Antimicrobial Susceptibility Testing Criteria Research Articles

Pyuria, bacteriuria and empirical antibiotic selection in pregnant women

Aims: In pregnancy, early diagnosis and proper treatment of urinary tract infections are crucial in preventing maternal and fetal comorbidities. Therefore, pregnant women should be screened for asymptomatic bacteriuria. This study aimed to evaluate the relationship between pyuria and bacteriuria and the susceptibility of uropathogens, as well as to review the empiric drug options for pregnant women. Methods: The presence of pyuria and bacteriuria in urine samples obtained from the pregnant outpatient clinic between January 2023 and December 2023 at Kırıkkale University Faculty of Medicine Hospital’s Infectious Diseases and Clinical Microbiology Laboratory was investigated. Uropathogens were identified and typed using the BD Phoenix™ M50 automated system for bacterial identification and antibiotic susceptibility testing, and antibiotic susceptibility was interpreted according to the European Committee on Antimicrobial Susceptibility Testing criteria. Results: A total of 1457 urine samples were evaluated in this retrospective study. Uropathogens were detected in 235 patients, while 301 samples were considered contaminated. Uropathogens were found to be susceptible to amoxicillin-clavulanate, trimethoprim-sulfamethoxazole, nitrofurantoin, and fosfomycin, in that order, for use in pregnant women. High resistance rates to third-generation cephalosporins were observed. Conclusion: According to the results of this study, local resistance rates against urinary pathogens in pregnant women should be determined at specific intervals, and empirical antibiotic therapy should be planned based on these data.

Estimation of epidemiological cut-off values for eight antibiotics used for treatment of bovine mastitis caused by Streptococcus uberis and Streptococcus dysgalactiae subsp. dysgalactiae

Interpretive criteria for antimicrobial susceptibility testing are lacking for most antimicrobials used for bovine streptococcal mastitis. The objectives of this study were to determine (tentative) epidemiological cut-off ((T)ECOFF) values for clinically relevant antibiotics used for treatment of bovine mastitis, and to estimate the proportion of acquired resistance (non-wild-types) in Streptococcus dysgalactiae subsp. dysgalactiae and Streptococcus uberis. A total of 255 S. uberis and 231 S. dysgalactiae subsp. dysgalactiae isolates were obtained in Denmark and Norway from bovine mastitis. The isolates were tested for susceptibility to 10 antibiotics using broth microdilution. In accordance with the European Committee on Antimicrobial Susceptibility Testing (EUCAST) standard operating procedure, additional published MIC distributions were included for the estimation of ECOFFs for cloxacillin, cephapirin, lincomycin and tylosin, and TECOFFs for amoxicillin, benzylpenicillin, cephapirin and oxytetracycline. The proportion of non-wild-type (NWT) isolates for the beta-lactams was significantly higher in the Danish S. uberis (45–55%) compared to the Norwegian isolates (10–13%). For oxytetracycline, the proportion of NWT was significantly higher in the Danish isolates, both for S. uberis (28% vs. 3%) and S. dysgalactiae (22% vs. 0%). A bridging study testing in parallel MICs in a subset of isolates (n = 83) with the CLSI-specified and the EUCAST-specified broths showed excellent correlation between the MICs obtained with the two methods. The new ECOFFs and TECOFFs proposed in this study can be used for surveillance of antimicrobial resistance, and - for antimicrobials licensed for streptococcal bovine mastitis - as surrogate clinical breakpoints for predicting their clinical efficacy for this indication.

Systematic investigation of the emerging pathogen of Tsukamurella species in a Chinese tertiary teaching hospital.

