Effects of rifaximin on bacterial virulence mechanisms at supra- and sub-inhibitory concentrations

Rifaximin, a poorly absorbed rifamycin derivative, exhibited time-dependent bactericidal activity and at concentrations as low as 1/32 of the minimum inhibitory concentration (MIC) caused morphological alterations in both susceptible and resistant bacterial strains. Spontaneous rifaximin-resistant clones appeared with an incidence of 2.6 x 10(-7). The percentage of Escherichia coli cells cured of various plasmids ranged from: 4.5-70% (Flac), 0-18% (pBP507), 7.7-43.8% (plasmid carrying ESBL genes) and 22.4-41.6% (plasmid encoding toxin from ETEC mex264). 8.4-18.2 and <0.1-18% of Staphylococcus aureus cells were cured (plasmid-mediated penicillinase), 9.5-58.6% of Morganella morganii (ESBL), 10.6-47.1% Citrobacter freundii (ESBL), 2.3-38.7% of Proteus mirabilis (ESBL) and 14.3-66.6% of Klebsiella pneumoniae (ESBL). Rifaximin reduced plasmid transfer from donor to recipient strains by >99%. The MIC of ceftazidime was reduced (2-4 dilutions) in the presence of rifaximin (0.5 x MIC) in ESBL producing strains. Rifaximin lowered the viability and virulence of the bacteria even though they developed resistance to the compound. In conclusion, the present findings add new features to the microbiological characteristics of rifaximin and suggest that if in vivo pathogens are exposed to sub-MICs of the drug, not only are their physiological functions compromised, but gene virulence and antibiotic resistance are not fully expressed.     

The effect of sub-inhibitory concentrations of rifaximin on urease production and on other virulence factors expressed by Klebsiella pneumoniae,Proteus mirabilis,Pseudomonas aeruginosa and Staphylococcus aureus

Rifaximin, a topical derivative of rifampin, inhibited urease production and other virulence factors at sub-MIC concentrations in strains involved in hepatic encephalopathy and the expression of methicillin resistance in Staphylococcus aureus. In particular, urease production was affected in all Proteus mirabilis and Klebsiella pneumoniae strains as well as in all tested Pseudomonas aeruginosa isolates. Other exotoxins, synthesized by P. aeruginosa, such as protease, gelatinase, lipase, lecithinase and DNAse were also not metabolized in the presence of rifaximin. This antibiotic inhibited pigment production in both P. aeruginosa and Chromobacterium violaceum, a biosensor control strain. Lastly, rifaximin affected haemolysin production in S. aureus and was able to restore cefoxitin susceptibility when the strain was cultured in the presence of sub-MICs of the drug. The present findings confirm and extend previous observations about the beneficial effects of rifaximin for the treatment of gastrointestinal diseases, since in this anatomic site, it reaches a large array of concentrations which prevents enterobacteria from thriving and/or producing their major virulence factors.     

Antibiotic Susceptibility Patterns of Helicobacter pylori Strains Isolated from Northeastern Mexico

Abstract

There are reports of increased antibiotic resistance rates in Helicobacter pylori strains around the world. The aim of this study was to determine the susceptibility patterns in H. pylori strains isolated in Monterrey, Mexico. We studied 62 strains isolated from the same number of symptomatic adult patients. Metronidazole (Mtz), clarithromycin (Cla), amoxicillin (Amx) and tetracycline (Tet) were tested by the E-test method. We observed that 37.1% of the strains were resistant to Mtz (MIC ≥8 mg/L), and 8.1% to Cla (MIC ≥8 mg/L), but we did not observe resistance to Amx (MIC ≥2 mg/L) or Tet (MIC ≥4 mg/L). In northeastern Mexico, the percentage of resistant strains was similar to that observed in developed countries. These results confirm that it is necessary to evaluate the susceptibility patterns of H. pylori strains by geographic area.     

