Phenotypic and genotypic aminoglycoside resistance in blood culture isolates of coagulase-negative staphylococci from a single neonatal intensive care unit, 1989–2000

Antibiotic Resistance in Bacteria—A Review

Background: A global problem of multi-drug resistance (MDR) among bacteria is the cause of hundreds of thousands of deaths every year. In response to the significant increase of MDR bacteria, legislative measures have widely been taken to limit or eliminate the use of antibiotics, including in the form of feed additives for livestock, but also in metaphylaxis and its treatment, which was the subject of EU Regulation in 2019/6. Numerous studies have documented that bacteria use both phenotypis and gentic strategies enabling a natural defence against antibiotics and the induction of mechanisms in increasing resistance to the used antibacterial chemicals. The mechanisms presented in this review developed by the bacteria have a significant impact on reducing the ability to combat bacterial infections in humans and animals. Moreover, the high prevalence of multi-resistant strains in the environment and the ease of transmission of drug-resistance genes between the different bacterial species including commensal flora and pathogenic like foodborne pathogens (E. coli, Campylobacter spp., Enterococcus spp., Salmonella spp., Listeria spp., Staphylococcus spp.) favor the rapid spread of multi-resistance among bacteria in humans and animals. Given the global threat posed by the widespread phenomenon of multi-drug resistance among bacteria which are dangerous for humans and animals, the subject of this study is the presentation of the mechanisms of resistance in most frequent bacteria called as “foodborne pathoges” isolated from human and animals. In order to present the significance of the global problem related to multi-drug resistance among selected pathogens, especially those danger to humans, the publication also presents statistical data on the percentage range of occurrence of drug resistance among selected bacteria in various regions of the world. In addition to the phenotypic characteristics of pathogen resistance, this review also presents detailed information on the detection of drug resistance genes for specific groups of antibiotics. It should be emphasized that the manuscript also presents the results of own research i.e., Campylobacter spp., E. coli or Enetrococcus spp. This subject and the presentation of data on the risks of drug resistance among bacteria will contribute to initiating research in implementing the prevention of drug resistance and the development of alternatives for antimicrobials methods of controlling bacteria.

Detection of Resistant and Enterotoxigenic Strains of Staphylococcus warneri Isolated from Food of Animal Origin

The topic of this work is the detection of antimicrobial resistance to Staphylococcus warneri strains and the genes encoding staphylococcal enterotoxins. It is considered a potential pathogen that can cause various—mostly inflammatory—diseases in immunosuppressed patients. The experimental part of the paper deals with the isolation of individual isolates from meat samples of Oryctolagus cuniculus, Oncorhynchus mykiss, Scomber scombrus, chicken thigh, beef thigh muscle, pork thigh muscle, and bryndza cheese. In total, 45 isolates were obtained and subjected to phenotypic (plasma coagulase activity, nuclease, pigment, hemolysis, lecithinase, and lipase production) and genotypic analyses to confirm the presence of the S. warneri species. The presence of genes encoding staphylococcal enterotoxins A (three isolates) and D (six isolates) was determined by PCR. Using the Miditech system, the minimum inhibitory concentration for various antibiotics or antibiotics combinations was determined, namely for ampicillin; ampicillin + sulbactam; oxacillin; cefoxitin; piperacillin + tazobactam; erythromycin; clindamycin; linezolid; rifampicin; gentamicin; teicoplanin; vancomycin; trimethoprim; chloramphenicol; tigecycline; moxifloxacin; ciprofloxacin; tetracycline; trimethoprim + sulfonamide; and nitrofurantoin. Resistance to ciprofloxacin and tetracycline was most common (73%). At the same time, out of a total of 45 isolates, 22% of the isolates were confirmed as multi-resistant. Isolates that showed phenotypic resistance to β-lactam antibiotics were subjected to mecA gene detection by PCR.

Virulence Characteristics of mecA-Positive Multidrug-Resistant Clinical Coagulase-Negative Staphylococci

Coagulase-negative staphylococci (CoNS) are an important group of opportunistic pathogenic microorganisms that cause infections in hospital settings and are generally resistant to many antimicrobial agents. We report on phenotypic and genotypic virulence characteristics of a select group of clinical, mecA-positive (encoding penicillin-binding protein 2a) CoNS isolates. All CoNS were resistant to two or more antimicrobials with S. epidermidis strain 214EP, showing resistance to fifteen of the sixteen antimicrobial agents tested. Aminoglycoside-resistance genes were the ones most commonly detected. The presence of megaplasmids containing both horizontal gene transfer and antimicrobial resistance genetic determinants indicates that CoNS may disseminate antibiotic resistance to other bacteria. Staphylococcus sciuri species produced six virulence enzymes, including a DNase, gelatinase, lipase, phosphatase, and protease that are suspected to degrade tissues into nutrients for bacterial growth and contribute to the pathogenicity of CoNS. The PCR assay for the detection of biofilm-associated genes found the eno (encoding laminin-binding protein) gene in all isolates. Measurement of their biofilm-forming ability and Spearman’s rank correlation coefficient analyses revealed that the results of crystal violet (CV) and extracellular polymeric substances (EPS) assays were significantly correlated (ρ = 0.9153, P = 3.612e-12). The presence of virulence factors, biofilm-formation capability, extracellular enzymes, multidrug resistance, and gene transfer markers in mecA-positive CoNS clinical strains used in this study makes them powerful opportunistic pathogens. The study also warrants a careful evaluation of nosocomial infections caused by CoNS and may be useful in studying the mechanism of virulence and factors associated with their pathogenicity in vivo and developing effective strategies for mitigation.

An optimised dosing regimen versus a standard dosing regimen of vancomycin for the treatment of late onset sepsis due to Gram-positive microorganisms in neonates and infants aged less than 90 days (NeoVanc): study protocol for a randomised controlled trial

BACKGROUND

Vancomycin has been used in clinical practice for over 50 years; however, validated, pharmacokinetic (PK) data relating clinical outcomes to different dosing regimens in neonates are lacking. Coagulase negative staphylococci (CoNS) are the most commonly isolated organisms in neonatal, late-onset sepsis (LOS). Optimised use to maximise efficacy while minimising toxicity and resistance selection is imperative to ensure vancomycin's continued efficacy.

METHODS

NeoVanc is a European, open-label, Phase IIb, randomised, controlled, non-inferiority trial comparing an optimised vancomycin regimen to a standard vancomycin regimen when treating LOS known/suspected to be caused by Gram-positive organisms (excluding Staphylococcus aureus) in infants aged ≤ 90 days. Three hundred infants will be recruited and randomised in a 1:1 ratio. Infants can be recruited if they have culture confirmed (a positive culture from a normally sterile site and at least one clinical/laboratory criterion) or clinical sepsis (presence of any ≥ 3 clinical/laboratory criteria) in the 24 h before randomisation. The optimised regimen consists of a vancomycin loading dose (25 mg/kg) followed by 5 ± 1 days of 15 mg/kg q12h or q8h, dependent on postmenstrual age (PMA). The standard regimen is a 10 ± 2 day vancomycin course at 15 mg/kg q24h, q12h or q8h, dependent on PMA. The primary endpoint is a successful outcome at the test of cure visit (10 ± 1 days after the end of vancomycin therapy). A successful outcome consists of the patient being alive, having successfully completed study vancomycin therapy and having not had a clinical/microbiological relapse/new infection requiring treatment with vancomycin or other anti-staphylococcal antibiotic for > 24 h. Secondary endpoints include clinical/microbiological relapse/new infection at the short-term follow-up visit (30 ± 5 days after the initiation of vancomycin), evaluation of safety (renal/hearing), vancomycin PK and assessment of a host biomarker panel over the course of vancomycin therapy.

