Detection of ileS-2 gene encoding mupirocin resistance in methicillin-resistant Staphylococcus aureus by multiplex PCR

Identification of Candida albicans and non-MRSA Staphylococcus aureus in free-living amoebae isolated from the hospital wards; an alarm for distribution of nosocomial infections via FLA

Free-living amoebae (FLA) are isolated from the hospital environments and known as Trojan horses for medical essential microorganisms. This study aimed to investigate the prevalence and the presence of FLA and two critical agents of nosocomial infections, in the hospital wards. Sixty samples were collected from four communities and cultured onto non-nutrient agar (NNA). After total DNA extraction, FLA were characterized using PCR and sequencing. The presence of Candida albicans and Staphylococcus aureus was evaluated using real-time and conventional PCR, respectively. Acanthamoeba sp. was characterized in 30 (50%) samples. Two (6.6%) and one (3.3%) samples were positive for Vahlkampfiidae and Vermamoeba vermiformis, respectively . S. aureus was detected in 13 (43.3%) of samples, while none of them were positive for methicillin-resistant gene. C. albicans DNA was detected in one (3.3%) FLA-positive sample. The isolation of FLA from hospital suggests an essential role these eukaryotes in the inter-ward circulation of nosocomial infections.

Interspecies transfer of plasmid-borne gentamicin resistance between Staphylococcus isolated from domestic dogs to Staphylococcus aureus

As preconized by the One Health concept, the intimate relationship between pets and owners is a common source for the trade of microorganisms with zoonotic potential, and with them, antimicrobial resistance genes. In this work, we evaluated the presence of antimicrobial resistance genes, that are usually within mobile genetic elements, in a laboratory collection of 79 canine Staphylococcus strains, mostly Staphylococcus pseudintermedius and Staphylococcus coagulans. Resistance to tetracycline was observed in 34% of the strains, followed by resistance to erythromycin (21%) and gentamicin (19%). These phenotypes were partially correlated with the presence of the tetracycline resistance genes tet(M) and tet(K) in 64% and 44% of all strains, respectively; erythromycin resistance genes erm(A) and erm(C) in 53% and 23%; and gentamicin resistance gene aac(6')-aph(2″) in 26% of the strains. At least 45% of the strains harbored high- and/or low-molecular weight plasmids, whose transfer may be facilitated by their widespread biofilm-forming capacity, and absence of restrictive CRISPR systems. We selected eight plasmid-bearing and multidrug resistant strains, which were submitted to plasmid curing by stress with SDS. No strain lost resistance during stressing cultivation but, by conjugation experiments, the S. pseudintermedius strain 27 transferred its plasmid-borne resistance to gentamicin, conferred by the aac(6')-aph(2″) gene, to Staphylococcus aureus. The frequent empirical use of gentamicin to treat skin and ear infections in domestic dogs is likely to select resistant strains. Also, as demonstrated by our study, these strains can serve as gene reservoirs for human pathogens, such as S. aureus.

ACR Appropriateness Criteria® Radiologic Management of Portal Hypertension

Cirrhosis is a heterogeneous disease that cannot be studied as a single entity and is classified in two main prognostic stages: compensated and decompensated cirrhosis. Portal hypertension, characterized by a pathological increase of the portal pressure and by the formation of portal-systemic collaterals that bypass the liver, is the initial and main consequence of cirrhosis and is responsible for the majority of its complications. A myriad of treatment options exists for appropriately managing the most common complications of portal hypertension, including acute variceal bleeding and refractory ascites. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Inducible clindamycin resistance and erm genes in Staphylococcus aureus in school children in Kathmandu, Nepal

Aim:

Resistance to methicillin and Macrolide–Lincosamide and Streptogramins B and their association with erm genes in Staphylococcus aureus are unknown in Nepal.

Materials & methods:

Nonduplicate nasal swabs from 160 school children were collected from April to September 2018 and processed using standard microbiological procedures.

Results:

Out of 160 samples, 64 (40%) were S. aureus in which 17 (26.6%) were methicillin-resistance Staphylococcus aureus (MRSA). D-test identified 15 (23.4%) as inducible clindamycin-resistant, which were more prevalent in MRSA (76.4%) than methicillin-sensitive S. aureus (MSSA; 4.2%). 18.7% of isolates harbored the ermC gene followed by ermA (15.6%) and ermB (3.1%), and were more in MRSA than MSSA.

Conclusion:

To prevent treatment failure by inducible resistance, D-test must be performed on erythromycin-resistant and/or clindamycin-sensitive isolates.

With the increased prevalence of methicillin-resistant S. aureus in hospital- and community-acquired infections, there has been an upsurge in resistance toward Macrolide–Lincosamide–Streptogramin type B antibiotics. This has rendered therapy difficult, thereby increasing morbidity, length of hospital-stay and cost of treatment. Therefore, the correct identification and reporting of S. aureus isolates and their susceptibility patterns, more specifically, toward methicillin, clindamycin and erythromycin is very crucial.

Staphylococcus nepalensis, a commensal of the oral microbiota of domestic cats, is a reservoir of transferrable antimicrobial resistance

Staphylococcus nepalensis is a commensal bacterium from the oral microbiota of domestic cats, with a still obscure clinical importance. In this work, we analysed the ability of feline strains of S. nepalensis to transfer antimicrobial resistance genes to Staphylococcus aureus isolated from humans through plasmids. To this end, we first analysed all publicly available genomes from cat staphylococci using computational methods to build a pan-resistome. Genes that encode resistance to erythromycin, gentamicin, mupirocin and tetracycline, common to human and cat staphylococci and previously described to be located in mobile genetic elements, were chosen for the next analyses. We studied 15 strains of S. nepalensis, which were shown to be genetically different by GTG₅-PCR. As observed by disc diffusion, resistance to tetracycline was widespread (80 %), followed by resistance to erythromycin (40 %), gentamicin (27 %) and mupirocin (7 %). The strains were positive for several antimicrobial resistance genes and more than half of them harboured plasmids. The loss of plasmids and resistance genes in some strains were induced by stress with SDS. Through conjugation experiments, we observed that these plasmids can be transferred to S. aureus, thus increasing its potential to resist drug therapy. Our findings show that S. nepalensis, an underestimated inhabitant of the cat microbiota, can be a reservoir of antimicrobial resistance genes for S. aureus and, like many other staphylococci, be an overlooked and silent threat to their animal hosts and humans living with them.

