Longitudinally tracking fluoroquinolone resistance and its determinants in penicillin-susceptible and -nonsusceptible Streptococcus pneumoniae isolates in Hong Kong, 2000 to 2005

Systematic review of human gut resistome studies revealed variable definitions and approaches

In this review, we highlight the variations of gut resistome studies, which may preclude comparisons and translational interpretations. Of 22 included studies, a range of 12 to 2000 antibiotic resistance (AR) genes were profiled. Overall, studies defined a healthy gut resistome as subjects who had not taken antibiotics in the last three to 12 months prior to sampling. In studies with de novo assembly, AR genes were identified based on variable nucleotide or amino acid sequence similarities. Different marker genes were used for defining resistance to a given antibiotic class. Validation of phenotypic resistance in the laboratory is frequently lacking. Cryptic resistance, collateral sensitivity and the interaction with repressors or promotors were not investigated. International consensus is needed for selecting marker genes to define resistance to a given antibiotic class in addition to uniformity in phenotypic validation and bioinformatics pipelines.

Antibacterial activity of a DNA topoisomerase I inhibitor versus fluoroquinolones in Streptococcus pneumoniae

The DNA topoisomerase complement of Streptococcus pneumoniae is constituted by two type II enzymes (topoisomerase IV and gyrase), and a single type I enzyme (topoisomerase I). These enzymes maintain the DNA topology, which is essential for replication and transcription. While fluoroquinolones target the type II enzymes, seconeolitsine, a new antimicrobial agent, targets topoisomerase I. We compared for the first time the in vitro effect of inhibition of topoisomerase I by seconeolitsine and of the type II topoisomerases by the fluoroquinolones levofloxacin and moxifloxacin. We used three isogenic non-encapsulated strains and five non-vaccine serotypes isolates belonging to two circulating pneumococcal clones, ST63⁸ (2 strains) and ST156^9V (3 strains). Each group contained strains with diverse susceptibility to fluoroquinolones. Minimal inhibitory concentrations, killing curves and postantibiotic effects were determined. Seconeolitsine demonstrated the fastest and highest bactericidal activity against planktonic bacteria and biofilms. When fluoroquinolone-susceptible planktonic bacteria were considered, seconeolitsine induced postantibiotic effects (1.00−1.87 h) similar than levofloxacin (1.00−2.22 h), but longer than moxifloxacin (0.39−1.71 h). The same effect was observed in sessile bacteria forming biofilms. Seconeolitsine induced postantibiotic effects (0.84−2.31 h) that were similar to those of levofloxacin (0.99−3.32 h) but longer than those of moxifloxacin (0.89−1.91 h). The greatest effect was observed in the viability and adherence of bacteria in the postantibiotic phase. Seconeolitsine greatly reduced the thickness of the biofilms formed in comparison with fluoroquinolones: 2.91 ± 0.43 μm (seconeolitsine), 7.18 ± 0.58 μm (levofloxacin), 17.08 ± 1.02 μm (moxifloxacin). When fluoroquinolone-resistant bacteria were considered, postantibiotic effects induced by levofloxacin and moxifloxacin, but not by seconeolitsine, were shorter, decreasing up to 5-fold (levofloxacin) or 2-fold (moxifloxacin) in planktonic cells, and up to 1.7 (levofloxacin) or 1.4-fold (moxifloxacin) during biofilm formation. Therefore, topoisomerase I inhibitors could be an alternative for the treatment of pneumococcal diseases, including those caused by fluoroquinolone-resistant isolates.

Reactive Oxygen Species Production Is a Major Factor Directing the Postantibiotic Effect of Fluoroquinolones in Streptococcus pneumoniae