DISCUSSION

Based on previous pre-clinical data and a large meta-analysis of neonatal, PK/pharmacodynamic data, NeoVanc was set up to provide evidence on whether a loading dose followed by a short vancomycin course is non-inferior, regarding efficacy, when compared to a standard, longer course. If non-inferiority is demonstrated, this would support adoption of the optimised regimen as a way of safely reducing vancomycin exposure when treating neonatal, Gram-positive LOS.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02790996. Registered on 7 April 2016. EudraCT, 2015-000203-89. Entered on 18 July 2016.

Prevalence of Genes Encoding Aminoglycoside-Modifying Enzymes in Clinical Isolates of Gram-Positive Cocci in Iran: A Systematic Review and Meta-Analysis

Introduction: Several studies have investigated the genes encoding aminoglycoside-modifying enzymes (AMEs) among gram-positive cocci (GPC) such as Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), coagulase-negative staphylococci (CoNS), and Enterococcus spp. in Iran; however, a comprehensive analysis has not yet been performed. Thus, the present systematic review and meta-analysis was conducted to determine the prevalence of genes encoding AMEs among GPC in Iran. Methods: A systematic review of the data published in the English and Persian languages from January 2000 to October 2018 was performed by searching different electronic databases (Medline, Embase, Web of Science, and the Iranian Database). Meta-analysis was performed by using the Comprehensive Meta-Analysis (Biostat V2.2) software. Cochran's Q and I² statistics were used to test heterogeneity, and publication bias was assessed by using funnel plot and Begg's and Egger's tests. Results: Out of 117 studies, 28 were considered eligible for inclusion in the current meta-analysis. The most prevalent AMEs gene among GPC was aac(6')-Ie-aph(2'')-Ia, with a prevalence of 97.7% (95% CI; 94.4-99) in high-level gentamicin-resistant enterococci and 67.7% (95% CI; 59.2-75.2) in MRSA. The second most common gene was ant(4')Ia, with a prevalence of 45.3% (95% CI; 23.9-68.6) in MRSA. Conclusions: It was ultimately determined that the prevalence of AMEs genes among GPC had reached alarming levels in Iran; therefore, aminoglycosides should be prescribed with caution by clinicians. The implementation of a regional and nationwide surveillance system to monitor antimicrobial resistance, especially aminoglycosides, and increasing the awareness of AMEs genes among clinicians are essential to guiding empirical and pathogen-specific therapy.

Biofilm Formation by ica-Negative Ocular Isolates of Staphylococcus haemolyticus

Staphylococcus haemolyticus is the second most frequently isolated CoNS from ocular infections and human blood cultures. In this study, we examined 18 ocular S. haemolyticus isolates for their capacity to form biofilm and conducted detachment assay to determine the composition of the biofilm matrix and involvement of various elements in cell lysis. PCR identified the presence of biofilm-associated genes, and ica operon and CLSM visualized the components of the biofilm matrix. We found that PIA-independent biofilm formation is the characteristic feature of S. haemolyticus isolates, irrespective of the sources of isolation, and protein or DNA or both are the major components of the biofilm matrix. Cell lysis enabling DNA release was an essential step for biofilm attachment during the initial stages of biofilm development. The srtA transcript expression study indicates its role in the early stages of biofilm development. We found the presence of antibiotic resistance genes in the eDNA and gDNA thus suggesting the possible role of biofilm in horizontal gene transfer of antibiotic resistance determinants. The overall study indicates that S. haemolyticus formed the biofilm comprising of protein or DNA or both and srtA play a role in the initial development of biofilm.

Should First-line Empiric Treatment Strategies for Neonates Cover Coagulase-negative Staphylococcal Infections in Kenya?

BACKGROUND

Neonatal mortality remains high in sub-Saharan Africa, and a third of deaths are estimated to result from infection. While coagulase-negative staphylococci (CoNS) are leading neonatal pathogens in resource-rich settings, their role, and the need for early anti-Staphylococcal treatment in empiric antibiotic guidelines, is unknown in sub-Saharan Africa.

METHODS

We examined systematic clinical and microbiologic surveillance data from all neonatal admissions to Kilifi County Hospital (1998-2013) to determine associated case fatality and/or prolonged duration of admission associated with CoNS in neonates treated according to standard World Health Organization guidelines.

RESULTS

CoNS was isolated from blood culture in 995 of 9552 (10%) neonates. Case fatality among neonates with CoNS isolated from blood did not differ from other neonatal admissions (P = 0.2), and duration of admission was not prolonged [odds ratio (OR) = 0.9 (0.7-1.0), P = 0.040]. Neonates with CoNS were more likely to have convulsions [OR = 1.4 (1.0-1.8), P = 0.031] but less likely to have impaired consciousness or severe indrawing [OR = 0.8 (0.7-0.9), P = 0.025; OR = 0.9 (0.7-1.0), P = 0.065].

CONCLUSIONS

CoNS isolation in blood cultures at admission was not associated with adverse clinical outcomes in neonates treated according to standard World Health Organization guidelines for hospital care in this setting. There is no evidence that first-line antimicrobial treatment guidelines should be altered to increase cover for CoNS infections in neonates in this setting.

Distribution of genes encoding resistance to aminoglycoside modifying enzymes in methicillin-resistant Staphylococcus aureus (MRSA) strains

Today Methicillin-Resistant Staphylococcus aureus (MRSA) have acquired multiple resistance to a wide range of antibiotics including aminoglycosides. So, this study was aimed to investigate the rate of aminoglycoside resistance and the frequency of aminoglycoside resistance mediated genes of aac(Ia)-2, aph(3)-IIIa and ant(4')-Ia among MRSA strains. A total of 467 staphylococci isolates were collected from various clinical samples. S. aureus strains were identified by standard culture and identification criteria and investigating of presence of 16S rRNA and nuc genes. Cefoxitin disk diffusion, and oxacillin-salt agar screening methods were used to detect the MRSA strains with subsequent molecular identification for the presence of mecA gene. Antibiotic susceptibility of MRSA strains against aminoglycoside antibiotics was evaluated by using agar disk diffusion method. Multiplex PCR for the presence of aac(Ia)-2, aph(3)-IIIa and ant(4')-Ia encoding genes for aminoglycosides were performed for MRSA strains. From total staphylococci tested isolates, 262 (56.1%) were identified as S. aureus, of which 161 (61.45%) were detected as MRSA and all comprised mecA gene. The resistance pattern of MRSA strains to aminoglycoside antibiotics were: gentamicin 136 (84.5%); amikacin 125 (77.6%); kanamycin 139 (86.3%); tobramycin 132 (82%); and neomycin 155 (96.3%). The frequency of aac(Ia)-2, aph(3)-IIIa, and ant(4')-Ia genes among MRSA strains, were 64%, 42% and 11.8% respectively. In conclusion, as MRSA strains are of great concern in human infections, the results of present study could provide a useful resource for health sectors for choosing appropriate antibiotics for the effective treatment of infections due to MRSA strains.

