Misidentification of Cutibacterium namnetense as Cutibacterium acnes among clinical isolates by MALDI-TOF VitekMS: usefulness of gyrB sequencing and new player in bone infections.

The taxonomy modification of Propionibacterium sp. with the description of new species, especially Cutibacterium namnetense, raises the question of species distribution in routine clinical samples. We performed a retrospective study during 3 years before the implementation of MALDI-TOF. Two hundred sixty-nine isolates were included in the study. MALDI-TOF identification, 16S rRNA, and new developed gyrB partial sequencings were performed. The most representative species was C. acnes in 88% of the cases, regardless of the origin of the clinical sample. Eventually, we identified three C. namnetense strains, representing a 1.1% prevalence over the period of time, including two bone infections. MALDI-TOF databases should be regularly updated to incorporate new species. gyrB sequencing constitutes a both easy and relevant method to identify Cutibacterium sp. especially C. namnetense, a new player in bone infections.

Catheter-related bloodstream infection due to Tsukamurella pulmonis identified by MALDI-TOF spectrometry, 16S rRNA gene sequencing, and secA1 gene sequencing in an immunocompromised child: a case report and literature review.

Tsukamurella species are Gram-positive bacilli related to aerobic Actinomyces. Originally reported from the environment, Tsukamurella species have also been described in human infections, especially in bacteremia. A literature review analysis revealed that Tsukamurella spp. are often initially considered as contaminant microorganisms, especially due to bacterial identification issues. Here, we report a catheter-related bloodstream infection in an immunocompromised child caused by Tsukamurella pulmonis. Matrix-Assisted Laser Desorption/Ionization-Time Of Flight (MALDI-TOF) mass spectrometry allowed rapid genus-level identification and contributed to better patient care. However, accurate species-level identification required 16S rRNA gene sequencing and secA1 gene sequencing. Considering the increased number of Tsukamurella infections, the implementation of new Tsukamurella species in MALDI-TOF databases is required to be more discriminant.

Propionibacterium/Cutibacterium species-related positive samples, identification, clinical and resistance features: a 10-year survey in a French hospital.

A 10-year retrospective study of Propionibacterium/Cutibacterium-positive samples gathered from hospitalized patients was conducted at Nantes University hospital. A total of 2728 Propionibacterium/Cutibacterium-positive samples analyzed between 2007 and 2016 were included. Due to the implementation of MALDI-TOF identification in 2013, most non-Cutibacterium acnes isolates were identified a second time using this technology. Over that period, Cutibacterium acnes remained the most predominant species accounting for 91.5% (2497/2728) of the isolates, followed by Cutibacterium avidum (4.2%, 115/2728) and Cutibacterium granulosum (2.4%, 64/2728). Regarding the origin of samples, the orthopaedic department was the main Cutibacterium sample provider representing 51.9% (1415/2728) of all samples followed by the dermatology department (11.5%, 315/2728). Samples were recovered from various tissue locations: 31.5% (858/2728) from surgery-related samples such as shoulder, spine or hip replacement devices and 19.1% (520/2728) from skin samples. MALDI-TOF method revealed misidentification before 2013. Cutibacterium avidum was falsely identified as C. granulosum (n = 33). Consequently, MALDI-TOF technology using up-to-date databases should be preferred to biochemical identification in order to avoid biased species identification. Regarding antibiotic resistance, 14.7% (20/136) of C. acnes was resistant to erythromycin. 4.1% (41/1005) of C. acnes strains, 17.9% (12/67) of C. avidum strains and 3.6% (1/28) of C. granulosum strains were found resistant to clindamycin.

Carbapenemase-producing Enterobacteriaceae digestive carriage at hospital readmission and the role of antibiotic exposure.

BACKGROUND: Colonization by carbapenemase-producing Enterobacteriaceae (CPE) may persist for several months after hospital discharge, especially in patients with altered microbiota. AIM: To identify how many previously OXA-48 CPE-positive patients identified during an outbreak period were readmitted; to evaluate their CPE-positive or -negative digestive tract colonization at hospital readmission and during readmission stay; and to assess the role of antibiotic exposure on their CPE colonization status during readmission. METHODS: All CPE cohort patients from June 2013 to May 2016 (N = 189) were registered in a survey database and were systematically identified at readmission by a daily informatics and alert program using specific hospital population number. Each cohort patient was systematically screened for CPE colonization on the day of readmission and then weekly if the length of stay was more than six days. FINDINGS: In all, 114 (60.3%) patients previously CPE-colonized were readmitted to our hospital. Excluding the 12 patients who were not screened because their period of readmission was <24 h, 88 patients were negative (86.3%) and 14 were positive (13.7%) for CPE colonization at first hospital readmission. The 14 CPE-positive patients did not change their infectious status and remained CPE-positive during the study period. Of the 88 negative patients, 65 remained negative during the study period, and 23 subsequently became CPE-positive after the negative readmission screening. CPE-positive colonization was significantly associated with antibiotic exposure during readmission periods (P < 0.001). CONCLUSION: Negative screens at hospital readmission did not necessarily predict resolution of CPE carriage. Antibiotic exposure appears to influence the risk of remaining CPE positive.

