Susceptibility of Capnocytophaga to Antimicrobial Agents

Abstract

A total of 22 clinically isolated Capnocytophaga strains were tested for their susceptibility to antimicrobial agents frequently used in dental practice. All strains were susceptible to penicillin, ampicillin, cefadore, cefu-roxime, erythromycin, clindamycin and tetracycline. Metronidazole had poor activity against most strains.     

Determination of the In Vitro Susceptibility of 220 Mycobacterium fortuitum Isolates to Ten Antimicrobial Agents

Abstract

The authors investigated the In Vitro susceptibility to antimicrobial agents of 220 Mycobacterium fortuitum isolates originating from clinical samples (14) of patients attending the Hospital Universitario de Canarias and Hospital del Tórax, and from environmental sources (206): 3 from sea water, 10 from the water supply and 193 from sewage. The Minimum Inhibitory Concentration (MIC) was calculated using the broth microdilution method with Mueller-Hinton Broth without supplement. Amikacin was the most efficacious antimicrobial agent against all the isolates of M. fortuitum with an MIC which was considerably lower than its critical concentration. The good results achieved with amikacin In Vitro are confirmed by those obtained in vivo, with patients infected with M. fortuitum. No significant difference was found in the efficacy of amikacin and ofloxacin against all the isolates assayed.     

Combination of Ofloxacin and Other Antimicrobial Agents

Summary

We evaluated the combination of ofloxacin with piperacillin, gentamicin, vancomycin, rifampin, clindamycin, and metronidazole by the checkerboard agar dilution method against 165 isolates which included Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, Pseudomonas aeruginosa, Providencia stuartii, Acinetobacter, Staphylococcus aureus, Bacteroides fragilis, and Citrobacter perfringens. Synergy of piperacillin-ofloxacin was demonstrated for 50% and 40% respectively of E. cloacae and P. aeruginosa. Some ofloxacin and piperacillin-resistant isolates were susceptible with the combination. Ofloxacin-gentamicin was indifferent for aerobic gram-negative species. Ofloxacin and vancomycin or gentamicin was indifferent for S. aureus and E. faecalis, but rifampin-ofloxacin showed addition. Combination of ofloxacin and metronidazole or clindamycin or erythromycin was indifferent for aerobic and anaerobic species.

Ofloxacin could be combined with piperacillin with benefit against P. aeruginosa, but combination with aminoglycosides is not of benefit.     

Susceptibility of Eikenella corrodens to Antimicrobial Agents

Summary

Twelve Eikenella corrodens strains were isolated from dental infections and tested for their susceptibility to antimicrobial agents by an agar dilution method. All strains were susceptible to penicillin, ampicillin and tetracycline, and resistant to cephalexin and metronidazole and moderately resistant to erythromycin, gentamicin and cefaclor.     

In- Vitro Activity of Ciprofloxacin and Sixteen Other Antimicrobial Agents against Blood Culture Isolates

Summary

The in-vitro antibacterial activities of seventeen antimicrobial agents including ampicillin, amikacin, Augmentin, aztreonam, cefazolin, cefuroxime, cefotaxime, ceftizoxime, ceftriaxone, ciprofloxacin, cloxacillin, erythromycin, gentamicin, penicillin G, piperacillin and vancomycin were compared against 100 Gram-negative and Gram-positive strains isolated from blood culture specimens received at the King Abdulaziz University Hospital (KAUH), in Jeddah, Saudi Arabia.

The antibacterial susceptibility was determined by the minimal inhibitory concentration (MIC), using an agar dilution method. Ciprofloxacin exhibited the greatest activity, inhibiting 90% of the tested strains (MIC₉₀) at a concentration ranging from < 0.015-0.5 mg/L. Against cloxacillin resistant or susceptible strains of Staphylococcus aureus and coagulase-negative staphylococci, ciprofloxacin had similar activity with MIC₉₀, of 0.2 mg/L. Salmonella typhi and salmonella species which were resistant to ampicillin and augmentin remained sensitive to ciprofloxacin (Mid₉₀ < 0.015-0.125) mg/L.). Against gentamicin sensitive and resistant Pseudomonas aeruginosa and Pseudomonas species, ciprofloxacin MIC₉₀ was 0.5 and 1 mg/L respectively. Aminoglycosides, third generation cephalosporins, aztreonam and antipseudomonal penicillins, on the other hand, showed high MIC₉₀ well above the obtainable serum concentrations against Enterobacteriaceae and Pseudomonas species.     

