Kegg Pathway: beta-Lactam resistance

Biochemistry. 2009 Nov 17;
Schneider KD, Karpen ME, Bonomo RA, Leonard DA, Powers RA

The clinical efficacy of carbapenem antibiotics depends on their resistance to the hydrolytic action of beta-Lactamase enzymes. The structure of the class D beta-Lactamase OXA-1 as an acyl-complex with the carbapenem doripenem was determined to 1.4 A resolution. Unlike most class A and class C carbapenem complexes, the acyl carbonyl oxygen in OXA-1/doripenem is bound in the oxyanion hole. Interestingly, no water molecules were observed in the vicinity of the acyl linkage, providing an explanation for why carbapenems inhibit OXA-1. The side-chain amine of K70 remains fully carboxylated in the acyl structure, and the resulting carbamate group hydrogen bonds to the alcohol of the 6alpha-hydroxyethyl moiety of doripenem. The carboxylate attached to the beta-Lactam ring of doripenem is stabilized by a salt-bridge to K212 and a hydrogen bond with T213, in lieu of the interaction with an arginine side-chain found in most other beta-Lactamase/beta-Lactam complexes (eg. R244 in the class A member TEM-1). This novel set of interactions with the carboxylate results in a major shift of the carbapenem's pyrroline ring compared to the structure of the same ring in meropenem bound to OXA-13. Additionally, bond angles of the pyrroline ring suggest that after acylation, doripenem adopts the Delta1 tautomer. These findings provide important insights into the role that carbapenems may have in the inactivation process of class D beta-Lactamases.

Antimicrob Agents Chemother. 2009 Nov 16;
Henry X, Amoroso A, Coyette J, Joris B

Ceftobiprole is a new cephalosporin that exhibits a high affinity for the methicillin-resistant Staphylococcus aureus PBP2a. It was reported that ceftobiprole did not interact with a mutated form of the low-affinity Enterococcus faecium PBP5 (PBBP5fm) that when over-expressed confers a beta-Lactam resistance phenotype to the bacterium. Our results show that ceftobiprole binds to the unmutated PBP5fm to form a stable acyl-enzyme and that it is able to efficiently kill a penicillin-resistant Enterococcus faecium strain that has this protein.

Antimicrob Agents Chemother. 2009 Nov 16;
Tattevin P, Basuino L, Bauer D, Diep BA, Chambers HF

Beta lactam agents are the most active drugs for the treatment of streptococci and methicillin-susceptible Staphylococcus aureus endocarditis. However, methicillin-resistant S. aureus (MRSA) are resistant to all beta lactam agents licensed to date, and alternative treatments are limited. Ceftobiprole is a novel broad-spectrum cephalosporin that binds with high affinity to PBP 2a, the penicillin-binding protein that mediates methicillin resistance of staphylococci, and is active against MRSA. Ceftobiprole was compared to vancomycin, daptomycin, and linezolid, in a rabbit model of MRSA aortic valve endocarditis caused by the homogenously methicillin-resistant laboratory strain, COL. Residual organisms in vegetations were significantly fewer in ceftobiprole-treated rabbits than in any other treatment group (P < 0.05 for each comparison). In addition, the numbers of organisms in spleens and in kidneys were significantly lower in ceftobiprole-treated rabbits than in linezolid- and vancomycin-treated animals (P < 0.05 for each comparison). Anti-MRSA beta lactam agents such as ceftobiprole may represent a significant therapeutic advance over currently available agents for the treatment of MRSA endocarditis.

