Susceptibilities of oral and nasal isolates of Streptococcus mitis and Streptococcus oralis to macrolides and PCR detection of resistance genes

ChoK-ing the Pathogenic Bacteria: Potential of Human Choline Kinase Inhibitors as Antimicrobial Agents

Novel antimicrobial agents are crucial to combat antibiotic resistance in pathogenic bacteria. Choline kinase (ChoK) in bacteria catalyzes the synthesis of phosphorylcholine, which is subsequently incorporated into the cell wall or outer membrane. In certain species of bacteria, phosphorylcholine is also used to synthesize membrane phosphatidylcholine. Numerous human ChoK inhibitors (ChoKIs) have been synthesized and tested for anticancer properties. Inhibition of S. pneumoniae ChoK by human ChoKIs showed a promising effect by distorting the cell wall and retarded the growth of this pathogen. Comparison of amino acid sequences at the catalytic sites of putative choline kinases from pathogenic bacteria and human enzymes revealed striking sequence conservation that supports the potential application of currently available ChoKIs for inhibiting bacterial enzymes. We also propose the combined use of ChoKIs and nanoparticles for targeted delivery to the pathogen while shielding the human host from any possible side effects of the inhibitors. More research should focus on the verification of putative bacterial ChoK activities and the characterization of ChoKIs with active enzymes. In conclusion, the presence of ChoK in a wide range of pathogenic bacteria and the distinct function of this enzyme has made it an attractive drug target. This review highlighted the possibility of "choking" bacterial ChoKs by using human ChoKIs.

Identification of the Bacterial Biosynthetic Gene Clusters of the Oral Microbiome Illuminates the Unexplored Social Language of Bacteria during Health and Disease

Small molecules are the primary communication media of the microbial world. Recent bioinformatic studies, exploring the biosynthetic gene clusters (BGCs) which produce many small molecules, have highlighted the incredible biochemical potential of the signaling molecules encoded by the human microbiome. Thus far, most research efforts have focused on understanding the social language of the gut microbiome, leaving crucial signaling molecules produced by oral bacteria and their connection to health versus disease in need of investigation. In this study, a total of 4,915 BGCs were identified across 461 genomes representing a broad taxonomic diversity of oral bacteria. Sequence similarity networking provided a putative product class for more than 100 unclassified novel BGCs. The newly identified BGCs were cross-referenced against 254 metagenomes and metatranscriptomes derived from individuals either with good oral health or with dental caries or periodontitis. This analysis revealed 2,473 BGCs, which were differentially represented across the oral microbiomes associated with health versus disease. Coabundance network analysis identified numerous inverse correlations between BGCs and specific oral taxa. These correlations were present in healthy individuals but greatly reduced in individuals with dental caries, which may suggest a defect in colonization resistance. Finally, corroborating mass spectrometry identified several compounds with homology to products of the predicted BGC classes. Together, these findings greatly expand the number of known biosynthetic pathways present in the oral microbiome and provide an atlas for experimental characterization of these abundant, yet poorly understood, molecules and socio-chemical relationships, which impact the development of caries and periodontitis, two of the world's most common chronic diseases.IMPORTANCE The healthy oral microbiome is symbiotic with the human host, importantly providing colonization resistance against potential pathogens. Dental caries and periodontitis are two of the world's most common and costly chronic infectious diseases and are caused by a localized dysbiosis of the oral microbiome. Bacterially produced small molecules, often encoded by BGCs, are the primary communication media of bacterial communities and play a crucial, yet largely unknown, role in the transition from health to dysbiosis. This study provides a comprehensive mapping of the BGC repertoire of the human oral microbiome and identifies major differences in health compared to disease. Furthermore, BGC representation and expression is linked to the abundance of particular oral bacterial taxa in health versus dental caries and periodontitis. Overall, this study provides a significant insight into the chemical communication network of the healthy oral microbiome and how it devolves in the case of two prominent diseases.