High Prevalence of Extended Spectrum Beta-Lactamase Production Among Klebsiella pneumoniae Strains Isolated at a University Hospital in Turkey

Abstract

β-lactam susceptibility and β-lactamase patterns of a random sample of 44 Klebsiella pneumoniae strains that had been isolated from nosocomial infections at Dokuz Eyliil University Hospital in Izmir, were investigated. All strains were amoxycillin resistant but in the presence of clavulanic acid 26 became sensitive. Similarly 39 of the strains were resistant to ceftazidime and cefo-taxime; clavulanic acid restored sensitivity to ceftazidime in 28 and to cefo-taxime in 25 of these resistant strains. Extended spectrum β-lactamase (ESBL) production was positive in 84% of the isolates as determined by the double disk synergy test. Isoelectric focusing revealed that each strain produced one to four β-lactamases, pI 7.6 enzymes being the most prevalent. Other enzymes with pIs of 8.4, 8.2, 5.4, 7.8 were also detected. Resistance to ceftazidime was transferred from 18 of the 44 isolates to the recipient Escherichia coli K-12 at 37°C. The transconjugants were examined for their plasmid content and the plasmids were characterized by their size and resistance profile. Fourteen different restriction pattern groups were identified with Eco R1. The results indicate a high prevalence of ESBL production in nosocomial K. pneumoniae isolates in Izmir and have major implications concerning the clinical use of later generation cephalosporins.     

Lincomycin Resistance in Methicillin-Resistant Staphylococcus aureus Strains of Hospital Origin

Summary

A total of 170 Staphylococcus aureus strains isolated during a one-year period at the University Hospital of Patras Medical School were examined for resistance to a battery of antimicrobial agents by disk diffusion and minimum inhibitory concentration (MIC) determination. Fifty-five isolates were lincomycin- and methicillin-resistant (LMRSA). In the group of 55 LMRSA isolates 13 were also resistant to vancomycin. All the LMRSA isolates were not typed by the international set and the experimental phages 88A and 25 at routine typing dilution (RTD), while 18 isolates were lysed by phages at 100XRTD and 1000XRTD. Reverse phage-typing and heat shock treatment of the LMRSA isolates had no effect on their typability. Plasmid profiles coupled with restriction endonuclease analysis of plasmid DNA established that the LMRSA isolates represent different strains. Membrane-protein profiles by polyacrylamide gel electrophoresis (PAGE) showed that LMRSA strains could belong to one group. This method proved useful and sensitive for characterization of LMRSA.     

In Vitro Activity of Cefpirome (HR 810) against Enterococci and Staphylococci

Summary

The inhibitory activity of cefpirome (HR 810), a new cephalosporin derivative for parenteral use, was tested by agar dilution methods against Enterococcus faecatis (100 strains), Staphylococcus aureus (40 strains) and coagulase-negative staphylococcal species (60 strains) in comparison with other beta-lac ta m antibiotics.

For E. faecalls, the cefpirome minimum inhibitory concentration (MIC) range was 2-128 μg/ml, with an MIC,, of 8 μg/ml, and an MIC₉₀, of 64 μg/ml. The optimal bactericidal activity against strains with MICs of ≤ 8 μg/ml occurred at 2-4 times the MIC, and the reduction in the initial inoculum was 99.9-99.7% after 24 h incubation at these concentrations.

Mec gene-negative staphylococci (both S. aureus and coagulase- negative species) had cefpirome MICs of 0.25-2 μg/ml (MIC₅₀ 0.5 μg/ml, MIC₉₀ 1 μg/ml). Mec gene-positive strains had MICs of 0.5-128 μg/ml (MIC₅₀ 2 μg/ml, MIC₉₀ 32 μg/ml). Strains with borderline resistance to oxacillin which did not harbor the mec gene and which were susceptible to cefpirome maintained their susceptibility even when high-density inocula were used and after several passages in media containing the antibiotic.

These studies present some potential advantages of cefpirome over other cephalosporins in the inhibitory activity against Gram-positive cocci.     

