1. The New β-
Lactamases
Neha Sharma

2. Introduction
 Major defense of the Gram negative bacteria against the β-
lactam antibiotics
 These antibiotics have a common four-atom ring known as a
beta-lactam.
Hydrolysis of the β-lactam ring & decarboxylation of the intermediate
 The lactamase enzyme breaks the β-lactam ring
open, deactivating the molecule's antibacterial properties
 Co-evolved with the β-lactam antibiotics since they came
into clinical use.

3.  Earlier increased in microbes in which they were
uncommon (e.g. Staph. aureus) and then spread to
pathogens that had previously lacked them ( e.g. H.
influenzae and N. gonorrhea)
 Introduction of the newer “resistant” β-lactam antibiotics
like cephamycins, oxyimino-cephalosporins,
carbepenems & monobactams 20 yrs back, resulted in
the emergence of a newer set of ESBLs, AmpC enzymes
and carbapenemases.

4. Classification of β-lactamases
Ambler Molecular Classification
 AA similarity and 10 structure.
 Classes A, C & D have serine residues at their active
site.
 Class B are metallo-β-lactamases that require Zn & Ca
ions for their actions.
 Classes A (TEM/SHV) & D (OXA) were plasmid
mediated.
 Class B & C were chromosomal mediated.

5. Bush-Jacoby-Medieros Functional
Classification
 Based on functional similarities i.e. substrate and
inhibitor profile.
 4 main groups (1 to 4) and multiple subgroups.
 More of immediate relevance to clinicians and
μbiologists because it considers β-lactamase
inhibitors and substrates that are clinically
relevant.

6. Classification

7. Detection of ESBL Production

9. Class A β-lactamases
 Broad and Expanded spectrum β-lactamases
 Include TEM, SHV, CTX-M types commonly.
 BES, GES/IBC family, PER, SFO, TLA & VEB are members
too.
 Hydrolyze all classes of penicillins, Ist, IInd, IIIrd, IVth
gen. cephalosporins & monobactams.
 Co-resistant to quinolones, aminoglycosides &
sulphamethoxazole.

10.  Cephamycins and carbapenems are not
affected them, though the latter are the
most consistent in their action.
 Inhibited by β-lactamase inhibitors
 ESBL producing organisms may lose their
outer membrane proteins, not related to β-
lactamase production & become resistant
to cephamycins too.

11. TEM type β-lactamases
 TEM-1, TEM-2 are broad spectrum against which
IIIrd, IVth gen. cephalosporins & monobactams were
active.
 TEM-10, TEM-12 & TEM-26 are ESBLs, in majority
now, active against the above, though rarely
accompanied by resistance to inhibitors too.
 Useful to follow the spread of individual resistance
genes.

12. SHV Type β-lactamases
 SHV = sulphydryl variable
 SHV-1 is a broad spectrum
β-lactamase similar to TEM-1.
 Most commonly found in K.pneumoniae.
 Are the most common clinically isolated in Europe and
USA.

13.  Within 15 yrs, SHV-2 were found in every
inhabited continent, implying that selection
pressure from third-generation cephalosporins
in the first decade of their use was responsible.
 SHV ESBLs have been detected in a wide range
of Enterobacteriaceae & outbreaks of SHV-
producing P. aeruginosa & Acinetobacter spp.
have now been reported.
 SHV-5 and SHV-12 are among the most
common.

14. CTX-M ESBLs
 Most common group of ESBLs not belonging to the
previous two were termed CTX-M to highlight their
greater activity against cefotaxime than cefepime or
ceftazidime.
 Belying their name, they now hydrolyse ceftazidime
more than cefotaxime.
 Mainly been found in strains of Salmonella enterica
serovar Typhimurium and E. coli.

15.  Widespread findings of CTX-M-type ESBLs in
China and India, is speculated that CTX-M-type
ESBLs are now actually the most frequent ESBL
type worldwide.
 Tazobactam exhibits an almost 10-fold greater
inhibitory activity than clavulanic acid against
CTX-M-type β-lactamases
 CTX-M-15 are the most widespread in
India, Middle East, Europe and the USA.

