Interpretation of Diffusion Susceptibility Data Obtained with 50-μg Carbenicillin Discs Against Gram-Negative Organisms

A total of 284 clinical isolates of various species of Enterobacteriaceae, Pseudomonas aeruginosa, P. maltophilia, and Acinetobacter anitratum were tested for susceptibility to carbenicillin by the standardized Bauer-Kirby disc diffusion technique and a microtiter broth dilution method. The data obtained led to the following proposed criteria for the interpretation of the results of disc susceptibility tests. Enterobacteriaceae that yield zones of inhibition equal to or greater than 20 mm in diameter around 50-mug discs of carbenicillin are designated as sensitive to the drug; isolates that yield zones measuring from 18 to 19 mm in diameter are reported as of equivocal (intermediate) susceptibility to the drug, whereas those enterobacterial isolates that are characterized by zones of inhibition of 17 mm or less in diameter are interpreted as resistant to carbenicillin. Isolates of P. aeruginosa, P. maltophilia, and A. anitratum yielding zones of 14 mm or more in diameter around 50-mug discs of carbenicillin are reported as sensitive, whereas those isolates that are characterized by zones of 13 mm or less in diameter are reported as resistant to this drug.     

Susceptibility of Pseudomonas aeruginosa to Carbenicillin

Ninety clinical isolates of Pseudomonas aeruginosa were examined for susceptibility to carbenicillin by the broth dilution and disc diffusion methods. Inhibition zone diameters varied at given minimal inhibitory concentration levels of the antibiotic. Nevertheless, the results obtained allowed the proposal of the following tentative criteria for the interpretation of inhibition zones. Pseudomonadaceae yielding zones of inhibition measuring at least 10 and 16 mm in diameter around 25-and 100-mug discs, respectively, are sensitive to this antibiotic when examined by the standardized Bauer-Kirby method of disc susceptibility testing. Isolates characterized by zones of less than 100 mm in diameter around 25-mug discs should be tested with 100-mug discs before they are reported as sensitive or resistant to carbenicillin.     

Susceptibility of Recent Isolates of Pseudomonas aeruginosa to Gentamicin, Polymyxin, and Five Penicillins, with Observations on the Pyocin and Immunotypes of the Strains

The susceptibilities of recently isolated strains of Pseudomonas aeruginosa to gentamicin, polymyxin B, carbenicillin, ampicillin, penicillin G, and two newer penicillins were tested with the inocula-replicating technique by using undiluted and 10(-3) dilutions of the cultures. With either inoculum, polymyxin B was the most active agent, and a comparison with previous data from this laboratory showed that the susceptibility of P. aeruginosa to this antibiotic had not changed over the past 20 years. Gentamicin was nearly as active as polymyxin, all but 2 of the 141 strains tested with the diluted inoculum being inhibited by 6.25 mug/ml or less. AB-2288, an agent resembling carbenicillin, was four times more active than carbenicillin or BLP-1654; the last two were equally active against the 10(-3) inoculum. A more marked inoculum effect was noted with the penicillin analogues tested, the increase in minimum inhibiting concentration with the undiluted culture being eight-fold for carbenicillin and at least 16-fold for AB-2288 and BLP-1654. Pyocin typing and serotyping failed to demonstrate any clearly predominating types.     

In Vitro Susceptibility of Pseudomonas aeruginosa to Carbenicillin and the Combination of Carbenicillin and Gentamicin

One hundred and eleven strains of Pseudomonas aeruginosa isolated from clinical material were studied for susceptibility to carbenicillin. Of the strains, 80% were inhibited by 125 mug/ml or more. The combination of carbenicillin and gentamicin was shown to have inhibitory and bactericidal synergistic effect on 15 of 16 strains of P. aeruginosa tested. There was poor correlation between the single-disc sensitivity method and the tube dilution method.     

