The discovery of the naturally occurring mechanism
based inhibitor clavulanic acid, which causes potent
& progressive inactivation of β- lactamases has
created renewed interest in β- lactam combination
This interest has led to the design & synthesis of
additional mechanism based β- lactamase
Inhibitors, such as sulbactum & tazobactam, &
isolation of naturally occurring β- lactams such as
thienamycins, which both inhibit β- lactamases &
interact with PBP’s.
β- lactam Antibiotics
β-lactam antibiotics are a broad class of antibiotics that include
penicillin derivatives, cephalosporins, monobactams,
carbapenems, and β-lactamase inhibitors that is, any antibiotic
agent that contains a β-lactam nucleus in its molecular structure.
Common β-lactam antibiotics:
Development of Resistance
Widespread use of β- lactams, the largest family of
antibiotics in current clinical use, has inevitably led
to the emergence of resistant bacteria.
The commonly encountered mechanism of
resistance is that attributable to production of β-
lactamases, a group of enzymes capable of
catalyzing the hydrolysis of the β- lactam ring.
The existence of these enzymes was recognized as
earlier as 1940 soon after the isolation of penicillin,
& fears relating to their plasmid-mediated spread
through out the bacterial population have been fully
FAILURE OF ANTIBIOTICS DUE TO
Current Rate of
% increase in
Methicillin/S. aureus 54.5% 43%
β- lactamases Classification
These enzymes are divided as:
1) Class A contains enzymes from Gram-positive bacteria. The
majority of them are transmissible, plasmid-mediated enzymes,
often referred to as penicillinases because their preferred
substrates are penicillins.
2) Class B contains broad-spectrum metallo-enzymes which mainly
3) Class C contains predominately chromosomally mediated enzymes
from Gram-negative bacteria whose preferred substrates are
cephalosporins are thus referred to as cephalosporinases.
4) Class D includes enzymes capable of hydrolyzing the more β-
lactamase stable isoxazolyl penicillins.
Two strategies have evolved to combat β- lactamases-
i. Development of classes of β- lactam antibiotics with improved
ii. Identification of β- lactamase inhibitors for co-administration with
the other antibiotics.
β- lactamase Inhibitors
Although they exhibit negligible antimicrobial
activity, they contain the beta-lactam ring.
Their sole purpose is to prevent the inactivation of
beta-lactam antibiotics by binding the beta-
lactamases, and, as such, they are co-administered
with beta-lactam antibiotics.
1. clavulanic acid
Systematic (IUPAC) name: (2R,5R,Z)-3-(2-hydroxyethylidene)-
7-oxo-4-oxa-1-aza-bicyclo[3.2.0] heptane-2-carboxylic acid
Clavulanic acid can be considered as the most important & representive
among the inhibitors of β- lactamases.
It is first clinically useful β- lactamase inhibitor was identified as a natural
product from a strain of Streptomyces clavuligerus.
Structurally it is a 1-oxopenam lacking the 6-acyl amino side chain of
penicillins but possessing a 2-hydroxy ethylidene moiety at C-2
Clavulanic AcidClavulanate Potassium
Clavulanic acid was invented around 1974/75 by
British scientists working at the drug company
Clavulanic acid exhibits very weak antibacterial
activity, comparable with that of 6- amino penicillanic
acid therefore is not useful as an antibiotic.
It is however, a potent inhibitor of S. aureus β-
lactamase & plasmid-mediated β- lactamases
elaborated by Gram negative bacilli.
Mechanism of action
Clavulanic acid has negligible intrinsic antimicrobial
activity, despite sharing the β-lactam ring that is
characteristic of beta-lactam antibiotics.
However, the similarity in chemical structure allows
the molecule to act as a competitive inhibitor of beta-
lactamases secreted by certain bacteria to confer
resistance to beta-lactam antibiotics.
This inhibition restores the antimicrobial activity of
beta-lactam antibiotics against a lactamase-secreting
Despite this, some bacterial strains have emerged that
are even resistant to such combinations.
