Macrolide and fluoroquinolone (levofloxacin) resistances among Streptococcus pneumoniae strains: significant trends from the SENTRY Antimicrobial Surveillance Program (North America, 1997-1999)

Increased incidence of cytomegalovirus coinfection in HCV-infected patients with late liver fibrosis is associated with dysregulation of JAK-STAT pathway

Herein, we examined the association between cytomegalovirus (CMV) coinfection and the progression of liver fibrosis in hepatitis C virus (HCV) infection, and investigated the effect of CMV coinfection on JAK-STAT pathway. CMV DNAemia was detected by PCR in DNA from controls (n = 120), and HCV patients with early (F0-F1, n = 131) and late (F2-F4, n = 179) liver fibrosis. By quantitative real time PCR (qRT-PCR), we examined the profile of 8 JAK-STAT transcripts in PBMCs RNA from 90 HCV patients (39 CMV positive and 51 CMV negative), 4 CMV mono-infected patients, and 15 controls. Our results demonstrated higher incidence of CMV in F2-F4 group than in control (OR 5.479, 95% CI 3.033–9.895, p < 0.0001) or F0-F1 groups (OR 2, 95% CI 1.238–3.181, p = 0.005). qRT-PCR showed downregulation of STAT2 (p = 0.006) and IRF7 (p = 0.02) in CMV positive group compared to CMV negative one. The downregulation of STAT2 and IRF7 was mainly in CMV positive patients with late fibrosis compared to CMV negative patients (p = 0.0007 for IRF7 and p = 0.01 for STAT2). Our results are the first to report that CMV coinfection is a possible risk factor for the progression of HCV-induced liver fibrosis, and thereby CMV screening and treatment are important for HCV patients.

Intrauterine infection with parvovirus B19 and CMV: implications in early and late gestation fetal demise

In utero viral infections have been associated with an adverse pregnancy outcome and may have a causative role in the unexplained fetal death file. Parvovirus B19 and cytomegalovirus are among the most common pathogens implicated in fetal loss cases. Parvovirus B19 has been reported to account for cases of spontaneous abortions, intrauterine fetal death and nonimmune hydrops fetalis, whereas cytomegalovirus accounts for nonimmune hydrops fetalis, intrauterine growth retardation and congenital anomalies. This review aims to summarize the current literature in an attempt to underline the need for routine screening, close follow-up and prevention. A better understanding of the pathogenetic mechanisms of viral infections during the crucial time of organogenesis, along with early detection, may contribute to the reduction in stillbirth rate.

Global fluoroquinolone resistance epidemiology and implictions for clinical use

This paper on the fluoroquinolone resistance epidemiology stratifies the data according to the different prescription patterns by either primary or tertiary caregivers and by indication. Global surveillance studies demonstrate that fluoroquinolone resistance rates increased in the past years in almost all bacterial species except S. pneumoniae and H. influenzae, causing community-acquired respiratory tract infections. However, 10 to 30% of these isolates harbored first-step mutations conferring low level fluoroquinolone resistance. Fluoroquinolone resistance increased in Enterobacteriaceae causing community acquired or healthcare associated urinary tract infections and intraabdominal infections, exceeding 50% in some parts of the world, particularly in Asia. One to two-thirds of Enterobacteriaceae producing extended spectrum β-lactamases were fluoroquinolone resistant too. Furthermore, fluoroquinolones select for methicillin resistance in Staphylococci. Neisseria gonorrhoeae acquired fluoroquinolone resistance rapidly; actual resistance rates are highly variable and can be as high as almost 100%, particularly in Asia, whereas resistance rates in Europe and North America range from <10% in rural areas to >30% in established sexual networks. In general, the continued increase in fluoroquinolone resistance affects patient management and necessitates changes in some guidelines, for example, treatment of urinary tract, intra-abdominal, skin and skin structure infections, and traveller's diarrhea, or even precludes the use in indications like sexually transmitted diseases and enteric fever.

In vitro pharmacodynamics of moxifloxacin versus levofloxacin against 4 strains of Streptococcus pneumoniae: 1 wild type, 2 first-step parC mutants, and 1 pump mutant

Levofloxacin binds topoisomerase IV, whereas moxifloxacin preferentially binds DNA gyrase. Most 1st-step pneumococcal mutants have alterations in the parC gene of topoisomerase IV. Because of differential binding affinity, moxifloxacin may have superior activity against 1st-step mutants compared with levofloxacin. The purpose of this work was to compare rates and extent of bacterial killing of genetically characterized Streptococcus pneumoniae with moxifloxacin and levofloxacin. Four strains of S. pneumoniae were used: a wild type, 2 first-step parC mutants, and a pump mutant. Using an in vitro pharmacodynamic model run in duplicate, we exposed bacteria to unbound moxifloxacin and levofloxacin peaks of 2 and 4.5 mg/L, respectively, which emulated clinical dosing. Additional experiments were done in which the area under the curve (AUC)/MIC ratio of 1 agent was matched to the competing drug's clinical dose AUC/MIC ratio. Time kill curves were analyzed for rate and extent of bacterial kill and regrowth. Pre- and postexposure MIC and polymerase chain reaction (PCR) testing were done. Moxifloxacin and levofloxacin displayed similar rates and extent of bacterial kill for the wild type, efflux pump type, and parC mutant 27-1361B. Moxifloxacin initially achieved a faster rate of kill, regardless of the AUC/MIC ratio, against parC mutant 7362 (P < 0.05) but not an advantage in time to 3 log kill. Postexposure MIC values were elevated for strain 7362 in 2 moxifloxacin experiments and 1 levofloxacin experiment. Post-PCR analysis revealed new gyrA mutations for all 3 isolates. Both moxifloxacin and levofloxacin are effective against multiple strains of S. pneumoniae.

Detection of cytomegalovirus in human placental cells by polymerase chain reaction

Human cytomegalovirus (HCMV) is the most common cause of viral intrauterine infection. Progress in rapid, specific, and dependable detection of HCMV has recently been achieved by the use of DNA hybridization techniques and other molecular methods. We examined 21 placentas after delivery for the presence of HCMV DNA by polymerase chain reaction (PCR). To test the reliability of the PCR for the detection of HCMV DNA in clinical specimens, two simple PCR assays and a real-time quantitative PCR were used. PCR analysis of villous and decidual cells showed that HCMV DNA was present in 16 placentas (76.2%). Transmission of HCMV infection to chorionic villi was confirmed in 11 organs (52.4%), and congenital infections in newborns were detected in 9 cases (42.8%). These results suggest that HCMV genome detection in placentas at later gestational ages is common. Our results demonstrated that detection of HCMV DNA in placental tissues by DNA amplification provides a specific and sensitive method for diagnosis of intrauterine HCMV infection.