Prevalence of Haemophilus influenzae with alteration of PBP 3 sequence over a 1-year period in a French hospital: focus on a clinical failure after ceftriaxone treatment.

Among 547 Haemophilus influenzae isolates recovered in our center, 45 displayed a phenotype of loss of PBP 3 affinity (8.2%). Two isolates with 6 substitutions in PBP 3 showed decreased susceptibility to third-generation cephalosporins. Clinical data revealed clinical failure after ceftriaxone treatment in a context of bronchitis in a patient with pulmonary sarcoidosis.

Duodenoscopy: an amplifier of cross-transmission during a carbapenemase-producing Enterobacteriaceae outbreak in a gastroenterology pathway.

Carbapenemase-producing Klebsiella pneumoniae (OXA-48 CPE) were identified in five patients who underwent an endoscopy with the same duodenoscope in October 2015. The endoscope was the only epidemiological link between these cases. A transient contamination of the duodenoscope following a failure in the disinfection process may have been the cause of transmission.

Community-acquired Clostridium difficile infections.

OBJECTIVE: To describe the management and treatment of community-acquired C. difficile infections (CDI) and to evaluate family physicians' (FP) knowledge and practice. PATIENTS AND METHODS: Observational study from December 2013 to June 2014. All community-acquired CDI case patients diagnosed in the community or at the University Hospital of Nantes were prospectively included. A questionnaire was mailed to 150 FPs of the area of Nantes. RESULTS: A total of 27 community-acquired CDI case patients were included (incidence: 7.7 case patients/100,000 inhabitants). Mean age was higher among case patients diagnosed at hospital (69years) compared with those diagnosed in the community (44years). Fifteen patients were treated at home (55%) and 22 received a first-line treatment with metronidazole. Only one patient did not receive any prior antibiotic treatment. Amoxicillin-clavulanic acid was mainly prescribed (68%) for respiratory and ENT infections (40%). Twenty-three patients were cured on Day 7 and three had complications (two deaths). Thirty-one of 47 FPs reported to have already managed CDI patients. Twenty-two FPs reported to usually treat patients with uncomplicated CDI at home, 21 to refer patients to a specialist, and three to hospital. Forty-one FPs reported to prescribe a CD toxin test only after recent antibiotic exposure and 30 when patients are at risk of CDI. CONCLUSION: The incidence and impact of community-acquired CDIs may be underestimated and the unjustified use of antibiotics may promote their emergence. FPs are not used to treat CDIs as more than 50% prefer referring patients to hospital or to a specialist.

Systematic analysis of the relationship between antibiotic use and extended-spectrum beta-lactamase resistance in Enterobacteriaceae in a French hospital: a time series analysis.

The influence of hospital use of antibiotics other than cephalosporins and fluoroquinolones on extended-spectrum beta-lactamase (ESBL) resistance among Enterobacteriaceae is poorly known. Our objective was to explore the association between ESBL and hospital use of various classes of antibacterial agents. The relationship between monthly use of 19 classes of antibacterial agents and incidence of nosocomial ESBL-producing Enterobacteriaceae in a French hospital was studied between 2007 and 2013. Five antibiotic classes were significantly and independently associated with ESBL resistance. Uses of tetracyclines (link estimate ± SE, 0.0066 ± 0.0033), lincosamides (0.0093 ± 0.0029), and other antibacterial agents (0.0050 ± 0.0023) were associated with an increased incidence, while nitrofurantoin (-0.0188 ± 0.0062) and ticarcillin and piperacillin with or without enzyme inhibitor (-0.0078 ± 0.0031) were associated with a decreased incidence. In a multivariate model including 3rd- and 4th-generation cephalosporins, fluoroquinolones, amoxicillin, and amoxicillin-clavulanate, 3rd- and 4th-generation cephalosporins (0.0019 ± 0.0009) and fluoroquinolones (0.0020 ± 0.0008) were associated with an increased ESBL resistance, whereas amoxicillin and amoxicillin-clavulanate were not. Hospital use of tetracyclines and lincosamides may promote ESBL resistance in Enterobacteriaceae. Nitrofurantoin and ticarcillin and piperacillin with or without enzyme inhibitor should be considered as potential alternatives to broad-spectrum cephalosporins and fluoroquinolones to control the diffusion of ESBL resistance.