高龄患者血液感染常见革兰阴性杆菌及其耐药性分析

目的分析本院80~100岁高龄患者血液感染常见革兰阴性杆菌的种类及其耐药状况,为本院合理使用抗生素提供依据。方法采用BacT/Alert 3D血培养仪对血液标本进行阳性鉴定;VITEK-2Compact全自动微生物鉴定仪进行鉴定;K-B纸片扩散法对抗菌药物进行敏感性测定;使用WHONET 5.4分析软件分析数据。结果本院高龄患者血液培养阳性标本中共分离出革兰阴性杆菌108株,以肠杆菌科细菌为主,其次为非发酵菌,前者主要为大肠埃希菌52株(48.15%)和肺炎克雷伯菌37株(34.26%),后者主要包括铜绿假单胞菌10株(9.26%)和鲍曼不动杆菌8株(7.41%)。其中大肠埃希菌和肺炎克雷伯菌对亚胺培南的耐药率分别为1.92%和13.51%,两者对氨苄西林、氨苄西林/舒巴坦、头孢唑林、头孢呋辛的耐药率均高于50.00%;铜绿假单胞菌和鲍曼不动杆菌对亚胺培南的耐药率分别为20.00%和25.00%,后者对其他抗菌药物的耐药率均高于前者。结论碳青酶烯类抗生素可作为本院高龄患者常见革兰阴性杆菌所致血液感染的首选药物;但在治疗中应考虑细菌的耐药特点及患者的代谢特点合理选择抗生素。     

Antipseudomonal Activity of α-Sulfoaminopenicillins

A series of penicillins characterized by the presence of a sulfoamino or a modified sulfoamino group in the side chain was subjected to in vitro antimicrobial screening tests. Although the most potent members of the series were less active than benzylpenicillin against gram-positive bacteria and comparably active against most gram-negative bacteria, they were, on the average, 8 to 16 times more effective against strains of Pseudomonas aeruginosa. In other comparative laboratory tests against P. aeruginosa, these compounds were about as active as carbenicillin and four to eight times more active than ampicillin. An examination of structure-activity relationships indicated that maximal potency was obtained with penicillins having an alpha-(aromatic or heteroaromatic)-alpha-sulfoaminoacetamido side chain. The compound with an alpha-phenyl group was comparable in activity to those having an alpha-(2- or 3-thienyl) group, whereas any modification in position or structure of the alpha-sulfoamino group reduced activity. Results of studies with a cell-free P. aeruginosa beta-lactamase suggest that the marked inhibitory effects of alpha-sulfoamino penicillins for P. aeruginosa can be attributed, at least in part, to their high degree of resistance to this enzyme. Some derivatives, however, had weak antipseudomonal activity, despite possessing a high degree of beta-lactamase resistance.     

Various methods to assay carbenicillin activity against Pseudomonas aeruginosa]

It was shown that the cultures of Pseudomonas aeruginosa were sensitive to 75-100 micrograms/ml and resistant to 25-50 micrograms/ml of carbenicillin when tested by the method of serial dilutions in the synthetic medium developed by the authors and in Jorgensen's medium. The cultures were incubated for 4 and 16 hours, respectively. The data did not confirm the resistance of the cultures to 25-75 and 100 micrograms/ml carbenicillin when it was determined with the serial dilution method in Pal's medium and the disk diffusion method, respectively. The advantages of the medium developed by the authors for testing P. aeruginosa sensitivity to carbenicillin are discussed.     

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.     

Antibiotic resistance of Pseudomonas aeruginosa strains isolated from patients with infected burns

Sensitivity to 15 drugs of 248 P. aeruginosa strains isolated from patients with infected burns was studied by the method of agar dilution. All of the strains were resistant to polymyxin M, ceporin, erythromycin and oleandomycin. Most of the strains were resistant to streptomycin, monomycin, ampicillin and rifadin. Moderate resistance of the strains to carbenicillin, morphocycline, vibramycin, kanamycin, tetraolean and tetracycline was observed: the maximum concentrations of these antibiotics (128 microgram/ml) inhibited the growth of 85, 69, 63, 51.8, 43.6 and 41.2 per cent of the strains respectively. Gentamicin proved to be most active against the strains of P. aeruginosa and inhibited 87 per cent of the strains when used in the therapeutic doses. The study provided recomendation of the drugs for parenteral and local use in treatment of burns infected with P. aeruginosa.     

