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The effect of gentamicin against 130 clinical isolates of Pseudomonas aeruginosa was compared with that of two investigational aminoglycoside antibiotics, tobramycin and amikacin. Minimal inhibitory concentration data indicated that, on a weight basis, tobramycin was two to four times as active as gentamicin against most isolates. However, 14 of 18 organisms highly resistant to gentamicin (≥80 μg/ml) were also highly resistant to tobramycin. Amikacin was the least active aminoglycoside on a weight basis, but none of the isolates were highly resistant to this antibiotic. When therapeutically achievable concentrations were used, adding carbenicillin to gentamicin or to tobramycin enhanced inhibitory activity against those isolates susceptible (≤5 μg/ml) or moderately resistant (10 to 40 μg/ml) to the aminoglycoside. Such synergy was seldom demonstrated for isolates highly resistant to gentamicin or tobramycin. The combination of carbenicillin and amikacin enhanced inhibition against all but two of the isolates. Both tobramycin and amikacin offer in vitro advantages over gentamicin against P. aeruginosa .

Hospital isolates of Escherichia coli resistant to tetracycline (TC) were studied to identify mechanisms which regulate TC resistance levels and ability to transfer TC resistance. Antibiotic resistance patterns, resistance levels to TC, and ability to transfer TC resistance were determined for the isolates. Similar data were obtained for the transferable plasmids after transfer to several new host strains of E. coli . Of the 110 isolates, 50% were able to transfer TC resistance by conjugation. There was a nearly linear relationship between the minimum inhibitory concentration (MIC) of TC for the hospital strains and the percentage of strains at a given MIC that could transfer TC resistance. The strains that were simultaneously resistant to tetracycline, streptomycin, and ampicillin had relatively high MICs of TC and high ability to transfer TC resistance. These results and surveys of TC-resistant E. coli by others suggest that TC resistance levels and transmissibility may be influenced by other resistance markers. The isolates which did not transfer TC resistance by conjugation were tested for the presence of TC resistance plasmids by mobilization or by transformation with deoxyribonucleic acid from the isolates. Evidence for plasmid-mediated TC resistance was found in 92 (84%) of the 110 hospital strains.

The cephalosporin group of antibiotics has a poor record in therapy of gonorrhea. In this study a new parenteral cephalosporin C derivative, cefazolin, was examined alone and with probenecid, and the two regimens were compared with aqueous procaine penicillin G plus probenecid in the treatment of uncomplicated gonorrhea. Two grams of cefazolin resulted in nine t ailures among 31 patients (29%). The same dose of cefazolin plus 1.0 g of probenecid resulted in six failures among 31 patients (19.3%). The control schedule of 4.8 X 106 units of aqueous procaine penicillin G plus 1.0 g of probenecid resulted in only one failure among 30 patients (3.3%). Levels of cefazolin were determined in sera of 10 patients; at 6 hr the mean serum level in patients who had received cefazolin plus probenecid was twice that in those who had received cefazolin alone. Serum levels of cefazolin were at least 10 times the mean minimal inhibitory concentration of cefazolin of 2.76 p[g/ml at 6 hr in eight of 10 subjects.

Thirty-five patients with a variety of serious infections caused by anaerobic bacteria responded to clindamycin. Cure was achieved in 27 of the 32 patients with pleuropulmonary and intra-abdominal infections. Mean serum concentrations of clindamycin for the 8 h after intramuscular administration of clindamycin in these patients were at least 2.5 times the minimal inhibitory concentration of clindamycin for more than 90% of anaerobes. This experience suggests that clindamycin is an excellent and relatively safe antibiotic for treatment of infection caused by anaerobes when combined with surgery (when indicated) or other antibiotics active against aerobic gram-negative bacilli, if present.

17 patients with maxillary sinusitis were given a single dose of either penicillin only, or penicillin in combination with tetracycline. Samples of sinus secretions were aspirated at intervals and, simultaneously, a blood sample was obtained. The antibiotic concentrations were determined by an agar diffusion method using paper discs as diffusion centres. Neither penicillin nor tetracycline showed any uniform relationship between the concentrations in serum and secretion after a single dose. In 8 of the 20 secretions, the concentrations of penicillin exceeded the upper limit of minimal inhibitory concentration (MIC) for bacterial sensitivity group 1, i.e. 0.25 μg/ml. A rise in the serum concentration of penicillin was associated with a greater chance of attaining this value. The tetracycline concentration exceeded 1.0 μg/ml (the upper limit of MIC in group 1) in only 3 of 16 secretions. In 2 patients receiving repeated doses tetracycline accumulated in the secretions resulting in concentrations abo...

A membrane fraction from Pseudomonas aeruginosa KM 338 was shown to catalyze in vitro peptidoglycan synthesis from uridine 5′-diphosphate- N -acetylmuramyl- l -alanyl- d - glutamyl-meso-diaminopimelyl- d -alanyl- d -alanine and uridine 5′-diphosphate- N -acetylglucosamine. Synthesized peptidoglycan was partially cross-linked by transpeptidation, which was accompanied by the release of d -alanine. This reaction was strongly inhibited by 25 and 50 μg of penicillin G and carbenicillin per ml respectively, whereas the intact cells were relatively resistant to penicillins (minimal inhibitory concentration of penicillin G and carbenicillin, 30 and 0.125 mg/ml, respectively). Soluble d -alanine carboxypeptidase present in P. aeruginosa KM 338 was studied as well, which was found almost completely inhibited by penicillin G and carbenicillin (10 μg/ml).