J Mol Biol. 2009 Nov 10;
Thomas VL, McReynolds AC, Shoichet BK

Preorganization of enzyme active sites for substrate recognition typically comes at a cost to the stability of the folded form of the protein; consequently, enzymes can be dramatically stabilized by substitutions that attenuate the size and preorganization "strain" of the active site. How this stability-activity tradeoff constrains enzyme evolution has remained less certain, and it is unclear whether one should expect major stability insults as enzymes mutate towards new activities or how these new activities manifest structurally. These questions are both germane and easy to study in beta-Lactamases, which are evolving on the timescale of years to confer resistance to an ever-broader spectrum of beta-Lactam antibiotics. To explore whether stability is a substantial constraint on this antibiotic resistance evolution, we investigated extended-spectrum mutants of class C beta-Lactamases, which had evolved new activity versus third-generation cephalosporins. Five mutant enzymes had between 100-fold and 200-fold increased activity against the antibiotic cefotaxime in enzyme assays, and the mutant enzymes all lost thermodynamic stability (from 1.7 kcal mol(-)(1) to 4.1 kcal mol(-)(1)), consistent with the function-stability hypothesis. Intriguingly, several of the substitutions were 10-20 A from the catalytic serine; the question on how they conferred extended-spectrum activity arose. Eight structures, including complexes with inhibitors and extended-spectrum antibiotics, were determined by X-ray crystallography. Distinct mechanisms of action, including changes in the flexibility and ground-state structures of the enzyme, are revealed for each mutant. These results explain the structural bases for the antibiotic resistance conferred by these substitutions and their corresponding decrease in protein stability, which will constrain the evolution of new antibiotic resistance.

Antimicrob Agents Chemother. 2009 Nov 2;
Bae S, Lee J, Lee J, Kim E, Lee S, Yu J, Kang Y

Antimicrobial susceptibility patterns and beta-Lactam resistance mechanisms of 544 H. influenzae isolates through the nationwide Acute Respiratory Infections Surveillance (ARIS) network in Korea during 2005 and 2006 were determined. resistance to ampicillin was 58.5%, followed by cefuroxime (23.3%), clarithromycin (18.7%), cefaclor (17.0%), amoxicillin/clavulanate (10.4%), and chloramphenicol (8.1%). Levofloxacin and cefotaxime were the most active agents tested in this study. beta-Lactamase production (52.4%) was the main mechanism of ampicillin resistance, with the rate (96.1%) of TEM-1 type beta-Lactamase. According to their beta-Lactam resistance mechanisms, all isolates were classified into the following groups: beta-Lactamase-negative, ampicillin-sensitive (BLNAS) strains (n= 224; 41.5%); beta-Lactamase-positive, ampicillin-resistant (BLPAR) strains (n = 255; 47.2%); beta-Lactamase-negative, ampicillin-resistant (BLNAR) strains (n = 33; 6.1%); and beta-Lactamase-positive, amoxicillin/clavulanate-resistant (BLPACR) strains (n = 28; 5.2%). Among the BLNAR and BLPACR strains, there were various patterns of multiple amino acid substitutions in penicillin binding protein 3. Particularly, among BLNAR, group III isolates, which had three simultaneous substitutions (Met377Ile, Ser385Thr, and Leu389Phe) were identified for the first time in Korea. Three group III strains displayed the highest minimum inhibitory concentration of cefotaxime (1-2 mug/ml). The results indicate the importance of monitoring a changing situation pertaining to the increase and spread of BLNAR and BLPACR strains of H. influenzae for appropriate antibiotic therapy for patients with RTIs in Korea.

Biochim Biophys Acta. 2009 Oct 31;
Nitanai Y, Shimamura T, Uchiyama T, Ishii Y, Takehira M, Yutani K, Matsuzawa H, Miyano M

The extended-spectrum beta-Lactamases are associated with antibiotic resistance. Toho-1 R274N/R276N, a Class A beta-Lactamase of CTX-M-type, efficiently hydrolyzes first generationcephalosporins (for example, cephalothin), in addition to cefotaxime, a third generation cephalosporin. However, this enzyme only marginally hydrolyzes the third generation cephalosporin ceftazidime, and the monobactam aztreonam. The deacylation defectiveness of the mutant Toho-1 E166A/R274N/R276N, which lacks the deacylation activity, results in the accumulation of the complex of an acylated-enzyme intermediate analog. For drug design, it would be useful if a quantitative prediction of a catalytic property were available without the need of enzymatic measurements. Therefore, we examined whether there is a correlation between the thermal stability of a catalytic intermediate (analog) and its kinetic parameters. First we measured the hydrolytic kinetics of the 14 species of beta-Lactam antibiotics by Toho-1 R274N/R276N, and also measured the thermal stability of the accumulated acyl-intermediates of Toho-1 E166A/R274N/R276 by differential scanning calorimetry. Here we report the correlation of these parameters. The logarithm of the catalytic efficiency for Toho-1 R274N/R276N, log(k(cat)/K(m)) exhibited the best linear correlation with T(m,) which is the heat-denaturation temperature midpoint of the corresponding acylated complex of Toho-1 E166A/R274N/R276N. The correlation coefficient was 0.947, indicating that a relationship exists between the kinetic parameters and the stability of the intermediates. The results demonstrate a new method for investigating the catalytic properties of enzymes against any substrates, and a new approach to designing enzymes.

