Synergistic hemolysis exhibited by species of staphylococci

Staphylococcus capitis: insights into epidemiology, virulence, and antimicrobial resistance of a clinically relevant bacterial species

SUMMARYStaphylococcus capitis is divided into two subspecies, S. capitis subsp. ureolyticus (renamed urealyticus in 1992; ATCC 49326) and S. capitis subsp. capitis (ATCC 27840), and fits with the archetype of clinically relevant coagulase-negative staphylococci (CoNS). S. capitis is a commensal bacterium of the skin in humans, which must be considered an opportunistic pathogen of interest particularly as soon as it is identified in a clinically relevant specimen from an immunocompromised patient. Several studies have highlighted the potential determinants underlying S. capitis pathogenicity, resistance profiles, and virulence factors. In addition, mobile genetic element acquisitions and mutations contribute to S. capitis genome adaptation to its environment. Over the past decades, antibiotic resistance has been identified for S. capitis in almost all the families of the currently available antibiotics and is related to the emergence of multidrug-resistant clones of high clinical significance. The present review summarizes the current knowledge concerning the taxonomic position of S. capitis among staphylococci, the involvement of this species in human colonization and diseases, the virulence factors supporting its pathogenicity, and the phenotypic and genomic antimicrobial resistance profiles of this species.

Novel Anti-virulence Compounds Disrupt Exotoxin Expression in MRSA

Hemolysins are lytic exotoxins expressed in most strains of S. aureus , but hemolytic activity varies between strains. We have previously reported several novel anti-virulence compounds that disrupt the S. aureus transcriptome, including hemolysin gene expression. This report delves further into our two lead compounds, loratadine and a structurally related brominated carbazole, and their effects on hemolysin production in MRSA. To gain understanding into how these compounds affect hemolysis, we analyzed these exotoxins at the DNA, RNA, and protein level after in vitro treatment. While lysis of red blood cells varied between strains, DNA sequence variation did not account for it. We hypothesized that our compounds would modulate gene expression of multiple hemolysins in a laboratory strain and a clinically relevant hospital-acquired strain of MRSA, both with SCC mec type II. RNA-seq analysis of differential gene expression in untreated and compound-treated cultures revealed hundreds of differentially expressed genes, with a significant enrichment in genes involved in hemolysis. The brominated carbazole and loratadine both displayed the ability to reduce hemolysis in the laboratory strain, but displayed differential activity in a hospital-acquired strain. These results corroborate gene expression studies as well as western blots of alpha hemolysin. Together, this work suggests that small molecules may alter exotoxin production in MRSA, but that the directionality and/or magnitude of the difference is likely strain-dependent.

Solving polymicrobial puzzles: evolutionary dynamics and future directions

Polymicrobial infections include various microorganisms, often necessitating different treatment methods than a monomicrobial infection. Scientists have been puzzled by the complex interactions within these communities for generations. The presence of specific microorganisms warrants a chronic infection and impacts crucial factors such as virulence and antibiotic susceptibility. Game theory is valuable for scenarios involving multiple decision-makers, but its relevance to polymicrobial infections is limited. Eco-evolutionary dynamics introduce causation for multiple proteomic interactions like metabolic syntropy and niche segregation. The review culminates both these giants to form evolutionary dynamics (ED). There is a significant amount of literature on inter-bacterial interactions that remain unsynchronised. Such raw data can only be moulded by analysing the ED involved. The review culminates the inter-bacterial interactions in multiple clinically relevant polymicrobial infections like chronic wounds, CAUTI, otitis media and dental carries. The data is further moulded with ED to analyse the niche colonisation of two notoriously competitive bacteria: S.aureus and P.aeruginosa. The review attempts to develop a future trajectory for polymicrobial research by following recent innovative strategies incorporating ED to curb polymicrobial infections.

Searching for Virulence Factors among Staphylococcus lugdunensis Isolates from Orthopedic Infections: Correlation of β-hemolysin, hemolysin III, and slush Genes with Hemolytic Activity and Synergistic Hemolytic Activity

Staphylococcus lugdunensis is an emerging high-virulent pathogen. Here, the presence and expression of virulence genes (icaA, fbl, vwbl, fbpA, slush A, B and C, and genes of the putative β-hemolysin and hemolysin III) and the ability to induce synergistic hemolytic activity and hemolysis after 24, 48 and 72 h were investigated in a collection of twenty-two S. lugdunensis clinical isolates. The collection of isolates, mainly from implant orthopedic infections, had previously been grouped by ribotyping/dendrogram analysis and studied for biofilm matrices, biomasses and antibiotic resistances. Two isolates, constituting a unique small ribogroup sharing the same cluster, exhibited an amplicon size of the slush operon (S. lugdunensis synergistic hemolysin) which was shorter than the expected 977 bp. This outcome can predict the genetic lineage of the S. lugdunensis strains. One isolate (cra1342) presented two deletions: one of 90 bp in slush A and the other of 91 bp in slush B. Another isolate (N860314) showed a single 193 bp deletion, which encompassed part of the slush B terminal sequence and most of slush C. The isolate N860314 was devoid of hemolytic activity after 24 h, and the first consideration was that the deleted region deals with the coding of the active enzymatic site of the slush hemolysin. On the other hand, cra1342 and N860314 isolates with different slush deletions and with hemolytic activity after 24 and 48 h, respectively, could have replaced the hemolytic phenotype through other processes.

Staphylococcus xylosus and Staphylococcus aureus as commensals and pathogens on murine skin

Skin ulcers, skin dermatitis and skin infections are common phenomena in colonies of laboratory mice and are often found at increased prevalence in certain immunocompromised strains. While in many cases these skin conditions are mild, in other cases they can be severe and lead to animal morbidity. Furthermore, the presence of skin infections and ulcerations can complicate the interpretation of experimental protocols, including those examining immune cell activation. Bacterial species in the genus Staphylococcus are the most common pathogens recovered from skin lesions in mice. In particular, Staphylococcus aureus and Staphylococcus xylosus have both been implicated as pathogens on murine skin. Staphylococcus aureus is a well-known pathogen of human skin, but S. xylosus skin infections in humans have not been described, indicating that there is a species-specific difference in the ability of S. xylosus to serve as a skin pathogen. The aim of this review is to summarize studies that link S. aureus and S. xylosus to skin infections of mice and to describe factors involved in their adherence to tissue and their virulence. We discuss potential differences in mouse and human skin that might underlie the ability of S. xylosus to act as a pathogen on murine skin, but not human skin. Finally, we also describe mouse mutants that have shown increased susceptibility to skin infections with staphylococcal bacteria. These mutants point to pathways that are important in the control of commensal staphylococcal bacteria. The information here may be useful to researchers who are working with mouse strains that are prone to skin infections with staphylococcal bacteria.

