Susceptibility of Neisseria gonorrhoeae to seven antibiotics in vitro

One hundred consecutive isolates of N. gonorrhoeae were tested for susceptibility to penicillin, ampicillin, tetracycline, erythromycin, kanamycin, cephaloridine and cephalexin by an agar dilution method. Relative resistance to penicillin was frequent. For 39% of isolates the minimum inhibitory concentration (MIC) of penicillin was 0.05 U./ml. or less; in 55% the MIC was 0.5 to 2.0 U./ml. Ampicillin was slightly more active than penicillin G: all isolates were inhibited by 0.5μg./ml. or less. Resistance to tetracycline and erythromycin was frequent with MIC of 1 μg./ml. or greater observed in 32 and 24% of isolates respectively. The MIC of kanamycin for all gonococci was 8 μg./ml. or greater. Cephalexin was slightly more active than cephaloridine, though each drug exhibited a wide range of MIC values. Gonococcus isolates resistant to penicillin (MIC of 1.0 U./ml. or greater) tended to be resistant to the other antibiotics tested.     

Therapeutic Agents in Acne Vulgaris: I. Tetracycline

A total of 120 consecutive patients with pustular and cystic acne vulgaris were selected for study. Patients were assigned a placebo and a tetracycline medication in a random method. Of the 53 patients who were given tetracycline, 45 showed some response, which was fair in 19 and excellent in 26. Of the 55 patients who received placebo, 24 showed no response while 31 showed some improvement. No side effects were reported. The difference in response between the two groups is statistically significant. It is concluded that administration of 250 mg. tetracycline four times daily, even for periods as short as two weeks, enhances the likelihood of improvement of cystic or pustular acne vulgaris.     

Changes in antibiotic sensitivity in strains of Staphylococcus aureus, 1952-78.

Two hundred strains of Staphylococcus aureus isolated from outpatients with infections of the skin and subcutaneous tissues were tested for sensitivity to penicillin, erythromycin, tetracycline, sodium fusidate, methicillin, clindamycin, chloramphenicol, and gentamicin. One hundred and sixty-three (81.5%) of the strains were resistant to penicillin and 16 (8%) resistant to tetracycline. Incidence of resistance to other antibiotics was low. No strain was resistant to chloramphenicol, gentamicin, or methicillin. When compared with results of earlier studies, there was an increase in the incidence of resistance to penicillin and tetracycline, but no appreciable increase in resistance to other antibiotics.     

Psychiatric care and politics.

The minimum inhibitory concentrations (MIC''s) of penicillin, ampicillin, tetracycline, erythromycin, spectinomycin and sulfadiazine were determined for 732 isolates of Neisseria gonorrhoeae collected in 1973-74. Comparison of the results of this survey with data from other Canadian studies showed that the percentage of isolates resistant to tetracycline had not changed since 1966, but that the percentage of erythromycin-resistant isolates had decreased. After an initial increase in 1966 the percentage of penicillin-resistant isolates stabilized. Spectinomycin-resistant isolates were not found. Positive correlations were observed between the MICs of the antibiotics tested; the highest positive correlations were between penicillin and ampicillin and between penicillin and tetracycline. A positive correlation was also noted between penicillin resistance and increasing spectinomycin MICs. Finally, a significant seasonal variation in MICs was found, the trend being towards increasing MICs during the summer.     

Antimicrobial resistance among Brazilian Corynebacterium diphtheriae strains

The increasing problems with multidrug resistance in relation to Corynebacterium, including C. diphtheriae, are examples of challenges confronting many countries. For this reason, Brazilian C. diphtheriae strains were evaluated by the E-Test for their susceptibility to nine antibacterial drugs used in therapy. Resistance (MIC < 0.002; 0.38 microg/ml) to penicillin G was found in 14.8% of the strains tested. Although erythromycin (MIC90 0.75 microg/ml) and azithromycin (MIC90 0.064 microg/ml) were active against C. diphtheriae in this study, 4.2% of the strains showed decreased susceptibility (MIC 1.0 microg/ml) to erythromycin. Multiple resistance profiles were determined by the disk diffusion method using 31 antibiotics. Most C. diphtheriae strains (95.74%) showed resistance to mupirocin, aztreonam, ceftazidime, and/or oxacillin, ampicillin, penicillin, tetracycline, clindamycin, lincomycin, and erythromycin. This study presents the antimicrobial susceptibility profiles of Brazilian C. diphtheriae isolates. The data are of value to practitioners, and suggest that some concern exists regarding the use of penicillin.     

