In Vitro Antimicrobial Activity of Five Newly Approved Antibiotics against Carbapenemase-Producing Enterobacteria-A Pilot Study in Bulgaria

To solve the problem with pan-drug resistant and extensively drug-resistant Gram-negative microbes, newly approved drugs such as ceftazidime/avibactam, cefiderocol, plazomicin, meropenem/vaborbactam, and eravacycline have been introduced in practice. The aim of the present study was to collect carbapenemase-producing clinical Enterobacterales isolates, to characterize their carbapenemase genes and clonal relatedness, and to detect their susceptibility to commonly used antimicrobials and the above-mentioned newly approved antibiotics. Sixty-four carbapenemase producers were collected in a period of one year from four Bulgarian hospitals, mainly including Klebsiella pneumoniae (89% of the isolates) and also single Proteus mirabilis, Providencia stuartii and Citrobacter freundii isolates. The main genotype was blaNDM-1 (in 61%), followed by blaKPC-2 (23%), blaVIM-1 (7.8%) and blaOXA-48 (7.8%). Many isolates showed the presence of ESBL (blaCTX-M-15/-3 in 76.6%) and AmpC (blaCMY-4 in 37.5% or blaCMY-99 in 7.8% of isolates). The most common MLST type was K. pneumoniae ST11 (57.8%), followed by ST340 (12.5%), ST258 (6.3%) and ST101 (6.3%). The isolates were highly resistant to standard-group antibiotics, except they were susceptible to tigecycline (83.1%), colistin (79.7%), fosfomycin (32.8%), and aminoglycosides (20.3-35.9%). Among the newly approved compounds, plazomicin (90.6%) and eravacycline (76.3%) showed the best activity. Susceptibility to ceftazidime/avibactam and meropenem/vaborbactam was 34.4% and 27.6%, respectively. For cefiderocol, a large discrepancy was observed between the percentages of susceptible isolates according to EUCAST susceptibility breakpoints (37.5%) and those of CLSI (71.8%), detected by the disk diffusion method. This study is the first report to show patterns of susceptibility to five newly approved antibiotics among molecularly characterized isolates in Bulgaria. The data may contribute to both the improvement of treatment of individual patients and the choice of infection control strategy and antibiotic policy.

Mixed (multiple-genotype) Helicobacter pylori infections in Bulgarian patients

The aim of the study was to evaluate the frequency and characteristics of mixed (multiple-genotype) Helicobacter pylori infections (MGIs) in 155 Bulgarian symptomatic patients (21 children and 134 adults). MGIs were common (36.1%), including double-strain (34.8%) and triple-strain infections (1.3%). None of the 8 ulcer patients harbored multiple subtypes. We detected 18 multiple allelic combinations, of which the most frequent subtypes (17.4%) were vacA s1as2 and vacA s1cs2. The 2 patients with triple-strain infections had vacA s1bs1cs2i1i2/iceA1A2 and vacA s1as1cs2 subtypes. They were both adult men with chronic gastritis and both were examined in 2022. The prevalence of MGIs (51.7%) was 2-fold higher in 2020 to 2022 than in 2015 to 2019 (26.3%). Putative factors for the increase may be the patient's characteristics and COVID-19 pandemic-associated factors. MGI rates corresponded to the high infection seroprevalence (72.4% in 2011) in Bulgaria. The evolution and clinical importance of mixed H. pylori infections merit extensive evaluation.

Clostridioides difficile resistance to antibiotics, including post-COVID-19 data

INTRODUCTION

Updating data on Clostridioides difficile antibiotic resistance is important for treatment improvement of C. difficile infections (CDIs).

AREAS COVERED

Results from 20 countries were included. The mean resistance to 2 mg/l vancomycin, 2 mg/l metronidazole, 4 mg/l moxifloxacin, and 4 mg/l clindamycin was 4.7% (0 to ≥ 26% in two studies), 2.6% (0 to ≥ 40% in 3 studies), 34.9% (6.6->80%), and 61.0% (30->90%), respectively. Resistance to erythromycin (>60-88%), rifampin (>23-55.0%), imipenem (0.6 to > 78% in a clone), tigecycline (0-<5.0%), and fidaxomicin (0-2%) was also found. Resistance to ≥ 5 antibiotics of different classes was reported in some countries. High resistance and multidrug resistance were observed in hypervirulent and epidemic strains. Although only 1% of COVID-19 patients had CDIs, the proportion might be underestimated.

EXPERT OPINION

C. difficile antimicrobial susceptibility varied by country/region, study period, and circulating ribotypes. For CDI treatment, fidaxomicin (preferably) or vancomycin is recommended, while metronidazole is suitable for mild infections. New approaches, including biotherapeutics (Rebyota), strains, antibiotics (ridinilazole and ibezapolstat), and monoclonal antibodies/cocktails merit further evaluation. Because of the resistance rate variations, C. difficile antibiotic susceptibility should be regularly monitored. Post-COVID-19 resistance should be separately presented. Some discrepancies between vancomycin and metronidazole results need to be clarified.