Analysis of the Presence of the Virulence and Regulation Genes from Staphylococcus aureus (S. aureus) in Coagulase Negative Staphylococci and the Influence of the Staphylococcal Cross-Talk on Their Functions

Coagulase-negative staphylococci (CoNS) are increasingly becoming a public health issue worldwide due to their growing resistance to antibiotics and common involvement in complications related to invasive surgical procedures, and nosocomial and urinary tract infections. Their behavior either as a commensal or a pathogen is a result of strict regulation of colonization and virulence factors. Although functionality of virulence factors and processes involved in their regulation are quite well understood in S. aureus, little is known about them in CoNS species. Therefore, the aim of our studies was to check if clinical CoNS strains may contain virulence factors and genes involved in resistance to methicillin, that are homologous to S. aureus. Moreover, we checked the presence of elements responsible for regulation of genes that encode virulence factors typical for S. aureus in tested isolates. We also investigated whether the regulation factors produced by one CoNS isolate can affect virulence activity of other strains by co-incubation of tested isolates with supernatant from other isolates. Our studies confirmed the presence of virulence factor and regulatory genes attributed to S. aureus in CoNS isolates and indicated that one strain with an active agr gene is able to affect biofilm formation and δ-toxin activity of strains with inactive agr genes. The cognition of prevalence and regulation of virulence factors as well as antibiotic resistance of CoNS isolates is important for better control and treatment of CoNS infections.

Frequent dissemination and carriage of an SCCmec-mecC hybrid in methicillin-resistant Mammaliicoccus sciuri in farm animals from Tunisia

OBJECTIVES

In this study, we aimed to assess the extent of dissemination of methicillin-resistant Mammaliicoccus sciuri in animal farms in Tunisia and evaluate the distribution of virulence and methicillin resistance genes in the M. sciuri population.

METHODS

Staphylococci and mammaliicocci isolated from unhealthy animals and healthy humans from adjacent farms in Tunisia were characterized for antimicrobial susceptibility, biofilm formation, agglutination, and hemolysis abilities. Mammaliicoccus sciuri relatedness and content in antibiotic resistance and virulence genes were analyzed by whole-genome sequencing (WGS).

RESULTS

Mammaliicoccus sciuri was the most prevalent species (46.2%), showing the highest resistance rates to fusidic acid (94.6%), oxacillin (73%), penicillin (40.5%), clindamycin (37%), ciprofloxacin (27%), and cefoxitin (24.3%). Some isolates carried genes encoding resistance to nine different antibiotic classes. mecA was found in 35% of M. sciuri and mecC in 16.2%. All isolates carrying mecC were of S. sciuri subspecies carnaticus and carried the hybrid element SCCmec-mecC. Mammaliicoccus sciuri were able to produce strong biofilm (27%) and have clumping ability (16%). Additionally, they carried genes for capsule production (cap8, 100%), iron-regulated surface determinants (isdE, 24%; isdG, 3%), and virulence regulation (clpC and clpP, 100%). Single nucleotide polymorphisms (SNPs) analysis showed that 17 M. sciuri cross-transmission events probably occurred between different animal species and farms. Moreover, SCCmec was estimated to have been acquired five times by S. sciuri subsp. carnaticus.

CONCLUSION

Multidrug resistant and pathogenic M. sciuri were frequently disseminated between different animal species within the farm environment. mecA and mecC can be disseminated by both frequent acquisition of the SCCmec element and clonal dissemination.

Pathogenicity and virulence of Staphylococcus aureus

Staphylococcus aureus is one of the most frequent worldwide causes of morbidity and mortality due to an infectious agent. This pathogen can cause a wide variety of diseases, ranging from moderately severe skin infections to fatal pneumonia and sepsis. Treatment of S. aureus infections is complicated by antibiotic resistance and a working vaccine is not available. There has been ongoing and increasing interest in the extraordinarily high number of toxins and other virulence determinants that S. aureus produces and how they impact disease. In this review, we will give an overview of how S. aureus initiates and maintains infection and discuss the main determinants involved. A more in-depth understanding of the function and contribution of S. aureus virulence determinants to S. aureus infection will enable us to develop anti-virulence strategies to counteract the lack of an anti-S. aureus vaccine and the ever-increasing shortage of working antibiotics against this important pathogen.

Bacterial Community Interactions During Chronic Respiratory Disease

Chronic respiratory diseases including chronic rhinosinusitis, otitis media, asthma, cystic fibrosis, non-CF bronchiectasis, and chronic obstructive pulmonary disease are a major public health burden. Patients suffering from chronic respiratory disease are prone to persistent, debilitating respiratory infections due to the decreased ability to clear pathogens from the respiratory tract. Such infections often develop into chronic, life-long complications that are difficult to treat with antibiotics due to the formation of recalcitrant biofilms. The microbial communities present in the upper and lower respiratory tracts change as these respiratory diseases progress, often becoming less diverse and dysbiotic, correlating with worsening patient morbidity. Those with chronic respiratory disease are commonly infected with a shared group of respiratory pathogens including Haemophilus influenzae, Streptococcus pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, and Moraxella catarrhalis, among others. In order to understand the microbial landscape of the respiratory tract during chronic disease, we review the known inter-species interactions among these organisms and other common respiratory flora. We consider both the balance between cooperative and competitive interactions in relation to microbial community structure. By reviewing the major causes of chronic respiratory disease, we identify common features across disease states and signals that might contribute to community shifts. As microbiome shifts have been associated with respiratory disease progression, worsening morbidity, and increased mortality, these underlying community interactions likely have an impact on respiratory disease state.

Selective pressures during chronic infection drive microbial competition and cooperation

Chronic infections often contain complex mixtures of pathogenic and commensal microorganisms ranging from aerobic and anaerobic bacteria to fungi and viruses. The microbial communities present in infected tissues are not passively co-existing but rather actively interacting with each other via a spectrum of competitive and/or cooperative mechanisms. Competition versus cooperation in these microbial interactions can be driven by both the composition of the microbial community as well as the presence of host defense strategies. These interactions are typically mediated via the production of secreted molecules. In this review, we will explore the possibility that microorganisms competing for nutrients at the host–pathogen interface can evolve seemingly cooperative mechanisms by controlling the production of subsets of secreted virulence factors. We will also address interspecies versus intraspecies utilization of community resources and discuss the impact that this phenomenon might have on co-evolution at the host–pathogen interface.

Mass spectrometric identification of phenol-soluble modulins in the ATCC® 43300 standard strain of methicillin-resistant Staphylococcus aureus harboring two distinct phenotypes

Staphylococcus aureus subsp. aureus Rosenbach (ATCC® 43300™) is a representative methicillin-resistant S. aureus (MRSA) strain that is used as a quality control strain for testing the methicillin susceptibility of clinical isolates. It has been consistently observed that colonies with two different colors (golden yellow and white) grow from the ATCC stock on blood agar plates. In this study, staphylococcal peptide and protein profiling was performed using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. From the extract of the potentially hemolytic 43300 strain, we identified a single significant peak at an observed mass-to-charge (m/z) value of 2306.9, which correlates well with the predicted mass of formylated phenol-soluble modulin α2, a major staphylococcal virulence factor. Subsequent liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed that the hemolytic 43300 cells predominantly produced various phenol-soluble modulins (PSMs) and their export proteins, including four α type PSM peptides, PSMβ1, PSM-mec, PmtC and PmtD. However, none of the PSM peptides was detected in the presumably non-hemolytic 43300 strain, but the export proteins PmtC and PmtD. We found that this MRSA standard strain expresses two distinct phenotypes and that their phenotypic features are more likely associated with PSM toxin production. Therefore, careful attention is needed when MRSA reference strains are utilized for the diagnosis and susceptibility testing of MRSA in clinical settings.