Activity of gatifloxacin tested against isolates from pediatric patients: report from the SENTRY Antimicrobial Surveillance Program (North America, 1998-2003)

The SENTRY Antimicrobial Surveillance Program has monitored the activity of antimicrobial agents worldwide since 1997. The increasing number of clinical failures with established anti-infectives (penicillins, other beta-lactams, macrolides) among pediatric patients has stressed the importance for alternative therapeutic options. Ciprofloxacin has been recently approved for expanded use as treatment of complicated urinary tract infections in children, and gatifloxacin has been used successfully in clinical trials in selected children with severe or refractory otitis media. We evaluated the activity of gatifloxacin against strains isolated from children < 7 years of age and compared this to the general patient population (all ages included) using the SENTRY Program database. A total of 59826 North American isolates were collected, of which 4641 were from children (< 7 years old); all isolates were tested using reference broth microdilution methods. In contrast to the general population (GP), gatifloxacin resistance rates were very low among isolates from this younger patient group. Gatifloxacin susceptibility rates were > 84% for all pathogens evaluated in younger patients. All Streptococcus pneumoniae strains from children < 7 years old were susceptible to gatifloxacin, and susceptibility among the Enterobacteriaceae species was > 98%. The greatest difference in susceptibility rates between the younger children and the GP was observed among nonfermentative gram-negative bacilli (95.0-100% versus 64.8-83.7%, respectively) and Enterococcus faecalis (94.7% versus 58.4%). Gatifloxacin susceptibilities of Pseudomonas aeruginosa and Acinetobacter spp. isolates from the pediatric population were > or = 95% (> 97% for ciprofloxacin) compared to the GP at only 64.8-69.1%. In conclusion, gatifloxacin remains very active against bacterial isolates from children < 7 years, indicative of the limited exposure of this population to fluoroquinolones. Continued resistance surveillance will be necessary to monitor the activity of the fluoroquinolone class as they are introduced for specific clinical indications into the pediatric age groups, especially if re-studied against S. pneumoniae (refractory otitis media) and P. aeruginosa (cystic fibrosis associated pneumonia).

Guide to selection of fluoroquinolones in patients with lower respiratory tract infections

Newer fluoroquinolones such as levofloxacin, moxifloxacin, gatifloxacin and gemifloxacin have several attributes that make them excellent choices for the therapy of lower respiratory tract infections. In particular, they have excellent intrinsic activity against Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and the atypical respiratory pathogens. Fluoroquinolones may be used as monotherapy to treat high-risk patients with acute exacerbation of chronic bronchitis, and for patients with community-acquired pneumonia requiring hospitalisation, but not admission to intensive care. Overall, the newer fluoroquinolones often achieve clinical cure rates in > or =90% of these patients. However, rates may be lower in hospital-acquired pneumonia, and this infection should be treated on the basis of anticipated organisms and evaluation of risk factors for specific pathogens such as Pseudomonas aeruginosa. In this setting, an antipseudomonal fluoroquinolone may be used in combination with an antipseudomonalbeta-lactam. Concerns are now being raised about the widespread use, and possibly misuse, of fluoroquinolones and the emergence of resistance among S. pneumoniae, Enterobacteriaceae and P. aeruginosa. A number of pharmacokinetic parameters such as the peak concentration of the antibacterial after a dose (C(max)), and the 24-hour area under the concentration-time curve (AUC24) and their relationship to pharmacodynamic parameters such as the minimum inhibitory and the mutant prevention concentrations (MIC and MPC, respectively) have been proposed to predict the effect of fluoroquinolones on bacterial killing and the emergence of resistance. Higher C(max)/MIC or AUC24/MIC and C(max)/MPC or AUC24/MPC ratios, either as a result of dose administration or the susceptibility of the organism, may lead to a better clinical outcome and decrease the emergence of resistance, respectively. Pharmacokinetic profiles that are optimised to target low-level resistant minor subpopulations of bacteria that often exist in infections may help preserve fluoroquinolones as a class. To this end, optimising the AUC24/MPC or C(max)/MPC ratios is important, particularly against S. pneumoniae, in the setting of lower respiratory tract infections. Agents such as moxifloxacin and gemifloxacin with high ratios against this organism are preferred, and agents such as ciprofloxacin with low ratios should be avoided. For agents such as levofloxacin and gatifloxacin, with intermediate ratios against S. pneumoniae, it may be worthwhile considering alternative dose administration strategies, such as using higher dosages, to eradicate low-level resistant variants. This must, of course, be balanced against the potential of toxicity. Innovative approaches to the use of fluoroquinolones are worth testing in further in vitro experiments as well as in clinical trials.

Antimicrobial drug prescribing for pneumonia in ambulatory care

Higher levels of fluoroquinolone use were associated with increasing age and later study year.

To determine patterns and predictors of antimicrobial drug use for outpatients with community-acquired pneumonia, we examined office visit and pharmacy claims data of 4 large third-party payer organizations from 2000 to 2002. After patients with coexisting conditions were excluded, 4,538 patients were studied. Despite lack of coexisting conditions, fluoroquinolone use was commonly observed and increased significantly (p < 0.001) from 2000 to 2002 (24%–39%), while macrolide use decreased (55%–44%). Increased age correlated with increased fluoroquinolone use: 18–44 years (22%), 45–64 years (33%), and >65 years (40%) (p < 0.001). Increased use of fluoroquinolones occurred in healthy young and old patients alike, which suggests a lack of selectivity in reserving fluoroquinolones for higher risk patients. Clear and consistent guidelines are needed to address the role of fluoroquinolones in treatment of outpatient community-acquired pneumonia.

Role of efflux mechanisms on fluoroquinolone resistance in Streptococcus pneumoniae and Pseudomonas aeruginosa

Prokaryotic efflux mechanisms can effectively increase the intrinsic resistance of bacteria by actively transporting antibiotics out of cells, thus reducing the effective concentration of these agents. The fluoroquinolones, similar to most other antimicrobial classes, are susceptible to efflux mechanisms, particularly in Gram-negative organisms, such as Pseudomonas aeruginosa. Resistant P. aeruginosa clones isolated after fluoroquinolone therapy frequently over express at least one of the multiple efflux pump mechanisms found in this organism. Gram-positive bacteria, such as Streptococcus pneumoniae, also possess efflux mechanisms, though their effect on fluoroquinolone resistance seems to be more limited and selective. In the future, efflux pump inhibitors may offer effective adjunctive therapy to antibiotics for the treatment of difficult infections by efflux mutants. In the meantime, appropriate antibiotic selection and optimal dosing strategies should aim to eradicate the causative pathogen before a resistant efflux mutant can emerge.

Randomized, investigator-blinded, multicenter study of gatifloxacin versus amoxicillin/clavulanate treatment of recurrent and nonresponsive otitis media in children

BACKGROUND

Decreased susceptibility of pathogens to currently used agents for recurrent otitis media has provided the impetus for identifying new antimicrobial options.

OBJECTIVE

To compare gatifloxacin with amoxicillin/clavulanate in children with recurrent or nonresponsive acute otitis media (AOM).

METHODS

Included in this multicenter randomized trial were 413 patients, ranging in age from 6 months to 7 years, who had recurrent AOM (at least 3 episodes in the previous 6 months or 4 episodes in the previous 12 months) and/or had failed antibiotic therapy for AOM within 14 days of enrollment. Diagnosis required evidence of acute inflammation and otoscopic findings of middle ear effusion; baseline tympanocentesis was optional and encouraged. Children were randomly assigned (2:1) to 10 days of oral therapy with gatifloxacin suspension (10 mg/kg of body weight once daily) or amoxicillin/clavulanate suspension (45/6.4 mg/kg/d in 2 divided doses).