Antimicrobial resistance and genomic screening of clinical isolates of thermophilic Campylobacter spp. from south-east Queensland,Australia

AIM: To screen 90 clinical isolates of thermophilic Campylobacter species for putative resistance to ampicillin, erythromycin and tetracycline and perform numerical analysis to determine isolate relatedness. METHODS AND RESULTS: Disc diffusion, E-test MIC and agar dilution methods were performed. Disc diffusion testing showed 87 (97%) isolates appeared resistant to ampicillin at 10 microg; 14 (16%) resistant to tetracycline at 30 microg; and three (3.4%) resistant to erythromycin at 15 microg. E-test MICs showed a range of 0.5 to >256 mg l(-1) for ampicillin; 16 to >256 mg l(-1) for tetracycline; and >256 mg l(-1) for erythromycin. E-test showed 68% correlation (+/-1 log2 dilution) with agar dilution for ampicillin, 100% for erythromycin and 64% for tetracycline. Disc diffusion testing showed 100% correlation with agar dilution for erythromycin and tetracycline, and 77% for ampicillin. Numerical analyses of restriction endonuclease (RE) fragment profiles suggested a high level of isolate variation. CONCLUSION: The incidence of resistance of thermophilic Campylobacter spp. to erythromycin and tetracycline is low in south-east Queensland. SIGNIFICANCE AND IMPACT OF THE STUDY: Disc diffusion susceptibility testing may be used to screen thermophilic Campylobacter spp. for putative resistance to erythromycin and tetracycline. Agar dilution should be used to determine ampicillin susceptibility.     

Influence of Serum and Calcium on the Bactericidal Activity of Gentamicin and Carbenicillin on Pseudomonas aeruginosa

Because calcium was found to be antagonistic in vitro to the activity of colistin and polymyxin B on Pseudomonas aeruginosa, the effects of calcium and serum on gentamicin and carbenicillin were also examined. Serum was antagonistic to gentamicin in antibiotic tube dilution tests on five strains of P. aeruginosa. Serum was not antagonistic to carbenicillin in tube dilution tests. Physiologic concentrations of calcium antagonized the activity of gentamicin but not carbenicillin. The antagonism observed with gentamicin was less than that previously seen with colistin. The antagonistic effect of calcium and serum was removed by a chelating agent. Gentamicin and carbenicillin may be more active in vivo against P. aeruginosa than colistin or polymyxin B.     

Klebsiella, Enterobacter, and Serratia: Biochemical Differentiation and Susceptibility to Ampicillin and Three Cephalosporin Derivatives

Three hundred twenty-nine strains of the tribe Klebsielleae were compared by several biochemical tests and by susceptibility to selected antibiotics. Biochemical tests included urease, amino acid decarboxylase, and hydrogen sulfide production; fermentation of lactose and dextrose; motility; and tests in the IMViC (indole, methyl red, Voges-Proskauer, citrate) series. The isolates were: Klebsiella species, 67.5%; Enterobacter species, 28%, and Serratia species, 4.5%. Minimal inhibitory concentrations of cephaloridine, cephalothin, and a new cephalosporin, cephalexin, and of ampicillin were determined by the agar dilution procedure. Cephalosporins at 20 mug/ml or less inhibited 90% of the Klebsiella strains but only 15% of the Enterobacter strains. Ampicillin inhibited 27% of Enterobacter strains and 17% of Klebsiella strains. Serratia isolates were insensitive to the cephalosporins and ampicillin. The results suggest that precise identification of this group to the generic level can be accomplished readily in the clinical laboratory and that such information is helpful in the preliminary selection of an antibiotic for treatment of clinical infections.     

Preliminary characterization of a food-borne multiple-antibiotic-resistant Salmonella typhimurium strain

Plasmid characterization studies were conducted on a Salmonella typhimurium strain isolated from pasteurized milk and from a symptomatic patient during the 1985 Illinois salmonellosis outbreak. This strain (Hf) was reported to possess an unusual plasmid profile which distinguished it from all Salmonella strains isolated in the United States prior to 1984. Antibiotic susceptibility testing revealed that the strain was resistant to tetracycline, erythromycin, clindamycin, sulfisoxazole, sulfadiazene, triple sulfa, cefoperazone, streptomycin, mezlocillin, piperacillin, carbenicillin, penicillin, ampicillin, and kanamycin. Plasmid analysis revealed that the strain possessed four plasmids with sizes of approximately 158, 98, 10.2, and 6.0 kilobase pairs (kb). Successive transfer at 43 degrees C led to increased antibiotic sensitivity in 75.5% of the isolates screened. Electroporation and calcium chloride treatment were each used to transform plasmid-free Escherichia coli strains with the plasmid pool from S. typhimurium Hf. Plasmids introduced by transformation ranged in size from 4.4 to 23.2 kb and correlated with resistance to penicillin G, ampicillin, carbenicillin, cephalothin, cefoperazone, cefamandole, mezlocillin, piperacillin, and in some cases, tetracycline and kanamycin. DNA-DNA hybridization experiments localized these resistance genes to a highly duplicated 6.3-kb fragment of the total EcoRI restriction digest of the S. typhimurium Hf plasmid pool.     

