2x Minimum Inhibitory Concentration Research Articles

Antibacterial mechanism of Malaysian Carey clay against food-borne Staphylococcus aureus

Depending on their chemical structure and geochemistry, clay minerals can display potent antibacterial properties against a range of bacterial pathogens. Malaysian Carey clay was evaluated for its antibacterial activity against food-borne Staphylococcus aureus ATCC 13565 strains. The minimum inhibitory concentration (MIC) and minimum bactericidal activity (MBC) of both Carey clay leachates and suspension were 125 mg/mL and 250 mg/mL, respectively. Time-kill assay revealed that 2x MIC and 4x MIC Carey clay in both leachate and suspension forms resulted in complete killing of S. aureus. Antibacterial mechanism was investigated through imaging of bacterial morphology using TEM and determination of reactive oxygen species (ROS) using NBT assay. Imaging of bacterial morphology using TEM showed abnormalities, including disrupted cell walls following exposure to Carey clay, and the antibacterial activity was associated with generation of ROS. Our study suggests that Carey clay displays promising functionality as a natural antibacterial agent in the food industry.

ANTIBACTERIAL ACTIVITY OF DR. RIDZ ANTI-ACNE NANOSERUM® AGAINST SKIN BACTERIA THAT CAUSE ACNE VULGARIS

Cutibacterium acnes, Staphylococcus epidermidis, and Staphylococcus aureus are commonly associated with the pathogenesis of acne vulgaris. Skincare products that contain natural ingredients have become a trend to treat acne. Dr.Ridz Anti-Acne Nanoserum® product was formulated with the extract of Cassia alata leaf and Piper betle. The aim of this study was to determine the antibacterial activity of this formulated product against against C. acnes, S. epidermidis, and S. aureus. The minimum inhibitory concentration (MIC) value and the minimum bactericidal concentration (MBC) were determined using a broth microdilution and a streak plate method, respectively. The rate of killing by this product was tested using time-kill assay (TKA) at 0.5x MIC, 1x MIC, and 2x MIC with incubation periods of 2, 4, 6, 8 10, 12, and 24 hours. The MIC values showed that this product inhibited S. epidermidis and S. aureus better than C. acnes. From the calculation of the MBC/MIC ratio, this product showed bactericidal effects against all tested bacteria. The time-kill studies showed that the killing effect of this product was concentration-dependent, and the highest antibacterial activity was observed at the concentration of 2x MIC against all tested bacteria. In conclusion, Dr.Ridz Anti-Acne Nanoserum® exhibits the best antibacterial activities against S. epidermidis and showed a bactericidal effect towards all tested bacteria. .

Effect of naturally isolated hydroquinone in disturbing the cell membrane integrity of Pseudomonas aeruginosa MTCC 741 and Staphylococcus aureus MTCC 740

Nosocomial pathogens cause various health problems in human and many novel drugs are under investigation to combat the pathogens. The present study explains the naturally derived hydroquinone possible mode of action against Pseudomonas aeruginosa MTCC 741 and Staphylococcus aureus MTCC 740. Time kill studies, cell viability assays, membrane potential assays, and potassium release assays were carried out to study the mode of action. Time kill studies revealed the rapid death of bacterial pathogens exposed to 4X MIC (Minimum inhibitory concentration) of the hydroquinone. Cell viability assay results showed that nearly half of the cell destruction of test pathogens occurred within one hour. Transmission electron microscopic (TEM) observations revealed the disruption of the cell membrane, which caused severe ultrastructural changes in both test pathogens. Hydroquinone dissipated the membrane potential of test pathogens, as confirmed by the depolarization of membrane potential, increases in permeability and leakage of intracellular potassium ions. At the concentration of 2X MIC hydroquinone in 5 min, about 91.41% and 84.85% potassium ions were released from P. aeruginosa MTCC 741 and S. aureus MTCC 740, respectively. This is the first report on the mode of action of naturally derived hydroquinone against clinical pathogens.

Effects of Tigecycline Combined with Azithromycin Against Biofilms of Multidrug-Resistant Stenotrophomonas maltophilia Isolates from a Patient in China.