The In Vitro Activity of Trospectomycin against Anaerobic Bacteria

Abstract

The authors evaluated the activity of trospectomycin, a new aminocyclitol which is characterized by good antibacterial and broad spectrum activity, in comparison with clindamycin and ampicillin on a sample of recent isolates: Bacteroides fragilis (15 strains), Bacteroides urealyticus (5 strains), Bacteroides vulgatus (5 strains), Bacteroides spp. (15 strains), Prevotella melaninogenica (6 strains), Porphyromonas asaccha-rolytica (7 strains), Mobiluncus spp. (3 strains), Peptococcus niger (3 strains), Peptococcus variabilis (9 strains), Peptococcus spp (30 strains), Peptostreptococcus anaerobius (5 strains), Peptostreptococcus asaccharolyticus (3 strains), Peptostreptococcus spp. (25 strains) and Propioni-bacterium spp. (7 strains). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined for all strains by microtiter serial dilutions in Wilkins-Chalgren broth in an anaerobic chamber in an atmosphere of 10% H₂, 10% CO₂, 80% N₂. All the drugs tested exert their activity against Gram-positive and Gram-negative anaerobic isolates. In particular, trospectomycin is quite active against Gram-positive cocci (MIC 90 = 4 - 8 mg/l), Gram-negative rods (MIC 90 = 8 - 16 mg/l), Gram-positive rods (MIC 90 = 4 mg/l) and Mobiluncus spp. (MIC 90 = 0.5 mg/l).     

The First Steps Towards Fluoroquinolone Resistance in Hungarian Pneumococci

Abstract

The incidence of fluoroquinolone resistance among Hungarian routine laboratory Streptococcus pneumoniae isolates, collected in 2000-2002, in common with other European countries, was very low; only 5/304 strains (1.64%) were resistant to ciprofloxacin (MIC = 4 μg/ml), and the other fluoroquinolones showed full efficacy. However, we could identify the Lys-137-Asp amino acid change, caused by a point mutation in the QRDR of the parC gene, in five strains. Additionally, we observed a definite shift in the minimum inhibitory concentrations (MICs) of all fluoroquinolones towards higher values throughout the study period. These two findings, coupled with the increasing consumption figures of fluoroquinolones, suggest that pneumococcal resistance looks poised to develop in Hungary.     

Emerging Antimicrobial Resistances Among Proteus mirabilis in Europe: Report from the MYSTIC Program (1997-2001)

Abstract

Resistance patterns that are currently problematic in Europe can vary greatly within the same species over time, among various patient populations and among geographic regions on the same continent. The results from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program, which monitors carbapenem resistance rates in institutions using meropenem, were used to determine resistance differences among Proteus mirabilis. MIC results from 688 P. mirabilis strains were classified into 4 patient care groups: ICU (n=426), neutropenia patients (NP; n=145), general wards (n=97) and cystic fibrosis patients (CF; n=20). A total of 40 centers from 12 European countries have participated since 1997, divided into 3 geographic regions (East, North, South). All testing was performed by NCCLS reference methods and interpretive criteria, including screening of extended-spectrum β-lactamase (ESBL) phenotypes. Over the monitored interval the resistance rates varied for each agent without a clear trend toward a greater rate. Rank order of susceptibility was: meropenem (99%) > piperacillin/tazobactam (TAZ; 96%) > cefepime (95%) > ceftazidime (CAZ; 94%) > imipenem (IPM; 92%). Ciprofloxacin (CIP) was the least active agent tested (MIC₉₀, 4 μg/ml; 86% susceptible). Unexpectedly, 3.6% of P. mirabilis were imipenem-resistant (MIC, >16 μg/ml). Greater rates of resistance were found for strains from NP and CF patients, and from eastern or southern European sites, usually associated with epidemic clusters. Generally susceptible species such as P. mirabilis have recently emerged as therapeutic problems in European medical centers following mutations that compromise CIP, CAZ and aminoglycoside use. Imipenem also showed decreased susceptibility of greater than 7% compared to less than 1% for meropenem. Continued surveillance by the MYSTIC Program appears to be a prudent practice to focus effective empiric treatment regimens.     