Importance of Multifaceted Approaches in Infection Control: A Practical Experience from an Outbreak Investigation

BACKGROUND

This study presents the results of a multidisciplinary, nosocomial MRSA outbreak investigation in an 8-bed medical intensive care unit (ICU). The identification of seven MRSA positive patients in the beginning of 2014 led to the closure of the ward for several weeks. A multidisciplinary, retrospective investigation was initiated in order to identify the reason and the source for the outbreak, describe MRSA transmission in the department and identify limitations in infection control.

METHODS

The investigation comprised an epidemiological description of MRSA cases from 2012 to 2014 and a characterization of MRSA isolates, including phage-, spa- and PFGE-typing. Additionally, MRSA screening was performed from the hospital staff and the environment. To identify the reason for the outbreak, work-related, psychological and behavioral factors were investigated by impartial audits and staff interviews.

RESULTS

Thirty-one MRSA cases were registered during the study period, and 36 isolates were investigated. Molecular typing determined the outbreak strain (phage type 54/812, PFGE type A4, spa type t003) and identified the probable index case. Nasal carriage in one employee and a high environmental contamination with the outbreak strain was documented. Important gaps in nursing procedures and general management were identified. Elevated stress levels and communication problems preceded the outbreak. Compliance with hand hygiene and isolation procedures was evaluated as appropriate.

CONCLUSION

This study demonstrates the complexity of controlling hospital-associated infections. The combined use of different typing methods is beneficial for outbreak investigations. Psychological, behavioral and other work-related factors have an important impact on the spread of nosocomial pathogens. These factors should be addressed and integrated in routine infection control practice.

Functional characteristics of the Staphylococcus aureus δ-toxin allelic variant G10S

Staphylococcus aureus δ-toxin is a member of the phenol-soluble modulin (PSM) peptide family. PSMs have multiple functions in staphylococcal pathogenesis; for example, they lyse red and white blood cells and trigger inflammatory responses. Compared to other PSMs, δ-toxin is usually more strongly expressed but has only moderate cytolytic capacities. The amino acid sequences of S. aureus PSMs are well conserved with two exceptions, one of which is the δ-toxin allelic variant G10S. This variant is a characteristic of the subspecies S. argenteus and S. aureus sequence types ST1 and ST59, the latter representing the most frequent cause of community-associated infections in Asia. δ-toxin G10S and strains expressing that variant from plasmids or the genome had significantly reduced cytolytic and pro-inflammatory capacities, including in a strain background with pronounced production of other PSMs. However, in murine infection models, isogenic strains expressing the two δ-toxin variants did not cause measurable differences in disease severity. Our findings indicate that the widespread G10S allelic variation of the δ-toxin locus has a significant impact on key pathogenesis mechanisms, but more potent members of the PSM peptide family may overshadow that impact in vivo.

Staphylococcus epidermidis and Staphylococcus haemolyticus: Molecular Detection of Cytotoxin and Enterotoxin Genes

Although opportunistic pathogens, coagulase-negative staphylococci (CoNS), including Staphylococcus epidermidis and Staphylococcus haemolyticus, have long been regarded as avirulent organisms. The role of toxins in the development of infections caused by CoNS is still controversial. The objective of this study was to characterize the presence of enterotoxin and cytotoxin genes in S. epidermidis and S. haemolyticus isolates obtained from blood cultures. Cytotoxin genes were detected by PCR using novel species-specific primers. Among the 85 S. epidermidis and 84 S. haemolyticus isolates, 95.3% and 79.8%, respectively, carried at least one enterotoxin gene. The most frequent enterotoxin genes were sea (53.3%), seg (64.5%) and sei (67.5%). The seg gene was positively associated with S. epidermidis (p = 0.02), and this species was more toxigenic than S. haemolyticus. The hla/yidD gene was detected in 92.9% of S. epidermidis and the hla gene in 91.7% of S. haemolyticus isolates; hlb was detected in 92.9% of the S. epidermidis isolates and hld in 95.3%. Nosocomial Staphylococcus epidermidis and S. haemolyticus isolates exhibited a high toxigenic potential, mainly producing the non-classical enterotoxins seg and sei. The previously unreported detection of hla/yidD and hlb in S. epidermidis and S. haemolyticus using species-specific primers showed that these hemolysin genes differ between CoNS species and that they are highly frequent in blood culture isolates.

Evolution of resistance to a last-resort antibiotic in Staphylococcus aureus via bacterial competition

Antibiotic resistance is a key medical concern, with antibiotic use likely being an important cause. However, here we describe an alternative route to clinically relevant antibiotic resistance that occurs solely due to competitive interactions among bacterial cells. We consistently observe that isolates of Methicillin-resistant Staphylococcus aureus diversify spontaneously into two distinct, sequentially arising strains. The first evolved strain outgrows the parent strain via secretion of surfactants and a toxic bacteriocin. The second is resistant to the bacteriocin. Importantly, this second strain is also resistant to intermediate levels of vancomycin. This so-called VISA (vancomycin-intermediate S. aureus) phenotype is seen in many hard-to-treat clinical isolates. This strain diversification also occurs during in vivo infection in a mouse model, which is consistent with the fact that both coevolved phenotypes resemble strains commonly found in clinic. Our study shows how competition between coevolving bacterial strains can generate antibiotic resistance and recapitulate key clinical phenotypes.

Multi-virulence-locus sequence typing of Staphylococcus lugdunensis generates results consistent with a clonal population structure and is reliable for epidemiological typing

Staphylococcus lugdunensis is an emergent virulent coagulase-negative staphylococcus responsible for severe infections similar to those caused by Staphylococcus aureus. To understand its potentially pathogenic capacity and have further detailed knowledge of the molecular traits of this organism, 93 isolates from various geographic origins were analyzed by multi-virulence-locus sequence typing (MVLST), targeting seven known or putative virulence-associated loci (atlLR2, atlLR3, hlb, isdJ, SLUG_09050, SLUG_16930, and vwbl). The polymorphisms of the putative virulence-associated loci were moderate and comparable to those of the housekeeping genes analyzed by multilocus sequence typing (MLST). However, the MVLST scheme generated 43 virulence types (VTs) compared to 20 sequence types (STs) based on MLST, indicating that MVLST was significantly more discriminating (Simpson's index [D], 0.943). No hypervirulent lineage or cluster specific to carriage strains was defined. The results of multilocus sequence analysis of known and putative virulence-associated loci are consistent with a clonal population structure for S. lugdunensis, suggesting a coevolution of these genes with housekeeping genes. Indeed, the nonsynonymous to synonymous evolutionary substitutions (dN/dS) ratio, the Tajima's D test, and Single-likelihood ancestor counting (SLAC) analysis suggest that all virulence-associated loci were under negative selection, even atlLR2 (AtlL protein) and SLUG_16930 (FbpA homologue), for which the dN/dS ratios were higher. In addition, this analysis of virulence-associated loci allowed us to propose a trilocus sequence typing scheme based on the intragenic regions of atlLR3, isdJ, and SLUG_16930, which is more discriminant than MLST for studying short-term epidemiology and further characterizing the lineages of the rare but highly pathogenic S. lugdunensis.