PurposeOur aim was to investigate in vitro biofilm formation by S. maltophilia and the effects of antibacterial agents used to prevent biofilm formation.MethodsTwo trimethoprim/sulfamethoxazole-resistant S. maltophilia strains were isolated from the pleural effusion of a patient with cancer. The minimum inhibitory concentrations (MICs) of amikacin, azithromycin, cefoperazone/sulbactam, and tigecycline were determined. The checkerboard method was used to determine the fractional inhibitory concentration indices (FICIs). A crystal violet biofilm assay and confocal laser scanning microscopy (CLSM) were used to observe biofilm formation. In vitro effects of azithromycin combined with tigecycline on biofilms of S. maltophilia strains were tested.ResultsThe two S. maltophilia isolates were confirmed to produce strong biofilms. Crystal violet biofilm assay and CLSM analysis of S. maltophilia biofilm were in the initial adhesive stage after 2 h incubation. Biofilm was in the exponential phase of growth at 12 h and reached maximal growth at 36–48 h. Compared with tigecycline or azithromycin alone, the combination of tigecycline and azithromycin increased the inhibiting effect S. maltophilia biofilm biomass after incubation for 12 h. Compared with the control group, in almost all strains treated with tigecycline and azithromycin, the biofilm was significantly suppressed significance (P<0.001). We found that 2x MIC azithromycin combined with 1x MIC tigecycline had the best inhibiting effect against the biofilm, the biofilm inhibition rates of three strains were all over 60%, the biofilm thickness was inhibited from 36.00 ± 4.00 μm to 8.00 μm, from 40.00 μm to 6.67± 2.31 μm, and from 32.00 μm to 13.33 ± 2.31 μm in SMA1, SMA2 and ATCC17666, respectively.ConclusionAzithromycin combined with tigecycline inhibited biofilm formation by S. maltophilia. Our study provides an experimental basis for a possible optimal treatment strategy for S. maltophilia biofilm-related infections.

Bioprospection of novel synthetic monocurcuminoids: Antioxidant, antimicrobial, and in vitro cytotoxic activities

The irrational use of medications has increased the incidence of microbial infections, which are a major threat to public health. Moreover, conventional therapeutic strategies are starting to become ineffective to treat these infections. Hence, there is a need to develop and characterize novel antimicrobial compounds. Phytochemicals are emerging as a safe and accessible alternative to conventional therapeutics for treating infectious diseases. Curcumin is extracted from the dried rhizome of the spice turmeric (Curcuma longa (Zingiberaceae)). However, the bioavailability of curcumin is low owing to its lipophilic property and thus has a low therapeutic efficacy in the host. A previous study synthesized structural variants of curcumin, which are called monocurcuminoids (CNs). CNs are synthesized based on the chemical structure of curcumin with only one methyl bridge. The biological activities of four previously synthesized CNs (CN59, CN63, CN67, and CN77), curcumin, and turmeric powder were examined in this study. Gas chromatography-tandem mass spectrometry analysis of curcumin and turmeric powder revealed similar peaks, which indicated the presence of curcumin in turmeric powder. The antioxidant activity of the test compounds was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) assays. The ABTS radical scavenging activities of the test compounds were similar to those of vitamin C. The minimum inhibitory concentration (MIC) values of the test compounds against seven microbial strains were in the range of 4.06–150 μg/mL. The MIC value was equal to minimum bactericidal concentration value for CN63 (150 μg/mL) and CN67 (120 μg/mL) against Staphylococcus aureus. The treatment combination of CN77 (8.75 or 4.37 μg/mL) and turmeric powder (9.37 or 4.68 μg/mL) exerted synergistic growth-inhibiting effects on Aeromonas hydrophila, Candida albicans, and Pseudomonas aeruginosa. Photodynamic therapy using 2X MIC of CN59 decreased the growth of Enterococcus faecalis by 4.18-fold compared to the control group and completely inhibited the growth of Escherichia coli. The results of the hemolytic assay revealed that the test compounds were not cytotoxic with half-maximal inhibitory concentration values ranging from 49.65–130.9 μM. The anticoagulant activity of most compounds was comparable to that of warfarin but higher than that of heparin. This indicated that these compounds target the intrinsic coagulation pathway. These results demonstrated that these CNs are a safe and promising alternative for curcumin.

