Development of the quantitative micro-test for slime production by coagulase-negative staphylococci

Biofilm-Forming Ability of Pathogenic Bacteria Isolated from Retail Food in Poland

ABSTRACT

Biofilms have a significant impact on food safety in the food industry. Many foodborne outbreaks have been associated with pathogenic bacterial strains that can form a biofilm. The present study was conducted under the Official Control and Monitoring Program in Poland to examine the ability of pathogenic bacteria collected from retail food samples to form biofilms. Biofilm formation was assessed by qualitative detection of extracellular polymeric substances on Congo red agar, by adherence to glass with the tube method, by the crystal violet biofilm (CV) assay, and by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. A total of 40 isolates from food samples (10 strains each of Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, and Bacillus cereus) were examined. The strains were classified as adherent, slightly adherent, or nonadherent; biofilm production was classified as weak (WBP), moderate (MBP), or strong (SBP); and metabolic activity was classified as weak (WMA), moderate (MMA), or high (HMA). The incubation conditions and time influenced the amount of biofilm formed as well as did the growth medium. In the test tubes with Luria-Bertani broth (LBB), 22.5% of the strains were adherent and 77.5% were slightly adherent. Stronger adhesion was obtained in brain heart infusion (BHI) with 2% sucrose; 60% of the isolates were classified as adherent. With the CV assay with LBB, SBP was noted for 7.5% of the strains after 24 h of incubation and for 37.5% of the strains after 48 h. In BHI plus 2% sucrose, SBP was noted for 42.5 and 37.6% of the strains after 24 and 48 h, respectively. With the MTT assay with LBB, HMA was found for 15% of the strains after 24 h of incubation and for 25% of the strains after 48 h. In BHI plus 2% sucrose, 70 and 85% of the incubated strains were classified as HMA after 24 and 48 h, respectively.

HIGHLIGHTS

Correlation between biofilm formation and antimicrobial susceptibility pattern toward extended spectrum β-lactamase (ESBL)- and non-ESBL-producing uropathogenic bacteria

BACKGROUND

Urinary tract infections (UTIs) are the most common bacterial infection encountered worldwide and are associated with significant morbidity and mortality.

METHODS

The present study was undertaken to investigate the biofilm-forming ability, antibiotic susceptibility patterns and extended spectrum β-lactamase (ESBL) production of seven uropathogenic isolates comprising both Escherichia coli and Klebsiella pneumoniae. The morphological, cultural and biochemical tests for the identification of the isolates, antibiotic susceptibility test, detection of ESBL production, biofilm formation on 96-well microtiter plate and Congo red agar (CRA) media are performed.

RESULTS

The antimicrobial susceptibility profiles obtained in this study showed that the most active drugs gentamicin, amikacin and imipenem (100% sensitivity) were followed by amoxicillin-clavulanic acid (85% sensitivity), co-trimoxazole, ciprofloxacin (57% sensitivity) ceftazidime and kanamycin (50% sensitivity). All the isolates showed resistance to amoxicillin followed by ceftriaxone and cefotaxime (71% resistance), and the scenario gets more complicated because of the production of ESBL by five isolates (three E. coli isolates and two K. pneumoniae). The strains were also able to form biofilm as tested on CRA medium and by microtiter plate assay. The correlation between ESBL, non-ESBL and biofilm-producing E. coli and K. pneumonia was determined along with the multiple drug resistance patterns of E. coli and K. pneumonia.

CONCLUSIONS

The findings of the study indicate that the emergence and rapid spread of such multidrug-resistant pathogens are of great concern. Early detection of ESBL-producing pathogen is of paramount clinical importance; therefore, strict infection control practices as well as therapeutic guidance for confirmed infection can be rapidly initiated.

Phenotypic and Molecular Aspects of Staphylococcus spp. Isolated from Hospitalized Patients and Beef in the Brazilian Amazon

The aim of this study was to characterize and compare Staphylococcus spp. isolated from hospitalized patients and beef marketed in the city of Porto Velho-RO, Brazil. The isolates were subjected to antibiogram tests, adherence capacity tests, detection of the mecA gene, and epidemiological investigation by the random amplified polymorphic DNA (RAPD) technique, using the primers M13 and H12. Among the 123 Staphylococcus spp. isolates, 50 were identified as S. aureus and 73 as coagulase-negative Staphylococcus; among the latter, 7 species were identified. It was observed that the coagulase-negative Staphylococcus isolates showed greater adhesion ability than S. aureus. The profile of antimicrobial susceptibility was different among isolates, all of which were susceptible to vancomycin and linezolid, and had high penicillin resistance rates, varying according to the bacterial class and the source. In this study, all strains were negative for mecA gene detection; however, 36% of S. aureus and 17% of coagulase-negative Staphylococcus were resistant to oxacillin. The genetic relationship of these bacteria, analyzed by RAPD, was able to discriminate the species of coagulase-negative Staphylococcus strains of S. aureus along its origin. It was concluded that the isolates of Staphylococcus spp. derived from beef and human infections differ genetically. Thus, it is suggested that isolates from beef, which were grouped within hospital isolates, were probably carried via contact with beef in hospital professionals or patients.

