Salmonella and Fluoroquinolones: Where are we now? …Salmonella enterica subspecies enterica serovar Typhi Salmonella enterica serovar Typhi Salmonella ser. Typhi Salmonella Typhi

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Salmonella and Fluoroquinolones: Where are we now?

Eszter Deak, PhD, D(ABMM) Chief, Clinical Microbiology Santa Clara Valley Medical Center San Jose, CA [email protected]

Disclosures

Nothing to Disclose

Salmonella – Current Taxonomy

§ Two major species § Salmonella bongori (uncommon in human infections) § Salmonella enterica §  Six subspecies including Salmonella enterica subsp. enterica

§ >2500 serovars

Salmonella enterica subspecies enterica serovar Typhi Salmonella enterica serovar Typhi Salmonella ser. Typhi Salmonella Typhi or S. Typhi

Typhoidal Salmonella = S. Typhi and S. Paratyphi A-C

WHO Collaborating Centre for Reference and Research on Salmonella

Salmonella Infections

§ Typhoidal § Require antimicrobial therapy from any source § Usually ceftriaxone or fluoroquinolones in adults

§ Non-typhoidal § Systemic sources require antimicrobial therapy § Gastroenteritis § Usually self-limiting §  Therapy NOT recommended due to prolongation of carrier state §  Therapy indicated for:

§  Severe diarrhea §  Patients with underlying medical conditions (e.g., immunosuppression)

Specimen: Stool Diagnosis: Diarrhea (29 yo otherwise healthy lab tech)

Salmonella spp. (non-typhoidal)

Should we do more?

Salmonella spp. AST and Reporting

“(2) Susceptibility testing is indicated for typhoidal Salmonella (S. Typhi and Salmonella Paratyphi A–C) isolated from extraintestinal and intestinal sources. Routine susceptibility testing is not indicated for nontyphoidal Salmonella spp. isolated from intestinal sources.”

CLSI M100-S24. Table 2A.

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Specimen: Stool Diagnosis: Diarrhea (29 yo otherwise healthy lab tech)

Salmonella spp. (non-typhoidal)

“Gastroenteritis due to non-typhoidal Salmonella spp. is generally self-limiting in patients without underlying

medical issues.”

Final Report with Optional Comment


“(2) When fecal isolates of Salmonella spp. are tested, only ampicillin, a fluoroquinolone, and trimethoprim-sulfamethoxazole should be reported routinely. In addition, for extraintestinal isolates of Salmonella spp., a third-generation cephalosporin should be tested and reported, and chloramphenicol may be tested and reported if requested.”


WARNING: For Salmonella spp., first- and second-generation cephalosporins, cephamycins and aminoglycosides may appear active in vitro, but are not effective clinically and should not be reported as susceptible.


Report Do Not Report*

Ampicillin 1st or 2nd generation cephalosporins

Ciprofloxacin (fluoroquinolone) not for children

Cephamycins

Trimethoprim- sulfamethoxazole Aminoglycosides

Ceftriaxone (extraintestinal)

Chloramphenicol (if requested)

* May test susceptible in vitro but not effective clinically CLSI M100-S24. Table 2A.

Why do we need reliable ASTs for fluoroquinolones (FQs) and Salmonella

§ Salmonella big global health concern § Widespread resistance to ampicillin, chloramphenicol, TMP-SMX in many parts of world § WHO recommends FQ (oral) or ceftriaxone (parenteral) for

uncomplicated typhoid fever FQ usually = ciprofloxacin or ofloxacin or levofloxacin

(see Sjolund-Karlsson et al. 2011. Antimicrob Agents Chemother. 55:3985.)

Basnyat et al. 2005. Clin Infect Dis. 41: 1467.

Global Incidence - Typhoid Fever

WHO Background document: The diagnosis, treatment and prevention of typhoid fever. 2003.

MDR

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Salmonella spp. Fluoroquinolones (FQs) Issue § Typhoid fever

§ High morbidity/mortality if untreated or untreatable § FQs good (inexpensive, PO route) for treatment of

salmonellosis, including typhoid fever § Emerging resistance!!