Phytochemical Analysis, In vitro Antibacterial Activity and Rate of Kill of Different Fractions of Dacryodes edulis Leaf

Dacryodes edulis is a fruit tree attaining a height of 18–40 meters mostly grown around the house and rarely in the forest. It has a relatively short trunk and a deep, dense crown and it is native to Africa hence often called African pear. The leaves are a compound with 5-8 pairs of leaflets. Acetone extract/solvent fractions of the leaves of Dacryodes edulis were used. The in vitro antibacterial activities and rate of kill of different fractions were investigated. The phytochemical screening was done by some chemical tests, antibacterial activity by agar well diffusion method and rate of kill was carried out on S. aureus and E. coli organisms. The fractions exhibited antibacterial activities with zones of inhibition ranged between 20 and 30 mm by Aqueous (AQU) fraction while Dichloromethane (DCM) fraction ranged between 22 and 32 mm. The standard antibiotics, streptomycin ranged between 10 and 20 mm and ampicillin between 11 and 27 mm. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of both fractions had range values between 0.78 and 6.25 mg/mL. The phytochemical screening revealed the presence of alkaloids, tannins, saponins, flavonoids, terpenoid and glycoside. Overall, the two fractions had better activities than the standard antibiotics used. The time kill assay showed that the percentage of the cells killed increased with increasing concentrations of the fractions, as well as, contact time intervals. The AQU fraction killed 100% of Escherichia coli and Staphylococcus aureus cells at concentration of 4.68 mg/mL (3 X MIC) within 120 min while DCM fraction killed 100% of Escherichia coli cells within 90 min at a concentration of 4.68 mg/mL and killed 100% of S. aureus cells within 120 min at a concentration of 3.12 mg/mL (2X MIC). In conclusion, D. edulis leaf fraction has a broad spectrum antibacterial activity, with the AQU and DCM fractions being bactericidal as exemplified by the killing rate and MIC index of 2 (ratio of MBC/MIC) for both fractions.

&lt;I&gt;In vitro&lt;/I&gt; evaluation of the inhibitory effect of 3, 5-dichloro-2- pyridone on &lt;I&gt;Mycobacterium tuberculosis&lt;/I&gt; H37Rv

Purpose: To investigate the anti-tuberculosis potential of twelve commercially available pyridone analogues against Mycobacterium tuberculosis H37Rv strain.Methods: Twelve commercially available pyridone-based compounds were screened against M. tuberculosis H37Rv using different susceptibility tests. The most active or lead compound was further evaluated in detail for its anti-tuberculosis (anti-TB) potential. Kill kinetics was used to determine the dynamics of its anti-TB activity in vitro.Results: Compounds d, j and k were potent against M. tuberculosis H37Rv, with minimum inhibitory concentrations (MICs) of 10, 5 and 10 μg/mL, respectively. The standard anti-TB drugs used in this study (positive control drugs) demonstrated MIC of 2.5 μg/mL. The anti-TB effect of compound j was comparable with those of the standard drugs (RIF, LVX, AMK, EMB and INH). The minimum bactericidal concentration (MBC) of compound j was 10 μg/mL. It produced an MIC of 5 μg/mL in agar proportion method (APM). However, its MIC in Middlebrook 7H9 broth supplemented with 10 % fetal bovine serum (FBS) and 4 % bovine serum albumin (BSA) increased 4- and 8-fold, respectively. The bactericidal effect of compound j was time- and concentration-dependent at dilutions above 2x MIC. Combination of compound j with RIF, LVX or AMK exhibited fractional inhibitory concentration index (ΣFIC) of 1, indicative of additive drug-drug interactions. However, combination with INH or EMB produced a ΣFIC of 2. None of the tested drug combinations was antagonistic.Conclusion: Compound j exhibits potent time- and concentration-dependent antimicrobial effect against M. tuberculosis H37Rv. Thus, it may be suitable as an adjunct to current treatment of drug sensitive and drug-resistant TB.&#x0D; Keywords: Tuberculosis, Mycobacterium tuberculosis, Pyridone analogs, Antimicrobial activity, Antibiotics

Activity of ceftazidime-avibactam alone and in combination with polymyxin B against carbapenem-resistant Klebsiella pneumoniae in a tandem in vitro time-kill/in vivo Galleria mellonella survival model analysis