The activities of cephaloridine, cephalothin, and ampicillin against dense cultures of 103 ampicillin-resistant gram-negative bacilli were compared in a turbidimetric system. The organisms were divided into two groups according to their behavior in conventional minimal inhibitory concentration titrations: those fully resistant to ampicillin at a concentration of 500 /ug/ml and those inhibited by 32-500 Mtg of ampicillin/ml. Of the 83 strains in the first group, most were more sensitive to cephalothin than to cephaloridine, whereas the 20 strains in the second group exhibited a number of interesting properties peculiar to them. On the basis of thise and previous results, six distinct categories of resistance to f-lactam antibiotics have been detected among enterobacteria. When tested by conventional titration with a comparatively low bacterial inoculum, cephalosporins often appear to be very active against enterobacteria regardless of the sensitivity of such strains to ampicillin, but a marked inoculum effect is found [1-6]. Our own turbidimetric studies [7] have shown that dense

Broth dilution minimal inhibitory concentration (MIC) readings were compared after different incubation periods and with different inoculum concentrations. The purpose was to determine the best conditions for obtaining early results as close as possible to overnight readings. Initially, 76 antibiotic-organism combinations were tested using the International Collaborative Study technique and inoculum and were read after 3, 8, and 18 h of incubation. Approximately 28% of tests showed fourfold or greater increases in MICs after 18 h of incubation compared with the 3-h readings. No overnight MICs were lower than early readings. MICs of single antibiotics against seven organisms were also read with an automatic particle counter to confirm the validity of the visual readings. Experiments were made to determine whether inoculum manipulation could reconcile the differences between 3- and 18-h MIC results. One hundred and eight organism-antibiotic combinations were tested comparing 3-h MIC readings using an inoculum of 10 7 organisms per ml with overnight readings using 10 5 per ml. In 71 cases, readings with both inocula were within the range tested and 57 (86%) were within ±1 log 2 of each other and followed an approximately normal distribution. Improved comparability between early read and overnight MICs thus may be achieved by inoculum manipulation, and this may be a suitable approach in the future development of automated procedures.

By disk diffusion antimicrobial susceptibility testing, 11% of 313 consecutive strains of Pseudomonas aeruginosa , examined during July to October 1973, were resistant to gentamicin (minimal inhibitory concentration 12.5 to >100 μg/ml), and a further 31% were moderately resistant (6.25 to 12.5 μg/ml) to gentamicin at the University of Alberta Hospital in Edmonton, Canada. Of 45 gentamicin-resistant strains from that hospital, none possessed R-factors or gentamicin-inactivating enzymes. Eight of 13 strains obtained from three American sources, which contained gentamicin-acetylating (12 strains) or -adenylating (1 strain) activity, conjugally transferred both gentamicin resistance and antibiotic-inactivating activity. P. aeruginosa recipients were much more effective for detection of transferable gentamicin resistance than Escherichia coli recipients, although not all P. aeruginosa were equally as effective as recipients. One strain, POW 151, transferred resistance to both carbenicillin and gentamicin as well as to several other antibiotics. R-factors detected belonged to P-2 and P-3 (Com 6, C) incompatibility groups. Expression of gentamicin resistance due to acetylation of gentamicin was subject to marked phenotypic lag, especially in recipient strain P. aeruginosa 280. This was shown to result in the failure to detect gentamicin resistance transfer if the concentration of gentamicin in selection media was too high (>2.5 μg/ml for strain 280). Some but not all recipients were changed in pyocine type upon acquisition of R-factors.

Micrococcus radiodurans strains R I and R II5 were tested for susceptibility to several antibiotics by the standardized Bauer-Kirby disc diffusion and tube dilution techniques, using different size of inoculum irradiated at doses of 150, 300, 500 and 750 krad; a control without irradiation. The size of inoculum had a variable effect on susceptibility, depending on the strain of M radiodurans , the antibiotics, and the dose of irradiation. In general, strain R I was more sensitive to the antibiotics and the radiation than R II5 . The minimal inhibitory concentration (MIC) and the minimal bactericidal (MBC) of the antibiotics against M radiodurans were determined.

The activities of polymyxin B sulphate, colistin (polymyxin E) sulphate and their sulphomethyl derivatives were compared by continuous turbidimetric monitoring of dense cultures of an Escherichia coli strain exposed to these agents. Judged by the concentration of antibiotic which caused a rapid fall in opacity of the culture, polymyxin B sulphate and colistin sulphate had similar activities, but the sulphomethyl compounds differed considerably: sulphomyxin sodium induced lysis of the culture at a concentration four times that of the parent compound, whereas colistin sulphomethate sodium induced a delayed fall in opacity consistent with recruitment of activity as the inactive sulphomethyl derivative was broken down to the parent compound. Durign overnight incubation, regrowth of cultures which had initially succumbed to polymyxin action occurred, apparently due to the selection of phenotypically resistant variants from within the population. In this way cultures could easily be adapted to growth in concentrations of antibiotic well above the conventionally-determined minimum inhibitory concentration. The comparative ease of adaptation was in the order: colistin sulphomethate greater than sulphomyxin greater than colistin sulphate greater than polymyxin B sulphate.

The activity of minocycline and tetracycline against 23 isolates of Acinetobacter calcoaceticus var. anitratus (syn. Herellea vaginicola ) and 178 strains of Serratia marcescens was determined by disk and microdilution methods. The results indicate that minocycline is highly active against this species of Acinetobacter , all but one strain being inhibited by 0.007 μg of the antibiotic per ml. Tetracycline was also active, though to a lesser degree, against A. calcoaceticus . Of the 178 strains of S. marcescens tested, only seven (3.9%) had a minimum inhibitory concentration of 2 μg or less of minocycline per ml. Tetracycline was less active than minocycline against S. marcescens ; with 2 μg of tetracycline per ml, only 2 of 152 (1.3%) strains were inhibited. At concentrations of 8 and 16 μg of minocycline per ml, which can be achieved in the urine with the usual doses, 44.9 and 63.5% of S. marcescens strains were inhibited, which implies its possible usefulness for the therapy of urinary tract infection due to this organism.