§ Clinical response rates to ciprofloxacin are poorer for isolates with “decreased ciprofloxacin susceptibility” (MICs of 0.12 – 1.0 µg/ml) § Longer infection clearance times § Treatment failures § Relapses § Need to test!!

§ Optimal method for detection of FQ resistance not defined for S. enterica § Nalidixic acid does not detect all mechanisms of fluoroquinolone

resistance § Need easy test (disk diffusion) to differentiate isolates that are “S”

vs. “not S”! Crump et al. 2008. Antimicrob Agents Chemother. 52:1278. Parry et al. 2010. Antimicrob Agents Chemother. 54:5201.

Increasing Resistance or Partial Resistance to Ciprofloxacin in Salmonella, 1999-2011

0

10

20

30

40

50

60

70

80

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

% R

esis

tant S. Typhi

non-typhoidal

CDC NARMS

The Scoop on FQs § Nalidixic Acid first quinolone (1960s)

§  By product of chloraquine § Narrow spectrum of activity – Gram negatives in UTIs

§ Fluorine atom added to quinolone molecule (1980s) §  Fully synthetic, no pre-existing resistance genese to this class in

nature § Next generation late 80’s, early 90’s (ciprofloxacin, ofloxacin,

norfloxacin, enoxacin) §  More readily absorbed, ↑ activity to Gram (-)

§ Newer FQs late 90’s (levofloxacin, gatifloxacin, moxifloxacin) §  Broad spectrum with enhanced activity to many Gram (-) and Gram (+)

§ Q and FQ resistance common, widespread § Resistance rising independently, numerous times (15 independent

gyrA mutations in last decade) in fully susceptible orgs, maintained through selective pressure

§  Fitness benefit

Resistance to FQs in Salmonella

§ Chromosomal mutations § Altered FQ binding site § Quinolone resistance

determining region (QRDR)

§  2 target enzymes §  DNA gyrase

§  gyrA, gyrB §  Topoisomerase IV

§  parC, parE

§ Outer membrane impermeability, Overexpression of efflux pump systems §  AcrAB-TolC

Porin

DNA gyrase

Topo isomerase

Efflux Pumps

Enzyme Mutations

Decreased Permeability

FQ Resistance Mechanisms in Salmonella?

§ Several FQ resistance mechanisms described for Enterobacteriaceae

§ Late 1990’s, plasmid-mediated mechanisms identified § Quinolone target protection § qnrA, qnrB, qnrS, qnrC, qnrD § Correlation with ESBLs?

§ Modification of quinolones by acetyltansferase § Aac(6’)-lb-cr

§ Active efflux pumps § QepA, OqxAB

Fluoroquinolone Resistance Mechanism Genotypes/Phenotypes

Genotype Phenotype

Ciprofloxacin MIC (µg/ml) Nalidixic Acid

Wild type (No resistance) 0.008-0.06 Usually susceptible

Chromosomal gyrA (single mutation) 0.12 - 2.0 Usually resistant

Chromosomal gyrB (single mutation)

0.12 – 0.5

Usually susceptible

Chromosomal gyrA, gyrB (multiple mutations)

≥4.0 Resistant

PMQR (e.g. qnr or aac(6’)-lb-cr) 0.12 - 2.0 Often susceptible

PMQR, plasmid-mediated quinolone resistance - newer mechanism and less common than chromosomal gyrase mutations

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Detection of FQ Resistance in Salmonella - CLSI M100 Recommendations

§ Several revisions over past 3 years § Changes driven by: § Recognition of several emerging FQ resistance mechanisms not detected by traditional methods

§ Reports documenting clinical therapeutic failure in patients infected with low-level FQ resistant isolates

§ Re-evaluation of FQ pharmacokinetics and pharmacodynamics

Salmonella spp. Fluoroquinolone AST and Reporting History

CLSI Standard Fluoroquinolone Breakpoints M100-S14 (2004) Screen extra-intestinal Salmonella with ciprofloxacin

