Antimicrobial Susceptibility Of Clinical Isolates Research Articles

Effects of systemic administration of sitafloxacin on subgingival microflora and antimicrobial susceptibility profile in acute periodontal lesions

The aim of this study was to assess the effect(s) of systemic administration of sitafloxacin on subgingival microbial profiles of acute periodontal lesions. Antimicrobial susceptibility of clinical isolates was also investigated. Patients with acute phases of chronic periodontitis were subjected to clinical examination and microbiological assessment of their subgingival plaque samples by culture technique. Sitafloxacin was then administered (100 mg/day for 5 days) systemically. The clinical and microbiological examinations were repeated 6–8 days after administration. Susceptibilities of clinical isolates to various antimicrobials were determined using the broth and agar dilution methods. From the sampled sites in 30 participants, a total of 355 clinical isolates (34 different bacterial species) were isolated and identified. Parvimonas micra, Prevotella intermedia and Streptococcus mitis were the most prevalent cultivable bacteria in acute sites. Systemic administration of sitafloxacin yielded a significant improvement in clinical and microbiological parameters. Among the antimicrobials tested, sitafloxacin was the most potent against the clinical isolates with an MIC90 of 0.12 μg/ml at baseline. After administration, most clinical isolates were still highly susceptible to sitafloxacin although some increase in MICs was observed. The results suggest that systemic administration of sitafloxacin is effective against subgingival bacteria isolated from acute periodontal lesions.

Antimicrobial Susceptibilities of Clinical Isolates of HACEK Organisms

The "HACEK" organisms are a group of fastidious Gram-negative bacteria that cause a variety of infections, including infective endocarditis. Antimicrobial susceptibility testing is not universally available, and therapy for these infections is often empirical. We report the antimicrobial susceptibilities of 70 clinical HACEK isolates to 18 antimicrobials. All isolates were susceptible to ceftriaxone and levofloxacin, indicating that these agents remain appropriate empirical choices for the treatment of infections with this group of organisms.

Relation between the Antimicrobial Susceptibility of Clinical Isolates of Pseudomonas aeruginosa from Respiratory Specimens and Antimicrobial Use Density (AUD) from 2005 through 2008

To examine the relation between annual trends in the antimicrobial susceptibility of Pseudomonas aeruginosa and drug usage, we compared annual changes in the susceptibility rates of P. aeruginosa clinical isolates during a 4-year period and annual trends in the overall usage of antimicrobials during the same period. We studied annual trends in MIC(90)/MIC(50), antimicrobial use density (AUD), and antimicrobial susceptibility rates based on clinical breakpoints for 150 strains of P. aeruginosa isolated from respiratory specimens at Dokkyo Medical University Hospital from 2005 through 2008. The MIC(90)/MIC(50) of antimicrobials effective against P. aeruginosa in years 2005, 2006, 2007, and 2008 were as follows: imipenem, 32/2, 32/1, 8/2, and 16/1 microg/mL; meropenem, 8/1, 8/1, 4/0.5, and 4/0.5 microg/mL; and biapenem, 16/1, 32/0.5, 4/0.5, and 8/0.5 microg/mL, indicating that susceptibility to carbapenems increased slightly. The MIC(90)/MIC(50) was 4/0.25, 2/0.125, 1/0.125, and 2/0.25 microg/mL for ciprofloxacin, 8/4, 8/4, 4/4, and 8/4 microg/mL for amikacin, 64/16, 64/16, 64/16, and 64/16 microg/mL for sulbactam/cefoperazone, 8/2, 16/2, 32/2, and 8/2 microg/mL for ceftazidime, indicating little change. The AUDs of fourth-generation cephalosporins increased from 2005 to 2008 (16.2, 18.4, 28.0, and 23.0), while the AUDs of carbapenems decreased (25.7, 23.7, 10.9, and 12.5). The decrease in the AUDs of carbapenems was associated with increased susceptibility rates of P. aeruginosa to carbapenem derivatives. A continuous understanding of trends in the resistance of P. aeruginosa and various other pathogens is essential for designing countermeasures against nosocomial infections, including the proper and effective use of antimicrobials.

