Intro to ID part 2 Flashcards
Gram positive - gram stain testing
gram positive bacteria have a large peptidoglycan cell wall and appear purple in a gram stain test result
Gram negative - gram stain testing
Gram negative have a line cell wall and appear as a pink or red color on a gram stain test result
What are the two groups of gram positive
Cocci and Bacilli
Gram Positive Cocci Anaerobic
Peptococcus
peptostreptococcus
Gram Positive Cocci aerobic Catalase + and Coagulase +
Straphylococcus aureus
Gram Positive Cocci aerobic Catalase + and Coagulase -
All other straphylococcus species
Gram Positive Cocci aerobic catalase - alpha-hemolysis (partial)
Streptococcus pneumoniae
Viridans streptococci
Gram Positive Cocci aerobic catalase - beta-hemolysis (full)
Streptococcus Pyogenes
Streptococcus agalactiae
Gram Positive Cocci aerobic catalase - Gamma-hemolysis (none)
Enterococcus Faecium
Enterococcus faecalis
Gram Positive Bacilli Anaerobic Spore forming
Clostridium Species
Clostridioides difficile
Gram Positive Bacilli Anaerobic non-spore forming
cutibacterium
actinomyces
Gram Positive Bacilli Aerobic spore forming
Bacillus species
Gram positive Bacilli Aerobic non-spore forming
Corynebacterium
Lactobacillus species
Listeria
Monocytogenes
Biochemistry testing
Catalase test will tell us if it is staphylococci (catalase positive) or Streptococci (catalase - )
Coagulase test will tell us if its staphylococcus aureus (coagulase +) or staphylococcus coagulase negative
Agar appearance for hemolytic testing
This is done on cocci catalase negative aerobic species
alpha- hemolytic is a partial result and tells us its oral flora
Beta- hemolytic is a full result and tells us its skin pharynx and genitourinary
Gamma-hemolytic has no result and tells us it is gastrointestinal
You receive a call from the microbiology lab informing you that patient JR has Gram-
positive cocci growing in the blood. They don’t have a full identification but tell you the
organism is catalase positive, coagulase positive. Which of the following organisms could
be growing in JR’s blood?
a) Staphylococcus aureus
b) Staphylococcus epidermidis
c) Streptococcus pyogenes
d) Enterococcus faecalis
A
Since the result is catalase positive it means it is staphylococcus aureus and with a positive coagulase testing it further confirms straphylococcus aureus
Gram negative aerobic Cocci
Neisseria species
Moraxella catarrhalis
Gram negative aerobic Coccobacilli
Haemophilus species
Gram negative anaerobic cocci
Veillonella species
Gram negative anaerobic bacilli
bacteroides species
fusobacterium speices
Prevotella species
gram negative aerobic bacilli Enterobacterales Lactose fermenters - IMPORTANT
Means they are oxidase negative
CEEK
Citrobacter
Enterobacter
E. Coli
Klebsiella
gram negative aerobic bacilli Enterobacterales non-lactose fermenters - IMPROTANT
Means they are oxidase positive
Morganella morganii
Proteus
Providencia
salmonella
Serratia marcescens
Shigella
gram negative aerobic bacilli lactose fermenters
means they are oxidase positive
Aeromonas hydrophila
pasteurella multocida
vibrio cholerae
gram negative aerobic bacilli non-lactose fermenters
oxidase negative
pseudomonas
acinetobacter
alcaligenes
burkholderia cepacia
stenotrophomonas maltophilia
gram negative aerobic bacilli Fastidious
Campylobacter
Helicobacter
Bartonella
HACEK* organisms
Atypical
These will not stain on a gram test
Chlamydia trachomatis
Legionella pneumophila
Mycoplasma pneumonia
Spirochetes
treponema pallidum
Borrelia burgdorferi
What does lactose fermentation tell us
helps us identify and distinguish between enteric vs non-enteric lactose fermenters
You receive a call from the microbiology lab informing you that patient ZE has Gram
negative rods growing in the blood. They don’t have a full identification but tell you the
organism is a non-enteric non-lactose fermenter. Which of the following organisms could
be growing in JR’s blood?
a) Pseudomonas aeruginosa
b) Citrobacter freundii
c) Morganella morganii
d) Aeromonas hydrophila
A
B is a Enteric coded lactose fermenter
C is a enteric coded non-lactose fermenter
D is non-enteric coded lactose fermenter
what are Penicillin Binding proteins
Also known as PBPs
These play a role in cell wall synthesis, cell shape, and structural integrity
Binding to PBPs 1A, 1B, 2, and 3 result in bacterial effect
Transpeptidase is the most important PBP as it catalyzes the final cross linking in the peptidoglycan structure
Intrinsic Resistance
when the species is always been resistant to the given antibiotic due to absence of a target site or the bacterial cell impermeability
Acquired resistance
when species is initally susceptible but develop resistance due to some mechanism due to mutation in bacterial DNA or Acquisition of new DNA
Aquired resistance examples
Plasmid - transferable between organisms
Transposons - move from plasmid to chromosome or vice versa
Conjugation - most common
Which of the following describes the difference between Gram-positive and Gram-negative bacteria?