MIC ≤1 µg/mL for nalidixic acid resistance as predictor of decreased ciprofloxacin susceptibility

M100-S21 (2011) One set of breakpoints for all Enterobacteriaceae including Salmonella spp. Reliability of Nalidixic acid screen for reduced ciprofloxacin susceptibility in extraintestinal isolates of Salmonella spp. questioned

M100-S22 (2012) Lower ciprofloxacin breakpoints for S. Typhi and extraintestinal Salmonella spp.

M100-S23 (2013) Lower ciprofloxacin, levofloxacin and ofloxacin breakpoints for use with all Salmonella spp. Establish ciprofloxacin disk breakpoints

M100-S24 (2014) No changes

Fluoroquinolone Resistance Mechanism Genotypes/Phenotypes

Genotype Phenotype

Ciprofloxacin MIC (µg/ml) Nalidixic Acid

Wild type (No resistance) 0.008-0.06 Usually susceptible

Chromosomal gyrA (single mutation) 0.12 - 2.0 Usually resistant

Chromosomal gyrB (single mutation)

0.12 – 0.5

Usually susceptible

(2-16 µg/mL) Chromosomal gyrA, gyrB (multiple mutations)

≥4.0 Resistant

PMQR (e.g. qnr or aac(6’)-lb-cr) 0.12 - 2.0 Often susceptible

(8-32 µg/mL)

PMQR, plasmid-mediated quinolone resistance - newer mechanism and less common than chromosomal gyrase mutations

Uncommon in nontyphoidal in US, common in Asia and Europe

1-11% of S. Typhi in US, UK

Ciprofloxacin Reference MIC: Search for Surrogate FQ Disk § Levofloxacin § Nalidixic acid § Ofloxacin § Enoxacin § Norfloxacin § Pefloxacin

What Criteria are Used to Determine if AST Results are Acceptable?

Criteria Definition Acceptable limits

Essential Agreement (EA)

MIC within +/- doubling dilution of the REF MIC ≥90%

Categorical Agreement (CA) Same S, I, or R result ≥90%

Essential agreement (EA) = # isolates within +/- 1 two-fold dilution of REF MIC X 100 Total # isolates tested

Categorical agreement (CA) = # isolates with same S, I, R result as REF MIC X 100 Total # isolates tested

What Criteria are Used to Determine if AST Results are Acceptable? (cont’d)

Error Type Results Acceptable Error Rate

REF Method AST Validating N≥30 N≥100 Very Major (VME) R S 0 ≤3% (min 35 R

isolates) Major (ME) S R <5% ≤3%

Minor (mE)

S I

Major + Minor ≤10%

Major + Minor

≤7%

R I I S I R

CA ≥90% ≥90%

Cumitech 31A. ASM Press, 2009

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Calculating % Errors Very Major Error (VME) = # with VME (false R) X 100 Total # “R” isolates tested

Major Error (ME) = # with ME (false S) X 100 Total # “S” isolates tested

Minor Error (mE) = # with mE X 100 Total # isolates tested

How Many Organisms? § Not specified by CLIA § Minimum of 30

§ Selection Criteria § Represent clinical isolates tested § Variety of susceptibility profiles § Some around breakpoints

Patel et al. 2013. Clin Micro Newsletter. 35:103-109.