RESULTS

: Clinical cure was obtained in 90.2% (222 of 246) of patients in the gatifloxacin group and 84.3% (102 of 121) of those in the amoxicillin/clavulanate group (95% confidence interval, -1.9-12.9) 3-10 days after treatment ended. Gatifloxacin was associated with higher clinical cure rates than was amoxicillin/clavulanate in children younger than 2 years of age (92.0% versus 80.0%, respectively). Cure rates by pretreatment pathogen in the gatifloxacin and amoxicillin/clavulanate groups were 92.1% (35 of 38) versus 88.9% (16 of 18) for Streptococcus pneumoniae infections and 88.2% (30 of 34) versus 92.3% (12 of 13) for Haemophilus influenzae infections, respectively. Sustained clinical cures 3-4 weeks after treatment ended were obtained in 74.4% (183 of 246) of patients treated with gatifloxacin and 72.7% (88 of 121) of those treated with amoxicillin/clavulanate. Adverse events considered drug-related occurred with similar frequency in the 2 groups. Six patients (2.2%) in the gatifloxacin group and 2 patients (1.5%) in the amoxicillin/clavulanate group developed transient symptoms of mild or moderate arthralgia.

CONCLUSIONS

In this comparative evaluation of fluoroquinolone therapy in children with AOM, gatifloxacin was similar in clinical efficacy to amoxicillin/clavulanate 45/6.4 mg/kg/d for treatment of recurrent/nonresponsive infections.

Relationship between increased levofloxacin use and decreased susceptibility of Streptococcus pneumoniae in the United States

Increasing reports of fluoroquinolone-non-susceptible Streptococcus pneumoniae are of clinical concern. We examined the relationship between outpatient fluoroquinolone use and susceptibility of community-acquired S. pneumoniae isolates. Using multivariable general linear modeling, US SENTRY Antimicrobial Surveillance Program and Intercontinental Medical Statistics data (1997-2002) were analyzed to determine the influence of selected patient-, institution-, and geographic region-specific factors, including local fluoroquinolone usage, on the minimum inhibitory concentration (MIC) of levofloxacin against S. pneumoniae. Levofloxacin MIC50, MIC90, and MIC range (n = 384 from 26 hospitals) were 1, 1, and < or =0.5 to >4 microg/mL, respectively. Variables associated with changes in geometric mean MIC included geographical region (P < 0.0001), medical service (P = 0.0002), study year (P = 0.0006), primary diagnosis group (P = 0.02), and 2 interactions (duration of hospital stay before isolate collection by bed capacity, P = 0.06, and levofloxacin use by geographical region, P = 0.08; P < 0.001 when study year was removed from the model). MIC increased with levofloxacin use across all geographical regions, with increases of 54% and 126% in the southwest and west, respectively. In contrast to other fluoroquinolones, increased levofloxacin use, along with other variables, was associated with decreased pneumococcal susceptibility. Given the US environment of increasing pneumococcal resistance, these data may be useful in better understanding factors related to emergence of fluoroquinolone resistance.

A validated PCR-based method to detect Listeria monocytogenes using raw milk as a food model--towards an international standard

A PCR assay with an internal amplification control was developed for Listeria monocytogenes. The assay has a 99% detection probability of seven cells per reaction. When tested against 38 L. monocytogenes strains and 52 nontarget strains, the PCR assay was 100% inclusive (positive signal from target) and 100% exclusive (no positive signal from nontarget). The assay was then evaluated in a collaborative trial involving 12 European laboratories, where it was tested against an additional 14 target and 14 nontarget strains. In that trial, the inclusivity was 100% and the exclusivity was 99.4%, and both the accordance (repeatability) and the concordance (reproducibility) were 99.4%. The assay was incorporated within a method for the detection of L. monocytogenes in raw milk, which involves 24 h of enrichment in half-Fraser broth followed by 16 h of enrichment in a medium that can be added directly into the PCR. The performance characteristics of the PCR-based method were evaluated in a collaborative trial involving 13 European laboratories. In that trial, a specificity value (percentage of correct identification of blank samples) of 81.8% was obtained; the accordance was 87.9%, and the concordance was 68.1%. The sensitivity (correct identification of milk samples inoculated with 20 to 200 L. monocytogenes cells per 25 ml) was 89.4%, the accordance was 81.2%, and the concordance was 80.7%. This method provides a basis for the application of routine PCR-based analysis to dairy products and other foodstuffs and should be appropriate for international standardization.

Antibiotic selection pressure and resistance in Streptococcus pneumoniae and Streptococcus pyogenes

We correlated outpatient antibiotic use with prevalence of penicillin-nonsusceptible Streptococcus pneumoniae (PNSP), macrolide-resistant S. pneumoniae (MRSP), and macrolide-resistant S. pyogenes (MRGAS) in 20 countries. Total antibiotic use was correlated with PNSP (r = 0.75; p < 0.001), as was macrolide use with MRSP (r = 0.88; p < 0.001) and MRGAS (r = 0.71; p = 0.004). Streptococcal resistance is directly associated with antibiotic selection pressure on a national level.

Potential role of fluoroquinolone therapy in childhood otitis media

Increased resistance of pneumococci and other pathogens to available antibiotics raises concerns about bacteriologic and clinical failure in children with acute otitis media. Few therapeutic options exist for patients with recurrent infections or recent treatment failure. The limited experience from the compassionate use of fluoroquinolones in pediatrics and pediatric studies has not been linked unequivocally with arthrotoxicity, the primary safety concern in children. Newer 8-methoxyfluoroquinolones may have a role in selected cases associated with multidrug-resistant pathogens.

New Developments in Antibacterial Choice for Lower Respiratory Tract Infections in Elderly Patients

Elderly patients are at increased risk of developing lower respiratory tract infections compared with younger patients. In this population, pneumonia is a serious illness with high rates of hospitalisation and mortality, especially in patients requiring admission to intensive care units (ICUs). A wide range of pathogens may be involved depending on different settings of acquisition and patient's health status. Streptococcus pneumoniae is the most common bacterial isolate in community-acquired pneumonia, followed by Haemophilus influenzae, Moraxella catarrhalis and atypical pathogens such as Chlamydia pneumoniae, Legionella pneumophila and Mycoplasma pneumoniae. However, elderly patients with comorbid illness, who have been recently hospitalised or are residing in a nursing home, may develop severe pneumonia caused by multidrug resistant staphylococci or pneumococci, and enteric Gram-negative bacilli, including Pseudomonas aeruginosa. Moreover, anaerobes may be involved in aspiration pneumonia. Timely and appropriate empiric treatment is required in order to enhance the likelihood of a good clinical outcome, prevent the spread of antibacterial resistance and reduce the economic impact of pneumonia. International guidelines recommend that elderly outpatients and inpatients (not in ICU) should be treated for the most common bacterial pathogens and the possibility of atypical pathogens. The algorithm for therapy is to use either a selected beta-lactam combined with a macrolide (azithromycin or clarithromycin), or to use monotherapy with a new anti-pneumococcal quinolone, such as levofloxacin, gatifloxacin or moxifloxacin. Oral (amoxicillin, amoxicillin/clavulanic acid, cefuroxime axetil) and intravenous (sulbactam/ampicillin, ceftriaxone, cefotaxime) beta-lactams are agents of choice in outpatients and inpatients, respectively. For patients with severe pneumonia or aspiration pneumonia, the specific algorithm is to use either a macrolide or a quinolone in combination with other agents; the nature and the number of which depends on the presence of risk factors for specific pathogens. Despite these recommendations, clinical resolution of pneumonia in the elderly is often delayed with respect to younger patients, suggesting that optimisation of antibacterial therapy is needed. Recently, some new classes of antibacterials, such as ketolides, oxazolidinones and streptogramins, have been developed for the treatment of multidrug resistant Gram-positive infections. However, the efficacy and safety of these agents in the elderly is yet to be clarified. Treatment guidelines should be modified on the basis of local bacteriology and resistance patterns, while dosage and/or administration route of each antibacterial should be optimised on the basis of new insights on pharmacokinetic/pharmacodynamic parameters and drug interactions. These strategies should be able to reduce the occurrence of risk factors for a poor clinical outcome, hospitalisation and death.

