[Evaluation of the activity of antibiotics against Listeria. Therapeutic perspectives]

The activity of different antibiotics was considered by studying the results reported in literature and during the IXth International Symposium on the Problems of Listeriosis. Listeria susceptibility to antibiotics did not change. Ampicillin was always one of the most effective and used antibiotics against Listeria. The association with an aminoglycoside produced a synergistic effect, which made the bactericidal activity quicker, in vitro as in vivo on animal. More recent molecules like third generation cephalosporins or fluoro-piperazinyl-quinolones had poor activity against Listeria.

[Multicenter study of the activity of pefloxacin on bacteria isolated in a hospital milieu]

Minimal inhibitory concentrations (MICs) of pefloxacin were evaluated by agar dilution for 3422 bacterial strains isolated in nine hospitals. Enterobacteriaceae proved very sensitive to pefloxacin: 62 p. 100 of 1743 strains tested had MIC less than or equal to 0.12 and 90 p. 100 less than or equal to 1 microgram/ml; but the percent of strains with MIC greater than or equal to 2 varied among the different groups of Enterobacteriaceae: 2.7 p. 100 for E. coli to 39 p. 100 for Serratia. 55 p. 100 for Pseudomonas and 81 p. 100 of Acinetobacter were inhibited by 1 micrograms/ml or less (mode MIC 1 and 0.5 micrograms/ml). Haemophilus sp.: 0.03 and 0.06 micrograms/ml and Gonococci were very sensitive to pefloxacin. The spectrum of pefloxacin extended to Gram positive cocci: MIC of Staphylococci were 0.06 to 8 micrograms/ml (mode MIC: 0.5); Enterococci, other Streptococci and Pneumococci were less sensitive: 2 and 4 micrograms/ml for the majority of strains. Concerning anaerobic bacteria, pefloxacin was more active against Clostridium (0.5 to 1 microgram/ml generally), than against Bacteroides (4 to 16 micrograms/ml).

[Comparative sensitivity of 207 strains of strict anaerobic bacteria to piperacillin and 4 other antibiotics]

The MIC of two hundred and seven anaerobic bacterial strains was determined by an agar dilution method for five antibiotics (piperacillin, ampicillin, carbenicillin, cefalotin, metronidazole). 100% of the strains were susceptible to carbenicillin (MIC less than or equal to 128 mg/l), 97% to piperacillin (MIC less than or equal to 16), 86% to metronidazole (MIC less than or equal to 4), 70% to ampicillin (MIC less than or equal to 4) and 68% to cefalotin (MIC less than or equal to 8). Amongst bêta-lactam compounds, piperacillin and ampicillin determined the lowest MIC for Bacteroides fragilis, Fusobacterium, Clostridium and Gram-positive cocci. Amongst Bacteroides fragilis strains, the lowest MIC were obtained with metronidazole.

Reliability of the bronchoscopic protected catheter brush in intubated and ventilated patients

The reliability of a bronchoscopic protected catheter brush (BPCB) in the diagnosis of lower respiratory tract infection was studied in 17 intubated and ventilated patients, including seven patients free from such infection (group 1) and ten patients with suspected infection (group 2). A first sample was obtained in the lower trachea by aspiration through the fiberoptic bronchoscope and a second in a distal bronchus by the BPCB procedure. In group 1, all BPCB cultures were sterile, although lower tracheal cultures yielded two or more bacterial species, showing that uncontaminated specimens can be obtained by the BPCB procedure. In three patients of group 2, BPCB cultures remained sterile as a nonbacterial pulmonary disease was certified by open lung biopsy. In seven patients from group 2, BPCB cultures yielded all of the organisms isolated simultaneously by reference methods (ie, cultures of blood or pleural fluid, serologic tests, and open lung biopsy). In two of these patients, contamination of the BPCB specimens was ascertained by the reference method bacterial results. In this study the BPCB procedure was able to obtain uncontaminated specimens in intubated and ventilated patients and was mainly accurate in identifying the bacterial etiologic agents of lower respiratory tract infections.