Long-term oropharyngeal colonization by C. albicans in children with cystic fibrosis

This longitudinal prospective study aimed to determine the prevalence of oropharyngeal colonization by C. albicans in children with cystic fibrosis (CF), and observe the continuity of candidal colonization and the changes in production of virulence factors, susceptibility to antifungal agents and RAPD patterns of the isolates. Thirty-seven children with CF were followed-up for oropharyngeal C. albicans colonization for 18 months. The colonization rate was detected in 54%. All isolates were susceptible to amphotericin B, but those isolated from one patient were resistant to fluconazole. Biofilm production, secretory acid proteinase, phospholipase and esterase activity rates were 30%, 60%, 75% and 80%, respectively. RAPD analysis with the primers OPE-03 and OPE-18 was performed for genotyping. RAPD patterns of the strains isolated from the same patient were related to each other, whereas they were not related with other strains isolated from different patients. Two C. albicans strains isolated from the same patient were found to be unrelated to one another. As a result, long-lasting colonization of the oropharyngeal mucosa of children with CF by endogenous C. albicans isolates having the same RAPD pattern was demonstrated. Colonization prevalance and development of resistance to antifungal agents and the increased production of virulence factors were not correlated.

The Isolation and the Biofilm Formation of Uropathogens in the Patients with Catheter Associated Urinary Tract Infections (UTIs)

BACKGROUND

Urinary tract infections are the most commonly acquired bacterial infections and they account for an estimated 25-40% of the nosocomial infections. The microbial biofilms pose a public health problem for the persons who require indwelling medical devices, as the microorganisms in the biofilms are difficult to treat with antimicrobial agents.

AIMS

The present study included the isolation and the biofilm formation of the uropathogens in patients with catheter associated urinary tract infections.

METHODS AND MATERIALS

This prospective analysis which was carried out over a period of two months, included 50 urine samples from catheterized patients with symptoms of UTI. Following their isolation and identification, all the isolates were subjected to the biofilm detection by the tube adherence method and the Congo Red agar method.

RESULTS

E.coli was found to be the most frequently isolated uropathogen 35(70%), followed by Klebsiella pneumoniae 8(16%), Pseudomona aeruginosa 2(4%), Acinetobacter spp 1(2%), coagulase negative Staphylococci 3(6%) and Enterococci spp 1(2%). In the current study, 30 (60%) strains were positive in vitro for the biofilm production.

CONCLUSION

To conclude, there was significant bacteriuria in all the symptomatic catheterized patients and E.coli was the most frequent isolate. Diabetes (44%) was the most common factor which was associated with the UTIs in the catheterized patients.

Catheter colonization and abscess formation due to Staphylococcus epidermidis with normal and small-colony-variant phenotype is mouse strain dependent

Coagulase-negative staphylococci (CoNS) form a thick, multilayered biofilm on foreign bodies and are a major cause of nosocomial implant-associated infections. Although foreign body infection models are well-established, limited in vivo data are available for CoNS with small-colony-variant (SCV) phenotype described as causative agents in implant-associated infections. Therefore, we investigated the impact of the Staphylococcus epidermidis phenotype on colonization of implanted PVC catheters and abscess formation in three different mouse strains. Following introduction of a catheter subcutaneously in each flank of 8- to 12-week-old inbred C57BL/6JCrl (B6J), outbred Crl:CD1(ICR) (CD-1), and inbred BALB/cAnNCrl (BALB/c) male mice, doses of S. epidermidis O-47 wild type, its hemB mutant with stable SCV phenotype, or its complemented mutant at concentrations of 10(6) to 10(9) colony forming units (CFUs) were gently spread onto each catheter. On day 7, mice were sacrificed and the size of the abscesses as well as bacterial colonization was determined. A total of 11,500 CFUs of the complemented mutant adhered to the catheter in BALB/c followed by 9,960 CFUs and 9,900 CFUs from S. epidermidis wild type in BALB/c and CD-1, respectively. SCV colonization was highest in CD-1 with 9,500 CFUs, whereas SCVs were not detected in B6J. The minimum dose that led to colonization or abscess formation in all mouse strains was 10(7) or 10(8) CFUs of the normal phenotype, respectively. A minimum dose of 10(8) or 10(9) CFU of the hemB mutant with stable SCV phenotype led to colonization only or abscess formation, respectively. The largest abscesses were detected in BALB/c inoculated with wild type bacteria or SCV (64 mm(2) vs. 28 mm(2)). Our results indicate that colonization and abscess formation by different phenotypes of S. epidermidis in a foreign body infection model is most effective in inbred BALB/c followed by outbred CD-1 and inbred B6J mice.