Anaerobes in specific infectious and noninfectious diseases: new developments

With the buildup of new research data, newer associations between anaerobic bacteria and diseases/conditions were evaluated. The aim of the mini-review was to draw attention and to encourage further multidisciplinary studies of the associations. We considered microbiome-disease correlations such as a decrease of fecal Faecalibacterium prausnitzii abundance in inflammatory bowel disease (IBD) and IBD recurrence, suggesting that F. prausnitzii could be a good biomarker for IBD. A link of subgingival Porphyromonas gingivalis with cardiovascular diseases was reported. Decreased Roseburia abundance was observed in the gut of Alzheimer's and Parkinson's disease patients. Akkermansia muciniphila was found to improve adipose/glucose metabolism, however, its intestinal abundance was observed in neurodegenerative diseases as well. Severe Clostridioides difficile infections have been reported in neonates and young children. Carcinogenic potential of anaerobes has been suggested. Fusobacterium nucleatum was implicated in the development of oral and colorectal cancer, Porphyromonas gingivalis and Tannerella forsythia were linked to esophageal cancer and Cutibacterium acnes subsp. defendens was associated with prostate cancer. However, there are some controversies about the results. In a Swedish longitudinal study, neither P. gingivalis nor T. forsythia exhibited oncogenic potential. The present data can enrich knowledge of anaerobic bacteria and their multifaceted significance for health and disease and can draw future research directions. However, more studies on large numbers of patients over prolonged periods are needed, taking into account the possible changes in the microbiota over time.

Clostridioides difficile, a New “Superbug”

Clostridioides difficile is a Gram-positive, spore-forming, anaerobic bacterium. The clinical features of C. difficile infections (CDIs) can vary, ranging from the asymptomatic carriage and mild self-limiting diarrhoea to severe and sometimes fatal pseudomembranous colitis. C. difficile infections (CDIs) are associated with disruption of the gut microbiota caused by antimicrobial agents. The infections are predominantly hospital-acquired, but in the last decades, the CDI patterns have changed. Their prevalence increased, and the proportion of community-acquired CDIs has also increased. This can be associated with the appearance of hypervirulent epidemic isolates of ribotype 027. The COVID-19 pandemic and the associated antibiotic overuse could additionally change the patterns of infections. Treatment of CDIs is a challenge, with only three appropriate antibiotics for use. The wide distribution of C. difficile spores in hospital environments, chronic persistence in some individuals, especially children, and the recent detection of C. difficile in domestic pets can furthermore worsen the situation. “Superbugs” are microorganisms that are both highly virulent and resistant to antibiotics. The aim of this review article is to characterise C. difficile as a new member of the “superbug” family. Due to its worldwide spread, the lack of many treatment options and the high rates of both recurrence and mortality, C. difficile has emerged as a major concern for the healthcare system.

Geographic distribution of antibiotic resistance of Helicobacter pylori: A study in Bulgaria

Prevalence of antibiotic resistant Helicobacter pylori was compared between 50 patients living outside the capital city and 50 matched pairs of capital city residents (CCRs). H. pylori isolates from 2018 to 2022 were included. Resistance rates in CCRs and those living elsewhere were 4.0 and 6.0% to amoxicillin, 48.0 and 42.0% to metronidazole, 30 and 30% to clarithromycin, and 4.0 and 4.0% to tetracycline, respectively. Levofloxacin resistance was higher (38.0%) in the capital city vs 20.0% (P = 0.047) in the country. Odd ratio for levofloxacin resistance between pair-matched groups was 2.45 (95% CI, OR 1.0-6.02, P value = 0.05) and relative risk for fluoroquinolone resistance was 1.90 (95% CI for RR 0.98-3.67) for CCRs vs residents in other regions. Resistance rates to levofloxacin and clarithromycin were worryingly high in our study, most probably due to the high quinolone consumption (2.86 DDD/day in 2017) in Bulgaria and the increase in macrolide, lincosamide and streptogramin consumption, especially of azithromycin, by >42% with the start of COVID-19 pandemic. Briefly, antibiotic resistance of H. pylori has a dynamic change, and it can display different patterns in certain geographic regions. The results imply that antibiotic consumption should be carefully controlled and unjustified use of levofloxacin should be restricted, especially in some large cities. Antibiotic policy should be further strengthened and regular monitoring of resistance in various geographic regions is needed for treatment optimization.

Evolution of Helicobacter pylori Resistance to Antibiotics: A Topic of Increasing Concern

Antibiotic resistance among Helicobacter pylori strains is the major cause of eradication failure. Resistance prevalence is dynamic and can greatly vary among countries over the years. We revealed H. pylori resistance trends for five antibiotics in 14 countries through articles predominantly published in 2018-2022, since the latest data can best show the most recent trends in resistance evolution. Amoxicillin resistance generally exhibited no evolution, yet it increased in Bulgaria, Iran, China, and Vietnam. Metronidazole resistance exhibited different trends, including an increase, a decrease and no evolution in six, three, and five studies, respectively. Clarithromycin resistance increased in Australia, Belgium, Bulgaria, Italy, Iran, and Taiwan, but remained stable in France, Spain, Russia, China, Chile, and Colombia. Tetracycline resistance was low and stable except in Iran. Levofloxacin resistance increased in four European and six other countries/regions, without significant increases in France, Spain, and Chile. In Chile, triple resistance also increased. In countries such as France and Spain, resistance to most antibiotics was stabilized, while in Bulgaria, Belgium, Iran and Taiwan, resistance to three or more agents was reported. Use of non-recommended regimens, national antibiotic consumption, patient's compliance, host factors, strain virulence, migrations, and azithromycin overuse during the COVID-19 pandemic can influence resistance evolution. New drugs, eradication regimens and diagnostic methods, such as next-generation sequencing can improve H. pylori infection control.

