Distribution of tetracycline resistance genes tet(M), tet(O), tet(L) and tet(K) in blood isolates of viridans group streptococci harbouring erm(B) and mef(A) genes. Susceptibility to quinupristin/dalfopristin and linezolid

Pathogenesis, epidemiology and control of Group A Streptococcus infection

Streptococcus pyogenes (Group A Streptococcus; GAS) is exquisitely adapted to the human host, resulting in asymptomatic infection, pharyngitis, pyoderma, scarlet fever or invasive diseases, with potential for triggering post-infection immune sequelae. GAS deploys a range of virulence determinants to allow colonization, dissemination within the host and transmission, disrupting both innate and adaptive immune responses to infection. Fluctuating global GAS epidemiology is characterized by the emergence of new GAS clones, often associated with the acquisition of new virulence or antimicrobial determinants that are better adapted to the infection niche or averting host immunity. The recent identification of clinical GAS isolates with reduced penicillin sensitivity and increasing macrolide resistance threatens both frontline and penicillin-adjunctive antibiotic treatment. The World Health Organization (WHO) has developed a GAS research and technology road map and has outlined preferred vaccine characteristics, stimulating renewed interest in the development of safe and effective GAS vaccines.

Neonatal colonization of group B Streptococcus in China: Prevalence, antimicrobial resistance, serotypes, and molecular characterization

BACKGROUND

Group B Streptococcus (GBS) remains a leading cause of neonatal mortality and morbidity. This study aimed to determine the prevalence, antimicrobial susceptibility, serotypes, and molecular characterization of GBS colonized in neonates.

METHODS

A cross-sectional study was conducted using a multistage sampling method. Swabs for GBS identification were taken from infants' ear, oral cavity, and umbilicus immediately after birth. All GBS isolates were tested for antimicrobial susceptibility, resistance genes, serotyping, multilocus sequence typing, and virulence genes.

RESULTS

Of the 1,814 neonates, 1.3% tested positive for GBS, with 66.7% tested as multidrug resistant. All GBS isolates were susceptible to penicillin, but rates of resistance to tetracycline and erythromycin were high (70.8%), with the predominant resistance genes being tetM and ermB. The predominant serotype was III, followed by Ia and Ib, and the most common genotypes were sequence type (ST) 19, ST10, and ST485. Notably, we found that ST19 and ST17 isolates were associated with serotype III, resistant to tetracycline, erythromycin, and clindamycin, and carrying ermB, tetM, and rib; ST10 and ST12 isolates were associated with serotype Ib, resistant to erythromycin and clindamycin, and carrying ermB and alphaC; and ST485 isolates were associated with serotype Ia and carrying mefA/E, tetM, and epsilon.

CONCLUSIONS

These findings indicate a high prevalence of multidrug-resistant GBS and specific phenotype-genotype combinations for GBS clones.

Phenotypic and genotypic antimicrobial susceptibility pattern of Streptococcus spp. isolated from cases of clinical mastitis in dairy cattle in Poland

Mastitis of dairy cattle is one of the most frequently diagnosed diseases worldwide. The main etiological agents of mastitis are bacteria of the genus Streptococcus spp., in which several antibiotic resistance mechanisms have been identified. However, detailed studies addressing this problem have not been conducted in northeastern Poland. Therefore, the aim of our study was to analyze, on phenotypic and genotypic levels, the antibiotic resistance pattern of Streptococcus spp. isolated from clinical cases of mastitis from dairy cattle in this region of Poland. The research was conducted using 135 strains of Streptococcus (Streptococcus uberis, n = 53; Streptococcus dysgalactiae, n = 41; Streptococcus agalactiae, n = 27; other streptococci, n = 14). The investigation of the antimicrobial susceptibility to 8 active substances applied in therapy in the analyzed region, as well as a selected bacteriocin (nisin), was performed using the minimum inhibitory concentration method. The presence of selected resistance genes (n = 14) was determined via PCR. We also investigated the correlation between the presence of resistance genes and the antimicrobial susceptibility of the examined strains in vitro. The highest observed resistance of Streptococcus spp. was toward gentamicin, kanamycin, and tetracycline, whereas the highest susceptibility occurred toward penicillin, enrofloxacin, and marbofloxacin. Additionally, the tested bacteriocin showed high efficacy. The presence of 13 analyzed resistance genes was observed in the examined strains [gene mef(A) was not detected]. In most strains, at least one resistance gene, mainly responsible for resistance to tetracyclines [tet(M), tet(K), tet(L)], was observed. However, a relationship between the presence of a given resistance gene and antimicrobial susceptibility on the phenotypic level was not always observed.