Tsukamurella species have been clinically regarded as rare but emerging opportunistic pathogens causing various infections in humans. Tsukamurella pneumonia has often been misdiagnosed as pulmonary tuberculosis due to its clinical presentation resembling tuberculosis-like syndromes. Tsukamurella species have also been confused in the laboratory with other phylogenetic bacteria, such as Gordonia. This study aimed to investigate the clinical, microbiological, and molecular characteristics; species distribution; and antimicrobial susceptibility of Tsukamurella species. Immunodeficiency and chronic pulmonary disease appeared to be risk factors for Tsukamurella pneumonia, and the presence of bronchiectasis and pulmonary nodules on imaging was highly correlated with this infection. The study confirmed that groEL (heat shock protein 60) and secA (the secretion ATPase) genes are reliable for identifying Tsukamurella species. Additionally, the ssrA (stable small RNA) gene showed promise as a tool for discriminating between different Tsukamurella species with the shortest sequence length. In terms of antimicrobial susceptibility, quinolones, trimethoprim/sulfamethoxazole, amikacin, minocycline, linezolid, and tigecycline demonstrated potent in vitro activity against Tsukamurella isolates in our study. The study also proposed a resistance mechanism involving a substitution (S91R) within the quinolone-resistance-determining region of the gyrA gene, which confers resistance to levofloxacin and ciprofloxacin. Furthermore, we found that disk diffusion testing is not suitable for testing the susceptibilities of Tsukamurella isolates to ciprofloxacin, imipenem, and minocycline. In conclusion, our systematic investigation may contribute to a better understanding of this rare pathogen. IMPORTANCE Tsukamurella species are rare but emerging human pathogens that share remarkable similarities with other mycolic acid-containing genera of the order Actinomycetales, especially Mycobacterium tuberculosis. Consequently, misdiagnosis and therapeutic failures can occur in clinical settings. Despite the significance of accurate identification, antimicrobial susceptibility, and understanding the resistance mechanism of this important genus, our knowledge in these areas remains fragmentary and incomplete. In this study, we aimed to address these gaps by investigating promising identification methods, the antimicrobial susceptibility patterns, and a novel quinolone resistance mechanism in Tsukamurella species, utilizing a collection of clinical isolates. The findings of our study will contribute to improve diagnosis and successful management of infections caused by Tsukamurella species, as well as establishing well-defined performance and interpretive criteria for antimicrobial susceptibility testing.

Detection of blaCTX-M-15 in an integrative and conjugative element in four extensively drug-resistant Haemophilus parainfluenzae strains causing urethritis

Haemophilus parainfluenzae is a commensal organism with rising numbers of multidrug-resistant (MDR) strains. This pathogen is of increasing clinical relevance in urogenital infection. The aim of this work was to identify and characterise the molecular mechanisms of resistance associated with four cephalosporin-resistant H. parainfluenzae strains collected from patients with urethritis. Antimicrobial resistance was determined by microdilution following European Committee on Antimicrobial Susceptibility Testing criteria. Strains were then analysed by whole-genome sequencing to determine clonal relationship and the molecular basis of antimicrobial resistance. Finally, a phylogenetic analysis was performed on all urogenital MDR strains of H. parainfluenzae previously isolated in our hospital. All strains were resistant to β-lactams, macrolides, tetracycline, fluoroquinolones, chloramphenicol, cotrimoxazole, and aminoglycosides. The resistance profile was compatible with the presence of an extended-spectrum β-lactamase (ESBL). Whole-genome sequencing detected blaCTX-M-15 that conferred high minimum inhibitory concentrations to cephalosporins in two novel integrative and conjugative elements (ICEHpaHUB6 and ICEHpaHUB7) that also harboured a blaTEM-1 β-lactamase. This study shows a novel blaCTX-M-15 ESBL carried in an integrative conjugative element in four extensively drug-resistant H. parainfluenzae strains. This resistance determinant could be transmitted to other sexually transmitted pathogens and this is a cause for concern.

In Vitro Activity of Ceftaroline and Comparators against Bacterial Isolates Collected Globally from Patients with Skin and Soft Tissue Infections: ATLAS Program 2019-2020.