Oral antibiotic therapy for the treatment of infective endocarditis: a systematic review

Background

The role of oral antibiotic therapy in treating infective endocarditis (IE) is not well established.

Methods

We searched MEDLINE, EMBASE and Scopus for studies in which oral antibiotic therapy was used for the treatment of IE.

Results

Seven observational studies evaluating the use oral beta-lactams (five), oral ciprofloxacin in combination with rifampin (one), and linezolid (one) for the treatment of IE caused by susceptible bacteria reported cure rates between 77% and 100%. Two other observational studies using aureomycin or sulfonamide, however, had failure rates >75%. One clinical trial comparing oral amoxicillin versus intravenous ceftriaxone for streptococcal IE reported 100% cure in both arms but its reporting had serious methodological limitations. One small clinical trial (n = 85) comparing oral ciprofloxacin and rifampin versus conventional intravenous antibiotic therapy for uncomplicated right-sided S. aureus IE in intravenous drug users (IVDUs) reported cure rates of 89% and 90% in each arm, respectively (P =0.9); however, drug toxicities were more common in the latter group (62% versus 3%; P <0.01). Major limitations of this trial were lack of allocation concealment and blinding at the delivery of the study drug(s) and assessment of outcomes.

Conclusion

Reported cure rates for IE treated with oral antibiotic regimens vary widely. The use of oral ciprofloxacin in combination with rifampin for uncomplicated right-sided S. aureus IE in IVDUs is supported by one small clinical trial of relatively good quality and could be considered when conventional IV antibiotic therapy is not possible.

High Frequency of Isolation of Antibiotic-Resistant Oral Viridans Streptococci from Children in Kuwait

Antimicrobial resistance among the Viridans group of streptococci (VGS) has emerged as a hindrance to effective antibiotic therapy. Our objective was to evaluate the prevalence of antibiotic-resistant VGS in healthy children. Plaque samples were collected from tooth and tongue surfaces of 102 healthy subjects. Serially diluted samples were inoculated onto BHI agar plates and Mitis Salivarius Agar (MSA) plates and incubated as appropriate. Representative colonies were identified to species level by standard methods. Susceptibility of the VGS was performed by determining the minimum inhibitory concentrations (MICs) of 11 antibiotics using Etest. Of the 540 VGS isolates from both sites, 58% were from the tooth surfaces and 42% from the tongue. The most prevalent were S. salivarius (21.5%) and S. sanguis (16.3%). Imipenem and vancomycin had excellent activities. Resistance rates to trimethoprim, amoxicillin, piperacillin, erythromycin, cefuroxime and cephalothin, were 60.7, 40.8, 34.7, 32.6, 27.5 and 25.3%, respectively. Resistance rates to penicillin and clindamycin were 15.9% and 15.4%, respectively. The majority of the erythromycin-resistant isolates were from the tongue; 41% versus 29%. At the species level, 26% and 23% of S. salivarius and 23% and 14% of S. mutans from the tooth and tongue, respectively were resistant to penicillin. The data show species-related and site-related variations in the susceptibility pattern and an emerging high prevalence of antibiotic-resistant VGS. The difference in the susceptibilities between the species underscores the importance of accurate-identification and the need for surveillance of antimicrobial resistance among clinical isolates in our hospitals.

Molecular investigation of macrolide and Tetracycline resistances in oral bacteria isolated from Tunisian children

OBJECTIVE

This study aims to investigate the antibiotic susceptibility of strains isolated from the oral cavity of Tunisian children.

DESIGN

Strains were isolated from the oral cavity of Tunisian children (60 caries-actives and 30 caries-free). Molecular characterization was assessed by PCR assay to detect erythromycin methylase gene (ermB), macrolide efflux (mefI) and tetracycline resistance genes (tetM and tetO).

