Introduction to Antibacterial Therapy
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Transcript Introduction to Antibacterial Therapy
Introduction to Antibacterial
Therapy
Clinically Relevant Microbiology and
Antibiotic Use
Edward L. Goodman, MD
July 22, 2010
Outline
Basic Clinical Bacteriology
Antibiotics
– Categories
– Pharmacology
– Mechanisms of Resistance
Goodman’s Scheme for the Major
Classes of Bacterial Pathogens
Gram Positive Cocci
Gram Negative Rods
Fastidious Gram Negative Organisms
Anaerobes
Gram Positive Cocci
Gram stain: clusters
Catalase pos = Staph
Coag pos = S aureus
Coag neg = variety of
species
Chains and pairs
Catalase neg =
streptococci
Classify by hemolysis
Type by specific CHO
Staphylococcus aureus
>95% produce penicillinase (beta lactamase) =
penicillin resistant
At PHD ~60% of SA are hetero (methicillin)
resistant = MRSA (less than national average)
Glycopeptide (vancomycin) intermediate (GISA)
– MIC 8-16
– Eight nationwide
First VRSA reported July 5, 2002 MMWR
– Seven isolates reported (5/7 from Michigan)
– MICs 32 - >128
– No evidence of spread w/in families or hospital
Evolution of Drug
Resistance in S. aureus
Penicillin
Methicillin
Methicillin-resistant
Penicillin-resistant
S. aureus
S. aureus (MRSA)
[1970s]
[1950s
S. aureus
]
[1997]
Vancomycin
[1990s]
Vancomycin-
resistant
S. aureus
Vancomycin
[ 2002 ]
intermediateresistant
S. aureus
(VISA)
Vancomycin-resistant
enterococci (VRE)
MSSA vs. MRSA
Surgical Site Infections
(1994 - 2000)
Controls MSSA SSI MRSA SSI
(n=193) (n=165)
(n=121)
Death, no. (%)
4(2.1)
11(6.7)
25(20.7)
LOS after
surg., median
5
14
23
52,791
92,363
Hosp. charges, 29,455
median $
CID. 2003;36: 592-598.
Coagulase Negative Staph
Many species – S. epidermidis most
common
Mostly methicillin resistant (65-85%)
Often contaminants or colonizers – use
specific criteria to distinguish
– Major cause of overuse of vancomycin
S. lugdunensis is rarely a contaminant
– Causes destructive endocarditis
Nosocomial Bloodstream
Isolates
All gramnegative
(21%)
Viridans
streptococci
(1%)
Other
(11%)
SCOPE Project
Coagulasenegative
staphylococci
(32%)
Candida
(8%)
Enterococci
(11%)
Staphylococci
aureus (16%)
Clin Infect Dis 1999;29:239-244
Streptococci
Beta hemolysis: Group A,B,C etc.
Invasive – mimic staph in virulence
S. pyogenes (Group A)
– Pharyngitis,
– Soft tissue
Invasive
TSS
– Non suppurative sequellae: ARF, AGN
Other Beta hemolytic
S. agalactiae (Group B)
– Peripartum/Neonatal
– Diabetic foot
– Bacteremia/endocarditis/metastatic foci
Group C/G Streptococcus
– large colony variants: similar clinical illness as GAS
plus bacteremia, endocarditis, septic arthritis
– Small colony variants = Strept milleri
Viridans group
Anginosus sp.
Bovis sp.: Group D
Mutans sp.
Salivarius sp.
Mitis sp.
Streptococcus anginosus
Group
Formerly ‘Streptococcus milleri’ or
‘Streptococcus intermedius’.
S. intermedius; S. constellatus; S. anginosus
Oral cavity, nasopharynx, GI and
genitourinary tract.
S. anginosus Group
Propensity for invasive pyogenic infections ie.
abscesses.
Grow well in acidic environment
polysaccharide capsule resists phagocytosis
produce hydrolytic enzymes: hyaluronidase,
deoxyribonucleotidase, chondroitin
sulfatase, sialidase
S. anginosus Group
Oral and maxillofacial infections
Brain, epidural and subdural abscesses
intraabdominal abscesses
empyema and lung abscesses
bacteremias usually secondary to an
underlying focus of infection.
Look for the Abscess!