Antimicrobial susceptibility of clinical isolates from earthquake victims in Wenchuan

On 12 May 2008, an earthquake measuring 8.0 on the Richter scale struck Wenchuan County, Sichuan, China. Between 12 May and 11 June, 1823 victims were hospitalized in West China Hospital. These patients were severely injured, and most of their wounds were contaminated. Here, the results of bacteriological identification and antibiotic susceptibility testing of 725 non-duplicate isolates from earthquake victims are presented. Gram-negative bacilli were most frequently isolated (71.3%). Only 18.9% of isolates were Gram-positive bacteria; Candida spp. accounted for 9.7%, and Gram-negative cocci for 0.1%. After anaerobic culture, four Clostridium sordellii strains and one Clostridium bifermentans strain were isolated from deep wounds. Specimen culture from earthquake victims revealed a spectrum of pathogens and antibiotic susceptibilities that was different from that usually encountered in West China Hospital, especially concerning methicillin-resistant Staphylococcus aureus, extended-spectrum β-lactamase producers, and multidrug-resistant (MDR) non-fermenting Gram-negative bacilli. The pathophysiology of the injuries in earthquake victims was different from that in the patients who were not earthquake victims. A combination of environmental bacteria with a high proportion of Gram-negative bacteria was often observed in the earthquake victims. Approximately 26% of all earthquake victims were shown to be carriers of MDR microorganisms. Therefore, appropriate microbiological assessment upon admission, and identification of patients to be put in quarantine, is of paramount importance.

Antimicrobial susceptibility of clinical isolates of aerobic Gram-positive cocci and anaerobic bacteria in 2004

Antimicrobial susceptibility of clinical isolates of aerobic Gram-positive cocci and anaerobic bacteria in 2004

Antimicrobial susceptibility of clinical isolates of aerobic Gram-negative bacteria in 2004

Antimicrobial susceptibility of clinical isolates of aerobic Gram-negative bacteria in 2004

Antimicrobial susceptibility of clinical isolates of non-jejuni/coli campylobacters and arcobacters from Belgium

To determine the susceptibility of non-jejuni/coli campylobacters and arcobacters isolated from diarrhoeal stool specimens in Belgium. The MICs were determined using Etest for six antimicrobial agents including ampicillin, erythromycin, nalidixic acid, ciprofloxacin, gentamicin and tetracycline for the most frequently isolated non-jejuni/coli campylobacter and arcobacter strains in two University Hospital laboratories between 1995 and 2005. In total, 85 Campylobacter upsaliensis, 20 Campylobacter concisus, 11 Campylobacter fetus, 61 Arcobacter butzleri and 10 Arcobacter cryaerophilus isolates were tested. Most C. upsaliensis strains were susceptible to ampicillin (100%), gentamicin (100%), ciprofloxacin (94.1%) and tetracycline (100%), whereas 11.8 and 12.9% were resistant to nalidixic acid and erythromycin, respectively. For A. butzleri, 78.7% of isolates were susceptible to ampicillin and erythromycin. Most A. butzleri isolates were susceptible to ciprofloxacin (96.7%), nalidixic acid (82.0%), gentamicin (100%) and tetracycline (100%). All C. concisus strains were fully susceptible to ampicillin and tetracycline, but 5% of them were resistant to gentamicin, ciprofloxacin and erythromycin. Nearly all C. fetus and A. cryaerophilus strains were susceptible to erythromycin but the results should be interpreted with caution since only a small number of strains were tested. Fluoroquinolones should be considered in the treatment of severe C. upsaliensis and A. butzleri infection. When clinically indicated, erythromycin remains the first choice for the treatment of intestinal campylobacteriosis caused by C. concisus and C. fetus.

Antimicrobial susceptibility of clinical isolates of aerobic gram-positive cocci and anaerobic bacteria in 2002

Antimicrobial susceptibility of clinical isolates of aerobic gram-positive cocci and anaerobic bacteria in 2002

Antimicrobial susceptibility of clinical isolates of aerobic gram-negative bacteria in 2002

Antimicrobial susceptibility of clinical isolates of aerobic gram-negative bacteria in 2002

Effect of oxygen limitation on the in vitro antimicrobial susceptibility of clinical isolates of Pseudomonas aeruginosa grown planktonically and as biofilms

Pseudomonas aeruginosa, the predominant causative pathogen of chronic lung infection in patients with cystic fibrosis, may grow under anaerobic conditions as biofilms in the lungs of cystic fibrosis patients. To determine if growth under anaerobic conditions affects the antimicrobial susceptibility of P. aeruginosa, the susceptibility of clinical isolates of P. aeruginosa grown planktonically and as biofilms to a range of antibiotics was determined. Growth under anaerobic conditions did not reduce the ability of ceftazidime, meropenem, aztreonam, piperacillin, or piperacillin/tazobactam to inhibit planktonic growth, with MIC50 values for these antibiotics remaining unchanged or decreasing. However, tobramycin was less effective at inhibiting planktonic bacterial growth under anaerobic conditions, with the MIC50 of tobramycin increasing twofold. Growth under anaerobic conditions also decreased the bactericidal activity of tobramycin, with the MBC50 of tobramycin increasing fourfold. The killing kinetics of tobramycin was also examined under aerobic and anaerobic conditions for selected isolates. When isolates 6A and 12A were grown aerobically, concentration-dependent decreases in total viable count were apparent with tobramycin. In contrast, when these isolates were grown anaerobically, tobramycin at the same concentrations did not decrease the total viable count. When isolates were grown as biofilms under both aerobic and anaerobic conditions, isolate- and concentration-dependent differences in killing of the biofilms by tobramycin were apparent. However, tobramycin at concentrations up to 128 mg/l was unable to eradicate biofilms of any of the isolates tested, whether biofilms were grown aerobically or anaerobically. These results show that oxygen limitation may reduce, in a strain-dependent manner, the susceptibility to tobramycin of P. aeruginosa grown planktonically and as biofilms.