Antimicrobial resistance and production of biofilms in clinical isolates of coagulase-negative Staphylococcus strains

Coagulase-negative Staphylococcus (CNS) strains are frequently associated with bacteremia and hospital-acquired infections. 293 CNS strains were isolated from 744 samples from a dialysis center in S. M. de Tucumán, Argentina, from hemocultures, catheters and urine and identified as S. epidermidis, S. haemolyticus, S. saprophyticus, S. hominis and S. cohnii. 13 antibiotics were tested for antibacterial resistance. 75% of S. saprophyticus, 66% of S. epidermidis and 57% of S. haemolyticus was resistant to erythromycin and 50% of S. haemolyticus was resistant to ciprofloxacin. OXA resistance was found in 43% of S. haemolyticus. Presence of PBP 2a in OXA-R strains was confirmed with the modified agglutination assay (MRSA) and presence of the mecA gene. 15 strains with intermediate halos for vancomycin and teicoplanin showed a MIC in solid and liquid medium <or=1 microg/ml and <or=4 microg/ml respectively, which means that they were susceptible. 30% of the CNS strains produced biofilms: 42% of S. haemolyticus and 40% of S. epidermidis. 76% of the S. epidermidis and 59% of the S. haemolyticus biofilm-producing strains were isolated from catheters. The disc-diffusion technique together with the agglutination assay proved to be fast and reliable, which is of essential importance in intensive care units. Rapid identification of CNS strains, detection of resistance to methicillin and biofilm production are decisive for a prompt and appropriate antimicrobial therapy and limited use of inappropriate glycopeptides.

An in vitro study of adherence of coagulase-negative staphylococci to bone chip columns

Coagulase-negative staphylococci (CNS) have become a dominant cause of bone infections and their adherence to the infected bones is a prerequisite for the initiation of these infections. In the present study we investigated and compared the adherence of CNS bacteria to human, chicken and rabbit bones. The study was performed using columns made of bone powder from the three different sources, and measurement of the extent of adhesion to bones of CNS bacteria as an in vitro model which is based on particles of matrix that are closely related to the natural matrix. The adhesion to rabbit bone was relatively high, while adhesion to both human and chicken bone columns was lower and almost identical. Pretreatment of the CNS bacteria with sodium periodate, beta-galactosidase or proteinase K significantly inhibited by 50-60% the adhesion to human bones. Pretreatment of CNS bacteria with subinhibitory concentrations of vancomycin or tunicamycin increased their adherence to human bones several-fold. When the bones were pretreated with vancomycin a considerable increase in the adhesion rate of the bacteria to human and chicken bones was seen. A smaller increase in adherence was observed after pretreatment of human bones with the antibiotic tunicamycin. Salicylic acid or benzalkonium chloride (BZC) also resulted in an increase in adhesion to these pretreated bones. From the results obtained it seems that pretreatment of the CNS bacteria with certain reagents exposes adhesins on the surface of the CNS bacteria. On the other hand, pretreatment of the bones with other reagents may enable a better exposure of receptors located on the bone cells and, as a consequence, may improve the adhesion of the CNS bacteria to the treated bones.

Assessment of ica operon carriage and biofilm production in Staphylococcus epidermidis isolates causing bacteraemia in bone marrow transplant recipients

The clinical significance of coagulase-negative staphylococci isolated from blood culture is typically assessed on the basis of a combination of clinical and microbiological criteria. However, these criteria are difficult to apply to haematology patients who are highly immunosuppressed and from whom blood cultures are obtained most frequently through a central venous catheter. This study analysed 112 episodes of Staphylococcus epidermidis bacteraemia that occurred in 79 bone marrow transplant recipients. In 73 (65%) episodes, only one blood culture set was positive for S. epidermidis, while 39 (35%) episodes grew S. epidermidis from multiple blood cultures. Nine patients had two or more episodes of bacteraemia with the same strain, as determined by pulsed-field gel electrophoresis (PFGE). The PFGE method also showed that 34 (31%) isolates belonged to seven clusters, indicating the persistence of certain clones in the environment. Of the 109 isolates analysed, 59 (54%) produced biofilm and 91 (83.5%) carried the ica operon. Isolates that produced biofilm were observed to colonise central venous catheters faster than non-biofilm-producing isolates (18 vs. 37 days; p 0.03). No clinical features were associated with carriage of the ica operon, but the ica operon was carried more frequently by the isolates that formed clusters.

