Plasmid-mediated Beta-lactamases Research Articles

Detection of beta-lactam antibiotic resistance in aquatic Enterobacteriaceae isolates

Abstract Production of the beta-lactamase enzymes is the primary resistance mechanism caused by unconcious consumption of the beta-lactam group of antibiotics in Enterobacteriaceae. Combined disc tests were performed for extended-spectrum beta-lactamase (ESBL) confirmation (n = 15) and class C beta-lactamase (AmpC) confirmation (n = 6) after the disc diffusion test was applied in a total of 27 Enterobacteriaceae strains from Western Black Sea, Lake Manyas and Lake Iznik. Plasmid-mediated blaTEM, blaSHV, blaCTX-M , blaIMP genes, CIT, MOX, FOX gene groups and chromosomal blaAmpc gene of E. cloacae were investigated using the polymerase chain reaction (PCR). Three E. coli strains were shown to produce ESBL, while one E.coli and three E. cloacae strains were confirmed for AmpC production by disc tests. blaTEM (n = 2), blaSHV (n = 4), blaCTX-M (n = 2), blaTEM + blaSHV (n = 1), blaCTX-M + CIT (n = 1), blaSHV + CIT (n = 1) genes and/or gene groups were detected in 11 E. coli isolates; while blaSHV (n = 3) was observed in three Klebsiella strains (two K. oxytoca and one K. pneumoniae). With this study, the aquatic environments of Turkey were proved to be the reservoirs of antibiotic-resistance determinants of plasmid-mediated beta-lactamases in environmental wild-type bacteria transmitted by horizontal gene transfer.

Tracking Multidrug-Resistant Klebsiella pneumoniae from an Italian Hospital: Molecular Epidemiology and Surveillance by PFGE, RAPD and PCR-Based Resistance Genes Prevalence.

Antimicrobial-resistant Klebsiella pneumoniae represent a global public health concern. K. pneumoniae strains isolated during 2010 and 2014-2016 within a single hospital of Molise Region, Central Italy, were analyzed testing antimicrobial susceptibility, clonality by pulsed-field gel electrophoresis (PFGE) and random amplified polymorphic DNA (RAPD)-PCR, and prevalence of carbapenem resistance genes by PCR. Forty isolates (23 wild-type in 2010 and 17 non-wild-type in 2014-2016) were collected from hospitalized patients (65.2 ± 18.1years old, 75% male, 80% from intensive care unit-ICU). K. pneumoniae showed multidrug-resistant profiles and 15 resistotypes were identified (discriminatory power D = 0.88). The 69.6 and 17.4% of isolates in 2010 resulted intermediate and resistant to imipenem, respectively, and 91.3% was sensitive to meropenem, while 88.2% of isolates of 2014-2016 were resistant to both antibiotics. PFGE identified 16 clusters versus 23 by RAPD, 26 pulsotypes versus 33 RAPD patterns (D ≥ 0.97). PFGE separated strains according to isolation period and identified an outbreak occurred in the ICU during December 2014 and January 2015. No strains harbored blaGES, blaIMP, blaNDM-1, and blaOXA-48 genes, as well as AmpC plasmid-mediated beta-lactamases genes. Only K. pneumoniae isolated during 2014-2016 were blaKPC positive. Prevalence of blaVIM was 87 and 76.5% during 2010 and 2014-2016, respectively. No strains colistin-resistant harbored mcr-1 plasmid-mediated resistance gene. The study findings underline an increased circulation of multidrug-resistant K. pneumoniae within the hospital, and the acquisition of carbapenem resistance mechanism. The implementation of surveillance and molecular characterization of isolates are needed to identify outbreaks, reduce the spread of resistance, and guide empirical therapy.

Emergence of co-production of plasmid-mediated AmpC beta-lactamase and ESBL in cefoxitin-resistant uropathogenic Escherichia coli.