Moving towards the immunodiagnosis of staphylococcal intramammary infections

Bovine mastitis is the primary disease of dairy cattle that has a great impact on the dairy industry. It is estimated that worldwide economic losses due to mastitis range between US$82 and US$131 per cow/year. A fast and efficient diagnosis of the disease remains a major bottleneck that directly influences the speed with which treatment decisions and management are undertaken. Microbiological culture remains the gold standard in the identification of bacteria that cause mastitis, but the method has inherent limitations, such as a delay in obtaining results and cost, and requires special care during the collection and processing of the sample. For this reason, multiple groups have devoted efforts to develop alternative methods that, preferably, can be easily accomplished in the field. The specificity of the antigen-antibody reaction has enabled the emergence of major diagnostic methods used in clinical practice, such as immunoassays, which have significant advantages in terms of speed, sensitivity, specificity, and portability. Commercially, immunodiagnostics have been used in the detection of various diseases in cattle. However, in several cases, only a presumptive diagnosis can be made, which requires confirmation using culture-based methods. This review discusses the immunological-based assays developed since the 1990s for the detection of Staphylococcus aureus, which is considered the primary pathogen of contagious bovine mastitis. Although no ideal antigens ensure the accurate performance of tests and the costs need to be reduced to allow for good market competitiveness, immunoassays, particularly lateral flow immunoassay and immunoagglutination, have emerged as promising tests to be used in the field.

Synergistic hemolysis between β-lysin–producing Staphylococcus species and Rothia nasimurium in primary cultures of clinical specimens obtained from dogs

Nonhemolytic isolates of catalase-positive, Gram-positive cocci were observed that produced strong synergistic hemolysis with colonies of Staphylococcus pseudintermedius and Staphylococcus schleiferi subsp. coagulans in primary cultures of clinical specimens from dogs. The isolates appeared similar to nonhemolytic staphylococci but were not identified with conventional biochemical tests or commercial biochemical test kits. Partial 16S ribosomal RNA gene sequences from each of 9 tested isolates were nearly identical to that of Rothia nasimurium. The isolates produced positive Christie–Atkins–Munch–Peterson test reactions with Staphylococcus aureus (ATCC strain 25923) and Staphylococcus intermedius Hajek (ATCC strain 49052). The latter was identified in the current study as S. pseudintermedius. Rothia nasimurium appears to be a previously unreported commensal organism in dogs. Its potential significance as an opportunistic contributor to polymicrobial infections in dogs is not known.

Some Virulence Factors of Staphylococci Isolated From Wound and Skin Infections in Shahrekord, IR Iran

Background:

Staphylococci release a large number of enzymes. Some of these, such as coagulase, beta- lactamase, hemolysins and biofilms are considered indices of pathogenicity.

Objectives:

The aim of the current study was based on the isolation and identification of Staphylococcus aureus and coagulase negative Staphylococci (CNS) strains from various skin lesions and examining their biofilms, beta- lactamase, hemolysins production and antibiotic resistance pattern.

Materials and Methods:

Sixty one infected wounds and 39 skin infections samples were collected and examined. After the culture and identification, examination for production of hemolysins, beta- lactamase, biofilm and susceptibility toward 9 antimicrobials was performed.

Results:

Out of 75 isolated Staphylococci, sixty (80%) were biofilm producers. Two overall prevalence of 28.5% and 100% of ß-lactamase production were recorded for isolated S. aureus and CNS, respectively. Twenty out of 49 (40.8%), the same number of α- and β- hemolytic S. aureus, were isolated while six (12.24%) were ∂ -hemolysin producers. Twenty two of Twenty six (84.6%) isolates of CNS, were hemolysin producers that all were ∂ type. The S. aureus isolates from wound infections, show a high sensitivity pattern to all examined antibiotics, this sensitivity pattern for isolates from skin dermatitis is relatively low, though.

Conclusions:

High percentage of hemolysins, biofilm and beta lactamase production by isolated Staphylococci, suggests an important role of these virulence factors in the pathogenesis of isolated Staphylococci from dermatitis lesions. The S. aureus isolates from wound infections, show a high sensitivity pattern to all examined antibiotics. Only ciprofloxacin was found to be active against all isolates from dedermatitis lesions.

Staphylococcus aureus β-toxin production is common in strains with the β-toxin gene inactivated by bacteriophage

BACKGROUND

Staphylococcus aureus causes life-threatening infections, including infective endocarditis, sepsis, and pneumonia. β-toxin is a sphingomyelinase encoded for by virtually all S. aureus strains and exhibits human immune cell cytotoxicity. The toxin enhances S. aureus phenol-soluble modulin activity, and its activity is enhanced by superantigens. The bacteriophage φSa3 inserts into the β-toxin gene in human strains, inactivating it in the majority of S. aureus clonal groups. Hence, most strains are reported not to secrete β-toxin.

METHODS

This dynamic was investigated by examining β-toxin production by multiple clonal groups of S. aureus, both in vitro and in vivo during infections in rabbit models of infective endocarditis, sepsis, and pneumonia.

RESULTS

β-toxin phenotypic variants are common among strains containing φSa3. In vivo, φSa3 is differentially induced in heart vegetations, kidney abscesses, and ischemic liver compared to spleen and blood, and in vitro growth in liquid culture. Furthermore, in pneumonia, wild-type β-toxin production leads to development of large caseous lesions, and in infective endocarditis, increases the size of pathognomonic vegetations.

CONCLUSIONS

This study demonstrates the dynamic interaction between S. aureus and the infected host, where φSa3 serves as a regulator of virulence gene expression, and increased fitness and virulence in new environments.

A proposal to unify two subspecies of Staphylococcus equorum: Staphylococcus equorum subsp. equorum and Staphylococcus equorum subsp. linens

Twelve isolates from jeotgal, a Korean high-salt-fermented seafood, identified as Staphylococcus equorum were compared by phenotypic and genotypic methods to determine their precise taxonomic identities at the subspecies level. Four strains and three strains had complete 16S rRNA gene sequence matches with S. equorum subsp. equorum DSM 20674(T) and S. equorum subsp. linens DSM 15097(T), respectively. Five strains showed 99.9 % identity with the sequences of both type strains. In our DNA-DNA hybridization analyses among two type strains and two isolates, the similarities were over 72 % and were higher than the similarities presented at the subspecies proposal. Physiological characteristics such as sugar utilization, β-galactosidase activity, novobiocin resistance and salt tolerance, which were adopted for subspecies separation, could not be applied to assign the isolates to a taxonomic unit. Antibiotic susceptibility, hemolytic activity, biofilm formation and protein profiles did not present markers to divide the isolates into either of the subspecies. Multilocus sequence typing of the sequences of the 16S rRNA gene and five housekeeping genes did not produce any coherent relationship among the isolates and type strains. Repetitive element-PCR fingerprinting using ERIC (enterobacterial repetitive intergenic consensus) primers classified 12 isolates to three genotypes, and the genotypes of both type strains coincided with two isolates expressing different characteristics. Based on these phenotypic and genotypic analyses results, we propose to unify the present two subspecies of S. equorum into one species, S. equorum.

