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Minimum inhibitory and bactericidal concentrations of various antibiotics were determined for 90 strains of five organisms by Sensititre and compared with those obtained by conventional methods. Results by both methods corrleated well. The advantages and limitations of Sensititre are discussed.
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The beta-lactamase activity of 510 recently isolated Enterobacteriaceae was investigated with a quantitative photometric test. Beta-lactamase could be detected in 55 percent of the Enterobacteriaceae. At the same time minimal inhibition concentration (MIC) of beta-lactam antibiotics was determined. There was no correlation between MIC values and lactamase activity. For correct antibacterial therapy the clinician requires information on the lactamase activity of isolated bacteria in addition to the antibiogram. The qualitative test is useful for screening.
New, safe antimicrobial agents are needed to prevent and overcome severe bacterial, viral, and fungal infections. Based on our previous experience and that of others, we postulated that herbal essential oils, such as those of origanum, and monolaurin offer such possibilities. We examined in vitro the cidal and/or static effects of oil of origanum, several other essential oils, and monolaurin on Staphylococcus aureus, Bacillus anthracis Sterne, Escherichia coli, Klebsiella pneumoniae, Helicobacter pylori, and Mycobacterium terrae. Origanum proved cidal to all tested organisms with the exception of B. anthracis Sterne in which it was static. Monolaurin was cidal to S. aureus and M. terrae but not to E. coli and K. pneumoniae. Unlike the other two gram-negative organisms, H. pylori were extremely sensitive to monolaurin. Similar to origanum, monolaurin was static to B. anthracis Sterne. Because of their longstanding safety record, origanum and/or monolaurin, alone or combined with antibiotics, might prove useful in the prevention and treatment of severe bacterial infections, especially those that are difficult to treat and/or are antibiotic resistant.
Pathogens and spoilage organisms occurring in meat products were screened in laboratory media, according to a method of Eklund (1983), in order to determine the specific inhibitory effect of lactate on growth of these microorganisms under optimum growth conditions (pH 6.5, 20 degrees C). In general, Gram-positive bacteria were more sensitive towards lactate than Gram-negative bacteria. It was shown especially, that strains that were able to grow at water activities of 0.95 and below in the presence of NaCl (Staphylococcus aureus, Listeria monocytogenes, Brochothrix thermosphacta) were inhibited by sodium lactate (NaL). It appeared, that yeasts were resistant to large amounts of NaL (> 10% w/v). However, NaL had a specific inhibitory effect on growth of these organisms when compared to the effect of NaCl. These results indicate that lactate addition to food products with a pH near neutrality offers good prospects for shelf life prolongation.
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Several multilaboratory collaborative studies using broth microdilution and agar dilution (gonococcal tests only) methods of susceptibility testing were performed to establish quality-control (QC) giudelines. Replicate dilution tests with multiple lots of media were performed with National Committee for Clinical Laboratory Standards recommended QC strains (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Enterococcus faecalis ATCC 29212, and Staphylococcus aureus ATCC 29213) by using the following antimicrobials: biapenem, DU-6859a, FK-037, levofloxacin, and grepafloxacin. In addition QC MIC ranges, using appropriate medium modification for Haemophilus influenzae ATCC 49247 and Neisseria gonorrhoeae ATCC 49226 were reported on four (DU-6859a, FK-037, levofloxacin, and grepafloxacin) and two (ceftizoxime and FK-037) antimicrobials, respectively.
In the present study, we compared the actual inoculum density from inoculated broth microdilution wells to the targeted inoculum size (10(5) CFU/well) when the inoculum was prepared using a McFarland nephelometer to achieve the standard density. Three target inoculum sizes (10(5), 5 x 10(5), and 10(6) CFU/well) were used to compare the effect of slight inoculum size increases of both ATCC and clinical strains of anaerobes on MICs of various antimicrobials. Actual colony counts of Bacteroides fragilis, Bacteroides thetaiotaomicron, Eubacterium lentum, and Veillonella parvula ranged from 0.7 x 10(5) to 1.4 x 10(5) CFU/well. As the inoculum size rose above the desired 10(5) CFU/well level, the MICs of certain antimicrobials became elevated. Ceftizoxime, cefotaxime, and ceftriaxone MICs rose 4- to 16-fold with as little as 0.5 log10 increase in inoculum size. Other increases were also noted with E. lentum and Clostridium perfringens, but were primarily between the low and high inoculum sizes. Results with cefoxitin, cefotetan, mezlocillin, and imipenem did not show an appreciable increased inoculum effect. This study demonstrates that the variation in organism size among anaerobes (both between species and within species) does make a difference in actual inoculum size and certain anaerobes may require special adjustment to ensure proper MIC results from susceptibility testing.