In-vitro activity of several antimicrobial agents against methicillin-resistant Staphylococcus aureus (MRSA) isolates expressing aminoglycoside-modifying enzymes: potency of plazomicin alone and in combination with other agents

This study investigated the in-vitro activity of clinically relevant aminoglycosides and new antimicrobial agents-plazomicin, ceftobiprole and dalbavancin-against 55 methicillin-resistant Staphylococcus aureus (MRSA) isolates producing aminoglycoside-modifying enzymes (AMEs). The checkerboard method was used to assess synergism between plazomicin and four antibiotics (fosfomycin, ceftobiprole, cefoxitin and meropenem), and time-kill assays were performed for the most active combinations. Among the aminoglycosides tested, plazomicin was the most active agent against MRSA, with >90% of isolates being inhibited at a minimum inhibitory concentration (MIC) of ≤1 mg/L. MIC₅₀ and MIC₉₀ values for ceftobiprole and dalbavancin were 2 and 4 mg/L, and 0.125 and 0.125 mg/L, respectively. The most prevalent AME gene was aac(6')Ie-aph(2″)Ia (87.3%), followed by ant(4')Ia (52.7%) and aph(3')IIIa (52.7%). Plazomicin activity was not affected by the type or number of enzymes detected. In checkerboard and time-kill assays, indifference was the most common result achieved for the antibiotic combinations. Notably, no antagonism was observed with any combination tested. Overall, plazomicin in combination with meropenem had the highest synergistic effect, demonstrating synergy against seven isolates in the checkerboard assay and three isolates in time-kill curves. In conclusion, plazomicin showed potent activity against aminoglycoside-resistant MRSA isolates, regardless of the number and type of AMEs present. These findings indicate the potential utility of plazomicin in combination with meropenem for the treatment of MRSA infections.

Characterization of resistance to tetracyclines and aminoglycosides of sheep mastitis pathogens: study of the effect of gene content on resistance

AIMS

Mastitis causes economic losses and antimicrobials are frequently used for mastitis treatment. Antimicrobial resistance surveys are still rare in the ovine field and characterization of strains is important in order to acquire information about resistance and for optimization of therapy.

METHODS AND RESULTS

Bacterial pathogens recovered in milk samples from mastitis-affected ewes were characterized for resistance to tetracyclines and aminoglycosides, members of which are frequently used antimicrobials in small ruminants. A total of 185 strains of staphylococci, streptococci, and enterococci, common mastitis pathogens, were tested for minimal inhibitory concentration (MIC) to tetracycline, doxycycline, minocycline, gentamicin, kanamycin, streptomycin, and for resistance genes by PCR. Effects of different tet genes arrangements on MICs were also investigated. Staphylococci expressed the lowest MIC for tetracycline and tet(K) was the most common gene recovered; tet(M) and tet(O) were also found. Gene content was shown to influence the tetracycline MIC values. Enterococci and streptococci showed higher MICs to tetracyclines and nonsusceptible strains always harboured at least one ribosomal protection gene (MIC above 8 μg ml(-1) ). Streptococci often harboured two or more tet determinants. As regards the resistance to aminoglycosides, staphylococci showed the lowest gentamicin and kanamycin median MIC along with streptomycin high level resistant (HLR) strains (MIC >1024 μg ml(-1) ) all harbouring str gene. The resistance determinant aac(6')-Ie-aph(2″)-Ia was present in few strains. Streptococci were basically nonsusceptible to aminoglycosides but neither HLR isolates nor resistance genes were detected. Enterococci revealed the highest MICs for gentamicin; two str harbouring isolates were shown to be HLR to streptomycin.

CONCLUSION

Evidence was obtained for the circulation of antimicrobial-resistant strains and genes in sheep dairy farming.

SIGNIFICANCE AND IMPACT OF THE STUDY

Tetracycline MIC of 64 μg ml(-1) and high-level resistance were detected for streptomycin (MIC >1024 μg ml(-1) ), so that effectiveness of common treatments may be at risk.

Understanding Bacterial Isolates in Blood Culture and Approaches Used to Define Bacteria as Contaminants: A Literature Review

BACKGROUND

Interpretation of blood culture isolates is challenging due to a lack of standard methodologies for identifying contaminants. This problem becomes more complex when the specimens are from sick young infants, as a wide range of bacteria can cause illness among this group.

METHODS

We used 43 key words to find articles published between 1970 and 2011 on blood culture isolates and possible contaminants in the PubMed database. Experts were also consulted to obtain other relevant articles. Selection of articles followed systematic methods considering opinions from more than 1 reviewer.

RESULTS

After reviewing the titles of 3869 articles extracted from the database, we found 307 relevant to our objective. Based on the abstracts, 42 articles were selected for the literature review. In addition, we included 7 more articles based on cross-references and expert advice. The most common methods for differentiating blood culture isolates were multiple blood cultures from the same subject, antibiograms and molecular testing. Streptococcus pneumoniae, Hemophilus influenzae, Neisseria meningitidis and group A and B streptococcus were always considered as pathogens, whereas Bacillus sp., Diphtheroids, Propionibacterium and Micrococcus were commonly regarded as contaminants. Coagulase-negative staphylococci were the most frequent isolates and usually reported as contaminants unless the patient had a specific condition, such as long-term hospitalization or use of invasive devices (catheters).

CONCLUSIONS

Inaccurate interpretation of blood culture may falsely guide treatment and also has long-term policy implications. The combination of clinical and microbiological knowledge, patient's clinical history and laboratory findings are essential for appropriate interpretation of blood culture.

Characterization of Resistance to Aminoglycosides in Methicillin-Resistant Staphylococcus aureus Strains Isolated From a Tertiary Care Hospital in Tehran, Iran

Background:

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common nosocomial pathogens which can cause a broad spectrum of infections.

Objectives:

The current study aimed to describe the frequency and antibiotic susceptibility patterns of clonal groups of gentamicin-resistant strains of MRSA isolated from a tertiary care hospital in Tehran, Iran.

Materials and Methods:

A total of 301 S. aureus isolates were collected during January to November 2012. All of the isolates were identified at the species level and typed using the Phene-Plate (PhP) system. The antibiotic susceptibility patterns of the MRSA strains and the presence of different aminoglycoside resistance genes were determined.