RESULTS

A total of 21 species were isolated and identified. Antimicrobial susceptibility revealed that the resistance rate to antibiotics was as follow: erythromycin (22%), tetracycline (15.6%), cefotaxim, (7.3%), trimethoprim-sulfamethoxazol (37.6%), nitrofurantoine (2.8%), pristinamycin (17.4%), quinupristin-dalfopristin (15.6%), and rifampicin (3.7%). The majority of mefI positive strains (31.2%) were isolated from the carious children (n=34) in comparison with 8.25% from the control group (n=9). In addition, frequency of strains caring resistance genes were as follow: 12.84% for ermB, 9.17% for tetM and 27.52% for tetO from the carious children in comparison to 0.092%, 3.67% and 3.67% from the caries free group respectively.

CONCLUSION

Multi-resistance strains towards macrolides and tetracycline were recorded. The majority of strains carrying antibiotics resistance genes were isolated from the caries active children. The presence of multi-resistant bacteria in the oral cavity can be the major cause of antibiotic prophylaxis failure in dental practise.

Prevalence of resistance phenotypes and genotypes to macrolide, lincosamide and streptogramin antibiotics in Gram-positive cocci isolated in Tunisian Bone Marrow Transplant Center

To investigate the prevalence of resistance to macrolide, lincosamide and streptogramin (MLS) antibiotics in Gram-positive cocci isolated in a Bone Marrow Transplant Center of Tunisia, we tested the antibiotic susceptibility of 172 clinical isolates of Staphylococcus epidermidis, Streptococcus mitis and Enterococcus faecium to macrolide erythromycin and spiramycin, the lincosamide clindamycin and the streptogramin pristinamycin. These three groups of organisms were mostly resistant to macrolides and lincosamide, but were commonly susceptible to pristinamycin. The resistance phenotypes of erythromycin-resistant isolates were determined by the five-disc test with erythromycin, spiramycin, lincomycin, clindamycin and pristinamycin, which showed that most exhibited constitutive MLS resistance. In order to determine the prevalence of the resistance genotypes and the resistance mechanisms, the prevalence of the erythromycin resistance methylase (erm) (A), erm(B), erm(C), msr(A) and macrolide efflux (mef) (A) genes in the erythromycin-resistant isolates was identified by polymerase chain reaction (PCR) analysis. The resistance was due mainly to the presence of ermB in E. faecium (80%), ermC in S. epidermidis (53%) and mefA in S. mitis (65%).

Antibiotic Resistance of Non-Pneumococcal Streptococci and Its Clinical Impact

Viridans streptococci (VGS) form a phylogenetically heterogeneous group of species belonging to the genus Streptococcus (1). However, they have some common phenotypic properties. They are alfa- or non-haemolytic. They can be differentiated from S. pneumoniae by resistance to optochin and the lack of bile solubility (2). They can be differentiated from the Enterococcus species by their inability to grow in a medium containing 6.5% sodium chloride (2). Earlier, so-called nutritionally variant streptococci were included in the VGS but based on the molecular data they have now been removed to a new genus Abiotrophia (3) and are not included in the discussion below. VGS belong to the normal microbiota of the oral cavities and upper respiratory tracts of humans and animals. They can also be isolated from the female genital tract and all regions of the gastrointestinal tract (2, 3). Several species are included in VGS and are listed elsewhere (2, 3). Clinically the most important species belonging to the VGS are S. mitis, S. sanguis and S. oralis.

Molecular bacterial diversity and bioburden of commercial airliner cabin air

Culture-independent, biomarker-targeted bacterial enumeration and identification strategies were employed to estimate total bacterial burden and diversity within the cabin air of commercial airliners. Samples from each of 4 flights on 2 commercial carriers were collected via air-impingement. The total viable microbial population ranged from below detection limits to 4.1 x 10(6) cells/m(3) of air, as assessed by the ATP assay. A gradual accumulation of microbes was observed from the time of passenger boarding through mid-flight, followed by a sharp decline in bacterial abundance and viability from the initiation of descent through landing. Representatives of the alpha-, beta-, and gamma-Proteobacteria, as well as Gram-positive bacteria, were isolated in varying abundance. Neisseria meningitidis rRNA gene sequences were retrieved in great abundance from Airline A followed by Streptococcus oralis/mitis sequences. Pseudomonas synxantha sequences dominated Airline B clone libraries, followed by those of N. meningitidis and S. oralis/mitis. The cabin air samples examined herein housed low bacterial diversity and were often dominated by a particular subset of bacteria: opportunistic pathogenic inhabitants of the human respiratory tract and oral cavity.