Antimicrobial resistance in methicillin-resistant Staphylococcus aureus to newer antimicrobial agents

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) result in significant morbidity and mortality for patients in both community and health care settings. This is primarily due to the difficulty in treating MRSA, which is often resistant to multiple classes of antibiotics. Understanding the mechanisms of antimicrobial resistance (AMR) in MRSA provides insight into the optimal use of antimicrobial agents in clinical practice and also underpins critical aspects of antimicrobial stewardship programs. In this review we delineate the mechanisms, prevalence, and clinical importance of resistance to antibiotics licensed in the past 20 years that target MRSA, as well as new drugs in the pipeline which are likely to be licensed soon. Current gaps in scientific knowledge about MRSA resistance mechanisms are discussed, and topics in the epidemiology of AMR in S. aureus that require further investigation are highlighted.

Distribution of resistance genes encoding ESBLs in Enterobacteriaceae isolated from biological samples in health centers in Ouagadougou, Burkina Faso

Objective

Resistance to antibiotics most especially third generation cephalosporins has assumed a worrisome dimension globally. Genes conferring these resistance which are mediated by enzymes known as extended spectrum beta-lactamases (ESBLs) are now wide spread among several Enterobacteriaceae species. However there is paucity of data regarding the distribution of these genes in Burkina Faso. Hence this prospective study aims to determine the prevalence and distribution of ESBL encoding genes in ESBL producing Enterobacteriaceae strains isolated from clinical samples of patients attending the three major hospitals in Ouagadougou Burkina Faso.

Results

ESBL-encoding genes were assayed in 187 ESBL producing Enterobacteriaceae strains. Among these isolates, the prevalence of ESBL-producing strains with blaTEM, blaSHV and blaCTX-M genes were 26.2% (49/187), 5.9% (11/187) and 40.1% (75/187) respectively. The association of ESBL encoding genes with health centers was statistically significant (p = 0.0209). Approximately 39.6% of E. coli harbored CTX-M and Klebsiella spp. 5.9%. This study demonstrates the dissemination of TEM, SHV and CTX-M genes in ESBL producing Enterobacteriaceae strains in Ouagadougou. Continuous spread of these bacteria poses great public health risk, thus increased surveillance and regulation of antibiotics use is imperative in Burkina Faso.

Antimicrobial resistance and underlying mechanisms in Staphylococcus aureus isolates

OBJECTIVE

To investigate the antimicrobial susceptibility of 97 clinical Staphylococcus aureus (S. aureus) strains against 14 antimicrobials and corresponding resistance mechanisms.

METHODS

The antimicrobial susceptibility of the isolates was determined using a disk diffusion method and antimicrobial resistance genes were screened by polymerase chain reaction. Mutations responsible for ciprofloxacin and rifampicin resistance were investigated by polymerase chain reaction and DNA sequencing.

RESULTS

All isolates were found to be susceptible to vancomycin. Various rates of resistance to penicillin (83.5%), ampicillin (77.3%), erythromycin (63.9%), tetracycline (16.5%), amoxicillin/clavulanic acid (16.5%), ciprofloxacin (15.5%), trimethoprim/sulfamethoxazole (15.5%), oxacillin (13.4%), fusidic acid (12.4%), rifampin (6.2%), clindamycin (6.2%), gentamicin (6.2%) and mupirocin (5.2%) were determined. In addition, different combinations of resistance genes were identified among resistant isolates. Ciprofloxacin resistant isolates had mutations in codon 84 (Ser84Leu) and 106 (Gly106Asp) in the gyrA gene. Mutations in grlA were mostly related to Ser80Phe substitution. Leu466Ser mutation in the rpoB gene was detected in all rifampin resistant isolates. All methicillin resistant S. aureus isolates were SCCmec type V.

CONCLUSIONS

In conclusion, it was determined that the isolates were resistant to different classes of antimicrobials at varying rates and resistance was mediated by different genetic mechanisms. Therefore, continuous monitoring of resistance in S. aureus strains is necessary to control their resistance for clinically important antimicrobials.

Current and Emerging Topical Antibacterials and Antiseptics: Agents, Action, and Resistance Patterns

Bacterial skin infections represent some of the most common infectious diseases globally. Prevention and treatment of skin infections can involve application of a topical antimicrobial, which may be an antibiotic (such as mupirocin or fusidic acid) or an antiseptic (such as chlorhexidine or alcohol). However, there is limited evidence to support the widespread prophylactic or therapeutic use of topical agents. Challenges involved in the use of topical antimicrobials include increasing rates of bacterial resistance, local hypersensitivity reactions (particularly to older agents, such as bacitracin), and concerns about the indiscriminate use of antiseptics potentially coselecting for antibiotic resistance. We review the evidence for the major clinical uses of topical antibiotics and antiseptics. In addition, we review the mechanisms of action of common topical agents and define the clinical and molecular epidemiology of antimicrobial resistance in these agents. Moreover, we review the potential use of newer and emerging agents, such as retapamulin and ebselen, and discuss the role of antiseptic agents in preventing bacterial skin infections. A comprehensive understanding of the clinical efficacy and drivers of resistance to topical agents will inform the optimal use of these agents to preserve their activity in the future.

Isolation and genetic characterization of Lysinibacillus sphaericus strains found in mosquito larvae (Diptera: Culicidae)

Introduction

Lysinibacillus sphaericus is a highly effective and specific bioinsecticide used for the control of Culicidae larvae.

Objective

This study aimed to identify and characterize L. sphaericus strains isolated from Culex quinquefasciatus larvae in Brazil.

Methods

C. quinquefasciatus larvae were collected from streams in the urban area of São Paulo state. L. sphaericus strains were identified through cytomorphology, biochemical, and physiological analyses. Qualitative bioassays were performed to evaluate the toxicity of the strains against C. quinquefasciatus. The crystal compound protein pattern of L. sphaericus strains was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Five reference strains were used as standards in all tests performed. Repetitive extragenic palindromic elements-polymerase chain reaction (REP-PCR) was utilized in an attempt to differentiate pathogenic and nonpathogenic isolates.

Results

Twenty-one strains were isolated. Only one presented toxic activity against C. quinquefasciatus. REP-PCR results identified 23 patterns among the 26 strains used in the study, and the fragment analysis showed low similarity (16%) between L. sphaericus isolates and the five reference strains.

Conclusion

Comparison of strains isolated in this study using REP-PCR showed a low similarity to other strains, demonstrating the high intraspecific variability for L. sphaericus.