Results:

Of the 301 S. aureus isolates, 90 (29.9%) strains were confirmed as MRSA, and they showed high resistance to penicillin, ciprofloxacin, kanamycin, tobramycin, erythromycin, and tetracycline. On the other hand, 43 of the 90 strains (47.8%) were resistant to gentamicin. Aac (6’)-Ie + aph (2’’), ant (4’)-Ia, aph (3’)-IIIa, and ant (6)-Ia were detected in 65.6%, 42.2%, 20%, and 47.8% of the gentamicin-resistant strains, respectively. Diverse PhP types consisting of seven common types and four single types were identified among the strains.

Conclusions:

Our results illustrated the presence of clonal groups of highly gentamicin-resistant strains of MRSA in hospitals in Tehran. The PhP typing method provided useful information for both clonal dissemination and determining the epidemiological links of the clonal groups of the MRSA strains.

Determination of antimicrobial resistance profile and inducible clindamycin resistance of coagulase negative staphylococci in pediatric patients: the first report from Iran

BACKGROUND

Currently, coagulase negative staphylococci (CoNS) have got much attention as a serious health problem especially in neonates and children. High incidence of antibiotic resistance, in particular methicillin resistance, has complicated the treatment of these organisms. The aim of this study is to determine the susceptibility to different antimicrobial agents and the prevalence of macrolideslincosamides-streptogramins B (MLSB) resistance in CoNS isolates obtained from pediatric patients.

METHODS

Totally 157 CoNS isolates from various clinical samples were examined for antibiotic resistance using disk diffusion and E-test methods. Double-disk test was applied to detect constitutive and inducible MLSB resistance (cMLSB and iMLSB) phenotypes.

RESULTS

Resistance to methicillin was seen in 98 (62.4%) isolates. All isolates were susceptible to vancomycin and linezolid. The prevalence of resistance to antibiotics tested was as follows: fusidic acid (n=58, 36.9%), gentamicin (n=73, 46.5%), ciprofloxacin (n=81, 51.6%), clindamycin (n=112, 71.3%), erythromycin (n=129, 82.2%) and trimethoprim/sulfamethoxazole (n=133, 84.7%). iMLSB phenotype was seen in 14 (8.9%) isolates, and 18 (11.5%) and 98 (62.4%) isolates showed MS and cMLSB phenotypes, respectively. We observed that high overall antibiotic resistance rates were associated significantly with methicillin resistance. Conversely, iMLSB phenotype was correlated neither with methicillin resistance nor with invasiveness.

CONCLUSION

Given the similarity observed between the prevalence of iMLSB and MS phenotypes, the performance of disk diffusion induction test is strongly recommended in our region.

Detecting the frequency of aminoglycoside modifying enzyme encoding genes among clinical isolates of methicillin-resistant Staphylococcus aureus

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) plays an important role in causing many serious nosocomial infections. In this study, the antimicrobial susceptibility and the frequency of aminoglycoside modifying enzyme encoding genes among clinical isolates of methicillin-resistant Staphylococcus aureus was investigated from two university hospitals of Zanjan province of Iran.

METHODS

In this study, the antimicrobial susceptibility of MRSA isolates to various antibiotics was investigated by the disk diffusion method. Multiplex PCR assays were used for the determination of aminoglycoside modifying enzyme (AME) genes and staphylococcal cassette chromosome mec (SCCmec) types in MRSA strains.

RESULTS

All 58 MRSA isolates were sensitive to vancomycin. Resistance to penicillin G, oxacilin, gentamicin, erythromycin, clindamycin, kanamycin, and tobramycin was found in 96.4%, 98.3%, 51.7%, 53.4%, 55.2%, 62% and 58.6% of the isolates, respectively. The most prevalent AME genes were aac(6')/aph(2'') (48.3 %) followed by ant(4)-Ia (24%). The aph(3')-Ia gene was the least frequent AME gene among MRSA isolates (19%). Of the 58 tested MRSA isolates, 5 (8.6%) were harboured SCCmec type I, 11 (19%) SCCmec type II, 20 (34.5%) SCCmec type III, 17 (29.3%) SCCmec type IVa, 1 (1.7%) SCCmec type IVb, 2 (3.4%) SCCmec type IVc, 11 (19%) SCCmec type IVd, and, 18 (31%) SCCmec type V. Nineteen isolates were not typeable.

CONCLUSION

In conclusion, the aac (6')/aph (2'') was the most common aminoglycoside modifying enzyme gene and SCCmec type II and V were the most frequent types detected in hospital isolates, respectively.

The prevalence of aminoglycoside-modifying enzymes among coagulase negative staphylococci in Iranian pediatric patients

In spite of widespread emergence of aminoglycoside resistance, these drugs are still used in the treatment of staphylococcal infections. This study aimed to investigate the distribution of aminoglycoside resistance and genes encoding aminoglycoside - modifying enzymes (AMEs) as well as Staphylococcal Cassette Chromosome mec (SCCmec) type in coagulase negative staphylococci (CoNS) in pediatric patients. Totally, 93 CoNS isolates were examined for susceptibility to aminoglycosides using disk diffusion and/or E-test methods. AMEs genes and SCCmec types were detected using multiplex PCR. Strain typing was performed using repetitive extragenic palindromic (REP) - PCR assay. The non-susceptibility rates to kanamycin, tobramycin, gentamicin, amikacin and netilmicin were 73%, 59%, 49.5%, 16% and 7.5%, respectively. aac(6')-Ie-aph(2″)-Ia, ant(4')-Ia and aph(3')-IIIa were encountered in 56 (60.2%), 38 (40.8%) and 18 (19.3%) isolates, respectively. In aac(6')-Ie-aph(2″)-Ia- positive isolates, the non- susceptibility rates to kanamycin, gentamicin, tobramycin, amikacin and netilmicin were 83%, 74%, 73%, 49% and 43%, respectively. SCCmec types included type IV (n = 31), I (n = 17), II (n = 5), III (n = 4), and V (n = 2). Three isolates had two types; I + III (n = 2) and III + IV (n = 1) whereas 11 isolates were non-typeable. AMEs genes carriers were distributed frequently into type IV. We found diverse fingerprint patterns among our isolates. In conclusion, there was a strong correlation between alarming rate of aminoglycoside resistance and methicillin resistance. Discordances between phenotypic and genotypic detection of aminoglycoside resistance were discernible. AMEs genes might be related to SCCmec types.

Prevalence of antibiotic resistance in multi-drug resistant coagulase-negative staphylococci isolated from invasive infection in very low birth weight neonates in two Polish NICUs

BACKGROUND

Multi-drug resistant coagulaso-negative staphylococci (CNS) have become an increasing problem in nosocomial infections connected with the presence of medical devices. The paper aimed to analyze the prevalence of antibiotic resistance in CNS isolated from invasive infection in very low birth weight (VLBW) neonates.

METHODS

Continuous prospective target surveillance of infections was conducted in 2009 at two Polish NICUs that participated in the Polish Neonatology Surveillance Network (PNSN). The study covered 386 neonates with VLBW (≤1500 g), among which 262 cases of invasive infection were detected with predominance of CNS (123; 47%). Altogether, 100 CNS strains were analyzed. The resistance phenotypes were determined according to EUCAST. Resistance genes: mecA, ermA, ermB, ermC, msrA, aac(6')/aph(2''), ant(4')-Ia and aph(3')-IIIa were detected using multiplex PCR.