Comparative activity and spectrum of broad-spectrum β-lactams (cefepime, ceftazidime, ceftriaxone, piperacillin/tazobactam) tested against 12,295 staphylococci and streptococci: report from the SENTRY antimicrobial surveillance program (North America: 2001-2002)

A contemporary collection of 12,295 North American isolates (2001-2002) consisting of Staphylococcus aureus (50%), coagulase-negative staphylococci (12%), Streptococcus pneumoniae (24%), beta-hemolytic streptococci (12%), and viridans-group streptococci (2%) were tested against broad-spectrum beta-lactams (cefepime, ceftazidime, ceftriaxone, imipenem, piperacillin/tazobactam) and comparator agents using a reference broth microdilution method to determine their continued effectiveness for empiric antimicrobial therapy. All isolates were very susceptible to vancomycin, linezolid and quinupristin/dalfopristin (>98%). Oxacillin-susceptible staphylococci were also highly susceptible to the tested beta-lactams (>98%) with the exception of ceftazidime (93%). beta-hemolytic streptococci were exquisitely susceptible (>99%) to penicillin and all other agents except for clindamycin (94%) and erythromycin (81%). Viridans group streptococci were routinely less susceptible than were other streptococci. S. pneumoniae remained susceptible to most agents (>91%) with the exceptions of erythromycin (74%) and penicillin (69%). Among beta-lactams tested against S. pneumoniae, ceftriaxone and cefepime continued to be very active against penicillin-susceptible (>99%) and intermediate (>98%) strains, but less active (80% and 82%, respectively) against penicillin-resistant isolates. These findings confirm that the newer cephalosporins (cefepime and ceftriaxone) among broad-spectrum beta-lactam agents have a spectrum of activity that remains comprehensive for the commonly isolated Gram-positive pathogens.

Worldwide trends in antimicrobial resistance among common respiratory tract pathogens in children

BACKGROUND

Respiratory tract infections among children are a common reason for health care provider visits and the primary reason for antimicrobial prescribing in this population. The increased prevalence of resistance among Streptococcus pneumoniae and Haemophilus influenzae pathogens poses a serious challenge in the successful treatment of respiratory tract infections caused by these pathogens.

METHODS

This paper reviews worldwide trends in antimicrobial resistance among common respiratory tract pathogens, highlighting data obtained from the pediatric population where available.

RESULTS

S. pneumoniae resistance to beta-lactams is mediated through alterations in the penicillin-binding proteins and macrolide resistance to acquisition of efflux or methylation genes. The mechanisms of resistance to the fluoroquinolones include target enzyme alterations via genetic mutations and transport out of the bacterial cell via an efflux pump. Beta-lactamase production is the primary mechanism of resistance to penicillins among H. influenzae isolates. Although S. pneumoniae with reduced susceptibility to penicillin was first documented > 30 years ago, resistance has increased at an alarming rate worldwide in the past decade. According to recent surveillance data, the worldwide prevalence of S. pneumoniae with reduced susceptibility to penicillin is 18.2%. Beta-lactamase production among H. influenzae ranges from approximately 4% in Russia to 26% in the United States and to 31% in France. The prevalence of beta-lactamase-negative, ampicillin-resistant H. influenzae remains very low (< 1%) worldwide, except in Japan, where the incidence is higher. In general, the highest rates of resistance are observed in isolates obtained from children, and risk factors for infection with a resistant pathogen include young age, the site of infection, day-care center attendance and recent antimicrobial use.

CONCLUSIONS

Increased prevalence of antimicrobial resistance among respiratory tract pathogens isolated from children and adults is evident worldwide. Treatment of infections caused by S. pneumoniae and H. influenzae with older agents or ineffective dosing regimens may not eradicate infections and may contribute to the spread of resistance. These observations confirm the need for appropriate antimicrobial use to halt or at least limit the spread of resistance.

Telithromycin- and fluoroquinolone-resistant Streptococcus pneumoniae in Taiwan with high prevalence of resistance to macrolides and beta-lactams: SMART program 2001 data

There is a high prevalence of beta-lactam- and macrolide-resistant Streptococcus pneumoniae in Taiwan. To understand the in vitro susceptibilities of recent isolates of S. pneumoniae to fluoroquinolones and telithromycin (which is not available in Taiwan), the MICs of 23 antimicrobial agents for 936 clinical isolates of S. pneumoniae isolated from different parts of Taiwan from 2000 to 2001 were determined by the agar dilution method. Overall, 72% of isolates were not susceptible to penicillin (with 61% being intermediate and 11% being resistant) and 92% were resistant to erythromycin. Telithromycin MICs were >or=1 microg/ml for 16% of the isolates, and for 99% of these isolates the MICs of all macrolides tested were >or=256 microg/ml; all of these isolates had the constitutive macrolide-lincosamide-streptogramin B phenotype. Eighty-eight percent of the isolates were resistant to three or more classes of drugs. The ciprofloxacin MICs were >or=4 microg/ml for six (0.6%) isolates from five patients collected in 2000 and 2001, and the levofloxacin MICs were >or=8 microg/ml for five of these isolates. Seven isolates for which ciprofloxacin MICs were >or=4 microg/ml, including one isolate recovered in 1999, belonged to three serotypes (serotype 19F, five isolates; serotype 23A, one isolate; and serotype 23B, one isolate). The isolates from the six patients for which ciprofloxacin MICs were >or=4 microg/ml had different pulsed-field gel electrophoresis profiles and random amplified polymorphic DNA patterns, indicating that no clonal dissemination occurred over this time period. Despite the increased rate of fluoroquinolone use, the proportion of pneumococcal isolates for which ciprofloxacin MICs were elevated (>or=4 microg/ml) remained low. However, the occurrence of telithromycin resistance is impressive and raises concerns for the future.

Linezolid resistance since 2001: SENTRY Antimicrobial Surveillance Program

BACKGROUND

The oxazolidinone class of antimicrobials has demonstrated remarkable activity against gram-positive cocci. Linezolid has proven to be a first-line therapeutic option for vancomycin-resistant strains. Linezolid clinical trial results and subsequent published case reports cite rare resistance emerging in patients receiving prolonged therapy.

OBJECTIVE

To report the initial linezolid-resistant organisms from cases obtained through the SENTRY Antimicrobial Surveillance Program, after screening >40,000 gram-positive cocci without resistance between 1998 and 2000.

METHODS

During 2001-2002, 8 resistant strains (from 8 different patients) located in 6 states from 7 different participating SENTRY institutions in the US were identified among bloodstream, respiratory, skin and soft tissue, and urinary tract infection isolates of Enterococcus faecalis, Enterococcus faecium, Staphylococcus epidermidis, and Streptococcus oralis. Resistance was detected by reference broth microdilution methods and confirmed by identical results using Etest (AB BIODISK, Solna, Sweden) and the standardized disk diffusion method.

RESULTS

Minimum inhibitory concentration (MIC) and disk diffusion tests showed elevated MICs (> or =8 microg/mL) and small inhibitory zone diameters (< or =15 mm) for all strains to both linezolid and the investigational oxazolidinone AZD2563. Vancomycin resistance was detected in 2 of the 8 linezolid-resistant strains. All enterococci and the viridans-group streptococcus (S. oralis) strain showed resistance to erythromycin. E. faecium strains were resistant to penicillins, but susceptible to quinupristin/dalfopristin. Only 3 of the patients had previously received the drug.

