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Clinical Microbiology > Midterm 2 > Flashcards

Midterm 2 Flashcards

1
Q

Bacteriuria

A

Presence of bacteria in urine
Does not necessarily imply infection
Do not treat if asymptomatic (except maybe in case of pregnancy or invasive urinary tract procedure)

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2
Q

Three most common signs of cystitis (bladder UTI)

A

Dysuria, increased frequency of urination, and increased urgency of urination

Also absence of systemic symptoms (eg no fever)

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3
Q

Conditions that mimic/mask cystitis

A

Urethritis (eg chlamydia or gonnorhea infection), vulvitis (eg HSV infection), vaginitis/bacterial vaginosis

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4
Q

Cystitis

A

UTI confined to bladder

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5
Q

Pyelonephritis

A

More invasive UTI (upper tract)
Inflammation of kidney and renal pelvis
More symptomatic symptoms, like fever, flank pain, nausea, chills, malaise, headache

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6
Q

Prostatitis

A

Inflammation/infection of prostate gland

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7
Q

Intrarenal abscess/perinephric abscess

A

Collection of pus in kidney or in the soft tissue surrounding the kidney

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8
Q

Things that would make a UTI “Uncomplicated”

A

Non-pregnant premenopausal woman of childbearing age, not chronic, no comorbidities, lower tract

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9
Q

Things that would make a UTI “Complicated”

A

Pregnant person, elderly person, male person, child, chronic, comorbid, upper tract

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10
Q

Two types of recurrent infection

A

Relapse: recurrence by same organism (may indicate therapy failure/resistance)

Re-infection: recurrence by different organism (may indicate abnormality increasing your susceptibility to infection)

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11
Q

UTI pathogenesis

A

Patients intestinal flora enter urinary tract via urethra
Catheter, nephrostomy tube, surgery, urinary stones make this more likely to happen
Organisms enter and persist in urinary tract

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12
Q

UTI risk factors

A

Aging (diabetes mellitus, urinary stasis, incontinence, impaired immmunity), urinary tract obstruction, impaired bladder innervation

Female: short urethra, sexual intercourse, contraceptives that alter normal flora, pregnancy (anatomy altered)
Males: prostatic hypertrophy, anal intercourse

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13
Q

UTI etiology

A

Usually a single pathogen
90% Enterobactales
70% E. Coli

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14
Q

E. Coli virulence factors

A

Adherence (P fimbria bind to P blood group antigen on uro-epithelial cells)
Hemolysins, Colicin V (resist complement-dependent serum bactericide)
K antigen (upper tract infection associated)
Type1 fimbria (interbacterial binding and biofilm formation)

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15
Q

Classical UTI pathogens

A

Proteus, Morganella, Providencia

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16
Q

Virulence factors of classical UTI pathogens

A

urease producing: increase urine pH, lead to crystal/stone formation, promotes biofilm formation
Highly motile
Fimbria for attachment

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17
Q

Staphylococcus saprophyticus

A

Uropathogen typically associated with younger, sexually active females, responsible for 1-5% of cystitis, identified by resistance to novobiocin
Also coagulase negative

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18
Q

Dipstick urinalysis

A

Detect nitrites (specific) and leukocytes (sensitive) —> indicators of infection

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19
Q

Urine culture

A 
SBA/MacConkey agar/chromogenic agar
Commonly contaminated during collection therefore threshold for significant organism presence = 10^5 bacteria/mL (10^8/L)
# bacteria = # colonies X dilution factor
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20
Q

Urine clean catch mid stream specimen collection method

A

Most frequently used method

Urethra cleaned, first void urine allowed to pass to clear urethra, then mid-stream collected in sterile container

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21
Q

Collection bag for urine specimen collection

A

Used for children who lack bladder control, very often contaminated, most meaningful result is a negative culture

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22
Q

Urine specimen collection via indwelling catheter

A

Insert needle into catheter or through diaphragm to withdraw urine
Preferable to obtain from new catheter rather than old

23
Q

Urine specimen collection via cytoscope

A

Cytoscope is inserted into the bladder via urethra

24
Q

Urine specimen collection via subrapubic asperation/straight catheter

A

Most invasive
Specimen obtained directly from bladder
Low contamination risk therefore significance cutoff is much lower