One hundred and seventy-one strains of anaerobes were tested for susceptibility to carbenicillin by using agar dilution, broth dilution, and two disk diffusion methods. The minimal inhibitory concentration (MIC) for 67% of 51 strains of Bacteroides fragilis , 7 of 9 strains of Bacteroides melaninogenicus , and all of 8 strains of Eubacterium was 100 μg or less per ml. The MICs of the remaining anaerobes were 50 μg or less per ml. The broth dilution results were felt to be the most accurate of the four methods utilized.

The in vitro activity of amphotericin B and 5-fluorocytosine against 40 isolates of different species of Candida was studied. Synergism was seen in 35 of 40 organisms studied (88%) with achievable serum concentrations of the antibiotics. Synergism was striking in many strains that were resistant to 5-fluorocytosine. When the minimal inhibitory concentration of 5-fluorocytosine was greater than 400 mug/ml, synergism was seen in 18 of 20 isolates of Candida (90%).

In vitro antibacterial activities of ampicillin and amoxycillin were compared against pigmented and non-pigmented strains of Serratia marcescens. Ampicillin appeared more effective than amoxycillin; three-fourths of all strains consistently exhibited an ampicillin minimum inhibitory concentration (MIC) of at least one tube less than that recorded for amoxycillin. Complete cross resistance was not observed as has previously been inferred. Further, greater bactericidal activity was demonstrated with ampicillin; minimum bactericidal concentrations (MBC) were either the same as or one tube greater than the MIC. MBC's for amoxycillin, however, were significantly higher; often four to five times greater than the MIC. Ampicillin exhibited greater bactericidal activity as inferred from differences observed in the biological lesions induced, as recorded through observations by scanning electron microscopy (SEM). Spheroplasts were the predominant morphological alteration induced by ampicillin. In contrast, only filament formation, which demonstrated a degree of reversibility, was induced by amoxycillin.

The Pseudomonas R factor RP1 determines an inducible tetracycline resistance similar to that described for Escherichia coli R factors. The level of RP1-determined resistance measured by minimal inhibitory concentration testing is dependent on the host bacteria and corresponds to the magnitude of decrease in tetracycline accumulation by RP1-containing organisms. The tetracycline resistance mechanism is inactivated at low temperatures. The effect of metabolic inhibitors on tetracycline accumulation by susceptible organisms under various conditions indicates a possible nonspecific effect of cellular energy metabolism on tetracycline uptake.

In tube dilution studies, large discrepancies between inhibitory and bactericidal concentrations of BL-P1654 against Pseudomonas were observed. To explain these discrepancies which were not observed with carbenicillin, the kinetics of bacterial killing by these two penicillins were evaluated and compared. The kinetics of bacterial killing by both antimicrobial agents were characteristic of a penicillin, with killing initiating simultaneously with growth. Kill curves revealed the presence of a small number of cells resistant to BL-P1654 which were not detectable macroscopically. Studies on microbial resistance also showed the presence of a small but consistent number of cells resistant to BL-P1654 over a broad range of concentrations above its minimal inhibitory concentration. This pattern of resistance was not observed with carbenicillin. Thus, the discrepancies between inhibitory and bactericidal concentrations of BL-P1654 were not due to any unusual bacteriostatic activity but rather due to a small number of resistant cells whose presence could be detected only by sensitive subculturing techniques.

The minimal inhibitory concentrations of clindamycin and gentamicin alone and in combinations were determined by a microdilution method for 163 aerobic, facultative, and anaerobic clinical isolates. All 77 strains of Staphylococcus aureus, Diplococcus pneumoniae, Streptococcus pyogenes , and anaerobic bacteria (except for three strains of Clostridium ) were inhibited by 1.6 μg or less of clindamycin per ml. Gentamicin did not interfere with the activity of clindamycin within the range of concentrations tested (0.1 to 100 μg/ml); for some strains combinations were synergistic. Sixty-two (94%) of 66 strains of Enterobacteriaceae and Pseudomonas aeruginosa were inhibited by 6.2 μg or less of gentamicin per ml. Combinations of clindamycin and gentamicin were indifferent for 29 strains and synergistic for 33 strains. All 20 strains of enterococcus, three strains of Clostridium , three strains of Escherichia coli , and one strain of Proteus rettgeri were resistant to both clindamycin (minimal inhibitory concentration greater than 3.1 μg/ml) and gentamicin (minimal inhibitory concentration greater than 6.2 μg/ml). Combinations of clindamycin and gentamicin were indifferent for 16 and synergistic for 11 of the resistant strains. Except for clindamycin-sensitive isolates, synergy was usually observed only at concentrations of one or both drugs which are not readily obtainable in vivo. Antagonism was never observed.

SUMMARY 185 Brucella strains distributed among the various biotypes of Br. abortus, Br. melitensis and Br. suis and including representatives of Br. canis, Br. neotomae and Br. ovis, were examined for in vitro sensitivity to the antibiotic, spectinomycin. All Br. canis, Br. neotomae and Br. ovis strains tested were sensitive to spectinomycin, as were all strains examined of Br. abortus biotypes 1, 5 and 9, and Br. suis biotypes 1 and 5. Strains of the 3 Br. melitensis biotypes and the remaining biotypes of Br. abortus and Br. suis showed variable sensitivity. The minimum inhibitory concentration for sensitive strains ranged from 1–10 μg/ml and on most of these the antibiotic had an incomplete bactericidal action at therapeutic concentrations.