In- Vitro Susceptibility of Borrelia burgdorferi and Borrelia hermsii to Ten Antimicrobial Agents

Summary

The in-vitro activity of ten antimicrobial agents against four strains of Borrelia burgdorferi originating both in the United States and Europe and against one isolate of B. hermsii was investigated. Ceftriaxone, erythromycin and roxithromycin were the most active drugs against both Borrelia species studied, with minimum bactericidal concentrations ranging from 0.015 μg/ml to 0.125 μ/ml.     

Extended-Spectrum β-Lactamases Conferring Resistance to Monobactams and Oxyimino-Cephalosporins in Clinical Isolates of Serratia marcescens

Abstract

We studied antibiotic resistance patterns and extended-spectrum β-lactamases (ESβLs) production in Serratia marcescens strains isolated in our hospital during 1993. We examined 210 S. marcescens isolates. Of these, 172 were obtained from 49 patients admitted to an intensive care ward; 157 out of 172 were obtained from February to October and presented the same pattern of antibiotic resistance, including monobactams and oxyimino-cephalosporins. The remaining 15 out of 172 isolates (obtained from September to December) were susceptible to all drugs tested, with the exception of first generation cephalosporins. Thirty-eight additional isolates were recovered, during the same period, from 28 patients admitted to wards other than the intensive care unit; also these strains showed the high susceptibility pattern reported above.

Epidemic strains of S. marcescens produced three different types of β-lactamase with pI 5.4, 5.5, and 8.4. In contrast, non-epidemic strains produced only one type of β-lactamase with pI 8.4. Conjugation experiments showed that the β-lactamases having a pI of 5.4 and 5.5 (but not the one with pI 8.4) were plasmid-mediated. Since the β-lactamase with pI 5.5 was capable of hydrolyzing monobactams and oxyimino-cephalosporins it was classified as ESβL. Electrophoretic analysis showed that plasmids obtained from multiresistant strains were of about 54 kb; these plasmids appeared also to code for aminoglycoside resistance. Our data indicate that the plasmid-mediated production of ESβLs may contribute to the epidemic spread of Serratia marcescens in high-risk wards.     

In- Vitro Activity of Ampicillin/Sulbactam and Other Antibiotics against Clinical Isolates of Haemophilus sp. and Branhamella catarrhalis

Summary

The ampicillin/sulbactam combination is one of several such drug combinations of a beta-lactam and suicide inhibitor having a wide spectrum of activity.

These characteristics induced us to evaluate the in vitro activity of this combination towards 54 strains of Haemophilus sp. (38 beta-lactamase producers) and 20 strains of Branhamella catarrhalis (16 beta-lactamase producers).

All strains were isolated from sputum, sinusal aspiration and tympanocentesis.

In the case of Haemophilus sp beta-lactamase producers, minimal inhibitory concentrations of ampicillin were reduced 8 times by the use of the inhibitor; good results were also obtained for B. catarrhalis.

Haemophilus influenzae, B. catarrhalis together with Streptococcus pneumoniae are recognized as the major pathogens involved in upper respiratory tract infections. The increasing frequency of beta-lactamase producing strains has impaired the use of aminopenicillins.

The combination of an inhibitor and beta-lactam restore the activity of the latter, suggesting that this combination can serve as first choice in therapy.     

Time-Kill Evaluation of Antimicrobial Regimens Against Clinical Isolates of Penicillin-Resistant Streptococcus pneumoniae

Abstract

The rate of penicillin-resistant Streptococcus pneumoniae isolates in Spain is high. At present, penicillin and ceftriaxone are two drugs chosen for treating serious infections. In this study the bactericidal activity of four antimicrobial regimens against ten clinical isolates of S. pneumoniae (five with an intermediate resistance to penicillin and five highly resistant ones), was determined by means of kill kinetics studies using either penicillin, or ceftriaxone, in combination with vancomycin, or fosfomycin. The concentrations of the antimicrobial regimens (MICs 4x, 1x and ¼x) were within possible physiological levels. While the combinations of penicillin, or ceftriaxone, plus vancomycin showed a significant increase in bactericidal activity, the bacterial reductions obtained in combination with fosfomycin were greater, achieving synergistic effects. These results suggest that in vivo trials with a regimen composed of ceftriaxone and fosfomycin would be worthwhile.     

