Emergencnce of drug resistance in Enterococci

1. EMERGENCE OF DRUG RESISTANCE IN
ENTEROCOCCI
Moderator- Prof. Dr. Anima Xess
Presentor- Dr. Neelima Singh 1st yr MD std

2.  Introduction:
 Enterococcus species: A glimpse
 MIC definition
 Drug resistance in enterococcus: an overview
 Virulence factors in enterococci
 Clinical spectrum of enterococcal infection
 Antimicrobial susceptibility to various
antibiotics
 Role of Laboratories towards antibiotic
resistance

3.  Ability of a micro-organism to stop an
antimicrobial from working against it.
 Cause – Inappropriate use of antimicrobials.
 Result – Failure to respond to standard
treatment.
• Lead to prolonged illness.
• Greater risk of death.
• Patient remain infective for longer period
• Resistant strain may spread to other people.

4.  Proper hand wash should be practiced.
 Use of household disinfectant.
 Use of gloves on contact with body fluids that
may contain VRE, such as stool. Always wash
hands after removing gloves.
 Antibiotic sensitivity should be performed for
proper therapy.

5. • Genus Enterococcus includes the
enterococcal members previously classified
with group D streptococcus.
• They are normal residents of -
Gastrointestinal & biliary tracts.
Vagina.
Male urethra .

6.  On MacConkey medium, they produce tiny
deep-pink colonies.
 They are relatively heat resistant, surviving at
600C for 30 minutes.
 They typically appear as pairs of oval cocci, the
cells in a pair arranged at an angle to each
other.
 They are usually non-hemolytic, though some
strains may show alpha or beta hemolysis.

7. • Enterococci were distinguished from
streptococci by-
1. Their ability to grow at 45 C.
2. Growth in the presence of 6.5% NaCl.
3. Growth at pH 9.6.
4. Ability to hydrolyze esculin in presence of
40% bile.
5. Production of Pyrolidonyl arylamidase (PYR).

8.  Minimum Inhibitory Concentration (MIC)-
The MIC is defined as the lowest
concentration of antibiotic at which there is
no visible growth.
Expressed in range and in microgm/ml
 Cidal action is indicated by a reduction in the
number of colonies by 99%

9.  Enterococci have emerged as important agents
of human disease, largely because of their
resistance to antimicrobial agents to which
other streptococci are generally susceptible.
 E. faecalis is the most commonly isolated
species, causing about 70% of human
infections.

10.  Vancomycin resistant enterococci (VRE)
account for more than 30% of enterococcal
infections, and greater than 90%of VRE isolates
are E. faecium.
 Enterococci are often involved in serious
superinfections among patients receiving broad
spectrum antimicrobial therapy.

11.  Cytolysin/Hemolysin- 30% of E. faecalis produce an
extracellular protein, cidal for a no. of eukaryotic cells,
macrophages & PMNs.
 Proteases
a. Gelatinase Gel E
b. Extracellular serine protease Spr E
 Aggregation Substance protein-
o facilitate enterococcal adherence to cultured intestinal
and renal epithelial cells.
o Plasmids encoding ASP also carry antibiotic resistance
genes.

12.  Extracellular Surface Proteins -
o Enable the organisms to evade antibodies by their
ability to be retracted away from the cell surface.
o Involved in formation of biofilms.
 Correlation have been found between
possesion of various virulence factors and the
presence of resistance among clinical &
environmental strains of E. faecalis & E. faecium.

13.  Enterococcus species cause -
Complicated UTIs
Endocarditis
Intra-abdominal and pelvic infections
Wound & soft tissue infections
Neonatal sepsis
Rarely Meningitis.

14.  Presence of Enterococci in the urine is often
asymptomatic, and should not be treated with
antibiotics except under certain conditions –
Pregnant women
Patients undergoing urologic manipulations
Patients with significant underlying
co-morbidities.

15.  Resistance of Enterococci to various
antimicrobial agents contributes to their
pathogenicity.
 Resistant genes are acquired by –
Conjugative transfer mechanisms involving
plasmids
Transposons carrying multiple antibiotic
resistant genes

16.  Enterococci display intrinsic, low level
resistance to the aminoglycosides and
lincosamides.
 High level aminoglycoside resistance results
from acquisition of a transposon encoding
an aminoglycoside modifying enzymes that
confers resistance to all aminoglycosides
except streptomycin.
 These enzymes alter the structure of
aminogycoside molecule resulting in
decreased binding of the drug to its
ribosomal target.

17.  High level Streptomycin resistance(MIC
>2000microgm/ml) results from ribosomal
mutation involving a specific ribosomal
protein.
 HLR to aminoglycosides has disseminated
among enterococcal sps other than E.faecalis &
E.faecium and has been documented in E.avium,
E.casseliflavus, E.gallinarum, E.raffinosus &
E.mundtii.

18.  Many clinical laboratories use an automated
broth dilution system to screen for HLR to
aminoglycosides. After a minimum of 24 hrs
incubation any growth is considered resistant.
 Standard disk diffusion testing is also
performed using antibiotic disks with
gentamicin (120microgm) or streptomycin
(300microgm). Resistance is defined by a zone
diameter<6mm.

19.  Many strains of Enterococci, particularly
E.faecium , are intrinsically resistant to beta
lactams as they posses binding proteins with
low affinity for these drugs.
 Ampicillin resistance is seen in >90% of
E.faecium due to the presence of PBP5 which
has a decreased affinity for ampicillin.
 The cephalosporins are uniformly ineffective
against enterococci and should not be tested.