Challenges of controlling a large outbreak of OXA-48 carbapenemase-producing Klebsiella pneumoniae in a French university hospital.

A large outbreak of OXA-48 carbapenemase-producing Klebsiella pneumoniae at Nantes University Hospital was investigated. The index case had no history of travel or hospitalization abroad and had been hospitalized in the internal medicine department for more than one month when the epidemic strain was isolated from a urine sample in June 2013. Seventy-two secondary cases were detected by weekly screening for gastrointestinal colonization during the two phases of the outbreak from June to October 2013 (33 cases) and from November 2013 to August 2014 (39 cases). Spread of the epidemic strain was attributed to the proximity of, and staff movement between, the infectious diseases (32 cases) and the internal medicine (26 cases) departments; 14 secondary cases were also observed in the renal transplant department following the transfer of an exposed patient from the infectious diseases department. Most of the patients (90%) were colonized and no death was linked to the epidemic strain. More than 3000 contact patients were reviewed and 6000 rectal swabs were performed. Initial control measures failed to control the outbreak owing to the late detection of the index case. The late implementation of three successive cohort units, the large number of transfers between wards, and the frequent readmission of cases contributed to the incomplete success of control measures.

[Syphilis in Nantes tertiary care hospital between 2000 and 2010: a case series of 36 hospitalized patients]. / La syphilis au CHU de Nantes entre 2000 et 2010 : à propos de 36 patients hospitalisés.

PURPOSE: Syphilis infection increase has been observed since the early 2000s. The medical records of patients hospitalized for syphilis at the tertiary care hospital of Nantes between 2000 and 2010 were retrospectively reviewed. METHODS: Cases were selected on the basis of serological database of the laboratory of bacteriology and extraction from the PMIS. Syphilis cases were defined by both positive TPHA and VDRL tests. RESULTS: The number of positive serology testing was increased eightfold within ten years. Among the 36 patients with syphilis hospitalized cases, 97% were male, aged 17 to 75 years. Eighteen were HIV-infected patients. Among them, 94% were homosexuals and 67% had a history of sexually transmitted infections. The mean time between symptoms and diagnosis was significantly higher in non HIV-infected patients. Clinical forms of syphilis were cutaneomucous secondary syphilis with frequent systemic symptoms for 33%, neurosyphilis, including frequent uveitis for 50%, and gummatous tertiary syphilis involving bones for one patient. Secondary syphilis cases were treated with one to three doses of benzathine penicillin G. Late syphilis and cases of neurosyphilis were treated with penicillin G or ceftriaxone. Neurosensory sequelae accounted for 39% neurosyphilis cases. CONCLUSION: This study highlights the incidence increase of syphilis cases in France, frequent poor prognosis of neurosyphilis cases, and diagnosis difficulties, particularly in non HIV-infected patients. This emphasizes the broader use of syphilis serology for compatible medical situations.

[Interest of systematic syphilis serology testing prior to assisted reproductive technology cycles: a retrospective study in Nantes, France]. / Quel intérêt pour la réalisation systématique de la sérologie syphilis avant AMP ? Étude rétrospective au CHU de Nantes de 2000 à 2010.

INTRODUCTION: Syphilis has recently re-emerged in young adults. However, serological testing of patients undergoing assisted reproductive technology (ART) cycles and/or semen cryopreservation is not mandatory in every country. PATIENTS AND METHOD: We conducted a retrospective analysis on our local database to evaluate the prevalence of syphilis among infertile couples, and discuss the interest of systematic syphilis serology testing in these patients. RESULTS: Between 2000 and 2010, only one patient out of 4314 was diagnosed with chronic syphilis. CONCLUSION: This study illustrates that systematic serological screening for syphilis in couples referred for semen cryopreservation or ART only allows exceptionally rare diagnosis. The cost-effectiveness of this strategy should be reconsidered.