Plasmid-mediated AmpC (pAmpC) and ESBL co-production was detected in Escherichia coli a major etiologic agent of urinary tract infection. Isolates resistant to cefoxitin by CLSI methodology were tested for pAmpC beta-lactamase using phenylboronic acid and ESBLs by combined disk diffusion method. pAmpC/ESBL genes were characterized by PCR and sequencing. Transconjugation experiments were done to study the transfer of pAmpC and ESBL production from clinical isolates as donor to E. coli J53 AziR as recipient. Incompatibility groups of transmissible plasmids were classified by PCR-based replicon typing (PBRT). Among 148 urine culture positive isolates, E. coli was reported in 39.86% (59/148), with 93.22% (55/59) of cefoxitin resistance. pAmpC production was detected in 25, with varied distribution of blaCMY-2 and blaDHA-1type genes alone (n = 13 and 7 respectively) or in combination (n = 5). ESBL co-production was observed in 88% (22/25) of pAmpC producing isolates with predominance of blaTEM (n = 20). Twenty-three transconjugants showed transmission of pAmpC-and ESBL-resistant genes with co-carriage of blaCMY-2 and blaTEM (n = 15) in plasmids of IncF type (n = 9) being predominant, followed by IncI1 (n = 4) and IncH1 (n = 2) in combination. All clinical isolates were clonally diverse. Resistance against different beta-lactams in uropathogenic E. coli has been an emerging concern in resource- poor countries such as India. Knowledge on the occurrence of AmpC beta-lactamases and ESBL amongst this pathogen and its transmission dynamics may aid in hospital infection control.

Prevalence of fecal carriage of extended-spectrum- and metallo-β-lactamase-producing gram-negative bacteria among neonates born in a hospital setting in central Saudi Arabia.

BACKGROUND AND OBJECTIVECommensal neonatal fecal flora constitute a reservoir of antibiotic resistance. The aim of this study was to characterize the prevalence of fecal carriage of extended spectrum beta-lactamases (ESBLs) and carbapenemase producing gram-negative bacteria among 150 neonates who were born in two hospitals in central Saudi Arabia.PATIENTS AND METHODSFrom June 2012 to Janauary 2013, 150 healthy neonates ≤7 days of age were screened for intestinal enteric bacteria colonization and the influence of age, mode of delivery, body weight and breast feeding of neonates on colonzation rates. The isolates were identified manually and by VITEK 2 and antibiotic susceptibility was tested. Phenotypic tests were performed to seek ESBL and metallo-β-lactamase (MBL) producers in recovered isolates.RESULTSAmong 150 fecal specimens, 188 gram-negative rods were recovered. E coli (n=130; 69.1%) was the commonest organism followed by Klebsiella pneumoniae (n=23; 12.2%), Pseudomonas aeuroginosa (n=14; 7.5%), Acinetobacter baumannii (n=9; 4.8%), Enterobacter spp. (n=9; 4.8%) and Morganella morganii (n=3; 1.6%). E coli colonization during the first day of life was 95.5% (n=43/45), which was relatively higher than in subsequent days. The colonization rate of E coli among low weight babies (≤3 kg) was significantly higher than fully grown neonates (≥4 kg)(P=.03). The prevalence of ESBL and MBL was 15.0% (n=28/188) and 1.6% (n=3/188). The prevalence rates of ESBL in E coli, K pneumoniae, E cloacae, M morganii and E aerogenes were 16.9% (n=22/130), 4.3 % (n=1/23), 60% (n=3/5), 33.3% (n=1/3), and 25% (n=1/4), respectively. All E cloacae with ESBLs and MBLs were resistant to all tested antibiotics including carbapenems.CONCLUSIONWithin the first week of life, the most important determinants of gut enteric bacteria composition in neonates were age in days, body weight, mode of delivery, and type of neonatal feeding. The findings of ESBLs- and MBLs-producing enteric bacteria as neonate-gut colonizers may have wider implication or linkage to prevention of nosocomial and community-acquired infections by these strains.