Antimicrobial Resistance of Streptococcus pneumoniae at a University Hospital in Saudi Arabia

Abstract

The resistance pattern of 105 consecutive strains of Streptococcus pneumoniae isolated from patients at King Abdulaziz University Hospital (KAUH), Jeddah, Saudi Arabia over a 2-year period (March 1998 to February 2000) was determined with the minimal inhibitory concentration (MIC) method using E-test. Overall 6.7% of the isolates were penicillin resistant (MICs >2 mg/L), and 51% were intermediate (MICs 0.12 - 1 mg/L). The resistance rates to ampicillin, cefotaxime, ceftriaxone, imipenem, erythromycin and clarithromycin were 8.6%, 8.6%, 4.7%, 3.8%, 13%, and 21% respectively. High-level resistance was noted against cotrimoxazole and chloramphenicol, 76% and 68% respectively. Only 2.8% of S. pneumoniae were resistant to amoxycillin-clavu-lanate; no resistance to vancomycin was observed. Against penicillin-intermediate pneumococcal strains, vancomycin, ceftriaxone, cefotaxime and amoxycillin-clavulanate were the most active compounds. Against penicillin-resistant pneu-mococci, vancomycin was the most powerful agent, amoxycillin-clavulanate was half as active, whereas ceftriaxone, cefotaxime and imipenem were 4-fold less active than vancomycin. Fifty-six (53%) of the 105 pneumococcal strains were multi-drug resistant.     

Antimicrobial Resistance and Prevalence of Extended Spectrum β-Lactamase Among Clinical Isolates of Gram-Negative Bacteria in Riyadh

Abstract

The activity of ciprofloxacin, imipenem and 12 other commonly used antibiotics was evaluated against 106 documented clinical isolates from a medical Intensive Care Unit (ICU). The resistance rates to ceftriaxone, cefotaxime, aztreonam and ceftazidime were 42, 25, 24 and 21%, respectively. Apart from Pseudomonas aeruginosa, all isolates were sensitive to ciprofloxacin and imipenem. Complete cross resistance among tested β-lactam groups was uniformly evident in Enterobacter cloacae, Citrobacter freundii and P. aeruginosa. On the other hand, penicillins and second generation cephalosporins showed cross resistance among Escherichia coli and Klebseilla pneumoniae isolates. Induction experiments indicate that 70 and 62% of P. aeruginosa and E. cloacae or C. freundii produce class I cephalosporinase, respectively.

Among all tested isolates, plasmid mediated extended spectrum β-lactamase (ESBL) was detected in one isolate of K. pneumoniae. The plasmid mediated β-lactamase is transferable and inhibited by β-lactamase inhibitors. The transconjugates not only expressed resistance to extended spectrum β-lactams and aztreon-am but also toward tested aminoglycoside antibiotics, with the exception of gentamicin. The obtained transconjugates conferred high level resistance to cef-tazidime and aztreonam but considerably low resistance to ceftriaxone and cefotaxime. The isoelectric point for the extended-spectrum β-lactamase is 8.2.     

Eight-year (2002-2009) Summary of the Linezolid (Zyvox® Annual Appraisal of potency and Spectrum; ZAAPS) Program in European Countries

Abstract

The linezolid surveillance network (ZAAPS program) has been monitoring linezolid activity and susceptibility rates for eight years (2002-2009) in European medical centers. Samples from 12-24 sites annually in 11 countries were monitored by a central laboratory design using reference MIC methods with international and regional interpretations (EUCAST). A total of 13,404 Gram-positive pathogens were tested from 6 pathogen groups. Linezolid remained without documented resistance from 2002 through 2005, but beginning in 2006 resistant strains emerged at very low rates among Staphylococcus aureus (G2576T mutant in ireland, 2007), coagulase-negative staphylococci (CoNS; usually Staphylococcus epidermidis, France and italy in 2006-2009) and enterococci (Enterococcus faecium in Germany [2006, 2008, 2009] and E. faecalis in Sweden [2008], United Kingdom [2008] and Germany [2009]); all but one strain having a target mutation. A mobile cfr was detected in an italian CoNS strain (2008 and 2009), and clonal spread was noted for linezolid-resistant strains (pfGe results). Overall the linezolid susceptibility rates were >99.9, 99.7 and 99.6% for S. aureus, CoNS and enterococci, respectively; and all streptococcal strains were susceptible (MIC₉₀, 1 mg/L). In conclusion, the ZAAPS program surveillance confirmed high, sustained levels of linezolid activity from 2002-2009 and without evidence of MIC creep or escalating resistance in Gram-positive pathogens across monitored European nations.     