The objective of this study was to assess the in vitro activity of ceftaroline and a panel of comparator agents against isolates causing skin and soft tissue infections (SSTIs) collected in Africa/Middle East, Asia-Pacific, Europe, and Latin America from 2019-2020. Minimum inhibitory concentrations (MIC) were determined using European Committee on Antimicrobial Susceptibility Testing criteria. All the methicillin-susceptible Staphylococcus aureus (MSSA) isolates were susceptible to ceftaroline. Across all regions, ceftaroline demonstrated potent activity against methicillin-resistant S. aureus (MRSA, susceptibility 89.5-93.7%) isolates. Susceptibility to vancomycin, daptomycin, linezolid, teicoplanin, trimethoprim sulfamethoxazole, and tigecycline was ≥94.1% in MSSA and MRSA isolates. Against β-hemolytic streptococci isolates, ceftaroline demonstrated very potent activity (MIC90 0.008-0.03 mg/L) across all regions. All β-hemolytic streptococci isolates were susceptible to linezolid, penicillin, and vancomycin (MIC90 0.06-2 mg/L). Among the extended-spectrum β-lactamases (ESBL)-negative Enterobacterales tested (E. coli, K. pneumoniae, and K. oxytoca), susceptibility to ceftaroline was high (88.2-98.6%) in all regions. All ESBL-negative Enterobacterales were susceptible to aztreonam. Potent activity was observed for amikacin, cefepime, and meropenem (94.1-100%) against these isolates. Overall, ceftaroline showed potent in vitro activity against isolates of pathogens causing SSTIs. Continuous surveillance of global and regional susceptibility patterns is needed to guide appropriate treatment options against these pathogens.

How Yeast Antifungal Resistance Gene Analysis Is Essential to Validate Antifungal Susceptibility Testing Systems.

ObjectivesThe antifungal susceptibility testing (AFST) of yeast pathogen alerts clinicians about the potential emergence of resistance. In this study, we compared two commercial microdilution AFST methods: Sensititre YeastOne read visually (YO) and MICRONAUT-AM read visually (MN) or spectrophotometrically (MNV), interpreted with Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing criteria, respectively.MethodsOverall, 97 strains from 19 yeast species were measured for nine antifungal drugs including a total of 873 observations. First, the minimal inhibitory concentration (MIC) was compared between YO and MNV, and between MNV and MN, either directly or by assigning them to five susceptibility categories. Those categories were based on the number of MIC dilutions around the breakpoint or epidemiological cut-off reference values (ECOFFs or ECVs). Second, YO and MNV methods were evaluated for their ability to detect the elevation of MICs due to mutation in antifungal resistance genes, thanks to pairs or triplets of isogenic strains isolated from a single patient along a treatment previously analyzed for antifungal resistance gene mutations. Reproducibility measurement was evaluated, thanks to three quality control (QC) strains.ResultsYO and MNV direct MIC comparisons obtained a global agreement of 67%. Performing susceptibility category comparisons, only 22% and 49% of the MICs could be assigned to categories using breakpoints and ECOFFs/ECVs, respectively, and 40% could not be assigned due to the lack of criteria in both consortia. The YO and MN susceptibility categories gave accuracies as low as 50%, revealing the difficulty to implement this method of comparison. In contrast, using the antifungal resistance gene sequences as a gold standard, we demonstrated that both methods (YO and MN) were equally able to detect the acquisition of resistance in the Candida strains, even if MN showed a global lower MIC elevation than YO. Finally, no major differences in reproducibility were observed between the three AFST methods.ConclusionThis study demonstrates the valuable use of both commercial microdilution AFST methods to detect antifungal resistance due to point mutations in antifungal resistance genes. We highlighted the difficulty to conduct conclusive analyses without antifungal gene sequence data as a gold standard. Indeed, MIC comparisons taking into account the consortia criteria of interpretation remain difficult even after the effort of harmonization.

Prevalence of multidrug-resistant and extended-spectrum beta-lactamase-producing Escherichia coli in urban community wastewater