RESULTS

The most common species was S. epidermidis (63%), then S. haemolyticus (28%) and other CNS (9%). Among S. epidermidis, 98% of isolates were resistant to methicillin, 90% to erythromycin, 39% to clindamycin, 95% to gentamicin, 60% to amikacin, 36% to ofloxacin, 2% to tigecycline, 3% to linezolid and 13% to teicoplanin. Among S. haemolyticus isolates, 100% were resistant to methicillin, erythromycin and gentamicin, 18% to clindamycin, 50% to amikacin, 86% to ofloxacin, 14% to tigecycline and 4% to teicoplanin. No resistance to linezolid was detected for S. haemolyticus isolates. Moreover, all isolates of S. epidermidis and S. haemolyticus were susceptible to vancomycin. The mecA gene was detected in 98% of S. epidermidis isolates and all of S. haemolyticus ones. Among macrolide resistance isolates, the ermC was most common in S. epidermidis (60%) while msrA was prevalent in S. haemolyticus (93%). The ermC gene was indicated in all isolates with cMLSB, whereas mrsA was found in isolates with MSB phenotype. Of the aminoglycoside resistance genes, aac(6')/aph(2'') were present alone in 83% of S. epidermidis, whereas aac(6')/aph(2'') with aph(3')-IIIa were predominant in 84% of S. haemolyticus.

CONCLUSIONS

Knowing the epidemiology and antibiotic resistance of CNS isolated from invasive infection in VLBW neonates is a key step in developing targeted prevention strategies and reducing antibiotic consumption.

Genetic determinants of antimicrobial resistance in Gram positive bacteria from organic foods

Bacterial biocide resistance is becoming a matter of concern. In the present study, a collection of biocide-resistant, Gram-positive bacteria from organic foods (including 11 isolates from genus Bacillus, 25 from Enterococcus and 10 from Staphylococcus) were analyzed for genes associated to biocide resistance efflux pumps and antibiotic resistance. The only qac-genes detected were qacA/B (one Bacillus cereus isolate) and smr (one B. cereus and two Staphylococcus saprophyticus isolates). Efflux pump genes efrA and efrB genes were detected in Staphylococcus (60% of isolates), Bacillus (54.54%) and Enterococcus (24%); sugE was detected in Enterococcus (20%) and in one Bacillus licheniformis; mepA was detected in Staphylococcus (60%) and in one Enterococcus isolate (which also carried mdeA), and norE gene was detected only in one Enterococcus faecium and one S. saprophyticus isolate. An amplicon for acrB efflux pump was detected in all but one isolate. When minimal inhibitory concentrations (MICs) were determined, it was found that the addition of reserpine reduced the MICs by eight fold for most of the biocides and isolates, corroborating the role of efflux pumps in biocide resistance. Erythromycin resistance gene ermB was detected in 90% of Bacillus isolates, and in one Staphylococcus, while ereA was detected only in one Bacillus and one Staphyloccus, and ereB only in one Staphylococcus. The ATP-dependent msrA gene (which confers resistance to macrolides, lincosamides and type B streptogramins) was detected in 60% of Bacillus isolates and in all staphylococci, which in addition carried msrB. The lincosamide and streptogramin A resistance gene lsa was detected in Staphylococcus (40%), Bacillus (27.27%) and Enterococcus (8%) isolates. The aminoglycoside resistance determinant aph (3_)-IIIa was detected in Staphylococcus (40%) and Bacillus (one isolate), aph(2_)-1d in Bacillus (27.27%) and Enterococcus (8%), aph(2_)-Ib in Bacillus (one isolate), and the bifunctional aac(6_)1e-aph(2_)-Ia in Staphylococcus (20%), Enterococcus (8%) and Bacillus (one isolate). Chloramphenicol resistance cat gene was detected in Enterococcus (8%) and Staphylococcus (20%), and blaZ only in Staphylococcus (20%). All other antibiotic or biocide resistance genes investigated were not detected in any isolate. Isolates carrying multiple biocide and antibiotic determinants were frequent among Bacillus (36.36%) and Staphylococcus (50%), but not Enterococcus. These results suggest that biocide and antibiotic determinants may be co-selected.

Methicillin-resistant Staphylococcus capitis with reduced vancomycin susceptibility causes late-onset sepsis in intensive care neonates

BACKGROUND

Coagulase-negative staphylococci, mainly Staphylococcus epidermidis, are the most frequent cause of late-onset sepsis (LOS) in the neonatal intensive care unit (NICU) setting. However, recent reports indicate that methicillin-resistant, vancomycin-heteroresistant Staphylococcus capitis could emerge as a significant pathogen in the NICU. We investigated the prevalence, clonality and vancomycin susceptibility of S. capitis isolated from the blood of NICU infants and compared these data to adult patients.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted a retrospective laboratory-based survey of positive blood cultures in NICU infants ≥ 3 days of age (n = 527) and in adult ICU patients ≥ 18 years of age (n = 1473) who were hospitalized from 2004 to 2009 in two hospital centers in Lyon, France. S. capitis was the most frequent pathogen in NICU infants, ahead of S. epidermidis (39.1% vs. 23.5% of positive blood cultures, respectively). Conversely, S. capitis was rarely found in adult ICU patients (1.0%) compared to S. epidermidis (15.3%). S. capitis bloodstream isolates were more frequently resistant to methicillin when collected from NICU infants than from adult patients (95.6% vs. 53.3%, respectively). Furthermore, we collected and characterized 53 S. capitis bloodstream isolates from NICU infants and adult patients from six distant cities. All methicillin-resistant S. capitis isolates from NICU infants were clonally related as determined by pulsed-field gel electrophoresis. These isolates harbored a type V-related staphylococcal chromosomal cassette mec element, and constantly showed either vancomycin resistance (37.5%) or heteroresistance (62.5%). Conversely, the isolates that were collected outside of the NICU were genetically diverse and displayed much lower rates of vancomycin resistance and heteroresistance (7.7% and 23.1%, respectively).

CONCLUSIONS/SIGNIFICANCE

A clonal population of methicillin-resistant S. capitis strains has spread into several French NICUs. These isolates exhibit reduced susceptibility to vancomycin, which is the most widely used antimicrobial agent in the NICU setting.