Int J Artif Organs. 2009 Oct 31; 32(9): 630-634
Montanaro L, Baldassarri L, Corazzari T, Creti R, Ravaioli S, Cangini I, Pirini V, Maso A, Donati ME, Pegreffi F, Visai L, Campoccia D, Speziale P, Arciola CR

This report focuses on the molecular characterization of a Staphylococcus aureus strainisolated from a knee arthroprosthesis infection and recognized retrospectively as a carrier of the Panton-Valentine leukocidin gene. The stored microbiological isolate, which belonged to the strain collectionof the Research Unit on Implant Infections of the Rizzoli Orthopaedic Institute, was retrievedfor molecular analysis. Genotyping was carried out, revealing an interesting profile. In addition tothe positivity for the Panton-Valentine toxin gene, the results indicated that the isolate belonged tothe agr III group and was endowed with bbp and cna genes, both encoding for staphylococcal adhesinsthat bind bone proteins. The strain had the mecA gene for methicillin resistance, even thoughit was unable to resist any of the beta-Lactam or other antibiotics. Its gene configuration matched thatof other community-acquired methicillin-resistant and methicillin-susceptible Staphylococcus aureus(CA-MRSA and CA-MSSA) strains which have recently been reported worldwide. As far as we know,this is the first report on a PVL-positive S. aureus strain associated with an orthopedic implant (kneearthroprosthesis) infection.

Lancet. 2009 Oct 31; 374(9700): 1543-56
van der Poll T, Opal SM

Pneumococcus remains the most common cause of community-acquired pneumonia worldwide. Streptococcus pneumoniae is well adapted to people, and is a frequent inhabitant of the upper airways in healthy hosts. This seemingly innocuous state of colonisation is a dynamic and competitive process in which the pathogen attempts to engage the host, proliferate, and invade the lower airways. The host in turn continuously deploys an array of innate and acquired cellular and humoral defences to prevent pneumococci from breaching tissue barriers. Discoveries into essential molecular mechanisms used by pneumococci to evade host-sensing systems that are designed to contain the pathogen provide new insights into potential treatment options. Versatility of the genome of pneumococci and the bacteria's polygenic virulence capabilities show that a multifaceted approach with many vaccine antigens, antibiotic combinations, and immunoadjuvant therapies will be needed to control this microbe.

J Am Vet Med Assoc. 2009 Nov 1; 235(9): 1064-6
Weese JS, Faires M, Brisson BA, Slavic D

CASE DESCRIPTION: A 2-year-old dog was evaluated because of complications that developed following tibial plateau leveling osteotomy. Infection of the surgical site developed following removal of the failed implant. CLINICAL FINDINGS: The dog was lame with evidence of a deep surgical site infection, and Staphylococcus pseudintermedius was isolated from the surgical site. Results of in vitro testing indicated that the isolate was resistant to multiple antimicrobials but susceptible to cefoxitin. Subsequent testing confirmed that the isolate was methicillin-resistant S pseudintermedius and was in fact resistant to cefoxitin. TREATMENT AND OUTCOME: On the basis of results of follow-up testing, doxycycline was administered before and after surgery to remove the surgical implant. The dog recovered without further complications. CLINICAL RELEVANCE: Findings suggested that certain strains of methicillin-resistant S pseudintermedius, which appears to be an emerging pathogen in dogs, may be falsely identified as methicillin susceptible on the basis of results of testing for cefoxitin susceptibility because cefoxitin may not induce the mecA gene as reliably in S pseudintermedius as it does in Staphylococcus aureus. Isolates of S pseudintermedius should be considered to likely be methicillin resistant when multidrug resistance is identified, even if susceptibility to some beta-Lactam antimicrobials is reported.