Ceftazidime-avibactam is used clinically in combination with a polymyxin for the treatment of carbapenem-resistant Gram-negative infections; however, there are limited data to support this practice. The objective of this study was to evaluate the activity of ceftazidime-avibactam and polymyxin B alone and in combination against Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae in a tandem in vitro time-kill/in vivo Galleria mellonella survival model assay. Three KPC-3-producing K.pneumoniae clinical isolates were used for all experiments. All isolates harbored mutations in ompk35 and one isolate in ompk36; two isolates were susceptible to both ceftazidime-avibactam and polymyxinB, and one was resistant to both. Ceftazidime-avibactam was bactericidal against 2 of 3 strains at ≥2x minimum inhibitory concentration (MIC) whereas polymyxin B was not bactericidal against any strain at any concentration. Combinations at 1/4x or 1/2x MIC were not bactericidal or synergistic against any of the 3 isolates. In survival experiments, ceftazidime-avibactam at 4x MIC significantly improved larval survival over the untreated control strain whereas polymyxin B at 4x MIC did not. Combining polymyxin B with ceftazidime-avibactam at 4x MIC did not improve survival compared to ceftazidime-avibactam alone. This work indicates there is no improvement in in vitro bactericidal activity or in vivo efficacy when polymyxin B is combined with ceftazidime-avibactam against KPC-producing K.pneumoniae. This combination should be avoided in lieu of ceftazidime-avibactam alone or other potentially more efficacious, less toxic combination regimens.

Effect of Helicobacter pylori biofilm formation on susceptibility to amoxicillin, metronidazole and clarithromycin

The human gastric pathogen Helicobacter pylori forms biofilms in vitro and in vivo. We previously demonstrated that H. pylori biofilm formation in vitro decreased its susceptibility to clarithromycin (CAM). The aim of this study was to evaluate the effects of biofilm formation on amoxicillin (AMPC) and metronidazole (MNZ) susceptibility. In addition, we assessed the influence of biofilms of CAM resistant H. pylori on CAM susceptibility. It was shown that high levels of efflux pump gene transcripts were detected in biofilm cells of all H. pylori strains used in this study. H. pylori biofilm biomass was significantly decreased compared to initial biomass after treatment with the minimum inhibitory concentration (MIC) of AMPC. Similarly, the biofilm biomass of H. pylori decreased after treatment with MIC of MNZ, although the difference was not statistically significant. However, minimum bactericidal concentrations (MBCs) of AMPC or MNZ to biofilm cells were higher than those of planktonic cells. The biofilm biomasses of all of the CAM resistant strains were significantly decreased compared to initial biomass after treatment with 2x MIC of CAM. However, the viability of the CAM treated biofilm cells with 2x MIC of CAM was not significantly reduced compared to initial cell numbers with the exception of one strain. The viability of biofilm cells of all strains was higher than that of planktonic cells after treatment with various concentrations of CAM. These results indicate that biofilm cells were more resistant to these antibiotics than planktonic cells and that the assessment of the ability to form biofilms in H. pylori is important for eradication of this microorganism.

Time-kill assay and post-antibiotic effect of acetone extract from the stem bark of Canarium odontophyllum against Methicillin-resistant Staphylococcus aureus Mu50 strain

Canarium odontophyllum Miq. is an indigenous fruit found in Sarawak, Malaysia. Methicillin-resistant Staphylococcus aureus (MRSA) is a deadly pathogen that causes to hospital (HA-MRSA) and community (CA-MRSA) infections worldwide. Vancomycin has been the therapeutic drug of choice against MRSA but unfortunately this pathogen has developed some degree of resistance to vancomycin. This research aimed to evaluate the antimicrobial activity of the stem bark extract of C. odontophyllum against MRSA Mu50 strain. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of extract and vancomycin against MRSA were determined using broth microdilution method and streak plate method. The rate of killing by the extract against was determined using time-kill assay (TKA) at 1X MIC, 2X MIC, 4X MIC and 8X MIC of the extract. The post-antibiotic effect (PAE) time of extract 10X MIC against MRSA was also investigated. The extract exhibited bacteriostatic effect against MRSA Mu50 strain with MIC and MBC values of 1.563 mg/ml and 3.125 mg/ml, respectively. From TKA analysis, the extract was not capable of killing the Mu50 strain at 1XMIC and 2XMIC but it displayed bactericidal activity at higher concentrations tested. Interestingly, the acetone stem back extract of C. odontophyllum at 4XMIC showed comparable time-killing kinetic with the standard antibiotic in the study. The PAE time of the extract was 3.6 ± 0.51 hr against MRSA Mu50 compared to vancomycin at 2.4 ± 0.68 hr. In conclusion, the stem bark acetone extract from C. odontophyllum demonstrated concentration-dependent bactericidal effect with prolonged PAE time against MRSA Mu50 strain.