Increased Antibiotic Sensitivity in Pseudomonas aeruginosa Following Passage in Carbenicillin-containing Media

Twelve dissimilar clinical isolates and 4 type cultures of Pseudomonas aeruginosa have been repeatedly passaged on agar containing 200 μg carbenicillin/ml. Passaged variants were compared with control organisms for their sensitivities to a range of antibiotics initially by a multodisk test and subsequently by serial dilution in agar. Two of the variants, both derived from clinical isolates, showed pronounced increases in sensitivity to several antibiotics, particularly kanamycin, neomycin, gentamicin and colistin sulphate. In some instances the minimum inhibitory concentration (MIC) for the passaged variants was 32–64 times lower than that for the control organisms. These potentiations contrast with previous results obtained by other workers for P. aeruginosa . In addition, several other of our passaged variants developed a more moderate degree of enhanced sensitivity to a limited number of antibiotics. Eight (67%) of the clinical isolates and one type culture did not become more sensitive to any of the antibiotics tested following carbenicillin passage. Onset of increased antibiotic-sensitivity varied with the strain, particular antibiotic and medium employed for passage. Although the addition of sucrose (0·5 M) and magnesium sulphate (0·01 M) to the passage medium appeared to delay development of antibiotic-sensitivity their presence eventually encouraged larger potentiations in antibiotic activity. The significance of the conversion of P. aeruginosa into forms with increased susceptibility to several antibiotics during chemotherapy with carbenicillin is discussed.     

Preliminary characterization of a food-borne multiple-antibiotic-resistant Salmonella typhimurium strain.

Plasmid characterization studies were conducted on a Salmonella typhimurium strain isolated from pasteurized milk and from a symptomatic patient during the 1985 Illinois salmonellosis outbreak. This strain (Hf) was reported to possess an unusual plasmid profile which distinguished it from all Salmonella strains isolated in the United States prior to 1984. Antibiotic susceptibility testing revealed that the strain was resistant to tetracycline, erythromycin, clindamycin, sulfisoxazole, sulfadiazene, triple sulfa, cefoperazone, streptomycin, mezlocillin, piperacillin, carbenicillin, penicillin, ampicillin, and kanamycin. Plasmid analysis revealed that the strain possessed four plasmids with sizes of approximately 158, 98, 10.2, and 6.0 kilobase pairs (kb). Successive transfer at 43 degrees C led to increased antibiotic sensitivity in 75.5% of the isolates screened. Electroporation and calcium chloride treatment were each used to transform plasmid-free Escherichia coli strains with the plasmid pool from S. typhimurium Hf. Plasmids introduced by transformation ranged in size from 4.4 to 23.2 kb and correlated with resistance to penicillin G, ampicillin, carbenicillin, cephalothin, cefoperazone, cefamandole, mezlocillin, piperacillin, and in some cases, tetracycline and kanamycin. DNA-DNA hybridization experiments localized these resistance genes to a highly duplicated 6.3-kb fragment of the total EcoRI restriction digest of the S. typhimurium Hf plasmid pool.     

Synergistic Antibacterial Activity of Ampicillin-Cloxacillin Mixtures Against Proteus morganii

Synergistic antibacterial effects of mixtures of ampicillin and cloxacillin and induced penicillinases were investigated in 48 strains of Proteus. The serial tube dilution method was used to determine the minimal inhibitory concentration of ampicillin, cloxacillin, and 2:1 and 1:1 mixtures of ampicillin and cloxacillin. Production of penicillinases was determined by the cellulose acetate membrane method, with ampicillin, cloxacillin, mixtures of ampicillin and cloxacillin, penicillin G, and cephalothin as inducing agents and as substrates for penicillinase. Synergism occurred against P. morganii, but against no other species. The 1:1 ampicillin-cloxacillin combination was synergistic against 13 of 17 P. morganii strains; the 2:1 combination was synergistic against only 9 strains. Penicillinases, demonstrated in all species except P. mirabilis, hydrolyzed penicillin G and cephalothin. Although only P. vulgaris hydrolyzed ampicillin, no species of Proteus hydrolyzed cloxacillin or the ampicillin-cloxacillin mixtures. Penicillinases were, however, induced by ampicillin, cloxacillin, and the mixtures. There was no relationship between production of penicillinase and synergism with mixtures of ampicillin and cloxacillin.     