Synergistic antifungal activity of 5-fluorocytosine (5-FC) and amphotericin B was studied using an abbreviated checkerboard titration scheme. 5-FC was titrated in twofold increments (100 to 0.05 μg/ml) in the absence and presence of graded increments of amphotericin B (1.0. 0.5, 0.1, 0.05, and 0.01 μg/ml) in buffered yeast nitrogen base. A limited number of experiments were performed using expanded dual titration checkerboard schemes and growth curve studies. Forty-eight isolates of yeastlike organisms were tested; two were inhibited by the buffer system. Evidence of synergy, as indicated by a fourfold or greater reduction of the minimal inhibitory concentration of 5-FC in the presence of subinhibitory concentrations of amphotericin B, was seen with 11 of 46 isolates, or 24%, at the fungistatic level and with three isolates, or 7% at the fungicidal level. Indifferent results were obtained for 44 and 74% of the isolates, respectively, at the fungistatic and fungicidal levels. Antagonism was observed with three isolates.

A strain of Staphylococcus aureus was planted on filter membranes placed on Trypticase soy agar (BBL). After incubation, the membranes with growing staphylococci were transferred to Trypticase soy agar containing a subinhibitory concentration of penicillin (one-third minimal inhibitory concentration) and again incubated. The membranes were then returned to drug-free agar and incubated once more. Counts of the colony-forming units and electron microscopy were carried out at several time intervals. When grown on agar containing penicillin, the staphylococci formed what appeared to be abnormally large cells with multiple and unusually thick septa. Examination of a number of sections showed that these large cells were in reality clusters of staphylococci that had divided but failed to separate. When these large cells were subsequently grown on drug-free agar, smaller cells and normal staphylococci emerged. Subinhibitory concentrations of penicillin do not kill staphylococci; they seem to inhibit lysis of cross walls, preventing the separation of otherwise divided cells.

In vitro sensitivity to 5-fluorocytosine (5-FC) of 35 Candida strains (14 C. albicans, 10 C. tropicalis, 5 C. parapsilosis, 2 C. guilliermondii, 2 C. krusei, 2 C. pseudotropicalis), isolated from the eyes of patients suffering from various external ocular inflammations who had not been treated with 5-FC, was tested and compared to that of standard Candida species. The minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) of 5-FC for the strains isolated from ocular infections ranged from 0.06 to 1.95 mug/ml and from 0.24 to 7.81 mug/ml, respectively, indicating that no primary resistant strains to 5-FC were found in this series.

A system for the rapid and relatively synchromous germination of conidia from a clinical isolate of Aspergillus fumigatus is described. The polyene-mediated release of K plus from germinating conidia has been determined. Ungerminated conidia were insensitive to amphotericin B methyl ester (AME) at concentrations greater than 50 mug/ml, but rapidly became sensitive to 1 to 2 mug AME/ml during the intitial stages of germination. These findings have been correlated with minimum inhibitory concentration values obtained in studies of conidial germination and hyphal outgrowth using a variety of growth tests.

Dogs were used as a model for the study of the rate of appearance, peak concentrations, and rate of clearance of gentamicin sulfate in bronchial secretions. Gentamicin (dose, 1.7 mg/kg) was given by rapid intravenous infusion, by intramuscular injection, or as two divided intramuscular injections with a 4-hr interval. Intravenous infusion resulted in the highest bronchial concentrations of gentamicin, but the drug was cleared from the respiratory secretions in approximately 3 hr. In contrast, intramuscular injections gave low but more sustained bronchial levels of the drug. The time during which bronchial gentamicin concentrations exceeded a particular minimal inhibitory concentration for a susceptible bacterium such as Pseudomonas was related to the method of drug administration. Thus, to achieve the maximal antibiotic effectiveness, the minimal inhibitory concentration of gentamicin for the microorganism should be considered when the dose or frequency of parenteral gentamicin is prescribed.

Mannopeptins show in vitro antimicrobial activity against gram-positive and some gram-negative bacteria. The antimicrobial activity is unaffected by the addition of serum, and potentiated by alkaline pH or decrease in inoculum size. The antibiotics exert bectericidal effect at doses twice as high as the minimum inhibitory concentration. When the antibiotics were injected into mice through either intravenous, intraperitoneal, intramuscular or subcutaneous routes, the antimicrobial activity appeared within 15 minutes in the serum of mice and was slowly excreted in the urine. However, the antibiotics were poorly absorbed by the oral route. The antibiotics were capable of protecting mice from lethal infection produced by the intravenous injection of Staphylococcus aureus, Streptococcus pyogenes and the intraperitoneal injection of Shigella sp. and Escherichia coli, but ineffective against Salmonella typhosa.

Single doses of 3.5 g of ampicillin with 1.0 g of probenecid or of 3.0 g of amoxicillin alone were administered orally to 58 males and 56 females with uncomplicated gonococcal infection. The failure rate for genital or anal infection, or both, was 1.7% for ampicillin plus probenecid and 4.2% for amoxicillin alone. However, patients with oropharyngeal infection responded poorly. Seventy-five isolates of Neisseria gonorrhoeae recovered from patients in this study were all inhibited by 1.0 μg or less of ampicillin or amoxicillin per ml; penicillin G, ampicillin, and amoxicillin had similar activity in vitro against these isolates. Serum concentrations of amoxicillin in 10 volunteers remained above the minimal inhibitory concentration for most strains of N. gonorrhoeae for periods up to 10 h after a 3.0-g oral dose. After 2.0 g of ampicillin was given with probenecid, the serum levels during the 5- to 12-h period approached those achieved with 3.5 g of ampicillin plus probenecid, and actually exceeded levels attained during the same interval with 3.0 g of amoxicillin administered alone.