Antibiotic resistance (ABR) and the spread of multidrug-resistant and extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli via wastewater to environmental compartments are of rapidly growing global health concern. Health care facilities, industries and slaughterhouses discharge high loads of ABR bacteria with their wastewater. However, the general community is often the biggest indirect discharger. Yet, research focusing explicitly on this important diffuse source is rather scarce raising questions about variations in the occurrence of ESBL-producing E. coli in wastewater from different communities and over time.Between April 2019 and March 2020, wastewater from three socio-spatially different districts in the Ruhr Metropolis, Germany, and the receiving wastewater treatment plant was sampled monthly and analysed for the occurrence of ESBL-producing E. coli via culture-based methods. Isolates were validated with matrix assisted laser desorption ionization time of flight mass spectrometry and antibiotic resistance profiles were analysed via microdilution. Results were interpreted using the European Committee on Antimicrobial Susceptibility Testing criteria. The German Commission for Hospital Hygiene and Infection Prevention criteria were used for multidrug-resistance categorization.Phenotypic ESBL-producing E. coli could be isolated from every wastewater sample demonstrating that the general community is an important indirect discharger. The socio-spatially disadvantaged area displayed higher absolute loads of ESBL-producing E. coli compared to the other two areas, as well as higher adjusted loads for domestic discharge and inhabitants, particularly during winter, indicating a higher ABR burden. Thirty-two isolates (28.6%) were characterized as multidrug-resistant Gram-negative bacteria (3MRGN). Resistance profiles varied only for those antibiotics, which can be administered in outpatient care. Resistance levels tended to be around 10% lower in the socio-spatially advantaged area. This study shows that spatial and seasonal influences regarding the occurrence of ESBL-producing E. coli in wastewater from socio-spatially different communities are identifiable.

Temporal and Geographic Variation in Antimicrobial Susceptibility and Resistance Patterns of Enterococci: Results From the SENTRY Antimicrobial Surveillance Program, 1997-2016.

BackgroundThe SENTRY Antimicrobial Surveillance Program was established in 1997 and presently encompasses more than 750 000 bacterial isolates from over 400 medical centers worldwide. Among these pathogens, enterococci represents a prominent cause of bloodstream (BSIs), intra-abdominal (IAIs), skin and skin structure, and urinary tract infections (UTIs). In the present study, we reviewed geographic and temporal trends in Enterococcus species and resistant phenotypes identified throughout the SENTRY Program.MethodsFrom 1997 to 2016, a total of 49 491 clinically significant enterococci isolates (15 species) were submitted from 298 medical centers representing the Asia-Pacific (APAC), European, Latin American (LATAM), and North American (NA) regions. Bacteria were identified by standard algorithms and matrix-assisted laser desorption ionization–time of flight mass spectrometry. Susceptibility (S) testing was performed by reference broth microdilution methods and interpreted using Clinical and Laboratory Standards Institute/US Food and Drug Administration and European Committee on Antimicrobial Susceptibility Testing criteria.ResultsThe most common Enterococcus species in all 4 regions were Enterococcus faecalis (64.7%) and E. faecium (EFM; 29.0%). Enterococci accounted for 10.7% of BSIs in NA and was most prominent as a cause of IAIs (24.0%) in APAC and of UTIs (19.8%) in LATAM. A steady decrease in the susceptibility to ampicillin and vancomycin was observed in all regions over the 20-year interval. Vancomycin-resistant enterococci (VRE) accounted for more than 8% of enterococcal isolates in all regions and was most common in NA (21.6%). Among the 7615 VRE isolates detected, 89.1% were the VanA phenotype (91.0% EFM) and 10.9% were VanB. Several newer antimicrobial agents demonstrated promising activity against VRE, including daptomycin (99.6–100.0% S), linezolid (98.0%–99.6% S), oritavancin (92.2%–98.3% S), tedizolid (99.5%–100.0% S), and tigecycline (99.4%–100.0% S).ConclusionsEnterococci remained a prominent gram-positive pathogen in the SENTRY Program from 1997 through 2016. The overall frequency of VRE was 15.4% and increased over time in all monitored regions. Newly released agents with novel mechanisms of action show promising activity against VRE.

Antibiotic Susceptibility of Cronobacter spp. Isolated from Clinical Samples.