Relationship of Antibiotic Resistance Phenotype to the R-Pyocin Susceptibility Pattern in Clinical Isolates of Pseudomonas aeruginosa

Summary

One hundred sixteen clinical isolates of Pseudotnonas aeruginosa were collected from 7 hospitals in Athens. All strains were studied for their susceptibility to cefotaxime, ceftazidime, carbenicillin, aztreonam, imipenem, nalidixic acid, ciprofloxacin, gentamicin, and chloramphenicol. In addition, the R-pyocin susceptibility pattern was determined and the strains were O-serotyped and tested for their agglutination in acriflavine. The isolates included 53 strains resistant to both gentamicin and carbenicillin, 13 to carbenicillin only, 20 to gentamicin only, and 30 sensitive to gentamicin and carbenicillin. The multiresistant isolates displayed relatively higher resistance to all other antibiotics except aztreonam and cefotaxime. Remarkably 30 out of 53 multiresistant isolates reacted with one pyocin only, namely pyocin R2. This R-pyocin response was not encountered in any other strains of the other antibiotic resistance phenotypes. These isolates belonged to the 0–12 serogroup. The 0–12 serogroup was represented only in a minority of strains giving other R-pyocin reactions. It is interesting that strains reacting with pyocin R5 only were mostly susceptible to antibiotics. The results clearly indicate lipopolysaccharide-core mutations in multiresistant clinical isolates of P. aeruginosa. Despite the fact that the R-pyocin resistance pattern can not define the precise possible defect, the multiple and high level resistance associated with R2-pyocin reaction seems to be an interesting trait.     

Susceptibility of Malassezia pachydermatis to aminoglycosides

Previous studies have evaluated the action of gentamicin against Malassezia pachydermatis. The aim of this study was to evaluate in vitro susceptibility of M. pachydermatis to the aminoglycosides— gentamicin, tobramycin, netilmicin and framycetin. The minimum inhibitory concentration (MIC) of gentamicin was determined following methods M27‐A3 microdilution and Etest^®. The Etest^® was used to determine the minimum inhibitory concentration (MIC) of the tobramycin and netilmicin. The Kirby‐Bauer test was used to determine the antibiotic susceptibility to the framycetin. The MIC50 and MIC90 were 8.12 μg/mL and 32.5 μg/mL by microdilution method for gentamicin. The MIC50, determined by the Etest^®, was 8 μg/mL for gentamicin and netilmicin and 64 μg/mL for tobramycin. The MIC90 was 16 and 32 μg/mL for gentamicin and netilmicin respectively. The MIC90 was outside of the detectable limits for tobramycin. To framycetin, 28 strains (40%) of the 70 M. pachydermatis isolates tested showed a diameter of 22 mm, 22 strains (31.42%) showed a diameter of 20 mm, 16 strains showed a diameter of ≤ 18 mm, and only 5.71% of the isolates showed a diameter of ≥ 22 mm. This study provides evidence of high in vitro activity of the aminoglycosides—gentamicin, tobramycin, netilmicin and framycetin against M. pachydermatis. For gentamicin Etest^® showed similar values of MIC50 y MIC90 that the obtained by microdilution method. We considered Etest^® method could be a good method for these calculations with aminoglycosides.     

Sensitivity of Clinical Yeast Isolates in Kuwait against a Number of Antifungal Agents

Summary: Clinical yeast isolates were taken from 37 patients with presumptive skin candidiasis in Kuwait. In vitro sensitivity tests using amphotericin B, nystatin, miconazole nitrate, 5-fluorocytosine and chlorhexidine were carried out. Amphotericin B was found to be the most effective and 5-fluorocytosine the least.
Zusammenfassung: Von 37 Patienten wurden wegen vermuteter Candida-Mykose Hefen isoliert. In-vitro-Resistenztestungen wurden mit Amphotericin B, Nystatin, Miconazolnitrat, 5-Fluorocytosin und Chlorhexidin ausgeführt. Bei dieser Testung wurde Amphotericin B als die wirksamste und 5-Fluorocytosin als die am wenigsten wirksame Substanz ermittelt.     