We studied the molecular mechanisms involved in the postantibiotic effect of the fluoroquinolones levofloxacin and moxifloxacin in Streptococcus pneumoniae Wild-type strain R6 had postantibiotic effects of 2.05 ± 0.10 h (mean ± standard deviation [SD]) and 3.23 ± 0.45 h at 2.5× and 10× MIC of levofloxacin, respectively. Moxifloxacin exhibited lower effects of 0.87 ± 0.1 and 2.41 ± 0.29 h at 2.5× and 10× MIC, respectively. Fluoroquinolone-induced chromosome fragmentation was measured at equivalent postantibiotic effects for levofloxacin (2.5× MIC) and moxifloxacin (10× MIC). After 2 h of drug removal, reductions were approximately 7-fold for levofloxacin and 3-fold for moxifloxacin, without further decreases at later times. Variations in reactive oxygen species production were detected after 4 to 6 h of drug withdrawals, with decreases ≥400-fold for levofloxacin and ≥800-fold for moxifloxacin at 6 h. In accordance, after 4 to 6 h of drug withdrawal, the levofloxacin-induced upregulation of the fatCDEB operon, introducing iron in the bacteria, decreased up to 2- to 3-fold, and the moxifloxacin-induced upregulation of several genes involved in the production of pyruvate was reduced 3- to 7-fold. In accordance, lower postantibiotic effects (up to 1 h) were observed in strain R6 ΔspxB, lacking the main enzyme involved in oxygen peroxide production, than in R6. Although no change in the recovery of chromosome fragmentation was observed between R6 and R6 ΔspxB, 3.5 × 10³-fold lower reactive oxygen species production was observed in R6 ΔspxB, without changes after drug removal. These results show that reactive oxygen species are the main factors directing the postantibiotic effect of levofloxacin and moxifloxacin in S. pneumoniae.

Change in Pneumococcus Serotypes but not Mortality or Morbidity in Pre- and Post-13-Valent Polysaccharide Conjugate Vaccine Era: Epidemiology in a Pediatric Intensive Care Unit over 10 Years

AIM

Pneumococcus is a common commensal and an important pathogen among children for which immunization is available. Some serotypes occasionally cause severe pneumococcal disease with high mortality and morbidity. We reviewed all pneumococcal serotypes and mortality/morbidity in a pediatric intensive care unit (PICU) following universal pneumococcal conjugate vaccine (PCV) immunization.

METHODS

A 13-valent PCV was introduced in the universal immunization program in late 2011 in Hong Kong. We retrospectively reviewed all pneumococcal serotypes in the pre-(2007-11) and post-(2012-16) 13-valent PCV era.

RESULTS

There were 29 (1.9%) PICU patients with pneumococcal isolation, of which 6 died (20% motality). Serogroups 6 and 19 predominated before and Serogroup 3 after 2012. In the post-13-valent PCV era, the prevalence of pneumococcus isolation in PICU was increased from 1 to 2% (p = 0.04); Serogroup 3 was the major serotype of morbidity, despite supposedly under vaccine coverage. The majority of pneumococcus were penicillin-sensitive (94%) in the post 13-valent PCV era. All pneumococcus specimens were sensitive to cefotaxime and vancomycin. Binary logistic regression showed that there were reductions in Serogroup 6 (odds ratio [OR], 0.050; 95% confidence interval [CI], 0.004-0.574; p = 0.016) and Serogroup 19 (odds ratio [OR], 0.105; 95% confidence interval [CI], 0.014-0.786; p = 0.028) but not mortality or morbidity for patients admitted after 2012.

CONCLUSIONS

SPD is associated with significant morbidity and mortality, despite treatment with systemic antibiotics and ICU support. The expanded coverage of 13-valent PCV results in the reduction of Serotypes 6 and 19 but not mortality/morbidity associated with SPD in the setting of a PICU.

Upregulation of the PatAB Transporter Confers Fluoroquinolone Resistance to Streptococcus pseudopneumoniae

We characterized the mechanism of fluoroquinolone-resistance in two isolates of Streptococcus pseudopneumoniae having fluoroquinolone-efflux as unique mechanism of resistance. Whole genome sequencing and genetic transformation experiments were performed together with phenotypic determinations of the efflux mechanism. The PatAB pump was identified as responsible for efflux of ciprofloxacin (MIC of 4 μg/ml), ethidium bromide (MICs of 8-16 μg/ml) and acriflavine (MICs of 4-8 μg/ml) in both isolates. These MICs were at least 8-fold lower in the presence of the efflux inhibitor reserpine. Complete genome sequencing indicated that the sequence located between the promoter of the patAB operon and the initiation codon of patA, which putatively forms an RNA stem-loop structure, may be responsible for the efflux phenotype. RT-qPCR determinations performed on RNAs of cultures treated or not treated with subinhibitory ciprofloxacin concentrations were performed. While no significant changes were observed in wild-type Streptococcus pneumoniae R6 strain, increases in transcription were detected in the ciprofloxacin-efflux transformants obtained with DNA from efflux-positive isolates, in the ranges of 1.4 to 3.4-fold (patA) and 2.1 to 2.9-fold (patB). Ciprofloxacin-induction was related with a lower predicted free energy for the stem-loop structure in the RNA of S. pseudopneumoniae isolates (-13.81 and -8.58) than for R6 (-15.32 kcal/mol), which may ease transcription. The presence of these regulatory variations in commensal S. pseudopneumoniae isolates, and the possibility of its transfer to Streptococcus pneumoniae by genetic transformation, could increase fluoroquinolone resistance in this important pathogen.