Surrogate Disk for FQ Resistance in Salmonella spp. § Our definition –

§ A disk and zone cutoff that most reliably identifies Salmonella isolates that are not susceptible to FQs based on current ciprofloxacin susceptible or not susceptible (I + R) MIC breakpoints § No data to indicate monotherapy efficacious against “I” isolates

§ Assumption – ciprofloxacin MIC (using CLSI reference method) accurately differentiates FQ susceptible from FQ not susceptible isolates

§ Errors calculated: § VME = total false S/total not susceptible § ME = total false not susceptible/total susceptible

Performance of Disk Diffusion (DD) and Etest for Detection of FQ-R Salmonella enterica (n=136) No. of Isolates (% typhoidal) “R” Mechanism BMD MIC range (µg/mL)

Ciprofloxacin Nalidixic Acid

1 (0) aac(6’)-lb-cr 1.0 32

36 (0) qnr 0.12 - 1.0 4.0 – 32

45 (0) QRDR mutation 0.06 - 0.5 ˃128

29 (90) Not characterized 0.12 – 16 128 - ˃128

24 (25) None ≤0.08 – 0.06 2 – 16

Deak et al. 2015. J Clin Microbiol. 53:298. CLSI Agenda Book June 2014.

Distribution of Ciprofloxacin MICs (n=136)

0 5

10 15 20 25 30 35 40 45

<=0.0

6 0.1

2 0.2

5 0.5 1 2 4 >4

No.

of I

sola

tes

MIC (mcg/ml)

R mechanism known R mechanism unknown


S I (“Not S”) R (“Not S”)

Ciprofloxacin MIC vs Ciprofloxacin DD (n=136)

Current BP (%)

VME 0

ME 8.0

CA 98.5

≤30 mm

Ciprofl

oxacin M

IC (u

g/ml)

>16

16 1 1

8

4 1 1 2

2 1

1 1 1 2 4 3 1 1

0.5 1 1 10 6 8 3 2

0.25 1 1 1 2 5 8 12 8 2 1

0.12 4 3 3 6 2 1

0.06 1 1

0.03 1 2 1 2 1

0.015 1 7 4 3

<=0.008 1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Ciprofloxacin Disk Diffusion (mm)

MEs

11% mEs

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Ciprofloxacin MIC vs Nalidixic Acid DD (n=136)

Current BP (%)

VME 1.8

ME 20.0

CA 94.9

≤18 mm

Ciprofl

oxacin M

IC (u

g/ml)

>16

16 2

8

4 4

2 1

1 12 2 1 1 1

0.5 19 1 1 5 2

0.25 36 1 1 1 1 1

0.12 17 1

0.06 1 1

0.03 2 1 2 2

0.015 1 1 2 7 1 1 2

<=0.008 1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Nalidixic Acid Disk Diffusion (mm)

(VME – qnr’s)

64.7% mE, 81/88 mEs Cipro “I”, NAL “R”; 14 are PMQR

Ciprofloxacin MIC vs Levofloxacin DD (n=136)

MK Proposed

BP (%)

VME 1.0

ME 4.0

CA 98.5

≤27 mm

Ciprofl

oxacin M

IC (u

g/ml)

>16 16 1 1 8 4 2 2 2 1

1 7 2 3 1

0.5 1 1 1 6 8 6 4 4 1 0.25 4 9 19 5 4

0.12 2 3 9 4 1

0.06 2 0.03 1 1 2 1 1 1 0.015 4 7 1 1 1

<=0.008 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 Levofloxacin Disk Diffusion (mm)

Sjӧlund-Karlsson et al. 2014. J Clin Micro. 52:877-884

(VME - NAL >128) QRDR

ME

Ciprofloxacin MIC vs Pefloxacin DD (n=136)

Current BP (%)

VME 0

ME 12.0

CA 97.8

≤23 mm

Ciprofl

oxacin M

IC (u

g/ml)

>16 16 2 8 4 2 2 2 1

1 6 1 2 3 2

0.5 8 2 2 7 4 2 2 1 1 0.25 4 1 4 4 7 13 2 5 1

0.12 1 2 8 5 2 1

0.06 1 1 0.03 1 1 1 2 1 1 0.015 1 3 5 4 3

<=0.008 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Pefloxacin Disk Diffusion (mm)

How well do disks identify isolates that are “S” vs. “not susceptible” to FQs? Surrogate Agent and not-susceptible breakpoint1

VME %(N) False “S”1

ME %(N) False “R”2 CA (%)