CONCLUSIONS

Linezolid resistance remains rare, with only 8 isolates among 9833 (0.08%) monitored isolates identified between January 1, 2001, and June 30, 2002. Resistance, however, was no longer limited to enterococci. Clinical laboratories should test linezolid more widely to detect emerging resistance, especially for patients receiving oxazolidinone therapy. Longitudinal surveillance programs are warranted to detect a trend in the development of resistance, determine the molecular mechanism of resistance, and recommend alternative therapies or epidemiologic interventions.

Genetic relatedness of levofloxacin-nonsusceptible Streptococcus pneumoniae isolates from North America

We characterized 32 levofloxacin-nonsusceptible Streptococcus pneumoniae (LNSP) isolates obtained from a broad geographic region of North America over a 5-year period by using capsular serotypes, antimicrobial susceptibility profiles, BOX-PCR, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE). Sixteen international clones identified by the Pneumococcal Molecular Epidemiology Network also were included for comparison. Fifteen serotypes were represented, with serogroups 6, 9, 14, 19, and 23 accounting for 63% of isolates. Among isolates whose quinolone resistance-determining regions were sequenced, all contained gyrA and parC point mutations. Sixty-three percent were penicillin susceptible, and 84% were erythromycin susceptible. BOX-PCR analysis identified 39 different band patterns among 32 LNSP and 16 international clones and grouped 16 isolates, including 2 international clones, into seven unrelated groups of 2 to 4 isolates each. PFGE analysis identified 35 different band patterns among 32 LNSP and 16 international clones and grouped 21 isolates, including 3 international clones, into eight unrelated groups of 2 to 6 isolates each. MLST performed on 10 isolates identified five allelic profiles and separated 9 isolates into four groups of 2 to 3 isolates each. Overall, each typing method indicated that the LNSP were heterogeneous and that resistance to fluoroquinolones was not closely associated with a particular serotype or with coresistance to other antimicrobial classes and suggests that LNSP have likely arisen through independent mutational events as a result of selective pressure. However, seven LNSP were found to be related to three international clones by PFGE.

Five-year analysis of Haemophilus influenzae isolates with reduced susceptibility to fluoroquinolones: prevalence results from the SENTRY antimicrobial surveillance program

The appearance of resistance or reduced susceptibility to fluoroquinolones among Hemophilus influenzae has been documented for nearly a decade. Over this time, the use of fluoroquinolones for the treatment of respiratory infections including commonly isolated bacterial causes of community-acquired infections has markedly increased. The documentation of resistance to fluoroquinolones among Streptococcus pneumoniae and H. influenzae has also become more prevalent as measured by peer-reviewed publications. During 1997-2001, a total of 11,355 H. influenzae isolates were tested by reference broth microdilution methods from strains collected by the SENTRY Antimicrobial Surveillance Program (American and European medical centers). Strains with reduced susceptibility to fluoroquinolones (RSF) were detected during all five study years at an overall rate of 0.15%. Among the tested compounds, sitafloxacin (MIC(50,) 0.03 microg/ml) was the most potent agent against the RSF strains, followed by gemifloxacin (0.12 microg/ml) > garenoxacin = grepafloxacin = levofloxacin = moxifloxacin = trovafloxacin (0.5 microg/ml) > ciprofloxacin = sparfloxacin (1 microg/ml). Gene sequencing of the quinolone resistance determining region and epidemiologic typing of 30 RSF isolates showed diverse mutational events in gyr A and par C and multiple pulsed-field gel electrophoresis (PFGE) patterns among strains that was not consistent with clonal dissemination. Continued surveillance by global or national networks should continue to monitor for H. influenzae isolates that are refractory to fluoroquinolone therapy.

Comparative activity of garenoxacin (BMS 284756), a novel desfluoroquinolone, tested against 8,331 isolates from community-acquired respiratory tract infections: North American results from the SENTRY Antimicrobial Surveillance Program (1999-2001)

Emerging resistances to orally administered antimicrobials have escalated among bacteria causing community-acquired respiratory infections (CARTI). The spectrum and potency of garenoxacin, (formerly BMS 284756) was assessed against a collection of CARTI isolates from North American medical centers during a longitudinal surveillance study, the SENTRY Antimicrobial Surveillance Program (1999-2001). A total of 8,331 strains of Hemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae were tested by reference methods and compared to numerous other marketed antimicrobials. Nearly all (95.1%) M. catarrhalis were penicillin-resistant, 27.9% of H. influenzae were ampicillin-resistant and 35.0% of S. pneumoniae had MICs at > or = 0.12 microg/ml for penicillin. Garenoxacin was very active against the three monitored species with MIC(90) values of < or =0.06 microg/ml. Garenoxacin and other quinolones were equally active against the Gram-negative pathogens (except moxifloxacin which was at least twofold less potent versus M. catarrhalis). However, against pneumococci the rank order of potency (MIC(50) in microg/ml) was: gemifloxacin (0.015) > garenoxacin (0.06) > trovafloxacin = moxifloxacin (0.12) > gatifloxacin (0.25) > levofloxacin = ciprofloxacin (1). A trend toward greater resistance worldwide was observed for ciprofloxacin (MIC, > or = 4 microg/ml), increasing from 1.5% in 1999 to 6.8% in 2001. The highest quinolone resistance rate was observed in North America. Garenoxacin, a new desfluoro(6)quinolone, was documented to be very active in vitro (MIC, < or =2 microg/ml) against > 99.9% of all CARTI isolates in the SENTRY Program. Evolving resistances to other antimicrobial classes or among currently used quinolones appear to position this investigational desfluoro(6)quinolone as a potential treatment option for future clinical use in ambulatory patients.

Single and multi-step resistance selection study in Streptococcus pneumoniae comparing ceftriaxone with levofloxacin, gatifloxacin and moxifloxacin

Attempts were made to select resistant pneumococcal mutants by sequential subculturing of 12 clinically isolated pneumococci, [four were penicillin sensitive (MIC) 0.03-0.06 mg/l, four penicillin intermediate (MIC 0.25-0.5 mg/l) and four penicillin resistant (MIC 2-4 mg/l)] in sub-inhibitory concentrations of ceftriaxone, levofloxacin, gatifloxacin and moxifloxacin. Subculturing in gatifloxacin, levofloxacin, moxifloxacin and ceftriaxone selected 12 mutants (12/12), 10 mutants (10/12), 10 mutants (10/12) and three mutants (3/12), respectively. DNA sequencing of the quinolone-resistant mutants showed that most strains had mutations in GyrA at E85 or S81. This in vitro mutation study demonstrates a clear distinction between the low frequency of development of resistance with ceftriaxone exposure as opposed to the high frequency with quinolone exposure.