Methicillin and aminoglycoside resistance in Staphylococcus aureus isolates from bovine mastitis and sequence analysis of their mecA genes

Although methicillin-resistant Staphylococcus aureus (MRSA) were generally isolated from human beings; these agents were recently isolated from various animal species. It has been shown that MRSA isolates are not only resistant to beta-lactam antibiotics, but can also be resistant to the other commonly used antibiotics. In this study, 18 phenotypic methicillin resistant S. aureus isolates from bovine mastitis cases were analyzed by PCR for the presence of mecA gene encoding methicillin resistance and aac (6′)/aph(2″), aph(3′)-IIIa and ant(4′)-Ia genes encoding aminoglycoside resistance. Out of 18 S. aureus isolates (oxacillin MICs, ≥4 μg/ml), 3 were positive for mecA gene. Only one from 3 mecA positive isolates was positive for genes encoding aminoglycoside-modifying enzymes and this isolate carried aac(6′)/aph(2″) in combination with aph(3′)-IIIa gene. The aph(3′)-IIIa gene was detected in 3 isolates. These three isolates carrying the aminoglycoside-modifying enzyme genes were resistant to gentamicin, kanamycin and neomycin. The mecA gene of 3 MRSA isolates was sequenced. All three mecA genes of these isolates were identical to that found in human MRSA strains, except a one-base substitution at nucleotide position 757. From the data presented in this study, it can be concluded that MRSA isolated from bovine mastitis may be originated from human beings, but further studies are needed to investigate the possibility of zoonotic transfer of MRSA.

Arginine catabolic mobile element is associated with low antibiotic resistance and low pathogenicity in Staphylococcus epidermidis from neonates

The arginine catabolic mobile element (ACME) in Staphylococci encodes several putative virulence factors. ACME appears to have been transferred from Staphylococcus epidermidis into Staphylococcus aureus and is strongly associated with the epidemic and virulent S. aureus USA300. We sought to determine the distribution of ACME in 128 S. epidermidis blood culture isolates from neonates and to assess ACME's impact on antibiotic resistance, biofilm production, invasive capacity, and host inflammatory response. ACME was detected in 15/64 (23%) invasive blood culture isolates and 26/64 (40%) blood culture contaminants (p = 0.02). ACME-positive S. epidermidis isolates displayed less antibiotic resistance (p < 0.001) and were collected from more mature neonates (p = 0.001). Biofilm production was more prevalent among ACME-negative isolates (61/87) compared with ACME positive (18/41; p = 0.004). Among the 64 children considered having an invasive infection, ACME did not influence the maximum C-reactive protein level. In an in vitro whole-blood sepsis model, there were no differences in the inflammatory response between ACME-positive and ACME-negative isolates. We conclude that ACME in S. epidermidis from neonates was associated with less antibiotic resistance and also does not seem to be associated with increased pathogenicity.

Prevalence of genes for aminoglycoside-modifying enzymes in Staphylococcus epidermidis isolates from orthopedic postsurgical and implant-related infections

Staphylococcus epidermidis, a main etiologic agent of implant-related infections, is showing increasing resistance to several antibiotic substances, among them the aminoglycosides, a class of drugs playing a relevant role in current medical protocols to prevent and treat clinical infections. Here we investigated the prevalence of aac(6')-Ie-aph(2''), aph(3')-IIIa, and ant(4') genes, encoding for the three forms of aminoglycoside-modifying enzymes (AME), responsible for resistance to aminoglycoside antibiotics, in 70 clinical isolates of S. epidermidis from orthopedic postsurgical and implant-related infections. In addition, ermA and ermC, the two most common staphylococcal genes conferring antibiotic resistance to macrolides, lincosamides, and streptogramin B (MLS(B)) were included in this investigation. All isolates were characterized by automated ribotyping, so that the presence of antibiotic resistance determinants was investigated in strains exhibiting different ribopatterns. Interestingly, combinations of coexisting AME genes appeared to be typical of specific ribopatterns. The aac(6')-Ie-aph(2'') gene was the most prevalent AME gene, being observed in 44% of the isolates. As far as the determinants for MLS(B) antibiotics are concerned, the ermC gene was observed in 33% of the isolates, while ermA was detected in a single isolate. These results provide a detailed characterization in terms of antibiotic resistance determinants of clones of S. epidermidis frequently isolated from implant orthopedic infections, providing useful indications for more effectual future strategies of infection prevention/eradication based on the incorporation of antibiotic drugs in biomaterials.

Biofilm formation by Staphylococcus haemolyticus

Infections due to coagulase-negative staphylococci (CoNS) most frequently occur after the implantation of medical devices and are attributed to the biofilm-forming potential of CoNS. Staphylococcus haemolyticus is the second most frequently isolated CoNS from patients with hospital-acquired infections. There is only limited knowledge of the nature of S. haemolyticus biofilms. The aim of this study was to characterize S. haemolyticus biofilm formation. We analyzed the biofilm-forming capacities of 72 clinical S. haemolyticus isolates. A detachment assay with NaIO(4), proteinase K, or DNase was used to determine the main biofilm components. Biofilm-associated genes, including the ica operon, were analyzed by PCR, and the gene products were sequenced. Confocal laser scanning microscopy (CLSM) was used to elucidate the biofilm structure. Fifty-three isolates (74%) produced biofilms after growth in Trypticase soy broth (TSB) with glucose, but only 22 (31%) produced biofilms after growth in TSB with NaCl. It was necessary to dissolve the biofilm in ethanol-acetone to measure the optical density of the full biofilm mass. DNase, proteinase K, and NaIO(4) caused biofilm detachment for 100%, 98%, and 38% of the isolates, respectively. icaRADBC and polysaccharide intercellular adhesin (PIA) production were found in only two isolates. CLSM indicated that the biofilm structure of S. haemolyticus clearly differs from that of S. epidermidis. We conclude that biofilm formation is a common phenotype in clinical S. haemolyticus isolates. In contrast to S. epidermidis, proteins and extracellular DNA are of functional relevance for biofilm accumulation, whereas PIA plays only a minor role. The induction of biofilm formation and determination of the biofilm mass also needed to be optimized for S. haemolyticus.

Antibiotic resistance patterns of coagulase-negative staphylococcus strains isolated from blood cultures of septicemic patients in Turkey

The aim of this study is to determine antibiotic resistance patterns and slime production characteristics of coagulase-negative Staphylococci (CoNS) caused nosocomial bacteremia. A total of 200 CoNS strains were isolated from blood samples of patients with true bacteremia who were hospitalized in intensive care units and in other departments of Istanbul University Cerrahpasa Medical Hospital between 1999 and 2006. Among 200 CoNS isolates, Staphylococcus epidermidis was the most prevalent species (87) followed by Staphylococcus haemolyticus (23), Staphylococcus hominis (19), Staphylococcus lugdunensis (18), Staphylococcus capitis (15), Staphylococcus xylosus (10), Staphylococcus warneri (8), Staphylococcus saprophyticus (5), Staphylococcus lentus (5), Staphylococcus simulans (4), Staphylococcus chromogenes (3), Staphylococcus cohnii (1), Staphylococcus schleiferi (1), and Staphylococcus auricularis (1). Resistance to methicillin was detected in 67.5% of CoNS isolates. Methicillin-resistant CoNS strains were determined to be more resistant to antibiotics than methicillin-susceptible CoNS strains. Resistance rates of methicillin-resistant and methicillin-susceptible CoNS strains to the antibacterial agents, respectively, were as follows: gentamicin 90% and 17%, erythromycin 80% and 37%, clindamycin 72% and 18%, trimethoprim-sulfamethoxazole 68% and 38%, ciprofloxacin 67% and 23%, tetracycline 60% and 45%, chloramphenicol 56% and 13% and fusidic acid 25% and 15%. None of the strains were resistant to vancomycin and teicoplanin. Slime production was detected in 86 of 200 CoNS strains. Resistance to methicillin was found in 81% of slime-positive and in 57% of slime-negative strains. Our results indicated that there is a high level of resistance to widely used agents in causative methicillin-resistant CoNS strains. However fusidic acid has the smallest resistance ratio, with the exception of glycopeptides. Additionally, most S. epidermidis strains were slime-positive, with statistically significant (p<0.001) association between methicillin resistance and slime production.

