Detection of genes encoding aminoglycoside-modifying enzymes in staphylococci by polymerase chain reaction and dot blot hybridization

Effect of Ceftaroline, Vancomycin, Gentamicin, Macrolides, and Ciprofloxacin against Methicillin-Resistant Staphylococcus aureus Isolates: An In Vitro Study

Background: Methicillin-resistant Staphylococcus aureus (MRSA) infection remains a challenging threat because of limited treatment options. Ceftaroline was identified as having potent anti-MRSA activity. Aim: To evaluate the susceptibility of MRSA to gentamicin, macrolides, ciprofloxacin, vancomycin, and ceftaroline and to perform molecular characterization of different resistance genes as aminoglycoside modifying enzyme genes, ermA and ermC, and vanA and vanB genes. Patients and Methods: One hundred non-duplicate MRSA strains were isolated from different samples of hospitalized patients in Cairo University teaching hospitals from November 2015 to August 2016. Determination of antibiotic susceptibility was done using disk diffusion test and minimum inhibitory concentration followed by detection of resistance genes by multiplex polymerase chain reaction (PCR). Results: Of 100 MRSA isolates, 63 (63%) were resistant to gentamicin, erythromycin, clindamycin, and ciprofloxacin, however, all were sensitive to ceftaroline. Fifteen isolates (15%) were vancomycin intermediate resistant and were sensitive to ceftaroline as well. Conclusion: Ceftaroline was potent against MRSA, which was found to be non-susceptible to vancomycin, ciprofloxacin, erythromycin, clindamycin, and gentamicin and it may represent a successful treatment for MRSA infections.

The Prevalence of Colistin Resistant Strains and Antibiotic Resistance Gene Profiles in Funan River, China

Anthropogenic activities near urban rivers may have significantly increased the acquisition and dissemination of antibiotic resistance. In this study, we investigated the prevalence of colistin resistant strains in the Funan River in Chengdu, China. A total of 18 mcr-1-positive isolates (17 Escherichia coli and 1 Enterobacter cloacae) and 6 mcr-3-positive isolates (2 Aeromonas veronii and 4 Aeromonas hydrophila) were detected, while mcr-2, mcr-4 and mcr-5 genes were not detected in any isolates. To further explore the overall antibiotic resistance in the Funan River, water samples were assayed for the presence of 15 antibiotic resistance genes (ARGs) and class 1 integrons gene (intI1). Nine genes, sul1, sul2, intI1, aac(6')-Ib-cr, bla _CTX-M, tetM, ermB, qnrS, and aph(3')-IIIa were found at high frequencies (70-100%) of the water samples. It is worth noting that mcr-1, bla _KPC, bla _NDM and vanA genes were also found in water samples, the genes that have been rarely reported in natural river systems. The absolute abundance of selected antibiotic resistance genes [sul1, aac(6')-Ib-cr, ermB, bla_CTX-M, mcr-1, and tetM] ranged from 0 to 6.0 (log₁₀ GC/mL) in water samples, as determined by quantitative polymerase chain reaction (qPCR). The sul1, aac(6')-Ib-cr, and ermB genes exhibited the highest absolute abundances, with 5.8, 5.8, and 6.0 log₁₀ GC/mL, respectively. The absolute abundances of six antibiotic resistance genes were highest near a residential sewage outlet. The findings indicated that the discharge of resident sewage might contribute to the dissemination of antibiotic resistant genes in this urban river. The observed high levels of these genes reflect the serious degree of antibiotic resistant pollution in the Funan River, which might present a threat to public health.

Molecular characteristics of antimicrobial resistance and virulence determinants of Staphylococcus aureus isolates derived from clinical infection and food

BACKGROUND

Staphylococcus aureus (S. aureus) is an important human etiologic agent. An investigation of the characteristics of common genotypes of S. aureus relating to pathogenicity and antibiotic resistance may provide a foundation to prevent infection.

METHODS

This study collected 275 S. aureus isolates from Zhengzhou city in China, including 148 isolates from patient samples and 127 isolates from ready-to-eat food samples. Antimicrobial susceptibility testing was performed using the broth dilution method. Molecular characteristics of antimicrobial resistance, virulence, and genotypes were identified by polymerase chain reaction (PCR).