Antibacterial Effects of Glycyrrhetinic Acid and Its Derivatives on Staphylococcus aureus.

Staphylococcus aureus is a major pathogen in humans and causes serious problems due to antibiotic resistance. We investigated the antimicrobial effect of glycyrrhetinic acid (GRA) and its derivatives against 50 clinical S. aureus strains, including 18 methicillin-resistant strains. The minimum inhibitory concentrations (MICs) of GRA, dipotassium glycyrrhizate, disodium succinoyl glycyrrhetinate (GR-SU), stearyl glycyrrhetinate and glycyrrhetinyl stearate were evaluated against various S. aureus strains. Additionally, we investigated the bactericidal effects of GRA and GR-SU against two specific S. aureus strains. DNA microarray analysis was also performed to clarify the mechanism underlying the antibacterial activity of GR-SU. We detected the antimicrobial activities of five agents against S. aureus strains. GRA and GR-SU showed strong antibacterial activities compared to the other three agents tested. At a higher concentration (above 2x MIC), GRA and GR-SU showed bactericidal activity, whereas at a concentration of 1x MIC, they showed a bacteriostatic effect. Additionally, GRA and GR-SU exhibited a synergistic effect with gentamicin. The expression of a large number of genes (including transporters) and metabolic factors (carbohydrates and amino acids) was altered by the addition of GR-SU, suggesting that the inhibition of these metabolic processes may influence the degree of the requirement for carbohydrates or amino acids. In fact, the requirement for carbohydrates or amino acids was increased in the presence of either GRA or GR-SU. GRA and GR-SU exhibited strong antibacterial activity against several S. aureus strains, including MRSA. This activity may be partly due to the inhibition of several pathways involved in carbohydrate and amino acid metabolism.

English

Anadenanthera colubrina (Benth) Brenan, a plant known in the Northeastern Region of Brazil as angico, is widely used in traditional folk medicine to treat respiratory and inflammatory diseases. This study aimed to evaluate the antifungal activity, determine the minimum inhibitory concentration (MIC), the minimum fungicidal concentration and the fungal kinetics (death curve) in addition to the interactive effect of the dry extract of angico in association with the antifungals fluconazole and nystatin against yeasts of the genus Candida. The dry extract was obtained by rotoevaporation. Tests for evaluation of antifungal activity, determination of the MIC and the MFC as well as the evaluation of the interactive effect with conventional antifungal were done by disk diffusion and microdilution technique. For the evaluation of the angico&rsquo;s effect on fungal growth, death curve was utilized. The results show the angico&rsquo;s antifungal potential in all of the strains tested, having MIC of 1.0 mg/mL. It was observed that the fungal kinetics of 2x MIC, MIC and &frac12; MIC had similar effects; 6 h was their best time after incubation. There was fungistatic activity reduction (2 log 10 UFC/mL) from the initial inoculum of 1.0 mg/mL. Interactive effect was not observed when used in association with nystatin, but showed synergistic effect when used with fluconazole. In these data, one can see that angico is a species rich in biological activity; being promising species, the isolation and detection of its bioactive compounds is necessary. Key words: Angico, Candida albicans, natural product.

Morphological and Bactericidal Effects of Different Antibiotics on Helicobacter pylori.