Ciprofloxacin ≤ 30 mm

0.0

8.0 (2)

98.5

Levofloxacin ≤ 27 mm

1.0 (1)

4.0 (1)

98.5

Ofloxacin ≤ 24 mm

0.0

4.0 (1)

99.3

Nalidixic Acid ≤ 18 mm

1.8 (2)

20.0 (5)

94.9

Enoxacin ≤ 17 mm ≤ 23 mm

53.2 (59) 0.0

0.0 4.0 (1)

56.6 99.3

Norfloxacin ≤ 16 mm ≤ 27 mm

91.0 (101) 1.0 (1)

0.0 8.0 (2)

25.7 97.8

Pefloxacin ≤ 23 mm

0.0

12.0 (3)

97.8

CA, categoric agreement (same “S “ or “not S” result) 1 based on 111 “R” isolates 2 based on 25 “S” isolates


DD vs Ref MIC

Isolates With Zone Sizes Near the Breakpoint

0

5

10

15

20

25

30

35

40

45

50

<-5 -5 -4 -3 -2 -1 1 2 3 4 5 >5

% o

f iso

late

s

Ciprofloxacin DD Pefloxacin DD Ofloxacin Levofloxacin

Resistant zone sizes Susceptible zone sizes

DD generally accepted as precise to only +/- 3 mm

% Isolates +/- 3 mm of breakpoint 30% Levofloxacin 25% Ofloxacin 16.9% Ciprofloxacin 15.4% Pefloxacin

Pefloxacin 5 µg Zones1

1 BBL MHA II (single lot); Oxoid disks (single lot); 18 h incubation 20/47 ciprofloxacin non-susceptible isolates appeared similar

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y = -0.0175x - 1.3326

-8

-6

-4

-2

0

2

4

6

8

0 10 20 30 40 50 60 70

BD

Zon

e - O

xoid

Zon

e

Isolate #

BD vs. Oxoid

y = -0.0127x - 1.3697

-8

-6

-4

-2

0

2

4

6

8

0 10 20 30 40 50 60 70

MA

ST Z

one

- Oxo

id Z

one

Isolate #

MAST vs. Oxoid

y = -0.0048x + 0.0372

-8

-6

-4

-2

0

2

4

6

8

0 10 20 30 40 50 60 70

BD

Zon

e - M

AST

Zon

e

Isolate #

BD vs. MAST

Average difference: -0.13

Average difference: -1.83 Average difference: -1.97

Three lots of pefloxacin disks tested

-  Significantly larger zones with Oxoid

disks vs. BD and MAST (p<0.0001) -  ≈2 mm larger zones

-  No difference in S/R interpretation for 72 isolates tested

13-09-218 (QRDR) Ciprofloxacin MIC = 0.12 µg/ml

13-09-215 (QRDR) Ciprofloxacin MIC = 0.5 µg/ml

PEF #3

PEF #2

PEF #1 PEF #1

PEF #2

PEF #3

Now how can we detect Salmonella that are not susceptible to FQs?

S R S R I I

M100-S25. p. 49.

What is pefloxacin?

§ FQ introduced in early 1980s § Used for uncomplicated gonorrhoeae, UTIs, gastroenteritis, typhoid fever § Dupont. 1993. Drugs. 45:119.

§ Studies in Europe suggested pefloxacin disk superior in differentiating FQ “S” vs “not susceptible” isolates

§ Neither pefloxacin drug nor disk available in USA § CLSI added pefloxacin to address “global needs”

Current Salmonella FQ Breakpoints

Antimicrobial Disk

Content (µg)

MIC (µg/ml) Disk Diffusion (mm)

S I R S I R

Ciprofloxacin CLSI 5 ≤0.06 0.12-0.5 ≥1.0 ≥31 21-30 ≤20

FDA (S. Typhi only)