Nonfermentative gram-negative bacilli in cancer patients: increasing frequency of infection and antimicrobial susceptibility of clinical isolates to fluoroquinolones

Despite a decline in the frequency of gram-negative infections in cancer patients, there has been an increase in the proportion of such infections caused by nonfermentative gram-negative bacilli (NFGNB). We tested the in vitro activity of several quinolones against NFGNB isolated from cancer patients between February 2000 and February 2003, using a broth microdilution method. Ciprofloxacin was the most potent agent tested against Pseudomonas aeruginosa, although only 80% of isolates were susceptible to it. The newer quinolones (gatifloxacin, moxifloxacin, and garenoxacin) had better activity than ofloxacin, levofloxacin, and ciprofloxacin, against many other nonfermenters ( Stenotrophomonas maltophilia, P. fluorescens, and P. putida).

Current status of antimicrobial susceptibility of clinical isolates of Streptococcus pyogenes in Japan: report of a countrywide surveillance study

The growing number of macrolide-resistant strains of Streptococcus pyogenes is an increasing problem worldwide. In this study, we evaluated 62 clinical isolates of S. pyogenes obtained from the upper respiratory tract. Susceptibilities to penicillins, cephalosporins, fluoroquinolones, macrolides, and carbepenems were determined by minimal inhibitory concentrations (MICs). Expressions of macrolide-resistance genes (mefA, ermB, and ermTR) were also examined, by polymerase chain reaction (PCR). All strains were susceptible to beta-lactams. On the other hand, of the 62 S. pyogenes isolates, 6.5%, 6.5%, 6.5%, and 3.2% of the strains were resistant to azithromycin (AZM), roxithromycin (RXM), clarithromycin (CAM), and telithromycin (TEL), respectively. Four (6.5%) strains had a type of macrolide-resistance gene; there were two strains with ermB and two strains with ermTR, and these four strains were resistant to AZM, CAM (one strain was intermediately resistant), and RXM. Strains having ermB were resistant to TEL (MIC, > or = 8 microg/ml), while strains having ermTR were susceptible to TEL. Physicians and researchers need to take into consideration the macrolide resistance of some strains of S. pyogenes.

Antimicrobial susceptibility of clinical isolates of Enterobacteriaceae producing complex β-lactamase patterns including extended-spectrum enzymes

The antimicrobial susceptibility of 103 clinical isolates of Enterobacteriaceae to 11 antibiotics, was investigated, using a conventional inoculum size (5×10 5 CFU) and a higher inoculum size (5×10 8 CFU). All the isolates produced complex β-lactamase patterns, including an extended-spectrum β-lactamase (ESBL) of the TEM- or SHV-type plus other enzymes (a TEM-type or an SHV-type non-ESBL and/or a class C enzyme). The following repertoire of ESBLs was produced by the isolates: TEM-15, TEM-19, TEM-26, TEM-52, TEM-72, TEM-87, TEM-92, SHV-2a, SHV-5 and SHV-12, as assessed by sequencing. Production of the other enzymes was showed by analytical isoelectric focusing. Overall, meropenem was the most active agent and less influenced by inoculum size, while other β-lactams showed a lower activity and a significant inoculum size effect. In conclusion, from its in vitro performance, meropenem could be considered as the last resource drug against strains producing complex β-lactamase patterns including an ESBL.

Antimicrobial susceptibilities of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis isolated in two successive respiratory seasons in the US

Antimicrobial susceptibilities of clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis were determined in two consecutive respiratory seasons in the US and suggested that national susceptibilities to commonly tested antimicrobials changed only slightly from the 1999–2000 to the 2000–2001 respiratory season. However, a significant regional variation in S. pneumoniae susceptibilities was observed, as was a decrease in β-lactamase rates among H. influenzae from the 1999–2000 to 2000–2001 respiratory seasons.