Enterococci
Formerly considered Group D Streptococci
now a separate genus
Bacteremia/Endocarditis
Bacteriuria
Part of mixed abdominal/pelvic infections
Intrinsically resistant to cephalosporins
No bactericidal single agent (except ?Dapto)
Role in mixed flora intra-abdominal infection
trivial- therapy for 2° peritonitis need not cover
Gram Negative Rods
Fermentors
Oxidase negative
Facultative anaerobes
Enteric flora
Numerous genera
– Escherischia
– Enterobacter
– Serratia, etc
UTI, IAI, LRTI, 2°B
Non-fermentors
Pure aerobes
Pseudomonas (oxidase
+) and Acinetobacter
(oxidase -)
– Nosocomial LRTI,
bacteremia, UTI
– Opportunistic
– Inherently resistant
Fastidious Gram Negatives
Neisseria, Hemophilus, Moraxella, HACEK
Require CO2 for growth
Culture for Neisseria must be plated at bedside
– Chocolate agar with CO2
– Ligase chain reaction (like PCR) has reduced number
of GU cultures for N. gonorrhea
Can’t do MIC without culture
Increasing resistance to FQ not detected w/o culture
Anaerobes
Gram negative rods
– Bacteroides (gut/gu flora)
– Fusobacteria (oral and gut)
– Prevotella (mostly oral)
Gram positive rods
– Clostridia (gut)
– Proprionobacteria (skin)
Gram positive cocci
– Peptostreptococci and peptococci (oral, gut, gu)
Anaerobic Gram Negative
Rods
Fastidious
Produce beta lactamase
Endogenous flora
When to consider
– Part of mixed infections
– Confer foul odor
– Heterogeneous morphology
– Gram stain shows GNR but routine cults
negative
Antibiotic Classification
according to Goodman
Narrow Spectrum
– Active against only one of the four classes of
bacteria
Broad Spectrum
– Active against more than one of the classes
Boutique
– Highly specialized use
– Restricted to ID physicians
Narrow Spectrum
Active mostly against only one of the
classes of bacteria
– gram positive: glycopeptides, linezolid,
daptomycin, telavancin
– aerobic gram negative: aminoglycosides,
aztreonam
– anaerobes: metronidazole
Narrow Spectrum
GPC
GNR
Fastid
Anaer
++++
-----
-----
Linezolid ++++
-----
-----
Dapto/Te ++++
lavancin
AG
-----
-----
-----
only
clostridia
Only
gram pos
-----
++++
++
-----
Aztreon
-----
+++
+
-----
Metro
-----
-----
-----
++++
Vanc
Broad Spectrum
Active against more than one class
GPC (incl many MRSA) and anaerobes:
clindamycin
GPC (not MRSA*) and GNR: cephalosporins,
penicillins, sulfonamides, TMP/Sulfa (*include
MRSA), FQ
GPC (not MRSA*), GNR and anaerobes:
ureidopenicillins + BLI, carbapenems, tigecycline
(*MRSA), tetracyclines (*MRSA), moxiflox
GPC and fastidious: macrolides
Penicillins/Carbapenems
Strep
OSSA
GNR
Fastid
Anaer
Pen
++++
--
+/--
--
+/--
Amp/
amox
Ticar
++++
--
+
+/--
+/--
++
--
++
+/--
+
Ureid
+++
--
+++
+++
++
U+BLI +++
++++
++++
+++
++++
Carba
++++
++++
++++
++++
++++
Cephalosporins
FASTID ANAER
Ceph 1
GPC non GNR
-MRSA
++++
+
--
--
Ceph 2
++
++
+
--
cefoxitin ++
cefotetan
Ceph 3
+++
++
+
+++
+++
+++
--
Ceph 4
++++
+++
--
+++
Pharmacodynamics
MIC=lowest concentration to inhibit growth
MBC=the lowest concentration to kill
Peak=highest serum level after a dose
AUC=area under the concentration time
curve
PAE=persistent suppression of growth
following exposure to antimicrobial
Pharmocodynamics: Dosing for
Efficacy
Peak
MIC
Trough
Time
Parameters of antibacterial
efficacy
Time above MIC (non concentration killing) - beta
lactams, macrolides, clindamycin, glycopeptides
24 hour AUC/MIC - aminoglycosides,
fluoroquinolones, azalides, tetracyclines,
glycopeptides, quinupristin/dalfopristin
Peak/MIC (concentration dependent killing) aminoglycosides, fluoroquinolones, daptomycin
Time over MIC
For beta lactams, should exceed MIC for at least
50% of dose interval
Higher doses may allow adequate time over MIC
For most beta lactams, optimal time over MIC can
be achieved by continuous infusion (except
unstable drugs such as imipenem, ampicillin)
For Vancomycin, evolving consensus that troughs
should be >15 for most serious MRSA
infections, especially pneumonia and
bacteremia
– If MRSA MIC is 1.5 - 2, should avoid vancomycin in
favor of daptomycin, linezolid or tigecycline
Higher Serum/tissue levels are
associated with faster killing
Aminoglycosides
– Peak/MIC ratio of >10-12 optimal
– Achieved by “Once Daily Dosing”
– PAE helps
Fluoroquinolones
– 10-12 ratio achieved for enteric GNR
PAE helps
– not achieved for Pseudomonas
– Not always achieved for Streptococcus pneumoniae
Daptomycin
– Dose on actual body weight
AUC/MIC = AUIC
For Streptococcus pneumoniae, FQ should
have AUIC >= 30
For gram negative rods where Peak/MIC
ratio of 10-12 not possible, then AUIC
should >= 125.