Activities of 16-membered ring macrolides and telithromycin against different genotypes of erythromycin-susceptible and erythromycin-resistant Streptococcus pyogenes and Streptococcus pneumoniae

OBJECTIVES

To test four 16-membered macrolides (josamycin, spiramycin, midecamycin and rokitamycin) along with other compounds in the same class (erythromycin, clarithromycin, roxithromycin and azithromycin) plus clindamycin and telithromycin, against Streptococcus pyogenes and Streptococcus pneumoniae isolates with well-characterized resistance genotypes.

METHODS

Four hundred and eighty-six isolates of S. pyogenes and 375 isolates of S. pneumoniae were assayed for their macrolide susceptibilities and investigated by PCR to detect their different erythromycin resistance genes. All strains had been isolated over the period 2002-2003 from specimens of different human origin obtained in 14 different Italian centres.

RESULTS

All 16-membered macrolides showed very low MICs (MIC(50)s and MIC(90)s, < or =0.06-0.5 mg/L) for the erythromycin-susceptible isolates and for those with the M phenotype, but the telithromycin MICs for the M-type isolates were at least four times higher (MIC(90)s, 0.5 mg/L). In S. pyogenes, the MIC(50)s of 16-membered macrolides for the cMLS(B) isolates were > or = 256 mg/L, whereas that for telithromycin was 4 mg/L; the MIC(50)s of 16-membered macrolides and telithromycin ranged from < or = 0.06 to 0.5 mg/L for the iMLS(B) isolates with erm(A) and from 0.12 to > or = 256 mg/L for those with erm(B). In S. pneumoniae, the MIC(50)s of the 16-membered macrolides for the cMLS(B) isolates ranged from 0.5 to 128 mg/L, whereas for the iMLS(B) isolates their values ranged from < or = 0.06 to 4 mg/L; the MIC(50)s and MIC(90)s of telithromycin for both the cMLS(B) and the iMLS(B) isolates ranged from < or = 0.06 to 0.12 mg/L.

CONCLUSIONS

MICs ranged for all the drugs, except telithromycin, from < or = 0.06 to > or = 256 mg/L, with 15% to 30% resistant S. pyogenes for all drugs tested except clindamycin (8%) and telithromycin (5.4%) and 10% to 40% resistant S. pneumoniae for all drugs tested except telithromycin (0.3%). In both S. pyogenes and S. pneumoniae, erythromycin resistance related to a mef gene meant that telithromycin MICs were definitely higher than in erythromycin-susceptible isolates, although telithromycin susceptibility was preserved in all cases. In S. pyogenes, the activity of both 16-membered macrolides and telithromycin against the iMLS(B) strains proved to be dependent on the erm gene involved, being greater against isolates with erm(A).

Antibiotic susceptibility patterns and resistance genes of starter cultures and probiotic bacteria used in food

A survey of starter and probiotic cultures was carried out to determine the current antibiotic resistance situation in microbial food additives in Switzerland. Two hundred isolates from 90 different sources were typed by molecular and other methods to belong to the genera Lactobacillus (74 samples), Staphylococcus (33 samples), Bifidobacterium (6 samples), Pediococcus (5 samples), or were categorized as lactococci or streptococci (82 samples). They were screened for phenotypic resistances to 20 antibiotics by the disk diffusion method. Twenty-seven isolates exhibiting resistances that are not an intrinsic feature of the respective genera were further analyzed by microarray hybridization as a tool to trace back phenotypic resistances to specific genetic determinants. Their presence was finally verified by PCR amplification or Southern hybridization. These studies resulted in the detection of the tetracycline resistance gene tet(K) in 5 Staphylococcus isolates used as meat starter cultures, the tetracycline resistance gene tet(W) in the probiotic cultures Bifidobacterium lactis DSM 10140 and Lactobacillus reuteri SD 2112 (residing on a plasmid), and the lincosamide resistance gene lnu(A) (formerly linA) in L. reuteri SD 2112.