Cronobacter spp. have been recognized as causative agents of various severe infections in pre-term or full-term infants as well as elderly adults suffering from serious underlying disease or malignancy. A surveillance study was designed to identify antibiotic resistance among clinical Cronobacter spp. strains, which were isolated from patients of two hospitals between May 2007 and August 2013. Altogether, 52 Cronobacter spp. isolates were analyzed. Although MALDI-TOF mass spectrometry recognized all Cronobacter sakazakii and Cronobacter malonaticus strains, it could not identify Cronobacter muytjensii strain. Nevertheless, all strains were identified as Cronobacter spp. using multilocus sequence typing (MLST). Strains were tested against 17 types of antibiotics, using the standard microdilution method according to the 2018 European Committee on Antimicrobial Susceptibility Testing criteria. Three Cronobacter species were identified as C. sakazakii (n = 33), C. malonaticus (n = 18), and C. muytjensii (n = 1); all isolates were susceptible to all tested antibiotics. All strains were PCR-negative for blaTEM, blaSHV, and blaCTX-M β-lactamase genes, as well. Even though the results of this study showed that Cronobacter spp. isolates were pan-susceptible, continued antibiotic resistance surveillance is warranted.

Surveillance of iclaprim activity: in vitro susceptibility of Gram-positive skin infection pathogens collected from 2015 to 2016 from North America and Europe

Iclaprim is a diaminopyrimidine, which inhibits bacterial dihydrofolate reductase, and surveillance data prior to 2006 suggested that iclaprim was active against Gram-positive pathogens including emerging drug-resistant pathogens. In an era of increasing antimicrobial resistance, we undertook testing iclaprim and comparators against 931 Gram-positive clinical isolates from the United States and Europe collected between 2015 and 2016. Susceptibility testing was performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Minimum inhibitory concentration (MIC) interpretations were based on CLSI and European Committee on Antimicrobial Susceptibility Testing criteria. MIC50/MIC90 was 0.03/0.12 for all Staphylococcus aureus, 0.06/0.06 for methicillin-susceptible S. aureus, 0.03/0.12 for methicillin-resistant S. aureus, 0.12/0.5 for Streptococcus agalactiae, ≤0.015/≤0.015 for Streptococcus anginosus, 0.03/0.06 for Streptococcus dysgalactiae, and ≤0.015 /0.03 μg/mL for Streptococcus pyogenes. Iclaprim was active against a contemporary collection (2015–2016) of Gram-positive bacteria isolated from the skin or soft tissue from patients with SSSI from the United States and Europe.

Aerococcus urinae, Alloscardovia omnicolens, and Actinotignum schaalii: the AAA Minor League Team of Urinary Tract Infection Pathogens

In clinical microbiology laboratories, advancements in the methods used for routine organism identification have facilitated more accurate species level resolution. This, along with increasing knowledge regarding “new” pathogens, has provided new insights into biology and has revealed clinical associations not previously known. Aerococcus urinae, Alloscardovia omnicolens, and Actinotignum schaalii are Gram-positive bacteria associated with urinary tract infections but can also be members of the urinary tract microbiota. In addition, invasive infections have been reported for the three bacteria, usually with a urinary tract source. Importantly, the use of routine biochemical testing methods for identification of these bacteria can result in misidentification or the incorrect determination that they are not clinically significant. Of these bacteria, only A. urinae has antimicrobial susceptibility testing criteria and interpretative breakpoints. Microbiologists and clinicians need to be aware of these urinary tract pathogens and how to correctly identify them.

Surveillance of tedizolid activity and resistance: In vitro susceptibility of Gram-positive pathogens collected over 5 years from the United States and Europe

In vitro activity of tedizolid and comparators against 11,231 Gram-positive clinical isolates from the United States (84 centers) and Europe (115 centers) were summarized as part of the Surveillance of Tedizolid Activity and Resistance program between 2009 and 2013. Susceptibility testing was performed according to Clinical Laboratory and Standards Institute (CLSI) guidelines. Minimum inhibitory concentration (MIC) interpretations were based on CLSI and European Committee on Antimicrobial Susceptibility Testing criteria. Tedizolid inhibited 99.7% of all isolates at MIC ≤0.5 mg/L; activity was similar regardless of methicillin or vancomycin resistance phenotypes of Staphylococcus aureus and enterococci, respectively. Tedizolid MIC >1 mg/L was reported for 3 S. aureus, 4 coagulase-negative staphylococci, and 2 enterococcal isolates; all streptococci were inhibited at MIC ≤0.5 mg/L. Tedizolid was ≥4-fold more potent than linezolid against all groups, including resistant phenotypes. Tedizolid had potent/stable activity against a large, contemporary collection of Gram-positive clinical isolates, with low rates of resistance.