Pathol Biol (Paris). 2009 Oct 27;
Minchella A, Molinari L, Alonso S, Bouziges N, Sotto A, Lavigne JP

AIM OF STUDY: Monitor evolution of antibiotic resistance of Pseudomonas aeruginosa from 2002 to 2006 in our hospital to optimize antibiotherapy. PATIENTS AND METHOD: The infections/colonizations with P. aeruginosa have been identified by the hospital's informatic database. Bacteriological samples realized 48hours after patient's admission was considered as nosocomial. A Cochran-Armitage test was conducted to assess the evolution of resistance. RESULTS: During this period, 2098 infections/colonizations with P. aeruginosa have been identified. Bacteriological samples (68.5%) were nosocomial. Among the beta-Lactam antibiotics, ceftazidime and imipenem were the most active (R=16.8% and 15.2%, respectively), followed by piperacillin and piperacillin-tazobactam (R=24.8%, 18.4%, respectively). Amikacin and tobramycin were more active than gentamicin (R=19.9%; 22.2% and 40.6%, respectively). 28.9% of strains were resistant to ciprofloxacin. Nosocomial strains were significantly more resistant than non-hospital strains: ceftazidime: 17.9% versus 14.2%, p=0.0346; ticarcillin-clavulanic acid: 47.5% versus 39.6%, p=0.0009; piperacillin-tazobactam: 20.0% versus 14.8%, p=0.0046; ciprofloxacin: 30.7% versus 25.2%, p=0.0112. A significant increase in the resistance of nosocomial strains to ceftazidime, ticarcillin-clavulanic acid and piperacillin-tazobactam was noted. resistance from non-hospital strains to fluoroquinolones, aminoglycosides, ceftazidime, piperacillin and ticarcillin-clavulanic acid decreased significantly. CONCLUSION: P. aeruginosa is a predominantly nosocomial microorganism. There is a decrease of resistance for non-hospital strains. But the resistance of nosocomial strains to antibiotics widely prescribed in hospital is worrying.

Microb Drug Resist. 2009 Dec; 15(4): 317-21
Fernandes SA, Paterson DL, Ghilardi-Rodrigues AC, Adams-Haduch JM, Tavechio AT, Doi Y

Ten Salmonella enterica serovar Typhimurium isolates producing CTX-M-2 extended-spectrum beta-Lactamase were identified from clinical and poultry sources in two distant cities in Brazil between 2003 and 2004. They included two isolates from pediatric patients and eight isolates from poultry or its environment. All isolates exhibited coresistance to non-beta-Lactam antimicrobials including tetracycline and trimethoprim/sulfamethoxazole. The CTX-M-2 gene was located on transferable plasmids with sizes between 90 and 170 kb that also carried other resistance determinants in some isolates. By pulsed-field gel electrophoresis, the genetic similarity of the isolates including clinical and poultry ones ranged from 89% to 100%.

Microb Drug Resist. 2009 Dec; 15(4): 279-86
Ktari S, Arlet G, Verdet C, Jaoua S, Kachrid A, Ben Redjeb S, Mahjoubi-Rhimi F, Hammami A

Eighty-four isolates of Salmonella enterica serovar Livingstone were collected from patients hospitalized in a pediatric ward in Sfax Hospital (South Tunisia). These isolates were responsible for two nosocomial outbreaks in 2000 and 2002. Twenty-eight clinical isolates of S. enterica serovar Livingstone were also obtained in two other Tunisian hospitals in Monastir (Central Tunisia) and Tunis (North Tunisia), respectively, in 2002 and 2003. Pulsed-field gel electrophoresis yielded that these isolates were closely related. Antimicrobial susceptibility testing showed a particular beta-Lactam resistance phenotype, suggestive of the presence of an AmpC-type enzyme in 111 of the 112 clinical isolates. bla(ACC-1) was characterized by polymerase chain reaction (PCR) and sequence analysis in the 111 isolates. TEM-1 was characterized in all strains and SHV-2a in only two strains. The genetic organization of bla(ACC-1) was determined by PCR mapping and sequencing. The plasmid-borne bla(ACC-1) gene mapped immediately downstream from ISEcp1. This ISEcp1 insertion sequence was itself disrupted by IS26 insertion sequences. A supplementary deletion of 13 bp was observed in ISEcp1 upstream IS26, in all isolates from Tunis, except one. PCR analysis and sequencing also revealed the presence of tnpR, bla(SCO-1), gdha, IS1353, and TniB Delta 1.