Microbiological surveillance of the surgical intensive care unit in Zagreb--a pivot for guideline-based therapy of severe sepsis

The aim of this retrospective study was to create guidelines for therapy of severe sepsis in surgical intensive care unit (ICU) for unknown causative agent based on antimicrobial susceptibility of causative bacteria. Seventy-four patients with severe sepsis from surgical ICU in 2003.-2005. were included in study. Their clinical and microbiological data were analyzed from the medical records. Antimicrobial susceptibility of the strains isolated from the blood-culture was tested by disk diffusion method according to CLSI (Clinical Laboratory Standard Institution). APACHE II score was used to predict the severity of illness. Statistical significance difference between results was tested by Mann-Whitney test and chi2 test. Important problem remained type of sepsis: mono-agent sepsis presented less therapeutic problem than sepsis caused with two or more agents (mixed sepsis). Methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and Acinetobacter baumannii were predominant causative agents in both type of sepsis. There was remarkable increase of A. baumannii prevalence in 2005 compared to 2004 and to 2003. There was also decrease of MRSA prevalence in 2004 and 2005 compared to 2003. P. aeruginosa were the predominant causative agents in 2004. MRSA displayed good susceptibility to vancomycin and linezolide, whereas P. aeruginosa showed excellent susceptibility to ceftazidime and carbapenems. A. baumannii, third predominant causative agent, exhibited excellent susceptibility to ampicillin+ sulbactam and carbapenems. The recommended therapy is empirical and should cover all important pathogens.     

A new antimicrobial susceptibility testing method of Escherichia coli against ampicillin by MSPQC

A new antimicrobial susceptibility testing method by multi-channel series piezoelectric quartz crystal (MSPQC) was proposed. This method was used to test susceptibility of clinical Escherichia coli isolates against ampicillin. Both the minimum inhibitory concentrations (MICs) and interpretive categorization of clinical E. coli isolates were determined by proposed method. Comparing tests were run at the same time by the agar dilution method and the disk diffusion method. The experimental results showed that MSPQC method had a good agreement with the reference methods. Compared with those methods, the MSPQC method is simple, rapid, and convenient to perform. It can offer both a minimum inhibitory concentration (MIC) and an interpretive category result.     

Susceptibility of Genital Mycoplasmas to Antimicrobial Agents

The susceptibility of 11 T-strains, 12 strains of Mycoplasma hominis, and a single strain of M. fermentans to 15 antimicrobial agents was determined by study of inhibition of metabolic activity in a broth dilution system. All three species were inhibited by tetracycline, chloramphenicol, streptomycin, gentamicin, and kanamycin, and were relatively resistant to cephalothin, cephaloridine, polymyxin, vancomycin, and ampicillin. Three antimicrobial agents had significant differential effects on these species. Erythromycin was more active against T-strains than against M. hominis or M. fermentans. Lincomycin, clindamycin, and nitrofurantoin had greater activity against M. hominis and M. fermentans than against T-strains. The activity of the drugs tested was generally uniform over a wide range of inocula. The effect of pH and the difference between minimal inhibiting and minimal mycoplasmacidal concentrations of the drugs tested were consistent with expectations based on the effects of these drugs on bacteria.     

Use of ureidopenicillins for selection of plasmid vector transformants in Pseudomonas aeruginosa and Pseudomonas putida.

Broad-host-range plasmids coding for beta-lactamase were successfully selected after transformation of Pseudomonas strains. Transformants of both Pseudomonas aeruginosa and Pseudomonas putida containing plasmid pRO1614 were isolated in media containing low concentrations of piperacillin. These strains were also susceptible to other ureidopenicillins. Similar selections of transformants with carbenicillin, ampicillin, or ticarcillin required high concentrations of antibiotics and yielded backgrounds of spontaneous resistant mutants.