≤0.06 0.12-0.5 ≥1.0 ≥31 21-30 ≤20

Levofloxacin

CLSI ≤0.12 0.25-1.0 ≥2.0 ----- ----- -----

Ofloxacin

CLSI ≤0.12 0.25-1.0 ≥2.0 ----- ----- -----

Surrogate/Screening Agents for Detection of FQ Resistance Nalidixic Acid**

CLSI 5 ≤16 ----- ˃32 ≥19 14-18 ≤13

Pefloxacin*

CLSI 5 ----- ----- ----- ≥24 ----- ≤23

*Surrogate test for ciprofloxacin; **also surrogate but not labeled as such

Strains of Salmonella that test “nonsusceptible” to ciprofloxacin, levofloxacin, ofloxacin, pefloxacin, or nalidixic acid may be associated with clinical failure or delayed response in fluoroquinolone-treated patients with salmonellosis.

Surrogate Disk VME (%) ME (%) CA (%)

Ciprofloxacin 0.9 8.7 97.8

Nalidixic Acid 2.7 13.0 95.6

Pefloxacin 0.0 0.0 100

Surrogate Disks Compared to Levofloxacin MICs for S. enterica (113 not-susceptible isolates) § Levofloxacin commonly used in US hospitals as FQ § No Salmonella levofloxacin disk breakpoints formally

established

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Agent Performance [N (%)]

EA CA

Ciprofloxacin 131 (97.0) 135 (100)

Levofloxacin 125 (92.6) 135 (100)

Salmonella spp. (N=135) Etest vs. Ref MIC

Deak et al. 2015. J Clin Microbiol. 53:298.

EA, essential agreement (within +/- 1 dilution) CA, categoric agreement (same “S” or “not S” result)

Testing for FQ Resistance in the US § Pefloxacin disks not available in US § No surrogate agent will detect all FQ resistance mechanisms

§  aac-6-lb-cr alone will not test “R” to pefloxacin §  S. enterica ser. Typhi with QRDR mutation testing “S” to ciprofloxacin by BMD §  Nalidixic acid did not detect qnr mutations in 5.5% of isolates tested

§ MIC test for ciprofloxacin or levofloxacin §  Revised ciprofloxacin breakpoints by CLSI and by FDA (S. Typhi only) §  No commercial MIC susceptibility test panels with low enough drug

concentrations §  Etests compared well to BMD §  Not FDA approved with current breakpoints §  Need verification study §  Is it worth it?

§ Ciprofloxacin disks §  No issues with reading in developed labs §  Suitable alternative §  Surrogate agent for levofloxacin susceptibility (susceptible vs not-susceptible)

Salmonella spp. - Nalidixic Acid Test Antimicrobial

Agent DD (mm) MIC (µg/ml)

Susc Int Res Susc Int Res Nalidixic acid ≥19 14-18 ≤13 ≤16 - ≥32

“(39) Until laboratories can implement the current interpretive criteria for ciprofloxacin, levofloxacin, and/or ofloxacin, nalidixic acid may be used to test for reduced fluoroquinolone susceptibility in Salmonella. Strains of Salmonella that test resistant to nalidixic acid may be associated with clinical failure or delayed response in fluoroquinolone-treated patients with salmonellosis.

Note that nalidixic acid may not detect all mechanisms of fluoroquinolone resistance.”


Major Changes 2015 M100-S25

§ Enterobacteriaceae § Salmonella § Added pefloxacin disk diffusion test to

differentiate isolates “S” vs. “not susceptible” to fluoroquinolones

§ Added azithromycin disk diffusion and MIC test breakpoints for S. Typhi

WHO Background document: The diagnosis, treatment and prevention of typhoid fever. 2003.