25
Urine specimen transport
Info needed: method and date/time of collection Unrefridgerated: need to receive within 1-2 hours Refridgerated: need to receive within 24 hours If can’t get within 24 hours (e.g. lab far away), need to use Boric acid tube (maintains organism pliability but restricts growth
26
Antimicrobials for uncomplicated cystitis
``` Nitrofurantoin Fosfomycin TMP/SMX (>24% resistance, not ideal) Doxycycline (2nd line) Ciproflaxin (3rd line, only if NO other oral options) ```
27
Antimicrobials for pyelonephritis
Ciproflaxin (outpatient) | B-lactam + aminoglycoside (inpatient)
28
MRSA
Staph aureus resistant to all beta lactams (usually also other drugs) Hospital: hundreds of clonal groups, susceptible to vancomycin Community: several clonal groups, generally susceptible to TMP/SMX, doxycycline, and clindamycin
29
Mechanism of beta lactam resistance in MRSA
``` Production of novel PBP: PBP 2a, has reduced affinity for beta lactams but performs essential functions of PBPs MecA gene (acquired through transposition, chromosomal) ```
30
Detection of MRSA
Mueller-Hinton Agar + 4% NaCl (or sugar, something to increase osmotic stress) + 6ug/mL cefoxitin Growth = Methicillin resistant Chromogenic agar + 6ug/mL cefoxitin Growth = methicillin resistant, purple colour = staph aureus (both = MRSA)
31
How is CA-MRSA different from HA-MRSA?
More virulent than HA, but easier to treat than HA (resistant to fewer drugs)
32
CA-MRSA clinical presentation
``` Boils or draining pimples “Spider bites” or “bug bites” Sores that won’t heal Abscesses Systemic infections (e.g. pneumonia, blood infections) - uncommon but serious ```
33
Genetics of MRSA
MecA gene complex carried on staphylococcal cassette chromosome (SCC) Five types of SCC-mec (I-V) HA-MRSA = types I, II, or III SCC-mec, multidrug resistant CA-MRSA = type IV SCC-mec, usually only resistant to beta lactams and erythromycin
34
PVL toxin
Panton-Valentine lecocidin Cytotoxin present in <5% of MRSA Rare in HA-MRSA Encoded by two genes, lukS-PV and lukF-PV Destroys WBCs, causes severe tissue damage Associated with necrotic skin lesions/severe necrotizing pneumonia
35
VRE
Enterococci resistant to vancomycin | Intrinsic glycopeptide resistance
36
Identifying enterococcus
Glucopyranoside positive and yellow pigment = E. casseliflavus Glucopyranoside positive and no pigment = E. gallinarum Glucopyranoside negative and ampicillin resistant = E faecium Glucopyranoside negative and ampicillin sensitive = E. faecalis
37
Vancomycin mechanism of action
Complexes with D-Ala-D-Ala to inhibit cell wall synthesis
38
Mechanism of resistance in VRE
Change D-Ala to D-lac to prevent vancomycin binding | Rare, requires a full operon mutation (Van X, Van H, VanA ligase)
39
VRE genotypes
VanA: high resistance to Vancomycin and Teicoplanin, common in E. faecium and faecalis (more faecium than faecalis though) VanB: low to high resistance to vancomycin and susceptible to Teicoplanin, common in faecium and faecalis VanC: low resistance to vancomycin, susceptible to Teicoplanin, common in E. gallinarum, casseliflavus, flavrscens
40
ESBLs
Extended spectrum beta lactamases Plasmid borne, inhibited by clavulinic acid Activity against penicillins and 1st/2nd/3rd gen cephalosporins Do not hydrolyze cephamycins or carbapenems Most common in E. coli and Klebsiella spp. Detection: >5mm difference between zone of inhibition of cetroaxin disc and cetroaxin+cavulinic acid disc = positive for ESBL
41
AmpC beta lactamases
Inducible or de-repressed Not inhibited by clavulinic acid Chromosomal, but de-repressed ampC has mobilized on plasmids Enterobacter spp., Citrobacter spp., K. Aerogenes, Serratia
42
5 big carbapenemases
KPC, NDM (big threat), VIM, OXA-48, IMP
43
Detection of carbapenemase production
Modified carbapenem inactivation method 1. Incubate meropenem disc in broth 2. Place disk on susceptible E. Coli culture, as well as dry disc 3. Smaller/no inhibition zone = positive for carbapenemase production
44
Pneumonia
inflammatory condition of the lung primarily affecting alveoli
45
Signs and symtoms of pneumonia
Fever, cough (productive or dry), chest pain, shortness of breath
46
S. pneumoniae
Most common bacterial RTI cause Small gram positive diplococci, alpha hemoluytic, bile soluble, optochin S (other viridans strep are bile insoluble and optochin R), growth often enhanced in CO2 atmosphere, most are encapsulated Colonizes the nasopharynx (throat swabs useless for diagnosis, need swab from lower tract for it to mean anything)
47
S. Pneumoniae virulence factors
Most important is the capsule (aids in phagocytic escape, adherance and colonization) Pneumolysin (hemolysin): destroys ciliated epithelial cells, activates classical complement pathway, suppresses oxidative burst by phagocytic cells Secretory IgA protease
48
Pneumovax
Pneumococcal vaccine 23 different serotypes account for 90% of invasive strains Protection wanes with time and age Indications: advanced age, splenectomy, HIV/AIDS, lymphoma, myeloma, alcoholism, diabetes
49
PREVNAR
Conjugate vaccine for pneumococcus | Indicated for use in infants and adults
50
Pneumonia treatment
Historically penicillin (now resistance), cephalosporins (most often), macrolides, fluroquinolones (severe disease), vancomycin Amoxicillin is ok for mild-moderate disease
51
Two most common pathogens associated with COPD
H. Influenzae = #1, S. Pneumoniae = #2
52
COPD
Chronic obstructive pulmonary disease Umbrella term for progressive lung diseases like emphysema, chronic bronchitis, refractory asthma, and some forms of bronchiectasis Characterized by increasing breathlessness (main problem is breathing OUT, not in)
53
H. Influenzae
Most common cause of AE-COPD Small gram negatve bacilli Requires X factor (Haem) and V factor (NAD) for growth Will grow on chocolate agar (5% CO2) May be encapsulated (meningitis risk) Type b (Hib) responsible for most invasive disease (meningitis, epiglottitis), Hib vaccine has made this rare Majority of mucosal disease due to non-encapsulated strains
54
Treatment of RTI
Amoxicillin-clavulanate very effective (high dose) Fluoroquinolones very active, but contraindicated in children Newer macrolides reasonable activity 2nd/3rd gen cephalosporins effective

Clinical Microbiology (6 decks)

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