Detection of different colistin resistance mechanisms among multidrug resistant Klebsiella pneumoniae isolates in Bulgaria

The more frequent usage of colistin resulted in an increase of colistin resistance due to lipopolysaccharide modifications. The aim of this study was to reveal the prevalence and mechanisms of colistin resistance among multidrug-resistant Klebsiella pneumoniae isolates collected in Bulgaria. One hundred multidrug resistant K. pneumoniae isolates were collected in a period between 2017 and 2018. Among them, 29 colistin resistant and 8 heteroresistant isolates were observed and further investigated. Clonal relatedness was detected by RAPD and MLST. Сarbapenemases, two component system phoQ/phoP, pmrA/B, and mgrB were investigated by PCR amplification and Sanger sequencing. Among 37 colistin nonsusceptible isolates, we detected 25 NDM-1 producers. The isolates belonged mainly to ST11 (80%), and also to ST147, ST35, ST340, ST219 (1-2 members per clone). Nine colistin resistant isolates showed changes in mgrB. IS903B-like elements truncated mgrB in five isolates. In two isolates, premature stopcodon (Q30stopcodon) was observed and another two isolates did not amplify mgrB, possibly due to bigger deletion or insertion. No isolates showed phoQ/phoP and pmrA/B mutations except for pmrB (four isolates had R256G). All isolates with IS903B insertions belonged to ST11 clone. The mgrB alterations play major role in colistin resistance in K. pneumoniae isolates studied in the current work. We report truncation of mgrB by IS903 like element in colistin resistant NDM-1 producing K. pneumoniae ST11 clone in Bulgaria.

Molecular epidemiology, virulence and antimicrobial resistance of Bulgarian methicillin resistant Staphylococcus aureus isolates

Background

Severe infections of virulent methicillin-resistant Staphylococcus aureus (MRSA) are a serious health problem. The present study aimed to investigate clonal spread, virulence and antimicrobial resistance rates of Bulgarian MRSA isolates in 2016–2020.

Methods

Molecular identification and mecA gene detection were performed with PCR. Clonal relatedness was evaluated by RAPD PCR and MLST. MRSA epidemiology, virulence and resistance patterns were investigated by PCR.

Results

All 27 isolates were identified as S. aureus and were mecA positive, and all were susceptible to linezolid, tigecycline and vancomycin. The toxin genes hlg (in 92.6% of isolates), seb (77.8%), sei (77.8%), seh (59.3%), sej (55.6%), and seg (48.1%), were frequently found among the isolates. Epidemiological typing by RAPD identified 4 clones (16 isolates) and 11 were with a unique profile. MLST analysis of the same MRSA isolates showed five MLST clonal complexes and 11 ST types, including CC5 (33.3%) (ST5, ST221, ST4776), CC8 (22.2%) (ST8, ST239, ST72), CC15 (ST582), CC22 (14.8%) (ST217, ST5417), CC30 (ST30) CC398 (ST398), and CC59 (ST59). The isolates from CC5 showed higher virulence potential and almost all were macrolide resistant (ermB or ermC positive). CC8 isolates showed higher level of resistance.

Conclusion

To the best of our knowledge, this study is the first describing the clonal spreading of Bulgarian MRSA and the association with their virulence and resistance determinants. Monitoring of MRSA epidemiology, resistance and virulence profile can lead to better prevention and faster therapeutic choice in cases of severe infections.

Investigation of multidrug-resistant Helicobacter pylori in pediatric patients: A Bulgarian study and literature data

Antibiotic resistance of Helicobacter pylori strains from 106 symptomatic children was evaluated according to EUCAST breakpoints and rate of multidrug resistance (MDR) was analyzed. Overall resistance rates were amoxicillin 7.5%, metronidazole 25.5%, clarithromycin 34.0% and ciprofloxacin 14.1%. There were no significant differences in resistance rates according to patients' age (2-6 and 7-18 years) and sex. Combined resistance rate was 19.8%, including double, triple, and quadruple resistance in 13.2% (14 strains), 5.7% (6) and 0.9% (1) of the strains, respectively. MDR was found in 5.9% (5/84) of the children with gastritis and in two of the four children with celiac disease. The MDR was present in three children aged 4-6 years and in four children aged 10-17 years. The total MDR rate (6.6%) in Bulgarian children in 2012-2021 was higher than those in other studies based on EUCAST breakpoints such as those in pediatric patients in Slovenia in 2011-2014 (3.8%), Lithuania in 2013-2015 (0%) and Spain in 2014-2019 (0%), although being lower than those (20.7% in the untreated and 47.0% in the treated children) in China in 2019. In brief, it is of concern that MDR can strongly limit the choice of H. pylori therapy of one out of fifteen Bulgarian children and that overall resistance to both metronidazole and clarithromycin can hinder the treatment of 15.1% of the pediatric patients. Susceptibility-guided tailored eradication therapy of H. pylori infection should be more frequently implemented in the symptomatic children to avoid risks of both the infection itself and multiple antibiotic treatments.