Distribution of high-level mupirocin resistance among clinical MRSA

Mupirocin is a topical antibiotic for methicillin-resistant Staphylococcus aureus (MRSA) decolonization in hospital settings and nursing homes and is used as a highly effective antibiotic against MRSA. In this study, we aimed to evaluate the frequency of high-level mupirocin-resistant (HLMR) strains among the MRSA subtypes. A total of 188 clinical MRSA isolates were collected from 2011 to 2014, and their susceptibility to antimicrobial agents and vancomycin resistance was evaluated using disc diffusion method and micro-dilution method, respectively. Furthermore, the presence of mecA, SSCmec, mupA and mupB was assessed by PCR. All isolates were multi-drug resistant (MDR) but 2 strains (1.06%) were resistant to mupirocin. Minimum inhibitory concentration (MIC) of vancomycin for 8 strains (4.7%) was higher than 2 μg/ml. Of 188 isolates, 188 (100%), 64 (34.04%), 8 (4.3%), 150 (79.8%), 26 (13.8%), 2 (1.06) and 2 (1.06%) isolates possessed mecA, SCCmec types I, II, III, IV, mupA and mupB genes, respectively. Our data showed that despite infection control policy enforced by health care committee, the rate of mupirocin resistance among MRSA strains is continuously rising.

Antibiotic resistance genes detected in the marine sponge Petromica citrina from Brazilian coast

Although antibiotic-resistant pathogens pose a significant threat to human health, the environmental reservoirs of the resistance determinants are still poorly understood. This study reports the detection of resistance genes (ermB, mecA, mupA, qnrA, qnrB and tetL) to antibiotics among certain culturable and unculturable bacteria associated with the marine sponge Petromica citrina. The antimicrobial activities elicited by P. citrina and its associated bacteria are also described. The results indicate that the marine environment could play an important role in the development of antibiotic resistance and the dissemination of resistance genes among bacteria.

Mupirocin for Controlling Methicillin-ResistantStaphylococcus Aureus: Lessons From a Decade of Use at a University Hospital

Background:

From 1990 to 1995 at Hospital Universitario dementino Fraga Filho, patients colonized or infected with methicillin-resistantStaphylococcus aureus(MRSA) were treated with mupirocin to eliminate MRSA carriage. In 1995, 65% of MRSA patients at this hospital had mupirocin-resistant isolates. Starting in 1996, mupirocin use was restricted to patients colonized, but not infected, with MRSA.

Objectives:

To describe the use of mupirocin for controlling MRSA over a decade and to analyze the molecular epidemiology of mupirocin-resistant MRSA infections at this hospital.

Setting:

A 490-bed, tertiary-care university hospital.

Methods:

The incidence densities of patients with MRSA and acquisition of mupirocin by the hospital were calculated for the period 1992–2001.S. aureusisolates from 1999–2000 were analyzed by pulsed-field gel electrophoresis. Mupirocin-resistant MRSA isolates from 1994–1995 and 1999–2000 were analyzed forileS-2gene background polymorphisms.

Results:

The incidence density of MRSA patients increased slightly over time, whereas the purchase of mupirocin decreased dramatically. Mupirocin-resistant MRSA infections decreased from 65% in 1994–1995 to 15% in 1999–2000. The MRSA Brazilian clone, detected in 1992, was still highly prevalent. The sameileS-2 encoding plasmid found in 1994–1995 persisted in three identical MRSA isolates from 1999–2000 belonging to the Brazilian clone.

Conclusions:

After mupirocin use decreased, theileS-2 encoding plasmid persisted in only a few Brazilian clone isolates. Our data on mupirocin-resistant MRSA incidence and mupirocin use strongly suggested that restricted use was related to decreased rates of mupirocin resistance at our hospital. (Infect Control Hosp Epidemiol 2005;26:662-667)

Transfer of mupirocin resistance from Staphylococcus haemolyticus clinical strains to Staphylococcus aureus through conjugative and mobilizable plasmids

Coagulase-negative staphylococci are thought to act as reservoirs of antibiotic resistance genes that can be transferred to Staphylococcus aureus, thus hindering the combat of this bacterium. In this work, we analyzed the presence of plasmids conferring resistance to the antibiotic mupirocin-widely used to treat and prevent S. aureus infections in hospital environments-in nosocomial S. haemolyticus strains. About 12% of the 75 strains tested were resistant to mupirocin, and this phenotype was correlated with the presence of plasmids. These plasmids were shown to be diverse, being either conjugative or mobilizable, and capable of transferring mupirocin resistance to S. aureus Our findings reinforce that S. haemolyticus, historically and mistakenly considered as a less important pathogen, is a reservoir of resistance genes which can be transferred to other bacteria, such as S. aureus, emphasizing the necessity of more effective strategies to detect and combat this emergent opportunistic pathogen.

Prevalence of mupirocin resistance in Staphylococcus pseudintermedius

In the United States, veterinary use of mupirocin is primarily limited to the treatment of canine pyoderma caused by methicillin-resistant Staphylococcus pseudintermedius (MRSP). In this study, only 1 of 581 S. pseudintermedius isolates tested was resistant to mupirocin and carried the high-level mupirocin resistance gene, ileS2, on a plasmid.

Bacillus cereus infection outbreak in captive psittacines

This study reports an uncommon epizootic outbreak of Bacillus cereus that caused the sudden death of 12 psittacines belonging to the species Anodorhynchus hyacinthinus (1 individual), Diopsittaca nobilis (1 individual), Ara severa (1 individual) and Ara ararauna (9 individuals) in a Brazilian zoo. Post-mortem examination of the animals reveled extensive areas of lung hemorrhage, hepatic congestion, hemorrhagic enteritis and cardiac congestion. Histopathological examination of the organs showed the presence of multiple foci of vegetative cells of Gram-positive bacilli associated with discrete and moderate mononuclear inflammatory cell infiltrate. Seventeen B. cereus strains isolated from blood and sterile organs of nine A. ararauna were analyzed in order to investigate the genetic diversity (assessed by Rep-PCR) and toxigenic profiles (presence of hblA, hblC and hblD; nheA, nheB and nheC as well as cytK, ces and entFM genes) of such strains. Amplification of genomic DNA by Rep-PCR of B. cereus strains generated two closely related profiles (Rep-PCR types A and B) with three bands of difference. All strains were classified as belonging to the toxigenic profile I which contained HBL and NHE gene complexes, entFM and cytK genes. Altogether, microbiological and histopathological findings and the evidence provided by the success of the antibiotic prophylaxis, corroborate that B. cereus was the causative agent of the infection that killed the birds.