J Infect Chemother. 2009 Oct; 15(5): 274-8
Yamaguchi Y, Hanaki H, Yanagisawa C, Ikeda-Dantsuji Y, Hashimoto T, Yazaki H, Sugahara K, Yanagisawa T, Kawajiri H, Sato S, Ishizaki A, Tachihara-Sato R, Takahashi Y, Ono T, Kageyama Y, Kawaguchi T, Tamura A, Hagane K, Sunakawa K

It was reported that some methicillin-resistant Staphylococcus aureus (MRSA) show resistance to vancomycin (VCM) and beta-Lactam antibiotics; thus, they are termed beta-Lactam antibiotic-induced VCM-resistant MRSA (BIVR). The VCM resistance of MRSA is induced by the administration of beta-Lactam antibiotics, but this phenomenon can be difficult to detect in the clinical laboratory. We detected the BIVR strain in a 64-year-old man who had had a ventilator tube inserted directly into the windpipe during long-term VCM therapy. The patient was diagnosed with MRSA pneumonia and septicemia on July 5, 2007, and sulbactam/ampicillin (SBT/ABPC) was administered for 5 days. However, the fever recurred, and administration of VCM was resumed for 7 days from July 19. Fever developed again, and VCM was administered again for 14 days from September 30. BIVR and VCM-low-sensitive MRSA were isolated from blood on October 18 and 22, although the VCM trough concentration was 10.2 microg/ml. On October 27, we changed to a combination of fosfomycin (FOM) and arbekacin (ABK), and thereafter the fever quickly decreased and the clinical symptoms abated. We isolated five MRSA strains from the blood of the patient, three strains of VCM-sensitive MRSA, one strain of BIVR, and one strain of a VCM-low-sensitive MRSA. The DNA band patterns determined by pulsed-field gel electrophoresis were completely identical except for the VCM-low-sensitive MRSA, which was missing one band. Furthermore, the VCM-low-sensitive MRSA became sensitive to beta-Lactam antibiotics. Our results indicate the possibility that long-term VCM therapy is one of the factors that allow BIVR or VCM-low-sensitive MRSA to emerge, and this allows VCM therapy for MRSA to fail.

Appl Environ Microbiol. 2009 Oct 23;
Zhao S, Blickenstaff K, Glenn A, Ayers SL, Friedman SL, Abbott JW, McDermott PF

Ampicillin-resistant (AMP(R)) Salmonella (n=344) representing 32 serotypes isolated from retail meats from 2002-2006 were tested for susceptibility to 21 other antimicrobial agents, and screened for the presence of five beta-Lactamase gene families (blaCMY, blaTEM, blaSHV, blaOXA, blaCTX-M) and class 1 integrons. Among the AMP(R) isolates, 66.9% were resistant to >/=5 antimicrobials and 4.9% to >/= 10 antimicrobials. Co-resistance to other beta-Lactams was noted for amoxicillin/clavulanic acid (55.5%), ceftiofur (50%), cefoxitin (50%), and ceftazidime (24.7%), whereas less than 5% of isolates were resistant to piperacillin/tazobactam (4.9%), cefotaxime (3.5%), ceftriaxone (2%), and aztreonam (1.2%). All isolates were susceptible to cefepime, imipemen and cefquinome. No Salmonella producing extended-spectrum beta-Lactamases (ESBL) was found in this study. Approximately 7% of the isolates displayed a typical MDR-AmpC phenotype, resistance to ampicillin, chloramphenicol, streptomycin, sulfonamide, tetracycline (ACSSuT), plus resistance to amoxicillin/clavulanic acid, cefoxitin, and ceftiofur with decreased susceptibility to ceftriaxone (MIC >/=4ug/ml). PFGE results showed that several MDR clones were geographically dispersed in different types of meats throughout the five sampling years. Additionally, 50% of the isolates contained blaCMY, 47% carried blaTEM-1 and 2.6% carried both genes. Only 15% of the isolates contained class I integrons carrying various combinations of aadA, aadB and dfrA gene cassettes. The blaCMY, blaTEM and class 1 integrons were transferable through conjugation and/or transformation. Our findings indicate a varied spectrum of co-resistance traits is present in AMP(R) Salmonella in the U.S. meat supply, with a continued predominance of blaCMYand blaTEM genes in beta-Lactam resistant isolates.