RESULTS

In total, 34.18% (94/275) of S. aureus isolates were MRSA. Compared with food isolates, clinical isolates had significantly higher antibiotic resistance rates, carrying resistance genes such as acc(6')/aph(2'), aph(3')-III, ermA, and ermB and virulence genes such as tetM, sea, seb, pvl, and etb. MRSA-t030-agrI-SCCmecIII and MSSA-t002-agrII were the most common strain types among clinical strains, and MRSA-t002-agrII-SCCmecIII and MSSA-t002-agrII were the most common strain types among food strains. Additionally, some strains in the agr group were also spa type-specific, suggesting that there may be phenotypic consistency.

CONCLUSION

Clinical isolates contained higher numbers of resistance genes and demonstrated higher antibiotic resistance, while 2 source strains exhibited high toxicity. These results indicate that bacteria with different origins may have undergone different evolutionary processes. As resistance and virulence factors in food bacteria can be transmitted to humans, food handlers should strictly follow hygienic measures during food production to ensure the safety of human consumers.

Distribution of Aminoglycoside-Modifying Enzymes and Molecular Analysis of the Coagulase Gene in Clinical Isolates of Methicillin-Resistant and Methicillin-Susceptible Staphylococcus aureus

Enzymatic alteration of aminoglycosides by aminoglycoside-modifying enzymes (AMEs) is the major mechanism of resistance to aminoglycosides. The purpose of this study was to determine the frequency of AME genes, staphylococcal chromosomal cassette mec (SCCmec) types, and molecular analysis of the coagulase (coa) gene in Staphylococcus aureus strains isolated from clinical specimens. Totally, 102 S. aureus were tested by disk diffusion and microbroth dilution methods for susceptibility to aminoglycosides. AMEs genes and SCCmec types were determined by multiplex polymerase chain reaction (PCR). For polymorphism analysis, the 3' end region of the coa gene was amplified by PCR and the products were then subjected to restriction digestion with HaeIII enzyme. Of the 102 S. aureus, 42 (41.2%) were methicillin-resistant S. aureus (MRSA). Thirty-five (83%) of MRSA strains were resistant to kanamycin, 32 (76.2%) to tobramycin, 30 (71.4%) to gentamicin, 25 (59.5%) to amikacin, and 10 (23.8%) to netilmicin. The aac(6')-Ie-aph(2″) was the most frequent gene among MRSA isolates 19 (45.2%), followed by aph(3')-IIIa 8 (19%), ant(4')-Ia 6 (14.3%), and aph(2″)-Id 2 (4.8%). SCCmec types included type I 10 (23.8%), II 1 (2.4%), III 21 (50%), and IV 7 (16.7%). Three (7.2%) isolates were nontypeable. Digestion of the PCR products of the coa gene yielded 19 distinct restriction fragment length polymorphism patterns. In conclusion, given the alarming rate of resistance to aminoglycosides among MRSA, the monitoring of aminoglycoside resistance and AME genes should be performed to limit the spread of aminoglycoside resistance among MRSA isolates. Several variants of the coa gene were found in the studied isolates, although the majority of the MRSA isolates belonged to a limited number of coagulase types.

Nationwide molecular epidemiology of methicillin-resistant Staphylococcus aureus responsible for horse infections in France

Background

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) isolated in horse infections is not well documented, especially in France. The aim of the study was to evaluate the prevalence of MRSA isolates in horse infections from 2007 to 2013 in France and to characterize phenotypically and genotypically this collection.

Results

Out of 1393 S. aureus horse isolates, 85 (6.1%) were confirmed to be MRSA. Interestingly, the prevalence of MRSA significantly increased from 2007–2009 to 2010–2013 (0.7 vs. 9.5%, P <0.0001). Resistance to methicillin was due to the presence of the mecA gene in 84 strains (98.8%) while one strain (1.2%) possessed the mecC gene. The vast majority of the strains (83/85, 97.6%) was resistant to at least three different classes of antibiotics. Multi-locus sequence typing (MLST) showed that MRSA strains belonged mainly since not all belong to two sequence types (STs): ST398 (53/85, 62.4%) and ST8 (28/85, 32.9%). It is worth to note that all ST398 MRSA isolates were detected in the period 2010–2013. Other molecular typing methods were also used, such SCC_mec analysis, spa typing and rep-PCR (Diversilab, bioMérieux). All these four techniques were in good agreement, with spa typing and rep-PCR being more discriminative than MLST and SCC_mec typing.