Synergistic and additive effects of chromosomal and plasmid-encoded hemolysins contribute to hemolysis and virulence in Photobacterium damselae subsp. damselae

Photobacterium damselae subsp. damselae causes infections and fatal disease in marine animals and in humans. Highly hemolytic strains produce damselysin (Dly) and plasmid-encoded HlyA (HlyA(pl)). These hemolysins are encoded by plasmid pPHDD1 and contribute to hemolysis and virulence for fish and mice. In this study, we report that all the hemolytic strains produce a hitherto uncharacterized chromosome-encoded HlyA (HlyAch). Hemolysis was completely abolished in a single hlyAch mutant of a plasmidless strain and in a dly hlyApl hlyAch triple mutant. We found that Dly, HlyA(pl), and HlyAch are needed for full hemolytic values in strains harboring pPHDD1, and these values are the result of the additive effects between HlyApl and HlyAch, on the one hand, and of the synergistic effect of Dly with HlyApl and HlyAch, on the other hand. Interestingly, Dly-producing strains produced synergistic effects with strains lacking Dly production but secreting HlyA, constituting a case of the CAMP (Christie, Atkins, and Munch-Petersen) reaction. Environmental factors such as iron starvation and salt concentration were found to regulate the expression of the three hemolysins. We found that the contributions, in terms of the individual and combined effects, of the three hemolysins to hemolysis and virulence varied depending on the animal species tested. While Dly and HlyApl were found to be main contributors in the virulence for mice, we observed that the contribution of hemolysins to virulence for fish was mainly based on the synergistic effects between Dly and either of the two HlyA hemolysins rather than on their individual effects.

Characterization of Staphylococcus xylosus isolated from broiler chicken barn bioaerosol

In this study we isolated and characterized Staphylococcus xylosus, a coagulase-negative staphylococcal species considered as commensal and one of the prevalent staphylococcal species found in poultry bioaerosol. Isolates were obtained using air samplers and selective phenylethyl alcohol agar for gram-positive bacteria during 35-d periods at different times of the day. A total of 200 colonies were recovered and after basic biochemical tests were performed, presumptive staphylococci were subsequently identified by API Staph strips. A total of 153 (76.5%) staphylococci were found, among which 84 were S. xylosus (46 and 38 isolated inside and outside, respectively). Biofilm formation was observed in 86.9% of S. xylosus isolates, whereas 79.8% of them showed hemolytic activity. There was a strong correlation (92.5%) between biofilm formation and hemolytic activity. All 84 S. xylosus isolates were susceptible to amikacin, ampicillin/sulbactam, chloramphenicol, ciprofloxacin, gentamycin, kanamycin, linezolid, trimethoprim/sulfamethoxazole, and vancomycin. Resistance to nalidixic acid (86.9%), novobiocin (85.7%), penicillin (70.2%), lincomycin (46.4%), oxacillin (42.9%), ampicillin (27.4%), tetracycline (21.4%), erythromycin (11.9%), bacitracin (10.7%), and streptomycin (2.4%) was observed among the isolates. Resistance to tetracycline, lincomycin, erythromycin, and β-lactam antibiotics was occasionally linked to the tetK, linA, ermB, and blaZ genes, respectively. Random amplification of polymorphic DNA results showed similarity of 15 to 99% between isolates collected outside and inside the barn, indicating genetic diversity of these isolates. Our study indicates that characterization of poultry bioaerosol coagulase-negative staphylococcal species such as S. xylosus is necessary for assessing their safety status for both poultry and humans.

Direct and synergistic hemolysis caused by Staphylococcus phenol-soluble modulins: implications for diagnosis and pathogenesis

Phenol-soluble modulins are secreted staphylococcal peptides with an amphipathic α-helical structure. Some PSMs are strongly cytolytic toward human neutrophils and represent major virulence determinants during Staphylococcus aureus skin and blood infection. However, capacities of PSMs to lyse human erythrocytes have not been investigated. Here, we demonstrate that many S. aureus and Staphylococcus epidermidis PSMs lyse human erythrocytes. Furthermore, synergism with S. aureus β-toxin considerably increased the hemolytic capacities of several PSMs. This synergism may be of key importance in PSM and β-toxin-producing S. aureus or in mixed-strain or -species infections with PSM and β-toxin producers. Of specific interest, several PSMs, in particular PSMα peptides, contributed to a considerable extent to synergistic hemolysis with β-toxin or when using the β-toxin-producing strain RN4220 in CAMP assays. Thus, CAMP-type assays should not be used to detect or quantify S. aureus δ-toxin production, but may be used for an overall assessment of Agr functionality. Our study suggests an additional role of PSMs in staphylococcal pathogenesis and demonstrates that the repertoire of staphylococcal hemolysins is not limited to S. aureus and is much larger and diverse than previously thought.

Expression of δ-toxin by Staphylococcus aureus mediates escape from phago-endosomes of human epithelial and endothelial cells in the presence of β-toxin

Staphylococcus aureus is able to invade non-professional phagocytes by interaction of staphylococcal adhesins with extracellular proteins of mammalian cells and eventually resides in acidified phago-endosomes. Some staphylococcal strains have been shown to subsequently escape from this compartment. A functional agr quorum-sensing system is needed for phagosomal escape. However, the nature of this agr dependency as well as the toxins involved in disruption of the phagosomal membrane are unknown. Using a novel technique to detect vesicular escape of S. aureus, we identified staphylococcal virulence factors involved in phagosomal escape. Here we show that a synergistic activity of the cytolytic peptide, staphylococcal δ-toxin and the sphingomyelinase β-toxin enable the phagosomal escape of staphylococci in human epithelial as well as in endothelial cells. The agr dependency of this process can be directly explained by the location of the structural gene for δ-toxin within the agr effector RNAIII.

The influence of antibodies on Staphylococcus epidermidis adherence to polyvinylpyrrolidone-coated silicone elastomer in experimental biomaterial-associated infection in mice

Biomaterial-associated infection (BAI) is a major problem in modern medicine, and is often caused by Staphylococcus epidermidis. We aimed to raise monoclonal antibodies (mAbs) against major surface protein antigens of S. epidermidis, and to assess their possible protective activity in experimental BAI. Mice were vaccinated with a cell wall protein preparation of S. epidermidis. A highly immunodominant antigen was identified as Accumulation-associated protein (Aap). mAbs against Aap and against surface-exposed lipoteichoic acid (LTA) were used for passive immunization of mice in experimental biomaterial-associated infection. Neither anti-Aap nor anti-LTA mAbs showed protection. Either with or without antibodies, tissue surrounding the implants was more often culture positive than the implants themselves, but bacterial adherence to the implants was significantly increased in mice injected with anti-LTA. In vitro, anti-Aap and anti-LTA did show binding to S. epidermidis, but no opsonic activity was observed. We conclude that antibodies against S. epidermidis LTA or Aap showed no opsonic activity and did not protect mice against BAI. Moreover, the increase in binding to implanted biomaterial suggests that passive immunization may increase the risk for BAI.

