Antibiotic resistance: effect of different criteria for classifying isolates as duplicates on apparent resistance frequencies. (65/765)

OBJECTIVE: To investigate the effect of screening specimens and different criteria for exclusion of duplicate isolates when surveillance of antimicrobial resistances is performed. MATERIALS AND METHODS: Trends in resistance were analysed for recent isolates of selected organisms from Guy's and St Thomas' Hospitals with the use of various criteria for the exclusion of duplicates, including time since the last isolate and antibiogram pattern, and the effect of excluding screening specimens. RESULTS: There was a significant difference of about 8% in the apparent frequency of methicillin resistance in Staphylococcus aureus in inpatients if the time limit for duplicates was set at 5 rather than 30 days; it was about 10% if a 5 day limit was compared with a 365 day limit. There was also a significant difference, of 6-10%, in apparent resistance frequencies if isolates from screening specimens were excluded. Apparent gentamicin resistance rates in Klebsiella spp. varied between 11% and 28%, and the number of apparent patient isolates of gentamicinresistant organisms varied by up to 35%, depending on the duplicate exclusion criteria chosen. Effects were smaller, though still significant, for vancomycin resistance in Enterococcus spp. There was little effect for amoxicillin or cefuroxime resistance in Escherichia coli isolates from general practitioners, where the proportion of duplicates was small. CONCLUSION: Improved surveillance of antibiotic resistance is needed. However, care needs to be taken in setting the criteria for classifying isolates as duplicates and in comparing results where these criteria may be different or unknown.  (+info)

Induction of 4-hydroxycinnamate decarboxylase in Klebsiella oxytoca cells exposed to substrates and non-substrate 4-hydroxycinnamate analogs. (66/765)

The 4-hydroxycinnamate decarboxylase (4-HCD)-inducing activity of several substrate analogs toward Klebsiella oxytoca was investigated. Four E-cinnamate-class compounds, E-4-hydroxycinnamic acid (1), caffeic acid (2), ferulic acid (3) and E-2,4-dihydroxycinnamic acid (4), all of which were accepted as substrates, all of which were accepted as substrates of 4-HCD, enable K. oxytoca cells to induce the decarboxylase at a 2.0 mM concentration, while five non-substrate compounds of the E-cinnamate class so far tested were completely inactive. However, 6-hydroxy-2-naphthoic acid (11) and 7-hydroxycoumarin 3-carboxylic acid (14), both of which are non-cinnamate-class analogs of the substrate, acted as strong 4-HCD inducers, even at a 0.5 mM concentration. The 4-HCD-inducing activities of compounds 11 and 14 at 0.5 mM were 10-12-fold higher than that of substrate 1. Compound 11 maintained its 4-HCD-inducing activity toward cultured cells through the late-log and stationary phases, unlike 1 that induced 4-HCD only in the early log phase. SDS-PAGE electrophoresis of protein mixtures from the cultured cells exposed to any 4-HCD inducer indicated that the 21.5 kDa protein was always present.  (+info)

Comparative bactericidal activities of beta-lactam antibiotics determined in agar and broth media. (67/765)

Comparative bactericidal activities were determined utilizing a relatively large number of test strains, in both agar and broth media, with special reference to the time of exposure of the bacteria to certain beta-lactam antibiotics. It was apparent that the activities increase with time. The concentrations producing a 99.9% kill with cephalothin for Escherichia coli, Klebsiella sp., and carbenicillin for Pseudomonas aeruginosa were higher in broth than in agar. In contrast, those of benzylpenicillin for alpha-streptococcus (non-enterococcal) were higher in agar than in broth. If the bactericidal concentrations with 3-hour or 6-hour exposure to antibiotics were used as the criterion, these concentrations of carbenicillin for P. aeruginosa, and benzylpenicillin for alpha-streptococcus were, in particular, unusually high compared with the conventionally determined bacteriostatic concentrations (MICs).  (+info)

Relationship of indole production and antibiotic susceptibility in the Klebsiella bacillus. (68/765)

Of 2,442 Klebsiella strains isolated from clinical specimens at the University of Minnesota hospitals, 18.3% were found to be indole positive. A randomly selected equal number of indole-positive and indole-negative control isolates, characterized by 27 biochemical tests and by serotyping against 72 antisera, were tested against 14 antibiotics. The results indicated a greater incidence of multiple drug resistance among the indole-negative strains among those that produced indole. The organisms in the former group, in comparison to their indole-positive counterparts, were significantly more resistant to nitrofurantoin, tetracycline, chloramphenicol, neomycin, streptomycin, nalidixic acid, and kanamycin. Both groups of organisms were similar in their degree of resistance to ampicillin, carbenicillin, cephalothin, sulfisoxazole, colistimethate, polymyxin B, and gentamicin. The biochemical properties of the two indole groups were essentially identical. Correlation between serotype and multidrug resistance was inapparent.  (+info)

Isomaltulose synthase from Klebsiella sp. strain LX3: gene cloning and characterization and engineering of thermostability. (69/765)