What is the clinical relevance of drug-resistant pneumococcus?

PURPOSE OF REVIEW

Pneumococcal infections are a major cause of morbidity and mortality worldwide. In recent years, Streptococcus pneumoniae has shown increasing resistance to a several antibiotics, becoming a worldwide problem. The impact of antibiotic resistance of S. pneumoniae on clinical outcomes is still controversial. The principal reason for this controversy is the existence of several factors related to the patients and to the pathogen that may influence how antibiotic resistance patterns affect clinical outcomes. The aim of this review is to discuss current knowledge of the epidemiological data on antibiotic resistance; we also discuss mechanisms and risk factors for antibiotic resistance.

RECENT FINDINGS

The phenomenon of serotype replacement after the introduction of conjugate pneumococcal vaccinations and the escalation of antibiotic resistance worldwide remains an important issue in terms of their impact on clinical outcomes in pneumococcal disease. Antimicrobial resistance of pneumococcus leads to changes in the clinical presentation of pneumococcal disease, making it more difficult to diagnose and to treat. Consumption of antibiotics in the community is directly proportional to antimicrobial resistance. Carriage of S. pneumoniae and infection with antibiotic-resistant pneumococcus is associated with prior antibiotic therapy, extremes of age, presence of comorbidities (i.e. COPD), attendance at child day care centers, crowded conditions, intra-familial transmission, and nursing home residence.

SUMMARY

Antibiotic-resistant S. pneumoniae is a worldwide problem. The implementation of several strategies including vaccine campaigns, prudent use of current antibiotics, and programs for the surveillance of pneumococcal infections, could limit the increasing resistance of this pathogen to antimicrobials.

Biological and Epidemiological Features of Antibiotic-Resistant Streptococcus pneumoniae in Pre- and Post-Conjugate Vaccine Eras: a United States Perspective

Streptococcus pneumoniae inflicts a huge disease burden as the leading cause of community-acquired pneumonia and meningitis. Soon after mainstream antibiotic usage, multiresistant pneumococcal clones emerged and disseminated worldwide. Resistant clones are generated through adaptation to antibiotic pressures imposed while naturally residing within the human upper respiratory tract. Here, a huge array of related commensal streptococcal strains transfers core genomic and accessory resistance determinants to the highly transformable pneumococcus. β-Lactam resistance is the hallmark of pneumococcal adaptability, requiring multiple independent recombination events that are traceable to nonpneumococcal origins and stably perpetuated in multiresistant clonal complexes. Pneumococcal strains with elevated MICs of β-lactams are most often resistant to additional antibiotics. Basic underlying mechanisms of most pneumococcal resistances have been identified, although new insights that increase our understanding are continually provided. Although all pneumococcal infections can be successfully treated with antibiotics, the available choices are limited for some strains. Invasive pneumococcal disease data compiled during 1998 to 2013 through the population-based Active Bacterial Core surveillance program (U.S. population base of 30,600,000) demonstrate that targeting prevalent capsular serotypes with conjugate vaccines (7-valent and 13-valent vaccines implemented in 2000 and 2010, respectively) is extremely effective in reducing resistant infections. Nonetheless, resistant non-vaccine-serotype clones continue to emerge and expand.

