Functional characterization and clinical implication of a novel epidemic carbapenem-resistant Acinetobacter baumannii genetic marker

OBJECTIVES

The study aimed to evaluate the distribution and function of contact-dependent growth inhibition (CDI) systems associated with carbapenem-resistant Acinetobacter baumannii (CRAB) isolates.

METHODS

We examined these isolates by multilocus sequence typing (MLST) and PCR for the presence of CDI genes in CRAB and carbapenem-susceptible A. baumannii (CSAB) from patients with invasive disease in a medical center in Taiwan. Inter-bacterial competition assays were performed to characterize the in vitro function of the CDI system.

RESULTS

A total of 89 (61.0%) CSAB and 57 (39.0%) CRAB isolates were collected and examined. ST787 (20/57; 35.1%) was the most predominant sequence type among CRAB, followed by ST455 (10/57; 17.5%). More than half of the CRAB (56.1%, 32/57) belonged to CC455 and more than one third (38.6%, 22/57) to CC92. A novel CDI system, cdiTYTH1, was found in 87.7% (50/57) of the CRAB but only in 1.1% (1/89) of the CSAB isolates (P<0.00001). The cdiTYTH1 was also identified in 94.4% (17/18) of the previously genome-sequenced CRAB isolates and only one CSAB isolate from Taiwan. Two other previously reported CDI (cdi19606-1 and cdi19606-2) were not found in these isolates, except each in one CSAB. All 6 CRAB without cdiTYTH1 showed growth inhibition by a CSAB carrying cdiTYTH1 in vitro. All clinical CRAB isolates belonging to the predominant CC455 carried the newly identified cdiTYTH1.

CONCLUSIONS

This CDI system was widespread in CRAB clinical isolates and appeared to be an epidemic genetic marker for CRAB in Taiwan. The cdiTYTH1 was functional in vitro in bacterial competition assay.

Association between histo-blood group antigens and Pseudomonas aeruginosa-associated diarrheal diseases

BACKGROUND

Pseudomonas aeruginosa is not a common enteric pathogen. The association between human histo-blood group antigens (HBGAs) and P. aeruginosa enteric infection has not yet been studied.

METHODS

We collected stool samples from healthy children under 2 years of age for P. aeruginosa gut colonization rate. Saliva samples were collected from patients with P. aeruginosa-associated diarrheal diseases and normal healthy children. Genomic DNA was extracted from saliva samples for ABO blood group typing and FUT2 genotyping. Lewis phenotype was detected using ELISA assay.

RESULTS

A total of 85 patients with P. aeruginosa-associated diarrheal diseases and 105 healthy children were enrolled for collecting saliva specimens. The stool colonization rate was 5/101 (5%) in healthy children, 4/58 (6.9%) in infants, and 1/43 (2.3%) in children 1-2 years old, respectively. Blood group A was more frequent in patients with P. aeruginosa-associated diarrheal diseases 24/77 (31.2%) than in healthy children 18/102 (17.6%) (P = 0.035). All patients and healthy children were secretor positive. The distribution of weak-secretor genotype Se³⁸⁵/Se³⁸⁵ was 23/84 (27.4%) in patients with P. aeruginosa-associated diarrheal diseases and 17/104 (16.3%) in healthy children, respectively (P = 0.06). Patients with P. aeruginosa-associated diarrheal diseases had a higher percentage of Le^a+b+ phenotype 25/81 (30.9%) than healthy children 17/105 (16.2%) (P = 0.018). There was no association between ABO or secretor or Lewis status with the clinical severity of P. aeruginosa-associated diarrheal diseases.

CONCLUSION

Infants had a higher gut P. aeruginosa colonization rate than children. Children with blood group A and Le^a+b+ phenotype are prone to P. aeruginosa-associated diarrheal diseases.

Marine prebiotics mediate decolonization of Pseudomonas aeruginosa from gut by inhibiting secreted virulence factor interactions with mucins and enriching Bacteroides population

BACKGROUND

Pseudomonas aeruginosa intestinal carriage rates are significantly higher in immunosuppressed individuals and hospitalized patients who therefore have increased risk of infections and antibiotic-associated diarrhea. To combat intestinal dysbiosis and decolonize P. aeruginosa from gastrointestinal tract, we investigated the anti-adherence and gut microbiota modulation properties of marine prebiotic fucoidans.