The gene (palI) encoding isomaltulose synthase (PalI) from a soil bacterial isolate, Klebsiella sp. strain LX3, was cloned and characterized. PalI converts sucrose into isomaltulose, trehalulose, and trace amounts of glucose and fructose. Sequence domain analysis showed that PalI contains an alpha-amylase domain and (beta/alpha)(8)-barrel structures, suggesting that it belongs to the alpha-amylase family. Sequence alignment indicated that the five amino acid residues of catalytic importance in alpha-amylases and glucosyltransferases (Asp(241), Glu(295), Asp(369), His(145), and His(368)) are conserved in PalI. Purified recombinant PalI displayed high catalytic efficiency, with a Km of 54.6 +/- 1.7 mM for sucrose, and maximum activity (approximately 328.0 +/- 2.5 U/mg) at pH 6.0 and 35 degrees C. PalI activity was strongly inhibited by Fe3+ and Hg2+ and was enhanced by Mn2+ and Mg2+. The half-life of PalI was 1.8 min at 50 degrees C. Replacement of selected amino acid residues by proline significantly increased the thermostability of PalI. Simultaneous replacement of Glu(498) and Arg(310) with proline resulted in an 11-fold increase in the half-life of PalI at 50 degrees C.  (+info)

Beta-lactamases involved in resistance to broad-spectrum cephalosporins in Escherichia coli and Klebsiella spp. clinical isolates collected between 1994 and 1996, in Barcelona (Spain). (70/765)

The aim of this study was to evaluate the incidence of decreased susceptibility to broad-spectrum cephalosporins in Enterobacteriaceae that lack inducible chromosomal bla genes, and to determine the enzymes responsible for resistance. From all clinically relevant Enterobacteriaceae strains isolated between 1994 and 1996, 88 of 7054 Escherichia coli, seven of 581 Klebsiella pneumoniae and 23 of 166 Klebsiella oxytoca strains were studied because of their decreased susceptibilities to broad-spectrum cephalosporins (as reflected in intermediate susceptibilities and/or positive synergy tests and/or irregular crenellated inhibition zones). The most frequent mechanism implicated in decreased susceptibility to broad-spectrum cephalosporins displayed by E. coli and K. oxytoca was hyperproduction of chromosomal beta-lactamase, followed by plasmid-mediated SHV-1 hyperproduction in E. coli. In our hospital, the incidence of plasmid-mediated extended-spectrum beta-lactamases (ESBLs) between 1994 and 1996 was low. ESBLs were found in only 10 (0.14%) E. coli strains (six CTX-M-9, two TEM-12 and two SHV-2), in one (0.17%) K. pneumoniae strain (SHV-2) and in no K. oxytoca strains. The relatively wide variety of beta-lactamases that were detected among these common bacteria isolated from a single medical centre, including non-TEM- and non-SHV-derived ESBLs, appears epidemiologically remarkable.  (+info)

Piperacillin, a new penicillin active against many bacteria resistant to other penicillins. (71/765)

The in vitro activity of piperacillin, a new semisynthetic piperazine penicillin derivative, was evaluated against 626 clinical isolates and compared with the activity of other beta-lactam antibiotics. At a concentration of 0.1 microgram/ml, piperacillin inhibited all streptococci except enterococci. Non-beta-lactamase-producing staphylococci were inhibited by 1.6 microgram or less per ml. Both beta-lactamase- and non-beta-lactamase-producing Haemophilus were inhibited by 0.1 microgram/ml. Piperacillin inhibited non-beta-lactamase-producing Escherichia coli, Salmonella, and Shigella at a concentration of 6.3 micrograms/ml, but 20% of strains of these species containing type III beta-lactamase were not inhibited by 100 micrograms/ml. Piperacillin at 25 micrograms/ml, inhibited 83% of Citrobacter, 58% of Klebsiella, 88% of Enterobacter, and 50% of indole-positive Proteus, Acinetobacter, and Providencia. At 25 micrograms/ml, piperacillin inhibited 95% of Pseudomonas aeruginosa and 78% of Bacteroides fragilis. The minimal inhibitory concentration of piperacillin against Pseudomonas was affected by increasing the inoculum size and by pH. Minimum bactericidal concentrations against Pseudomonas and Serratia often were eightfold greater than the minimum inhibitory concentrations. Piperacillin was equal in activity to ampicillin against enterococci. It was more active than carbenicillin against E. coli, Klebsiella, Enterobacter, and Bacteroides. It was the most active penicillin against Pseudomonas and inhibited many strains of Pseudomonas for which the MICs of carbenicillin were above 200 micrograms/ml. Piperacillin was hydrolyzed by many different beta-lactamases. Synergistic activity of piperacillin was demonstrated when it was combined with amikacin, gentamicin, and cefazolin against P. aeruginosa and members of the Enterobacteriaceae. No antagonism was observed when piperacillin was combined with aminoglycosides; however, antagonism was observed rarely against E. coli when piperacillin was combined with cefazolin.  (+info)

In vitro study of clavulanic acid in combination with penicillin, amoxycillin, and carbenicillin. (72/765)

The activity of clavulanic acid alone and in combination with penicillin, amoxycillin, and carbenicillin was studied. Marked reductions in the minimum inhibitory concentrations (MICs) for a wide spectrum of beta-lactamase-producing clinical isolates were found. Of particular interest were the decreased MICs of penicillin for Bacteroides fragilis and beta-lactamase-producing strains of Neisseria gonorrhoea in the presence of the clavulanic acid. Beta-lactamase-producing strains of Escherichia coli, Klebsiella spp., and indole-negative Proteus also showed considerably increased susceptibility to amoxycillin in combination with clavulanic acid. Two beta-lactamase-producing strains of Pseudomonas aeruginosa remained resistant to carbenicillin in the presence of clavulanic acid.  (+info)