Isolation and molecular characterization of methicillin-resistant staphylococci from horses, personnel and environmental sites at an equine hospital in Turkey

The present study was carried out to assess the frequency of methicillin-resistant staphylococci (MRS) among racehorses (n=209) and veterinary personnel (n=13) as well as environmental surfaces (n=14) at an equine hospital in Adana, Turkey. In addition, species distribution, antimicrobial susceptibility, resistance genes, staphylococcal chromosomal cassette mec (SCCmec) type and clonality of these isolates were also investigated. MRS were identified by 16S rRNA sequencing, and typed by pulsed-field gel electrophoresis (PFGE). As a result, MRS was isolated in horses (48.3%), clinic staff (92.3%) and environmental samples (71.4%). Of the 123 MRS isolates, 118 isolates were identified as Staphylococcus lentus, and the remaining ones were found to be S. sciuri (n=3), S. intermedius (n=1) and S. fleuretti (n=1). All isolates were found to be susceptible against vancomycin, quinupristin-dalfopristin and rifampicin. Additionally, single or various combinations of resistance genes were detected among MRS isolates. SCCmec type II was identified in all isolates. Similar PFGE patterns were observed among MRS isolated from horses, humans, and environmental samples. Since MRS were concurrently isolated from horses and humans it is suggested that cross-transmission of MRS between horses and humans might occur. However, it cannot be ruled out that transmission is human to animal or animal to human.

Methicillin-resistant Staphylococcus pseudintermedius isolated from canine pyoderma in North China

AIMS

To determine the prevalence of carriage of methicillin-resistant Staphylococcus pseudintermedius (MRSP) among dogs with pyoderma from two small animal hospitals in North China during a 21-month period and to characterize these isolates.

METHODS AND RESULTS

Swabs were taken from 260 dogs with pyoderma, and the staphylococcal species isolated and methicillin resistance were confirmed phenotypically and genotypically. The identified MRSP isolates were characterized by multilocus sequence typing (MLST), spa typing, staphylococcal cassette chromosome (SCC) mec typing, testing for susceptibility to nine antimicrobial agents and SmaI-digested pulsed-field gel electrophoresis. Thirty-three (12·7%) dogs were positive for MRSP. The most prevalent genotypes detected among MRSP were ST71(MLST)-t06(spa)-II-III(SCCmec) (n = 22, 66·7%), followed by ST5-t19 (n = 8, 24·2%), ST126-III(n = 2, 6·1%) and ST6-t02-V (3·0%). All MRSP isolates showed extended resistance to tested antimicrobial agents. Eight different SmaI patterns were observed in 21 typeable MRSP isolates.

CONCLUSIONS

Clinical isolates of MSRP isolated from dogs in North China belonged to two major clonal lineages ST71 and ST5.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is the first report on MRSP from canine pyoderma in China. Further surveillance study is needed to gain more detailed data concerning this major clinical challenge in veterinary medicine.

Antimicrobial activity of marine sponges against coagulase-negative staphylococci isolated from bovine mastitis

Bovine mastitis remains worldwide a major challenge for the dairy industry despite the widespread implementation of control strategies. The increasing number of coagulase-negative staphylococci (CNS) causing mastitis and of bacteria resistant to conventional antibiotics has become a serious problem in recent years. Marine sponges are a rich source of bioactive compounds, and many species can be useful for the development of new antimicrobial drugs. In the present study, 49 CNS strains were isolated from bovine mastitis cases from 21 different dairy herds kept at farms in Southeast Brazil. Strains were analyzed for antimicrobial susceptibility and mecA gene detection. Fifty-nine percent of the CNS strains were resistant to at least one of the drugs tested and 12.2% were classified as multiresistant. Three strains carried the mecA gene, confering resistance to the beta-lactamic antibiotics. In addition, the CNS strains were submitted to in vitro screening for antimicrobial activities of extracts from marine sponges. Extracts from the sponge species Cinachyrella sp., Haliclona sp. and Petromica citrina showed antibacterial activity against 61% of the CNS strains, including strains resistant to conventional antibiotics. Extracts from P. citrina showed the largest spectrum of inhibitory activity. The aqueous extract inhibited 51% of the CNS strains and presented a bactericidal effect over susceptible and multiresistant-bacteria at a minimal inhibitory concentration of 1.024μg/ml. This study shows the potential of marine sponges as new sources of antibiotics and disinfectants for the control of CNS involved in bovine mastitis.

Genetic diversity, antimicrobial resistance and toxigenic profiles of Bacillus cereus isolated from food in Brazil over three decades

Bacillus cereus is an ever-present problem. It is widely distributed in several environments such as soil and plants and is commonly isolated from food and additives. In this study we analyzed 97 foodborne B. cereus sensu stricto strains isolated in Brazil in the 1980's, 1990's and 2000's in order to investigate the genetic diversity (assessed by Rep-PCR), antimicrobial resistance and toxigenic profiles (presence of hblA, hblC and hblD; nheA, nheB and nheC as well as cytK, ces and entFM genes) of such strains. The majority of the strains (79, 81.4%) were β-hemolytic. The NHE complex was found in 82 strains (84.5%) and HBL complex was found in 61 (62.9%) strains. All strains were negative to ces. The cytK-2 gene was found in 44 (45.4%) strains. The predominant toxigenic pattern was type I (32, 33%) which included strains positive for all toxin genes but ces. Computer assisted cluster analysis of Rep-PCR profiles showed a high genetic diversity. Seven major clusters comprising two or more strains were found and cluster 1 was predominant (ten strains, nine of them showing 100% similarity). This cluster included strains isolated in the 1980's and the 1990's. Cluster analysis of Rep-PCR profiles based on decade of isolation, source, hemolytic pattern, toxigenic and antibiotic resistance patterns revealed a similar clustering pattern as found in the analysis including all strains. The inability to observe a predominant band pattern when Rep-PCR cluster analysis was based on decade of isolation suggests that this diversity has been maintained over time. All strains were susceptible to gentamicin. We detected resistance to tetracycline (11 strains showing intermediate resistance and nine completely resistant strains), clindamycin (ten intermediate strains) and vancomycin (one strain). Clindamycin resistance showed statistical association with strains isolated in 2000's. The predominant resistance pattern was type A (72, 72.2%) which included strains susceptible to all drugs tested. Our results suggest that the majority of the strains present in several types of food in Brazil pose a potential risk to cause food poisoning due to the high prevalence of toxin genes found in these strains. However, additional studies involving cytotoxicity tests and affiliation of these strains to phylogenetic groups based on molecular data would be useful to better evaluate this potential and could provide a more accurate indication of the risk.

Diversity of plasmids and transmission of high-level mupirocin mupA resistance gene in Staphylococcus haemolyticus

The coagulase-negative staphylococci are known for their ability to acquire resistance genes, which limits the choice of therapeutic options for the treatment of infections caused by these microorganisms. In this study, the diversity of high-level mupirocin resistance plasmids (Mup(R) ) was investigated in four strains of Staphylococcus haemolyticus belonging to different pulsed-field gel electrophoresis (PFGE) types or subtypes, isolated in a Brazilian hospital. These strains harbor the mupA gene in large plasmids. In addition, the presence of IS257 sequences flanking the mupA gene was also shown. Two isolates belonging to two different PFGE types exhibited a similar polymorphism for a fragment of the mupA gene and the closest proximal flanking copies of the IS257, suggesting horizontal transmission of S. haemolyticus mupirocin resistance plasmids in the environment and a role of this species as a reservoir of the mupA gene.