Widespread dissemination of aminoglycoside resistance genes armA and rmtB in Klebsiella pneumoniae isolates in Taiwan producing CTX-M-type extended-spectrum beta-lactamases

Among 235 extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL) isolates collected from a nationwide surveillance performed in Taiwan, 102 (43.4%) were resistant to amikacin. Ninety-two of these 102 (90.2%) isolates were carrying CTX-M-type beta-lactamases individually or concomitantly with SHV-type or CMY-2 beta-lactamases. The armA and rmtB alleles were individually detected in 44 and 37 of these 92 isolates, respectively. One isolate contained both armA and rmtB. The coexistence of the aac(6')-Il and rmtB genes was detected in three isolates. CTX-M-type beta-lactamase genes belonging to either group 1 (CTX-M-3 and CTX-M-15) or group 9 (CTX-M-14) were found in all armA- or rmtB-bearing ESBL-producing K. pneumoniae isolates, and all were conjugatively transferable. All except one of the isolates bearing armA produced CTX-M enzymes of group 1, and the remaining isolate bearing armA produced a group 9 CTX-M-type beta-lactamase. On the contrary, in the majority of rmtB carriers, the CTX-M-type beta-lactamase belonged to group 9 (62.2%). Molecular typing revealed that the amikacin-resistant ESBL-producing K. pneumoniae isolates were epidemiologically unrelated, indicating that the acquisition of resistance was not through the spread of a resistant clone or a resistance plasmid. A tandem repeat or multiple copies of bla(CTX-M-3) were found in some armA-bearing isolates. An ISEcp1 insert was found in all CTX-M ESBL-producing K. pneumoniae isolates carrying armA or rmtB. In conclusion, the concomitant presence of a 16S rRNA methylase gene (armA or rmtB) and bla(CTX-M) among amikacin-resistant ESBL-producing K. pneumoniae isolates is widespread in Taiwan.

Clonality and occurrence of genes encoding antibiotic resistance and biofilm in methicillin-resistant Staphylococcus epidermidis strains isolated from catheters and bacteremia in neutropenic patients

Thirty methicillin-resistant Staphylococcus epidermidis strains isolated from catheters and blood cultures from neutropenic patients were studied. They were classified into 17 multidrug-resistance patterns. Polymerase cahin reaction analysis revealed that methicillin resistance was encoded by the mecA gene in all strains, and aminoglycosides resistance was due to aac(6')-Ie-aph(2'')-Ia (23 strains), ant(4')-Ia (13), and aph(3')-IIIa (1) genes. The aac(6')-Ie-aph(2'')-Ia gene was detected concomitantly with aph(3')-IIIa, and ant(4')-Ia genes in one and nine strains, respectively. Erythromycin resistance was encoded by the ermC (11 strains), ermA (6), and msrA (2) genes. The ermC gene was inducibly expressed in five strains, whereas the ermA was exclusively constitutively expressed. The icaA and icaC genes were detected in 19 strains; however, biofilm production was observed in only 16 strains. Most strains harbored multiple plasmids of variable sizes ranging from 2.2 to 70 kb, and two strains were plasmid-free. PFGE identified 15 distinct PFGE types, and five predominant genotypes were found. Our study showed the occurrence of complex genetic phenomenons. In unrelated strains, evidence of horizontal transfer of antibiotic-encoding genes and/or ica operon, and in indistinguishable strains, there is a quite good likelihood of independent steps of loss and/or gain of these genes. This genome dynamicity might have enhanced the invasiveness power of these methicillin-resistant S epidermidis strains.

Clonal dissemination of Staphylococcus epidermidis in an oncology ward

Coagulase-negative staphylococci (CoNS) are the main cause of catheter-related infections, especially among immunosuppressed and neutropenic patients, as well as a source of bacterial contamination in blood cultures. Using biochemical identification and pulsed-field gel electrophoresis (PFGE), we sought to identify possible clonal isolates of bacteremia in patients with central lines in an oncology ward (OW), with comparison to isolates that were recovered by venipuncture from an adult emergency room (ER). A total of 243 CoNS isolates were identified to species level from the OW (126) and ER (117), with Staphylococcus epidermidis isolates being the most common (OW, 79.4%; ER, 45.3%). PFGE demonstrated a predominant clone of S. epidermidis (major subtype A) which was 35.5 times more likely (odds ratio [OR] = 35.5; 95% confidence interval [CI] = 4.7 to 267.0; P < 0.00001) to be present in the OW versus the ER. These (CoNS or major subtype A) isolates were more frequently resistant to gentamicin (OR = 2.83; 95% CI = 1.23 to 6.53; P = 0.016) and less frequently resistant to trimethoprim-sulfamethoxazole (OR = 0.38; 95% CI = 0.18 to 0.80; P = 0.013). Subset analysis of S. epidermidis isolates 2 years after the study period showed the persistence of the clone of major subtype A within the OW. This study demonstrates the presence of a predominant clone among central line isolates from an OW that is not present in CoNS venipuncture isolates from an ER.

Neonatal immune responses to coagulase-negative staphylococci

PURPOSE OF REVIEW

Coagulase-negative staphylococci have emerged as the most common nosocomial pathogen in neonatal intensive care units worldwide. Our understanding of the interactions between coagulase-negative staphylococci and the immune system is incomplete, especially in the newborn. This review summarizes current knowledge on the human immune response to coagulase-negative staphylococci, with particular emphasis on the neonatal innate immune system.

RECENT FINDINGS

There are very limited data on innate immune responses to coagulase-negative staphylococci in neonates. Levels of serum proteins, including transplacental anti-coagulase-negative staphylococci immunoglobulin and complement, correlate with gestational age, and this relative deficiency in preterm infants contributes to their suboptimal opsonization and impaired bacterial killing of coagulase-negative staphylococci. In adults, coagulase-negative staphylococci elicit significant cytokine responses in vitro, which are probably partly mediated by Toll-like receptors, including Toll-like receptor type 2, but these pathways have not been characterized in the high-risk neonatal population.

SUMMARY

The susceptibility of human preterm neonates to coagulase-negative staphylococci relates partly to the immaturity of the neonatal immune response. Strategies to reduce the burden of coagulase-negative staphylococci infections require a thorough understanding of host-pathogen interactions, particularly the engagement of coagulase-negative staphylococci by the neonatal innate immune system.