Invasive Pulmonary Aspergillosis in Patients with Haematological Malignancies and Hematopoietic Stem Cell Transplantation: a Single-Center Study

Aim: The aim of this study was to evaluate the clinical significance of Aspergillus Galactomannan antigen (GM) test for the diagnosis of invasive pulmonary aspergillosis (IPA) in patient with hematological malignancies, including patients undergoing hematopoietic stem cell transplantation (HSCT).

Materials and methods: Between January 2016 and June 2019, ninety patients were tested for GM. A total of 134 blood and 19 bronchoalveolar lavage (BAL) samples were analyzed using Platelia Aspergillus Ag Enzyme-Immuno Assay (Bio-Rad Laboratories). The median age of patients was 63 years (range 25&ndash;81). Fifty-six patients (62.2%) were male. All patients were allocated into five groups on the basis of their GM results.

Results: A positive GM antigen test was detected in 16 patients (17.7%). Of these, ten had positive serum samples (group I). After re-testing, 1 patient from group I gave a negative result. Five patients with negative serum samples gave positive BAL results (group II). One patient had positive both serum and BAL samples (group III). Fifteen GM positive patients (9 from group I, group II, and III) were categorized as probable IPA. Thirty-six patients (40%) negative for GM (group IV) were considered with a possible IPA. IPA was excluded in 38 patients (42.2%) (group V). Anti-mould therapy was initiated in all 15 patients who were considered to be cases with probable IPA. IPA was the immediate cause of death in 3 cases (25%).

Conclusions: Our results demonstrated the clinical applicability of the GM test for screening of IPA in high-risk patients with hematological malignancies and HSCT.

Rifamycin use for treatment of Helicobacter pylori infection: a review of recent data

Helicobacter pylori eradication has become increasingly challenging. We focused on recent data about rifamycin resistance and rifamycin-containing regimens. Rifampin (rifampicin) resistance rates were <1-18.8% (often ≤7%), while those to rifabutin were 0-<4%. To detect rifabutin resistance by rifampin, 4 mg/l breakpoint was suggested. Eradication success by rifaximin-based regimens was disappointing (<62%), while that of rifabutin-containing regimens was 54.5->96%, reaching >81% in four studies. Some newer rifamycin analogs like TNP-2092 need further investigation. Briefly, although rifabutin-based regimens carry a risk of adverse effects or increasing mycobacterial resistance, they may be a rational choice for some multidrug-resistant H. pylori strains and as a third-line eradication therapy. Bismuth addition to rifabutin-based therapy and combined rifabutin-containing capsules (Talicia) are promising treatment options.

Molecular emm typing of Bulgarian macrolide-resistant Streptococcus pyogenes isolates

Group A streptococcus (GAS) is a human pathogen causing a broad range of infections, linked with global morbidity and mortality. Macrolide resistance rates vary significantly in different parts of the world. Driving factors of the emergence and spread of resistant clones are not clearly understood. We investigated 102 macrolide-resistant GAS strains collected during the period 2014-2018 from various clinical specimens from Bulgarian patients. Strains were characterized by the presence of mefA/mefE, ermA, and ermB using polymerase chain reaction and sequencing for mefA/mefE. Resistant strains were studied by emm sequence typing and emm-cluster system. Most prevalent emm types among the macrolide-resistant GAS strains were emm28 (22.55%), emm12 (17.65%), and emm4 (16.66%). Almost all (87.25%) of the macrolide-resistant isolates harboring ermB were emm28. The isolates that carried ermA were predominantly emm12 (38.24%) and emm77 (38.24%), with fewer emm89 (23.53%). The isolates harbored predominantly mefE (49 isolates) and only 9 strains carried mefA. The most prevalent emm clusters among the GAS isolates were E4 (40.20%), A-C4 (17.65%), and E1 (16.66%). The study's results suggest that dissemination of specific clones in GAS population may also be the reason for the increasing macrolide-resistance rate in our country.

Multidrug resistance in Helicobacter pylori: current state and future directions

Introduction: Helicobacter pylori antibiotic resistance has increased worldwide and multidrug resistance (MDR), which seriously hampers eradication success of the frequent chronic infection, has often been reported. Areas covered: H. pylori MDR rates are discussed, mostly from recent articles published since 2015. Present approaches and future directions to counteract the MDR are outlined. Expert opinion: Alarming presence of triple, quadruple and, in some studies, quintuple and sextuple resistance was detected. Primary MDR rates ranged from <10% in most European countries to >40% in Peru. Post-treatment or overall MDR rates were >23-36% in about half of the studies. MDR prevalence has varied both among and within the countries. Factors linked to the MDR are national antibiotic consumption, antibiotic misuse, treatment failures and bacterial factors such as mutations, efflux pumps, and biofilms. Important directions to counteract the MDR increase can be optimization of present and new eradication regimens, wider use of bismuth-containing regimens, assessment of benefit of vonoprazan, new antibiotics such as newer fluoroquinolones and oxazolidinone analogues, adjuvants involving N-acetylcysteine and probiotics, anti-biofilm approaches using anti-biofilm peptides and rhamnolipid and development of vaccines and non-invasive tests for resistance detection. However, more efforts and studies are required. Strain susceptibility testing is increasingly important.