Resistance Genes and Genetic Elements Associated with Antibiotic Resistance in Clinical and Commensal Isolates of Streptococcus salivarius

The diversity of clinical (n = 92) and oral and digestive commensal (n = 120) isolates of Streptococcus salivarius was analyzed by multilocus sequence typing (MLST). No clustering of clinical or commensal strains can be observed in the phylogenetic tree. Selected strains (92 clinical and 46 commensal strains) were then examined for their susceptibilities to tetracyclines, macrolides, lincosamides, aminoglycosides, and phenicol antibiotics. The presence of resistance genes tet(M), tet(O), erm(A), erm(B), mef(A/E), and catQ and associated genetic elements was investigated by PCR, as was the genetic linkage of resistance genes. High rates of erythromycin and tetracycline resistance were observed among the strains. Clinical strains displayed either the erm(B) (macrolide-lincosamide-streptogramin B [MLSB] phenotype) or mef(A/E) (M phenotype) resistance determinant, whereas almost all the commensal strains harbored the mef(A/E) resistance gene, carried by a macrolide efflux genetic assembly (MEGA) element. A genetic linkage between a macrolide resistance gene and genes of Tn916 was detected in 23 clinical strains and 5 commensal strains, with a predominance of Tn3872 elements (n = 13), followed by Tn6002 (n = 11) and Tn2009 (n = 4) elements. Four strains harboring a mef(A/E) gene were also resistant to chloramphenicol and carried a catQ gene. Sequencing of the genome of one of these strains revealed that these genes colocalized on an IQ-like element, as already described for other viridans group streptococci. ICESt3-related elements were also detected in half of the isolates. This work highlights the potential role of S. salivarius in the spread of antibiotic resistance genes both in the oral sphere and in the gut.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Genetic determinants and elements associated with antibiotic resistance in viridans group streptococci

OBJECTIVES

To investigate the distribution of erythromycin, tetracycline and chloramphenicol resistance mechanisms and determinants and the relevant genetic environments and elements in viridans group streptococci (VGS).

METHODS

A total of 263 VGS collected from routine throat swabs in 2010-12 and identified to the species level were studied. Antibiotic resistance determinants and the relevant genetic contexts and elements were determined using amplification and sequencing assays and restriction analysis.

RESULTS

The investigation provided original information on the distribution of resistance mechanisms, determinants and genetic elements in VGS. Erythromycin-resistant isolates totalled 148 (56.3%; 37 belonging to the cMLS phenotype and 111 belonging to the M phenotype); there were 72 (27.4%) and 7 (2.7%) tetracycline- and chloramphenicol-resistant isolates, respectively. A number of variants of known genetic contexts and elements carrying determinants of resistance to these antibiotics were detected, including the mega element, Φ10394.4, Tn2009, Tn2010, the IQ element, Tn917, Tn3872, Tn6002, Tn916, Tn5801, a tet(O) fragment from ICE2096-RD.2 and ICESp23FST81.

CONCLUSIONS

These findings shed new light on the distribution of antibiotic resistance mechanisms and determinants and their genetic environments in VGS, for which very few such data are currently available. The high frequency and broad variety of such elements supports the notion that VGS may be important reservoirs of resistance genes for the more pathogenic streptococci. The high rates of macrolide resistance confirm the persistence of a marked prevalence of resistant VGS in Europe, where macrolide resistance is, conversely, declining among the major streptococcal pathogens.

Multilocus sequence analysis of Streptococcus canis confirms the zoonotic origin of human infections and reveals genetic exchange with Streptococcus dysgalactiae subsp. equisimilis

Streptococcus canis is an animal pathogen that occasionally causes human infections. Isolates recovered from infections of animals (n = 78, recovered from 2000 to 2010 in three European countries, mainly from house pets) and humans (n = 7, recovered from 2006 to 2010 in Portugal) were identified by phenotypic and genotypic methods and characterized by antimicrobial susceptibility testing, multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE), and emm typing. S. canis isolates presented considerable variability in biochemical profiles and 16S rRNA. Resistance to antimicrobial agents was low, with the most significant being tet(M)- and tet(O)-mediated tetracycline resistance. MLST analysis revealed a polyclonal structure of the S. canis population causing infections, where the same genetic lineages were found infecting house pets and humans and were disseminated in distinct geographic locations. Phylogenetic analysis indicated that S. canis was a divergent taxon of the sister species Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis and found evidence of acquisition of genetic material by S. canis from S. dysgalactiae subsp. equisimilis. PFGE confirmed the MLST findings, further strengthening the similarity between animal and human isolates. The presence of emm-like genes was restricted to a few isolates and correlated with some MLST-based genetic lineages, but none of the human isolates could be emm typed. Our data show that S. canis isolates recovered from house pets and humans constitute a single population and demonstrate that isolates belonging to the main genetic lineages identified have the ability to infect the human host, providing strong evidence for the zoonotic nature of S. canis infection.

