Ricardo Fernández-Roblas

Evaluation of Quantitative Analysis of Cultures from Sonicated Retrieved Orthopedic Implants in Diagnosis of Orthopedic Infection

ABSTRACT To improve the microbiological diagnosis of device-related osteoarticular infections, we have developed a protocol based on the sonication of device samples, followed by concentration and inoculation of the sonicate in a broad variety of media in a quantitative manner. Sixty-six samples from 31 patients were included in the study (17 of them with clinical diagnosis of infection). The sonication procedure had a sensitivity of 94.1%, which is better than that of conventional cultures (88.2%). One case of contamination and six cases of unexpected positive cultures were detected (specificity of 42.8%): two of these were considered to represent true infection, while the other four were considered to be nonsignificant (corrected specificity of 50%), although the clinical importance of these isolates is questionable. When we analyzed the number of CFU, no breakpoint between significant and nonsignificant isolates could be established. Based on our results, the procedure of sonication of retrieved implants is better than conventional cultures for the diagnosis of device-related infections. The significance of some isolates in patients without clinical infection remains uncertain. However, they may become pathogens and cannot be routinely considered to be contamination.

PCR-hybridization after sonication improves diagnosis of implant-related infection

Purpose We wanted to improve the diagnosis of implant-related infection using molecular biological techniques after sonication. Methods We studied 258 retrieved implant components (185 prosthetic implants and 73 osteosynthesis implants) from 126 patients. 47 patients had a clinical diagnosis of infection (108 components) and 79 patients did not (150 components). The fluids from sonication of retrieved implants were tested in culture and were also analyzed using a modified commercial PCR kit for detection of Gram-positive and Gram-negative bacteria (GenoType BC; Hain Lifescience) after extraction of the DNA. Results 38 of 47 patients with a clinical diagnosis of infection were also diagnosed as being infected using culture and/or PCR (35 by culture alone). Also, 24 patients of the 79 cases with no clinical diagnosis of infection were identified microbiologically as being infected (4 by culture, 16 by PCR, and 4 by both culture and PCR). Comparing culture and PCR, positive culture results were obtained in 28 of the 79 patients and positive PCR results were obtained in 35. There were 21 discordant results in patients who were originally clinically diagnosed as being infected and 28 discordant results in patients who had no clinical diagnosis of infection. Interpretation For prosthetic joint infections and relative to culture, molecular detection can increase (by one tenth) the number of patients diagnosed as having an infection. Positive results from patients who have no clinical diagnosis of infection must be interpreted carefully.

In Vitro Susceptibilities of Rapidly Growing Mycobacteria to Telithromycin (HMR 3647) and Seven Other Antimicrobials

ABSTRACT The antimicrobial activities of telithromycin (HMR 3647) and seven other antimicrobials against 94 strains of rapidly growing mycobacteria were determined. Telithromycin at a concentration of 1 μg/ml inhibited Mycobacterium peregrinum (100%),Mycobacterium chelonae (80%), Mycobacterium abscessus-Mycobacterium mucogenicum (44.4%), andMycobacterium fortuitum (2.1%). All or most strains ofM. peregrinum, M. fortuitum, and M. mucogenicum were inhibited by 2 μg of quinolones per ml.

Epidemiology of infections due to nonpigmented rapidly growing mycobacteria diagnosed in an urban area

The objective was to determine the incidence, clinical significance, and epidemiology of the isolates of nonpigmented, rapidly growing mycobacteria (NPRGM) in Madrid, Spain. Patients with new isolates of NPRGM during 2005 were selected prospectively for review of clinical charts. Clinical significance was analyzed according internationally accepted criteria. Randomly amplified polymorphic DNA (RAPD) was used for the genotyping of the isolates. NPRGM were identified in 70 patients (1.51 cases/100,000 inhabitants). The species were M. abscessus (in 5 patients), M. chelonae (in 9), M. fortuitum (in 40), M. peregrinum (in 9), M. mageritense (in 5), M. mucogenicum (in 2), and M. alvei (in 1 patient). The isolates were clinically significant in 17 cases (24.3%, 0.39 cases/100,000 inhabitants): in 4 cases of M. abscessus, in 5 of M. chelonae, and in 9 of M. fortuitum. Only 10.7% of the respiratory isolates were significant, whereas 75% of the nonrespiratory ones were significant (p < 0.001). RAPD analysis showed no relationship among the 74 strains available for the study. No characteristic resistance pattern could be found, although 4 strains appeared to be resistant to amikacin. Significant isolates were mainly nonrespiratory ones. The most significant species was M. abscessus. No relationship between the various isolates was detected, ruling out interhuman transmission between these cases.

Activity of nine antimicrobial agents against Corynebacterium group D2 strains isolated from clinical specimens and skin.

The in vitro activities of nine antimicrobial agents against Corynebacterium group D2 strains isolated from clinical specimens and from healthy skin of hospitalized patients were studied. Ciprofloxacin, ofloxacin, norfloxacin, vancomycin, and teicoplanin were very active against these microorganisms. There were no significant differences in susceptibility between clinical and colonizing isolates.