a) Gram-positive have a thin cell wall; Gram-negative have a thick cell wall
b) Gram-positive have a thick cell wall; Gram-negative have a thin cell wall
c) Gram-positive have porin channels; Gram-negative lack porin channels
d) Gram-positive have PBP; Gram-negative lack PBPs
Mechanisms
B
what are the 4 mechanisms of antibiotic resistance
- Altered cell wall protein/ decreased porin production
- Increased efflux pumps
- increased drug inactivating enzymes
- modified drug target
mechanism of resistance
drug inactivating enzymes
Beta - lactamase
this enzyme will split an amide bond on a beta lactam ring resulting in hydrolyzing the drug and making it inactive
Two classes: Amber and Bush
there are two types Serine beta lactamases and Metallo beta lactamases
Ambler classification of beta lactamase
Class A
Narrow spectrum B lactamases - produced primarily by enterobacterales
Extended spectrum B lactamases (ESBL) - Enzyme example CTX-M-15
Serine carbapenemases - Enzyme example KPC-1, KPC-2, KPC-3
Ambler classification of beta lactamase
Class B
Metallo B lactamases - enzyme example NDM-1
Ambler classification of beta lactamase
Class C
Cephalosporinases - enzyme example AMP- C
Ambler classification of beta lactamase
Class D
OXA-type - enzyme example OXA-48
Ambler class A : ESBLs
Plasmid mediated
Treatment choice: Meropenem, Imipenem, Doripenem, Ertapenem
can also use piperacillin/tazobactam for Urinary source ONLY
Ambler class A: Carbapenemase
Treatment options:
B lactam: ceftazidime/avibactam, Meropenem/Vaborbactam, impienem/cilastatin/relebactam
non-B-lactam: plazomicin, eravacycline, omadacycline
Ambler class B: Metallo B lactamases
confer resistance to all B-lactams except monobactams
Treatment is limited but option is Cefiderocol
Ambler Class D: OXA type
Primairly found in Ainetobacter baumannii and Pseudomonas aeruginosa
Treatment options: Cefiderocol or Sulbactam/durlobactam
JM is a 45 YOM admitted with fever, chills, urinary frequency and urgency. Blood cultures are collected and 12
hour after admission rapid diagnostic testing identifies E.coli, CTX-M (+) in 4/4 bottles.
Q1) What type of antibiotic resistance is present?
a) Non-CP CRE
b) ESBL
c) NDM
d) KPC
B - ESBL
JM is a 45 YOM admitted with fever, chills, urinary frequency and urgency. Blood cultures are collected and 12
hour after admission rapid diagnostic testing identifies E.coli, CTX-M (+) in 4/4 bottles.
Q2) What is the recommended treatment option?
a) Meropenem
b) Meropenem/vaborbactam
c) Aztreonam + Ceftazidime/avibactam
d) Piperacillin/tazobactam
ESBL resistance present and patient should be started on A
Ambler Class C: AmpC
has 3 mechanisms but main focus is inducible via chromosomal encoded AmpC genes
Found in Hafina alvei, Enterobacter cloacae, Citrobacter freundii, Klebsiella aerogenes, Yersinia Enterocilitica (HECK-YES)
AmpC induction mechanism
Genetic mutation causes gene derepressed and eventually keeps this derepression stable meaning there is high levels of beta-lactamase production continuously and it is inactivating the drug
AmpC inducers
High susceptibility to AmpC hydrolysis
Strong inducers - penicillin and ampicillin
Weak inducers - ceftriaxone
AmpC inducers low susceptibility to AmpC hydrolysis
Strong inducers - carbapenems (imipenem, Meropenem, ertapenem)
Weak inducers - Cefepime
Treatment of stably derepressed mutants
First line cefepime
JH is a 65 YOM admitted with pyelonephritis (infection in the kidney) and started on IV ceftriaxone. However, he soon develops a fever and becomes hypotensive. Blood cultures are taken and result for E. cloacae.