Çeşitli Klinik Örneklerden İzole Edilen Stafilokok Türlerinde Vankomisin Direncinin Araştırılması

Introduction: Besides the few investigation demonstrating the vancomycin resistance towards Staphylococcus aureus in recent years, it has been also reported a decreased sensitivity of these bacteria to vancomycin. In the present study, it was aimed to evaluate sensitivity test in staphylococcus strains isolated from various clinical samples. Methods: A total of 164 staphylococcus strains consisting of Methicillin Resistant Staphylococcus aureus (n=93), and Methicillin Resistant Coagulase Negative Staphylococcus (n=71) were included in this study. The vancomycin agar screening and E-test methods were used to assess vancomycin sensitivity, and results were interpreted to Clinical and Laboratory Standard Institute and European Committee on Antimicrobial Susceptibility Testing criteria. Results: After assessing the strains by using E-Test, neither decreased sensitivity, nor resistance to vancomycin was determined according to Clinical and Laboratory Standard Institute. However, 3 of 6 Methicillin Resistant Staphylococcus aureus, and 1 of 7 Methicillin Resistant Coagulase Negative Staphylococcus reproduced in Brain Heart Infusion Agar were found to be resistant to vancomycin according to European Committee on Antimicrobial Susceptibility Testing. Conclusion: Because even small changes can be clinically significant, Minimum İnhibition Concentration value of vancomycin should be correctly determined.

Use of Monte Carlo simulation to determine pharmacodynamic cutoffs of amoxicillin to establish a breakpoint for antimicrobial susceptibility testing in pigs

To determine pharmacodynamic cutoffs with pharmacokinetic-pharmacodynamic principles and Monte Carlo simulation (MCS) for use of amoxicillin in pigs to set interpretive criteria for antimicrobial susceptibility testing. 191 plasma disposition curves of amoxicillin obtained from 21 IV, 104 IM, and 66 PO administrations corresponding to 2,098 plasma concentrations. A population model of amoxicillin disposition in pigs was developed for PO and IM administration. The MCS method was then used to determine, for various dosage regimens, the proportion of pigs achieving plasma amoxicillin concentrations greater than a selection of possible minimal inhibitory concentrations (MICs) ranging from 0.0625 to 4 mg/L for at least 40% of a 24-hour period. A target attainment rate (TAR) of 90% was never achieved with the breakpoint recommended by the Clinical and Laboratory Standards Institute (0.5 mg/L) when the usual recommended dosage (20 mg/kg/d) was used. Only by dividing the orally administered daily dose into 12-hour administration intervals was a TAR > 90% achieved when the total dose was at least 40 mg/kg for a pathogen having an MIC ≤ 0.0625 mg/L. For the IM route, the TAR of 90% could only be achieved for MICs of 0.0625 and 0.125 mg/L with the use of 15 and 30 mg/kg doses, respectively. Population kinetics and MCS are required to determine robust species-specific interpretive criteria (susceptible, intermediate, and resistant classifications) for antimicrobial susceptibility testing breakpoints (taking into account interanimal variability).

Recurrent Chronic Ambulatory Peritoneal Dialysis‐Associated Infection due to Rothia dentocariosa

Rothia dentocariosa is a commensal organism of the human oropharynx. Clinical infection due to this organism is rare. A case of recurrent peritoneal dialysis-related peritonitis caused by R dentocariosa and a review of the literature is reported. Isolation of R dentocariosa from dialysate fluid should not be dismissed as a contaminant. Although there are no interpretive criteria for antimicrobial susceptibility testing, R dentocariosa appears to be susceptible to a variety of antibiotics including beta-lactams, vancomycin and aminoglycosides. Optimal therapy of peritoneal dialysis peritonitis caused by this organism may also require removal of the catheter.