J Bacteriol. 2009 Oct 23;
Navratna V, Nadig S, Sood V, Prasad K, Arakere G, Gopal B

Penicillin binding proteins (PBPs) are membrane-associated proteins that catalyze the final step of murein biosynthesis. These proteins function either as transpeptidases or carboxypeptidases and in a few cases demonstrate transglycosylase activity. Both transpeptidase and carboxypeptidase activities of PBPs occur at the D-ala-D-ala terminus of a murein precursor containing the disaccharide pentapeptides N-acetylglucosamine and N-acetyl-muramicacid-L-ala-D-glu-L-lys-D-ala-D-ala. beta-Lactam antibiotics inhibit these enzymes by competing with the pentapeptide precursor for binding to the active site of the enzyme. Here we describe the crystal structure, biochemical characteristics and the expression profile of PBP4, a Low Molecular Mass (LMM) PBP from Staphylococcus aureus strain COL. The crystal structures of PBP4-antibiotic complexes reported here were determined by Molecular Replacement using the atomic coordinates deposited by the New York Structural Genomics consortium. While the pbp4 gene is not essential for the viability of S. aureus, the knockout phenotype of this gene is characterized by a marked reduction in cross-linked muropeptide and increased vancomycin resistance. Unlike other PBPs, we note that expression of PBP4 is not substantially altered in different experimental conditions nor does it change across representative hospital or community associated strains of S. aureus that were examined. In vitro data on purified recombinant S. aureus PBP4 suggests that it is a beta lactamase and is not trapped as an acyl intermediate with beta-Lactam antibiotics. Put together, the expression analysis and biochemical features of PBP4 provide a framework to understand the function of this protein in S. aureus and its role in antimicrobial resistance.

Pathol Biol (Paris). 2009 Oct 23;
Cuzon G, Naas T, Nordmann P

Emergence and dissemination of carbapenem resistance in the world represent a significant threat for management of hospital-acquired infections. From the early 2000s, Enterobacteriaceae that produce Klebsiella pneumoniae carbapenemases (KPC) have initially been reported from the USA and now worldwide, becoming the most important carbapenemase. These KPC producing-bacteria are mostly involved in nosocomial and systemic infections. They are mostly Enterobacteriaceae and more rarely Pseudomonas aeruginosa. KPC beta-Lactamases confer decreased susceptibility or resistance to virtually all beta-Lactams. Therefore, carbapenems (imipenem, meropenem, ertapenem) may become inefficient for treating enterobacterial infections with KPC-producing bacteria, which are in addition resistant to many other non beta-Lactam molecules, leaving only few available therapeutic options. Detection of KPC-producing bacteria may be difficult based on routine antibiotic susceptibility testing. Several phenotypic tests have been proposed, but until now, only molecular methods are reliable techniques for their identification. It is therefore critical to implement efficient infection control measures to detect patients who are colonized or infected with these pathogens in order to limit their spread.

New Microbiol. 2009 Jul; 32(3): 311-4
Corrente M, D'Abramo M, Latronico F, Greco MF, Bellacicco AL, Greco G, Martella V, Buonavoglia D

A methicillin-resistant (MR) Staphylococcus epidermidis strain was isolated from a saddle horse affected by osteolysis. MR coagulase-negative staphylococci (MRCNS) were isolated from 11 of 14 (78.8%) horses housed in the same riding club. By typing of the SCCmec region, almost the strains displayed a non typeable (NT) pattern and possessed the ccr type 2. Altogether, the high prevalence of MRCNS and the detection of NT SCCmec types support the hypothesis that horses may represent a reservoir of MRCNS for humans and that equine MRCNS may act as potential source of resistance genes for other staphylococci.

Diagn Microbiol Infect Dis. 2009 Nov; 65(3): 331-4
Jones RN, Stilwell MG, Rhomberg PR, Sader HS

