b -lattamasi Penicillinasi-cefalosporinasi-carbapenemasi
description
Transcript of b -lattamasi Penicillinasi-cefalosporinasi-carbapenemasi
-lattamasiPenicillinasi-cefalosporinasi-carbapenemasi
-lactamase
Clinically isolated distinct -lactamase now number > 1400.
The simplest classification is by protein sequence, four classes, A, B, C, and D,
Classes A, C, and D include enzymes that hydrolyze their substrates by forming an acyl
enzyme through an active site serine, whereas class B -lactamases are metalloenzymes that
utilize at least one active-site zinc ion to facilitate -lactam hydrolysis.
Two major classification schemes exist for categorizing -lactamase enzymes: Ambler classes A through D, based onamino acid sequence homology, and Bush-Jacoby-Medeiros groups 1 through 4, based on substrate and inhibitor profile. A “family portrait” reveals the structural similarity of class A, C, and D serine -lactamases . Class B -lactamases (“a class apart”) are metallo—lactamases (MBLs) .
Carbapenemases are β-lactamases that hydrolyze penicillins, in most cases cephalosporins, and to various degrees carbapenems and monobactams (the latter are not hydrolyzed by metallo-β-lactamases).
-lactamaseClassA enzymes
ClassA enzymes are very prevalent among bacteria, especially in the Enterobacteriaceae. TEM-1 and TEM-2 were some of the first beta-lactamases described in the 1960s. SHV-1 was discovered later. These enzymes can be encoded on conjugative plasmids,
which have served as genetic vehicles for wide dispersal of these resistance genes. SHV-1 is also found on the chromosome
of Klebsiella pneumoniae. TEM-1, TEM-2, and SHV-1 confer resistance to commonly used antibiotics, such as ampicillin and amoxicillin. Other important substrates for these three enzymes include carbenicillin, pipercillin, cefazolin, and cefuroxime. The extent of hydrolysis for these drugs can vary depending upon
the quantity of the -lactamase that is produced. Class A enzymes are inhibited by clavulanic acid (sulbactam,
tazobactam). In addition, clavulanic acid has proved useful in the laboratory for detection of some classA enzymes.
-lactamaseClassA ESBL enzymes
ESBLs hydrolyze penicillins, narrow- and extended-spectrum cephalosporins (including the anti-methicillin-
resistant S. aureus [MRSA] cephalosporin), and the monobactam aztreonam. In contrast, ESBLs cannot
efficiently degrade cephamycins, carbapenems, and –lactamase inhibitors. More than 200 different ESBLs have been identified, posing a significant risk to public health
and to hospitalized patients in intensive care units, where infection with an ESBL may lead to significant morbidity and mortality The majority of ESBLs are from the SHV,
TEM, and CTX-M families; less frequently they are derived from BES, GES-1, VEB, and PER enzymes, and sometimes
these enzymes do not belong to any defined family.
-lactamaseClass A serine carbapenemases
Class A serine carbapenemases include the nonmetallocarbapenamase of class A (NMC-A), IMI, SME, and KPC. Members of this group of -lactamases can hydrolyze
carbapenems as well as cephalosporins, penicillins, and aztreonam. These carbapenemhydrolyzing enzymes have been identified primarily in Enterobacter cloacae, Serratia
marcescens, and K. pneumoniae, bacteria which often harbor multiple resistance determinants, narrowing the range of
treatment options. The bla gene for the former two organisms is typically found on the chromosome, while the K.
pneumoniae carbapenemase blaKPC gene is carried on plasmids containing Tn4401. MICs of carbapenems in
carbapenemase-expressing strains can vary from moderately increased (2 to 4 g/ml) to resistant ( 32g/ml)
-lactamaseClass B metallo--lactamases
Class B enzymes are Zn- dependent -lactamases that demonstrate a hydrolytic mechanism different from that of the
serine -lactamases of classes A, C, and D. Organisms producing these enzymes usually exhibit resistance to penicillins,
cephalosporins, carbapenems, and the clinically available -lactamase inhibitors . Interestingly, the hydrolytic profile of MBLs
does not typically include aztreonam. MBLs likely evolved separately from the other Ambler classes, which have serine at
their active site. The blaMBL genes are located on the chromosome, plasmid, and integrons . P. aeruginosa, K.
pneumoniae, and A. baumannii produce class B enzymes encoded by mobile genetic elements. In contrast, Bacillus spp.,
Chryseobacterium spp., and Stenotrophomonas maltophilia possess chromosomally encoded MBLs, but the majority of these pathogens are generally not responsible for serious infections.