A multi-centre study on the phage typing of Listeria monocytogenes

The aim of this multicenter study was to determine and to standardize methods in order to have common basis for comparing results of phage typing of Listeria monocytogenes. Using a common set of Listeria strains, a standardized method, including media, bacterial growth conditions, application of viruses and reading of lytic reactions, was established. 29 bacteriophages were selected according to their host range. This phage typing system allowed phagovar determination of 54% of the serogroup 1/2 strains and 77% of the serogroup 4 strains of L. monocytogenes.

[Bacteriostatic and bactericidal effect of cefotaxime combinations on Staphylococcus aureus assessed by FIC and FBC-index determination]

Activity of cefotaxime associated with one of nine other antibiotics (amikacin, dibekacin, gentamicin, netilmicin, sisomicin, tobramycin, erythromycin, clindamycin, and chloramphenicol) was studied by a checkerboard method with determination of FIC and FBC-indices. Four S. aureus strains were used: one homogeneous methicillin-resistant strain (S1), one heterogeneous methicillin-resistant strain (S2), and two susceptible strains (S3 and S4). Strong synergism between cefotaxime and aminoglycosides was found only for S2, with no significant differences between aminoglycosides (index # 0.3). Cefotaxime and chloramphenicol showed synergistic or additive bacteriostatic activities and consistently antagonist bactericidal activities. Bactericidal activities of cefotaxime and erythromycin were likewise antagonistic, whereas cefotaxime and clindamycin occasionally exhibited in vitro synergism.

[Multicenter study of the in vitro effect of imipenem (N-formimidoyl-thienamycin) on hospital bacteria]

Minimal inhibitory concentrations (MICs) of imipenem were evaluated by agar dilution for 2 895 bacterial strains isolated in 9 hospitals. Imipenem proved highly active against Enterobacteriaceae, with an MIC less than or equal to 0.25 for 63% of the 1 556 tested strains, less than or equal to 1 for 89.6% and less than or equal to 4 for 99%. The different groups of Enterobacteriaceae exhibited similar mode MICs (0.12 to 0.25), with the exception of Serratia (0.25-0.5), P. mirabilis (0.5), indole-positive Proteus (2), and Providencia (1). MICs of most cefotaxime-resistant strains were within the susceptibility range. Imipenem also exhibited satisfactory activity against P. aeruginosa (mode MIC 1-2) and Acinetobacter sp. (mode MIC: 0.25-0.5). MICs ranged from 0.03 to 4 (mode MIC: 0.5) for Haemophilus sp. and 0.25 to 1 for Gonococci, regardless of beta-lactamase-production status. MICs for Meningococci were less than or equal to 0,06. Methicillin-susceptible Staphylococci had low MICs, ranging from 0.008 to 0.5 (mode MIC : 0.016); MICs for methicillin-resistant strains varied widely, from 0.016 to 64, and were higher after incubation at 30 degrees C. Streptococci, except for Enterococci, and Pneumococci were highly susceptible (usually 0.008-0.03); MICs for Enterococci varied from 0,12 to 32 (mode MIC: 1-2). Except for four C. difficile strains, all tested anaerobic strains were inhibited by concentrations less than or equal to 1 (mode MICs: 0.06 for C. perfringens and 0.03 for B. fragilis).

[Sensitivity to cefotiam of 494 hospital bacterial strains. Determination of minimal inhibitory concentration and comparison with other beta-lactams]

Susceptibility to cefotiam of 494 bacterial strains was studied by MIC determination using an agar dilution assay. Activity of cefotiam was also compared with that of six other beta-lactams (ampicillin, mezlocillin, ticarcillin, cefalotin, cefotaxime, and moxalactam) using an agar diffusion method. Cefotiam showed a wide antibacterial spectrum including more than 70% of Enterobacteriaceae (except Serratia), beta-lactamase-producing and non-beta-lactamase-producing Haemophilus influenzae, non-enterococcus streptococci, and penicillinase-producing and non-penicillinase-producing staphylococci susceptible to methicillin. Conversely, cefotiam was inactive against Pseudomonas aeruginosa, Acinetobacter anitratum, Streptococcus faecalis, and methicillin-resistant Staphylococcus aureus.