Conclusions

This study is the first epidemiological study in France with extensive characterization of MRSA isolates associated with horse infections in stud farms. It shows that there is a significant increase of MRSA prevalence between 2007 and 2013, which mainly results from the spread of ST398 clones. It also highlights the importance of horses as a potential reservoir of important antimicrobial resistance genes.

Frequency of Aminoglycoside-Resistance Genes in Methicillin-Resistant Staphylococcus aureus (MRSA) Isolates from Hospitalized Patients

Background

Staphylococcus aureus is one of the most important causative agents in community- and hospital-acquired infections. Aminoglycosides are powerful bactericidal drugs that are often used in combination with beta-lactams or glycopeptides to treat staphylococcal infections.

Objectives

The main objective of the present study was to determine the prevalence of aminoglycoside resistance among methicillin-resistant Staphylococcus aureus (MRSA) isolates in hospitalized patients in Sari and Tehran, Iran.

Methods

In this study, 174 MRSA strains isolated from different clinical samples, such as blood, sputum, tracheal exudates, bronchus, pleura, urine, wounds, and catheters, were collected from hospitalized patients in Tehran and Sari during 2014. Antibiotic susceptibility testing was performed against nine antibiotics with the Kirby-Bauer disk diffusion method according to CLSI guidelines. The MRSA strains were examined with oxacillin and cefoxitin disks. MRSA was then validated by detection of the mecA gene. PCR was used to evaluate the prevalence of the aminoglycoside-resistance genes aac (6’)-Ie/aph (2”), aph (3’)-IIIa, and ant (4’) among the MRSA isolates.

Results

The results of drug susceptibility testing showed that the highest rate of resistance was against erythromycin in Tehran (84.4%) and gentamicin (71.7%) in Sari. All isolates were sensitive to vancomycin, and all strains harbored the mecA gene. The aac (6’)-Ie/aph (2”), aph (3’)-IIIa, and ant (4’)-Ia genes were detected among 134 (77%), 119 (68.4%), and 122 (70.1%) of the isolates, respectively.

Conclusions

The present study showed a high prevalence of aminoglycoside-resistance genes among MRSA isolates in two cities in Iran.

Frequency distribution of genes encoding aminoglycoside modifying enzymes in uropathogenic E. coli isolated from Iranian hospital

Background

Escherichia coli is considered as the most common cause of urinary tract infection (UTI) and acquired multiple resistances to a wide range of antibiotics such as aminoglycosides. Enzymatic alteration of aminoglycosides (AMEs) by aminoglycoside- modifying enzymes is the main mechanism of resistance to these antibiotics in E. coli. The aim of this study was detection and investigation of frequency of genes encoding aminoglycoside modifying enzymes (aac(3)-IIa and ant(2′′)-Ia) in UPEC isolated from hospitalized patients in teaching hospital of Tehran, Iran.

Findings

A total of 276 UPEC were obtained from Urine samples in a hospital from Tehran. Antibiotic susceptibility to aminoglycosides was determined by disk diffusion method according CLSI guidelines in UPEC isolates. MICs of target antibiotics were determined by agar dilution method. All isolates were screened for the presence of the AMEs genes using the PCR. The results of disk diffusion showed 21%, 24.6%, 23.18%, 3.62% and 6.15% of isolates were resistant to Gentamicin, Tobramycin, Kanamicin, Amikacin and Netilmicin respectively. The agar dilution’s results (MICs) were high, 66.19% for Gentamicin. The aac (3)-IIa and ant(2″)-Ia genes were detected in (78.87%) and 47.88% of isolates respectively.

Conclusions

This study shows the high frequency of genes encoding (AMEs) aac(3)-IIa and ant(2”)-Ia genes and their relationship between different aminoglycoside resistance phenotypes.

Diversity of antibiotic resistance genes and staphylococcal cassette chromosome mec elements in faecal isolates of coagulase-negative staphylococci from Nigeria

BACKGROUND

Coagulase-negative staphylococci (CoNS) are opportunistic pathogens found as colonisers of the human gut. This study was carried out to examine the genetic resistance mechanisms in faecal isolates of CoNS. The study investigated 53 non-duplicate CoNS isolates obtained from the fresh stool samples of apparently healthy subjects in the community of Ile-Ife, South-Western Nigeria. Antibiotic susceptibility testing was assessed by the disc diffusion test while antibiotic resistance genes were analysed by PCR. mecA positive isolates were analysed by Staphylococcal Chromosome Cassette mec (SCCmec) and cassette chromosome recombinase (ccr) complex typing methods.