Antimicrobial Spectrum and Potency of Dalbavancin Tested Against Clinical Isolates from Europe and North America (2003): Initial Results from an International Surveillance Protocol

Abstract

Dalbavancin is a bactericidal dimethylaminopropyl amide glycopeptide derivative possessing an extended serum elimination half-life in humans that allows onceweekly dosing for the therapy of Gram-positive infections. Strains from this baseline surveillance protocol in North America (NA; USA and Canada) and Europe (EU, 14 countries) were sampled in 2003. A total of 7,765 Gram-positive isolates (3,695 from NA and 4,070 from EU) were tested by reference broth microdilution methods against dalbavancin and 10 comparator agents. Species were analyzed separately by resistance phenotypes such as methicillin- (oxacillin-) resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) and penicillin- resistant Streptococcus pneumoniae. Dalbavancin and other glycopeptides were very active against staphylococci (n=4648) with dalbavancin being 16- to 32- fold more potent than vancomycin (MIC₉₀, 0.06 versus 2 mg/L). MRSA rates were greater (31.6%) in NA than in EU (26.1%). Quinupristin/dalfopristin resistance (MIC, ≥ 2 mg/L; 0.1 - 0.5%) was documented more often in EU compared to NA. Dalbavancin (MIC₅₀, 0.03 - 0.06 mg/L) was active against enterococci, except VanA resistance phenotypes. VRE rates were lower in EU (8.3%) then in NA (35.9%) from this resistance-enhanced enterococcal collection. Streptococci (dalbavancin MIC₉₀, 0.016 - 0.03 mg/L) were generally most susceptible to glycopeptides (100.0%), quinupristin/dalfopristin (98.6 - 100.0%) and linezolid (100.0%); but dalbavancin was 16-fold more active than comparators. All vancomycin-susceptible enterococci and > 90% of vanB VRE had dalbavancin MIC values at ≤ 1 mg/L, but vanA VRE strains had dalbavancin MIC results ranging from 0.06 to > 8 mg/L (median MIC, ≥ 8 mg/L). Dalbavancin MIC values were not adversely influenced by geographic region or resistance phenotype (except vanA VRE). Infrequently isolated Gram-positive organisms such as Bacillus spp. (MIC₉₀, 0.12 mg/L), Corynebacterium spp. (MIC₉₀, 0.12 mg/L), Listeria monocytogenes (MIC₉₀, 0.25 mg/L) and Micrococcus spp. (MIC₉₀, 0.03 mg/L) were very susceptible to dalbavancin. In conclusion, these 2003 baseline resistance surveillance findings confirm the potent dalbavancin activity compared to several comparator agents against important Gram-positive pathogens. This high volume international survey indicates potential therapeutic roles for dalbavancin against many troublesome resistant Gram-positive phenotypes.     

Comparison of teicoplanin and vancomycin in vitro activity on clinical isolates of Staphylococcus aureus

Abstract

Ninety-one clinical isolates of Staphylococcus aureus have been tested with the Kirby Bauer and the Etest® method to determine the susceptibility to glycopeptides in the 2007–2010 period. Five strains (5·5%) were resistant to vancomycin and nine (9·9%) to teicoplanin. Teicoplanin showed a median minimal inhibitory concentration (MIC) of 1 mg/l (range 0·125–24 mg/l), an MIC50 of 1 mg/l, and an MIC90 of 2 mg/l; vancomycin had a median MIC of 1·5 mg/l (range 0·38–4 mg/l), an MIC50 of 1·5 mg/l, and an MIC90 of 2 mg/l. More isolates were distributed on higher values of MIC for vancomycin. Inhibition halos induced by vancomycin-impregnated paper diskettes were slightly larger than those by teicoplanin. Glycopeptide resistance among methicillin-resistant Staphylococcus aureus in Italy is an underestimated phenomenon, possibly due to the described underestimation of glycopeptides MICs by the automatic broth microdilution method, when compared to agar MIC assays. A teicoplanin MIC creep, as reported for vancomycin, cannot be assumed.     

