In vitro development of resistance of Streptococcus pneumoniae to beta-lactam antibiotics

Maximum levels of cross-contamination for 24 antimicrobial active substances in non-target feed. Part 4: β-Lactams: amoxicillin and penicillin V

The specific concentrations of amoxicillin and penicillin V in non-target feed for food-producing animals, below which there would not be an effect on the emergence of, and/or selection for, resistance in bacteria relevant for human and animal health, as well as the specific antimicrobial concentrations in feed which have an effect in terms of growth promotion/increased yield were assessed by EFSA in collaboration with EMA. Details of the methodology used for this assessment, associated data gaps and uncertainties, are presented in a separate document. To address antimicrobial resistance, the Feed Antimicrobial Resistance Selection Concentration (FARSC) model developed specifically for the assessment was applied. However, due to the lack of data on the parameters required to calculate the FARSC, it was not possible to conclude the assessment until further experimental data become available. To address growth promotion, data from scientific publications obtained from an extensive literature review were used. Levels in feed that showed to have an effect on growth promotion/increased yield were reported for amoxicillin, whilst for penicillin V no suitable data for the assessment were available. It was recommended to carry out studies to generate the data that are required to fill the gaps which prevented the calculation of the FARSC for these two antimicrobials.

Effect of amoxicillin use on oral microbiota in young children

Dental plaque samples from 40 children were screened for the presence of bacteria resistant to amoxicillin. Fifteen children had used amoxicillin and 25 had not used any antibiotic in the 3 months prior to sample collection. All (100%) of the children harbored amoxicillin-resistant oral bacteria. The median percentage of the total cultivable oral microbiota resistant to amoxicillin was 2.4% (range, 0.1 to 14.3%) in children without amoxicillin use and 10.9% (range, 0.8 to 97.3%) in children with amoxicillin use, with the latter value being significantly higher (P < 0.01). A total of 224 amoxicillin-resistant bacteria were isolated and comprised three main genera: Haemophilus spp., Streptococcus spp., and Veillonella spp. The biodiversity of the amoxicillin-resistant microbiota was similar among the isolates from children with and without previous antibiotic use. The amoxicillin MIC at which 90% of the isolates were inhibited for isolates from children who had used amoxicillin in the previous 3 months was higher (64 mg liter(-1)) than that obtained for the isolates from subjects who had not used antibiotics (16 mg liter(-1)). The majority of the amoxicillin-resistant isolates (65%) were also resistant to at least one of the three antibiotics tested (penicillin, erythromycin, and tetracycline), with resistance to penicillin (51% of isolates) being the most frequently encountered. However, significantly more (P < 0.05) of the amoxicillin-resistant isolates from subjects with previous amoxicillin use were also resistant to erythromycin. This study has demonstrated that a diverse collection of amoxicillin-resistant bacteria is present in the oral cavity and that the number, proportions, MICs, and resistance to erythromycin can significantly increase with amoxicillin use.

Penicillin-resistant and multidrug-resistant Streptococcus pneumoniae in a pediatric hospital in Zagreb, Croatia

Sixty-four penicillin-resistant Streptococcus pneumoniae isolates [benzylpenicillin minimal inhibitory concentrations (MICs) between 0.05 and 1.6 micrograms/ml] recovered at the Pediatric Hospital "Dr. Fran Mihaljevic" in Zagreb, Croatia between October 1990 and March 1993 were analyzed for serotype, antibiotic susceptibility patterns, and chromosomal relatedness using pulsed-field gel electrophoretic (PFGE) analysis of chromosomal DNA fragmented by digestion with the SmaI endonuclease. Hospital "Dr. Fran Mihaljevic" services the capital of Croatia and its vicinity. Most of the isolates were from nasopharyngeal carriage, but several isolates were from otitis media, sinusitis, and meningitis. Most isolates belonged to either serotype 23F (36/64) or 19F (12/64); the rest, including three 15C isolates, were in 11 additional distinct serotypes. The overwhelming majority (25/36) of the serotype 23F isolates had penicillin MIC values of 1-2 micrograms/ml and shared variants of a common PFGE pattern, closely related to the PFGE identified in multiresistant pneumococci of the same serotype with wide geographic spread to Spain, Portugal, France, and the United States. This group of bacteria was also resistant to tetracycline, chloramphenicol, and sulfamethoxazole/trimethoprim. In contrast to the relative genetic and phenotypic homogeneity of the more highly penicillin resistant isolates, pneumococci with penicillin MICs between 0.5 and 0.4 microgram/ml (29/64) were distributed in 13 different serotypes and as many as 20 distinct PFGE patterns.

Gradient plate method to induce Streptococcus pyogenes resistance

In recent years, increasing numbers of Streptococcus pyogenes (GAS) strains displaying resistance to macrolides have been reported in Finland, Japan, Asia and Spain. Antibiotic use has been shown to be a risk factor for infection with and carriage of drug-resistant streptococci. The aim of this study was to compare in-vitro development of resistance of streptococci to beta-lactams (penicillin, amoxycillin, cefotiam and cefuroxime) and erythromycin by serial passages in subinhibitory concentrations of antibiotics (subMICs) by gradient plate method. Three clinical strains of GAS were tested. Two were susceptible to erythromycin (MIC = 0.015 mg/L and 0.013 mg/L) and one resistant. Serial passages were performed daily by gradient plate method until a four-fold increase of the MIC was achieved. GAS variants obtained after serial passages in beta-lactams had MICs increased at least four-fold. They remained susceptible to these antibiotics. With erythromycin, final MICs reached intermediate and resistant level. Results obtained in this study with erythromycin are in good correlation with clinical studies showing that prior exposure to macrolides may help to facilitate the emergence of drug-resistant strains of streptococci.

Pneumococcal resistance patterns in Europe

The emergence of Streptococcus pneumoniae strains with decreased susceptibility to penicillin has been reported worldwide over the past 20 years. However, there are striking discrepancies in penicillin susceptibility among various European countries, suggesting that local conditions may affect clonal propagation or de novo selection of resistant strains. In the present study, data on penicillin resistance patterns, antibiotic use and mode of administration, and treatment compliance in five European countries (France, Spain, Germany, Italy, and the UK) were compared. High prevalence rates of penicillin-resistant pneumococci have been reported in Spain and France, where antibiotics are widely prescribed, and overall in Europe, patient compliance with more than 50% of oral antimicrobial prescriptions is inadequate. The low prevalence of penicillin resistance in Germany and the UK coincides with lower antibiotic consumption and better treatment compliance in these countries. Recent attempts to raise public awareness and to restrict and improve indications for antimicrobial agents have resulted in decreased pneumococcal resistance in Hungary and Iceland, suggesting that pneumococcal resistance can be reversed.

Enterobacter spp.: pathogens poised to flourish at the turn of the century

Knowledge of the genus Enterobacter and its role in human disease has expanded exponentially in recent years. The incidence of infection in the hospital and the community has increased. New clinical syndromes have been recognized. Enterobacter spp. have also been implicated as causes of other syndromes that traditionally have been associated almost exclusively with more easily treatable pathogens, such as group A streptococci and staphylococci. Rapid emergence of multiple-drug resistance has been documented in individual patients during therapy and in populations and environments with strong selective pressure from antimicrobial agents, especially the cephalosporins. Therapeutic options for patients infected with multiply resistant strains have become severely limited. Carbapenems or, alternatively, fluoroquinolones are the most predictively active options, although resistance to both classes has been observed on rare occasions. Enterobacter spp. appear well adapted for survival and even proliferation as the turn of the century approaches.