In Vitro Activities of Tigecycline and 10 Other Antimicrobials against Nonpigmented Rapidly Growing Mycobacteria

ABSTRACT We evaluated the in vitro activities of tigecycline and 10 other antibiotics against clinical isolates of nonpigmented rapidly growing mycobacteria. Fifteen collection strains and 165 clinical isolates were included in the study. Tigecycline showed the highest activity among all antibiotics studied: all the strains were inhibited by 1 mg/liter.

Changes in susceptibility ofSalmonella enteritidis, Salmonella typhimurium, andSalmonella virchow to six antimicrobial agents in a Spanish hospital, 1980–1994

To determine changes in the susceptibility patterns ofSalmonella enteritidis, Salmonella typhimurium, andSalmonella virchow over time, resistance to ampicillin, chloramphenicol, tetracycline, gentamicin, trimethoprim/sulfamethoxazole, and nalidixic acid was studied by the disk diffusion method in 1,024, 191, and 61 clinical isolates of these organisms, respectively. All isolates were recovered from 1980 to 1994 at a hospital in Madrid, Spain.Salmonella enteritidis isolates were less resistant (10.9%) thanSalmonella typhimurium (43.5%) andSalmonella virchow (36.1%; p<0.001). The incidence of resistance ofSalmonella enteritidis to ampicillin increased from 2.7% during the period 1980–1982 to 15.6% during 1992–1994 (p<0.001). The resistance ofSalmonella typhimurium to ampicillin, chloramphenicol, and tetracycline increased from 15.2%, 7.6%, and 21.2% respectively in 1980–1982 to 73.3%, 46.7%, and 73.3% in 1992–1994 (p<0.001). These marked increases in antimicrobial resistance suggest the need for public health interventions, several of which are discussed.

Microbiological Characterization and Clinical Significance of Corynebacterium amycolatum Strains

Abstract The laboratory records of patients with bacillus isolates identified as Corynebacterium xerosis were reviewed in an attempt to establish the clinical significance of the isolates, and the isolated strains were reidentified. Of the 22 strains available for reidentification, four were identified as Corynebacterium striatum and 18 as Corynebacterium amycolatum. Forty-one patients were considered to have Corynebacterium amycolatum isolates, and in 13 (31.7%) of these patients a genuine clinical infection occurred, comprising catheter-related infection in seven cases, surgical wound infection in five cases, and pilonidal cyst infection in one case. Most patients were treated with antimicrobial agents (vancomycin in seven cases and amoxicillin/clavulanic acid in four cases). All patients were cured. Corynebacterium amycolatum can cause genuine infection, usually hospital-acquired, and the clinical significance of isolates must be determined to ensure proper management of patients.

Inoculum effect and bactericidal activity of cefditoren and other antibiotics againstStreptococcus pneumoniae, Haemophilus influenzae, andNeisseria meningitidis

The inoculum effect on minimum inhibitory and minimum bactericidal concentrations of cefditoren, benzylpenicillin, ampicillin, cefotaxime, ceftriaxone, and meropenem against six clinical isolates each ofStreptococcus pneumoniae, Haemophilus influenzae, andNeisseria meningitidis was studied using inocula of approximately 104 to 105 and 107 to 108 cfu/ml. Vancomycin was also studied againstStreptococcus pneumoniae. The inoculum effect was observed only with benzylpenicillin and ampicillin against five of six strains ofHaemophilus influenzae. All antibiotics tested were bactericidal.

Importance of antibiotic penetration in the antimicrobial resistance of biofilm formed by non-pigmented rapidly growing mycobacteria against amikacin, ciprofloxacin and clarithromycin

OBJECTIVES To study the resistance of biofilms developed by non-pigmented rapidly growing mycobacteria (NPRGM) against amikacin, ciprofloxacin and clarithromycin in an in vitro model using clinical strains of different species. DESIGN Antimicrobial susceptibilities of different clinical strains of Mycobacterium abscessus, Mycobacterium chelonae, Mycobacterium fortuitum, Mycobacterium peregrinum, Mycobacterium mucogenicum and Mycobacterium mageritense using conventional techniques were measured. Biofilm resistance was measured by using the sandwich technique developed by Anderl et al. using a concentration of antibiotic of 50mg/L. Penetration of antibiotics through biofilm was measured using the same technique with minimal modifications. RESULTS NPRGM biofilms showed drug resistance (percentages of viable bacteria >1% of those of controls) against antibiotics that are commonly used for the treatment of infections caused by these organisms, although there are intraspecies differences between strains. We have detected differences in antibiotic penetration through biofilms with an important permeability barrier for ciprofloxacin. However, other mechanisms must be probably more important to explain the antimicrobial resistance of NPRGM biofilm. CONCLUSIONS Biofilms formed by NPRGM are resistant to amikacin, ciprofloxacin and clarithromycin. As no resistance differences between the tested antibiotics have been observed, it is likely that biofilm permeability of antibiotics is of low importance for antimicrobial resistance of biofilms.