METHODS

Proteomic analysis of culture supernatant was performed by LC-MS/MS. Using lectin-based enzyme-linked immunosorbent assay, hemagglutinin domain interaction and inhibition with biomolecules were studied. We investigated the role of nutritional grade fucoidans in a mouse model and used 16S ribosomal RNA sequencing to examine fecal microbiota composition.

RESULTS

Analysis of culture supernatant proteins indicated the secretion of two-partner secretion (TPS) family proteins, including TpsA1/CdiA2 and TpsA2/CdiA1. Lectin like activity at the N-terminal of TpsA due to a conserved hemagglutinin domain (Pfam identifier [ID] PF05860) mediates binding to mucins that carry multiple fucosylated glycans. Fucose-rich sulfated polysaccharides (fucoidans) and sulfated dextrans were found to be potent inhibitors of the recombinant N-terminal hemagglutinin domain of TpsA (TpsA-NT-HAD) binding to mucins. In a mouse model, antibiotic-induced dysbiosis was essential for P. aeruginosa gastrointestinal colonization. After prophylactic oral fucoidans supplementation, a higher proportion (60%) of the mice were decolonized over time and resisted re-colonization, this was associated with remarkable expansion of Bacteroides (post-infection day-3 abundance, 29-50%) and consequential reductions in bloom of Enterobacteriaceae and Enterococcaceae populations. In the non-supplemented group, Parabacteroides mediated recovery from dysbiosis but failed to decolonize P. aeruginosa.

CONCLUSIONS

Supplementing diet with marine prebiotic fucoidans can mediate earlier recovery from dysbiosis and decolonization of P. aeruginosa from gut by inhibiting secreted virulence factor (TpsA/CdiA) interaction with mucins and promoting the growth of beneficial Bacteroides population. We suggest the prophylactic use of nutritional grade fucoidans to decolonize P. aeruginosa from gastrointestinal tract of at-risk individuals to prevent infection and transmission of colonizing P. aeruginosa.

Microbiological and clinical characteristics of Streptococcus pneumoniae serotype 3 infection and risk factors for severe outcome: A multicenter observational study

BACKGROUND/PURPOSE

Serotype 3 has persisted to be an important cause of invasive pneumococcal disease in adults in the post-vaccine era. We aimed to investigate clinical and microbiological characteristics of Streptococcus pneumoniae serotype 3 infection in Taiwan and identify the risk factors associated with severe clinical outcome.

METHODS

A multicenter observational study was conducted to analyze serotype 3 isolates collected between 2012 and 2021. Demographics, comorbidities, and risk categories were statistically compared with clinical outcome. Antimicrobial susceptibility testing and multilocus sequence typing were performed.

RESULTS

A total of 146 isolates were collected, including 12 isolates regarded as colonizers. Among 134 infected cases, 54 (40.3%) were aged 65 and older. Mortality was significantly associated with diabetes mellitus, immunosuppression, immunodeficiency, high-risk status, and older age. Susceptibility rates were high to levofloxacin (98.9%), moxifloxacin (100%), vancomycin (100%), and ceftriaxone (97.3%). 25.3% (37/146) of the isolates showed intermediate susceptibility and 0.7% (1/146) showed resistance to penicillin. ST180 was the dominant sequence type. ST13 and ST9625 isolates were less susceptible to penicillin and ceftriaxone.

CONCLUSIONS

Serotype 3 infection showed a high mortality rate, especially in patients with older ages and comorbidities. Although the incidence rates decreased during the COVID-19 pandemic, serotype 3 remained as an important cause of infection after the implementation of PCV13. Developing a more effective vaccine against serotype 3 and monitoring the antimicrobial-resistant sequence types are necessary.