Prevalence of Type III Secretion Protein Exoenzymes and Antimicrobial Susceptibility Patterns from Bloodstream Isolates of Patients with Pseudomonas aeruginosa Bacteremia

Abstract

The purpose of this study was to determine the prevalence of two type III secretion effector proteins, exoU and exoS from bloodstream isolates of hospitalized patients with Pseudomonas aeruginosa (PSA) bacteremia, to characterize antimicrobial susceptibility patterns, and to compare mortality rates.

PSA bloodstream isolates and antibiotic susceptibility profiles were collected from a university-affiliated hospital. exoS and exoU genes were detected by polymerase chain reaction. Hospital mortality was assessed by medical chart review.

119 of 122 (97.5%) PSA bloodstream isolates contained either the exoS or exoU genes. exoS was the most prevalent (n=86; 70.5%) followed by exoU (n=31; 25.4%), both genes (n=2; 1.6%) or neither gene (n=3; 2.5%). Isolates containing the exoU gene were significantly more likely to be resistant to cefepime, ceftazidime, piperacillintazobactam, carbapenems, fluoroquinolones, and gentamicin (p<0.05 for all). Mortality was high in patients with PSA bacteremia and did not differ among patients infected with the exoS isolates (n=37; 43%) or exoU isolates (n=11; 35%).

One of two type III secretion effector proteins were almost universally present in PSA bloodstream isolates. Isolates containing the exoU gene were more likely to be resistant to multiple antibiotics.     

Susceptibility of Candida Species to Cilofungin (LY-121019)

The antifungal activity of a new semi-synthetic lipopeptide named cilofungin (LY-121019) was studied in vitro on 102 strains of Candida and Torulopsis glabrata. A standardized protocol for susceptibility testing by means of a microtiter Sabouraud broth dilution was used. The minimal inhibitory concentrations of cilofungin for C. albicans (N = 50) ranged from 0.039 to 5.0 micrograms/ml with a geometric mean of 0.47 micrograms/ml. The same results were obtained with C. tropicalis but one strain showed higher resistance (40 micrograms/ml) suggesting an Eagle effect. The MIC for T. glabrata ranged from 5.0-40.0 micrograms/ml. C. parapsilosis and C. krusei were less susceptible (5.0-40.0 micrograms/ml). These results indicate that cilofungin exhibits a potent inhibitory action on C. albicans and C. tropicalis. This effect was lower against the other species of Candida and T. glabrata studied.     

Antimicrobial Resistance in Gram-Negative Hospital Isolates: Results of the Turkish HITIT-2 Surveillance Study of 2007

Abstract

Resistance rates to amikacin, ciprofloxacin, ceftazidime, cefepime, imipenem, cefoperazone/sulbactam and piperacillin/tazobactam in Escherichia coli (n= 438)Klebsiella pneumoniae (n= 444)Pseudomonas aeruginosa (n= 210) and Acinetobacterbaumanni (n=200) were determined with e-test in a multicenter surveillance study (HITIT-2) in 2007. ESBL production in Escherichia coli and K. pneumoniae was investigated following the CLSI guidelines. Overall 42.0% of E.coli and 41.4% of K. pneumoniae were ESBL producers. In E. coli, resistance to imipenem was not observed, resistance to ciprofloxacin and amikacin was 58.0% and 5.5% respectively. In K. pneumoniae resistance to imipenem, ciprofloxacin and amikacin was 3.1%, 17.8% 12.4% respectively. In P. aeruginosa the lowest rate of resistance was observed with piperacillin/tazobactam (18.1%). A. baumanni isolates were highly resistant to all the antimicrobial agents, the lowest level of resistance was observed against cefoperazone/sulbactam (52.0%) followed by imipenem (55.5%). This study showed that resistance rates to antimicrobials are high in nosocomial isolates and show variations among the centers.     

In Vitro Susceptibility of Community-Acquired Urinary Tract Pathogens to Commonly Used Antimicrobial Agents in Spain: a Comparative Multicenter Study (2002-2004)

Abstract

The susceptibility patterns of 2724 uropathogens isolated in 9 Spanish regions during 2002, and 3013 obtained in 2004 were determined. The antibiotics tested were fosfomycin trometamol, amoxicillin, co-amoxiclav, cefixime, cefuroxime-axetil pipemidic acid, ciprofloxacin, trimethoprim plus sulphamethoxazole and nitrofurantoin.