Q1)What could explain his sudden decompensation?
a) E. cloacae harbors an ESBL gene and this was induced with ceftriaxone treatment
b) E. cloacae harbors a KPC gene and this was induced with ceftriaxone treatment
c) E. cloacae harbors an AmpC gene and this was induced with ceftriaxone treatment
d) E. cloacae harbors a NDM gene and this was induced with ceftriaxone treatment
2) What antibiotic change do you recommend?
a) Switch to Piperacillin/tazobactam
b) Switch to Cefepime
c) Switch to Ceftazidime
d) Switch to Aztreonam
Q1 C
Q2 B
Enzymatic inactivation: amino-glycoside- Modifying Enzyme
3 mechanisms
acetylation, nucleotidylation, Phosphorylation
Modify aminoglycoside structure by transferring the indicated chemical group to specific side chain
Altered target site: Cell wall precursor
Mechanism of Vancomycin resistance in enterococci Species
What is resistance mediated by and what is the treatment
normal action of vancomycin binds to D-alanine-D-alanine terminus of peptidoglycan precursors
Resistance alters this D-alanine- D-alanine to D-ala-D-lac or D-ser
Mediated by VanA or VanB (EXAM-Q)
Treatment of resistance is Daptomycin or linezolid
Altered Target site: Penicillin Binding Proteins
Leads to B lactam resistance
Due to decreased affinity of PBPs for antibiotic or change in amount of POP produced by bacteria
Methicillin-resistant staphylococcus aureus (MRSA) resistant due to expression of mecA gene
treatment is Ceftaroline, ceftobiprole
Other altered target sites
Ribosomal target
Responsible for macrolide resistance in S. Pneumoniae
ermB gene causes resistance with clindamycin
aminoglycoside resistance in gram negatives
Other altered target sites
DNA gyrase/Topoisomerase IV
Responsible for fluoroquinolone (ciprofloxacin, levofloxacin) resistance in Gram-negative and S. Pneumonia
Efflux pumps and porin channels
Efflux pumps if overexpressed can build resistance
Important resistance mechanism for P. aeruginosa against carbapenems & S. pneumoniae against
macrolide antibiotics
Porin channels can cause resistance because the rate of antibiotic diffusion depends on porin channels
Most commonly seen with Enterobacterales and carbapenem-resistant P. aeruginos
What is the mechanism of Staphylococcus aureus resistance to beta-lactams?
a) mecA gene
b) VanA gene
c) ermB gene
d) KPC gene
A. MecA
Bactericidal definition
killing of the organism by acting on areas such as the cell wall, cell membrane, bacterial DNA
Bacteriostatic Definition
Inhibit bacterial replication without killing the organism by inhibiting protein synthesis
Concentration Dependent
Optimize killing with high doses
Exert effect when concentrations well above organism MIC
Fluoroquinolones (Levofloxacin, Ciprofloxacin)
-Concentration-dependent bactericidal activity fAUC 0-24/MIC
Aminoglycosides (Gentamicin, Tobramycin, Amikacin)
- Concentration-dependent bactericidal activity
C max/MIC
- Optimal dosing achieved through Therapeutic drug monitoring and use of high dose extended interval
Time dependent
optimize duration of exposure to binding site
All β-lactam antibiotics (penicillin, cephalosporin, carbapenem, monobactam)
Time that free drug concentration remains above MIC correlates with clinical and microbiological outcomes
fT>MIC Penicillin: 50% - if its Q12h we want at least 6 hours free time is over MIC
fT>MIC Cephalosporin: 60-70%
◦ fT>MIC Carbapenem: 40%
◦ Antibacterial properties
◦ Not rapidly bactericidal
◦ Time-dependent bactericidal activity
◦ Little to no PAE
Beta- lactam Dosing Optimization
Maximize fT>MIC (as a % of dosing interval )
◦ Gram-negatives:
◦ Carbapenems: ≥40%; Penicillins: ≥50%; Cephalosporins: ≥ 60%
◦ Gram-positive: ≥40-50%
Strategies to maximize fT>MIC
◦ Increase dose, same interval (1g Q8h vs. 2g q8h)
◦ Same dose, shorter interval (1g Q12h vs. 1g Q6h)
◦ Continuous infusion
◦ Stability issues; need dedicated IV line
◦ Prolonged infusions
◦ Infuse dose over 3-4 hours
◦ Provides longer T>MIC than traditional infusions
AUC/MIC Dependent (Vancomycin)
◦ Time-dependent bactericidal activity; very long PAE for Gram-positive organisms
◦ PD Target: AUC0-24 /MIC
◦ Goal AUC0-24/MIC ≅ 400-600
- assumes organism AUC of 1 mcg/mL
◦ Prolonged, elevated AUC0-24/MIC ≥ 600-700 mg*h/L is a risk factor for nephrotoxicity
◦ Dosing is patient-specific and achieved through TDM using Bayesian programs
Which of the following describes the PK/PD parameters of meropenem?
a) Time-dependent antibiotic; fT>MIC 40% of the dosing interval
b) Concentration dependent antibiotic; fAUC/MIC
c) Time-dependent antibiotic; fT>MIC 80% of the dosing interval
d) Concentration dependent antibiotic; Cmax/MIC
Meropenem is a carbapenem meaning it is a time dependent drug so the correct answer is A
Summary PK/PD aminoglycosides
Concentration dependent
C Max/MIC; AUC/MIC
Cidal
Summary PK/PD B-lactams
Time dependent
FT>MIC
Cidal
Summary PK/PD Vancomycin
Time Dependent
AUC (0-24)/MIC
Cidal (Slowly)