Background:Helicobacter pylori (H. pylori) is a spiral Gram negative bacteria that can transform to the coccoid form in adverse conditions.Objectives:The aim of this study was to determine the in vitro morphological and bactericidal effects of metronidazole, amoxicillin and clarithromycin on H. pylori.Materials and Methods:The standard strain 26695 of H. pylori was cultured on Brucella agar (BA) and the minimum inhibitory concentrations (MICs) of three antibiotics were determined by E-test method. The bacteria were exposed to antibiotics at 1/2 MIC, MIC and 2X MIC concentrations in Brucella broth (BB). Induced coccoid forms were confirmed by Gram staining and light microscopy. The viability of cells as well as the susceptibility of viable coccoids to antibiotics were examined using the flow cytometry method.Results:All of the three antibiotics at sub-MIC induced coccoid forms. The highest rates of coccoids (> 90%) were induced at 0.008 μg/mL concentration (1/2 MIC) of amoxicillin, 72 hours postexposure. Metronidazole and clarithromycin with 1/2 MIC (0.5 and 0.125 µg/mL respectively) induced lower rates of coccoid forms (60% and 40% respectively). Potent bactericidal effects on coccoids were observed with Metronidazole at 2X MIC and clarithromycin at MIC (0.25 µg/mL) (80 - 90%). Amoxicillin with MIC and 2X MIC had no bactericidal effect on coccoid forms.Conclusions:Despite the good in vitro bactericidal effect of amoxicillin on spiral forms of H. pylori, this antibiotic has little effect on induced coccoids that may develop after the inappropriate in vivo antibacterial treatment. Hence, for successful therapy, it is essential not only to eradicate the spiral forms, but to eliminate the viable coccoids.

Impact of postantibiotic effect on bacterial adherence to vascular prostheses

The brief exposure of bacteria to high antibiotic concentrations can result in prolonged suppression of bacterial growth termed postantibiotic effect (PAE). Apathogenic Staphylococcus epidermidis strain (RP-62) was exposed to 2× and 6× minimum inhibitory concentrations (MIC) of cefazolin, vancomycin, or rifampin for 1 hr and incubated for 2 to 24 hr in inhibitory-free broth. PAE was defined as the difference in time required for a 1.0 log increase in test ( T) vs control ( C) cultures (PAE = T - C). PAE was observed only for rifampin: 6 hr at 2× MIC and 8 hr at 6X MIC. Bacterial adherence to Dacron grafts was calculated in PAE vs control cultures by a quantitative culture technique for graft specimens incubated 2 to 24 hr. A demonstrable PAE and its impact on adherence were found to be both antimicrobial and concentration dependent. A significant decrease in staphylococcal adherence to velour-knitted Dacron was demonstrated by rifampin at 2X MIC ( P < 0.05) and 6X MIC ( P < 0.01). This phenomena may be useful in reducing bacterial adherence and colonization of bioprosthetics in the perioperative period. Preoperative suppression of staphylococcal skin flora by high dose antimicrobials can alter the capacity of these organisms to adhere to vascular prosthetic grafts and, if incorporated into antibiotic prophylaxis regimens, may reduce graft colonization.

Kinetics of the actions of tetracyclines on Escherichia coli as studied by microcalorimetry.

Microcalorimetry was used to study the kinetics of the actions of various tetracyclines on a strain of Escherichia coli. Differences in the capacity to suppress the metabolism of this bacterium were observed. When the antibiotic was present from the start of the experiment, a heat production of 2.0 muW/ml was registered after 12.5 h using minocycline; the corresponding figures for doxycycline, oxytetracycline, and tetracycline were 7.3, 6.6, and 4.5 h, respectively. In these experiments, equal concentrations, i.e., half the minimum inhibitory concentration (MIC), of each drug were used. The MIC for all the tetracyclines tested, determined by the broth dilution technique, was 0.8 mug/ml. In other experiments, the antibiotic (concentration, 1.6 mug/ml = 2x MIC) was introduced into the growth vessel during the logarithmic growth phase of the organism. The extent and duration of the inhibitory effect on the metabolism, as judged from the decrease in heat production, varied with the different tetracyclines. Immediately after introduction, minocycline, doxycycline, oxytetracycline, and tetracycline decreased the heat production in decreasing order of potency. With tetracycline, the heat production rose after about 1 h, and with minocycline it rose after about 9 h. The heat production remained at a low level for at least 19 h when using doxycycline and oxytetracycline. The results indicate that microcalorimetry offers a means for studies of the kinetics of the antibacterial actions of antibiotics and provides information that cannot be obtained by conventional bacteriological techniques. This information may be of use, in conjunction with pharmacokinetic data, in establishing optimum doses and dose intervals in antibiotic therapy.