Detecção de Listeria monocytogenes pela técnica de PCR em leite contaminado artificialmente

Avaliou-se a técnica de PCR como opção para reduzir o tempo de detecção de Listeria monocytogenes no leite. Para tanto, amostras de leite desnatado esterilizado e de leite cru integral - com baixa, média e alta contagem de microrganismos aeróbios mesófilos - foram inoculadas experimentalmente com diversas concentrações de L. monocytogenes. Os resultados da reação de PCR foram comparados com os da cultura da amostra empregando-se metodologia padronizada tradicional. Não se detectou L. monocytogenes pela reação de PCR quando esta foi realizada a partir do caldo de enriquecimento de Listeria (LEB) após 24 horas de incubação, nem no leite desnatado esterilizado, nem no leite cru integral. Após 48 horas de enriquecimento em LEB, a bactéria foi detectada por PCR nas amostras de leite desnatado esterilizado, com a sensibilidade de 1UFC/mL, mas não nas amostras de leite cru integral. Pela metodologia tradicional, a bactéria foi recuperada de todos os ensaios. Entretanto, nas amostras de leite cru com altas contagens de aeróbios mesófilos, a sensibilidade da metodologia tradicional foi reduzida (a partir de 7UFC/mL). Melhores resultados foram obtidos quando a reação de PCR foi feita utilizando-se DNA obtido diretamente da colônia suspeita em meio sólido (Oxford e Palcam). Foi possível substituir os testes fenotípicos de identificação de L. monocytogenes pela técnica de PCR reduzindo-se o tempo de identificação da bactéria de vários dias para algumas horas.

Constitutive expression of the ileS-2 gene responsible for high-level mupirocin resistance in Staphylococcus aureus

Mupirocin is a topical antimicrobial agent that is used for the treatment of skin and postoperative wound infections, and the prevention of nasal carriage of meticillin-resistant Staphylococcus aureus (MRSA). However, the prevalence of mupirocin resistance in S. aureus, particularly in MRSA, has increased. High-level mupirocin resistance, with MICs ≥512 μg ml−1, is mediated by the ileS-2 gene, which is located on conjugative plasmids. In the present study, we investigated whether mupirocin influences the expression of the ileS-2 gene responsible for high-level mupirocin resistance, and we present some evidence that this gene is not upregulated but constitutively expressed in S. aureus.

Staphylococcus aureus as source of catheter-related bloodstream infection evaluated by PFGE and rep-PCR typing in a Brazilian hospital

Staphylococci are a common cause of catheter-related bloodstream infection (CR-BSI), and epidemiological typing is an important tool for effective infection control. This study evaluated by PFGE and rep-PCR whether Staphylococcus aureus strains isolated from skin and catheter tips were related to specimens isolated from blood. A prospective observational study, carried out in a clinical surgical ward at a Brazilian hospital between September 2000 and November 2002, investigated non-tunneled central venous catheters from 179 patients. S. aureus isolates were mainly obtained from blood (41.4%), while coagulase-negative staphylococci strains were more often isolated from the skin at the catheter insertion site (49.7%) and from the catheter tip (57.5%). Among the 21 strains isolated from 9 patients at 2 or 3 sites simultaneously, 9 were methicillin-resistant S. aureus (MRSA) and 12 were methicillin-susceptible S. aureus (MSSA). Seven patients harbored the same S. aureus strain isolated from the skin, blood and/or catheter tip cultures. MRSA isolates belonged to one PFGE pattern (type A- subtypes A(1), A(2) and A(3)), and to two rep-PCR patterns (a and b). MSSA isolates were distinguished in five PFGE (B to F) and in three rep-PCR (c, d and e) patterns. Both PFGE and rep-PCR methods indicated that the skin at the catheter insertion site was the origin of CR-BSI caused by S. aureus.

Distribution of superantigenic toxin genes in Staphylococcus aureus isolates from milk samples of bovine subclinical mastitis cases in two major diary production regions of China

To evaluate the distribution of most known staphylococcal superantigen (SAg) genes in Staphylococcus aureus isolated from bovine mastitis cases, a genetic analysis of 15 SAg genes and genotypes was performed in a total of 283 S. aureus isolates collected from milk samples of cows with subclinical mastitis in two major diary production regions of China. Almost 65% of the isolates possessed at least one toxin gene. The most frequently found genes were sea (36.0%) followed by sei (31.8%), seg (31.4%) and selm (26.9%). The genes see, selk, or selo were not found in any of the isolates tested. Overall, 28 SAg genotypes were observed, among which the genotypes sea-seg-sei-selm, seg-sei-selm-seln, and sea-sed-selj predominated at the rate of 8.8%, 7.4%, and 6.7%, respectively. Marked geographical variations were noticed in the distribution of individual SAg genes and genotypes among S. aureus isolates from the two different regions. The relationship between toxin genotypes and toxin genes encoding profiles of mobile genetic elements (MGEs) was analyzed, revealing that majority of SAg genes were present in certain MGEs, which were in accordance with current knowledge about MGEs carrying those genes. However, some gene combinations suggest the possibility of the existence of variants or new types of MGEs.

Detecção de Escherichia coli O157:H7 inoculada experimentalmente em amostras de leite cru por método convencional e PCR multiplex

Padronizou-se um método de reação em cadeia da polimerase (PCR) multiplex para detecção de Escherichia coli O157:H7 e avaliou-se a eficiência da PCR e de um método de cultivo convencional em placas na detecção desse patógeno experimentalmente adicionado em leite estéril e em leite cru com baixa contagem bacteriana total (média de 4,01 x 10³ UFC/ml) e com alta contagem bacteriana (média de 2,10 x 10(6) UFC/ml). Foram padronizadas duas reações de PCR com o uso dos primers: "A" (RfbF; RfbR e FLICh7F/FLICh7R) e "B" (SLT-IF/SLTIR e SLT-IIF/SLT-IIR). A detecção de E. coli O157:H7 (1UFC/ml) a partir do leite estéril e do leite cru com baixa contaminação bacteriana foi possível quando se utilizou o método de contagem em placas e a PCR. A sensibilidade dos dois métodos foi menor quando se testou o leite cru com alta contaminação microbiana, sendo o método convencional mais sensível. Os resultados indicam que a presença de outros microrganismos, em alta quantidade no leite, dificulta a detecção de E. coli O157:H7 pelos métodos utilizados.