The sensitivity of Haemophilus influenzae to penicillins in vitro, determined either by serial antibiotic dilution in broth or by the disc method on agar, is apparently profoundly influenced by inoculum size if the results are read by macroscopic inspection. Microscopic inspection of the growth, however, reveals that the turbidity in heavily inoculated broth containing concentrations higher than the minimal inhibitory concentration is the product of L forms which have failed to succumb to osmotic lysis. Similarly, minute colonies appearing in the `inhibition zone' of disc tests are composed of L forms. In both broth and agar tests reduction of the osmolality of the medium from 340 to 144 mOsm per kg failed to bring about lysis of organisms exposed either to ampicillin or amoxycillin. The significance of this remarkable osmotic stability of haemophilus L forms is discussed in relation both to testing of sensitivity of this organism to penicillins and to persistence of chronic haemophilus infections of the lower respiratory tract.

A novel diffusion zone method of quantitative assay of the antibiotic sensitivity of bacterial strains was tested on freshly isolated gonococci. Smoothly variable estimates of the minimum inhibitory concentration of penicillin for these strains was obtained with sufficient accuracy and precision (coefficient of variation c. 10 per cent.) by means of a simple graphical analysis and without replication. Such estimates were free from the chief sources of error associated with the commonly applied 'incorporation' and 'diffusion' methods. The method revealed that 816 isolates of gonococci obtained in the Bristol area during a 6-month period fell into a large 'sensitive' group (MIC c. 0.02 unit per ml.) and three smaller more resistant groups, and that this pattern occurred in three widely spaced centres within the area. It is suggested that the method is capable of revealing details of distribution that may be masked by the usual techniques and that it is of wide applicability.

Three aminoglycoside antibiotics and two penicillins were compared for their in vitro activity against 60 isolates of Serratia, Pseudomonas, Proteus mirabilis , and indole-positive Proteus sp. Testing was done by the agar dilution method using Mueller-Hinton broth solidified with 1.5% agar. The activity of amikacin, aminodeoxybutirosin, and gentamicin against Proteus and Pseudomonas , as related to their peak blood levels, showed no significant differences. Amikacin was the most active against Serratia marcescens . Results using Mueller-Hinton media in broth dilution tests correlated with the agar dilution method except for Pseudomonas aeruginosa . The minimal inhibitory concentration for aminoglycosides in agar was considerably greater than the minimal inhibitory concentration in Mueller-Hinton broth, and the disparity was related to the higher divalent cation concentration of agar. BL-P1654 and carbenicillin were similar except that carbenicillin was much more active against indole-positive Proteus sp. Additionally, the ratio of bactericidal to bacteriostatic concentrations of BL-P1654 was considerably greater than for carbenicillin.

In considerations of susceptibilty testing of bacteria, linear regression has been used to relate minimal inhibitory concentration and zone size. Although lacking in statistical validity, this technique has been used for aerobic bacteria. Reports of anaerobic testing show much greater variation about the regression line; the errors of misclassification have not been analyzed. A bivariate "error rate-bounded" classification scheme is proposed for relating minimal inhibitory concentration and zone size of bacteria. This method requires the following clinical input: (1) specification of breakpoints of susceptibility as determined by minimal inhibitory concentrations and the pharmacology of the antibiotic, (2) determination of the relative importance of two types of errors, false resistant classification and false susceptible classification, and (3) determination of the acceptable rate of error of false classification. Based on this input the classification scheme determines the zone size, which gives the minimal error of misclassification with the known data on zone diameter and minimal inhibitory concentration.

A unique seven-membered heterocyclic-ring inhibitor of adenosine deaminase was studied. One preparation of the compound inhibited replication of herpes simplex virus in the absence of adenine arabinoside. In this capacity, the minimal inhibitory concentration of deaminase inhibitor for herpes simplex virus type 1 (HSV-1), with 50 percent reduction of plaque-forming units as the end point, was 37.7 mug/ml. This activity compared favorably with the inhibitory activity of ara-hypoxanthine (34.1 mug/ml). Another preparation of deaminase inhibitor lacked antiviral activity. On the other hand, the adenosine deaminase inhibitor was active at a concentration of 0.009 mug/ml as a potentiator of the inhibition of HSV-1 by adenine arabinoside. The potentiation of adenine arabinoside by deaminase inhibitor is about 4,000 times more potent than the activity of the direct inhibitory effect on HSV-1. The nature of the possible contaminant of the preparation in question is unknown. Coformycin, another inhibitor of adenosine deaminase, had no antiviral activity in the absence of adenine arabinoside.

A streptomycete was isolated from an Easter Island soil sample and found to inhibit Candida albicans, Microsporum gypseum and Trichophyton granulosum. The antibiotic-producing microorganism was characterized and identified as Streptomyces hygroscopicus. The antifungal principle was extracted with organic solvent from the mycelium, isolated in crystalline form and named rapamycin. Rapamycin is mainly active against Candida albicans; minimum inhibitory concentration against ten strains ranged from 0.02 to 0.2 mug/ml. Its apparent activity against Microsporum gypseum and Trichophyton granulosum is lower because of its instability in culture media on prolonged incubation required by these fungi. No activity was observed against gram-positive and gram-negative bacteria. Acute toxicity in mice is low.

