Extended-spectrum beta-lactamases in Escherichia coli and Klebsiella spp. in European septicaemia isolates

Five per cent of Escherichia coli and klebsiella septicaemia isolates from the European Study Group on Antibiotic Resistance (ESGAR) study in 1987 to 1988 showed reduced susceptibility or resistance to cefotaxime, ceftazidime and/oraztreonam. Six of 15 isolates studied were susceptible to cefoxitin and MICs of cefuroxime, cefotaxime, ceftazidime and aztreonam were reduced by clavulanic acid. The isoelectric points of their beta-lactamases were in the range of 5.3-7.6. DNA hybridization showed that four of these beta-lactamases belonged to the TEM or SHV family. Transfer of cefotaxime resistance by conjugation was seen in two of the strains. Nine strains were resistant to cefoxitin (MIC > 16 mg/L) and MICs of cefuroxime, cefotaxime, ceftazidime and aztreonam were only slightly reduced in the presence of clavulanic acid. All nine strains produced at least one beta-lactamase of chromosomal origin with pI > 8.4, and four of these strains also harboured beta-lactamases with a pI range of 6.6-8.2. Cefoxitin resistance could be transferred by conjugation in one strain. Thus E. coli and Klebsiella spp. from the ESGAR septicaemia isolates were found to produce extended-spectrum beta-lactamases of both chromosomal and plasmid origin.

Characterization of Klebsiella oxytoca septicaemia isolates resistant to aztreonam and cefuroxime

Eleven clinical isolates of Klebsiella oxytoca from Stockholm hospitals were found to be resistant to aztreonam and cefuroxime, but susceptible to cefotaxime, ceftazidime and imipenem. Resistance could be overcome by combining the beta-lactams with the inhibitor clavulanic acid. Crude beta-lactamase preparations from the isolates inactivated aztreonam and cefuroxime rapidly. By isoelectric focusing, a single common beta-lactamase of pI 5.25 was detected. The K. oxytoca isolates belonged to three subgroups, based on their plasmid profiles and Bg/II restriction endonuclease digestion of plasmid DNA. It was concluded that resistance to aztreonam and cefuroxime in these isolates was conferred by a beta-lactamase distinct from TEM-1, TEM-2 and SHV-1, but possibly derived from TEM-like enzymes.

In vitro activity of cefepime, a new parenteral cephalosporin, against recent European blood isolates and in comparison with piperacillin/tazobactam

Cefepime, a new parenteral cephalosporin with broad antibacterial spectrum and stability to the hydrolysis to many bacterial beta-lactamases, was tested against recent blood culture isolates (369 strains of gram-negative bacilli and 131 strains of staphylococci) collected in 29 European laboratories by the microdilution method in Mueller-Hinton broth. Cefepime was very active against the gram-negative bacilli (MIC50 less than or equal to 0.016-0.064 mg/l; MIC90 0.064-4 mg/l) and less active against Pseudomonas (MIC50 4 mg/l; MIC90 greater than 16 mg/l) or Acinetobacter (MIC50 and MIC90 greater than 16 mg/l). The staphylococci were also inhibited (MIC50 8 mg/l; MIC90 16 mg/l). Cefepime was very active against bacteria producing different plasmid-encoded beta-lactamases (MIC 0.016-0.5 mg/l). Piperacillin was not active against the latter strains (MIC from 2 to greater than 64 mg/l), but the presence of the beta-lactamase inhibitor tazobactam restored the activity of piperacillin. The bactericidal activity of cefepime and piperacillin/tazobactam against beta-lactamase-producing strains was confirmed by the killing curve technique.

In-vitro activity of FCE 22101 against respiratory tract pathogens with reference to production of beta-lactamases

FCE 22101 is a new penem with broad antibacterial spectrum, excluding the pseudomonads, and has stability to many beta-lactamases. FCE 22101 and imipenem were very potent against the bacteria studied, including beta-lactamase producing strains, which can be isolated from patients with respiratory tract infections (MIC less than or equal to 8 mg/l). No strains were found to be resistant to FCE 22101. FCE 22101 was rapidly bactericidal and more stable to inactivation by beta-lactamases from Branhamella catarrhalis, Haemophilus influenzae, Enterobacter cloacae and Klebsiella pneumoniae than imipenem and ceftibuten. The other antibiotics tested varied in their activities against the respiratory tract pathogens.