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There is no single standard methodology for in vitro susceptibility testing for Chlamydia pneumoniae, but many investigators pre-incubate this organism with the cell monolayer for 1 h prior to adding antimicrobial and incubating for 72 h. The aim of this study was to determine the effect of extended C. pneumoniae pre-incubation, and extended incubation in the presence of antimicrobial, on the MICs of 5 antimicrobials. MICs were determined for 5 ATCC strains of C. pneumoniae by employing similar methods as those previously described in the literature. MICs were then determined following 1, 4, 6, 20 and 24 h C. pneumoniae pre-incubation. Finally, MICs were determined following 1 and 24 h C. pneumoniae pre-incubation, and 48 and 72 h incubation with antimicrobial and organism. Extending the incubation time in the presence of antimicrobial from 48 to 72 h had little or no effect on MICs. Similarly, pre-incubation periods of less than 20 h had little effect on MICs, but MICs increased significantly with 20 and 24 h pre-incubation.
A total of 140 non-replicate Streptococcus pneumoniae community isolates from Greek children collected during the period 1995-1997 were studied. Combined intermediate and high penicillin resistance rates were 23% in 1995, 29% in 1996, and 27% in 1997. The proportion of highly resistant isolates steadily increased from 2% in 1995 to 12% in 1997. There was no significant difference in penicillin resistance rates among colonizing and infecting isolates (23 and 27%, respectively). Over the study period, a clear shift towards higher penicillin MIC was observed among both the susceptible and resistant groups. Thus, penicillin resistance rates were equally high among colonizing and infecting isolates and resistance levels appeared to be gradually increasing throughout the entire S. pneumoniae population.
The antibiotic susceptibility pattern of Vibrio cholerae O139, Bengal, an emerging intestinal pathogen has been determined by the Kirby Bauer technique and the MIC values of some antibiotics against these strains by agar dilution technique. All the strains were susceptible to tetracycline, norfloxacin, ciprofloxacin and a majority was susceptible to gentamicin (95.7%) and nalidixic acid (82.9%). Only 51% were susceptible to cefotaxime and most strains were resistant to furazolidone (95.7%), ampicillin (87.3%) and co-trimoxazole (91.5%). The study shows the importance of judicious use of antibiotics in cholera cases and the need for monitoring the susceptibility status of these strains particularly because of their ability to cause extra-intestinal infections like septicaemia.
AIM: To investigate the distribution of antimicrobial resistance to phenicols in the fish pathogenic bacteria Aeromonas salmonicida, motile Aeromonas, Yersinia ruckeri, lactic bacteria and the nutritionally fastidious Flavobacterium psychrophilum. The last species was screened on two media (diluted Mueller-Hinton and peptone-enriched Anacker and Ordal), both supplemented with horse serum. METHODS AND RESULTS: Minimal inhibitory concentration (MIC) assessment, using the agar dilution method according to proposed standards, confirmed that chloramphenicol resistance was more frequent and expressed at higher levels than florfenicol resistance. A significant resistant population, highlighted by the bimodal distribution of MICs, was detected only for chloramphenicol in A. salmonicida. No link could be found with the geographical origin of the isolates or fish species. Other cases of resistance appeared randomly distributed or related to the natural properties of the bacterial species. Although the two media used for testing F. psychrophilum resulted in comparable performances in dilution methods, Anacker and Ordal was more adapted to disc diffusion tests. CONCLUSION: Despite wide use, resistance to florfenicol does not seem to occur frequently in French fish farms. SIGNIFICANCE AND IMPACT OF THE STUDY: It is important to maintain a surveillance, as development of florfenicol resistance has occasionally been documented. For this purpose, and for the species studied in this work, the recently proposed standards appear generally well-adapted.
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Three hundred and forty-five clinical isolates from patients treated with cefpirome were studied using an MIC methodology to develop tentative breakpoints for cefpirome, and to correlate clinical success with in-vitro susceptibility. No relationship between elimination, persistence and MIC of potential pathogens was found. There was, however, a close relationship between clinical cure and improvement and eradication of causative organisms. Based on the data, tentative breakpoints of less than 4 mg/L for sensitive and greater than 16 mg/L for resistance, at a cefpirome dose of 2.0 g bid or 1.0 g bid for urinary tract infection, are suggested.
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