-lactamaseClass C serine cephalosporinases
Class C AmpC –lactamases include CMY-2, P99, ACT-1, and DHA-1, which are usually encoded by chromosomal bla genes, although
plasmid-borne AmpC enzymes are becoming more prevalent. Organisms expressing the AmpC –lactamase are resistant to penicillins, -lactam–-lactamase inhibitor combinations, and
cephalosporins, including cefoxitin, cefotetan, ceftriaxone, and cefotaxime. AmpC enzymes poorly hydrolyze cefepime and are
inhibited by cloxacillin, oxacillin, and aztreonam. Members of the Enterobacteriaceae family, such as Enterobacter spp. and
Citrobacter spp., are AmpC -lactamase producers that resist inhibition by clavulanate and sulbactam, although Klebsiella spp.,
Salmonella spp., and Proteus spp. normally do not harbor chromosomal blaAmpC genes. Production of chromosomal AmpCs
in Gram-negative bacteria is at a low level (“repressed”) but can be “derepressed” by induction with certain -lactams, particularly
cefoxitin.
-lactamaseClass D serine oxacillinases
Class D -lactamases were initially categorized as “oxacillinases” because of their ability to hydrolyze oxacillin at a rate of at least 50% of that of benzylpenicillin, in contrast to the
relatively slow hydrolysis of oxacillin by classes A and C. In bacteria, OXA –lactamases can also confer resistance to
penicillins, cephalosporins, extended-spectrum cephalosporins (OXA-type ESBLs), and carbapenems (OXA-type
carbapenemases). OXA enzymes are resistant to inhibition by clavulanate, sulbactam, and tazobactam, (with some exceptions;
e.g., OXA-2 and OXA-32 are inhibited by tazobactam but not sulbactam and clavulanate, and OXA-53 is inhibited by
clavulanate). Examples of OXA enzymes include those rapidly emerging in A. baumannii (e.g., OXA-23 and OXA-24/40) and
constitutively expressed in P. aeruginosa (e.g., OXA-50).-
Inibitori delle β-lattamasi
Alcuni β-lattamici, derivati dalla ricerca di nuovi antimicrobici, sono stati inizialmente scartati a
causa della loro modesta potenza antibatterica nei confronti dei vari patogeni. Un numero ristretto di
queste molecole è stato in seguito identificato come capace di legarsi in modo covalente alle β-
lattamasi. Attraverso tale meccanismo l’enzima viene catturato e reso indisponibile per inattivare
l’altro eventuale farmaco presente.
Inibitori delle β-lattamasi
Gli inibitori suicidi oggi in uso sono: acido clavulanico, trovato in colture di
Streptomyces clavurigerus, tazobactam che è un sulfone dell’acido penicillanico e sulbactam che è un 6-desaminopenicillino sulfone. Questi
composti sono abbinati a penicilline o cefalosporine garantendo loro
immunità dalle più diffuse β-lattamasi.
Currently available lactamase inhibitors are effectively limited to many class A -lactamases, excluding the KPC carbapenemases.
Ceftolozane--tazobactamCXA-101 (oxyimino-aminothiazolyl cephalosporin) + tazobactam (beta-lactamase inhibitor) (2:1 ratio)
Microbiology Coverage •P. aeruginosa (MIC90 = 1-8 μg/ml)
•CXA-101 is not a substrate of the MexAB-OprM, MexCD-OprJ, MexEF-OprN, and MexXY efflux pumps nor the carbapenem-specific porin OprD in P. aeruginosa
Spectrum Gaps •Bacteria producing metallo-lactamases and certain ESBLs (OXA-15 and OXA-11, -14 and 16) confer losses of CXA-201 activity (MIC >32 μg/ml); derepression of ampC in P. aeruginosa can increase MIC up to 8-fold; MIC90 vs. MDR P. aeruginosa of >64 μg/ml
•Ceftazidime-R E. coli, K. pneumoniae ceftazidime-R or KPC producers, Enterobacter, Citrobacter, ESBL+ Proteus spp. (MIC90= 16/>16/>16/>16/>16 μg/ml)
•No activity against MRSA and other key gram-positives
IV only
The addition of tazobactam at 8 μg/ml resulted in restoring the susceptibility of 93% of the ESBL producers and 95% of the AmpC overproducers. Tazobactam was unable to lower MICs, however, for Enterobacteriaceae producing KPC carbapenemases
Molecole in evoluzione
Tra gli inibitori suicidi che non includono i beta-lattamici vi sono acido boronico, fosfonati (poco
stabili e sensibili alle fosfodiesterasi) e diazabiciclo
octanoniAvibactam inibisce B, C e D beta-
lactamasi, ma non le metallo beta-lattamasi.
E’ in fase di sperimentazione clinica
Avibactam DBO diazabiciclo octanoni
Avibactam has an extremely broad spectrum of activity against classes A and C serine -lactamases, including ESBLs and class A carbapenemases This molecule inhibits selected class D -lactamases including OXA-48, but apparently not other class D carbapenemases, as judged by the absence of synergy with imipenem against resistant strains of A. baumannii producing OXA-51 and OXA-58 and does not inhibit class B MBLs.