Kinetics of Antimicrobial Activity of Amoxicillin/Clavulanic Acid and Metronidazole against β-Lactamase-Producing Bacteroides fragilis Group

Summary

Bacteroides fragilis group are the most common anaerobic bacteria isolated in clinical specimens. The use of a beta-lactam with a β-lactamase inhibitor should result in a marked increase in the group's sensitivity to the β-lactams. Since the activity (MIC) shown by the amoxicillin + clavulanic acid combination against Bacteroides fragilis group is good, other parameters of in vitro activity have been studied. This study was also done with metronidazole. The minimum inhibitory concentration (MIC) was determined in 26 strains of Bacteroides fragilis group (14 B. fragilis; 5 B. thetaiotaomicron; 4 B. vulgatus; 3 B. distasonis). Likewise, the minimum bactericidal concentration (MBC), the killing curve, the sub-MIC and post-antibiotic effect were determined.

The MIC ranged between 0.5 and 32 mg/l. The MBC was two- to four-fold the MIC for amoxicillin/clavulanic acid, and one- to two-fold the MIC for metronidazole for most strains. The killing curve showed a continuous decrease, sloping most sharply between 0-2 hours and 6-8 hours. Amoxicillin + clavulanic acid showed a post-antibiotic effect between 2 and 4 hours. The inhibitory minimum antibiotic concentration was one-half the MIC for most strains.     

Cefaclor: A Contemporary Look at Susceptibility of Key Pathogens from Around the Globe

Abstract

The orally administered cephalosporin antibiotic, cefaclor, has been available for clinical use in many countries since 1979. Because widespread antibiotic use is often cited as a factor in the emergence of bacterial resistance to antibiotics, we sought to determine the degrees of resistance to cefaclor expressed by key pathogens recently isolated in 10 countries widely distributed around the world. Using the E-test ®, minimal inhibitory concentrations (MIC) were determined for cefaclor and several comparator antibiotics against approximately 700 fresh clinical isolates of each of six bacterial species. The results demonstrated that > 90% of Haemophilus influenzae (β-lactamase producing and non-producing), Haemophilus parainfluenzae (β-lactamase producing and non-producing), Moraxella catarrhalis (> 90% β-lactamase producing), and methicillin-susceptible Staphylococcus aureus, and 85% of Escherichia coli were susceptible to cefaclor at the NCCLS interpretive breakpoints. MIC distributions showed that there has been no change in the activity of cefaclor against penicillin-susceptible strains of Streptococcus pneumoniae since 1977.     

In Vitro Activity of Lomefloxacin (SC-47111) Against Enterobacteriaceae,Enterococci and Staphylococci

Summary

The activity of lomefloxacin, a new difluorinated quinolone, was tested against 190 Enterobacteriaceae strains (belonging to 23 different species), 70 enterococci and 70 staphylococci. As regards Enterobacteriaceae, the activity of lomefloxacin was the same as that of norfloxacin in 9 out of the 23 species tested, and only slightly lower in further 8 species. Minimum inhibitory concentrations (MIC) values for 90% of strains were 0.5 μg/ml in 2 species, 0.25 μg/ml in 6, 0.125 μg/ml in 4, and lower than 0.125 μg/ml in 8. Slightly higher values were obtained for Serratia marcescens (2 μg/ml), whilst, as already reported for the other new quinolones, the susceptibility of the Providencia genus was very poor, with MIC values up to 128 μg/ml for the vast majority of strains. Lomefloxacin proved bactericidal at the MIC in all the Enterobacteriaceae strains tested but 20. In the latter strains, however, bactericidal activity could be appreciated at values slightly exceeding MIC. As regards enterococci, the MIC for 90% of strains was 32 μg/ml. Minimum bactericidal concentration (MBC) was the same as the MIC for 78% of the strains tested and was only twofold higher in all the others. The new drug was also active against staphylococci having an MIC50 and MIC₉₀ of 0.5 and 2 μg/ml, respectively. It was bactericidal at the MIC for 62% of the strains and at twofold the MIC for all the others.     