Escherichia coli was the main pathogen in both studies (73% vs. 68.3%) followed by Proteus mirabilis (7.2% vs. 6.4%) and Klebsiella pneumoniae (5.4% vs. 5.2%). Enterococcus spp. (4.7% vs. 6.8%)Streptococcus agalactiae (1.7% vs.3.1%) and Staphylococcus saprophyticus (0.7% vs. 1.3%) were the most frequent Gram-positive pathogens. 31.3% of E. coli in 2002 and 32% in 2004 were susceptible to all antibiotics tested. Around 40% of E. coli were resistant to a single agent. 21.6-24.1% were resistant to two antibiotics. 35.4% of first period isolates, and 37.6% of second period ones were resistant to two or more classes of antibiotics. Fosfomycin (2.1- 2.8%) and nitrofurantoin (3.5-5.7%) had the lowest resistance rates for E. coli. Amoxicillin (58.2-58.7%), co-trimoxazole (30.8-33.8%) and ciprofloxacin (22.6-22.7%) showed the highest resistance rates, and their suitability as empiric treatments for UTI should probably be re-evaluated.     

In Vitro Activity of β-Lactam Antimicrobial Agents in Combination with Aztreonam Tested Against Metallob-β-Lactamase-Producing Pseudomonas aeruginosa and Acinetobacter baumannii

Abstract

We evaluate the antimicrobial interactions between aztreonam and selected beta-lactams when tested against metallo-β-lactamase (MβL)-producing clinical strains. Ten Pseudomonsa aeruginosa strains, including nine MβL-producers (IMP- 1, -2, -13, -16, VIM-1, -2, -7, SPM-1 and GIM-1) and five Acinetobacter baumannii strains, including three MβL-producers (IMP-1 and -2) were tested using time kill/bactericidal activity methods. Aztreonam at 4, 8 and 16 mg/L was combined with four other β-lactam antimicrobials (cefepime, ceftazidime, meropenem and piperacillin/tazobactam or ampicillin/sulbactam), each tested at the recognized susceptible breakpoint concentration. Enhanced activity (synergism or additive effect) was observed with four P. aeruginosa strains (IMP-16, VIM-2, SPM-1 and GIM-1 containing strains) and four A. baumannii strains, while antagonism was observed with two P. aeruginosa (IMP-16 and SPM-1-producing strains) and one A. baumannii (non-MβL) strain. All other strains showed indifferent interaction (variation of ± 1 log₁₀ CFU/ml) with any combination evaluated.     

Susceptibility of 228 Non-fermenting Gram-Negative Rods to Tigecycline and Six Other Antimicrobial Drugs

Abstract

The aim of the study was to determine the in vitro activity of tigecycline and 6 other antimicrobial drugs used in clinical practice against 228 clinical isolates of nonfermenting Gram-negative rods (NFGNRs) including Acinetobacter spp. Stenotrophomonas maltophilia, and Pseudomonas aeruginosa. Minimum inhibitory concentrations (MICs) were determined according to the recommendations of the Clinical and laboratory Standards institute. For tigecycline, we used the criteria approved by the FDA. Almost 50% of the clinical isolates of Acinetobacter spp. were resistant to piperacillin/tazobactam, ciprofloxacin, gentamicin, and ceftazidime. Strains of this microorganism were more susceptible to imipenem, and even more susceptible to colistin and tigecycline; no strains were resistant to tigecycline. Stenotrophomonas maltophilia showed even greater resistance to the drugs tested. Thus, all strains were resistant to imipenem and a large percentage (82.6%) were resistant to piperacillin/tazobactam. Resistance to the other agents tested was also high, with the exception of tigecycline, with only 3 resistant strains (MIC <8 mg/ml). Tigecycline, on the other hand, was scarcely active against Pseudomonas aeruginosa, which bears efflux pump systems such as MexXY-OprM. Almost 90% of strains were resistant to ciprofloxacin; only 8% were resistant to gentamicin; over half were colistin-intermediate or -resistant, and finally, approximately half of the strains were susceptible to the 3 beta-lactams studied. In conclusion, NFGNRs present variable susceptibility patterns, although they are generally highly resistant to antimicrobial agents including those considered more specific. Tigecycline, which showed good activity against most of the strains examined, broadens the spectrum of drugs available for the treatment of infections caused by these complex microorganisms.