[Impact of enterobacteriaceae-producing extended-spectrum beta-lactamases (ESBLE) incidence increasing on barrier precautions implementation in a university hospital]. / Impact de l'augmentation de l'incidence des entérobactéries productrices de bêta-lactamases à spectre étendu (EBLSE) sur l'application des précautions complémentaires dans un centre hospitalier universitaire.

AIM OF THE STUDY: The French national surveillance program of multidrug-resistant bacteria (MDR) shows an increase of enterobacteriaceae-producing extended-spectrum beta-lactamases (ESBLE) incidence. The objectives of this study were to assess: the incidence of EBLSE in a large French university hospital between 2005 and 2010, and the difference of barrier precautions implementation between ESBL and other MDR. METHODS: The ESBLE incidence measure used data from the laboratory of bacteriology. The application of isolation and barrier precautions was analyzed from the MRB national surveillance data over a 3-year period from 2006 to 2008. Data were entered and analyzed using Epi Info software. The Chi(2) test was used for the comparison of proportions. RESULTS: The overall incidence of ESBLE was significantly higher in 2010 than in 2005 (0.20/1000 patients-days vs 0.03/1000 patients-days, respectively) (P<0.001). The same was observed for Escherichia coli incidence with rates ranging from 0.02/1000 patients-days in 2005 to 0.15/1000 patients-days in 2010. Isolation precautions for patients with EBLSE were applied in relation for most patients with MRB (ESBLE vs others), without significant difference. CONCLUSION: The surveillance programme of MRB showed a significant increase of ESBLE, especially for E. coli. Isolation and barrier precautions were used for most patients with MRB, including ESBLE.

Semen cultures analysis: retrospective study during a 6-year period and interest in the management of infertility.

In the past decade, the number of couples consulting an assisted reproductive techniques (ART) center for infertility has increased in most European countries. In France, sperm bacterial examination must be performed every 6 months in couples undergoing in vitro fertilization (IVF) cycles, according to 2010 French ART Guidelines. The aim of this study was to analyze the results from such samples at Nantes University Hospital and to assess their potential value for infertile couples undergoing ART cycles. Between 2003 and 2008, semen cultures performed were analyzed according to bacterial enumeration, type and number of bacterial species, and their antibiotic resistance profile. A total of 14,119 semen cultures were performed, showing an annual increase of 45% from the start to the end of the study. The proportion of positive semen cultures was stable throughout the study period (40 to 45%). Many bacterial species were considered as contaminants (coagulase-negative staphylococci, alpha-hemolytic streptococci). For pathogen agents (in most cases, Enterobacteriaceae), the antibiotic resistance profile revealed mostly a susceptible phenotype. Finally, every positive bacterial result had direct consequences on the IVF cycle management, with subsequent reinforced advice on the hygiene procedure before sample collection and/or antibiotics prescription.

Correlation between the VITEK2 system and cefoxitin disk diffusion for the daily detection of oxacillin resistance in a large number of clinical Staphylococcus aureus isolates.

The aim of the present study was to compare the performance of the new VITEK2 AST-P551 card with the cefoxitin disk diffusion method for the daily detection of methicillin resistance with a high number of Staphylococcus aureus clinical isolates. Detection of the PBP2a protein or mecA gene was performed for each discordant case. Seventy (3.3%) isolates out of 2,107 clinical strains showed discordant results, two very major errors, four major errors and 64 minor errors. Fifty-nine (84%) discordant results were resolved, with a final overall agreement of 99.5%. Eleven (0.5%) strains remained discordant (minor error [mE]). Four of 370 MRSA strains were misclassified as susceptible in daily practice by the cefoxitin disk diffusion method. All of these strains were resistant to aminoglycosides and/or fluoroquinolones. The VITEK2 system is highly reliable for methicillin resistance detection at the routine level. Oxacillin-susceptible classified clinical strains with associated resistance patterns required attention.

[Pays de la Loire Pneumococcus Observatory: antimicrobial resistance of Streptococcus pneumoniae in 2007]. / Observatoire régional du pneumocoque en région Pays de la Loire: résistance de Streptococcus pneumoniae aux antibiotiques en 2007.