Detection of methicillin and mupirocin resistance in staphylococcal hospital isolates with a touchdown multiplex polymerase chain reaction

Staphylococcal hospital isolates (n = 166) were tested in a touchdown multiplex-polymerase chain reaction assay for the identification of methicillin and mupirocin resistance and discrimination of S. aureus (femA gene) from coagulase negative staphylococci and other bacteria. All isolates harbored the 16SrDNA (Staphylococcus genus specific internal control) gene, and 130 (78 %) the mecA (methicillin resistance) gene. Fifty-seven (44 %) of these were determined as methicillin-resistant S. aureus, while the remaining 73 (56 %) were methicillin-resistant coagulase-negative staphylococci. Seventy-five (45 %) isolates harbored the ileS-2 (high-level mupirocin resistance) gene and were determined as mupirocin-resistant. This assay represents a simple, rapid, reliable approach for the detection and discrimination of methicillin-and mupirocin-resistant staphylococci.

Molecular diagnostics of clinically important staphylococci

Bacterial species of the genus Staphylococcus known as important human and animal pathogens are the cause of a number of severe infectious diseases. Apart from the major pathogen Staphylococcus aureus, other species until recently considered to be nonpathogenic may also be involved in serious infections. Rapid and accurate identification of the disease-causing agent is therefore prerequisite for disease control and epidemiological surveillance. Modern methods for identification and typing of bacterial species are based on genome analysis and have many advantages compared to phenotypic methods. The genotypic methods currently used in molecular diagnostics of staphylococcal species, particularly of S. aureus, are reviewed. Attention is also paid to new molecular methods with the highest discriminatory power. Efforts made to achieve interlaboratory reproducibility of diagnostic methods are presented.

Interpretive criteria to differentiate low- and high-level mupirocin resistance in Staphylococcus aureus

Meticillin-resistant Staphylococcus aureus isolates were classified into three mupirocin susceptibility groups by the disc diffusion method using 5 and 200 μg mupirocin discs. The zone diameter observed for a 5 μg disc distinguished MupS from the resistant strains (either MupRL or MupRH). On the other hand, a 200 μg disc distinguished the high-resistance MupRH strains from the other two (MupS or MupRL). Thus, the concomitant use of 5 and 200 μg mupirocin discs allowed the clear distinction among the three mupirocin susceptibility groups, MupS, MupRL or MupRH.

Automated systems in the identification and determination of methicillin resistance among coagulase negative staphylococci

Coagulase-negative staphylococci (CoNS) are an important cause of nosocomial bacteremia, specially in patients with indwelling devices or those submitted to invasive medical procedures. The identification of species and the accurate and rapid detection of methicillin resistance are directly dependent on the quality of the identification and susceptibility tests used, either manual or automated. The objective of this study was to evaluate the accuracy of two automated systems--MicroScan and Vitek--in the identification of CoNS species and determination of susceptibility to methicillin, considering as gold standard the biochemical tests and the characterization of the mecA gene by polymerase chain reaction, respectively. MicroScan presented better results in the identification of CoNS species (accuracy of 96.8 vs 78.8%, respectively); isolates from the following species had no precise identification: Staphylococcus haemolyticus, S. simulans, and S. capitis. Both systems were similar in the characterization of methicillin resistance. The higher discrepancies for gene mec detection were observed among species other than S. epidermidis (S. hominis, S. saprophyticus, S. sciuri, S. haemolyticus, S. warneri, S. cohnii), and those with borderline MICs.

Decrease in the incidence of mupirocin resistance among methicillin-resistant Staphylococcus aureus in carriers from an intensive care unit

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious nosocomial problem, globally distributed. Decolonization with mupirocin can be used to control its dissemination.

OBJECTIVE

To determine the incidence of mupirocin resistance among MRSA carriers from an intensive care unit.

METHODS

We obtained 2723 nasal swabs during 3 years. Resistance to methicillin and mupirocin were verified (agar diffusion and the E test) and confirmed by polymerase chain reaction (PCR) (mecA for methicillin; ileS-2 and mupA for mupirocin). Plasmid-curing procedure and pulsed-field gel electrophoresis (PFGE) were employed in isolates exhibiting high resistance to mupirocin (HR-Mup) and in other selected organisms.

RESULTS

The overall incidence of HR-Mup among MRSA carriers during the studied period was 4.84% (8/165); however, the incidence decreased from 13.04% (6/46) in the first year to 3.5% (2/57) in the second year and was 0% in the last year (P = .02). LR-Mup, in contrast, increased significantly (P = .01).

CONCLUSION

Plasmid-curing procedure showed the plasmid location of genes responsible for HR-Mup. PFGE demonstrated that most MRSA, including the isolates with HR-Mup, were genetically related. The decline in HR-Mup may be attributable to the plasmid location of genes (ileS-2/mupA) and to the fact that all patients colonized with HR-Mup MRSA died or were discharged in a relatively short period of time.

Investigation of aminoglycoside modifying enzyme genes in methicillin-resistant staphylococci

Methicillin-resistant staphylococci may also be resistant to some other antibiotics as well as beta-lactams. In this study, co-existence of resistance to methicillin and aminoglycosides was genetically investigated in staphylococci. A total of 50 staphylococci from in-patients, 17 Staphylococcus aureus and 33 coagulase negative staphylococci (CNS) that contained mecA (gene encoding PBP 2a, an altered penicillin-binding protein) determined by polymerase chain reaction (PCR) were included in the study. Aminoglycoside modifying enzyme (AME) genes were investigated using multiplex-PCR. Aminocyclitol-6'-acetyltransferase-aminocyclitol-2''-phosphotransferase [aac(6')/aph(2'')] gene (encoding bifunctional acetyltransferases/phosphotransferases) was determined in 66% of the isolates, aminocyclitol-4'-adenylytransferase (ant(4')-Ia) gene (encoding phosphotransferases) in 24%, and aminocyclitol-3'-phosphotransferase (aph(3')-IIIa) gene (encoding nucleotidyltransferases) in 8%. Two isolates contained all these three genes. Thirty-six (72%) isolates had at least one of these genes. Three CNS and one S. aureus isolates sensitive to oxacillin had the mecA gene. In conclusion, a high rate of aminoglycoside resistance was determined in methicillin-resistant staphylococci. The aac(6')/aph(2'') was the most frequently detected.