Antimicrobial susceptibility of clinical isolates of Streptococcus pneumoniae from pediatric patients in the Republic of Korea and Japan

Antimicrobial susceptibility of clinical isolates of <I>Streptococcus pneumoniae</I> from pediatric patients in the Republic of Korea and Japan

Antimicrobial susceptibilities of clinical isolates of Haemophilus influenzae and Moraxella catarrhalis collected during 1999–2000 from 13 countries

To determine antimicrobial activity against Haemophilus influenzae and Moraxella catarrhalis. A central laboratory performed NCCLS susceptibility testing for all isolates and beta-lactamase and capsular serotype determinations for H. influenzae. A total of 2712 H. influenzae and 1079 M. catarrhalis were collected. H. influenzae susceptibilities were >90% for amoxicillin/clavulanate, cefaclor, loracarbef, cefprozil, cefuroxime, ciprofloxacin, azithromycin and clarithromycin and were <80% for trimethoprim/sulfamethoxazole and ampicillin. 19.3% were beta-lactamase positive. The most common serotype was type-b (5.6%); 86.1% were nontypeable. M. catarrhalis had MIC90 within therapeutic range for all antimicrobials except ampicillin. The conclusion of the study is that antimicrobials, except ampicillin and trimethoprim/sulfamethoxazole, remain good empiric choices against H. influenzae and M. catarrhalis.

Antibiotic susceptibility profiles of Bacteroides fragilis and Bacteroides thetaiotaomicron in Japan from 1990 to 1992.

The antimicrobial susceptibility of clinical isolates of Bacteroides fragilis and Bacteroides thetaiotaomicron collected from December 1990 through November 1992 was determined by the agar dilution technique. Metronidazole, imipenem, and cefoperazone/sulbactam remained highly active against both organisms. Rates of resistance to those agents were 0, 2%, and 0.9% in B. fragilis and 0, 0.9%, and 3% in B. thetaiotaomicron, respectively. Cefoxitin and other cephamycins were active against B. fragilis; rates of resistance to these agents did not tend to increase. With the inclusion of these data, the variation of rates of resistance to several agents was summarized for each year from 1987 to 1992. Rates of resistance to imipenem decreased in 1991 and 1992 among isolates of B. fragilis (2.3% in 1991, 1.8% in 1992) and B. thetaiotaomicron (2.4% in 1991, 0 in 1992). Rates of resistance to cefoxitin in B. thetaiotaomicron varied from 10% to 38% during these 6 years, though the distributional peak of MIC values did not change. The rate of resistance to ofloxacin in B. fragilis increased from 42% in 1989 to 81% in 1992. The rate of resistance to ampicillin in B. thetaiotaomicron was 68% in 1992--approximately 30% lower than before. Mostly, however, the rates of resistance to the antimicrobial agents examined did not change significantly.

A survey of antimicrobial susceptibility of clinical isolates of Enterococcus spp. from Irish hospitals

Nosocomial enterococcal infections are increasing. In order to establish the species distribution and antibiotic resistance patterns of enterococci in clinical specimens from hospitalized patients, we undertook a survey of 23 Irish hospitals. One thousand and five viable enterococcal strains were studied. Nine different species of enterococci were identified, including Enterococcus faecalis (84%); Enterococcus faecium (9%); and Enterococcus hirae (3%). The most common sites of isolation were the urinary tract (66%), wound and soft tissues (23%) and blood stream (3%). Many of the isolates were multiply antibiotic resistant. Ampicillin resistance was detected in 16%. Neither beta-lactamase production, nor high level penicillin resistance was detected. High level gentamicin resistance was evident in 7% of isolates and varied among species, e.g. 4% E. faecalis, 24% E. faecium, and 34% E. hirae. A number of isolates (23%) were also highly resistant to streptomycin. No clinically significant glycopeptide resistance was detected. The species distribution and incidence of multiple resistance was geographically widespread. This emphasizes the need for detailed speciation and in-vitro susceptibility testing along with the evaluation of alternative combination chemotherapeutic regimens for the management of serious enterococcal infection.

Antimicrobial susceptibilities of clinical isolates of Acinetobacter baumannii from Singapore

The in vitro activities of 17 antimicrobial agents alone or in combination against 70 clinical isolates of Acinetobacter baumannii from Singapore were determined by broth microdilution. The MICs of amoxicillin, ampicillin, ceftazidime, ceftriaxone, gentamicin, and piperacillin for 90% of the strains were > or = 128 micrograms/ml. Addition of sulbactam to ampicillin produced improved activity, whereas adding tazobactam to piperacillin did not. The MICs of amikacin, ciprofloxacin, and imipenem for 90% of the strains were 32, 32, and 16 micrograms/ml, respectively.

Frequency and antimicrobial susceptibility of clinical isolates of enterococci.

A study was performed to determine the frequency and antimicrobial susceptibility of Enterococcus species in clinical specimens. Of 943 aesculin-positive isolates, 873 (92%) were identified as enterococci (737 Enterococcus faecalis, 129 Enterococcus faecium and 7 other Enterococcus species). High-level resistance to gentamicin was found in 15.2% of Enterococcus faecalis, but not in Enterococcus faecium; 58% of Enterococcus faecium were resistant to gentamicin at a concentration of 64 mg/l. None of the isolates were shown to possess vancomycin resistance.