Molecular basis of resistance to macrolides and other antibiotics in commensal viridans group streptococci and Gemella spp. and transfer of resistance genes to Streptococcus pneumoniae

We assessed the mechanisms of resistance to macrolide-lincosamide-streptogramin B (MLS(B)) antibiotics and related antibiotics in erythromycin-resistant viridans group streptococci (n = 164) and Gemella spp. (n = 28). The macrolide resistance phenotype was predominant (59.38%); all isolates with this phenotype carried the mef(A) or mef(E) gene, with mef(E) being predominant (95.36%). The erm(B) gene was always detected in strains with constitutive and inducible MLS(B) resistance and was combined with the mef(A/E) gene in 47.44% of isolates. None of the isolates carried the erm(A) subclass erm(TR), erm(A), or erm(C) genes. The mel gene was detected in all but four strains carrying the mef(A/E) gene. The tet(M) gene was found in 86.90% of tetracycline-resistant isolates and was strongly associated with the presence of the erm(B) gene. The cat(pC194) gene was detected in seven chloramphenicol-resistant Streptococcus mitis isolates, and the aph(3')-III gene was detected in four viridans group streptococcal isolates with high-level kanamycin resistance. The intTn gene was found in all isolates with the erm(B), tet(M), aph(3')-III, and cat(pC194) gene. The mef(E) and mel genes were successfully transferred from both groups of bacteria to Streptococcus pneumoniae R6 by transformation. Viridans group streptococci and Gemella spp. seem to be important reservoirs of resistance genes.

Genetic basis of erythromycin resistance in oral bacteria

We determined the prevalence of erythromycin-resistant bacteria in the oral cavity and identified mef and erm(B) as the most common resistance determinants. In addition, we demonstrate the genetic linkage, on various Tn1545-like conjugative transposons, between erythromycin and tetracycline resistance in a number of isolates.

Macrolide resistance phenotypes of commensal viridans group streptococci and Gemella spp. and PCR detection of resistance genes

One hundred and sixty viridans group streptococci (VGS) and 26 Gemella spp. resistant to erythromycin were studied to detect macrolide lincosamide and streptogramin B (MLS(B)) phenotypes and to investigate resistance rates to other antibiotics. The M phenotype was most prevalent in both bacterial groups (59.6% in VGS, 69.2% in gemellae) and the iMLS(B) phenotype was found least often (9.3 and 13.9%, respectively). All isolates with M phenotype had the mef(A/E) gene, being prevalent the mef(E) subclass. cMLS(B) and iMLS(B) strains contained the erm(B) gene, alone or in combination with the mef(A/E) gene. Thirteen isolates were intermediately resistant to quinupristin/dalfopristin and 11 strains showed low susceptibility to telithromycin. Linezolid was active against all the isolates tested and tetracycline resistance was the major one in VGS (41.6%) and Gemella spp. (46.2%).

Three cases of viridans group streptococcal bacteremia in children with febrile neutropenia and literature review

Three cases of viridans group streptococcal bacteremia in 2 children with brain tumours and in 1 with autoimmune neutropenia are presented. All children were neutropenic. The 2 patients with malignancy also had mucositis. The isolated strains of viridans group streptococci showed considerable resistance to antibiotics. All patients were empirically treated with third generation cephalosporins and amikacin, before antibiotic sensitivities were available and recovered without complications. Viridans group streptococcal bacteremia should be suspected in neutropenic children, especially in the presence of mucositis. Prospective, randomized clinical trials of mouth antiseptics are needed to clarify the usefulness, if any, of such measures in the reduction of viridans group streptococcal bacteremia in this group of patients.