High prevalence of CTX-M-15 and first report of CTX-M-3, CTX-M-22, CTX-M-28 and plasmid-mediated AmpC beta-lactamase producing Enterobacteriaceae causing urinary tract infections in Bosnia and Herzegovina in hospital and community settings

To investigate molecular epidemiology of extended-spectrum β-lactamase/ESBL and plasmid-mediated AmpC β-lactamase/pAmpC producing Gram-negative bacteria causing urinary tract infections (UTIs) in Zenica-Doboj Canton, Bosnia and Herzegovina, in the period Decembar 2009-May 2010. Antibiotic susceptibility was determined by disc diffusion and broth microdilution according to CLSI guidelines. Double-disk synergy test was performed in order to screen for ESBLs/pAmpC beta-lactamases. PCR was used to detect bla(ESBL)/bla(ampC)/bla(carb) genes. Genetic relatedness of the strains was determined by pulsed-field-gel-electrophoresis (PFGE). Among 85 patients with UTIs caused by ESBL producing isolates, 44 (51.8%) were from in-patients and 41 (48.2%) from outpatients. Klebsiella spp. was the most frequently isolated from in-patients, in 28 (63.6%) cases. Among outpatients, Klebsiella spp./Escherichia coli were the most frequently isolated, in 19 (46.3%)/16 (39.0%) cases. Twenty-one (75.0%) from hospital and nine (47.4%) from outpatient Klebsiella spp. isolates were positive for blaTEM, whereas 27 (96.4%) from in-patients and 6 (31.6%) from outpatient were bla(CTX-M) positive (18 hospital and five outpatient isolates were encoding bla(CTX-M-15)). One Klebsiella oxytoca and one Enterobacter cloacae inpatient isolates were positive for blaCTX-M-28. One Klebsiella pneumoniae outpatient isolate were positive for bla(CTX-M-22) and one E. coli for bla(CTX-M-3). One hospital Proteus mirabilis strain was positive for bla(CMY-2) and two Klebsiella spp. strains for blaDHA-1, whereas two E. coli, one K. oxytoca and one Proteus vulgaris outpatient strains were positive for bla(CMY-2). Identification of bla(CTX-M-3), bla(CTX-M-22) and bla(CTX-M-28) among Enterobacteriaceae is uncommon. In this study we report the emergency of CMY-2 and DHA-1 plasmid-mediated beta-lactamases.

Emergency (clonal spread) of methicillin-resistant Staphylococcus aureus (MRSA), extended spectrum (ESBL)--and AmpC beta-lactamase-producing Gram-negative bacteria infections at Pediatric Department, Bosnia and Herzegovina.

Aim of this study was to investigate the prevalence of methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum (ESBL) and plasmid-mediated AmpC beta-lactamase producing Gram-negative bacteria in children. Antibiotic susceptibility of MRSA and beta-lactamase producing Gram-negative bacteria was determined by disc diffusion and broth microdilution methods according to CLSI guidelines. Methicillin resistance was confirmed by the presence of mecA gene by PCR. The genetic characterization of S. aures was performed using spa-typing and the algorithm based upon repeat pattern (BURP). Double-disk synergy test was used to screen for ESBL production. PCR was used to detect bla ESBL alleles. Genetic relatedness of the strains was tested by pulsed-field gel electrophoresis (PFGE). Among 23 MRSA, 12 (52.2 %) were obtained from newborns. MLST CC152 (spa-CC 355-595) (Balkan clone) was the most prevalent, 20 (87 %) cases. Among 24 beta-lactamase producing Gram-negative bacteria, 10 (41.7 %) were obtained from each newborns and one-year-old children; 14 (58.3 %) were from urine. Among 11 Klebsiella strains isolated from urine eight (73 %) produced CTX-M-15, and one CTX-M-3 beta-lactamase. Twenty (83 %) of CTX-M producers were coproduced by other types of beta-lactamases. Fifteen (65.2 %) MRSA isolates were clonally related. Five clones among 13 K. pneumoniae isolates were detected by PFGE suggesting clonal spread of β-lactamase producing Gram-negative bacteria. Pediatric infections caused by clonal spread of MRSA and beta-lactamase-producing Gram-negative bacteria are of major concern. Proper infection control measures should be implemented in order to avoid the transmission and major outbreaks.