Comparative in-vitro activity of the penem FCE 22101 against recent European blood culture isolates

Recent blood culture isolates (462 strains of Gram-negative bacilli and 288 strains of staphylococci) collected in 30 European laboratories were tested for susceptibility to five beta-lactam antibiotics by a microdilution method in Mueller-Hinton broth. The penem FCE 22101 and imipenem were very active against the Gram-negative bacilli, except the pseudomonads, FCE 22101 being four- to 16-fold less active (MIC50 2 mg/l; MIC90 8 mg/l) than imipenem MIC50 0.5 mg/l; MIC90 2 mg/l). Ceftibuten and ceftazidime were also active (MIC50 0.25 mg/l; MIC90 greater than 16 mg/l). The MIC of piperacillin (MIC50 8 mg/l; MIC90 greater than 64 mg/l) were two- to 16-fold reduced in the presence of the beta-lactamase inhibitor YTR-830 against these bacteria. Only imipenem and piperacillin inhibited the pseudomonads (MIC50 4 and 8 mg/l respectively; MIC90 16 mg/l and greater than 64 mg/l), with two-fold reduction in MIC50 of piperacillin in the presence of YTR-830. The staphylococci were very susceptible to FCE 22101 and imipenem (MIC50 less than or equal to 0.25 mg/l) except some cefazolin-resistant strains. In Staphylococcus aureus penem resistance was better expressed after bacterial growth at 30 degrees C. Some strains of Staph. epidermidis were susceptible to FCE 22101 but resistant to imipenem. The cephalosporins were not active against the staphylococci, and the presence of YTR-830 caused a four- to 16-fold reduction in MIC of piperacillin.

Laboratory- and species-specific interpretive breakpoints for disk diffusion tests of chloramphenicol susceptibility of Haemophilus influenzae

A total of 601 clinical isolates of Haemophilus influenzae isolated in six different regions of Sweden were tested for chloramphenicol susceptibility by using agar dilution MIC determinations and disk diffusion tests. For seven strains MICs were 4 micrograms/ml or higher, and for one strain the MIC was 2 micrograms/ml. All eight strains produced chloramphenicol acetyltransferase. For the remaining 593 strains, MICs were less than or equal to 1 microgram/ml, and the MICs for 50% and 90% of the strains were both 0.5 microgram/ml. Disk diffusion tests carried out by using revised interpretive criteria introduced in 1984 by the Swedish Reference Group for Antibiotics correctly identified the 593 strains as susceptible and the 8 strains as resistant. Quality assessments were performed in 29 clinical microbiology laboratories. The revised criteria for chloramphenicol disk diffusion testing gave rise to false resistance results in some laboratories. The interpretive accuracy improved when the interlaboratory variation was compensated for by using adjusted breakpoints. Such revision was possible through peak correction, single-strain regression analysis, and standard curve regression analysis. Peak-corrected breakpoints improved the accuracy from an overall incidence of false-resistant isolates of 4.4% to 2.3%. Single-strain regression analysis and standard curve regression analysis provided laboratory- and species-specific breakpoints which reduced false resistance rates of 0.14% and 0%, respectively.

The electrical conductivity of bovine milk in mastitis diagnosis

The electrical conductivity (EC) of milk is mainly a function of the electrolyte concentration in the milk and therefore raised in mastitis. The present investigation was aimed at elaborating, if possible, a diagnostic model for screening purposes based on EC determinations and consistent with the diagnostic procedures and interpretations commonly used in laboratory milk diagnosis in the Nordic countries (Klastrup 1975). According to this diagnosis (here called reference diagnosis) cell numbers above 300,000/ml (cell count or the corresponding CMT-score) in foremilk quarter samples during the main part of the lactation period and significantly above the lowest value on within-udder comparison during late lactation are considered indicative of mastitis and bacteriological examinations are made when called for.