Evaluation of Two Simple Assay Methods for Detecting Antibiotic Residues in Chicken and Pig Muscle

Using 2 paper disc assay procedures, Bacillus cereus and Sarcina lutea were challenged with extracts from chicken and pig muscle paste to which various antibiotics had been added. The first method could detect tetracycline, chlortetracycline, oxytetracycline, penicillin, erythromycin, tylosin and virginiamycin at or <1 μg/g of muscle paste, whilst the second method was necessary to detect the remaining 5 antibiotics at this level. Using the first assay procedure, penicillin, zinc bacitracin and the 3 tetracycline compounds could be detected below FAO/WHO maximum permissible levels for meat for human consumption, whilst the second method was necessary to meet requirements for streptomycin, erythromycin and tylosin. Spiramycin could not be detected by either method at the levels permitted by FAO/WHO. The minimum levels of detection obtained for flavomycin, virginiamycin and monensin were 0.2, 0.02 and 0.5–1.0 μg/g, respectively.     

Antimicrobial Susceptibility of Clostridium difficile from Different Sources

A total of 79 Clostridium difficile strains from healthy young and elderly adults, elderly patients without gastrointestinal disease, elderly patients receiving antibiotics without gastrointestinal complications, and elderly patients with antibiotic-associated diarrhea or pseudomembranous colitis were tested for their susceptibilities to 24 antimicrobial agents. All of the 79 strains were inhibited by low concentrations of rifampicin, metronidazole, fusidic acid, vancomycin, ampicillin, and penicillin G. The strains were highly resistant to aminoglycosides, trimethoprim, sulfamethoxazole, nalidixic acid, and cycloserine and often resistant to neomycin, cefoxitin, and cefalexin. Wide variations in the susceptibility of C. difficile strains to erythromycin, clindamycin, lincomycin, chloramphenicol, and tetracycline were found. Strains resistant to erythromycin, clindamycin, and lincomycin were more frequently found among strains isolated from elderly adults than those isolated from young adults, with particularly high frequency among strains isolated from elderly patients receiving antibiotics. None of the 23 strains isolated from healthy young adults was resistant to chloramphenicol. All of the 14 strains resistant to erythromycin, clindamycin, lincomycin, and chloramphenicol were sensitive to tetracycline and all of the 15 strains resistant to erythromycin, clindamycin, lincomycin, and tetracycline were sensitive to chloramphenicol. Only one out of 19 tetracycline-resistant strains was highly toxigenic, whereas 42 (70%) of 60 sensitive strains were highly toxigenic.     

Susceptibility of sixty-five non-oral clinical isolates of the Streptococcus milleri group to seven antimicrobial agents.

Antimicrobial susceptibilities of sixty-five non-oral Streptococcus milleri group clinical isolates to penicillin, gentamicin, lincomycin, ampicillin, chloramphenicol, tetracycline and erythromycin were determined by an agar dilution method. All strains were penicillin-sensitive (MIC < or = 0.031 microgram/ml) and the majority (64/65) were susceptible to erythromycin (MIC < or = 0.125 microgram/ml). Low-level resistance to gentamicin was observed, and the majority of strains possessed an MIC of 8 micrograms/ml. Lincomycin and ampicillin at 0.5 microgram/ml inhibited 52/65 and 61/65 strains, respectively. Of the isolates 92% were inhibited by chloramphenicol at < or = 2 micrograms/ml. Twenty-two S. milleri group strains (of which thirteen were vaginal isolates) were resistant to tetracycline (MIC > or = 8 micrograms/ml).     