Serotype transmission dynamics and reduced incidence of invasive pneumococcal disease caused by different serotypes after implementation of non-pharmaceutical interventions during COVID-19 pandemic

To block the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-COV-2), a number of non-pharmaceutical interventions (NPIs) are being implemented. Taiwan successfully controlled coronavirus disease 2019 (COVID-19) mainly through NPIs that were centred on facial masking, enhanced hand hygiene, social distancing, international travel controls, effective quarantine and contact-tracing policy [1, 2]. After the first case of COVID-19 was detected on 21 January, 2020, a rise in local demand for surgical masks and N95 respirators was observed and at least 50% of people spontaneously wore a facemask in public places from early February 2020 [3, 4]. Among the total of 799 COVID-19 cases reported in 2020, annual incidence rate of COVID-19 in Taiwan was remarkably low (0.238 per 100 000; n=56) for locally acquired (local) cases and high (3.153 per 100 000; n=743) for internationally acquired (imported) cases (Taiwan CDC, https://data.cdc.gov.tw/en/dataset). It is perceived that NPIs that are currently being implemented to reduce COVID-19 should also prevent both acquisition and transmission of other viral and bacterial respiratory tract infections [5–9]. In this observational study we examined the monthly incidence rates of invasive pneumococcal disease (IPD) and serotype distribution in age groups at high risk and from high pneumococcal transmission settings between January 2020 and February 2021. The differential serotype transmission dynamics revealed by various levels of reduction in IPD caused by different serotypes was discussed.

Significant reduction in the incidence rates of both vaccine and non-vaccine serotype invasive pneumococcal disease among children and adults during the COVID-19 pandemic were observed after the implementation of non-pharmaceutical interventionshttps://bit.ly/36CAute

d-mannose-sensitive pilus of Acinetobacter baumannii is linked to biofilm formation and adherence onto respiratory tract epithelial cells

BACKGROUND/PURPOSE

Acinetobacter baumannii is an important nosocomial pathogen. To better understand the role of CsuA/BABCDE pilus of A. baumannii in virulence, bacterial biofilm formation, adherence and carbohydrate-mediated inhibition were conducted.

METHODS

CsuA/BABCDE pilus-producing (abbreviated Csu pilus) operon of A. baumannii ATCC17978 was cloned for analysis of biofilm formation on an abiotic plastic plate, bacterial adherence to respiratory epithelial human A549 cells and carbohydrate-mediated inhibition. The carbohydrates used for inhibition of biofilm formation and adherence to A549 cells included monosaccharides, pyranosides, and mannose-polymers.

RESULTS

The Csu pilus of A. baumannii ATCC17978 was cloned and expressed into a non-pilus-producing Escherichia coli JM109, and was knocked out as well. The recombinant Csu (rCsu) pilus on E. coli JM109/rCsu pilus-producing clone observed by both electro-microscopy and atomic force microscopy showed abundant, while Csu-knockout A. baumannii ATCC17978 mutant appeared less or no pilus production. The E. coli JM109/rCsu pilus-producing clone significantly increased biofilm formation and adherence to A549 cells; however, the Csu-knockout mutant dramatically lost biofilm-making ability but, in contrast, increased adherence. Moreover, both of biofilm formation and adherence could be significantly inhibited by d-mannose and methyl-α-d-mannopyranoside in Csu pilus-producing E. coli JM109, whereas in A. baumannii ATCC17978, high concentration of carbohydrates was required for the inhibition, suggesting that Csu pilus is sensitive to d-mannose.

CONCLUSION

This is the first study confirming that Csu pilus of A. baumannii belongs to mannose-sensitive type 1 pilus family and contributes to biofilm formation and bacterial adherence to human epithelial cells.

Persistence of immunity in children immunised with 13-valent pneumococcal conjugate vaccine and impact on nasopharyngeal carriage: a cross-sectional study

In 500 children aged ≤10 years after 13-valent pneumococcal conjugate vaccine (PCV)13 immunisation in different schedules, serotypes 19A-specific and 19F-specific immunoglobulin G (IgG) were predicted to persist above 0.35 µg/mL for ≥10 years in all groups, likely due to PCV13-induced memory with natural boosting from residual diseases and colonisation. Generally, serotype-specific IgG could persist above 0.35 µg/mL longer (≥5 years) in the catch-up group than in the 2+1 and 3+1 immunisation groups. 14.5% of the carriage isolates belonged to PCV13 serotypes; statistical analysis revealed that a high serum IgG level (>10.96 µg/mL) will be required to eliminate the point-prevalence nasopharyngeal carriage of serotype 19A.