RESULTS

Resistance genes were detected only in isolates that showed resistance by phenotypic screening. The aac(6')-aph(2") gene was detected in all the three isolates resistant to gentamicin. Four of the five erythromycin resistant isolates were positive for the ermC gene, the remaining isolate carried the msrA gene. The tetK gene was detected in 6 of the 7 tetracycline resistant isolates while 4 possessed the tetM gene. Three of the isolates (S. haemolyticus, S. xylosus and S. capitis) had both genes. Several SCCmec types were found: SCCmec I- ccrABβ2-α2 (4 isolates: 3 S. epidermidis, 1 S. warneri), SCCmecIVb- ccrABβ2-α3 (1 isolate: S. epidermidis), SCCmecIVd- ccrABβ2-α3 (8 isolates: 3 S. epidermidis, 2 S. xylosus, 1 S. saprophyticus, 1 S. warneri, 1 S. capitis), and untypable (2 isolates: S. epidermidis).

CONCLUSION

This genetic background could be a reservoir for interspecies gene transfer among CoNS and S. aureus in the intestinal tract.

Emergence of methicillin-resistant Staphylococcus aureus in the Maternity Hospital, Kuwait

OBJECTIVE

To establish the relatedness of methicillin-resistant Staphylococcus aureus (MRSA) isolates in the Maternity Hospital, Kuwait.

MATERIALS AND METHODS

A total of 22 MRSA were isolated from 20 neonates and 1 mother in the Special Care Unit, Maternity Hospital, Kuwait. They were characterized using antibiogram, pulsed-field gel electrophoresis (PFGE), SCCmec typing, spa typing and multi locus sequence typing (MLST), and were screened for genes encoding Panton Valentine leukocidin (PVL) and capsular polysaccharide types 5 and 8.

RESULTS

The isolates were resistant to cadmium acetate (n = 22 or 100%), trimethoprim (n = 13 or 59.1%), gentamicin (n = 7 or 31.8%), ciprofloxacin (n = 5 or 22.7%), erythromycin and clindamycin (n = 2 or 9.1%), tetracycline (n = 2 or 9.1%) and fusidic acid (n = 2 or 9.1%). Eight isolates contained genes for PVL while 15 and 6 carried genes for types 5 and 8 capsular polysaccharide, respectively. Molecular typing distinguished 12 clones. Ten of these clones consisted of 20 isolates belonging to ST60-SCCmec-IV-t3935 (5 isolates), ST6-SCCmec-IV-t6269 (4 isolates), ST194-SCCmec-IV-t6892 (3 isolates), ST1-SCCmec-V-t2962 (2 isolates) and 1 isolate each of ST77-SCCmec-IV-t339, ST935-SCCmec-V-t1084, ST1317-SCCmec-V-t1548, ST9-SCCmec-V-t5801, ST627-SCCmec-IV-t1340 and ST2148-SCCmec-IV-t2810.

CONCLUSION

The study demonstrated the emergence of MRSA including novel ST60 and ST194 clones at the Maternity Hospital in Kuwait.

Surprising alteration of antibacterial activity of 5"-modified neomycin against resistant bacteria

A facile synthetic protocol for the production of neomycin B derivatives with various modifications at the 5'' position has been developed. The structural activity relationship (SAR) against aminoglycoside resistant bacteria equipped with various aminoglycoside-modifying enzymes (AMEs) was investigated. Enzymatic and molecular modeling studies reveal that the superb substrate promiscuity of AMEs allows the resistant bacteria to cope with diverse structural modifications despite the observation that several derivatives show enhanced antibacterial activity compared to the parent neomycin. Surprisingly, when testing synthetic neomycin derivatives against other human pathogens, two leads exhibit prominent activity against both methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) that are known to exert a high level of resistance against clinically used aminoglycosides. These findings can be extremely useful in developing new aminoglycoside antibiotics against resistant bacteria. Our result also suggests that new biological and antimicrobial activities can be obtained by chemical modifications of old drugs.