DNA gyrase
Quinolones
Cell wall synthesis
DNA-directed RNA
polymerase
Rifampin
ß-lactams &
Glycopeptides
(Vancomycin)
DNA
THFA
Trimethoprim
mRNA
Ribosomes
Folic acid
synthesis
DHFA
50
30
50
30
50
30
Protein
synthesis
inhibition
Macrolides &
Lincomycins
Sulfonamides
PABA
Protein synthesis
mistranslation
Aminoglycosides
Cohen. Science 1992; 257:1064
Protein synthesis
inhibition
Tetracyclines
Pathways of Common
Resistance Mechanisms
Impede access of drug to target
–
–
–
–
–
Beta lactamases: multiple classes
Aminoglycoside altering enzymes
Chloramphenicol altering enzymes
Altered porin channels – carbapenems
Efflux pumps - macrolides
Alterations in target
–
–
–
–
Altered binding proteins: MRSA, DRSP
Methylation of ribosomes: macrolides
Bypass metabolic pathways: TMP/Sulfa
Alteration in gyrases
Some Background on
Enterobacteriaceae
β-lactam antibiotics (derivatives of penicillin)
have long been the mainstay of treating infections
caused by Enterobacteriaceae.
However, resistance to β-lactams emerged several
years ago and has continued to rise.
– Extended spectrum β-lactamase producing
Enterobacteriaceae (ESBLs)
– Plasmid-mediated AmpC-type enzymes
Extended Spectrum Beta
Lactamases (ESBL)
Hyper production derived from TEM beta
lactamases
Predominantly in Klebsiella and E coli
Confer resistance to penicillins,
cephalosporins, monobactams
– Plasmids also confers R to FQ/AG
– Indications for carbapenems*
Amp C Beta Lactamases
Chromosomal cephalosporinases active against
– 1st - 3rd generation cephalosporins, penicillins even with BLI
Constituent or Inducible
Reside in periplasmic space
– Not easily detected when in low numbers
SPICE organisms possess Amp C
–
–
–
–
–
Serratia
Pseudomonas
Indole + Proteii
Citrobacter
Enterobacter
Indication for carbapenems* (imipenem, meropenem, ertapenem,
doripenem)
The Last Line of Defense
Fortunately, our most potent β-lactam class,
carbapenems, remained effective against
almost all Enterobacteriaceae.
Doripenem, Ertapenem, Imipenem, Meropenem
Unfortunately, “Antimicrobial resistance
follows antimicrobial use as surely as night
follows day”
Klebsiella Pneumoniae
Carbapenemase
KPC is a class A b-lactamase
– Confers resistance to all b-lactams including extended-
spectrum cephalosporins and carbapenems
Occurs in Enterobacteriaceae
– Most commonly in Klebsiella pneumoniae
– Also reported in: K. oxytoca, Citrobacter freundii,
Enterobacter spp., Escherichia coli, Salmonella spp.,
Serratia spp.,
Also reported in Pseudomonas aeruginosa (South
America)
Susceptibility Profile of KPC-Producing
K. pneumoniae
Antimicrobial
Interpretation
Antimicrobial
Interpretation
Amikacin
I
Chloramphenicol
R
Amox/clav
R
Ciprofloxacin
R
Ampicillin
R
Ertapenem
R
Aztreonam
R
Gentamicin
R
Cefazolin
R
Imipenem
R
Cefpodoxime
R
Meropenem
R
Cefotaxime
R
Pipercillin/Tazo
R
Cetotetan
R
Tobramycin
R
Cefoxitin
R
Trimeth/Sulfa
R
Ceftazidime
R
Polymyxin B
MIC >4μg/ml
Ceftriaxone
R
Colistin
MIC >4μg/ml
Cefepime
R
Tigecycline
S
Carbapenem resistance in
K. pneumoniae
NHSN Jan 2006- Sept 2007
CLABSI CAUTI VAP
Carbapenem
resistant
K. pneumoniae
11%
9%
4%
Pooled
8%
Hidron, A et al Infect Control Hospital Epidemiol. 2008;29:996
Geographical Distribution of
KPC-Producers
Frequent Occurrence
Sporadic Isolate(s)
Antibiotic Use and Resistance
Strong epidemiological evidence that
antibiotic use in humans and animals
associated with increasing resistance
Subtherapeutic dosing encourages resistant
mutants to emerge; conversely, rapid
bactericidal activity discourages
Hospital antibiotic control programs have
been demonstrated to reduce resistance
Historic overview on treatment of
infections
2000 BC: Eat this root
1000 AD: Say this prayer
1800’s: Take this potion
1940’s: Take penicillin, it is a miracle drug
1980’s – 2000’s: Take this new antibiotic, it
is a bigger miracle!
?2011: Eat this root!
Antibiotic Armageddon
“There is only a thin red line of ID
practitioners who have dedicated
themselves to rational therapy and control
of hospital infections”
Kunin CID 1997;25:240
Thanks to
Shahbaz Hasan, MD for allowing me to use
slides from his 6/6/07 Clinical Grand
Rounds on Streptococci
Eliane S Haron, MD for allowing me to use
the “Eat this root” slide
Jean B. Patel, PhD and CDR Arjun
Srinivasan, MD, Division of Healthcare
Quality Promotion at CDC for Kpc slides