Aminoglycoside Resistance in Members of theStaphylococcus sciuriGroup

This study investigated the prevalence of aminoglycoside resistance and genes encoding aminoglycoside-modifying enzymes in members of the Staphylococcus sciuri group. A total of 304 S. sciuri group member isolates (284 S. sciuri, 12 S. lentus, and 8 S. vitulinus) from humans (n = 34), animals (n = 133), and environmental sources (n = 137; out-hospital and hospital environment, food) were examined for their susceptibility to amikacin, gentamicin, isepamicin, kanamycin, neomycin, netilmicin, sisomicin, streptomycin, and tobramycin. The overall prevalence of resistance to aminoglycosides was low at 12.1%. Resistance to single aminoglycosides ranged from 0% to 7.2%. The aac(6')-Ie/aph(2"), ant(4')-Ia, and aph(3')-IIIa genes, either alone or in combination, were found in 16 out of 19 isolates showing resistance to nonstreptomycin aminoglycosides. Among the 22 isolates that showed resistance to streptomycin, the genes str and ant(6)-Ia were identified in 18 and 4 isolates, respectively.

Clonality of slime-producing methicillin-resistant coagulase-negative staphylococci disseminated in the neonatal intensive care unit of a university hospital

Methicillin-resistant coagulase-negative staphylococci (MR-CNS) (n = 132), isolated from pre-term neonates, were analysed to determine their antibiotic resistance patterns, clonal distribution, biofilm production and the presence of the ica operon. All MR-CNS were multiresistant, and 89% produced slime. A major clone was identified (77 isolates) among 115 Staphylococcus epidermidis isolates. Ten of 16 Staphylococcus haemolyticus isolates also belonged to a single clone. Most (80%) slime-positive isolates possessed all the ica genes tested, while the remaining 23 (20%) had a variety of gene combinations. The entire ica cluster was detected in three of 15 slime-negative isolates. One major and two minor slime-positive, multiresistant MR-CNS clones had disseminated among hospitalised pre-term neonates.

Coagulase-negative staphylococcal infections in the neonate and child: an update

Coagulase-negative staphylococcus (CONS) infection is the most common bloodstream infection treated in neonatal and pediatric intensive care units and significantly impacts patient mortality and morbidity. Staphylococcus epidermidis is the most common CONS species isolated clinically and investigated for its pathogenicity and virulence. Difficulties exist in the differentiation of CONS infection from culture contamination in clinical specimens, as CONS is a common skin commensal. Most CONS isolates have the mecA gene and exhibit beta-lactam resistance. The glycopeptide antibiotics, such as vancomycin, are the mainstay in therapy, although resistance has been reported. Arbekacin, linezolid, and streptogramins are newer antibiotics being evaluated as alternatives to glycopeptides. Monoclonal and polyclonal antibodies have been developed against the cell-wall components of staphylococcus and may hold promise for immune prophylaxis and treatment of CONS infection.

Presence of new mecA and mph(C) variants conferring antibiotic resistance in Staphylococcus spp. isolated from the skin of horses before and after clinic admission

Because of the frequency of multiple antibiotic resistance, Staphylococcus species often represent a challenge in incisional infections of horses undergoing colic surgery. To investigate the evolution of antibiotic resistance patterns before and after preventative peri- and postoperative penicillin treatment, staphylococci were isolated from skin and wound samples at different times during hospitalization. Most staphylococci were normal skin commensals and belonged to the common coagulase-negative group. In some cases they turned out to be opportunistic pathogens present in wound infections. MICs were determined for 12 antibiotics, and antibiotic resistance genes were detected by microarray. At hospital admission, horses harbored staphylococci that were susceptible to antibiotics or resistant to one group of drugs, mainly due to the presence of new variants of the methicillin and macrolide resistance genes mecA and mph(C), respectively. After 3 days, the percentage of Staphylococcus isolates displaying antibiotic resistance, as well as the number of resistance genes per isolate, increased moderately in hospitalized horses without surgery or penicillin treatment but dramatically in hospitalized horses after colic surgery as well as penicillin treatment. Staphylococcus species displaying multiple resistance were found to harbor mainly genes conferring resistance to beta-lactams (mecA and blaZ), aminoglycosides [str and aac(6')-Ie-aph(2')-Ia], and trimethoprim [dfr(A) and dfr(D)]. Additional genes conferring resistance to macrolides [mph(C), erm(C), and erm(B)], tetracycline [tet(K) and tet(M)], chloramphenicol [cat(pC221) and cat(pC223)], and streptothricin (sat4) appeared in several strains. Hospitalization and preventive penicillin use were shown to act as selection agents for multidrug-resistant commensal staphylococcal flora.

Coagulase-negative staphylococcal sepsis in neonates. Association between antibiotic resistance, biofilm formation and the host inflammatory response

BACKGROUND

Coagulase-negative staphylococci (CoNS) are the most prevalent pathogens causing late onset sepsis in neonates. They are often multiresistant to antibiotics, and the ability to form biofilm is considered their main virulence determinant.

METHODS

During a 12-year period, we identified 150 neonates having 164 suspected septic episodes with growth of CoNS in blood culture. We examined the relationship between antibiotic resistance, phenotypic biofilm production and genetic determinants for biofilm formation in different CoNS species and their correlation with neonatal inflammatory response.

RESULTS

Eighty-five episodes were classified as true sepsis, and 79 episodes of CoNS growth in blood culture were considered contaminations. Sixty-one percent of Staphylococcus epidermidis isolates produced biofilm compared with 26% of CoNS non-epidermidis (P < 0.001). We observed no difference in phenotypic biofilm production or genetic determinants for biofilm formation between invasive isolates and contaminants. C-reactive protein levels as a marker of inflammatory response were higher in CoNS sepsis caused by methicillin and aminoglycoside resistant versus susceptible isolates (P = 0.031). In contrast, there was a significant association between a lower C-reactive protein response and biofilm-positive isolates (P = 0.018). Antibiotic resistance was significantly correlated with biofilm production in S. epidermidis, but not in other CoNS species.

CONCLUSIONS

CoNS sepsis with biofilm-forming strains was associated with a decreased host inflammatory response, potentially limiting the immune system to counteract the infection. The impact of antibiotic resistance and virulence determinants on clinical outcome of neonatal CoNS sepsis warrants additional clinical studies.

Genetic methods for detection of antimicrobial resistance

Accurate and rapid diagnostic methods are needed to guide antimicrobial therapy and infection control interventions. Advances in real-time PCR have provided a user-friendly, rapid and reproducible testing platform catalysing an increased use of genetic assays as part of a wider strategy to minimize the development and spread of antimicrobial-resistant bacteria. In this review we outline the principal features of genetic assays in the detection of antimicrobial resistance, their advantages and limitations, and discuss specific applications in the detection of methicillin-resistant Staphylococcus aureus, glycopeptide-resistant enterococci, aminoglycoside resistance in staphylococci and enterococci, broad-spectrum resistance to beta-lactam antibiotics in gram-negative bacteria, as well as genetic elements involved in the assembly and spread of antimicrobial resistance.