Oxacillin- and mupirocin-resistant Staphylococcus aureus: in vitro activity of silver sulphadiazine and cerium nitrate in hospital strains

Nasal carriage is an important reservoir of oxacillin-resistant Staphylococcus aureus (ORSA). Mupirocin is a topical drug used to remove S. aureus from nares. However, isolates resistant to mupirocin have been reported all over the world. Silver sulphadiazine (SSD) is a topical agent, which when associated with cerium nitrate (CN), has been shown to be useful in the treatment of burn infections and could be an alternative drug for patient decolonization. Susceptibility to oxacillin in 203 S. aureus isolates was evaluated by the agar diffusion test, while the agar diffusion and agar dilution methods were used for mupirocin. A PCR-multiplex method was performed to detect the mecA and ileS-2 genes. Minimum inhibitory concentration (MICs) to SSD and CN, used alone or in association, were determined by the agar dilution method. One hundred and sixty-three (80.3%) strains were oxacillin-resistant, and 37 (18.2%) were mupirocin resistant. The MIC of SSD alone or in association with CN was 64 microg/mL, while for CN alone was 2048 microg/mL for all isolates. SSD presented anti-staphylococcal activity at concentrations (64 microg/mL) much lower than those commonly used in commercial preparations (10 mg/g) and had good activity against mupirocin-resistant strains, showing that this drug could be used for nasal decolonization in ORSA carries.

New quadriplex PCR assay for detection of methicillin and mupirocin resistance and simultaneous discrimination of Staphylococcus aureus from coagulase-negative staphylococci

Major challenges in diagnostic molecular microbiology are to develop a simple assay to distinguish Staphylococcus aureus from the less virulent but clinically important coagulase-negative staphylococci (CoNS) and to simultaneously determine their antibiotic resistance profiles. Multiplex PCR assays have been developed for the detection of methicillin- and mupirocin-resistant S. aureus and CoNS but not for the simultaneous discrimination of S. aureus from CoNS. We designed a new set of Staphylococcus genus-specific primers and developed a novel quadriplex PCR assay targeting the 16S rRNA (Staphylococcus genus specific), nuc (S. aureus species specific), mecA (a determinant of methicillin resistance), and mupA (a determinant of mupirocin resistance) genes to identify most staphylococci, to discriminate S. aureus from CoNS and other bacteria, and to simultaneously detect methicillin and mupirocin resistance. Validation of the assay with 96 ATCC control strains and 323 previously characterized clinical isolates, including methicillin- and mupirocin-sensitive and -resistant S. aureus and CoNS isolates and other bacteria, demonstrated 100% sensitivity, specificity, and accuracy. This assay represents a simple, rapid, accurate, and reliable approach for the detection of methicillin- and mupirocin-resistant staphylococci and offers the hope of preventing their widespread dissemination through early and reliable detection.

Genomic characterization of oxacillin-resistant Staphylococcus epidermidis and Staphylococcus haemolyticus isolated from Brazilian medical centres

Studies on the genetic diversity of oxacillin-resistant coagulase-negative staphylococcal (CNS) isolates are important for the control and prevention of infections. The present study evaluated the clonal diversity of oxacillin-resistant Staphylococcus epidermidis (ORSE) and Staphylococcus haemolyticus (ORSH) strains, isolated from patients in nine Brazilian medical centres by using pulsed-field gel electrophoresis (PFGE) after digestion of bacterial DNA using SmaI. PFGE analysis of ORSE (N=44) and ORSH (N=25) strains showed the presence of 29 restriction profiles clustered in 16 PFGE types, and 21 distinct profiles in 15 PFGE types, respectively, indicating a large genetic diversity among isolates of both of these species. Among the ORSE isolates, 23 (52%) strains belonged to two predominant PFGE types (named A and B), which were observed in most of the hospitals assessed, indicating the spread of these PFGE types in hospitals located in Rio de Janeiro. The spread of PFGE types of ORSH was also detected in some of the hospitals investigated. The results show that PFGE is a suitable tool for epidemiological studies of oxacillin-resistant CNS, and can be used as a basis for infection control procedures for these multiresistant organisms.

A decline in mupirocin resistance in methicillin-resistant Staphylococcus aureus accompanied administrative control of prescriptions

Susceptibility to mupirocin was assessed in methicillin-resistant Staphylococcus aureus isolates selected from eras corresponding to differences in usage rate and prescription policies at a Veterans Affairs medical center. The eras studied encompassed from the time of introduction of the drug to its widespread use, through recommended judicious use, and finally to subsequent stringent administrative control. Prescriptions declined from 3.0 to 0.1 per 1,000 patient days. Precipitous declines first in the numbers of isolates with high-level resistance (from 31% to 4%) and then in those with low-level resistance (from 26% to 10%) accompanied prescription control.

Experience in prevention of sternal wound infections in nasal carriers of Staphylococcus aureus

Nosocomial and surgical-site infections are significant burdens to the health care system that account for $5 billion and $1.6 billion each year in the United States, respectively. These infections are associated with significant morbidity and mortality rates, increased length of hospitalization, and increased treatment costs that are often not reimbursed by third-party payers. Approximately 40% of sternal wound infections in cardiac surgery patients are caused by Staphylococcus aureus and the prevalence of methicillin-resistant S aureus (MRSA) has risen dramatically in the past 2 to 3 decades. The economic burden that is associated with MRSA is significant; infections caused by MRSA cost approximately $3700 more to treat than infections caused by methicillin-sensitive S aureus, and the death rate for MRSA infection is nearly 3 times that of methicillin-sensitive S aureus. Thus, interventions to prevent nosocomial infection in patients who undergo cardiac surgery may improve outcomes and decrease costs. Advances in diagnostic testing may help to target intranasal antibiotic therapy to those patients who are most likely to receive a benefit. The LightCycler System is a fast and effective polymerase chain reaction-based diagnostic test that may be used to identify patients with nasal colonization of S aureus. Carrier status can be determined in a matter of hours rather than days as is the case with traditional culture techniques.

Coagulase-negative staphylococci: comparison of phenotypic and genotypic oxacillin susceptibility tests and evaluation of the agar screening test by using different concentrations of oxacillin

This study evaluated the oxacillin susceptibilities of 152 coagulase-negative staphylococcal (CoNS) strains of 12 species by disk diffusion; agar dilution; E-test; the slide latex agglutination test (Slidex MRSA Detection test; bioMérieux S/A, Paris, France); the agar screening test with 1, 2, 4, or 6 microg of oxacillin per ml and incubation for 24 or 48 h; and detection of the mecA gene by PCR. The results revealed that the agar screening test with 4 micro g of oxacillin per ml and incubation for 48 h was superior to any single phenotype-based susceptibility assay, presenting a sensitivity and a specificity of 100% each. For the different methods evaluated, the sensitivities and specificities were as follows: for disk diffusion, 94.2 and 91.8%, respectively; for the agar dilution test 100 and 73.5%, respectively; for E-test, 100 and 71.4%, respectively; and for the slide latex agglutination test, 97.1 and 98%, respectively. A good correlation was observed between oxacillin susceptibility testing results and PCR results for Staphylococcus epidermidis, S. haemolyticus, S. hominis subsp. hominis, and all mecA-positive strains. However, at least 60% of the mecA-negative isolates of the species S. saprophyticus, S. cohnii subsp. urealyticum, S. lugdunensis, and S. sciuri were erroneously classified as oxacillin resistant by the agar dilution test. Conversely, the slide latex agglutination test presented a high sensitivity (97.1%) and a high specificity (98%) for all CoNS species. Our results demonstrated the accuracy of the agar screening test with 4 micro g of oxacillin per ml and incubation for 48 h and the slide latex agglutination test for the appropriate detection of the oxacillin susceptibilities of CoNS isolates. Both assays are technically simple and can be easier to perform in routine laboratories than PCR.