Drug Alternatives to FQs for Salmonella

Drug Alternatives to FQs for Salmonella cont’d § No data on favorable high dose CIP monotherapy

outcomes § Ceftriaxone may be favorable

§ Empiric therapy with ceftriaxone § ESBLs and plasmid mediated cephalosporinases reported

worldwide §  2010 – 2.8% nontyphoidal Salmonella ceftriaxone “R” in CDC

National Antimicrobial Resistance Mponitoring System report §  2006-2007 Indian report – 6% “R” to ceftriaxone1

§ Confirm susceptibility

§ Empiric therapy with azithromycin

1 Nagshetty et al. 2010. J Infect Dev Ctries 4:70-73.

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Salmonella spp. % Susceptible USA 2012

Antimicrobial Agent

Breakpoint (µg/ml)

Non-typhoidal Salmonella

spp. (n=2236)

S. Typhi (n=326)

S. Paratyphi A (n=111)

Ampicillin ≤8.0 91.0 100 100

Ceftriaxone ≤1.0 97.2 100 100

Ciprofloxacin ≤0.06 96.4 31.6 4.5

Trimeth-sulfa ≤2/38 98.6 89.8 100

Azithromycin ≤16.0 99.9 100 100

*National Antimicrobial Resistance Monitoring System (NARMS)

http://www.cdc.gov/narms/

Why azithromycin for Salmonella Typhi? § Management of enteric fever generally includes

antimicrobial agents § Azithromycin distribution in vivo

§ Low serum concentration § Concentrates in PMNs, monocytes, lymphocytes, alveolar

macrophages; achieves high intracellular concentrations (≈ 80-200 times > serum concentration)

§ Azithromycin MICs lower than intracellular concentration

§ Salmonella Typhi is an intracellular pathogen § Successfully used for many years; very few clinical

failures §  Found to perform significantly better than ceftriaxone

Frenck R et al. 2004. Clin Infect Dis. 38:951–7. Girgis et al. 1999. Antimicrob Agents Chemother. 43:1441-4.

Salmonella Typhi Azithromycin Breakpoints

Antimicrobial Agent

Disk Content

(µg)

DD (mm) MIC (µg/ml) Comments

S I R S I R

Azithromycin 15 ≥13 - ≤12 ≤16 - ≥32 (33) Salmonella Typhi only: Interpretive criteria are based on MIC distribution data.

EUCAST: “Azithromycin has been used in the treatment of infections with Salmonella typhi (MIC ≤16 mg/L for wild type isolates) and Shigella spp.”

M100-S25. p. 49.

eucast.org *No dosing regimen *FDA breakpoints needed *Breakpoints based on epidemiological cutoff, in vitro activity

Salmonella USA, 2012 Distribution of Azithromycin MICs

National Antimicrobial Resistance Monitoring System (NARMS) http://www.cdc.gov/narms/

MIC µg/ml

Clinical Findings

MIC 64 µg/mL

Galas et al. CLSI Agenda Book June 2014.

Inner zone

Outer zone

MIC Method MIC (µg/ml)

Broth microdilution

8

Etest inner zone 4 Etest outer zone 1

Salmonella Typhi Azithromycin

Often observe “double” zones on

Etest and DD… read inner zone

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When should we test Salmonella spp.? What drugs?

§ Extraintestinal isolates § Typhoidal Salmonella from all sources § Other when requested (select patient populations?) § ampicillin, a fluoroquinolone, trimethoprim-sulfamethoxazole + 3rd

generation cephalosporin for extraintestinal isolates

How can we test fluoroquinolones? § Of commercial AST systems, only Etest currently encompasses new

low MIC breakpoints for ciprofloxacin (not FDA cleared with Salmonella breakpoints)

§ Ciprofloxacin disk diffusion, Nalidixic Acid screen § Pefloxacin for global needs

Should we test azithromycin? If yes, how? § On request only § Disk diffusion and MIC breakpoints for S. Typhi only

Acknowledgments UCLA, Los Angeles, CA § Janet Hindler § Romney Humphries § Anita Sokovic Statens Serum Institute, Copenhagen, Denmark § Robert Skov CDC, Atlanta, GA § Maria Sjolund-Karlsson

Salmonella and Fluoroquinolones: Where are we now? …Salmonella enterica subspecies enterica serovar Typhi Salmonella enterica serovar Typhi Salmonella ser. Typhi Salmonella Typhi

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