Reactive Oxygen Species Contribute to the Bactericidal Effects of the Fluoroquinolone Moxifloxacin in Streptococcus pneumoniae

We studied the transcriptomic response of Streptococcus pneumoniae to the fluoroquinolone moxifloxacin at a concentration that inhibits DNA gyrase. Treatment of the wild-type strain R6, at a concentration of 10× the MIC, triggered a response involving 132 genes after 30 min of treatment. Genes from several metabolic pathways involved in the production of pyruvate were upregulated. These included 3 glycolytic enzymes, which ultimately convert fructose 6-phosphate to pyruvate, and 2 enzymes that funnel phosphate sugars into the glycolytic pathway. In addition, acetyl coenzyme A (acetyl-CoA) carboxylase was downregulated, likely leading to an increase in acetyl-CoA. When coupled with an upregulation in formate acetyltransferase, an increase in acetyl-CoA would raise the production of pyruvate. Since pyruvate is converted by pyruvate oxidase (SpxB) into hydrogen peroxide (H2O2), an increase in pyruvate would augment intracellular H2O2. Here, we confirm a 21-fold increase in the production of H2O2 and a 55-fold increase in the amount of hydroxyl radical in cultures treated during 4 h with moxifloxacin. This increase in hydroxyl radical through the Fenton reaction would damage DNA, lipids, and proteins. These reactive oxygen species contributed to the lethality of the drug, a conclusion supported by the observed protective effects of an SpxB deletion. These results support the model whereby fluoroquinolones cause redox alterations. The transcriptional response of S. pneumoniae to moxifloxacin is compared with the response to levofloxacin, an inhibitor of topoisomerase IV. Levofloxacin triggers the transcriptional activation of iron transport genes and also enhances the Fenton reaction.

Penicillin-Resistant trend of Streptococcus pneumoniae in Asia: A systematic review

The high prevalence of resistance to penicillin by Streptococcus pneumoniaeis considered as a great concern, particularly in Asian countries. The aim of this study was to investigate the changing trend of penicillin-resistant S. pneumoniae (PRSP) in Asia over a 20 years period. A review of the literature was conducted using the PubMed database, Google Scholar, Scopus, two Persian scientific search engines "Scientific Information Database" (www.sid.ir), and "Mag Iran" (www.magiran.com) through 1993 to 2013. Our study provides a unique chance to investigate the changing trend in PSSP in Asia over a 20 years period. Susceptibility rates among different centers in each country varied widely. In Malaysia, the PSSP rate decreased from 97.2% in 1995-1996 to 69% in 2000. In Singapore, PSSP levels decreased from 72.6% in 1997 to 30.5% in 2007-2008. In Iran, PSSP ranged from 0% to 100%. In Taiwan, the rate of PSSP was 60.3% in 1995 and <50% in other years. In Lebanon, the rate of PSSP was less than 50% (ranging from 30.1% to 50%) in all published data. In Hong Kong, the level of penicillin susceptibility decreased from 71.1% during 1993-1995 to less 42% in 2007. Continuous surveillance of resistance data from clinical isolates as well as implementation of strict infection control policies is recommended. More studies are needed for better evaluation PSSP rate in some Asian countries such as Vietnam, Singapore, Philippines, Pakistan, Nepal, Kuwait, Korea and Indonesia.

Cardiopulmonary morbidity of streptococcal infections in a PICU

AIM

The streptococci are important bacteria that cause serious childhood infections. We investigated cardiopulmonary morbidity associated with streptococcal infection and pediatric intensive care unit (PICU) admission.

METHODS

A retrospective study between 2002 and 2013 of all children with a laboratory isolation of streptococcus.