Predictive value and cost-effectiveness analysis of a rapid polymerase chain reaction for preoperative detection of nasal carriage of Staphylococcus aureus

OBJECTIVE

To determine the accuracy and cost-effectiveness of a polymerase chain reaction (PCR) for detecting nasal carriage of Staphylococcus aureus directly from clinical specimens. CROSS-SECTIONAL STUDY: This occurred in a tertiary-care hospital in Cleveland, Ohio, and included 239 consecutive patients who were scheduled for a cardiothoracic surgical procedure. Conventional cultures and a PCR for S. aureus from nasal swabs were used as measurements. COST-EFFECTIVENESS ANALYSIS: Data sources were market prices and Bureau of Labor Statistics. The time horizon was the maximum period for availability of culture results (3 days). Interventions included universal mupirocin therapy without testing; initial therapy, with termination if PCR negative (treat-PCR); initial therapy, with termination if culture negative (treat-culture); treat PCR-positive carriers (PCR-guided treatment); and treat culture-positive carriers (culture-guided treatment). The perspective was institutional and costs and the length of time to treatment were outcome measures.

RESULTS

Sixty-seven (28%) of the 239 swabs grew S. aureus. Rapid PCR was 97.0% sensitive and 97.1% specific for the detection of S. aureus. For populations with prevalences of nasal S. aureus carriage of up to 50%, the PCR assay had negative predictive values of greater than 97%. PCR-guided treatment had the lowest incremental cost-effectiveness ratio (1.93 dollars per additional day compared with the culture strategy). Among immediate treatment strategies, treat-PCR was most cost-effective. The universal therapy strategy cost 38.19 dollars more per additional day gained with carrier identification compared with the PCR strategy.

CONCLUSION

Rapid real-time PCR is an accurate, rapid, and cost-effective method for identifying S. aureus carriers for preoperative intervention.

Multiplex PCR strategy for rapid identification of structural types and variants of the mec element in methicillin-resistant Staphylococcus aureus

Full characterization of methicillin-resistant Staphylococcus aureus (MRSA) requires definition of not only the bacterial genetic background but also the structure of the complex and heterologous mec element these bacteria carry, which is associated with drug resistance determinant mecA. We report the development, validation, and application of a multiplex PCR strategy that allows quick presumptive characterization of the mec element types based on the structural features that were shown to be typical of mec elements carried by several MRSA clones. The strategy was validated by using a representative collection of pandemic MRSA clones in which the full structure of the associated mec elements was previously determined by hybridization and PCR screenings and also by DNA sequencing. The method was tested together with multilocus sequence typing and other typing methods for the characterization of 18 isolates representative of the MRSA clones recovered during a hospital outbreak in Barcelona, Spain. The multiplex PCR was shown to be rapid, robust, and capable in a single assay of identifying five structural types of the mec element among these strains, three major and two minor variants, each one of which has been already been seen among MRSA characterized earlier. This technique should be a useful addition to the armamentarium of molecular typing tools for the characterization of MRSA clonal types and for the rapid tentative identification of structural variants of the mec element.

Mupirocin resistance in methicillin-resistant Staphylococcus aureus clinical isolates in a Spanish hospital. Co-application of multiplex PCR assay and conventional microbiology methods

A total of 1785 Staphylococcus aureus clinical isolates were collected in our hospital during 1998 (526), 1999 (564) and 2000 (695). Among them, one hundred and thirty (39, 33 and 58, respectively) were phenotypically assigned as methicillin-resistant Staphylococcus aureus (MRSA); sixteen of these isolates (3, 2 and 11, respectively) were detected as highly mupirocin-methicillin resistant Staphylococcus aureus (MMRSA). In this work, our goal was to characterize MRSA and MMRSA clinical isolates by co-application of phenotypic and genotypic methods in order to determine the MMRSA incidence in our hospital during the period 1998-2000. With this purpose we compared and integrated the results obtained using conventional microbiology methods with those obtained using a multiplex polymerase chain reaction (PCR) assay. Our results showed a good complementation between these two approximations to determine the incidence of MMRSA clinical isolates and permitted to estimate that such incidence increased from 7.7% in 1998 to 19% in 2000.

Emerging elevated mupirocin resistance rates among staphylococcal isolates in the SENTRY Antimicrobial Surveillance Program (2000): correlations of results from disk diffusion, Etest and reference dilution methods

Staphylococci cause one-third of all serious invasive infections in the SENTRY Antimicrobial Surveillance Program including bacteremias and lower respiratory tract infections. Staphylococci are also commensals of the skin and nasal passages; therefore, topical agents active against these organisms are valuable in preventing infections or transfer of the organisms between patients and/or health care workers. Mupirocin is a potent topical anti-staphylococcal compound, but its effectiveness has been compromised by emerging resistance. In early 2000, the SENTRY Program detected 302 mupirocin-resistant isolates (131 Staphylococcus aureus, and 171 coagulase-negative staphylococci [CoNS]) from the United States (19/25 medical centers), Canada (4/5), Latin America (3/9) and Europe (7/18). One hundred sixty-eight mupirocin-resistant and 59 susceptible isolates were tested further by reference MIC, Etest (AB BIODISK, Solna, Sweden) and disk diffusion (5-microg) methods. Mupirocin resistance rates for blood stream infections varied by geographic area: for S. aureus from 1.9 to 5.6%, and for CoNS from 12.8 to 39.9%. Using elevated mupirocin MIC results, two resistant populations were noted: low-level resistance at 8-128 microg/mL and high-level resistance at > or = 1024 microg/mL. Acceptable correlation was observed between Etest and disk diffusion results (r = 0.84) without serious intermethod interpretive errors. High-level resistant isolates had heavy growth with no visible zone around the disk; low-level resistant isolates produced hazy zones of inhibition, and susceptible strains had clear zones of inhibition at > or = 17 mm. As mupirocin resistance can be plasmid-mediated, the prudent and appropriate use of this topical agent is important to minimize the ongoing development of resistance. Local surveillance for emerging mupirocin resistance appears warranted particularly in the United States and Canada, pragmatically using a disk diffusion test screening. Where more precise data are needed, the Etest is a very accurate method for distinguishing mupirocin low-level from high-level resistance patterns.