Worldwide antimicrobial susceptibility patterns and pharmacodynamic comparisons of gatifloxacin and levofloxacin against Streptococcus pneumoniae: report from the Antimicrobial Resistance Rate Epidemiology Study Team

The use of fluoroquinolones for the treatment of community-acquired respiratory tract infection is increasing. Since for Streptococcus pneumoniae a ratio of the 24-h area under the concentration-time curve (AUC(24)) for the agent to the MIC (AUC(24)/MIC) greater than 30 for the fraction of unbound drug (f(u)) is the major pharmacokinetic-pharmacodynamic (PK-PD) parameter correlating with bacterial eradication by fluoroquinolones in nonclinical models of infection and in infected patients, the Antimicrobial Resistance Rate Epidemiology Study Team systematically compared the in vitro susceptibility patterns and estimated the probability of attainment of the PK-PD target ratios for gatifloxacin and levofloxacin against pneumococci worldwide. Monte Carlo simulation was used to estimate the probability that gatifloxacin or levofloxacin would achieve an f(u) AUC(24)/MIC ratio of 30 or greater. A total of 10,978 S. pneumoniae isolates collected from 1997 to 2000, each indexed by site of infection and geographic region (North America, Latin America, Europe, and Asia-Pacific), were used to estimate the probability mass functions of the microbiological activities for each region considered in the analysis. f(u) AUC(24) probability distribution functions were estimated by using data that were part of each product's submission accepted by the Food and Drug Administration. A 10,000-patient simulation was performed for each drug-organism-region combination. The percentages of strains susceptible to each drug by region were as follows: for gatifloxacin, North America, 99.6%; Latin America, 99.8%; Europe, 99.9%; and Asia-Pacific, 99.2%; for levofloxacin, North America, 99.6%; Latin America, 99.8%; Europe, 99.8%; and Asia-Pacific, 99.1%. The MIC at which 50% of isolates are inhibited (MIC(50)) and the MIC(90) of each drug by region were as follows: for gatifloxacin, North America, 0.25 and 0.5 mg/liter, respectively; Latin America, 0.25 and 0.5 mg/liter, respectively; Europe, 0.25 and 0.5 mg/liter, respectively; and Asia-Pacific, 0.25 and 0.5 mg/liter, respectively; for levofloxacin, North America, 1 and 2 mg/liter, respectively; Latin America, 1 and 2 mg/liter, respectively; Europe, 1 and 1 mg/liter, respectively; and Asia-Pacific, 1 and 1 mg/liter, respectively. The probabilities of attaining an f(u) AUC(24)/MIC ratio greater than 30 for each drug by region were as follows: for gatifloxacin, North America, 97.6%; Latin America, 98.3%; Europe, 99.1%; and Asia-Pacific, 98.8%; for levofloxacin, North America, 78.9%; Latin America, 84.1%; Europe, 87.1%; and Asia-Pacific, 86.5%. These results for a very large collection of recent clinical strains demonstrate that, globally, gatifloxacin is two- to fourfold more active than levofloxacin against S. pneumoniae and that gatifloxacin has an overall 14.3% higher probability of achieving clinically important PK-PD target ratios than levofloxacin.

Pharmacodynamics of 750 mg and 500 mg doses of levofloxacin against ciprofloxacin-resistant strains of Streptococcus pneumoniae

An in vitro pharmacokinetic model (IVPM) was used to evaluate the pharmacodynamics of the 750 mg and 500 mg doses of levofloxacin against 4 ciprofloxacin-nonsusceptible Streptococcus pneumoniae. Levofloxacin MICs ranged from 1.4 to 3.2 micro g/ml. Log-phase cultures (5 x 10(7) cfu/ml) were inoculated into the IVPM and exposed to the peak free-drug concentrations of levofloxacin achieved in human serum with each dose. Levofloxacin was dosed at 0 and 24 h, elimination pharmacokinetics were simulated, and viable counts were measured over 30 h. The 750 mg dose was rapidly bactericidal against all 4 strains, achieving eradication within 30 h. Against strains with levofloxacin MICs of 1.4 and 1.8 micro g/ml, the 500 mg dose exhibited pharmacodynamics similar to the 750 mg dose. In contrast, against strains with levofloxacin MICs of 2.6 and 3.2 micro g/ml, viable counts never fell below 10(4) cfu/ml. The rapid killing and eradication of these pneumococci by the 750 mg dose warrant the clinical evaluation of this new dose in the treatment of pneumococcal infections.

Gatifloxacin used for therapy of outpatient community-acquired pneumonia caused by Streptococcus pneumoniae

Gatifloxacin is an advanced-generation fluoroquinolone with demonstrated efficacy and safety as therapy for community-acquired pneumonia (CAP). As part of a phase IV postmarketing surveillance program (TeqCES), 136 outpatients with CAP whose sputum was culture-positive for Streptococcus pneumoniae were enrolled in an open-label trial of oral gatifloxacin 400 mg daily for 7 to 14 days. An antibiogram of isolates showed 100% susceptibility to gatifloxacin (MIC(90) 0.5 micro g/mL) and respective susceptibilities of 67%, 70%, and 80% to penicillin, erythromycin, and tetracycline. Clinical cure was achieved in 95.3% of evaluable patients, including seven patients infected with penicillin-resistant S. pneumoniae (MIC > or =2 micro g/mL). The bacteriologic eradication rate for S. pneumoniae was 94.5%. Diarrhea, nausea, and dizziness, the most common adverse events in CAP patients (<3%), were generally mild to moderate; no serious adverse events were recorded. These results support recommendations to treat CAP, particularly due to S. pneumoniae including multidrug-resistant strains, with the newer 8-methoxy-fluoroquinolone, gatifloxacin.

In vitro assessment of gatifloxacin spectrum and potency tested against Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae isolates from the Asia-Western Pacific component of the SENTRY antimicrobial surveillance program (1998-1999)

Fluoroquinolones, especially the newer agents, have an increased role in the management of respiratory tract infections worldwide. In the SENTRY Antimicrobial Surveillance Program for the Asia-Pacific Region for 1998 and 1999, 630 Streptococcus pneumoniae, 583 Hemophilus influenzae and 274 Moraxella catarrhalis isolates were examined to determine the comparative activity of the new fluoroquinolone, gatifloxacin, compared with those of ciprofloxacin, levofloxacin and trovafloxacin. Gatifloxacin was highly active against all three species. Decreased susceptibility (MIC >/=2 microg/mL) to gatifloxacin was noted in only seven strains of S. pneumoniae (3 of which were resistant); in three strains of H. influenzae (MIC >/= 0.12 microg/mL), and 2 M. catarrhalis (MIC > 2 microg/mL).

Spectrum and potency evaluation of a new oxazolidinone, linezolid: report from the SENTRY Antimicrobial Surveillance Program, 1998-2000

Resistance (R) among Gram-positive cocci has escalated in the last two decades to levels necessitating the development and use in the newer drug classes, oxazolidinones (linezolid) and streptogramins (quinupristin/dalfopristin [Q/D]). The SENTRY Antimicrobial Surveillance Program has monitored these classes before, during and after their release by various regulatory agencies. Over 30,000 Gram-positive strains were tested against >30 drugs by reference broth microdilution methods between 1998-2000 in four geographic regions (Asia-Western Pacific [APAC], Europe [EU], Latin America [LA], North America [NA]). The tested strains were 23,188 staphylococci; 5,103 enterococci and 2,045 streptococci. Among staphylococci, linezolid was active against all isolates (MICs, < or =4 microg/ml) regardless of susceptibility patterns of other antimicrobial agents. Similar results were noted for vancomycin (includes one VISA from Hong Kong), teicoplanin, and Q/D (<1% R). Gatifloxacin had the widest spectrum among fluoroquinolones (FQ) against Staphylococcus aureus (1.5-9.2% R) and coagulase-negative staphylococci (0.8-4.0%). Linezolid was also active against all enterococci (MIC50 and (90,) 2 microg/ml). Q/D was active against only 75.3% of vancomycin-resistant enterococci (VRE). The VRE rate was highest in NA (12.4%) > EU (3.2%) > LA (1.6%) > APAC (1.3%). Among streptococci, linezolid was consistently active (MIC(90,) 1 microg/ml) as were the glycopeptides and Q/D. Variable penicillin-R (MIC, > or = 2 microg/ml) was observed among regions: EU (32.5%) > APAC (15.1%) > LA (13.8%) > NA (9.6%), and macrolide-R was higher in EU (40.3%). Ciprofloxacin-R at > or =4 microg/ml in streptococcal strains was noted world wide highest in viridans group streptococci (18.4-25.6%). Linezolid remained active (MIC, < or =4 microg/ml) against all Gram-positive species strains tested in the SENTRY Program (1998-2000). Q/D, glycopeptides and newer FQ compounds were generally less effective in vitro. It remains a prudent practice to continue surveillance programs to detect emerging resistance patterns and recognize significant regional variations in the oxazolidinone susceptibilities.