The minimum inhibitory concentration (MIC) represents the concentration of antimicrobial at which there is complete inhibition of growth of organism. In order to determine the MIC of cloxacillin, 10 MRSA were previously detected from 40 clinical isolates of Staphylococcus aureus by polymerase chain reaction (PCR). Agar plate dilution test was used to determine the MIC of cloxacillin. The clinical samples were collected from Mymensingh Medical College Hospital, Mymensingh. The study was done in the Department of Medicine, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh from July 2006 to June 2007. The MIC of the cloxacillin for 5 MRSA strains were ≥32 (mg/ml), for 1 MRSA strain was ≥ 128(mg/ml) and for another 4 MRSA strains were above ≥128 (mg/ml). Antimicrobial susceptibility test of the isolated organisms were done by disc diffusion method. On antibiotic susceptibility test, MRSA strains showed 100% resistant against penicillin, oxacillin, cloxacillin and amoxycillin. Cent per cent susceptibility of MRSA was found against vancomycin, ciprofloxacin, erythromycin, fusidic acid and rifampicin. Key words: Minimum inhibitory concentration (MIC), antibiotic resistance, cloxacillin, methicillin-resistant Staphylococcus aureus (MRSA) DOI = 10.3329/bjvm.v6i1.1350 Bangl. J. Vet. Med. (2008). 6 (1): 121-126

Summary The relationship between pretreatment bacterial sensitivity to isoniazid, thiacetazone or PAS and the progress of East African patients with pulmonary tuberculosis treated with either isoniazid plus thiacetazone or isoniazid plus PAS has been studied in co-operative controlled trials. Patients were randomly allocated to treatment for one year, in-patients with isoniazid 200 mg. plus PAS (sodium salt) 10g daily, isoniazid 300 mg. plus thiacetazone 150 mg. daily, isoniazid 200 mg. plus thiacetazone 150 mg. daily or isoniazid 300 mg. plus thiacetazone 100 mg. daily and out-patients with isoniazid 200 mg. plus PAS (sodium salt) 10 g. daily or isoniazid 200 mg. plus thiacetazone 150 mg. daily. A total of 558 patients who complied with the clinical criteria for admission and who completed six months of treatment were divided into 497 patients with isoniazid-sensitive organisms initially (the INH-sensitive group) and 61 patients with isoniazid-resistant organisms in one or both of their pretreatment cultures (the INH-resistant group). All of the INH-resistant group denied, having received previous antituberculosis chemotherapy on admission, but when the 32 in-patients were requestioned later, six admitted to previous treatment with isoniazid. Moderate or greater radiographic improvement occurred during the first six months of treatment in 52% of the INH-sensitive group and in 36% of the INH-resistant group. Cavities became smaller or disappeared in 81% of the INH-sensitive group and in 69% of the INH-resistant group. The smear and culture results at three months were similar in the INH-sensitive and the INH-resistant groups receiving PAS plus isoniazid, but were more frequently negative in the INH-sensitive group than in the INH-resistant group treated with isoniazid plus thiacetazone. A negative culture at six months was obtained from 83% of 176 INH-sensitive patients and 52% of 21 INH-resistant patients treated with 10 PH and from 72% of 304 INH-sensitive patients and 38% of 39 INH-resistant patients treated with isoniazid plus thiacetazone. Cultures at six months were more often resistant to the second drug used in treatment (PAS or thiacetazone) in the INH-resistant group than in the INH-sensitive group. A negative culture at six months was obtained as often from the patients with pretreatment resistance to the two drugs used in treatment as from those with resistance only to isoniazid. The bacteriological progress of the patient was best associated with the proportion of the pretreatment strain growing on 0·2 μg./ml. isoniazid. less well associated with the proportion growing on 1.5 or 50μg./ml. and not associated with the minimal inhibitory concentration of isoniazid. Considerable variation was found between patients in the thiacetazone sensitivity of their pretreatment strains. The progress of 228 patients with initially isoniazid-sensitive organisms during treatment with isoniazid plus thiacetazone was studied in relation to pretreatment thiacetazone sensitivity. Moderate or greater radiographic improvement occurred during the first six months of treatment in 64% of 72 patients with pretreatment minimal inhibitory concentrations (MICs) of 1·0 μg./ml. thiacetazone or less, in 58% of 83 patients with MICs of 1·1–2·0 μg./ml. in 51% of 53 patients with MICs of 2·1–4·0 μg./ml., and in 22% of nine patients with MICs of more than 4·0 μg./ml. The corresponding proportions yielding a negative culture at six months were 79% of 75 patients, 75% of 87 patients, 68% of 53 patients and 50% of 10 patients, respectively. Similar associations were found between pretreatment sensitivity to thiacetazone and other measures of progress, namely, the emergence of isoniazid resistance at three months and at six months, and the classification of the bacteriological status of the patients at twelve months. Initial PAS sensitivity was investigated in 215 patients with initially isoniazid-sensitive organisms who were treated with PAS plus isoniazid in four chemotherapy studies in East Africa. PAS resistance was found in a pretreatment culture from 19 patients, but it was often not confirmed in further tests on the same culture in the same or in a different laboratory. The progress of the patients during treatment was similar in those with a PAS-resistant pretreatment culture and in those with sensitive cultures. Sporadic unconfirmed resistant results were obtained more often from East African than from British strains and it is suggested that strains of Indian origin which are known to have these characteristics, are sometimes present in East Africa.

The antibacterial effect of aqueous and ethanolic seed extracts of Dacryodes edulis was studied using agar diffusion technique. Extracts tested at a final concentration 2000;g/ml produced in vitro antibacterial activities in assays against food-borne bacterial isolates of Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Klebsiella aerogenes, Pseudomonas aeruginosa, Salmonella typhi and Proteus mirabilis. The highest zone of inhibition was obtained from ethanol extract at 2000;g/ml against Escherichia coli with a diameter of 28mm.The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the water extract ranged between 62.5-500;g/ml and 125-1000;g/ml respectively. The MIC and MBC of the ethanol extract ranged between 31.25-250;g/ml and 62.5-500;g/ml. The percentage inhibition of the isolates at 1000;g/ml was more in the ethanol extract (65.4-95.5%) compared to the water extract (30-2-60.2%). This study shows that the extracts of Dacryodes edulis have potential usage as a food preservative and pharmaceutical preparation. Keywords: Dacryodes edulis, Antibacterial activity, Aqueous, Ethanolic, Seed extract