Role of NCCLS in antimicrobial susceptibility testing and monitoring.

The role of NCCLS (formerly known as the National Committee for Clinical Laboratory Standards) in establishing guidelines for antimicrobial susceptibility testing, NCCLS's consensus-building process, and new interpretive criteria for antimicrobial susceptibility testing for 2002 are described. When revising and developing new guidelines, NCCLS uses an extensive process to reach consensus, while considering the clinical relevance, cost, and other practical implications of the proposed guidelines. NCCLS groups antimicrobials for susceptibility testing and reporting on the basis of their clinical efficacy, known patterns of microbial resistance, strategies to minimize the emergence of resistance, consensus recommendations, and cost to avoid unnecessary testing. NCCLS guidelines address quality control issues and current methodologies, such as conventional disk diffusion and microbroth dilution tests. In addition, new testing methods for the detection and confirmation of special resistance mechanisms (e.g., extended-spectrum beta-lactamase production) are recommended. In 2002, the minimum inhibitory concentration breakpoints for resistance and susceptibility of Streptococcus pneumoniae to cefotaxime and ceftriaxone in nonmeningitis infection were increased to more accurately predict clinical outcomes. Implementation of new NCCLS guidelines requires the education and collaboration of the laboratory, pharmacy, and medical staff. The NCCLS consensus-building process provides clinicians with clinically relevant and cost-effective strategies for antimicrobial susceptibility testing and reporting, guidelines and criteria for interpreting susceptibility test results, and guidelines for detecting emerging antimicrobial resistance. The use of specialized testing methods for detecting and confirming unusual or difficult-to-identify resistance mechanisms can improve the accuracy of reporting of resistance and avoid therapeutic failures. The implementation of new NCCLS guidelines requires collaboration and education of members of various institutional departments.

Gatifloxacin Susceptibility Testing Interpretive Criteria and Quality Control Guidelines for Dilution and Disk Diffusion Methods

Gatifloxacin (formerly AM-1155 or CG5501) is a newer 8-methoxy fluoroquinolone with a wide spectrum of antimicrobial activity.[1-4] Among the species inhibited by gatifloxacin are selected anaerobes, Chlamydia spp., Mycoplasma pneumoniae, mycobacteria, drug-resistant Streptococcus pneumoniae andNeisseria gonorrhoeae as well as many nonfastidious, rapid-growing bacteria. Gatifloxacin has excellent bioavailability, with an elimination half-life of 7 to 8 hours and peak serum concentrations of 3.35 and 5.41 mg/L, respectively, with single 400 and 600mg doses.[5] It penetrates macrophages and will concentrate 5to 7-fold within the cell. The drug was well tolerated and the intake of food had no adverse effect on the pharmacokinetic features, which allowed advancement to human clinical trials. The risk of phototoxicity was also considered low. In this study, we report the results of testing the activity of gatifloxacin against rapidly growing aerobic pathogens by 2 methods published by the National Committee for Clinical Laboratory Standards (NCCLS) to determine interpretive criteria for antimicrobial susceptibility testing.[6,7] In addition, the quality control guidelines were established for the gatifloxacin 5μg disks and broth microdilution tests by use of a 9-laboratory trial conforming to NCCLS study design.[8]

NEWER MACROLIDES

In clinical microbiology laboratories, advancements in the methods used for routine organism identification have facilitated more accurate species level resolution. This, along with increasing knowledge regarding “new” pathogens, has provided new insights into biology and has revealed clinical associations not previously known. Aerococcus urinae, Alloscardovia omnicolens, and Actinotignum schaalii are Gram-positive bacteria associated with urinary tract infections but can also be members of the urinary tract microbiota. In addition, invasive infections have been reported for the three bacteria, usually with a urinary tract source. Importantly, the use of routine biochemical testing methods for identification of these bacteria can result in misidentification or the incorrect determination that they are not clinically significant. Of these bacteria, only A. urinae has antimicrobial susceptibility testing criteria and interpretative breakpoints. Microbiologists and clinicians need to be aware of these urinary tract pathogens and how to correctly identify them.