Multidrug resistance in anaerobes

Multidrug resistance (MDR) in anaerobes is not a well-known topic. Bacteroides fragilis group isolates have numerous resistance determinants such as multidrug efflux pumps, cfiA and nimB genes and activating insertion sequences, and some isolates exhibited extensive drug-resistant patterns. MDR rates in B. fragilis group were from 1.5 to >18% and up to >71% in cfiA and nimB positive isolates carrying insertion sequences. MDR was present in >1/2 of Clostridioides difficile isolates, most often in epidemic/hypervirulent strains and unusually high metronidazole or vancomycin resistance has been reported in single studies. MDR was found in Prevotella spp. (in ≤10% of isolates), Finegoldia magna, Veillonella spp. and Cutibacterium acnes. Resistance in the anaerobes tends to be less predictable and anaerobic microbiology is required in more laboratories. New hopes may be new antibiotics such as eravacycline, cadazolid, surotomycin, ridinilazol or C. difficile toxoid vaccines; however, more efforts are needed to track the MDR in anaerobes.

Prevalence of Helicobacter pylori is still high among symptomatic Bulgarian children

Helicobacter pylori positivity was assessed among 656 symptomatic children in 2010-2017. Overall infection prevalence was 24.5% and a significantly higher rate was detected in girls (28.5%) compared to boys (20.0%). Moreover, in children with duodenal ulcer, H. pylori prevalence was higher (47.4%) compared with the rest (23.9%). On the contrary, the infection was detected 1.9-fold less frequently in patients with GERD (14.5%) compared with the other (27.0%) patients and 2.1-fold less often in the presence of duodenogastric reflux (bile) reflux (13.0%) compared with the absence of the reflux (27.0%). No significant difference was observed between the younger (aged ≤7 years, 20.0%) and the older (aged 8-18 years, 25.5%) patients. H. pylori infection rate in Bulgarian pediatric patients between 2010 and 2017 was 2.5-fold lower than that in 1996-2006. In conclusion, H. pylori infection is still an important concern for Bulgarian children, although having decreased by about 1.8%/yearly over 21 years. This study reveals the importance of H. pylori diagnostics even in the youngest symptomatic children and demonstrates an inverse association between either GERD or bile reflux and H. pylori infection.

Quinolone resistance mechanisms among third-generation cephalosporin resistant isolates of Enterobacter spp. in a Bulgarian university hospital

Background: There have been no reports in Bulgaria about quinolone resistance determinants among Enterobacter spp. Aims: To investigate plasmid and chromosomal quinolone resistance rates among 175 third-generation cephalosporin resistant Enterobacter spp. isolates (167 Enterobacter cloacae complex and eight Enterobacter aerogenes isolates) collected at a university hospital in Varna, Bulgaria, as well as to reveal their association with ESBL/AmpC production and a carriage of specific plasmid replicon types. Methods: PCR, isoelectric focusing, replicon typing, sequencing, and epidemiology typing were carried out. Results: A high level of combined third-generation cephalosporin and quinolone resistant Enterobacter spp. was found - 79.4%. The ESBL production rate was 87%, consisting mainly of CTX-M-15 among E. cloacae complex (in 76%) and CTX-M-3 among E. aerogenes (in 88%). Plasmid mediated quinolone resistance (PMQR) determinants were identified in 57% of the isolates. The most commonly detected PMQR determinants were qnrB (90%), consisting mainly of qnrB1 (in 61%), and qnrB9 (in 27%) of the isolates. Both alleles were transferred with CTX-M-15 genes; transconjugants showed HI2 replicons (for qnrB1 positive transconjugants) and were non-typeable (for qnrB9). One Enterobacter spp. isolate produced qnrB4. QnrA1, qnrS1, and aac(6')-Ib-cr were detected in single isolates only. QnrC, qnrD, qepA, and oqxAB genes were not found. QnrB was associated with CTX-M-15 production, and qnrS1 was linked to CTX-M-3. Alterations in 83 and 87 positions of gyrB in quinolone-resistance determining regions, and 80 position of parC were detected in high level quinolone resistant isolates. Among all the Enterobacter spp. isolates tested, one predominant clone A was identified (53%). Conclusion: Our data showed the necessity of more prudent use of quinolones and third-generation cephalosporins, because of the risk of promoting dissemination, and selection of multiple resistance determinants (ESBL, PMQR) among Enterobacter spp. isolates in Bulgaria.

Multicentre investigation of carbapenemase-producing Klebsiella pneumoniae and Escherichia coli in Bulgarian hospitals - Interregional spread of ST11 NDM-1-producing K. pneumoniae

AIM

The aim of this study was to investigate the mechanisms of beta-lactam-resistance and the clonal relatedness of carbapenem-nonsusceptible Klebsiella pneumoniae and Escherichia coli isolates, collected consecutively in eight centers in five Bulgarian cities from November 2014 to March 2018. Carbapenemase-producing enterobacteria were detected in all but one centers. Overall, 104 K. pneumoniae and one E. coli were analysed.

MATERIALS AND METHODS

Antimicrobial susceptibility and beta-lactamases were analysed. Conjugation experiments, plasmid fingerprinting and replicon typing, as well as MLST and ERIC-PCR were carried out.