Survival in the environment is a possible key factor for the expansion of Escherichia coli strains producing extended‐spectrum β‐lactamases

Acquired resistance to cephalosporins in Enterobacteriaceae is a global problem. After an outbreak at Uppsala University Hospital of extended-spectrum β-lactamase (ESBL)-positive Klebsiella pneumoniae producing CTX-M-15, there was a shift from AmpC to ESBL production among Escherichia coli isolates. To explore the basis for this epidemiological shift, 46 E. coli isolates (ESBLs, n = 23; AmpC, n = 23) were characterized with regard to genetic relatedness, β-lactamase, replicon and integron types, antibiotic resistance profiles, and genes encoding virulence factors. In addition, the survival in the environment and on hospital-associated materials was analysed. CTX-M-15 was the most frequent ESBL (78%). Only three (13%) of the AmpC enzymes were harboured on plasmids (CMY-2, DHA-1). Independent of plasmid-mediated beta-lactamase, IncF plasmids predominated and only class I integrons were detected. The ESBL producers carried more virulence genes (p = 0.04), exhibited a broader resistance phenotype (p = 0.01) and survived significantly longer (p = 0.03) on different materials than the AmpC-producing isolates. In conclusion, ESBL-producing isolates had properties which are likely to augment their competitiveness. Apart from antibiotic resistance and virulence factors, extended survival in the environment could be a selective trait for successful ESBL-producing E. coli strains.

Phenotypic Investigation of Plasmid-Mediated AmpC Beta-Lactamases in Escherichia coli and Klebsiella pneumoniae Strains Isolated from Various Clinical Specimens

Phenotypic Investigation of Plasmid-Mediated AmpC Beta-Lactamases in Escherichia coli and Klebsiella pneumoniae Strains Isolated from Various Clinical Specimens

Klinik Örneklerden İzole Edilen Escherichia coli ve Klebsiella pneumoniae Suşlarında Plazmidik AmpC Tipi Beta-Laktamaz Direncinin Araştırılması

Klinik Örneklerden İzole Edilen Escherichia coli ve Klebsiella pneumoniae Suşlarında Plazmidik AmpC Tipi Beta-Laktamaz Direncinin Araştırılması

PP-006 Plasmid-mediated TEM beta-lactamase in Escherichia coli clinical isolates from urinary tract infection in Mashhad, Iran

PP-006 Plasmid-mediated TEM beta-lactamase in Escherichia coli clinical isolates from urinary tract infection in Mashhad, Iran

Lectura interpretada del antibiograma de bacilos gramnegativos no fermentadores

Among non-fermenting Gram-negative rods, the most clinically important species are Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia, which are frequently multiresistant. P. aeruginosa resistance to beta-lactams depends on the production of chromosomal and plasmid-mediated beta-lactamases, altered permeability (loss of OprD porin is related to carbapenem-resistance) and active efflux systems, particularly MexAB-OprM. In aminoglycoside resistant strains, the main mechanism of resistance is the production of modifying enzymes; the efflux pump MexXY-OprM is also involved. Quinolone resistance in P. aeruginosa is related to changes in topoisomerases, altered permeability and efflux pumps. Multiresistance in A. baumannii may be associated with the acquisition of resistant islands carrying different resistant determining factors. Several broad- and extended-spectrum beta-lactamases have been shown in this microorganism, however the main mechanism of resistance to betalactams is the hyperproduction of the chromosomal cephalosporinase (AmpC) related to the presence of the ISAba1 in the promoter region of this gene. The main mechanism of resistance to carbapenems is the acquisition of carbapenemases type B (metallo-β-lactamases) or class D (oxacillinases), however the loss of a porin can also contribute to modulate the final MIC. The resistance to aminoglycosides has been associated with the production of modifying enzymes or the overexpression of efflux pump (AdeABC), whereas the resistance to quinolones is related to changes in the protein targets as well to the overexpression of efflux pump(s). S. maltophilia show resistance to beta-lactams including carbapenems due to the production of two beta-lactamases (L-1 and L-2). Aminoglycoside-modifying enzymes have also been described in this species. In contrast to that observed in other organisms, S. maltophilia resistance to quinolones has been mainly related to active efflux, rather than to targets alterations.