Mobile genetic element-encoded cytolysin connects virulence to methicillin resistance in MRSA

Bacterial virulence and antibiotic resistance have a significant influence on disease severity and treatment options during bacterial infections. Frequently, the underlying genetic determinants are encoded on mobile genetic elements (MGEs). In the leading human pathogen Staphylococcus aureus, MGEs that contain antibiotic resistance genes commonly do not contain genes for virulence determinants. The phenol-soluble modulins (PSMs) are staphylococcal cytolytic toxins with a crucial role in immune evasion. While all known PSMs are core genome-encoded, we here describe a previously unidentified psm gene, psm-mec, within the staphylococcal methicillin resistance-encoding MGE SCCmec. PSM-mec was strongly expressed in many strains and showed the physico-chemical, pro-inflammatory, and cytolytic characteristics typical of PSMs. Notably, in an S. aureus strain with low production of core genome-encoded PSMs, expression of PSM-mec had a significant impact on immune evasion and disease. In addition to providing high-level resistance to methicillin, acquisition of SCCmec elements encoding PSM-mec by horizontal gene transfer may therefore contribute to staphylococcal virulence by substituting for the lack of expression of core genome-encoded PSMs. Thus, our study reveals a previously unknown role of methicillin resistance clusters in staphylococcal pathogenesis and shows that important virulence and antibiotic resistance determinants may be combined in staphylococcal MGEs.

The extreme danger associated with Staphylococcus aureus infections is due to the combination of frequent antibiotic resistance, which prevents efficient treatment, with extraordinary virulence, which determines the severity of disease. S. aureus is known to exchange antibiotic resistance and virulence determinants between different strains, thereby spreading the capacity to cause serious infections in the S. aureus population. The genetic information for these determinants is usually found on so-called mobile genetic elements. It has been noted that such exchangeable elements carry genes for either virulence or antibiotic resistance, but not both. Here, we identified and characterized a potent toxin, whose gene is located within an element that encodes resistance to the important antibiotic methicillin. The toxin had strong capacity to kill human white and red blood cells and significantly affected the capacity of MRSA to cause disease. Our study shows that acquisition of methicillin resistance may be combined with gaining possession of potent toxins by a single event of genetic exchange, which likely represents an important feature accelerating the evolution of MRSA virulence.

Staphylococcus cohnii hemolysins - isolation, purification and properties

A total 355 of Staphylococcus cohnii isolates from hospital environment, patients (newborns), medical staff and from non-hospital environment were tested for hemolytic activity. Ninety-one % of S. cohnii ssp. cohnii and 74.5 % S. cohnii ssp. urealyticus strains exhibited hemolysis synergistic to S. aureus ATCC 25923 strain. Crude preparations of hemolysins of both bacterial subspecies presented delta-hemolysin, but not alpha- and beta-toxin activity. Highly pure hemolysins were obtained by semipreparative SDS-PAGE or by organic solvent extraction from the freeze-dried crude preparations. Native-PAGE and 2D-PAGE showed their high heterogeneity. Molar masses of single hemolysin units estimated by the Tris-Tricine-SDS-PAGE were calculated as 3.47 kDa for S. cohnii ssp. cohnii and 3.53 kDa for S. cohnii ssp. urealyticus.

Synergistic and antagonistic hemolytic activities of bacteria of genus Arcanobacterium and CAMP-like hemolysis of Arcanobacterium phocae and Arcanobacterium haemolyticum with Psychrobacter phenylpyruvicus

A total of 57 bacteria representing eight species of genus Arcanobacterium (A.) were investigated for hemolytic properties on blood agar containing sheep and rabbit blood and for CAMP-like reactions. An enhanced hemolysis on blood agar containing rabbit blood compared to sheep blood could be observed for A. haemolyticum, less pronounced for A. hippocoleae and A. pluranimalium. A synergistic hemolytic reaction with staphylococcal beta-hemolysin appeared to be constantly visible for A. hippocoleae, A. pluranimalium and A. pyogenes, with Streptococcus agalactiae for A. phocae and A. haemolyticum, with Rhodococcus equi for A. phocae, A. haemolyticum, A. pluranimalium and A. pyogenes and with A. haemolyticum for A. hippocoleae, A. pluranimalium and A. pyogenes, respectively. A reverse CAMP-reaction in the zone of staphylococcal beta-hemolysin could be observed for A.phocae and A.haemolyticum. In addition, a novel CAMP-like reaction could be noted between Psychrobacter phenylpyruvicus, identified by 16S rDNA sequencing, and A. phocae and A. haemolyticum. These synergistic or antagonistic hemolytic properties could possibly be used as additional criteria for identification of bacteria of genus Arcanobacterium.

SarZ is a key regulator of biofilm formation and virulence in Staphylococcus epidermidis

Biofilm-associated infection due to Staphylococcus epidermidis, the leading nosocomial pathogen, is a major problem for the public health system, but the regulation of this important phenotype is not completely understood. Using a highly discriminatory screening procedure for genes that influence biofilm formation, we identified the transcriptional regulator SarZ as a novel important determinant of biofilm formation and biofilm-associated infection, on the basis of the significant impact of sarZ on the transcription of the biosynthetic operon for biofilm exopolysaccharide. In addition, sarZ influenced the expression of a series of virulence genes, including genes that influence the expression of lipases and proteases, resistance to an important human antimicrobial peptide, and hemolysis. Our study indicates that the SarZ regulator has a key role in maintaining the typical S. epidermidis phenotype, which is characterized by pronounced biofilm formation and immune evasion, a likely reason for the success of S. epidermidis as a colonizing organism and pathogen in chronic, biofilm-associated infection.

Staphylococcus epidermidis is cleared from biomaterial implants but persists in peri-implant tissue in mice despite rifampicin/vancomycin treatment

Infections associated with implanted biomedical devices (BAI) are predominantly caused by Staphylococcus epidermidis. We previously observed in murine experimental BAI that S. epidermidis persists in peri-implant tissue rather than on the implanted biomaterial itself (Boelens et al., J Infect Dis 2000;181:1337-1349; Broekhuizen et al., Infect Immun 2007;75:1129-1136). To investigate the efficacy of rifampicin/vancomycin to clear S. epidermidis from implants and peri-implant tissues, mice with two implants were challenged with 10(7) cfu S. epidermidis per implant and received daily injections of rifampicin (25 mg/kg) and vancomycin (50 mg/kg). On the day of termination, implants and peri-implant tissue were collected and processed for culture and histology. After 1 and 8 days, implants of control mice were culture positive in 14/18 and 5/16 cases, respectively, and tissue biopsies were all culture positive. In the antibiotic-treated mice, bacteria were recovered from only 1/18 and 1/16 implants after 1 and 8 days, respectively, whereas the tissues were culture positive in 14/18 and 7/16 biopsies, respectively. In microscopy, bacteria were seen in the tissue at a distance of several cell layers from the tissue-implant interface, colocalized with host cells. Thus, although a regimen of rifampicin/vancomycin sterilized the implants, S. epidermidis persisted in peri-implant tissue, which might be an as yet unrecognized reservoir in the pathogenesis of BAI.

Peri-implant tissue is an important niche for Staphylococcus epidermidis in experimental biomaterial-associated infection in mice

Biomaterial-associated infections (BAI), which are predominantly caused by Staphylococcus epidermidis, are a significant problem in modern medicine. Biofilm formation is considered the pivotal element in the pathogenesis, but in previous mouse studies we retrieved S. epidermidis from peri-implant tissue. To assess the kinetics and generality of tissue colonization, we investigated BAI using two S. epidermidis strains, two biomaterials, and two mouse strains. With small inocula all implants were culture negative, whereas surrounding tissues were positive. When higher doses were used, tissues were culture positive more often than implants, with higher numbers of CFU. This was true for the different biomaterials tested, for both S. epidermidis strains, at different times, and for both mouse strains. S. epidermidis colocalized with host cells at a distance that was >10 cell layers from the biomaterial-tissue interface. We concluded that in mouse experimental BAI S. epidermidis peri-implant tissue colonization is more important than biofilm formation.

