per day or every other day)
Liquid stool should be examined fresh within 30 minutes, soft stool within 1 hour, and formed stool within 1 day