[Comparative effects of netilmicin and 4 other aminoglycosides on 1028 bacterial strains isolated in a hospital milieu]

The activity of netilmicin and four other aminoglycosides was studied by a diffusion method against 1 028 bacterial strains isolated in hospital. Nearly all the strains of Gram-negative bacilli were susceptible to amikacin; with netilmicin, tobramycin, gentamicin and dibekacin the percentages of susceptible strains were smaller, without any statistically significant differences between them. Amikacin and netilmicin were the most effective compounds against staphylococci. Netilmicin seemed to be the most effective compound, in vitro, against streptococci. The MIC of gentamicin and netilmicin of 224 strains showed the superior activity of netilmicin against K. pneumoniae, Proteus, P. aeruginosa and S. aureus.

[Antibiotic sensitivity of 139 strains of Listeria serotyped by the National Reference Center in 1983]

The susceptibility of 139 strains of Listeria towards eight antibiotics--penicillin, ampicillin, cephalotin, gentamicin, chloramphenicol, tetracycline, erythromycin and pefloxacin--was studied. All strains were susceptible to all antibiotics except pefloxacin. The lowest MIC (less than or equal to 0.5 mg/l) were obtained with penicillin, ampicillin, gentamicin and erythromycin. For tetracycline, cephalotin and chloramphenicol, MIC ranged from 0.5 to 16 mg/l. The MIC of pefloxacin varied from 4 to 16 mg/l.

[Antibacterial effects of the combinations of azlocillin with other antibiotics]

Evaluating the synergistic effects of antibiotic associations is by no means an easy task owing to the diversity of the test methods utilized for this purpose. Data extracted from 11 reports published between 1975 and 1982 and concerning associations of azlocillin with various aminoglycosides (gentamicin, sisomycin, netilmicin, amikacin, tobramycin and dibekacin) and with two beta-lactam antibiotics (cloxacillin and cefotaxime) are reviewed in this article. On the whole, a synergistic effect against Staphylococcus aureus, Pseudomonas aeruginosa and Enterobacteriaceae was most frequently observed with the azlocillin-aminoglycoside association. This effect was usually more pronounced with organisms showing low sensitivity to azlocillin and less pronounced with organisms resistant to aminoglycosides. As often pointed out, there is no general rule that would help predict with certainty from the sensitivity of a strain whether or not any given antibiotic association will act synergistically on that strain.

[Pharmacokinetics of azlocillin in the burn patient]

Pharmacokinetic values of azlocillin were determined in burned patients during the exudation and repair periods. A single dose of 80 mg/kg was administered intravenously over 30 min. Pharmacokinetic constants were calculated using an open two-compartment model. During the exudation period the ultimate serum half-lives (t 1/2 beta) were 1.17 to 1.4 h, 1.73 to 1.78 h and 3.3 h respectively with creatinine clearances of 111-131, 60-94 and 14 ml/min/1.73 m2. Renal clearances varied from 30.9 to 128 ml/min/1.73 m2. During the repair period little change was observed in t 1/2 beta, but renal clearance increased from 36.6 to 116 ml/min/1.73 m2 in one patient. It is concluded that azlocillin behaves in burned patients as in patients with impaired renal function.

[Critical study of the serological diagnosis of herpetic encephalitis. Apropos of 4 cases]

Virologic study was performed in four cases of Herpes simplex virus encephalitis. Herpes simplex virus type 1 was recovered from surgical brain biopsy specimens taken in three cases. Anti-HSV antibodies were assayed in simultaneous blood and cerebrospinal fluid samples by ELISA. CSF and serum specific antibody ratios were compared to those of antibodies directed against other viral antigens whenever possible. A significant and early increase in this CSF/serum ratio was demonstrated in two patients. The diagnostic value of this serological method is discussed, as an alternative to viral isolation from brain biopsy specimens.