The essential oil of Carum carvi L. seeds was screened for its antimicrobial activity against ten pathogenic bacteria and six phytopathogenic fungi. The essential oil showed promising inhibitory activity against all the test bacteria, even at 2 ìl/disc. The minimum inhibitory concentration (MIC, 100-300 ppm) and minimum bactericidal concentration (MBC, 200-400 ppm) values of essential oil were determined. The antifungal screening of the essential oil showed 100% inhibition of radial mycelial growth of all the test fungi at 100 ppm. The MIC and minimum fungicidal concentration (MFC) values were found to vary from 50-300 ppm and 200-400 ppm respectively. The essential oil extracted by hydrodistillation from seeds of C. carvi was analyzed by gas chromatography-mass spectrometry (GC-MS). About 10 compounds had been identified in the seeds oils, accounting for more than 99.7% of the oils. The main components of the seeds oil were thymol (48.20%), o-cymene (19.29%), ϒ-terpinen (17.61%) and trimethylene dichloride (8.81%). Keywords: Antimicrobial activities; Carum carvi; Essential oil; GC-MS; ThymolDOI: http://dx.doi.org/10.3329/bjm.v25i2.4867 Bangladesh J Microbiol, Volume 25, Number 2, December 2008, pp 85-89

Antiviral activity of geodin obtained from a soil fungus was studied employing the Newcastle disease virus—chick embryo fibroblasts culture system. In a plate assay method, the minimum inhibitory concentration was about 9 μg/ml and cytotoxicity was detected at 36 μg/ml. Hemagglutinin synthesis was completely suppressed in a tube assay method when 4 μg/ml of geodin was added after the infection (50 plaque forming units/cell), but at this concentration cytotoxic effect of the antibiotic was observed. At sub-inhibitory concentrations, a dose response was shown in the yield of hemagglutinin and infective virus at 16 hr after the infection, and at this time cytopathic effect was partially or completely arrested depending on the antibiotic concentrations even when complete inhibition of hemagglutinin synthesis was not observed. Geodin did not have any effect on the activity of free virus particles and their adsorption to host cells. The inhibition site of geodin exists somewhere between viral adsorption and vir...

The antibacterial activity of methanol extract from the root bark of Akanda (Calotropis gigantea L.) and its petroleum ether, chloroform and ethyl acetate fractions were investigated. Both of methanol extract and its chloroform fraction showed activity against Sarcina lutea, Bacillus megaterium and Pseudomonas aeruginosa. Petroleum ether fraction showed activity against Bacillus subtilis and Shigella sonnei whereas ethyl acetate fraction showed activity against Pseudomonas aeruginosa and Escherichia coli at 20ìg/disc, 30ìg/disc and 40ìg/disc doses. Among the tested materials, methanol extract and its chloroform fraction showed comparatively better results. Minimum inhibitory concentration (MIC) for methanol extract and each fraction were also determined by serial dilution technique. Keywords: Methanol extract, Akonda (Calotropis gigantea), Petroleum ether fraction, Chloroform fraction and Ethyl acetate fraction.   DOI = 10.3329/bjsir.v43i3.1156Bangladesh J. Sci. Ind. Res. 43(3), 397-404, 2008

The effect of furylfuramide (FF) on germination and outgrowth of two bacterial spores was studied in a slide culture, in order to define the point at which FF acts to prevent the developmental process, from a morphological point of view. Concentrations of FF higher than minimal inhibitory concentration (MIC) did not interfere with the reduction of refractility. However, the developmental process stopped there, and the germinated spores eventually lysed before elongation occurred, shedding the empty spore coats. At less than MIC, many distorted cells appeared and gradually lysed. The bacteriostatic action of FF was shown as a result of the prolongation of their outgrowth. FF acted to arrest the development of bacterial spores not at germination, but after the stage from “swelling” to “emergence”. A discrepancy between the two organisms existed in that many refractile spores of B. coagulans, isolated from spoiled fish sausage, still remained on the culture after 35 hours at 37°C, but not in the case of B. subtilis.

SummaryThe growth of Pseudomonas aeruginosa was studied in stationary broth cultures (11 mm deep) exposed to 100% oxygen at 3 atmospheres absolute (3 ATA). During exposure, growth was greatly inhibited. Cultures transferred to air after high pressure oxygen (HPO) resumed logarithmic growth at rates similar to unexposed cultures, but lag periods increased. The minimal inhibitory concentration (MIC) of polymyxin B was determined for 6 strains of P. aeruginosa after exposure to HPO for 3, 6 and 12 hours. The longer the exposure, the lower the MIC. Regardless of the strain, after 3 hours exposure to HPO about 75% of the amount of antibiotic required for the MIC of unexposed cultures was needed; after 6 hours exposure, about 50%; and after 12 hours exposure, about 30%. This suggests that it may be possible to increase the therapeutic effectiveness of an antibiotic administered at its maximum dosage if exposure of the patient to HPO can also bathe the infecting microorganisms with oxygen.

Crystal violet has an antibacterial action against Escherichia coli, Staphylococcus aureus, Streptococcus faecalis and Bacillus subtilis. The effect of the dye, measured as minimum inhibitory concentration or retardation of growth, increases as the pH rises from 6 to 8. Of the four species E. coli is most resistant to the dye; the resistances of the other organisms are similar. The mode of action put forward by Steam & Stearn (1928) that the action of crystal violet is due to the formation of an unionized complex of bacteria with dye, is supported. Gram-negative organisms, such as E. coli, have high isoelectric points and contain less acidic components than Gram-positive bacteria which usually have lower isoelectric points, so the former combine with crystal violet less readily and are more resistant to the dye. In extension of this theory, the negative charge on bacteria is increased as the pH of the medium is increased, and the organisms become more sensitive to dye. Evidence is presented which refutes the theory of a poising of the redox potential by crystal violet suggested by Dubos (1929) and Ingraham (1933).