Identification of Staphylococcus hyicus by polymerase chain reaction mediated amplification of species specific sequences of superoxide dismutase A encoding gene sodA

A species specific PCR test, based on manganese-dependent superoxide dismutase A encoding gene sodA, was developed for the identification of Staphylococcus hyicus, an important bacterial pathogen in pigs. The designed primers allowed a rapid and reliable identification of phenotypically characterized S. hyicus, isolated in Russia, Germany and Denmark. No cross reactivities could be observed investigating staphylococcal reference strains representing 18 different species and subspecies. The use of the described primers might improve a future diagnosis of this bacterial pathogen.

Staphylococcus epidermidis and Staphylococcus xylosus in a secondary root canal infection with persistent symptoms: a case report

The aim of this case report is to highlight the importance of maintaining the aseptic chain during endodontic treatment. This paper describes a clinical situation in which persistent symptoms had developed after the first appointment to treat a vital pulp case. Microbiological analysis of the case indicated that symptoms were probably due to a secondary root canal infection by two species of coagulase-negative staphylococci--Staphylococcus epidermidis and Staphylococcus xylosus. Symptoms had persisted in spite of using various intracanal antimicrobial agents and systemic antibiotic therapy.

Evaluation of two commercial systems and a new identification scheme based on solid substrates for identifying coagulase-negative staphylococci from bovine mastitis

Coagulase-negative staphylococci (CNS), mainly isolated from bovine mastitis (n = 89, representing 11 different species), were used to evaluate two commercial identification systems: ID 32 Staph and Staph-Zym. The level of agreement between the ID 32 Staph and Staph-Zym systems and conventional methods was 77 and 94%, respectively. An alternative method, based on solid biochemical substrates, is also presented. This can be used for identifying novobiocin-sensitive CNS strains from bovine mastitis.

Identification of streptococci isolated from various sources by determination ofcfbgene and other CAMP-factor genes

In the present study, the CAMP-factor (cfb) gene of streptococci of serological group B (Streptococcus agalactiae) and the CAMP-factor (cfu) gene of S. uberis could be amplified by polymerase chain reaction. A cfb specific amplicon could be observed for all 128 phenotypically CAMP-positive S. agalactiae, for the phenotypically CAMP-negative S. agalactiae strain 74-360, and for 2 S. difficile reference strains. A cfu specific amplicon could be observed for all 7 phenotypically CAMP-positive S. uberis. Four S. agalactiae strains isolated from 4 cows with mastitis appeared to be phenotypically CAMP-negative and negative in the cfb gene PCR. The CAMP-positive and CAMP-negative isolates, including both S. difficile, could be identified as S. agalactiae by amplification of a S. agalactiae specific part of the V2 region of the 16S rRNA and a species-specific part of the 16S-23S rRNA intergenic spacer region. Amplification of an internal fragment of the cfb gene with a reduced annealing temperature yielded positive reactions not only for CAMP-positive S. agalactiae, but also for phenotypically CAMP-positive S. pyogenes (n = 4), S. canis (n = 28), and S. uberis (n = 7), indicating a close relation of the CAMP genes of these 4 species. The relation could be further demonstrated by sequencing the internal fragment of the CAMP-factor (cfg) gene of S. canis and comparing the sequence with those of S. agalactiae, S. pyogenes, and S. uberis.Key words: CAMP factor, cfb, cfu, S. canis.

Identification of coagulase-positive staphylococci isolated from bovine milk

A total of 414 coagulase-positive staphylococcal strains obtained at the mastitis laboratory, National Veterinary Institute, Uppsala, Sweden, were studied. One hundred and seventy seven strains were used for a frequency study. Ninety-seven per cent were identified as Staphylococcus aureus, 2% as Staphylococcus intermedius and 1% as Staphylococcus hyicus. Two hundred and thirty seven strains with atypical hemolysis reactions on bovine blood agar were randomly selected, with the aim to increase the number of S. intermedius and S. hyicus strains available for testing. Eight different characteristics, including physiological, enzymatical and biochemical properties, were used to identify the coagulase-positive Staphylococcus species. The results of this study suggest that the following tests should be included for correct identification of the 3 different species of coagulase-positive staphylococci: P agar supplemented with acriflavin, beta-galactosidase and hemolytic reaction on chocolate agar. These 3 tests are simple and quick to perform and enable accurate for easy differentiation of the 3 coagulase-positive Staphylococcus species.

Cytotoxic activity of coagulase-negative staphylococci in bovine mastitis

Secreted toxins play important roles in the pathogenesis of bacterial infections. In this study, we examined the presence of secreted cytotoxic factors of coagulase-negative staphylococci (CoNS) from bovine clinical and subclinical mastitis. A 34- to 36-kDa protein with cell-rounding cytotoxic activity was found in many CoNS strains, especially in Staphylococcus chromogenes strains. The protein caused cell detachment and cell rounding in several cell lines, including HEp-2, Int 407, CHO-K1, and Y-1 cells. Native protein recovered from nondenatured polyacrylamide gel electrophoresis showed both cytotoxic activity and casein hydrolysis activity. The purified protein had a pH optimal at 7.2 to 7.5 and a pI of 5.1 and was heat labile. The proteolytic activity could be inhibited by zinc and metal specific inhibitors such as 1, 10-phenanthroline and EDTA, indicating that it is a metalloprotease. Protein mass analysis and peptide sequencing indicated that the protein is a novel metalloprotease. Different bacterial strains expressed variable levels of 34- to 36-kDa protease, which may provide an indication of strain virulence.

Staphylococcus lugdunensis--a potential pathogen in oral infection

OBJECTIVE

The purpose of this study was to investigate the pathogenicity of Staphylococcus lugdunensis in acute oral infection.

STUDY DESIGN

S. lugdunensis was isolated from patients with acute oral infections and from healthy control subjects. Antibiotic susceptibility, in vitro cellular toxicity, in vivo virulence, and hemolytic activity testing and dot blot analysis were performed. The statistical significance of in vitro cellular toxicity was determined by means of analysis of variance.

RESULTS

Isolated from the infected patients, S. lugdunensis showed resistance to penicillin, ampicillin, methicillin, cephalothin, and clindamycin, exhibited virulence in vivo, and showed delta-like hemolysin activity. Four of the 6 strains of S. lugdunensis gave synergistic hemolysis. In dot blot analysis, S. lugdunensis showed a positive reaction to the probe of the delta-hemolysin gene in S. aureus.

CONCLUSIONS

The results suggest that S. lugdunensis may be a potential pathogen in acute oral infection.

Epidemiological and biological characteristics of methicillin-resistant staphylococcal infections in a Mexican hospital

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) has spread worldwide since 1960. However, there is little information concerning methicillin-resistant coagulase-negative staphylococci (MRCNS) infections.