Retrospective Study of an Outbreak in a Kuwaiti Hospital of Multidrug-Resistant Klebsiella pneumoniae Possessing the New SHV-112 extended-Spectrum Beta-Lactamase

Abstract

Patients infected with bacteria producing extendedspectrum beta-lactamases (ESBL) are at higher risk of mortality and morbidity. Several mutations in genes encoding SHV, tem and CTX-m beta-lactamases have been associated with ESBL activity. This paper describes a new SHV mutation in ESBL-producing strains of Klebsiella pneumoniae isolated in Kuwait. The study included 13 K. penumoniae strains isolated from patients admitted to the Amiri hospital of Kuwait. The production of ESBL in all strains was confirmed by Vitek system and e-test. All the ESBL genes were amplified by PCR and examined by DNA sequencing. All these ESBL-positive isolates were resistant to ceftazidime and cefotaxime. DNA sequencing revealed an A815G point mutation in the bla _SHV gene causing an asparagine (AAT) to aspartic acid (GAT) mutation at position 253 of the enzyme. This new mutation was assigned the unique number SHV-112, and the Genebank accession number EU477409. This study reports a new mutation in the SHV gene in K. pneumoniae with ESBL capability. There could be other mutations still to be found in ESBL genes of K. pneumoniae in Kuwait and probably in other middle eastern countries, and researchers in the region should make use of molecular techniques to look for more novel mutations in ESBL-producing strains of K. pneumoniae.     

Comparative In- Vitro Activity of Fourteen Antibiotics Against Clinical Isolates of Enterococci

Summary

The in-vitto antibacterial activities of fourteen antimicrobial agents, including ampicillin, amikacin, Augmentin, ceftazidime, cefotaxime, ceftriaxone, ciprofloxacin, erythromycin, gentamicin, penicillin G, piperacillin, rifampicin, streptomycin and vancomycin, were compared against 195 enterococcal strains isolated from clinical specimens received at the King Abdulaziz University Hospital in Saudi Arabia. The antibacterial susceptibility was determined by the minimal inhibitory concentration (MIC) using an agar dilution method. Ampicillin, Augmentin and vancomycin exhibited the greatest activity, inhibiting 90% of the tested strains (MIC90) at 2 μg/ml, followed by penicillin G and piperacillin with MIC90 of 4 μg/ml. Erythromycin, third generation cephalosporins, aminoglycosides and rifampicin, on the other hand, had poor activity against enterococci with MIC90s well above the obtainable serum concentrations. The clinical implications of resistance to aminoglycosides and the alternative antimicrobial therapy in serious entrococcal infections are discussed in the text.     

Extended-Spectrum β-lactamase-Producing Escherichia coli Isolated in the Al-Amiri Hospital in 2003 and Compared with Isolates from the Farwania Hospital Outbreak in 1994-96 in Kuwait

Abstract

Extended-spectrum -lactamases (ESBLs) are a major problem in Kuwait and an accurate method for their detection is essential. This study was designed to evaluate the efficacy of the commercial system (Vitek 2) to identify ESBLs in clinical isolates of Escherichia coli and relate this to their identification by agar dilution methods for use in a diagnostic laboratory. The presence of the major ESBLs parental enzyme groups was confirmed by PCR and the similarity of the strains was determined by pulsed field gel electrophoresis (PFGE) on DNA, cleaved using XbaI endonuclease, to identify clonal spread.

Seventy-one separate E. coli isolates from 65 patients were tested. Sixty-two isolates were from 56 patients from the Al-Amiri Hospital and nine isolates from neonates from Farwania Hospital. The isolates were screened for ESBL activity by the Vitek 2 system. Isolates showing positive results were further tested with Etest ESBL strips and by the disc approximation methods. All the isolates were flagged as ESBL-positive by the Vitek 2 advanced expert system (AES). Isolates from all the 65 patients were detected as ESBL positive by the Etest, only if both ESBL strips were used. The double disc approximation test using five different antibiotics could detect ESBL presence in isolates from only 46 patients. In this test, the synergy with cefepime was the most sensitive in ESBL detection, showing their presence in 41 isolates. PCR with primers for bla _TEM and bla _SHV demonstrated that one or both of these enzymes in all isolates. PFGE revealed that many different clones were present amongst the isolates.

The epidemiology of ESBL E. coli in Kuwait is complex. Many distinct strains are already present in the population, as shown by the results of PFGE. Several testing methods may be required to detect all strains harboring ESBLs.