Aminoglycosides resistance in clinical isolates of Staphylococcus aureus from a University Hospital in Bialystok, Poland

Staphylococcus aureus obtained from a University Hospital in Poland were characterized in relation to resistance to aminoglycoside antibiotics and the distribution of the genes encoding the most clinically relevant aminoglycoside modifying enzymes (AMEs). Of a total of 118 S. aureus, 45 (38.1%) isolates were found to be resistant to at least one of the tested antibiotics. All aminoglycoside resistant isolates except one 44 (97.8%) were resistant to kanamycin. The majority of strains 37 (82.2%) and 32 (71.1%) expressed resistance to neomycin and tobramycin, respectively. Eleven strains (24.4%) were resistant to gentamicin or amikacin. All S. aureus strains were sensitive to netilmicin. The most prevalent resistance gene was aac(6')-Ie+aph(2') found in 13 (28.9%) strains and 12 (26.7%) isolates carried ant(4')-Ia gene, whilst aph(3')-IIIa gene was detected in only 7 (15.6%) isolates. Additionally, the ant(6)-Ia and str genes were detected in 14 (31.1%) and 2 (4.4%) strains, respectively. Ten (22.2%) strains resistant to amikacin, tobramycin, kanamycin or neomycin did not harbor any of the above-noted genes.

Reverse engineering antibiotic sensitivity in a multidrug-resistant Pseudomonas aeruginosa isolate

Antibiotic resistance is a pervasive and growing clinical problem. We describe an evaluation of a reverse engineering approach for identifying cellular mechanisms and genes that could be manipulated to increase antibiotic sensitivity in a resistant Pseudomonas aeruginosa isolate. We began by chemically mutating a broadly resistant isolate of P. aeruginosa and screening for mutants with increased sensitivity to the aminoglycoside amikacin, followed by performing whole-genome transcriptional profiling of the mutant and wild-type strains to characterize the global changes occurring as a result of the mutations. We then performed a series of assays to characterize the mechanisms involved in the increased sensitivity of the mutant strains. We report four primary results: (i) mutations that increase sensitivity occur at a high frequency (10(-2)) relative to the frequency of those that increase resistance (10(-5) to 10(-10)) and occur at a frequency 10(4) higher than the frequency of a single point mutation; (ii) transcriptional profiles were altered in sensitive mutants, resulting in overall expression patterns more similar to those of the sensitive laboratory strain PAO1 than those of the parental resistant strain; (iii) genes found from transcriptional profiling had the more dramatic changes in expression-encoded functions related to cellular membrane permeability and aminoglycoside modification, both of which are known aminoglycoside resistance mechanisms; and finally, (iv) even though we did not identify the specific sites of mutation, several different follow-up MIC assays suggested that the mutations responsible for increased sensitivity differed between sensitive mutants.

Characterisation of non-multiresistant methicillin-resistant Staphylococcus aureus (including EMRSA-15) in Kuwait Hospitals

This study characterised non-multiresistant methicillin-resistant Staphylococcus aureus (nmMRSA) isolates from Kuwait hospitals to ascertain whether they were community-acquired MRSA (CA-MRSA). Forty-two nmMRSA isolates obtained between July 2001 and October 2003 were analysed by staphylococcal cassette chromosome mec (SCCmec) typing, bacteriophage typing, production of Panton-Valentine leukocidin (PVL), urease and staphylococcal enterotoxins A, B, C and D, TSST-1, and by pulsed-field gel electrophoresis (PFGE). Forty-one isolates were SCCmec type IV, and one isolate was SCCmec type III. The isolates belonged to six PFGE patterns, with two types, A and D, distributed in six and four hospitals, respectively. Most (n = 26; 61.9%) isolates produced urease. These isolates were mainly from wound and skin infections, showed low-level methicillin resistance (MIC 8-48 mg/L), and nine carried genes for PVL. These characteristics, together with their carriage of the type-IV SCCmec, identified the isolates as CA-MRSA. Ten of the 16 urease-negative isolates produced staphylococal enterotoxin C; 12 reacted weakly with phage 75, and were resistant to clindamycin and/or erythromycin, which are characteristics of EMRSA-15. Thus, this study identified the co-existence of two types of nmMRSA, i.e., CA-MRSA and EMRSA-15, in Kuwait hospitals.