METHODS

In order to study the clinical and epidemiological characteristics of methicillin-resistant staphylococci (MRS) infections and to determine the relationship between MRS and both synergistic hemolysis (SH) and slime production (SP), a laboratory-based survey and non-matched case-control study were carried out at a tertiary-care center in Mexico City. In regard to patients, from May 1991 to October 1992, 46 cases of MRS infection and 86 patients (controls) infected by methicillin-susceptible staphylococci (MSS) were included. Clinical and epidemiologic variables were analyzed. The isolates were identified and tested for antimicrobial susceptibility by standard methods. An MIC of oxacillin > or = 8 micrograms/mL was defined as an MRS.

RESULTS

During the study, 94 nosocomial staphylococcal infections were diagnosed: S. aureus, 35 and CNS, 59; 43 (45.7%) by MRS (rate of MRS infections was 1.12 per 100 in-patients); 2 MRSA; 41 MRCNS, and only 19 were symptomatic. Three infections were community-acquired, including one MRSA and two MRCNS. After multivariate analysis, the significant risk factors were previous antimicrobial therapy (p = 0.013) and catheter-related (p = 0.009) and urinary-tract source (p = 0.0001). Forty-nine percent of MRS showed SH while only 15% of MSS (p < 0.001) showed SH, especially in 10/10 MR-S. hemolyticus. Additionally, 48% of MRCNS showed SP, as did 18% of MSCNS (p = 0.019), particularly in 15/20 MR-S. epidermidis. Of all MRS isolates, 38% showed a homogeneous phenotype, a trait associated with multi-drug resistance (p < 0.01) and SH (p < 0.001).

CONCLUSIONS

CNS predominated as the cause of MRS infections in our setting. The homogenous phenotype was associated with SH and multi-drug resistance.

Identification of coagulase-positive staphylococci isolated from bovine milk

A total of 414 coagulase-positive staphylococcal strains obtained at the mastitis laboratory, National Veterinary Institute, Uppsala, Sweden, were studied. One hundred and seventy seven strains were used for a frequency study. Ninety-seven per cent were identified as Staphylococcus aureus, 2% as Staphylococcus intermedius and 1% as Staphylococcus hyicus. Two hundred and thirty seven strains with atypical hemolysis reactions on bovine blood agar were randomly selected, with the aim to increase the number of S. intermedius and S. hyicus strains available for testing. Eight different characteristics, including physiological, enzymatical and biochemical properties, were used to identify the coagulase-positive Staphylococcus species. The results of this study suggest that the following tests should be included for correct identification of the 3 different species of coagulase-positive staphylococci: P agar supplemented with acriflavin, beta-galactosidase and hemolytic reaction on chocolate agar. These 3 tests are simple and quick to perform and enable accurate for easy differentiation of the 3 coagulase-positive Staphylococcus species.

Exoprotein and slime production by coagulase-negative staphylococci isolated from goats' milk

Milk from mastitis-free goats from French herds was examined for the presence of coagulase-negative staphylococci (CNS), and 165 positive isolates were evaluated for their capacity to produce exoproteins. Most isolates were identified as Staphylococcus caprae (N = 91) or S. xylosus (N = 36), but members of at least nine other species were present. Overall, some 57% of isolates produced toxins with phenotypic properties of alpha-hemolysin, and 75% produced toxins resembling S. aureus beta and/or delta-hemolysins. Thermostable desoxyribonuclease (TNAse) was secreted by 29% of isolates and thermolabile DNAse by 66%. Slime was produced by 42% of our cultures and, although none of them showed activity to insoluble elastase, over 70% lysed the soluble substrate. No clinical consequences were observed to correlate with exoprotein production, which proved to be inconstant within individual CNS species.

Distribution of the synergistic haemolysin genes hld and slush with respect to agr in human staphylococci

Several staphylococcal species express a synergistic activity which potentiates hemolysis by beta-hemolysin. In Staphylococcus aureus, this activity is mediated by the delta-hemolysin, coded by the hld gene within the agr locus. In S. lugdunensis, the equivalent activity results from the production of 3 small peptides coded by an operon named slush, distinct from hld and located outside the agr region. We examined 15 clinically relevant staphylococcal species for the presence of hld, slush and agr by specific hybridisation. All species contained a recognizable agr-related locus. Three species never produced synergistic haemolysis and contained neither hld nor slush. Of the 12 producer strains, 5 contained hld, apparently within the agr region, 4 contained slush and one (S. caprae) contained both. Two other producer species (S. hominis and S. simulans) hybridised to neither probe.

Synergistic hemolytic activity of Staphylococcus lugdunensis is mediated by three peptides encoded by a non-agr genetic locus

Some strains of the coagulase-negative Staphylococcus lugdunensis produce a synergistic hemolytic activity (SLUSH), phenotypically similar to the delta-hemolysin of S. aureus. Reverse-phase high-pressure liquid chromatography of supernatants from S. lugdunensis 307 yielded three late-eluting peaks of 3.5 kDa with synergistic hemolytic activity. A degenerate oligonucleotide probe was designed from partial amino acid sequences of the 23-amino-acid (aa) tryptic fragments from one of the three peaks and hybridized to a single 2.8-kb HindIII chromosomal fragment. The relevant portion of this fragment was cloned by PCR, and sequencing showed the presence of three related open reading frames (ORFs), SLUSH-A, SLUSH-B, and SLUSH-C, preceded by an unrelated short potentially coding sequence (ORF-X), cotranscribed on a polycistronic 838-nucleotide mRNA. The amino acid sequences of the peptides from the three peaks align perfectly with the predicted sequences from the three SLUSH ORFs (peak I = SLUSH-B; peak II = SLUSH-C; peak III = SLUSH-A). These three peptides are closely related (amino acid homology, >76%) and do not show significant homology to S. aureus delta-hemolysin but do resemble a Salmonella typhimurium invasin and the "gonococcal growth inhibitor," a bacteriocin secreted by Staphylococcus haemolyticus. The predicted ORF-X gene product is a 24-aa peptide with no homology to the SLUSH peptides.

Virulence of Staphylococcus epidermidis in a mouse model: significance of extracellular slime

The ability to produce large quantities of biofilm on solid surfaces in vitro is believed to distinguish potentially pathogenic strains of Staphylococcus epidermidis from commensals. Biofilm consists of staphylococcal cells encased in a matrix of extracellular polysaccharide (also referred to as slime), firmly adherent to each other and to the underlying surface structure. The association of slime with colonization of catheter surfaces in vivo has been examined extensively. Less attention has been paid to the contribution of slime to infections that occur in the absence of an inserted device. In a mouse model of subcutaneous infection without an implanted device 10 S. epidermidis strains (5 slime-positive, 5 slime-negative) produced abscesses; thus a foreign body is not essential for the expression of virulence by S. epidermidis. Biofilm-positive strains produced significantly more abscesses, that persisted longer than biofilm-negative strains. In these chronic infections, large numbers of staphylococci were associated with macrophages and viable staphylococci were cultured from specimens of pus collected at autopsy. Thus slime or components of slime appear to delay the clearance of S. epidermidis from host tissues, possibly by interfering with intracellular killing mechanisms. However, differences in the capacity to produce abscesses, within both the slime-positive and slime-negative groups, indicate that other factors also contribute to the virulence of S. epidermidis.