Antibiotic Susceptibility of Anaerobic Ruminal Bacteria

This study demonstrated that 15 species of ruminal bacteria with no previous history of contact with antibiotics are susceptible to bacitracin, chloramphenicol, chlortetracycline, erythromycin, novobiocin, oleandomycin, oxytetracycline, penicillin, tetracycline, tylosin, and vancomycin. A number of the species were not inhibited by kanamycin, neomycin, polymyxin, and streptomycin. The data suggest that antibiotic-resistant cells occur within susceptible cultures of these species. Streptococcus bovis FD-10 and a nonruminal anaerobe, Bacteroides melaninogenicus BE-1, showed similar antibiotic susceptibilities.     

Determination of Antibiotic Susceptibility of Rickettsia by the Plaque Assay Technique

Plaque formation by various rickettsiae was completely inhibited by commercial antibiotic discs impregnated with tetracycline, chloramphenicol, nitrofurantoin, and erythromycin; partial inhibition was observed around discs containing nalidixic acid and sulfisoxazole, but no inhibition was seen around discs containing cephalothin, ampicillin, oxacillin, kanamycin, polymyxin B, streptomycin, or penicillin.     

Novel microbiological system for antibiotic detection in ovine milk

This article presents a microbiological system composed of a “BT” bioassay (Beta-lactams and Tetracyclines) and a “QS” bioassay (Quinolones and Sulfonamides). The “BT” bioassay contains spores of Geobacillus stearothermophilus, bromocresol purple and cloramphenicol in a culture medium (incubation time: 2.45 h), while the “QS” bioassay uses spores of Bacillus subtilis, trifenyltetrazolium – toluidine blue and trimethoprim in a suitable culture medium (incubation time: 5.5 h). The detection capability (CC_β) of 27 antimicrobial agents in ovine milk were determined by logistic regression models. Thus, the “BT” bioassay detects amoxycillin, ampicillin, penicillin “G”, cloxacillin, oxacillin, cephalexin, cefoperazone, ceftiofur, chlortetracycline, oxytetracycline, tetracycline, neomycin, gentamycin and tylosin, while “QS” bioassay detects: ciprofloxacin, enrofloxacin, marbofloxacin, sulfadiazine, sulfadimethoxine, sulfamerazine, sulfamethazine, sulfamethoxazole, sulfathiazole, erythromycin, lincomycin and spiramycin at levels close to their respective Maximum Residue Limits. The simultaneous use of both bioassays detects a large number of antibiotics in milk given each method's adequate complementary sensitivity.     

Erythromycin and penicillin resistance mechanisms among viridans group streptococci isolated from blood cultures of adult patients with underlying diseases

The aim of the study was to evaluate the species distribution, antimicrobial susceptibility and erythromycin-penicillin resistance mechanisms of viridans streptococci (VGS) isolates from blood cultures of adult patients with underlying diseases. Fifty VGS blood culture isolates were screened for their antibiotic susceptibilities against penicillin G, erythromycin and tetracycline by E-test. Clindamycin, cefotaxime, chloramphenicol, levofloxacin, linezolid and vancomycin susceptibility were performed by broth microdilution method. Erythromycin and penicillin resistance genotypes, ermB and mefA/E, pbp1a, pbp2b and pbp2x are amplified using PCR method. The clinical isolates included Streptococcus mitis (n. 19), S.oralis (n. 13), S.sanguinis, S.parasanguinis (n. 6, each), S.salivarius, S.vestibularis (n. 2, each), S.constellatus, S.sobrinus (n. 1, each). The percentage resistance against erythromycin and penicillin was 36% and 30%, respectively. The genotypic carriage rate of erythromycin resistance genes were: 56% ermB, 28% mefE, 8% ermB+mefE. Penicillin-resistant isolates carried pbp2b (33.3%) and pbp2x (20%) genes. Twenty-four VGS isolates were recovered from patients with cancer. S.mitis and S.oralis predominated among patients with cancer who had erythromycin and penicillin resistance isolates. The importance of classical antimicrobial agents like penicillin and erythromycin warrants the continuous surveillance of invasive VGS isolates and can guide better treatment options especially in patients with underlying diseases.     