[In vitro action of moxalactam on hospital bacteria. Results of a multicenter survey]

The high potency of Moxalactam on three major groups of bacteria, i.e. Enterobacteriae, Haemophilus and Bacteroïdes, predicted by previous studies, has been confirmed by the study of hospital strains in this multicenter investigation. Among these groups, the proportion of resistant strains is very low. However, Moxalactam is not superior to older agents on staphylococci, Streptococci and Listeria, and is less active than certain new agents on Pseudomonas. Moxalactam is one of the best "third generation" cephalosporins. It is remarkable by its potency against Bacteroides fragilis and its weak activity on Streptococci and Pneumococci. The unanswered question concerns the future of resistant strains: will they remain exceptional or will they multiply?

[In vitro activity of cefatiolene (RP 42,980) against hospital bacteria. Comparison with cefotaxime and lamoxactam. Results of a multicenter study]

This work reports a multicenter study of antibacterial activity of cefatiolene (RP 42 980), a new third generation cephalosporin, in comparison with cefotaxime and lamoxactam. On the basis of MIC, activity of the three products is similar or Gram negative rods, but cefotaxime is a little more active on Enterobacteriaceae. The activity against Staphylococci requires further studies, indeed the determination of IC 50 of some strains showed a better activity of cefatiolene, but this was not observed by determination of MIC. As cefotaxime and contrary to lamoxactam, cefatiolene is active at low concentrations on other Streptococci than Enterococci, but a little on Bacteroides.

[Contribution of rapid methods to the diagnosis of Haemophilus influenzae infections and the conduct of antibacterial treatment]

In the last decade medical microbiologists could make use of a great number of techniques that allow to shorten length of time of report from the arrival of specimens in laboratory. The direct microscopical examination has been considerably revalued: it is very important. Now it can be completed by use of reagents that allow the presumptive identification of various bacteria. For Hemophilus influenzae the efforts are devoted only to serovar b. In the absence of visible bacteria, the research of the presence of bacterial antigen is now possible. The semiautomatic apparatus allows also to watch over the cultures and to detect the beginning of development more accurately than macroscopically. Finally, for antibiotic sensitivity test, we can also use the automatic apparatus that shortens length of time of report to clinician.

[Bactericidal activity of antibiotics as a function of pharmacokinetic constants. II. Effect of pharmacokinetic parameters (C max and Ke) on the bactericidal activity of gentamicin]

The authors studied the influence of certain pharmacokinetic parameters on the bactericidal activity of gentamicin using an experimental model simulating the variations of antibiotic concentration. These parameters are the maximal concentration (C max) and the elimination constant (Ke). The bactericidal activity of gentamicin was studied on the strain of E. coli ATCC 25922. The result is that an influence of C max on the bactericidal activity is more important than that of Ke from these experiments. Considering only bacteriological parameters, the rapid intravenous injection will be superior to slow perfusion. However, the pharmacological parameters must be considered and modify also these conclusions.

[Bactericidal activity of antibiotics as a function of pharmacokinetic constants. I. Experimental dynamic model simulating variations in the concentrations of antibiotics]

In order to study the bactericidal effect of antibiotics in a system approaching actual therapy, a dynamic model which simulates concentration variations was developed. This was done using a dialysis intermediary. Three aminoglycosides (amikacin, gentamicin, tobramycin) were taken in a system resembling the serum rates of the normal individual. The apparatus is fairly accurate, the variation coefficients being of the order of 10 to 14%. This model enables the simulation of numerous therapeutic situations. It is however limited to only dialysable antibiotics.

[Influence of antibiotic disk charge on concordance curve of cefotaxime ]

The activity of new cephalosporins is considerably higher than that of the first molecules. However antibiotic desk charge used for the agar diffusion method is still 30 micrograms. The disk diffusion - MIC distribution is not linear. The authors observed the influence of disk charge on the aspect of this distribution in order to determine the change permitting the best linearity. One hundred sixty five strains were studied using the agar diffusion and dilution methods. Their MICs were distributed from 0.015 to 128 mg/l. The disk charges studied were 5, 10, 15, 20, 25 and 30 micrograms. The results confirmed the parabolic aspect of concordance curve. This phenomenon was observed at higher disk charges (20, 25 and 30 micrograms). The linearity is better with the curves calculated from 5 and 10 micrograms. The correlation coefficients between these two charges were 0.92. However the inhibition diameters in 5 micrograms were too small to permit a clear differentiation between resistant and intermediate strains. The best discrimination is obtained with 10 micrograms. The zone diameter breakpoints were greater than or equal to 18 mm for susceptible 12 to 17 mm for intermediate, and less than or equal to 11 mm for resistant.