RESULTS

KPC-2 (51%) and NDM-1 (47%) were the main carbapenemases identified. KPC-2 producing K. pneumoniae were classified into 10 MLST-types. The four dominating MLST-types ST29, ST15, ST336 and ST902 comprised 79% of the KPC-2 producers. All but one of the NDM-1 producing isolates belonged to the MLST-type ST11 and were found in seven centers. Furthermore, single K. pneumoniae isolates producing VIM-1 (ST147) and OXA-48 (ST15) were identified. In addition to the carbapenemases, the ESBLs CTX-M-15, CTX-M-3, and SHV-12 as well as AmpC enzyme CMY-4 were found. The FIIAs-replicon-type was found in all KPC-2 producers while the A/C-replicons dominated in NDM-1 producing isolates. The single NDM-1 producing E. coli was determined as MLST-Type ST10 (Warwick scheme).

CONCLUSION

The interregional clonal expansion of NDM-1 producing ST11 K. pneumoniae and the dissemination of bla_KPC-2 carrying plasmids were responsible for the spread of carbapenemase-producing K. pneumoniae in Bulgaria. Our findings highlight the urgency to prevent dissemination of these highly transmissible and dangerous lineages.

Status of Helicobacter pylori cag pathogenicity island (cagPAI) integrity and significance of its individual genes

One of the most important virulence factors of H. pylori is the intact cagPAI. The aim of the present study is to investigate cagPAI intactness among Bulgarian H. pylori isolates, its associations with clinical outcomes and vacA alleles, and to evaluate the significance of individual cagPAI genes.

MATERIAL AND METHODS

Totally, 156 isolates from 156 patients with endoscopic findings for duodenal or gastric ulcer (33 subjects), non-ulcer disease (121) and other diseases, such as Crohn's disease and hepatitis (2) were tested. Polymerase chain reaction (PCR) was used to detect 14 essential cagPAI genes, including cagA, as well as vacA s, i and m alleles.

RESULTS

CagA positive were 81.4% of all H. pylori isolates. Intact cagPAI was found in 64.1% of the all isolates, 16.7% and 19.2% showed complete and partial cagPAI absence, respectively. The prevalence of all cagPAI genes and intact cagPAI was significantly higher in isolates from ulcer patients compared with those from non-ulcer patients (p = 0.001). The most frequently missing genes among the isolates with partially deleted cagPAIs were cagE or/and cagY (28 of 30 isolates). Overall prevalence of vacA s1a allele was 80.1% and that of vacA i1 was 64.1%. The vacA s1a, m1 and i1 alleles were more prevalent in H. pylori isolates from ulcer patients (p = 0.03, p = 0.009, and p = 0.0003, respectively) and were associated with isolates with intact cagPAI.

CONCLUSIONS

In Bulgaria the prevalence of intact cagPAI was high. cagE or/and cagY absence was the most important predictor of cagPAI status.

Bacteriocin-like inhibitory activities of seven Lactobacillus delbrueckii subsp. bulgaricus strains against antibiotic susceptible and resistant Helicobacter pylori strains

The aim of the study was to detect anti-Helicobacter pylori activity of seven Lactobacillus delbrueckii subsp. bulgaricus (GLB) strains by four cell-free supernatant (CFS) types. Activity of non-neutralized and non-heat-treated (CFSs1), non-neutralized and heat-treated (CFSs2), pH neutralized, catalase-treated and non-heat-treated (CFSs3), or neutralized, catalase- and heat-treated (CFSs4) CFSs against 18 H. pylori strains (11 of which with antibiotic resistance) was evaluated. All GLB strains produced bacteriocin-like inhibitory substances (BLISs), the neutralized CFSs of two GLB strains inhibited >81% of test strains and those of four GLB strains were active against >71% of antibiotic resistant strains. Two H. pylori strains were BLIS resistant. The heating did not reduce the CFS activity. Briefly, all GLB strains evaluated produced heat-stable BLISs, although GLB and H. pylori strain susceptibility patterns exhibited differences. Bacteriocin-like inhibitory substance activity can be an advantage for the probiotic choice for H. pylori infection control.

SIGNIFICANCE AND IMPACT OF THE STUDY

In this study, anti-Helicobacter pylori activity of seven Lactobacillus delbrueckii subsp. bulgaricus (GLB) strains was evaluated by four cell-free supernatant (CFS) types. The GLB strains produced heat-stable bacteriocin-like inhibitory substances (BLISs) with a strong anti-H. pylori activity and some neutralized, catalase- and heat-treated CFSs inhibited >83% of the test strains. Bacteriocin-like inhibitory substance production of GLB strains can render them valuable probiotics in the control of H. pylori infection.

Dissemination of successful international clone ST15 and clonal complex 17 among Bulgarian CTX-M-15 producing K. pneumoniae isolates

A total of 82 extended spectrum beta-lactamase (ESBL) producing Klebsiella pneumoniae and 4 Klebsiella oxytoca isolates were collected in 2014 from four geographical areas in Bulgaria and their multilocus sequence type (MLST) and transferability of the ESBL encoding genes were investigated. The predominant type was CTX-M-15 (87%), followed by CTX-M-3 (9%), SHV-12 or SHV-2 (2%) and CTX-M-14 (1%). The CTX-M-15 producers belonged to ST15 (34.1%) and to a lesser extent to CC17 (ST16, ST17, ST336). The CTX-M-15 transconjugants showed a presence of R, A/C₂ and F replicons. The CTX-M-3 producers were assigned to ST29, ST70, ST432, ST542 and ST15 types and the transconjugants carried M₂ replicons. To the best of our knowledge, this is the first report that fully describes the MLST types among Bulgarian ESBL producing K. pneumoniae and the first report of the detection of IncR plasmid replicon type in our country.