RESULTS

There were 40 (2.3%) PICU patients with streptococcal isolations including Streptococcus pyogenes (Group A streptococcus, GAS, n = 7), Streptococcus agalactiae (Group B streptococcus, GBS, n = 5), Streptococcus pneumoniae (SP, n = 20), alpha-hemolytic (n = 4), beta-hemolytic (n = 2) and gama-hemolytic (n = 2) streptococci. Comparing among GAS, GBS and SP, respiratory isolates were more likely positive for GAS or SP (P = 0.033), whereas cerebrospinal fluid was more likely positive for GBS (P = 0.002). All GAS and GBS, and the majority of SP (90%) were sensitive to penicillin. All SP specimens were sensitive to cefotaxime and vancomycin. These infections were associated with high PICU mortality of 43%, 20% and 25%, respectively. Isolation of streptococci was associated with a 30% mortality and high rates of need for mechanical ventilatory and inotropic supports. Patients with GAS, SP or any streptococcal isolation had relative risks [95% confidence interval (CI), P value] of PICU deaths of 7.5 (CI 3.1-18.1, P < 0.0001), 4.5 (CI 2.0-9.8, P < 0.0002) and 5.7 (CI 3.4-9.5, P < 0.0001), respectively. In SP, older children had significantly higher prevalence of premorbid conditions such as malignancy, mental retardation/cerebral palsy ± seizure disorders, chromosomal or genetic disorders (P = 0.003) than children <5 years of age. Serotypes were available for some of these specimens that included 19A, 6B, 3 and 6C. There were four SP deaths with multiorgan system failure and hemolytic uremic syndrome (two 19A and two serotype 3).

CONCLUSIONS

Severe streptococcal infections are associated with significant morbidity and mortality despite treatment with systemic antibiotics and intensive care unit support. GAS and SP affect the lungs of children, whereas GBS more likely causes meningitis in infants. The expanded coverage of newer polyvalent pneumococcal vaccines can probably prevent infections by serotypes 19A, 19F, 6B and 3.

Fluoroquinolone-resistant pneumococci: dynamics of serotypes and clones in Spain in 2012 compared with those from 2002 and 2006

In Spain, rates of ciprofloxacin resistance in pneumococci were low during the last decade (2.6% in 2002 and 2.3% in 2006). In 2012, the rate remained at 2.3%, equivalent to 83 of 3,621 isolates. Of the 83 resistant isolates, 15 showed a low level (MIC of 4 to 8 μg/ml) and 68 a high level (MIC of 16 to 128 μg/ml) of ciprofloxacin resistance. Thirteen low-level-resistant isolates had single changes in ParC, one had a single ParE change, and one did not present any mutations. High-level-resistant isolates had GyrA changes plus additional ParC and/or ParE changes: 51, 15, and 2 isolates had 2, 3, or 4 mutations, respectively. Although 24 different serotypes were observed, 6 serotypes accounted for 51.8% of ciprofloxacin-resistant isolates: 8 (14.5%), 19A (10.8%), 11A (7.2%), 23A (7.2%), 15A (6.0%), and 6B (6.0%). A decrease in pneumococcal 7-valent conjugate vaccine (PCV7) serotypes was observed from 2006 (35.7%) to 2012 (16.9%), especially of serotype 14 (from 16.3% to 2.4%; P<0.001). In comparison with findings in 2006, multidrug resistance was greater in 2012 (P=0.296), mainly due to the increased presence and/or emergence of clonal complexes associated with non-PCV7 serotypes: CC63 expressing serotypes 8, 15A, and 19A; CC320 (with serotype 19A); and CC42 (with serotype 23A). Although rates of ciprofloxacin resistance remained low and stable throughout the last decade, changes in serotype and genotype distributions were observed in 2012, notably the expansion of a preexisting multidrug-resistant clone, CC63, and the emergence of the CC156 clone expressing serotype 11A.

Regional epidemiology of invasive pneumococcal disease in Asian adults: epidemiology, disease burden, serotype distribution, and antimicrobial resistance patterns and prevention

OBJECTIVES

To summarize published data on the clinical and economic burden, epidemiology, antimicrobial resistance levels, serotype prevalence, and prevention strategies for pneumococcal disease among adults in Asia.

METHODS

We performed a systematic search of the PubMed database for relevant, peer-reviewed articles published between January 1995 and December 2011, covering China, Hong Kong, India, Indonesia, Japan, Malaysia, Pakistan, the Philippines, Singapore, South Korea, Taiwan, Thailand, and Vietnam.

RESULTS

Taiwan and Thailand had the most comprehensive epidemiological data on adult pneumococcal disease. Very little relevant data were found for Indonesia, Pakistan, the Philippines, and Vietnam; surveillance is urgently needed in these countries. The emergence and spread of resistance emphasize the importance of vaccination to prevent infection in adults at increased risk for serious pneumococcal disease. Vaccination policies and opinions on the efficacy of vaccination vary widely in Asian countries, although a new option in the form of a pneumococcal conjugate vaccine is now available.