Hyperexpression of type III secretion system of Salmonella Typhi linked to a higher cytotoxic effect to monocyte-derived macrophages by activating inflammasome

Inflammasome activation is an important host response to infectious diseases, but the difference in inflammasome activation between typhoid fever and non-typhoidal Salmonella infection has been rarely studied. To determine whether inflammasome activation in macrophages after S. Typhi and S. Typhimurium infection is different, we measured pyroptosis, caspase-1 activation, and IL-1β secretion in monocyte-derived macrophages infected with S. Typhi or S. Typhimurium both in vitro and ex vivo. The role of Vi capsule and virulence genes in Salmonella pathogenicity island-1 (SPI-1), belonging to type III secretion system, was also examined. S. Typhi caused more pyroptosis, caspase-1 activation, and IL-1β production than S. Typhimurium did, predominantly within 2 h of infection, in the context of high number of infecting bacteria. Mutagenesis and complementation experiments confirmed that SPI-1 effectors but not Vi were associated with greater inflammasome activation. The expression levels of invA and hilA were significantly higher in S. Typhi than in S. Typhimurium at early log phase in SPI-1 environment. Thus, S. Typhi, relative to its non-typhoidal counterpart, S. Typhimurium, induces greater SPI-1-dependent inflammasome activation in monocyte-derived macrophages. This finding may explain why S. Typhi causes a hyperinflammatory state at bacteremic stage in typhoid fever.

Activation of apoptosis by Salmonella pathogenicity island-1 effectors through both intrinsic and extrinsic pathways in Salmonella-infected macrophages

BACKGROUND

Salmonella enterica serovar Typhimurium, a non-typhoidal food-borne pathogen, causes acute enterocolitis, bacteremia, extraintestinal focal infections in humans. Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) contribute to invading into host cellular cytosol, residing in Salmonella-containing vacuoles for intracellular survival, and inducing cellular apoptosis. This study aimed to better understand the mechanism underlying apoptosis in Salmonella-infected macrophages.

METHODS

S. Typhimurium SL1344 was used to evaluate extrinsic and intrinsic apoptosis pathways in THP-1 monocyte-derived macrophages in response to Salmonella infection.

RESULTS

Activated caspase-3-induced apoptosis pathways, including extrinsic (caspase-8-mediated) and intrinsic (caspase-9-mediated) pathways, in Salmonella-infected macrophages were verified. THP-1 cells with dysfunction of TLR-4 and TLR-5 and Salmonella SPI-1 and SPI-2 mutants were constructed to identify the roles of the genes associated with programmed cell death in the macrophages. Caspase-3 activation in THP-1 macrophages was induced by Salmonella through TLR-4 and TLR-5 signaling pathways. We also identified that SPI-1 structure protein PrgH and effectors SipB and SipD, but not SPI-2 structure protein SsaV, could induce apoptosis via caspase-3 activation and reduce the secretion of inflammation marker TNF-α in the Salmonella-infected cells. The two effectors also reduced the translocation of the p65 subunit of NF-κB into the nucleus and the expression of TNF-α, and then inflammation was diminished.

CONCLUSION

Non-typhoid Salmonella induced apoptosis of macrophages and thereby reduced inflammatory cytokine production through the expression of SPI-1. This mechanism in host-pathogen interaction may explain why Salmonella usually manifests as occult bacteremia with less systemic inflammatory response syndrome in the bloodstream infection of children.

Characterization of the role of global regulator FliA in the pathophysiology of Pseudomonas aeruginosa infection

FliA is known to be a sigma factor that regulates bacterial flagella gene expression. Accumulating evidence suggests that FliA is involved in bacterial behavior other than motility. To elucidate the contribution of FliA to Pseudomonas aeruginosa pathophysiology, we analyzed the biological properties and gene expression profiles of a ΔfliA mutant. Transcriptome analysis results demonstrated that the expression levels of flagella biogenesis genes decreased dramatically in the mutant; consequently, the ΔfliA mutant failed to synthesize flagella and exhibited reduced motility. The ΔfliA mutant displayed stronger hemolytic and caseinolytic activities, as well as pyocyanin production. The expression of type 6 secretion system-II genes and interbacterial competition activity was decreased in the ΔfliA mutant. Direct evidence of fliA participation in virulence was obtained from analysis of hypervirulent strain B136-33. Adhesion to and cytotoxicity toward mammalian cells and penetration through cell layers were noted; furthermore, the colonization ability of the fliA::Tn5 mutant in the intestines of laboratory mice was compromised. Notably, the fliA-overexpressing strain displayed phenotypes similar to that of the fliA-defective strain, indicating that optimal FliA levels are critical to bacterial physiology. Our findings indicate that FliA plays diverse roles in P. aeruginosa, not only in flagella biosynthesis, but also in pathophysiology.