Primary Helicobacter pylori resistance in elderly patients over 20 years: A Bulgarian study

We evaluated the antibiotic susceptibility of 233 Helicobacter pylori strains isolated in the period 2011-2016, involving 62 strains from elderly patients aged 66-93years and 171 strains from younger adults. To assess resistance evolution, primary resistance rates in 92 strains from as many patients aged ≥60years in 1996-2003 were compared with those in 85 strains from infected patients in the same age group in 2011-2016. In the patients aged >65years evaluated during the last 6 years, amoxicillin resistance according to EUCAST and prior breakpoints was 1.6 and 0%, respectively. Resistance rates were the same by both breakpoint systems to metronidazole (35.5%), clarithromycin (22.6%), tetracycline (1.6%) and levofloxacin (32.3%). In 2011-2016, there were no significant differences between resistance rates in the subjects aged >65years and the younger adults. Notably, during the last 6 years, double/triple resistance was found in 21.0% of the subjects aged >65years. Moreover, the prevalence of quinolone primary resistance (30.0%) was significantly (3.4-fold) higher than that (8.9%) observed in 1996-2003. Briefly, the presence of both combined resistance and a strikingly high primary levofloxacin resistance in the elderly implies a cautious antibiotic choice for H. pylori eradication. In vitro susceptibility testing of the strains is highly important in this age group. The results can be linked to more frequent comorbidities and co-infection treatment in older compared with younger patients and, additionally, to the national antibiotic consumption. The high prevalence of quinolone resistance in the elderly patients is an alarming finding.

Actinomycosis: a frequently forgotten disease

Actinomycosis is a rare subacute or chronic, endogenous infection mainly by Actinomyces species, showing low virulence through fimbriae and biofilms. Cervicofacial, thoracic, abdominal, pelvic and sometimes cerebral, laryngeal, urinary and other regions can be affected. Actinomycosis mimics other diseases, often malignancy. Disease risk in immunocompromised subjects needs clarification. Diagnosis is often delayed and 'sulfur granules' are helpful but nonspecific. Culture requires immediate specimen transport and prolonged anaerobic incubation. Imaging, histology, cytology, matrix-assisted laser desorption ionization time-of-flight mass spectrometry and molecular methods improve the diagnosis. Actinomycetes are β-lactam susceptible, occasionally resistant. Treatment includes surgery and/or long-term parenteral then oral antibiotics, but some 1-4-week regimens or oral therapy alone were curative. For prophylaxis, oral hygiene and regular intrauterine device replacement are important.

Clarithromycin Resistance Mutations in Helicobacter pylori in Association with Virulence Factors and Antibiotic Susceptibility of the Strains

Antibiotic resistance is the major cause for Helicobacter pylori eradication failure. H. pylori clarithromycin resistance mutations were evaluated in 84 (82 phenotypically clarithromycin resistant and 2 intermediately susceptible) strains by allele-specific PCR and 3'-mismatched PCR. Many (57.1%) of these strains were metronidazole resistant. Prevalence of cagA(+), cagE(+), vacA s1a, m1, i1, and i2 strains was 76.2%, 58.0%, 82.1%, 35.7%, 50.0%, and 50.0%, respectively. A2143G, A2142G, A2142C, and A2143G+A2142G mutation rates were 64.3%, 23.8%, 1.2%, and 10.7%, respectively. Strains harboring the A2142G mutation showed 5.3-fold higher clarithromycin MIC50 than those harboring the A2143G mutation. The A2143G mutation alone was 1.7-fold more common in vacA i2 strains compared with vacA i1 strains, while the A2142G mutation alone was 3-fold more frequent in vacA i1 strains than vacA i2 strains and 3.1-fold more common in metronidazole-susceptible compared with metronidazole-resistant strains. Briefly, clarithromycin resistance mutations were significantly linked to vacA i allele and metronidazole susceptibility. This is the first report about associations between the A2143G mutation and less virulent vacA i2 strains, and between the A2142G mutation and more virulent vacA i1 strains. As the 2143G mutation often predicts eradication failure by clarithromycin-based regimens, the results may be linked to the better eradication of more virulent strains compared with the less virulent strains.

Clonal dissemination of multilocus sequence type ST15 KPC-2-producing Klebsiella pneumoniae in Bulgaria

A total of 36 consecutive clinical and two fecal-screening carbapenem-resistant Klebsiella pneumoniae isolates from two Bulgarian university hospitals (Varna and Pleven) were investigated. Susceptibility testing, conjugation experiments, and plasmid replicon typing were carried out. Beta-lactamases were characterized by isoelectric focusing, PCR, and sequencing. Clonal relatedness was investigated by RAPD and multilocus sequence typing (MLST). Most of the isolates demonstrated multidrug resistance profile. Amikacin and tigecycline retained good activity with susceptibility rates of 95 and 87%, respectively. The resistance rate to colistin was 63%. Six RAPD- and MLST-types were identified: the dominating MLST-type was ST15 (27 isolates), followed by ST76 (six isolates), and ST1350 (two isolates). ST101, ST258, and ST151 were detected once. All except one of the K. pneumoniae produced KPC-2, mostly in combination with CTX-M-15, while for one isolate (ST101) the enzymes OXA-48 and CTX-M-14 were found. All KPC-2-producing transconjugants revealed the presence of IncFII plasmid. The OXA-48- and CTX-M-14-producing isolate showed the presence of L/M replicon type. The dissemination of KPC-2-producing K.pneumoniae in Bulgaria is mainly due to the sustained spread of successful ST15 clone and to a lesser extent of ST76 clone. This is the first report of OXA-48 producing ST101 K. pneumoniae in Bulgaria.