16. Other Class A ESBLs
 Uncommon, mostly in P. aeruginosa & at limited
areas.
 VEB 1 & 2 in South East Asia.
 Others are PER-1, GES-1 & 2, IBC-2, PES-1 and may
be found in Enterobacteriaceae too.
 BES-1, IBC-1, SFO-1 & TLA-1 found only in
Enterobacteriaceae.
 Include some carbapenemases as well.

17. Class B β-lactamases
 Also called the Metallo β lactamases.
 Are Zn dependant enzymes with a different
mechanism of action.
 Exhibit resistance to
penicillins, cephalosporins, carbapenems and β
lactamase inhibitors.
 Their hyrdolytic profile doesn’t include
Aztreonam.
 Types include Plasmid-mediated IMP-type
carbapenemases, VIM and NDM-1 (New Delhi
metallo-β-lactamase)

18. NDM-1 (New Delhi metallo-β-
lactamase)
 Originally described from New Delhi in 2009
 widespread in Escherichia coli and Klebsiella
pneumoniae from India and Pakistan.
 As of mid-2010, NDM-1 carrying bacteria have
been introduced to other countries (including
the United States and UK)
 It’s the so called “super bug” spread due to
the large number of tourists travelling from
these countries.

19. Class C β-lactamase
 Known as the serine cephalosporinases.
 Mainly Amp C plasmid induced enzymes.
 Substrates include the penicillins,
cephalosporins plus cephamycins and β
lactam – β lactamase inhibitor combinations.
 Cefepime is poorly hydrlolysed by it.
 They are mainly inhibited by cloxacillin,
oxacillin and aztreonam.
 Responsible for the resistance emerging in
Enterobacter cloacae.

20. Class D serine oxacillinases
 Initially found to hydrolyse oxacillin at a slow
rate.
 Confer resistance to
penicillins, cephalosporins, extended
spectrum cephalosporins, carbapenems
and β lactamase inhibitors.
 In vitro sodium chloride and chelating
agents like EDTA inhibit some carbapenem
hydrolysing oxacillinases.

21. Carbapenemases
 Source of concern because they are active
against cephalosporins and carbapenems.
 Include class A, B and D β lactamases.
 Examples are
Plasmid mediated IMP type in enteric
Gram negative organisms, Pseudomonas and
Acinetobacter species.
VIM family of carbapenemases
KPC enzymes
OXA – type β lactamases

22. Factors influencing β
lactamase expression
 Expanded spectrum activity may decrease
intrinsic hydrolytic activity like in TEM and SHV
which can be compensated for by increased
gene dosage or a promoter with increased
activity.
 Active efflux mechanism as in Pseudomonas
allows selective enzymes with limited hydrolytic
activity to inactivate the drug.
 Decreased expression of OMPs required like in K.
pneumoniae allow resistance to develop to
specific drugs.

23. Genetics of β lactamases
 PLASMIDS: predominate in ESBLs and hospital
outbreaks if unifocal in origin like TEM but may
be multifocal too like in SHV and spread world
wide.
 TRANSPOSONS: TEM – 1 and TEM – 2
 CHROMOSOMES: Klebsiella strains producing
SHV – 1
 INTEGRONS: Genes are incorporated into the
genome but have their origin elsewhere. So
the reservoir is large with ubiquitous spectrum.
Eg. CTX – M, Amp – C type

24. Risk factors Predisposing to infection by
β lactamase producing organisms
 Diabetes mellitus
 Previous antimicrobial exposure
(quinolones, third generation
cephalosporins, penicillin)
 Previous hospital admissions
 Older age
 Male patients
 Prolonged ICU and hospital stay.
 Increased severity of illness
 Use of a CVC/CAC, urinary catheter, ventilatory
assistance

25. Thank you