The antimicrobial resistance patterns and associated determinants in Streptococcus suis isolated from humans in southern Vietnam, 1997-2008

Background

Streptococcus suis is an emerging zoonotic pathogen and is the leading cause of bacterial meningitis in adults in Vietnam. Systematic data on the antimicrobial susceptibility profiles of S. suis strains isolated from human cases are lacking. We studied antimicrobial resistance and associated resistance determinants in S. suis isolated from patients with meningitis in southern Vietnam.

Methods

S. suis strains isolated between 1997 and 2008 were investigated for their susceptibility to six antimicrobial agents. Strains were screened for the presence and expression of tetracycline and erythromycin resistance determinants and the association of tet(M) genes with Tn916- like transposons. The localization of tetracycline resistance gene tet(L) was determined by pulse field gel electrophoresis and Southern blotting.

Results

We observed a significant increase in resistance to tetracycline and chloramphenicol, which was concurrent with an increase in multi-drug resistance. In tetracycline resistance strains, we identified tet(M), tet(O), tet(W) and tet(L) and confirmed their expression. All tet(M) genes were associated with a Tn916-like transposon. The co-expression of tet(L) and other tetracycline resistance gene(s) encoding for ribosomal protection protein(s) was only detected in strains with a minimum inhibitory concentration (MIC) of tetracycline of ≥ 64 mg/L

Conclusions

We demonstrated that multi-drug resistance in S. suis causing disease in humans in southern Vietnam has increased over the 11-year period studied. We report the presence and expression of tet(L) in S. suis strains and our data suggest that co-expression of multiple genes encoding distinct mechanism is required for an MIC ≥ 64 mg/L to tetracycline.

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.

A new tetracycline efflux gene, tet(40), is located in tandem with tet(O/32/O) in a human gut firmicute bacterium and in metagenomic library clones

The bacterium Clostridium saccharolyticum K10, isolated from a fecal sample obtained from a healthy donor who had received long-term tetracycline therapy, was found to carry three tetracycline resistance genes: tet(W) and the mosaic tet(O/32/O), both conferring ribosome protection-type resistance, and a novel, closely linked efflux-type resistance gene designated tet(40). tet(40) encodes a predicted membrane-associated protein with 42% amino acid identity to tetA(P). Tetracycline did not accumulate in Escherichia coli cells expressing the Tet(40) efflux protein, and resistance to tetracycline was reduced when cells were incubated with an efflux pump inhibitor. E. coli cells carrying tet(40) had a 50% inhibitory concentration of tetracycline of 60 microg/ml. Analysis of a transconjugant from a mating between donor strain C. saccharolyticum K10 and the recipient human gut commensal bacterium Roseburia inulinivorans suggested that tet(O/32/O) and tet(40) were cotransferred on a mobile element. Sequence analysis of a 37-kb insert identified on the basis of tetracycline resistance from a metagenomic fosmid library again revealed a tandem arrangement of tet(O/32/O) and tet(40), flanked by regions with homology to parts of the VanG operon previously identified in Enterococcus faecalis. At least 10 of the metagenomic inserts that carried tet(O/32/O) also carried tet(40), suggesting that tet(40), although previously undetected, may be an abundant efflux gene.

In vitro susceptibility of viridans group streptococci isolated from blood in southwest Finland in 1993-2004

We studied in vitro activity against invasive viridans group streptococci (VGS) of penicillin and 4 newer antibiotics, i.e. telithromycin, linezolid, levofloxacin and quinupristin-dalfopristin. Also 7 other antibiotics were tested. Antibiotic susceptibility of 263 VGS blood isolates, collected from southwest Finland during a 12-y period was determined. We wished to discover whether there is an increasing trend of antimicrobial resistance among VGS in Finland. Our results showed that penicillin is still a good choice for treating VGS infections based on the considerably low resistance percentage, 2.3%. Also newer antibiotics showed good in vitro activity: susceptibilities for telithromycin, linezolid and levofloxacin were 100%, 98.9% and 94.6%, respectively. However, quinupristin-dalfopristin was not as effective as described in previous studies, with only 57% susceptibility.

Multiplex PCR for simultaneous detection of macrolide and tetracycline resistance determinants in streptococci

Resistance to macrolides and tetracyclines is increasing among streptococci and co-occurs as their resistance determinants are carried on the same mobile element. We developed a multiplex PCR to facilitate simultaneous and specific detection of resistance determinants for both macrolides [erm(A), erm(B), and mef(A/E)] and tetracyclines [tet(M), tet(O), tet(K), and tet(L)] in streptococci.