OBJECTIVES: Between 1st January and 31st December 2007, 331 Streptococcus pneumoniae strains were collected from 20 participating laboratories in the Pneumococcus Network Pays de la Loire county to assess their susceptibility to antibiotics and to evaluate serogroups of strains. METHOD: The coordinating centre performed MICs of penicillin G, amoxicillin and cefotaxime by the reference agar dilution method. Results were interpreted according to CA-SFM breakpoints. Sensitivity to other antibiotics were studied and serotyping of each strain performed. RESULTS: Three hundred and thirty one strains were isolated in 2007. They were collected from 30 cerebrospinal fluids, 239 blood samples, 53 middle ear fluids and nine pleural fluids. The percentage of pneumococci with decreased susceptibility to penicillin G (PDSP) was 39% and was higher in children (51%) than in adults (35%). The PDSP were often multidrug resistants especially with a high percentage of resistance to erythromycin (87.6% versus 8.4% for pneumococci sensitive to penicillin G). Finally, the most prevalent serogroup was the serogroup 19 (29.6% of isolates). CONCLUSION: A decrease of PDSP was observed since 2001 and high-level resistant strains to beta-lactams remain low. The rate of PDSP in Pays de la Loire is in the national average.

[Retrospective study of serological tests for syphilis diagnosis at Nantes University hospital, between 1999 and 2006]. / Etude rétrospective des sérologies de syphilis au CHU de Nantes, de 1999 à 2006.

Since 2000, a resurgence of syphilis cases was observed in France and, particularly, in Paris area. The aim of this study was to evaluate the evolution of syphilis prevalence in Nantes area and its impact on our laboratory activity. Between 1999 and 2006, serological tests for syphilis performed at the laboratory were analysed according to the results of these tests, the age and patient sex and the wards. We treated about 32,000 serological tests, over an eight-year period. The number of tests increased by 7.5% per year and patients with a positive result were multiplied by three. These patients were men for 78%, with an average age of 43.4 years. The serological tests providing positive results were in general from two sectors, the anonymous and free detection center and the internal medicine ward and infectious diseases unit. Our study highlighted a strong increase in the number of positive tests, since 2001, with a clear orientation towards a sex male ratio in our area. This inclination currently did not show any decrease, at the opposite to what was observed by the InVS in Paris area.

Correlation of agar dilution and VITEK2 system for detection of resistance to macrolides, lincosamides and pristinamycin among Staphylococcus aureus and Staphylococcus epidermidis: association with genotypes.

The performance of the VITEK2 system was evaluated against the agar dilution reference procedure for testing susceptibility of Staphylococcus aureus and Staphylococcus epidermidis to macrolides, lincosamides and streptogramins (MLS). Eighty clinical isolates were selected according to their resistance phenotype and genotype. Results for erythromycin and clindamycin showed 100% agreement; results for lincomycin showed agreement of 78%, with one very major error and 17 minor errors; and results for pristinamycin showed agreement of 46%, with one major error and 43 minor errors. Most isolates resistant to lincomycin and streptogramin A (L SgAr phenotype) were falsely susceptible to lincomycin, and intermediately-resistant or resistant to pristinamycin, with the VITEK2 system. No resistance gene was detected. Most (80%) isolates resistant constitutively to MLS (MLS(r)BC phenotype) were falsely intermediately-resistant to pristinamycin with the VITEK2 system. The erm(A) gene was more common than erm(C) in MLS(r)BC strains. Resistance to pristinamycin alone (SgA SgB PTr phenotype), or associated with either lincomycin resistance (L SgA SgB PTr phenotype) or constitutive MLS(B) resistance (MLS(BC) SgA PTr phenotype), was well-characterised without discordant results. Resistance to pristinamycin was always associated with resistance to streptogramin A, encoded by the vga(A), vga(B), vgb(A) and vat(A) genes in association with the erm(A) or erm(C) genes.

[Should we screen for colonization to control the spread of multidrug resistant bacteria?]. / Quelles stratégies découlent de la surveillance des bactéries multirésistantes aux antibiotiques afin de mieux maîtriser leur diffusion?

Should we screen for colonization to control the spread of multidrug-resistant bacteria? A multidrug-resistant bacteria surveillance program was performed in 1999 at Laënnec Hospital (Nantes, France). After a 3-year period, the results permit us to determine the strategy to strengthen their spread. In 2001, Staphylococcus aureus resistant to methicillin represented 45% of the 202 multidrug-resistant bacteria isolated. The global incidence rate per 100 admissions remained stable between 1999 and 2001 (0.42%), but those of infections acquired in our institution decreased significantly from 0.27% in 1999 to 0.18% in 2001 (P < 0.05), particularly in medical care units (P < 0.04). In spite of this surveillance program and hygiene trainings, the global incidence remained stable during the study period, even if our action contributed to decrease the incidence of S. aureus resistant to methicillin acquired in our institution. Isolation precautions and screening for colonization policy in intensive care units are not sufficient to control the spread of MRB at hospital level. They should be strengthened by procedures for the transfer of infected or colonized patients and by antibiotic use control.