Context: Development of resistance in human pathogens against conventional antibiotic necessitates searching indigenous medicinal plants having antibacterial property. Seven medicinal plants used actively in folklore, ayurvedic and traditional system of medicine were selected for the evaluation of their antimicrobial activity for this study. Objectives: Evaluation of the effectiveness of some medicinal plant extracts against four Gram-positive and five Gram-negative bacteria. Materials and Methods: The antibacterial activity of the crude ethanolic extracts obtained from the leaves of seven medicinal plants; viz., Andrographis paniculata , Catharanthus roseus , Adhatoda vasica , Vitex vegundo , Aloe vera , Flacortia ramontchi and Nyctanthes arbortristis were tested against nine bacteria at concentrations of 300-, 400- and 500 μg/ml. Standard antibiotic disc kanamycin (30μg/ml) was used for comparison. The minimum inhibitory concentration (MIC) of ethanolic extracts of the leaves of these medicinal plants were determined by testing the extracts on four Gram-positive and five Gram-negative bacteria by serial tube dilution method. Results: All the extracts have notable antimicrobial activities against the test organisms. The ethanolic extracts of the leaves showed the highest antimicrobial activities against Bacillus megaterium and Shigella dysenteriae for An. paniculata, Ad. vasica and Al. vera; Bacillus subtilis and Salmonella typhi for C. roseus and N. arbortristis ; Staphylociccus aureus and Salmonella typhi for V. vegundo ; and Bacillus subtilis and Shigella sonnei for F. ramontchi respectively. The extract of the plants had MIC values ranging from 32 to 128 mg/ml. All plant extracts showed no MIC against Shigella shiga and against Sarcina lutea only C. roseus showed MIC 128 mg/ml. Conclusion: The results revealed that the ethanolic extracts of the plants under present investigation have notable antimicrobial activities. Keywords : medicinal plants; antimicrobial screening; MIC; bacteria. DOI: http://dx.doi.org/10.3329/jbs.v18i0.8788 JBS 2010; 18(0): 128-133

Antimicrobial properties of chitosan extracted from indigenous shrimp processing waste were determined against one gram-negative (Salmonella Paratyphi) and one gram-positive bacterium (Staphylococcus aureus) in vitro. The antimicrobial activities of chitosan were explored by calculation of the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) in media supplemented with 128, 138, 168, 192, 240, 288, 300 and 320 ppm chitosan solution adjusted to pH 6 or 7. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of the prepared chitosan was 288 and 300 ppm for both bacterial strains. These results indicate that chitosan from indigenous shrimp processing waste could be used as an effective antibacterial agent in the food industry. DOI: http://dx.doi.org/10.3329/jbcs.v24i2.9707 Journal of Bangladesh Chemical Society, Vol. 24(2), 185-190, 2011

Bliss, Eleanor A. (Bryn Mawr College, Bryn Mawr, Pa.) and Burr M. Alter. Bacterial resistance to antibiotics in vivo. II. Population patterns among staphylococci. J. Bacteriol. 84:125–129. 1962—The general level of resistance to streptomycin of a sensitive strain of Staphylococcus aureus was increased by exposure to the antibiotic in vivo. Although a rise in the minimal inhibitory concentration of streptomycin in broth was seen infrequently, over half the cultures from treated mice showed a shift in the population pattern toward greater tolerance for the antibiotic. A similar change did not occur in staphylococci after exposure in vivo to penicillin or chlortetracycline. Except in the case of highly resistant mutants, the level of population tolerance for streptomycin appears to be related to the concentration of the antibiotic in the tissues of the host, since strains already possessed of a measure of resistance failed to gain in resistance when exposed to streptomycin in vivo. The mechanism of survival and outgrowth of the occasional highly resistant mutant is considered.

Studies on hamycin susceptibility of 84 Candida strains showed that all the strains tested had a minimal inhibitory concentration of 0·16 μg/ml or under. It was possible to develop a high degree of in vitro resistance to hamycin in strains of C. albicans and C. tropicalis. Hamycinresistant variants did not exhibit any cross-resistance to nystatin and amphotericin B. A complete to partial loss of resistance was observed in all hamycin-resistant strains after repeated transfers in antibiotic-free medium. A majority of resistant variants showed alterations in some of their morphological and cultural properties.

In vitro and in vivo antimicrobial activities of lividomycin A were investigated. This substance showed a wide range of antimicrobial activity against most of Gram-positive bacteria including Mycobacterium tuberculosis and was also effective against Gram-negative bacteria including Pseudomonas aeruginosa, but was ineffective for streptococci, diplococci and fungi. The in vitro antimicrobial activity of lividomycin A was the greatest in media of pH 7.8. The minimum inhibitory concentration (MIC) was affected by inoculum size, but the addition of serum caused only slight fluctuation of MIC. In vitro development of resistance to lividomycin A in P. aeruginosa and M. tuberculosis was much slower than that to kanamycin, but was comparable in Staphylococcus aureus. In resistant mutants developed in vitro, cross resistance was observed among lividomycin A, kanamycin and gentamicin. In clinical isolates, however, no distinct cross resistance was found among these three antibiotics. Lividomycin A showed a positive protecting effect for the experimental infections in mice with several bacteria such as S. aureus, P. aeruginosa, Klebsiella pneumoniae and Escherichia coli. It was fairly effective for the experimental infection with the kanamycin-resistant strains of E. coli and P. aeruginosa producing the kanamycin-phosphorylating enzyme.