Comparison and Transferability of theerm(B) Genes between Human and Farm Animal Streptococci

To obtain better insights into the possible exchange of resistance genes between human and animal streptococci, the sequences of the erm (B) genes of streptococcal isolates from humans, pigs, pork carcasses, chickens, and calves were compared. Identical erm (B) gene sequences were present in strains from humans, pigs, pork carcasses, and calves. During in vitro mating experiments, the erm (B) gene was exchanged between porcine Streptococcus suis and human S. pneumoniae, S. pyogenes, and S. oralis strains. The presence of different tetracycline resistance genes and the int Tn 1545 gene was determined in animal streptococci carrying the erm (B) gene. Although tet(M) and int Tn 1545 genes were detected in 24% of the porcine and pork carcass streptococcal strains, the tet(O) gene was the predominant tetracycline resistance gene in these strains (81%). The latter gene was co-transferred with the erm (B) gene from porcine S. suis strains to human streptococci in the mating experiments. These results show that, identical erm (B) gene sequences were present in animal and human streptococci and that transfer of the erm (B) gene from porcine S. suis to human streptococci and vice versa is possible, but probably occurs at a low frequency.

Efflux-mediated antimicrobial resistance

Antibiotic resistance continues to plague antimicrobial chemotherapy of infectious disease. And while true biocide resistance is as yet unrealized, in vitro and in vivo episodes of reduced biocide susceptibility are common and the history of antibiotic resistance should not be ignored in the development and use of biocidal agents. Efflux mechanisms of resistance, both drug specific and multidrug, are important determinants of intrinsic and/or acquired resistance to these antimicrobials, with some accommodating both antibiotics and biocides. This latter raises the spectre (as yet generally unrealized) of biocide selection of multiple antibiotic-resistant organisms. Multidrug efflux mechanisms are broadly conserved in bacteria, are almost invariably chromosome-encoded and their expression in many instances results from mutations in regulatory genes. In contrast, drug-specific efflux mechanisms are generally encoded by plasmids and/or other mobile genetic elements (transposons, integrons) that carry additional resistance genes, and so their ready acquisition is compounded by their association with multidrug resistance. While there is some support for the latter efflux systems arising from efflux determinants of self-protection in antibiotic-producing Streptomyces spp. and, thus, intended as drug exporters, increasingly, chromosomal multidrug efflux determinants, at least in Gram-negative bacteria, appear not to be intended as drug exporters but as exporters with, perhaps, a variety of other roles in bacterial cells. Still, given the clinical significance of multidrug (and drug-specific) exporters, efflux must be considered in formulating strategies/approaches to treating drug-resistant infections, both in the development of new agents, for example, less impacted by efflux and in targeting efflux directly with efflux inhibitors.

In vitro activity of telithromycin against viridans group streptococci and Streptococcus bovis isolated from blood: antimicrobial susceptibility patterns in different groups of species

The in vitro activities of penicillin, erythromycin, clindamycin, and telithromycin were determined against 155 viridans group streptococci (VGS) and 18 Streptococcus bovis blood isolates. Heterogeneity in the susceptibility patterns and macrolide resistance phenotypes and genotypes in the different groups of VGS was detected. We found seven telithromycin-resistant S. bovis isolates all harboring the erm(B) gene.

Distribution of theerm(B) Gene,tetracycline Resistance Genes, and Tn1545-like Transposons in Macrolide- and Lincosamide-Resistant Enterococci from Pigs and Humans

The distribution of the erm (B) and the tetracycline resistance genes tet(K), tet(L), tet(M), tet(O), and tet(S) was investigated among macrolide- and lincosamide-resistant enterococci originating from humans, pigs, and pork carcasses. The presence of transposons of the Tn916/Tn1545 family was also traced in these isolates. Furthermore, the porcine strains were tested for the presence of glycopeptide resistance genes vanA and vanB. The erm(B) gene was found in 85% of the porcine and in all human isolates. Ninety-eight percent of the porcine and 89% of the human erm(B)-positive enterococci carried the tet(M) gene. Seventy-seven percent and 70%, respectively, of these strains harbored a Tn1545-like element. Tet(L) was observed in 68% of the porcine and in 65% of the human enterococci. The other tetracycline resistance genes were very rare and the glycopeptide resistance genes vanA and vanB were not detected among the porcine isolates. The similar frequencies of resistance genes and the highly mobile Tn1545-like transposon among porcine and human enterococci might indicate exchange of resistant strains or their resistance genes between humans and pigs or the existence of a common reservoir.

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.