In vitro activity of the new ketolide telithromycin compared with those of macrolides against Streptococcus pyogenes: influences of resistance mechanisms and methodological factors.

One hundred and seven clinical isolates of Streptococcus pyogenes, 80 susceptible to macrolides and 27 resistant to erythromycin A (MIC >0.5 microgram/ml), were examined. The erythromycin A-lincomycin double-disk test assigned 7 resistant strains to the M-phenotype, 8 to the inducible macrolide, lincosamide, and streptogramin B resistance (iMLS(B)) phenotype, and 12 to the constitutive MLS(B) resistance (cMLS(B)) phenotype. MICs of erythromycin A, clarithromycin, azithromycin, roxithromycin, and clindamycin were determined by a broth microdilution method. MICs of telithromycin were determined by three different methods (broth microdilution, agar dilution, and E-test methods) in an ambient air atmosphere and in a 5 to 6% CO(2) atmosphere. Erythromycin A resistance genes were investigated by PCR in the 27 erythromycin A-resistant isolates. MICs of erythromycin A and clindamycin showed six groups of resistant strains, groups A to F. iMLS(B) strains (A, B, and D groups) are characterized by two distinct patterns of resistance correlated with genotypic results. A- and B-group strains were moderately resistant to 14- and 15-membered ring macrolides and highly susceptible to telithromycin. All A- and B-group isolates harbored erm TR gene, D-group strains, highly resistant to macrolides and intermediately resistant to telithromycin (MICs, 1 to 16 microgram/ml), were all characterized by having the ermB gene. All M-phenotype isolates (C group), resistant to 14- and 15-membered ring macrolides and susceptible to clindamycin and telithromycin, harbored the mefA gene. All cMLS(B) strains (E and F groups) with high level of resistance to macrolides, lincosamide, and telithromycin had the ermB gene. The effect of 5 to 6% CO(2) was remarkable on resistant strains, by increasing MICs of telithromycin from 1 to 6 twofold dilutions against D-E- and F-group isolates.

Relative potential for selection of fluoroquinolone-resistant Streptococcus pneumoniae strains by levofloxacin: comparison with ciprofloxacin, sparfloxacin and ofloxacin.

The aim of this study was to evaluate the relative potential of levofloxacin to select for resistance in Streptococcus pneumoniae in comparison with ciprofloxacin, sparfloxacin and ofloxacin. Two S. pneumoniae strains were studied; HBD 153 (parental strain, serotype 3) and HBD 964 (selected from the parental strain in an experimental mouse peritonitis infection model). MICs for the two strains were, respectively: 2 and 2 mg/L for ciprofloxacin; 2 and 4 mg/L for ofloxacin; 0.5 and 1 mg/L for sparfloxacin; 2 and 2 mg/L for levofloxacin. In-vitro, with 4 x MIC as the selection concentration, no mutant was obtained with strain HBD 153 (mutation frequency < 10(-8). With HBD 964, the mutation frequency was 9 x 10(-7) for ofloxacin, 10(-7) for ciprofloxacin, 4 x 10(-5) for sparfloxacin and < 10(-8) for levofloxacin. In an immunosuppressed mouse peritonitis model (20 mice per dose), the S. pneumoniae strains were studied with sc doses of ciprofloxacin, sparfloxacin and ofloxacin at 50 mg/kg od, and with sc levofloxacin at a dose of 10 and 50 mg/kg od, or 10 and 50 mg/kg bid. The MICs for strains isolated after antibiotic treatment and the mutation frequencies at 4 x MIC were determined. Against HBD 153, sparfloxacin was the most active treatment, followed by levofloxacin 10 mg/kg and 50 mg/kg bid, but strains identical to HBD 964 (showing a resistant variant at 4 x MIC) were selected by sparfloxacin. Against HBD 964, levofloxacin (10 mg/kg and 50 mg/kg) was the most active drug. Highly resistant mutants were selected by ofloxacin and ciprofloxacin, but not by sparfloxacin and levofloxacin. In conclusion, the relative potential of levofloxacin to select for fluoroquinolone-resistant S. pneumoniae is lower than that of ciprofloxacin, ofloxacin and sparfloxacin both in vitro and in vivo.