Potency and antimicrobial spectrum update for piperacillin/tazobactam (2000): emphasis on its activity against resistant organism populations and generally untested species causing community-acquired respiratory tract infections

The in vitro activity of piperacillin/tazobactam and several comparison broad-spectrum compounds was assessed against recent clinical isolates of Gram-positive and -negative bacteria from geographically diverse medical centers in Europe, North and Latin America participating in various surveillance programs in 2000. Several organisms were characterized for phenotypic expression of various resistant determinants such as extended-spectrum beta-lactamase (ESBL) or amp C cephalosporinase hyperproduction, and vancomycin resistance in enterococci (VRE). Piperacillin/tazobactam retained activity (MIC50) against oxacillin-susceptible Staphylococcus spp. (0.12-0.5 microg/ml), Bacillus spp. (0.5 microg/ml), vancomycin-susceptible enterococci (>4 microg/ml), and Corynebacterium spp. (2 microg/ml; not including C. jeikeium) with susceptibility rates of 100.0, 91.7, 85.7 and 81.8%, respectively. Piperacillin/tazobactam inhibited all Streptococcus spp. strains at < or = 16 microg/ml, including penicillin-resistant strains many of which were co-resistant to erythromycin (90%) and other beta-lactams. A specific breakpoint for these streptococci when testing piperacillin/tazobactam appears needed to prevent false-resistant reports using penicillin as a class representative. The carbapenems among beta-lactams were the most active agents against the ESBL-producing species of Escherichia coli and Klebsiella pneumoniae and those strains which hyper-express amp C enzymes including Citrobacter spp. and Enterobacter spp. Piperacillin/tazobactam only exhibited modest activity against the "amp C resistance group" strains (68.8% susceptible or intermediate, MIC < or = 64 microg/ml). Piperacillin/tazobactam (MIC50, 8 microg/ml; 79.5% susceptible) was the most active agent tested against multi-drug resistant isolates of Pseudomonas aeruginosa. Against sampled Haemophilus influenzae (39.2% ampicillin-resistant), piperacillin/tazobactam (MIC(90,) < or = 0.06 microg/ml), ceftriaxone and ceftazidime inhibited 100.0% of the isolates at < or = 0.25 microg/ml. These in vitro surveillance results from the year 2000 on three continents, demonstrated a sustained potent activity of piperacillin/tazobactam against selected problematic nosocomial and community-acquired pathogens. The potential importance of these findings is that this beta-lactamase inhibitor combination can be used an empiric treatment of serious infections in hospital environments where resistance has emerged, as well as covering nearly all isolates of fastidious respiratory tract pathogens acquired in the community setting.

Appropriate use of antibiotics for respiratory infections: review of recent statements and position papers

Respiratory infections are among the most common reasons for prescribing antibiotics. The excessive use of antibiotics in ambulatory practice has contributed to the emergence and spread of antibiotic resistance. The appropriate use of antimicrobial agents for respiratory infections could potentially reduce the emergence of antibiotic resistance. This article reviews recent guidelines and position papers on the appropriate antibiotic treatment for respiratory infections. There is a wide consensus that antibiotics are not appropriate for the treatment of most cases of acute bronchitis, pharyngitis, and rhinosinusitis. The recently published community-acquired pneumonia guidelines emphasized the importance of selecting antibiotic regimens active against both typical and atypical pathogens. However, there is disagreement regarding the routine use of the new quinolones.

Levofloxacin treatment failure in a patient with fluoroquinolone-resistant Streptococcus pneumoniae pneumonia

The frequency of fluoroquinolone-resistant Streptococcus pneumoniae has increased as fluoroquinolone administration for treatment of respiratory tract infections has increased. Levofloxacin treatment failed in a patient who had pneumococcal pneumonia and had received three previous courses of levofloxacin therapy. Susceptibility testing revealed high-level resistance to levofloxacin (minimum inhibitory concentration [MIC] > 32 microg/ml), and cross-resistance to moxifloxacin (MIC 4 microg/ml), trovafloxacin (6 microg/ml), and gatifloxacin (12 microg/ml). Sequencing of the quinolone-resistance determining region revealed a mutation of serine-81 to phenylalanine (Ser81-->Phe) in the gyrA region of DNA gyrase and a Ser79-->Phe mutation in the parC region of topoisomerase IV The patient was treated successfully with intravenous ceftriaxone followed by oral cefprozil. Clinicians must be aware of local resistance patterns and the potential for fluoroquinolone treatment failures in patients with infections caused by S. pneumoniae.

In vitro activities of tigecycline (GAR-936) against recently isolated clinical bacteria in Spain

The antimicrobial activities of tigecycline (GAR-936) were compared with those of other agents against 1,087 strains recently isolated in 12 Spanish medical centers. Tigecycline showed activity against a wide spectrum of aerobic and anaerobic bacteria, including strains such as methicillin-resistant Staphylococcus aureus, coagulase-negative staphylococci, penicillin-resistant Streptococcus pneumoniae, Enterococcus faecium, Acinetobacter baumannii, and Stenotrophomonas maltophilia.

Influence of CO(2) incubation on quinolone activity against Streptococcus pneumoniae and Haemophilus influenzae

Quinolone activity can be influenced by the pH change that occurs during CO(2) incubation when testing capnophilic organisms such as Streptococcus pneumoniae and Haemophilus influenzae. This study compares the activity of ciprofloxacin, clinafloxacin, enrofloxacin, fleroxacin, grepafloxacin, levofloxacin, moxifloxacin, norfloxacin, ofloxacin, pefloxacin, sparfloxacin, trovafloxacin, and the glycopeptide vancomycin, under ambient air and supplemental CO(2) incubation conditions. Etest (AB BIODISK, Solna, Sweden) was used to determine the MIC values of 30 S. pneumoniae strains including S. pneumoniae ATCC 49619 and 6030; and 29 H. influenzae strains including H. influenzae ATCC 49247 and 49766, incubated with and without 5% CO(2.) Reference broth microdilution and agar dilution tests were performed under similar conditions. Results determined that MIC values of all quinolones agreed (> or = 95%) within +/- one log(2) dilution for the three test methods tested under identical incubation conditions. Quinolone MICs for S. pneumoniae were minimally influenced by CO(2,) while MIC values for H. influenzae ranged from 0.5 to two log(2) dilutions higher when incubated in the CO(2) environment. The differences in quinolone activity against H. influenzae may be due to a combination of pH effects and enhanced growth in the CO(2) test conditions. Quality control and interpretative criteria, especially for H. influenzae and quinolones published by the National Committee for Clinical Laboratory Standards, may not be fully applicable to results obtained under CO(2) incubation. This may generate potential therapeutic interpretive dilemmas in the susceptibility testing of H. influenzae, where clinical isolates require CO(2) to sustain acceptable growth.