Genetic analysis of virulence and antimicrobial-resistant plasmid pOU7519 in Salmonella enterica serovar Choleraesuis

BACKGROUND

Zoonotic Salmonella enterica serovar Choleraesuis (S. Choleraesuis), causing paratyphoid in pigs and bacteremia in humans, commonly carry a virulence plasmid and sometimes a separate antimicrobial-resistant plasmid or merging together. This study aimed to analyze the likely mechanism of how to form a virulence-resistance chimera of plasmid in S. Choleraesuis.

METHODS

Whole plasmid sequence of pOU7519 in S. Choleraesuis strain OU7519 was determined using shotgun cloning and sequencing. Sequence annotation and comparison were performed to determine the sequence responsible for the formation of a chimeric virulence-resistance pOU7519. Other chimeric plasmids among the collected strains of S. Choleraesuis were also confirmed.

RESULTS

The sequence of pOU719, 127,212 bp long, was identified to be a chimera of the virulence plasmid pSCV50 and a multidrug-resistant plasmid pSC138 that have been found in S. Choleraesuis strain SC-B67. The pOU7519 is a conjugative plasmid carrying various mobile DNAs, including prophages, insertion sequences, integrons and transposons, especially a Tn6088-like transposon. By dissecting the junction site of the pSCV50-pSC138 chimera in pOU7519, defective sequences at integrase gene scv50 (int) and its attachment site (att) were found, and that likely resulted in a stable chimera plasmid due to the failure of excision from the pSCV50-pSC138 chimera. Similar structure of chimera was also found in other large plasmids.

CONCLUSION

The deletion of both the int and att sties could likely block chimera excision, and result in an irreversible, stable pSCV50-pSC138 chimera. The emergence of conjugative virulence and antimicrobial-resistant plasmids in S. Choleraesuis could pose a threat to health public.

Invasive pneumococcal disease caused by ceftriaxone-resistant Streptococcus pneumoniae in Taiwan

BACKGROUND

Invasive pneumococcal disease (IPD) was associated with mortality, but the risk factors associated with mortality remains controversial.

METHODS

A retrospective cohort study was designed. All patients with IPD from 2011 to 2013 admitted in a medical center were screened and collected for their clinical presentations and laboratory characteristics.

RESULTS

Approximately half of the 134 IPD isolates derived from these patients belonged to three major serotypes (19A, 6A and 3), which are included in 13-valent pneumococcal conjugate vaccine (PCV13), but not in 7-valent pneumococcal conjugate vaccine (PCV7). Ceftriaxone resistance according to non-meningitis criteria was identified in 38% of the IPD isolates, and was the major independent risk factor associated with inappropriate initial therapy that subsequently contributed to mortality of the patients. Infection by serotype 6A, 15B, 19A, 19F, or 23F was the major independent risk factor associated with ceftriaxone resistance (non-meningitis criteria). 77.6% of these isolates belonged to additional PCV13 serotypes, with more than 40% expressing resistance to ceftriaxone. In terms of serotype coverage, PCV13 covered 94.1% of the IPD isolates with ceftriaxone resistance, in comparison to 21.6% only by PCV7.

CONCLUSIONS

The increase of ceftriaxone resistance in pneumococci in part driven by PCV7 vaccination in Taiwan is worrisome. The use of PCV13 in children as well as in the elderly population is likely to offer protection from the infection caused by ceftriaxone-resistant pneumococci. It is important to give an effective drug such as penicillin, fluoroquinolones or vancomycin in 2 days for improving outcome of IPD patients.

Epidemiology of culture-confirmed infections of Streptococcus pneumoniae (2012-2015) and nasopharyngeal carriage in children and households in Taiwan (2014-2015)

PURPOSE

An observational study was performed to investigate the carriage rate and serotypes of Streptococcus pneumoniae in the 13-valent pneumococcal conjugate vaccine (PCV13) era in Taiwan.

METHODOLOGY

From March 2014 to March 2015 a total of 500 healthy children and their households (631 adults) were enrolled from two large medical centres for nasopharyngeal carriage survey. Clinical isolates were prospectively collected from June 2012 to May 2015 at Chang Gung Memorial Hospital. We applied a multiplex polymerase chain reaction in addition to culture to detect S. pneumoniae.