Phenotypic and genetic characterization of resistance against macrolides and lincosamides in Streptococcus gallolyticus strains isolated from pigeons and humans

The macrolide and lincosamide (ML) resistance phenotype of 65 pigeon and 30 human Streptococcus gallolyticus strains was determined by the disk diffusion method. Constitutive resistance against the tested antibiotics was seen in 13 human and 28 pigeon strains. Simultaneous screening for the presence of erm(B) and mef(A) genes using PCR revealed that the erm(B) gene was present in 40 out of these 41 phenotypically resistant S. gallolyticus strains while the mef(A) gene was detected in only one resistant and one susceptible human-derived strain. The erm(B) genes of 10 human and 10 pigeon S. gallolyticus strains were sequenced and compared. Four human and seven pigeon strains possessed exactly the same sequence for the erm(B) gene. The sequence of the erm(B) gene of the remaining strains differed in one to five nucleotides. These findings could indicate a possible exchange of resistance genes between human and pigeon strains.

Prevalence and characterization of the mechanisms of macrolide, lincosamide and streptogramin resistance in viridans group streptococci

The presence of erm genes conferring constitutive and inducible resistance, as well as that of the mefA gene conferring only constitutive resistance, was investigated using PCR in 70 erythromycin resistant (MIC>or=1 mg/l) strains of viridans group streptococci (VGS) (18 Streptococcus mitis biotype 1, 16 S. mitis biotype 2, 15 S. oralis, 12 S. salivarius and nine S. sanguis) isolated from the oropharynx of healthy Greek children. All of the 56 isolates belonging to resistance phenotype M harbored the mefA gene. All of the 14 isolates constitutively resistant to macrolides and lincosamides (phenotype CR) harbored the ermB gene. Co-presence of both genes was not observed, whereas class A erm gene (previously known as ermTR) was not detected. Our results are consistent with a possible role of VGS as a reservoir of resistance genes now prevalent in pathogenic species of streptococci.

High prevalence of inducible erythromycin resistance among Streptococcus bovis isolates in Taiwan

Susceptibilities to 13 antimicrobial agents were determined by measurement of MICs for 60 isolates of Streptococcus bovis from blood cultures. Thirty-eight isolates (63.3%) had high-level resistance to erythromycin (MICs, >or=128 microg/ml). Among the 38 erythromycin-resistant strains, 21 isolates (55%) had inducible resistance to macrolides-lincosamides-streptogramin B (iMLS isolates) and 17 (45%) had constitutive resistance to macrolides-lincosamides-streptogramin B (cMLS isolates). Tetracycline resistance was also found among all of the erythromycin-resistant strains. None of the strains displayed resistance to penicillin, chloramphenicol, or vancomycin. Detection of erythromycin resistance genes by PCR and sequencing indicated that all 17 cMLS isolates were positive for the ermB gene and that 7 of 21 iMLS isolates carried the ermB gene and the remaining 14 iMLS isolates carried the ermT gene. Sequence analysis of amplified partial ermB fragments (594 bp) from S. bovis isolates revealed a 99.8% nucleotide identity and a 100% amino acid homology compared with the sequences from gene banks. The sequences of amplified fragments with primers targeted for ermC were shown to be very similar to that of ermGT (ermT) from Lactobacillus reuteri (98.5% nucleotide identity). This is the first report to describe the detection of the ermT class of erythromycin resistance determinants in S. bovis. The high rate of inducible erythromycin resistance among S. bovis isolates in Taiwan was not reported before. The iMLS S. bovis isolates were shown to be heterogeneous by randomly amplified polymorphic DNA analysis. These results indicate that the prevalence of inducible erythromycin resistance in S. bovis in Taiwan is very high and that most of the resistant strains carry the ermT or the ermB gene.