Action of Lincomycin on Staphylococci

On a solid medium, 0.1 to 1 μg/ml of lincomycin hydrochloride had a bacteriostatic effect upon 95 of 100 strains of staphylococci. Using cellophane transfers, we observed a bactericidal effect upon 54 of these strains after 3 to 14 hr of contact with 1 μg/ml. Five staphylococcal strains resistant to 100 μg/ml of lincomycin were also resistant to penicillin G, streptomycin, erythromycin, tetracycline, chloramphenicol (three strains), and rovamycin (three strains). Other staphylococcal strains resistant to methicillin, ampicillin, tetracycline, streptomycin, chloramphenicol, and erythromycin were sensitive to lincomycin.     

Antibiotic-resistant Propionibacterium acnes on the skin of patients with moderate to severe acne in Stockholm

The objective was to study the prevalence and antibiotic susceptibility patterns of Propionibacterium acnes strains isolated from patients with moderate to severe acne in Stockholm, Sweden and to determine the diversity of pulsed-field gel electrophoresis types among resistant P. acnes strains. One hundred antibiotic-treated patients and 30 non-antibiotic-treated patients with moderate to severe acne participated in the investigation. Facial, neck and trunk skin samples were taken with the agar gel technique. The susceptibility of P. acnes strains to tetracycline, erythromycin, clindamycin and trimethoprim-sulfamethoxazole was determined by the agar dilution method. The genomic profiles of the resistant strains were determined by pulsed-field gel electrophoresis. In the group of patients treated with antibiotics, resistant P. acnes strains were recovered in 37%, while in the non-antibiotic group of patients the incidence of resistant strains was 13%. Thus antibiotic-resistant P. acnes strains were significantly more often isolated from antibiotic-treated patients with moderate to severe acne than from non-antibiotic-treated patients (odds ratio, 3.8; P=0.01). There was a genetic diversity among the P. acnes strains. Forty-four different patterns of SpeI DNA digests were detected and two predominant clones were found. P. acnes strains exhibited different antibiotic susceptibility patterns and identical genotypes or vice versa. A person can be colonized with different strains with varying degrees of antibiotic resistance. The risk of increased resistance of P. acnes must be considered when treating acne patients with antibiotics, and especially long-term therapy should be avoided.     

Antimicrobial drug resistance in Staphylococcus aureus isolated from cattle in Brazil

Isolates of Staphylococcus aureus obtained from apparently healthy cattle in the State of Paraiba, Brazil were characterized in relation to resistance to 21 antimicrobial agents. Among the 46 isolates obtained, resistance to penicillin was most frequent, followed by resistance to cadmium, streptomycin, arsenate, tetracycline, mercury, erythromycin and kanamycin/neomycin. All isolates were susceptible to fusidic acid, ethidium bromide, cetrimide, chloramphenicol, benzalkonium chloride, doxycycline, gentamicin, methicillin, mnocycline, novobiocin, rifamycin, tylosin and vancomycin. Only six isolates were susceptible to all the drugs tested. With respect to the antibiotics, multi-resistant isolates were uncommon. These results are probably a consequence of the peculiarities of local drug usage pressures. In relation to metal ions, resistance to mercury was rare while resistance to arsenate was relatively frequent, which contrasts with the situation for human Staph. aureus strains. After treatment with ethidium bromide, elimination of resistance to penicillin, tetracycline, streptomycin, erythromycin and cadmium was observed, which was consistent with the genetic determinants being plasmid-borne.     

Sigma B对单核细胞增生李斯特菌耐受抗生素作用的影响

单核细胞增生李斯特菌是重要的革兰阳性食源性致病菌。近年来的报道显示出该菌耐受抗生素的能力有不断增强的趋势,为了探讨其耐药机制,对Sigma B（σB,李斯特菌中应对环境胁迫的主要调控因子）在抗生素耐受性中的作用进行了初步研究。检测和比较单核细胞增生李斯特菌标准菌株EGDe和其σB缺失突变菌株EGDeΔsigB对盘尼西林青霉素、氨苄西林青霉素、利福平、硫酸庆大霉素、四环素盐酸和红霉素6种抗生素的最小抑菌浓度（MIC）;在测定的MIC的基础上,利用MTT（噻唑蓝活体染色法）法比较EGDe和EGDeΔsigB在1×MIC、2×MIC和8×MIC的氨苄西林青霉素、红霉素和利福平3种抗生素中的生长活性。EGDe对盘尼西林青霉素（0.16μg/mL）、四环素盐酸（0.25μg/mL）和硫酸庆大霉素（0.5μg/mL）的MIC高于EGDeΔsigB（分别为0.08、0.125和0.125μg/mL）;而对氨苄西林青霉素、红霉素和利福平的MIC 2种菌株没有差别,分别为0.19、0.125和0.032μg/mL;与EGDe相比,EGDeΔsigB在氨苄西林青霉素、红霉素和利福平培养基中的生长活性较差,对抗生素的抑制更为敏感,而且随着这3种抗生素浓度的增加,其抑制程度也随之增强。Sigma B在单核细胞增生李斯特菌对抗生素的耐受中起到重要调节作用。     