Prevalence of plasmid-mediated AmpC beta-lactamases in Escherichia coli and Klebsiella spp. isolated in children

To study the plasmid-mediated AmpC β-lactamases and the genotypes of Escherichia coli and Klebsiella spp. in children. Escherichia coli and Klebsiella spp. of strains were isolated at our division from January to December 2009. Cefoxitin disk diffusion method was used to screen Escherichia coli and Klebsiella spp. for phenotypic AmpC enzyme. Multiple PCR method was adopted to test the genotypes of AmpC enzyme-positive Escherichia coli and Klebsiella spp.strains. Of all Escherichia coli and Klebsiella spp., 65 were insensitive to cefoxitin disk and 17 strains carried DHA type AmpC gene. The prevalence of plasmid-mediated AmpC enzyme in Escherichia coli and Klebsiella spp. was 26.2% (17/65). Among plasmid-mediated AmpC enzyme isolates, 14 (38.9%) Klebsiella pneumoniae strains, 2 (7.7%) Escherichia coli strains and 1 (33.3%) Klebsiella oxytoca strains carried the DHA-1 AmpC gene. The genes of MOX, CIT, DHA, ACC, MIR and FOX were not found in other 48 strains. The identified plasmid-mediated AmpC genes are all of DHA-1 genotype in Escherichia coli and Klebsiella spp. The prevalence of plasmid-mediated AmpC enzyme in Klebsiella pneumoniae isolates is relatively high in children.

Characterization of conjugative plasmids carrying antibiotic resistance genes encoding 16S rRNA methylase, extended-spectrum beta-lactamase, and/or plasmid-mediated AmpC beta-lactamase

In this study, we identified extended-spectrum beta-lactamase (ESBL) and plasmid-mediated AmpC beta-lactamase which were associated with 16S rRNA methylase gene on the conjugative plasmid. Among 82 clinical isolates of Enterobacteriaceae that carry 16S rRNA methylase gene (64 strains, armA, and 18 strains, rmtB), bla(SHV-12) was detected either alone or combined with bla(DHA-1), bla(CTX-M-3), and bla(CTX-M-14) in 30 strains carrying armA and 6 strains carrying rmtB. The bla(CTX-M-3) was detected in 13 of 64 strains carrying armA but no strains carrying rmtB. Whereas bla(CTX-M-14) was detected in 15 of 18 strains carrying rmtB but only 2 of 64 strains carrying armA. Overall, bla(SHV-12) and bla(CTX-M-14) was the most common ESBL gene which was associated with armA and rmtB, respectively. In addition, we found that bla(CTX-M-3) localized with armA on the same IncL/M plasmid and bla(CTX-M-14) localized with rmtB on the same IncA/C plasmid. Restriction fragment length polymorphism of conjugative plasmids and pulsed-field gel electrophoresis of genomic DNAs revealed that intercellular horizontal transfer of conjugative plasmid and clonal transmission have been occurred at the same time.

Characterization of a Novel AmpC-Type Plasmid-Mediated β-Lactamase from an Escherichia coli Strain Isolated in China

The aim of this work was to study the phenotypic and molecular characterization of a novel plasmid-mediated AmpC beta-lactamase from Escherichia coli E384. Conjugation experiments, isoelectric focusing, pulsed-field gel electrophoresis, plasmid profiling, and Southern blot as well as PCR, sequencing techniques, and susceptibility testing were carried out to investigate the underlying mechanism of resistance. The kinetic parameters were determined to characterize the novel enzyme. MIR-4 beta-lactamase, pI 8.2, is a novel variant with four substitutions of amino acids compared with the sequence of MIR-1. E. coli E384 displays resistance to eight beta-lactam antimicrobial agents and three fluoroquinolones. The minimal inhibitory concentrations of beta-lactam in combination with beta-lactamase inhibitors show no significant synergy. Kinetic parameters suggest that the novel enzyme effectively hydrolyzes broad-spectrum beta-lactams. The same hybridization signal was detectable only in the 54-kb plasmid band that hybridized with the bla (CTX-M)- and bla(ampC)-specific probes. This is the first description of a plasmid-mediated MIR-4 enzyme in China. This study illustrates the importance of molecular surveillance in tracking AmpC-producing strains at general hospitals and emphasizes the need for epidemiological monitoring.