20. • Serious infections with enterococci were
usually treated with penicillin or
ampicillin in combination with an
aminoglycoside.
• But due to lack of reliable penicillin-
aminoglycoside synergism, vancomycin
became a first line drug.
• In 1986,however, a high level glycopeptide
resistance in E. faecium and E. faecalis
heralded a major change in the
enterococcal susceptibility.

21. Antibiotic Susceptible Intermediate Resistant
Penicillin/
Ampicillin
<8 - >16
Vancomycin <4 8-16 >32
Teicoplanin <8 16 >32

22. • The glycopeptide vancomycin and teicoplanin
act by binding to the “D-alanyl-D-alanine”
terminus of cell wall peptidoglycan
intermediates and inhibiting cell wall cross-
linking.
• In glycopeptide resistant strains, the “D-alanyl-
D-alanine” desipeptide is replaced by D-alanyl-
D-lactate” or by “D-alanyl-D-serine.”

23. • Acquired glycopeptide resistance in
Enterococcus species corresponds to eleven
different van gene clusters based on DNA
sequences and organisation.
• These gene clusters encode either a D-alanyl-D-
lactate(vanA,vanD,&vanM)ligase enzyme or D-
alanyl-D-
serine(vanC1,vanC2,vanC3,vanE,vanG,vanL,&va
nM)ligase enzyme for synthesis of
peptidoglycan precursors with low affinities
for glycopeptide agents.

25.  These eleven genotypes have correlated
resistance phenotypes
(VanA,VanB,VanC1,VanC2,VanC3,VanD,VanE
,VanG,VanL,VanM&VanN) with VanA &
VanB phenotypes being most prevalent and
important clinically.
 Genes encoding VanA & VanB phenotypes are
carried on transposons that may be inserted
into the chromosome or into plasmids.

26.  E.faecalis & E.faecium isolates that have the vanA
genotype & VanA phenotype display
vancomycin & teicoplanin inducible,
transposon mediated high level resistance to
both vancomycin(MIC64-1000microgm/ml) &
teicoplanin(16-512microgm/ml).

27.  Historically many laboratories used the
vancomycin agar dilution screen test to detect
VRE. Agar plates contain BHI media
supplemented with 6microgm vancomycin per
ml. A0.5 MacFarland isolate suspension is used
to spot a 10 to 15mm diameter area on the plate
providing a final inoculum of 105 to 106 per
spot.
 The presence of more than one colony or haze
of growth indicates resistance.

28.  Automated systems may also be used to detect
glycopeptide resistanse in enterococci.
 For example Vitek 2, BD Phoenix, Microscan,
Vitek Legacy etc.
 Several laboratory developed multiplex
methods using PCR and real time PCR have
been developed to primarily detect the vanA &
vanB gene clusters that are of utmost clinical
importance.

29.  Another enterococcal phenomenon is that of
vancomycin dependence.
 This refers to strains of enterococci that grow
only in the presence of vancomycin.
 Vancomycin dependent enterococci(VDE) were
first described in 1994, when these organisms
were cultured from the urine of a patient
receiving long-term therapy with vancomycin.
 VDE strains are relatively uncommon.

30.  Linezolid and Daptomycin are newer agents
that have been used to treat serious invasive
infections due to VRE.
 Linezolid breakpoints have been published for
disk diffusion ( 30microgm). If a clear zone is
not found, an MIC method should be used to
perform repeat testing.

31.  In vitro susceptibility testing of Daptomycin
requires the presence of standardised levels of
calcium.
 Disk diffusion testing is unreliable for this
reason and should not be used for daptomycin
susceptibility.
 Daptomycin Etest strips may be used along
with calcium supplemented MHA.

32.  The results of penicillin, ampicillin,vancomycin
and the screen for HLR to gentamicin &
streptomycin should be reported for all
E.faecalis & E.faecium isolates recovered from
serious infections.
 Laboratories should also have protocols for
performing extended susceptibility testing on
other antibiotics( daptomycin,linezolid).

33.  This protocol should include criteria for
referral of multidrug-resistant isolates to a
reference laboratory for confirmatory
susceptibility testing.
 Infection Prevention and Control and/or
public health agencies should be immediately
notified of patients suspected or confirmed to
have VRE.

34.  Hirdon AI,Edward JR ,PatelJ, et al. NHSN annual update CDC,2006-2007, Infection Control
Hospital 2008; 29:996-1011.
 Jett BD, Jensen HG, Atkuri, et al.Evaluation of therapeutic measures for traeting
endophthalmitis caused by isogenic toxin producing E. faecalis strains. Investigation
OphthalmVis Sci 1995; 16:533-535
 Arias CA, Murray BE,. The rise of the enterococcus: beyond vancomycin resistance.Nat,
rev.2012;64:233-235.
 Chow JW,Thal LA,Perri MB.et al. Plasmid associated hemolysin and aggregation substance
proteins contributers to virulence in experimental enterococcal endocarditis. Antomicrobe
Agents 1993;68:688-691
 Paganelli FK, Mootskipan bn, et al.Optimising future traetment of enteroccoccal infections,
Trends Microbiology 2012;20:40-49
 Rubins JR, Jannof bh,Pneumolysin a multifunctional Pneumococci virulence factor. J LabClin
Med 1998;131:21-27.
 Zeng J, Teng F, Murray BE,et al. Gelatinase is important for translocation of Enterococcus
faecalis across polarised human enterocyte. Infect Immun 2005;73:449-453.
 Murdoch DR, Mirrette S, Harrel LJ, et al. Comparison of microdilution broth synerggy quad
plate and disk diffusion method for detection of high level aminoglycoside resistance in
enterococci, J Clin Moicrobiology2003;41:2703-2705.
 Gary W. Procop, Elmer W. Koneman Gail L. Woods. Color atlas and textbook of diagnostiv
microbiology seventh edition.2015;1125-1139