Sensitivity to antibacterial preparations of the pathogenic staphylococci isolated from carriers]

After discontinuation of the use of antibiotics for sanation of the carriers of pathogenic staphylococci among the staff of a maternity unit, the number of the strains resistant to penicillin, streptomycin, chlortetracycline, tetracycline, levomycetin, erythromycin, monomycin and neomycin decreased 1.3, 2.9, 10,4.3,5.5,1.5,3.9 and 2.4 times respectively. The differences were statistically reliable. The causes of the antibiotic resistance decrease require further investigation.     

Gonococcal Antibiotic Resistance in Los Angeles

One hundred and thirty-five gonococcal isolates collected from Los Angeles in 1972 were studied for antibiotic susceptibility to penicillin, ampicillin, carbenicillin, tetracycline, minocycline, doxycycline and spectinomycin. Only 12 percent of the isolates were sensitive to 0.05 μg per ml of penicillin while 35 percent required at least 0.5 μg per ml for inhibition of growth. The results were slightly better with ampicillin and nearly the same with carbenicillin. Nineteen percent of the isolates required at least 1.0 μg per ml of tetracycline for inhibition of growth and the results were similar with either minocycline or doxycycline. Forty-nine percent were sensitive to 2.0 μg per ml spectinomycin, but 37 percent required at least 8.0 μg per ml for inhibition of growth.In this study nine of eleven isolates resistant to 1.0 μg per ml of tetracycline were also resistant to both penicillin and spectinomycin. Six came from endocervical sites of female patients who contributed only 37 percent of the total number of isolates studied.Correlation between the agar dilution and disc diffusion methods was satisfactory with penicillin but not with ether tetracycline or spectinomycin.     

Microviscosity of mouse splenocyte cytoplasmic membrane modified by some antibiotics

This study has assessed the changes in the polarization fluorescence of 1,6-diphenyl-1,3,5-hexatriene in the splenic membrane of mice treated with clindamycin, penicillin, cefoxitin, cefamandole, cephaloridine, tetracycline, and erythromycin. The data show that most of the antibiotics tested modified membrane activity, as was shown by the changes in membrane microviscosity parameters.     

Combined action of penicillin, tetracycline and rifampicin on R. sibirica and R. prowazekii in experiments on chick embryos

The effect of combinations of penicillin, tetracycline and rifampicin on R. prowazekii (the causative agent of typhus) and R. sibirica (the causative agent of tick-borne rickettsiosis of the North Asia) was studied. It was shown that tetracycline and penicillin used in combination had a summation effect on both R. sibirica and R. prowazekii. The dose of each antibiotic was 2 times lower than the doses of the antibiotics used alone. However, R. sibirica was less sensitive to this combination than R. prowazekii: the minimum rickettsiocidic doses of the combination were 0.5 mg of tetracycline + 10000 units of penicillin per embryo with respect to R. sibirica and 0.1 mg of tetracycline + 10000 units of penicillin per embryo with respect to R. prowazekii. The combinations of rifampicin with penicillin or tetracycline in the concentrations used had no rickettsiocidic effect on either R. sibirica or R. prowazekii. However, it should be noted that these combinations had a synergistic action and provided a rickettsiostatic effect on R. prowazekii: the dose of rifampicin in its combination with penicillin was decreased 10 times and in the combination of rifampicin with tetracycline the doses of both rifampicin and tetracycline were decreased 10 times. Still, penicillin even in a dose of 20000 units per embryo had only a rickettsiostatic effect on R. sibirica and R. prowazekii.