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.

New enzymes from environmental cassette arrays: functional attributes of a phosphotransferase and an RNA-methyltransferase

By targeting gene cassettes by polymerase chain reaction (PCR) directly from environmentally derived DNA, we are able to amplify entire open reading frames (ORFs) independently of prior sequence knowledge. Approximately 10% of the mobile genes recovered by these means can be attributed to known protein families. Here we describe the characterization of two ORFs which show moderate homology to known proteins: (1) an aminoglycoside phosphotransferase displaying 25% sequence identity with APH(7") from Streptomyces hygroscopicus, and (2) an RNA methyltransferase sharing 25%-28% identity with a group of recently defined bacterial RNA methyltransferases distinct from the SpoU enzyme family. Our novel genes were expressed as recombinant products and assayed for appropriate enzyme activity. The aminoglycoside phosphotransferase displayed ATPase activity, consistent with the presence of characteristic Mg(2+)-binding residues. Unlike related APH(4) or APH(7") enzymes, however, this activity was not enhanced by hygromycin B or kanamycin, suggesting the normal substrate to be a different aminoglycoside. The RNA methyltransferase contains sequence motifs of the RNA methyltransferase superfamily, and our recombinant version showed methyltransferase activity with RNA. Our data confirm that gene cassettes present in the environment encode folded enzymes with novel sequence variation and demonstrable catalytic activity. Our PCR approach (cassette PCR) may be used to identify a diverse range of ORFs from any environmental sample, as well as to directly access the gene pool found in mobile gene cassettes commonly associated with integrons. This gene pool can be accessed from both cultured and uncultured microbial samples as a source of new enzymes and proteins.

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

OBJECTIVES

To investigate the prevalence of aminoglycoside resistance and genes encoding aminoglycoside-modifying enzymes (AME) in blood culture isolates of coagulase-negative staphylococci (CoNS) from neonates.

MATERIALS AND METHODS

A total of 180 isolates from 148 patients collected in a single neonatal unit over a 12 year period were examined for susceptibility to gentamicin, tobramycin, netilmicin, amikacin and arbekacin by Etest and/or disc diffusion. AME genes were detected by PCR.

RESULTS

The overall non-susceptibility rates to gentamicin, tobramycin, netilmicin, amikacin and arbekacin were 66%, 68%, 52%, 38% and 1%, respectively. Gentamicin non-susceptibility rates were 4% and 91% in methicillin-susceptible and -resistant isolates, respectively. aac(6')-Ie-aph(2'')-Ia, aph(3')-IIIa and/or ant(4')-Ia were encountered in 125 (69%), 1 (0.5%) and 30 (16.6%) isolates, respectively. Forty-six (26%) isolates negative for AME genes were susceptible to all aminoglycosides. In contrast, 115 (92%), 91 (73%) and 66 (53%) of aac(6')-Ie-aph(2'')-Ia positive isolates were non-susceptible to gentamicin, netilmicin and amikacin, respectively. Only one isolate showed arbekacin resistance. However, aac(6')-Ie-aph(2'')-Ia positive isolates and isolates with gentamicin MIC > or =128 mg/L displayed a significant reduction in arbekacin inhibition zones.

CONCLUSIONS

A high prevalence of aminoglycoside resistance was detected and associated with methicillin resistance. Discrepancies between phenotypic and genetic detection of aminoglycoside resistance were discerned. Gentamicin was the preferred substrate for phenotypic detection of aac(6')-Ie-aph(2'')-Ia. Arbekacin showed favourable antibacterial activity even in aac(6')-Ie-aph(2'')-Ia-positive isolates. We suggest including arbekacin in future clinical trials of empirical treatment of late onset neonatal sepsis.

Versatility of aminoglycosides and prospects for their future

Aminoglycoside antibiotics have had a major impact on our ability to treat bacterial infections for the past half century. Whereas the interest in these versatile antibiotics continues to be high, their clinical utility has been compromised by widespread instances of resistance. The multitude of mechanisms of resistance is disconcerting but also illuminates how nature can manifest resistance when bacteria are confronted by antibiotics. This article reviews the most recent knowledge about the mechanisms of aminoglycoside action and the mechanisms of resistance to these antibiotics.