[Expression of staphylococci resistance to oxacillin and cefalotin ]

The comportment to oxacillin (OXA) and cefalotin (CFT) of 32 strains of staphylococci - 18 Staphylococcus aureus and 14 coagulase-negative staphylococci (SCN) - was studied by three different methods, on three types of media, with or without 5 p. cent of NaCl and incubated at two temperatures (30 degree C-37 degree C). S. aureus showed always a cross-resistance to OXA and CFT. Three types were recognized : "susceptible" (S) and "high level resistant" (RO) types, whose comportment did not vary with culture conditions; "heterogenous resistant" type (RH) for which the OXA - resistance expression was better at 30 degree C and on salt medium. SCN did not always present a cross-resistance. In addition to S, RO and RH types, one strain showed a dissociated resistance to OXA and CFT, with a better expression at 30 degree C and on salt medium; one strain, which appeared to be susceptible by discs method, presented a resistant population level higher than that of the susceptible reference strain, whatever the culture conditions were.

[Comparative activity of cefsulodin on Pseudomonas aeruginosa, Acinetobacter and Enterobacteriaceae (author's transl)]

Cefsulodin, a new semi-synthetic cephalosporin, is characterized by its activity against P. aeruginosa. In this study the authors compared this new molecule with other four betalactamines, carbenicillin, ticarcillin, azlocillin and mezlocillin, and two aminoglycosides, amikacin and netilmicin. Two hundred and forty five strains studied were 100 Pseudomonas aeruginosa, 20 Acinetobacter, 42 Proteus, 21 Serratia, 22 Enterobacter, 20 Klebsiella and 20 E. coli. One hundred twenty strains of these showed carbenicillin resistant phenotype. MIC were determined by the agar dilution method. Cefsulodin was only active on Pseudomonas aeruginosa. MICs were at least 16 mg/l in the other species. On carbenicillin susceptible P. aeruginosa strains, the average MIC of cefsulodin, amikacin and netilmicin was 1 mg/l, and MICs of azlocillin, mezlocillin, ticarcillin and carbenicillin were 4-8 mg/l, 8 mg/l, 16 mg/l and 32 mg/l, respectively. On carbenicillin resistant P. aeruginosa, ticarcillin and mezlocillin were not effective and MICs of azlocillin and cefsulodin were 16 mg/l and 4-8 mg/l, respectively. However, MICs were between 64 and 128 mg/l in 20 p. cent of carbenicillin resistant strains.

[Comparison of light-scattering index 50% (LSI50) and inhibitory concentration 50% (CI50) (author's transl)]

The "Autobac" apparatus permitted the rapid determination of the light-scattering index 50% (LSI50) and inhibitory concentration 50% (CI50) of eight antibiotics -- kanamycin, amikacin, lividomycin, gentamicin, tobramycin, sisomicin, netilmicin and colistin -- for the strain of Escherichia coli ATCC-25922. The results were compared with those of the reference method using an agar dilution method. The percentage of inhibition (% I) was obtained from LSI by applying the formula % I = 10(-(GIXLSI)). The growth index (GI) has an influence on the values of the rapid method. The best results were observed in the GI ranges of 1.2 to 1.7. For all the antibiotics except tobramycin and colistin, the CI50 values of the two methods were very similar. The values of LSI50 were not assimiliated to those of CI50. These three parameters had a small variability. The averages of standard deviation were 0.23 log2 for the CI50 of the reference method, 0.24 log2 for the CI50 of the rapid method and 0.32 log2 for the LSI50. The "Autobac" enables the determination of CI50 by a simpler and faster technique.