Ceftazidime-avibactam
Microbiology •Covers ESBL-producing Enterobacteriaceae and P. aeruginosa isolates producing class A and C β-lactamases, including KPC producers as well as AmpC-overexpressing strains
Spectrum Gaps •Not active against bacteria producing metallo-lactamases, OXA or VEB ESBLs, OXA carbapenemases in A. baumannii, NDM-1 producers, and efflux-mediated ceftazidime resistance in P. aeruginosa
IV only
Ceftaroline - avibactam
•Gram-positives: MRSA, VRSA, MRSE, VRE ( E. faecalis, amp-sensitive), S. pneumoniae, S. pyogenes
•Gram-negatives: H. influenzae, M. catarrhalis, ESBL-producing Enterobacteriaceae, wild type Acinetobacter, KPC-producers
•Atypicals: No coverage •Anaerobes: No, requires combination with metronidazole Spectrum
Gaps: Acinetobacter producing OXA β-lactamases , Enterobacteriaceae producing metallo-β-lactamases, P. aeruginosa producing AmpC or with reduced outer membrane permeability, amp-resistant E. faecalis
Mutant Selection: Frequencies for stable mutants from 25 enterobacteria with ESBL, AmpC or KPC β-lactamases were mostly < 10-9
IV only
Aztreonam-Avibactam
Monobactams are hydrolyzed by ESBLs
but are inherently stable to hydrolysis
by MBLs, an avibactam-aztreonam combination resulted
inhibitory to MBL-producing pathogens.
MK 7655
MK-7655, a new member of the DBO series. A combination of imipenem and MK-7655 has excellent activity against a KPC-2-producing isolate of K. pneumoniae and displays moderate improvements in the imipenem efficacy against most AmpC-overexpressing isolates of P. aeruginosa.
Imipenem-MK7655
Spectrum with Imipenem
•Gram-positives: streptococci, MSSA, MSSE, non-VRE
•Gram-negatives: At 4-8 μg/ml MK-7655, imipenem MICs of all strains were below the resistant breakpoint of IPM for Pseudomonas and Klebsiella containing KPCs
•Atypicals: No coverage
•Anaerobes: Coverage of B. fragilis and others Spectrum Gaps: VRE, MRSA, Stenotrophomonas spp., Burkholderia spp. strains containing class D metalloproteases; high levels of AmpC or KPC; certain class A β-lactamases Mutant Selection: 10-8 - 10-9 for 2 isolates of P. aeruginosa; 2 x10-7 to <3 x 10-8 for KPC+ K. pneumoniae for imipenem + MK-7655
IV only
Preclinical Findings
•Restored activity of imipenem to kill rapidly
•Low protein binding (20%)
RPX7009RPX7009, a boronic acid-containing -lactamase inactivator with inhibitory activity against class A and class C
serine -lactamases, particularly highlighting both in vitro and in vivo
activity against KPC-producing K. pneumoniae. Boronic acid inhibitors of PBPs and of classes A, C, and D -
lactamases had previously been identified, but none has achieved success as a clinical candidate. Preclinical testing of RPX7009
indicated that the inhibitor had no off-target effects, and it was well tolerated at high doses, with no
safety signals that would preclude future development
Biapenem-RPX7009
Biapenem (“RPX- 2003”) is a broad-spectrum carbapenem with in vitro activity against Gram-negative and Gram-positive bacteria similar to that of meropenem. Like other carbapenems, biapenem is not affected by the presence of
ESBLs but is labile to hydrolysis by both serine and metallo-carbapenemases. Although
carbapenem resistance is increasing, 75% of recent Japanese pseudomonal isolates were susceptible to biapenem and meropenem.
Pharmacologically, biapenem is notable for its low proconvulsive activity compared to that of
imipenem
Carbapenem + carbapenem
A combination of ertapenem and doripenem in both an in vitro chemostat and an in vivo murine thigh infection model. Overall, the combination of doripenem plus ertapenem
demonstrated enhanced efficacy over either agent alone (2011)
Double-Carbapenem Therapy Not Proven To Be More Active than Carbapenem Monotherapy against KPC-Positive Klebsiella
pneumoniae (2012)
Ertapenem plus doripenem or meropenem were given in three patients suffering from pandrug-resistant, KPC-2-positive
Klebsiella pneumoniae bacteremia (2 patients) and urinary tract infection (1 patient), respectively. All responded
successfully, without relapse at follow-up. The results obtained should probably be attributed to ertapenem’s increased affinity
for the carbapenemases hindering doripenem/meropenem degradation in the environment of the microorganism (2013)
Enzimi autolitici
La lisi cellulare ottenuta con le penicilline non è dovuta alla semplice inibizione della sintesi del peptidoglicano ma all’induzione di enzimi: un’amilasi che scinde i legami tra i tetrapeptidi e, una glucosilasi che scinde il glucano.
Quando questi enzimi sono inattivati o per mutazione o per crescita dei batteri a basso pH, la penicillina ha effetti batteriostatici.