Species prevalence and antibacterial resistance of enterococci isolated in Kuwait hospitals

This study investigated the species prevalence and antibacterial resistance among enterococci isolated in Kuwait hospitals. They consisted of 415 isolates of Enterococcus faecalis (85.3 %), Enterococcus faecium (7.7 %), Enterococcus casseliflavus (4.0 %), Enterococcus avium (1.2 %), Enterococcus durans (1.0 %), Enterococcus gallinarium (0.5 %) and Enterococcus bovis (0.2 %) isolated from urine (36.6 %), blood (10.4 %), wound swabs (11.0 %), stool samples (12.0 %), high vaginal swabs (9.0 %), endocervical swabs (3.0 %) and miscellaneous sources (18.0 %). All of them were susceptible to linezolid. Fifty-two (12.5 %) isolates were ampicillin resistant but none of them produced beta-lactamase. They were resistant to erythromycin (63.3 %), tetracycline (60.5 %), ciprofloxacin (40.0 %), chloramphenicol (28.0 %), vancomycin (2.6 %), and teicoplanin (2.6 %). Fourteen, 19 and 20 % of them expressed high-level resistance to gentamicin, kanamycin and streptomycin, respectively. All of the vancomycin-resistant strains carried the vanA phenotype and genotype. There was no evidence of clonal spread of the vancomycin-resistant isolates.

Antibiotic resistance of enterococci isolated at a teaching hospital in Kuwait

Enterococci isolated in a teaching hospital were studied for their resistance to different antibiotics. Minimum inhibitory concentrations to high-level aminoglycosides and glycopeptide antibiotics were determined by agar dilution and E-test methods respectively. Genes encoding aminoglycoside-modifying enzymes were detected by the polymerase chain reaction (PCR). 195 enterococci were isolated from urines (54.3%), wounds (16.4%), blood (10.2%), and miscellaneous sources (18.9%). They consisted of E. faecalis (88.7%), E. faecium (9.2%), E. casseliflavus (1.5%) and E. bovis (0.5%). None of the enterococci produced penicillinase but 3.5% of them were resistant to ampicillin. They were also resistant to high-level gentamicin (15.9%), kanamycin (22.0%), streptomycin (21.0%), tetracycline (65.1%), erythromycin (62.6%), ciprofloxacin (36.1%), chloramphenicol (26.1%), vancomycin (3.0%) and teicoplanin (2.0%). Most of the high-level aminoglycoside-resistant isolates contained genes coding the bifunctional aminoglycoside modifying enzymes AAC(6')-APH(2"), APH(3') and ANT(6') but not the ANT(4') enzyme. The results demonstrated a low prevalence of vancomycin resistance among Enterococci in this hospital.

Antibiotic resistance in Staphylococcus isolates obtained from fecal samples of healthy children

Thirty-nine Staphylococcus isolates with different mechanisms of resistance were recovered from the feces of 50 healthy children and tested for their susceptibilities to 17 antibiotics. The percentages of resistance of the staphylococci to some antibiotics were as follows: penicillin, 87%; erythromycin, 64%; tobramycin, 36%; tetracycline, 20.5%; kanamycin, 15%; and gentamicin, 13%. The mecA gene was detected in nine coagulase-negative staphylococci.

High therapeutic index of factor C Sushi peptides: potent antimicrobials against Pseudomonas aeruginosa

Factor C protein isolated from the horseshoe crab, Carcinoscorpius rotundicauda, has endotoxin binding capability. Synthetic peptides of 34 amino acids based on the sequence of two regions of factor C (Sushi 1 and Sushi 3) as well as their corresponding mutants exhibited activities against 30 clinical isolates of Pseudomonas aeruginosa. Collectively, all four peptides demonstrated exceptionally effective bactericidal activity against P. aeruginosa with 90% minimal bactericidal concentrations (MBC(90)s) in the range of 0.06 to 0.25 microg/ml (16 to 63 nM). Viable bacteria were reduced by 90% after 7 min and were totally eradicated within 40 to 50 min. These peptides are minimally hemolytic against both rabbit and human erythrocytes even at concentrations up to 1,600-fold their MBC(90)s. Both in vitro and in vivo studies indicate that cytotoxic effects are small even at 1,000-fold their MBC(90)s. Furthermore, the Sushi peptides are tolerant of high-salt and adverse pH conditions. These findings demonstrate the promising therapeutic potential of the Sushi peptides.