Nested polymerase chain reaction in the diagnosis of congenital cytomegalovirus infection

OBJECTIVE

Human cytomegalovirus infection is highly prevalent in Indian population. It is the commonest congenitally acquired infection causing various anomalies. The diagnosis of infection in neonates is difficult as IgM may not be detected in all cases. The polymerase chain reaction is reported as alternative and better option in these patients. However, there is lack of data to substantiate this preference in a resource poor country like India.

METHODS

Blood samples from 930 neonates/fetuses were first tested for specific anti-CMV IgM antibodies using mu-capture enzyme linked immunosorbent assay, Mac-ELISA. Nested PCR was first standardised on clinically and therapeutically confirmed cases of CMV disease. In the second phase blood samples randomly from 20 babies suspected of CMV infection were collected for serology and PCR and both tests were run independently. Twenty healthy controls were also included. IgM ELISA and PCR were performed on these samples and results of these 20 samples were compared to evaluate the sensitivity and specificity of each method.

RESULTS

Out of 930 serum samples of suspected congenital CMV infection 188 (20.2%) were found positive for CMV specific IgM antibodies. While comparing the results of 40 paired samples, PCR was found to be highly specific (100%) but less sensitive than Mac-ELISA (95%) with negative predictive value of 100% and positive predictive value of 95%. Thus in congenital CMV infection Mac-ELISA was less costly, less cumbersome and more user friendly.

CONCLUSION

The Mac-ELISA seem to have parallel sensitivity and specificity as PCR for diagnosing congenital CMV infection.

Fluoroquinolone susceptibility, resistance, and pharmacodynamics versus clinical isolates of Streptococcus pneumoniae from Indiana

The in vitro activity and pharmacodynamics (AUC(0-24)/MIC) of levofloxacin, gatifloxacin, moxifloxacin, and gemifloxacin were evaluated against 307 clinical isolates of Streptococcus pneumoniae from Indianapolis, Indiana. Organisms were collected between January 1999 and April 2000, and MICs were determined by broth microdilution. Serum concentration-time profiles were simulated for the following oral regimens administered once daily: levofloxacin 500 mg and 750 mg; gatifloxacin 400 mg; moxifloxacin 400 mg; gemifloxacin 320 mg. Free 24 h area under the serum concentration-time curves (AUC(0-24)) were calculated, and the average AUC(0-24)/MIC was calculated for each regimen. Differences in AUC(0-24)/MIC among agents were determined by analysis of variance (Scheffe post-hoc test, p < 0.05). Overall, gemifloxacin was the most potent agent tested. Five (1.7%), 4 (1.3%), and 2 (0.7%) isolates were resistant to levofloxacin, gatifloxacin, and moxifloxacin, respectively. None of the isolates was resistant to gemifloxacin. Gemifloxacin AUC(0-24)/MIC was significantly greater than all other regimens (p < 0.0001), with the exception of moxifloxacin. However, the percent of isolates for which an AUC(0-24)/MIC >or= 30-50 can be achieved is similar for gemifloxacin, moxifloxacin, gatifloxacin, and levofloxacin 750 mg. Large comparative studies are needed to determine if the differences in AUC(0-24)/MIC among fluoroquinolones are clinically significant.

Comparative antimicrobial activity of ABT-773, a novel ketolide, tested against drug-resistant Gram-positive cocci and Haemophilus influenzae

The antimicrobial activity of ABT-773, a novel ketolide, was tested against 618 Gram-positive strains collected from various surveillance programmes between 1997 and 2000. ABT-773 has potent activity against Streptococcus pneumoniae (MIC90, < or = 0.03-0.12 mg/l), beta-haemolytic streptococci (MIC90, < or = 0.03 mg/l) and viridans group streptococci (MIC90, < or = 0.03 mg/l), including erythromycin-resistant strains. In contrast, ABT-773 was less active against erythromycin-resistant Staphylococcus aureus (31% susceptible at < or = 0.25 mg/l), coagulase-negative staphylococci (41% susceptible) and enterococci (30% susceptible). Haemophilus influenzae (MIC90, 4 mg/l) was less inhibited by the two ketolides tested, and ABT-773 was generally two- to fourfold more potent than telithromycin. The ketolides appear to have potential clinical use against some Gram-positive species resistant to macrolides.

Worldwide prevalence of antimicrobial resistance in Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in the SENTRY Antimicrobial Surveillance Program, 1997-1999

The in vitro activities of numerous antimicrobials against clinical isolates of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis from patients with bloodstream and respiratory tract infections in the United States, Canada, Europe, Latin America, and the Asia-Pacific region were studied in the SENTRY Antimicrobial Surveillance Program. Penicillin resistance (minimum inhibitory concentration, > or =2 microg/mL) was noted in all 5 geographic regions, and a high and increasing rate of macrolide resistance among S. pneumoniae isolates was observed. Elevated rates of resistance to clindamycin, trimethoprim-sulfamethoxazole, chloramphenicol, and tetracycline were seen. beta-Lactamase-mediated resistance in H. influenzae to amoxicillin and variable trimethoprim-sulfamethoxazole resistance by region were documented. Resistance to several drugs continues to emerge among pneumococci worldwide, but more stable resistance patterns have been noted for H. influenzae and M. catarrhalis. Continued surveillance of this pathogen group appears to be prudent.

Multi-laboratory assessment of the linezolid spectrum of activity using the Kirby-Bauer disk diffusion method: Report of the Zyvox Antimicrobial Potency Study (ZAPS) in the United States

The in vitro activity of linezolid against common Gram-positive pathogens was compared to that of penicillin or ampicillin or oxacillin (depending upon genus), cefazolin, erythromycin, clindamycin, quinupristin/dalfopristin, levofloxacin, nitrofurantoin and vancomycin by disk diffusion methods. One hundred and six centers (31 states in US) tested recent clinical isolates of Staphylococcus aureus, coagulase-negative staphylococci, Enterococcus faecium, E. faecalis, Streptococcus pneumoniae, and other streptococci. Testing was conducted using the standardized disk diffusion method and concurrent quality control testing was performed. Strains with linezolid zone diameters of < or = 20 mm were requested for referral to the microbiology monitor for confirmation. A total of 3,100 isolates (97% compliance) were tested. Susceptibility (zone diameters, > or = 21 mm) of staphylococci and streptococci to linezolid was reported in 100% and 99.4% of staphylococci and streptococci, respectively. Susceptibility (zone diameters, > or = 23 mm) of enterococci to linezolid was 96.0% with only three isolates (0.4%) reported as resistant (zone diameters, < or = 20 mm; unconfirmed). Among a total of nine isolates (0.3%) reported to have zone diameters 20 mm, six were not submitted for further testing, two were contaminated with Gram-negative bacilli and one was determined to be linezolid-susceptible. There were no differences in linezolid susceptibility in the vancomycin- or oxacillin- or penicillin-resistant subsets of strains. This susceptibility pattern for US medical centers is indicative of the excellent and nearly complete in vitro activity against the key Gram-positive pathogens for which linezolid has received US Food and Drug Administration indications for clinical use.