RESULTS

S. pneumoniae was isolated from 12.0 % of the children and 3.6 % of the households. In the children's cohort only 23.3 % of the isolates could be assigned to PCV13 serotypes; non-vaccine serotypes were predominant (76.6 %) and the most frequently detected non-vaccine serotypes were 15A/F and 15B/C (both 13.3 %), followed by 23A (6.7 %). In the household cohort, 21.7 % belonged to PCV13 serotypes, and 78.3 % to non-vaccine serotypes. Clinical analysis of culture-confirmed pneumococcal infection showed that infection caused by PCV13 serotypes decreased by 47 % from 83 % in 2012-2013 to 44 % in 2014-2015, while infection caused by non-PCV13 serotypes increased from 17 to 56 %. Among the carriage isolates a significantly higher percentage belonged to serogroup 15 compared to serogroup 19 (26.6 vs 6.66 %, 2014-2015; P=0.003). Therefore, clinical isolates belonging to serogroup 15 were more prevalent than those belonging to serogroup 19 (44.1 vs 32.3 %, 2014-2015; P=0.318).

CONCLUSION

The isolation of non-vaccine serotypes and unknown serotypes after the introduction of PCV13 in children highlights the importance of continued surveillance for emerging serotypes.

Low Serum Fetuin-A as a Biomarker to Predict Pneumococcal Necrotizing Pneumonia and Hemolytic Uremic Syndrome in Children

Streptococcus pneumoniae, a neuraminidase-producing pathogen, can cause invasive pneumococcal disease (IPD) with or without hemolytic uremic syndrome (HUS) in humans. We aimed to identify serum sialoglycoproteins that are targeted by neuraminidases in severe pneumococcal infection. We hypothesized that serum sialoglycoprotein such as fetuin-A can serve as a biomarker to predict IPD or HUS. We constructed serum sialoglycoprotein profiles before and after pneumococcal neuraminidase treatment using liquid chromatography-tandem mass spectrometry (LC-MS/MS), a proteomic approach. An observational study was conducted using clinical data and serum samples from pediatric patients with pneumococcal infection to verify the predictive role of fetuin-A in IPD. Serum fetuin-A levels were determined by enzyme-linked immunosorbent assay. The most abundant serum sialoglycoproteins identified by LC-MS/MS after neuraminidase treatment and peanut lectin capture were immunoglobulins, apolipoproteins, fibrinogens, keratins, complement system proteins, and fetuin-A. Serum fetuin-A levels in the HUS patients were significantly lower (207 ± 80 mg/L, P < 0.001) than in patients with lobar pneumonia (610 ± 190 mg/L) as well as the healthy controls (630 ± 250 mg/L). In comparing HUS with necrotizing pneumonia and lobar pneumonia, the ROC area under the curve was 0.842; a cutoff value of 298 mg/L yielded sensitivity of 92.9% (95% CI: 68.5-98.7%) and specificity of 71.9% (95% CI: 54.6-84.4%). This observational study with validation cohorts of patients with HUS, complicated pneumonia, and lobar pneumonia demonstrates the high performance of low serum fetuin-A levels as a biomarker to predict severe IPD and HUS in children.

The prevalence of erythromycin resistance in group B streptococcal isolates at a University Hospital in Taiwan

Due to reduced antibiotic consumption in Taiwan, erythromycin resistance rate had decreased in Streptococcus pyogenes, but it increased in Streptococcus pneumoniae. The objectives of the present study were (1) to determine the erythromycin and clindamycin resistance rate and minimum inhibitory concentration (MIC) of the group B streptococcus (GBS) clinical isolates, and (2) to investigate the mechanism responsible for the macrolide, lincosamide, and group B streptogramin (MLS(B)) resistance. A total of 1,395 GBS isolates were collected from June 2001 to April 2007. Forty-four percent of the GBS isolates were resistant to erythromycin, and 39% were resistant to clindamycin. The annual erythromycin resistance rate increased from 32% in 2001 to 51% in 2004; a significant decrease was observed in 2005 (47%), 2006 (42%), and 2007 (38%). Percentage of erythromycin-resistant isolates with erm(B) gene significantly increased from 72% in 2001 to 90% in 2007. We found that the plasmid encoded zeta gene was present in 13% of the resistant isolates, along with erm(B). When compared to our previous study (1991 to May 2001), the overall erythromycin resistance rate increased from 30% to 44%. erm(B) was the major resistant determinant, and zeta toxin encoding plasmid has a limited role in mediating erythromycin resistance unlike in GAS isolates as reported earlier.