We evaluated the susceptibility rates for piperacillin/tazobactam tested against Pseudomonas aeruginosa isolates from the Asia-Pacific (APAC), Europe (EU), Latin America (LA), and North America (NA) for 1997 to 2007. A total of 25 460 isolates were tested originating from APAC (4441), EU (7695), LA (4277), and NA (9047). All testing was performed by reference broth microdilution methods. The samples were collected from >110 medical centers and samples averaging >30 nations/year. For this analysis, results from 1997 to 2007, 1997 to 1999, 2005 to 2007, APAC, EU, LA, and NA were assessed against several broad-spectrum beta-Lactams, including cefepime, ceftazidime, imipenem, meropenem, and piperacillin alone, for a total of 12 agents overall. Using P. aeruginosa breakpoints (< or =64 microg/mL), piperacillin/tazobactam had the broadest coverage (% susceptible) in 2 regions (EU, LA) and, overall, at 83.6% followed by meropenem (83.0%) > imipenem (79.7%) > piperacillin (79.5%) > cefepime (77.5%) > ceftazidime (75.8%). Other non-beta-Lactam activity results were ciprofloxacin at only 71.5% susceptible, but tobramycin and polymyxin B had higher susceptibility rates (81.0% and 99.5%, respectively). Trends toward piperacillin/tazobactam resistance were noted between 1997 to 1999 and 2000 to 2007 in APAC (-11.6% susceptibility), NA (-4.0%), and EU (-2.3%). LA susceptibility rates were lowest overall but actually increased recently by +2.9% (current rate, 79.4% susceptible). For beta-Lactamase inhibitor combinations, susceptibility rates were higher for piperacillin/tazobactam when compared in all regions with piperacillin alone (+2.6-7.1%) and greatest for LA isolates. In contrast, ticarcillin/clavulanate susceptibility rates were lower than ticarcillin tested alone in NA (-1.5%, antagonism), and this agent only inhibited 70.3% of isolates worldwide. In conclusion, piperacillin/tazobactam remained a very active beta-Lactam when tested in vitro against clinical isolates of P. aeruginosa found in the SENTRY Program (1997-2007). Trends toward slightly decreased susceptibility were noted in all regions over the last decade (except LA); only polymyxins had susceptibility rates at >90%. resistance surveillance programs should be sustained to document emerging resistance patterns of old and newer agents for difficult-to-treat pathogens such as P. aeruginosa.

J Infect Dis. 2009 Nov 15; 200(10): 1566-73
Galloway-Peña JR, Nallapareddy SR, Arias CA, Eliopoulos GM, Murray BE

BACKGROUND: The Enterococcus faecium genogroup, referred to as clonal complex 17 (CC17), seems to possess multiple determinants that increase its ability to survive and cause disease in nosocomial environments. METHODS: Using 53 clinical and geographically diverse US E. faecium isolates dating from 1971 to 1994, we determined the multilocus sequence type; the presence of 16 putative virulence genes (hyl(Efm), esp(Efm), and fms genes); resistance to ampicillin (AMP) and vancomycin (VAN); and high-level resistance to gentamicin and streptomycin. RESULTS: Overall, 16 different sequence types (STs), mostly CC17 isolates, were identified in 9 different regions of the United States. The earliest CC17 isolates were part of an outbreak that occurred in 1982 in Richmond, Virginia. The characteristics of CC17 isolates included increases in resistance to AMP, the presence of hyl(Efm) and esp(Efm), emergence of resistance to VAN, and the presence of at least 13 of 14 fms genes. Eight of 41 of the early isolates with resistance to AMP, however, were not in CC17. CONCLUSIONS: Although not all early US AMP isolates were clonally related, E. faecium CC17 isolates have been circulating in the United States since at least 1982 and appear to have progressively acquired additional virulence and antibiotic resistance determinants, perhaps explaining the recent success of this species in the hospital environment.

FEMS Microbiol Lett. 2009 Nov; 301(1): 50-6
Girlich D, Kolb A, Naas T, Nordmann P

The two chromosomally encoded beta-Lactamases, OXA-22 and OXA-60, from Ralstonia pickettii are inducible by beta-Lactam molecules. Disruption of RP3 abolished induction of both beta-Lactamases and the resistance to pH, osmolarity and survival in the stationary phase, suggesting that RP3 might be a global regulator. Interactions between RP3, OXA-22 and OXA-60 were investigated at a transcript and protein level using 5'-rapid amplification of cDNA ends experiments, real-time reverse transcription (RT)-PCR and footprinting assays. The rp3 gene was actively transcribed and the promoter sequences corresponded to a nontypical sigma(70)-type promoter. RT-PCR analysis showed that rp3 expression as well as that of the bla(OXA) genes was positively regulated: the level of transcripts of rp3, bla(OXA-22) and bla(OXA-60) genes were, respectively, increased 20-, 100- and 2000-fold upon imipenem induction. DNAse I footprinting showed that RP3 specifically bound to tandem repeats centered at positions -55.5 and -73.5 upstream from the bla(OXA-22) and bla(OXA-60) transcriptional start sites. Interestingly, the binding site at bla(OXA-60) overlapped the -35 region of the rp3 promoter, although the region essential for induction lies at the beginning of the orf-rp3. This result indicates that RP3 is most probably only one component of a novel regulatory system involved in the expression of beta-Lactamases in R. pickettii.