Predominance of IncL/M and IncF plasmid types among CTX-M-ESBL-producing Escherichia coli and Klebsiella pneumoniae in Bulgarian hospitals

Our objective was to investigate the plasmid replicon-types involved in spread of ESBLs among Bulgarian Klebsiella pneumoniae and Escherichia coli. Sixty-three isolates, with transferable beta-lactam resistance determinants, collected between 2007 and 2009 in six medical institutions, were analysed with respect to their antimicrobial susceptibility, ESBL-, RAPD-, and plasmid replicon-type. Phylogenetic typing and screening for the O25b-ST131 lineage were carried out for E. coli. The predominant ESBLs were CTX-M-15 (81%) among E. coli and CTX-M-3 (58%) among K. pneumoniae. Other sporadically found ESBLs were SHV-12 and TEM-139, and for the first time in Bulgaria, CTX-M-1 and CTX-M-14. Replicon typing revealed that plasmids carrying blaCTX-M-3 exclusively belonged to IncL/M-type, while blaCTX-M-15 was predominantly (94%) associated with IncF-type plasmids. Among E. coli, 59% of the isolates were clonally related. Isolates of that cluster produced CTX-M-15, belonged to the O25b-ST131 lineage, predominantly harboured plasmids with the FIA replicon, and were found in five centres. Among CTX-M-3-producing K. pneumoniae, two prevailing RAPD-types were found, one remained restricted to one centre and the second was found in three centres. The incompatibility groups IncN and IncA/C linked with blaSHV-12 respectively blaTEM-139 were found only once. To the best of our knowledge, this is the first detailed investigation of plasmids carrying ESBL genes among Bulgarian isolates demonstrating wide distribution of conjugative IncF plasmids among CTX-M-15-producing E. coli and IncL/M plasmids among CTX-M-3 positive K. pneumoniae isolates.

Serotypes, antimicrobial susceptibility, and beta-lactam resistance mechanisms of clinical Haemophilus influenzae isolates from Bulgaria in a pre-vaccination period

OBJECTIVE

To determine the serotypes, antimicrobial susceptibility, and beta-lactam resistance mechanisms of Haemophilus influenzae strains isolated from invasive and respiratory tract infections (RTIs) prior to the introduction of Haemophilus influenzae type b (Hib) vaccination in Bulgaria.

METHODS

A total of 259 isolates were serotyped by polymerase chain reaction. Susceptibility to antibiotics and beta-lactamase production were determined, and DNA sequencing of the ftsI gene was performed for ampicillin non-susceptible strains.

RESULTS

The invasive H. influenzae infections in children were mainly due to serotype b (94.5% in meningitis and 88.9% in other invasive cases). Non-typeable strains (97.4%) were the most frequently found H. influenzae strains in RTIs both in children and adults. Non-susceptibility to ampicillin occurred in 22% of all strains. Ceftriaxone and levofloxacin were the most active agents tested. Ampicillin resistance occurred in 34.4% of invasive strains, and beta-lactamase production was the only mechanism found. Among respiratory tract isolates, ampicillin non-susceptible strains (18%) were classified into the following groups: beta-lactamase-positive, ampicillin-resistant (BLPAR) strains (7.2%); beta-lactamase-negative, ampicillin-non-susceptible (BLNAR) strains (8.2%); and beta- lactamase-positive, amoxicillin-clavulanate-resistant (BLPACR) strains (2.6%). Among 21 BLNAR and BLPACR strains there were 9 different patterns of multiple-amino acid substitutions in penicillin-binding protein 3. Of these, most isolates (81.0%) belonged to group II, defined by the Asn526Lys substitution.

CONCLUSIONS

Beta-lactamase production was more common among invasive strains than in respiratory isolates. BLNAR and BLPACR H. influenzae were found only among respiratory tract isolates.

Significance of Helicobacter pylori vacA intermediate region genotyping-a Bulgarian study

The significance of the intermediate (i) region of the Helicobacter pylori vacA gene as a virulence factor associated with the severity of gastric disease is still disputable. The aim of the present study was to evaluate the prevalence and significance of vacA i alleles alone or in combination with other vacA alleles in symptomatic Bulgarian patients and to find out possible associations between vacA i genotype and patients' disease, age, sex, and other H. pylori virulence factors. Unlike vacA s1 and m1, vacA i1 prevalence was significantly higher (75.0%) in strains from peptic ulcer patients than in strains from nonulcer patients with gastric diseases (58.6%) (P = 0.022). Less virulent vacA s1 i2 m2 strains were more prevalent in females (P = 0.03), and cagA(+) was associated with vacA i1, s1, m1, and their combinations. In conclusion, vacA i status is a better predictor for the strain virulence than other vacA alleles.