Typing of SHV Extended-Spectrum β-Lactamases by Pyrosequencing in Klebsiella pneumoniae Strains with Chromosomal SHV β-Lactamase

ABSTRACT In Klebsiella pneumoniae , the cooccurrence of chromosomal and plasmid-mediated beta-lactamases can hinder their accurate molecular detection. We developed a fast and reliable method that allows the typing of isolates carrying more than one SHV gene. The method is based on pyrosequencing the DNA sequence corresponding to amino acid positions 35, 238, and 240.

Identification of plasmid-mediated extended-spectrum and AmpC β-lactamases in Enterobacter spp. isolated from dogs

The genetic determinants involved in reduced susceptibility to third-generation cephalosporins and aztreonam were identified in ten canine Enterobacter isolates associated with opportunistic infections in three veterinary hospitals in Brisbane, Australia. All isolates were evaluated by a combination of phenotypic (broth microdilution and disc susceptibility, modified disc diffusion and IEF) and genotypic (PFGE, plasmid analysis, Southern blot hybridization, bacterial conjugation, PCR and sequencing) methods to investigate genetic relatedness and to identify plasmid-mediated resistance genes, in particular beta-lactamase genes responsible for extended-spectrum cephalosporin resistance. The ten canine isolates were genotypically diverse based on PFGE and belonged to either Enterobacter cloacae or Enterobacter hormaechei on the basis of 16S rRNA gene sequence analysis. Plasmid profiles were also diverse. Nine isolates contained a transmissible blaSHV-12-carrying plasmid (approximately 140 kb) that also conferred resistance to chloramphenicol, gentamicin, spectinomycin, tetracycline, trimethoprim and sulfonamides. In all plasmid-mediated extended-spectrum beta-lactamase (ESBL)-producing isolates including transconjugants, blaSHV-12 was shown to reside in a approximately 6.5 kb plasmid fragment. The remaining isolate that was not an ESBL producer possessed an AmpC beta-lactamase gene (blaCMY-2) on a approximately 93 kb transmissible plasmid. This plasmid did not contain any other antimicrobial resistance genes. Additional plasmid-mediated beta-lactamases identified in some isolates included bla(TEM) and blaOXA-10. This is the first report of canine Enterobacter isolates containing transmissible plasmid-mediated blaSHV-12 and blaCMY-2 resistance genes. Therefore, Enterobacter isolated from opportunistic infections in dogs may be an important reservoir of plasmid-mediated resistance genes, which could potentially be spread to other members of the Enterobacteriaceae.

Community-Acquired Methicillin Resistant Staphylococcus aureus Skin Infection

Staphylococcus aureus is one of the most common pathogens in skin and soft tissue infections, as well as in potentially serious nosocomial infections in patients who acquire it when hospitalized. Penicillin was introduced in the 1940's as an effective treatment against S. aureus. However, shortly after penicillin's introduction, penicillin resistance to S. aureus emerged due to a plasmid-mediated beta-lactamase enzyme. In 1959, a semisynthetic penicillin, methicillin was introduced to overcome the resistance problem. However, within a year, bacteria resistant to methicillin and other penicillinase stable beta-lactams, were present. Worldwide emergence of methicillin-resistant S aureus (MRSA) was established by the 1980's. Since that time, MRSA has become widespread in hospitals and long-term care facilities around the world, accounting for numerous nosocomial infections. Recently, there has been an alarming increase in the incidence of community-acquired MRSA (CA-MRSA). Patients with CA-MRSA began to be reported in the early 1990's and its prevalence has continued to increase. This paper summarizes the current information known about CA-MRSA as it relates to skin infections including populations at risk, clinical presentation, and treatment options.

Cloning and sequencing of the gene encoding the AmpC beta-lactamase of Morganella morganii.