Most commonly, the potassium salt potassium
clavulanate is combined with amoxicillin (co-
amoxiclav) [brand name Augmentin]
Timetin (potassium clavulanate plus ticarcillin)
Clavulanic acid has also been isolated from
S. jumonjinensis the P-hydroxypropionyl
Derivative of clavulanic
acid was obtained (though only isolated as
its benzyl ester) from Streptomyces clavuligerus
Clavulanic Acid Analogs
Diazotization/bromination of 6-APA followed by oxidation, gave the
6,6-dibromopenicillanic acid sulfone which on catalytic
hydrogenation provided sulbactam.
It is irreversible inhibitor
of several β- lactamases.
compared with clavulanic
acid sulbactum is modest
inhibitor the class-A
improved potency against
class-C, although at level
considered to be a little
Sulbatam is penicillanic acid sulfone or 1,1
Fixed-dose combination of ampicillin sodium &
sulbatam sodium, marketed under trade name
Unasyn have been approved for use in U.S.
Tazobactam is a penicillanic acid sulfone that is similar in structure
It is more potent β- lactamase inhibitor than sulbatam & have
slightly broder spectrum of activity than clavulanic acid.it has very
weak antibacterial activity.
Tazobatam is available in injectable combination with piperacillin
trade name Zosyn.
Interaction of sulbactam, clavulanic acid and tazobactam
with penicillin-binding proteins of imipenem-resistant
and -susceptible acinetobacter baumannii
Carl Urban a b Eddie Go a Noriel Mariano a James J. Rahal a c a
Infectious Disease Section, Department of Medicine, The New York
Hospital Medical Center of Queens, 56-45 Main Street, Flushing, New
York 11355-5095, USA b Department of Microbiology, Cornell
University Medical College, New York, USA c Department of
Medicine, Cornell University Medical College, New York, USA
*Corresponding author. Tel: (718) 670-1525; Fax: (718) 3539819.
AbstractWe have encountered clinical isolates of Acinetobacter baumannii
which are resistant to all available antibiotics used in hospitals except for
polymyxin B and the beta-lactamase inhibitor, sulbactam. To investigate the
mechanisms of this unique activity, affinities of sulbactam and other beta-
lactamase inhibitors for penicillin binding proteins were compared using
imipenem-resistant and imipenem-sensitive isolates. The results of competition
binding experiments indicate that all three beta-lactamase inhibitors bound to
imipenem-susceptible Acinetobacter. Binding of sulbactam was greater than that
of tazobactam and not detected with clavulanic acid to penicillin binding proteins
of the imipenem-resistant strain of Acinetobacter.
Effect of clavulanic acid, sulbactam and tazobactam on three
different ß-lactamases from Bacteroides uniformis,Clostridium
butyricwn and Fusobacterium nucleatum
M. Hedberg, L. Lindqvist, K. Tunér and C.E. Nord* Department of
Microbiology, Huddinge University Hospital. Karolinska Institute S-141 86
Huddinge, Sweden and National Bacteriological Laboratory S-105 21 Stockholm,
The effect of three ß-lactamase inhibitors clavulanic acid, sulbactam and
tazobactam used in clinical practice were compared for their activity against purified
ß-lactamases from Bacreroides uniformis, Clostridium butyricum and
Fusobacterium nucleatum. The enzymes from B. uniformis and C. butyricum were
produced in fermenters under controlled growth conditions and the enzyme from F.
nucleatum was produced in batch cultures. Purification of the ß-lactamases was
achieved by anion-exchange chromatography, gel filtration and FPLC-technique. The
degree of inactivation of ß-lactamase activity was determined spectrophotometrically
with nitrocefin as the substrate. The inhibitors in various concentrations were
preincubated at 30°C together with the enzyme for different time periods (0·5–120
min) before determination of the remaining ß-lactamase activity. The inhibitors all
decreased the activity of the ß-lactamases investigated. Clavulanic acid and
sulbactam were capable of reducing the enzyme activity of the B. uniformis ß-
lactamases more effectively than the C. butyricum and F. nucleatum ß-lactamases. All
ß-lactamases tested were more susceptible to tazobactam than to clavulanic acid