Insertion sequence 1515 in the ply gene of a type 1 clinical isolate of Streptococcus pneumoniae abolishes pneumolysin expression

A serotype 1 Streptococcus pneumoniae strain isolated by blood culture from a woman with pneumonia was found to harbor insertion sequence (IS) 1515 in the pneumolysin gene, abolishing pneumolysin expression. To our knowledge, this is the first report of an IS in the pneumolysin gene of S. pneumoniae.

Presence of plasmid pA15 correlates with prevalence of constitutive MLS(B) resistance in group A streptococcal isolates at a university hospital in southern Taiwan

OBJECTIVES

To investigate the role of a plasmid bearing the erm(B) gene on the prevalence of the macrolide, lincosamide and group B streptogramin (MLS(B)) phenotype of group A streptococci (GAS) and to characterize the plasmid and determine the clonal relation between the erythromycin-resistant isolates.

METHODS

Two hundred and five erythromycin-resistant GAS isolates were collected from 1990 to 2006. Colony hybridization, PCR, plasmid curing and PFGE techniques were used to analyse the mechanisms behind the phenotypes.

RESULTS

Among the 56 isolates with constitutive MLS(B) (cMLS(B)) resistance, 53 isolates harboured a plasmid, pA15, of 19 kb. erm(B) was on pA15 and it confered a cMLS(B) resistance phenotype. The prevalence rate of the pA15-containing isolates was 36.3% from 1993 to 1995, but the plasmid could not be detected from 2004 to 2006. To link the high-level resistance to pA15, clinical isolate A15 was selected and pA15 was cured by novobiocin. In the plasmid-cured strain SW503, the erythromycin MIC decreased from 256 to 0.032 mg/L. By electroporation, pA15 was re-introduced into the plasmid-cured erythromycin-susceptible strain, and the high-level erythromycin resistance was restored. Plasmid pA15 was also transferred to group B streptococci and group C streptococci by electroporation. In all the pA15-containing isolates, emm1 type was present and pulse type J was predominant (48 of 54 isolates).

CONCLUSIONS

The plasmid pA15 mediated cMLS(B) resistance in the mid-1990s, but pA15 was not detected in the clinical isolates from 2004 onwards, which correlates with the absence of cMLS(B) resistance in this region.

Inducible clindamycin resistance in Staphylococcus aureus isolates causing bacteremia at a university hospital in southern Taiwan

A major concern while prescribing clindamycin to treat infections caused by inducible macrolide, lincosamide, and group B streptogramin (iMLS(B))-resistant strains is clinical therapy failure. In this study, we determined the prevalence, mechanism, and clonality of the iMLS(B) phenotype in oxacillin-resistant Staphylococcus aureus (ORSA) and oxacillin-susceptible S. aureus (OSSA). Among the 729 OSSA isolates collected from July 1995 to March 2006, 72 (10%) were clindamycin sensitive (Cli(s)) and erythromycin resistant (Erm(r)), and 55 (8%) had the iMLS(B) phenotype. In the 709 ORSA isolates collected from January 1997 to March 2006, 31 (4%) were Cli(s) and Erm(r), and 29 (4%) isolates demonstrated the iMLS(B) phenotype. In OSSA, ermC was the predominant (51 of 55 isolates) genetic determinant responsible for the iMLS(B) phenotype, whereas in ORSA, ermA was predominant (27 of 29). Pulsed-field gel electrophoresis showed that 8 pulsed types (RA to RH) were present in ORSA isolates (n = 27), and pulsed type RC was predominant in 17 isolates with 5 identifiable subtypes (RC1 to RC5); this type was prevalent from November 1997 to June 2004. In the OSSA (n = 24) isolates, 14 different pulsed types (SA to SN) were identified, but none was predominant. These results indicate that the incidence of iMLS(B) resistance phenotype is higher in OSSA than ORSA in Taiwan, and the genetic determinants responsible for the iMLS(B) phenotype vary in OSSA and ORSA.