CONCLUSIONS

Increased awareness of the public health and economic benefits of pneumococcal vaccination is critically needed to help both the public and policymakers in making changes to vaccination policies in the region. Maximizing access to pneumococcal vaccines will decrease the number of hospitalizations, complications, and deaths associated with pneumococcal disease.

The newer fluoroquinolones

Clinicians have enthusiastically used fluoroquinolones owing to their good safety profile and wide range of indications. This article reviews fluoroquinolone pharmacology, pharmacodynamic principles, and fluoroquinolone resistance mechanisms, highlighting recent trends in the epidemiology of fluoroquinolone resistance among gram-negative organisms and Streptococcus pneumonia. Important fluoroquinolone safety concerns are discussed, along with indications for the most commonly used fluoroquinolones--ciprofloxacin, levofloxacin, and moxifloxacin.

Childhood pneumococcal diseases and serotypes: can vaccines protect?

OBJECTIVES

To describe pneumococcal diseases in pediatric intensive care unit (PICU) and non-PICU patients.

METHODS

The clinical, serotypes, and antibacterial sensitivity patterns of all children admitted to the pediatric wards (including PICU) of a university-affiliated teaching hospital from 2007 through 2009 with pneumococcal isolates were reviewed.

RESULTS

Twelve cases of pneumococcal disease in children from 2007 through 2009 were reported. Five patients were admitted to PICU and 7 were general pediatric admissions. Four patients (2 PICU and 2 general pediatric) had received full or partial 7-valent pneumococcal vaccinations. All four patients recovered following systemic antibiotic treatment without sequelae. The serotypes of all PICU and some general pediatric cases were available and included 3, 6B, 19A and 19F. All isolates were sensitive to vancomycin. 50% were intermediate resistant/resistant to penicillin and 17% resistant to cefotaxime. PICU cases required longer total hospital stay (23 days vs 5 days, p=0.013). Three patients were ventilated and one received inotropic support. There was no death in this series.

CONCLUSIONS

Pneumococcal disease may develop despite prior vaccination. The expanded coverage of newer polyvalent pneumococcal vaccines might have prevented some, but not all, of these admissions.

The newer fluoroquinolones

Clinicians have enthusiastically used fluoroquinolones owing to their good safety profile and wide range of indications. This article reviews fluoroquinolone pharmacology, pharmacodynamic principles, and fluoroquinolone resistance mechanisms, highlighting recent trends in the epidemiology of fluoroquinolone resistance among gram-negative organisms and Streptococcus pneumonia. Important fluoroquinolone safety concerns are discussed, along with indications for the most commonly used fluoroquinolones-ciprofloxacin, levofloxacin, and moxifloxacin.

Antimicrobial susceptibility and molecular epidemiology of Streptococcus pneumoniae isolated from Shanghai, China

In this study, the antimicrobial resistance profiles of pneumococci isolated from respiratory specimens of patients from Shanghai, China, in 2004 and 2005 are described. Non-susceptible rates to penicillin and erythromycin among paediatric isolates (n=122) were 63.1% and 94.3%, respectively, whilst those of adult isolates (n=39) were 20.5% and 69.2%, respectively (P<0.0001 and P<0.0002). Nineteen serotypes were identified among 103 tested strains, 73.8% of which belonged to 19F, 14, 23F, 6B and 19A. The erm(B) gene was detected in 51 erythromycin-resistant strains (52.6%), the mef(E) gene in 5 strains (5.2%) and both erm(B) and mef(E) in 41 strains (42.3%). Among 45 sequence types (STs) determined by multilocus sequence typing (MLST) in these 103 isolates, 25 STs were new assignments and 9 STs contained 10 new alleles. On the other hand, 46 (68.7%) of 67 penicillin-non-susceptible S. pneumoniae and 51 (52.6%) of 97 macrolide-resistant S. pneumoniae were characterised as belonging to four international resistant clonal complexes, Taiwan(19F)-14, Spain(23F)-1, Spain(6B)-2 and Taiwan(23F)-15. Our findings indicate that the spread of international resistant clones played a predominant role in the emergence and increase of resistance in Shanghai. Conjugate vaccination may be a promising method to prevent the increase in pneumococcal resistance.