The chromosomal beta-lactamase gene of a clinical isolate of Morganella morganii was cloned in Escherichia coli and sequenced. The beta-lactamase had a pI of 7.4 and conferred a typical AmpC susceptibility pattern. The insert obtained was found to encode a protein of 379 amino acids. Its deduced amino acid sequence revealed it to be a class C beta-lactamase: 39-56% identity with chromosomal AmpC beta-lactamases of Serratia marcescens, Yersinia enterocolitica, Citrobacter freundii, Enterobacter cloacae and Escherichia coli; and 37-56% identity with plasmid-mediated beta-lactamases (MOX-1, CMY-1, FOX-1, ACT-1, LAT-1, BIL-1 and CMY-2). The ampC gene was linked to a gene only part of which (450 bp) was cloned homologous to the regulatory ampR genes of chromosomal class C beta-lactamases.

A plasmid-mediated CMY-2 beta-lactamase from an Algerian clinical isolate of Salmonella senftenberg.

Multiresistance to antibiotics including beta-lactams, e.g. cefoxitin, was transferred by conjugation to Escherichia coli strain C1a from a clinical isolate of Salmonella senftenberg recovered from stools of an Algerian child. The susceptibility pattern to beta-lactams was similar to the profile mediated by an AmpC-type beta-lactamase. By biochemical analysis, typical AmpC-type enzyme substrate and inhibition profiles were obtained. Finally, an ampC plasmid-encoded beta-lactamase gene was cloned and sequenced. Its deduced amino acid sequence confirmed its identity as a class C beta-lactamase. It showed 99.5% sequence identity with the plasmid-mediated beta-lactamase CMY-2. The differences in the amino acid sequences of the two enzymes were located in the signal peptide.

Pharmacology Review

Cefepime is the only fourth-generation cephalosporin licensed for use in the United States. It is being used increasingly for treatment of infections caused by resistant gram-negative bacteria in older infants and children. Some hospitals have replaced antipseudomonal third-generation cephalosporin antibiotics (eg, ceftazidime) with cefepime because of high rates of infection caused by resistant gram-negative bacteria. Although cefepime generally is not used to treat infections in neonates, it is important for neonatologists to be familiar with the characteristics of the drug because there are a few circumstances in which cefepime may be appropriate therapy for an older infant hospitalized in a neonatal intensive care unit. It is important to understand the unique differences of the drug compared with older cephalosporins. The cephalosporin antibiotics are derivatives of cephalosporin C, a natural antibiotic derived from the fungus Emericellopsis minimum . Cephalosporins have a beta-lactam ring as their major structural component, and their spectrum of activity varies, depending on substitutions at the 3 and 7 positions of the cephalosporin nucleus. Traditionally, these antibiotics are grouped by their spectrum of activity against antimicrobial organisms (Table 1). First-generation cephalosporins are active against most gram-positive bacteria (except enterococci and Listeria ) and have limited activity against some gram-negative organisms. Second-generation cephalosporins have increased activity against gram-negative organisms. Cephamycins, which generally are classified with the second-generation cephalosporins, have enhanced activity against anaerobic bacteria. The third-generation cephalosporins have extended potency against gram-negative bacteria but are generally less active against susceptible staphylococci. Cefepime hydrochloride is a newer semisynthetic, broad-spectrum fourth-generation cephalosporin antibiotic. The other antibiotic in this class is cefpirome, which is not available for use in the United States. | | First Generation | Second Generation | Third Generation | Fourth Generation | |:----------:| ---------------- | ----------------- | ---------------- | ----------------- | | Oral | Cefadroxil | Cefaclor | Cefdinir | | | | Cephalexin | Cefprozil | Cefpodoxime | | | | Cephradine | Cefuroxime axetil | | | | | | Loracarbef | | | | Parenteral | Cefazolin | Cefamandole | Cefoperazone | Cefepime | | | Cephalothin | Cefuroxime | Cefotaxime | | | | Cephapirin | | Ceftizoxime | | | | | Cephamycins | Ceftriaxone | | | | | Cefotetan | Ceftazidime | | | | | Cefoxitin | | | Table 1. Generations of Cephalosporins Cefepime differs from the third-generation cephalosporins by having a quaternized N-methylpyrrolidine substitution at the C3 position of the cephem nucleus and an alkoxyimino group at the C7 position …