Esp-independent biofilm formation by Enterococcus faecalis

Enterococcus faecalis is a gram-positive opportunistic pathogen known to form biofilms in vitro. In addition, this organism is often isolated from biofilms on the surfaces of various indwelling medical devices. However, the molecular mechanisms regulating biofilm formation in these clinical isolates are largely unknown. Recent work has suggested that a specific cell surface protein (Esp) of E. faecalis is critical for biofilm formation by this organism. However, in the same study, esp-deficient strains of E. faecalis were found to be capable of biofilm formation. To test the hypothesis that Esp is dispensable for biofilm formation by E. faecalis, we used microtiter plate assays and a chemostat-based biofilm fermentor assay to examine biofilm formation by genetically well-defined, non-Esp-expressing strains. Our results demonstrate that in vitro biofilm formation occurs, not only in the absence of esp, but also in the absence of the entire pathogenicity island that harbors the esp coding sequence. Using scanning electron microscopy to evaluate biofilms of E. faecalis OG1RF grown in the fermentor system, biofilm development was observed to progress through multiple stages, including attachment of individual cells to the substratum, microcolony formation, and maturation into complex multilayered structures apparently containing water channels. Microtiter plate biofilm analyses indicated that biofilm formation or maintenance was modulated by environmental conditions. Furthermore, our results demonstrate that expression of a secreted metalloprotease, GelE, enhances biofilm formation by E. faecalis. In summary, E. faecalis forms complex biofilms by a process that is sensitive to environmental conditions and does not require the Esp surface protein.

The effects of magnesium, calcium and EDTA on slime production by Staphylococcus epidermidis strains

Effect of magnesium, calcium and EDTA on slime production by 15 slime-positive and 13 slime-negative Staphylococcus epidermidis strains isolated from various clinical specimens was determined. The slime production on tryptic soy broth was significantly enhanced after addition of 128 mumol/L Mg2+. Similarly, the addition of Ca2+ caused a significant increase in slime production of all tested strains when concentration of Ca2+ exceeded 64 mumol/L. In contrast, in the presence of EDTA the slime production by all strains was significantly reduced. Hence Ca2+ and Mg2+ increase slime production of S. epidermidis. This finding is important in the context of the pathogenesis of biomedical implant infections caused by S. epidermidis.

Detection of differential gene expression in biofilm-forming versus planktonic populations of Staphylococcus aureus using micro-representational-difference analysis

Microbial proliferation and biofilm formation on biologic or inert substrates are characteristics of invasive Staphylococcus aureus infections and is associated with phenotypic alterations such as reduced antimicrobial susceptibility. To identify genes which are typically expressed in biofilms, a micro-representational-difference analysis (micro-RDA) was adapted for gram-positive bacteria and used with cDNA derived from populations of S. aureus DSM 20231 growing in a biofilm or plankonically. In comparison to previously described cDNA RDA protocols, micro-RDA has the advantages that only minimal quantities of total RNA are needed and, most importantly, that total RNA can be used since the large amount of rRNA in total RNA does not interfere with the micro-RDA procedure. Using a series of spiked controls with various amounts of MS2 RNA in a background of total RNA from S. aureus, the equivalent of five copies of MS2 per cell were detectable after three rounds of subtractive enrichment. Five genes were identified as being differentially expressed in biofilm versus planktonic cultures. These genes revealed homology to a threonyl-tRNA synthetase, a phosphoglycerate mutase, a triosephosphate isomerase, an alcohol dehydrogenase I, and a ClpC ATPase. Differential levels of expression were subsequently confirmed by standard Northern blotting. In conclusion, micro-RDA is a sensitive and specific method to detect transcripts differentially expressed as a function of different S. aureus growth conditions.

Slime-producing properties of coagulase-negative staphylococci isolated from blood cultures

OBJECTIVE: To evaluate five methods for the determination of slime-producing properties in coagulase-negative staphylococci (CNS). METHODS: One hundred and sixty-two strains of CNS considered as 'contaminants' and 162 strains associated with 'bacteremia' were tested with the tube test with tryptic soy broth, the tube test with brain---heart infusion broth supplemented with 5% sucrose, the Congo red agar method, and the microtiter-plate test with trypan blue and crystal violet, both with tryptic soy broth. RESULTS: Of the 324 strains tested, 188 were negative and 58 were positive with all methods. The remaining 78 strains were positive with one or more methods. CONCLUSIONS: There was a significant difference (p<0.001) in slime production between 162 strains of CNS pertaining to 'bacteremia' and 162 strains considered as 'contaminants', with 84 (51.8%) and 52 (32.8%) positive, respectively. The slime-producing strains were significantly more resistant (p<0.001) to cloxacillin, tobramycin, gentamicin, trimethoprim, erythromycin and ciprofloxacin.

Further characterization of Staphylococcus epidermidis transposon mutants deficient in primary attachment or intercellular adhesion

Biofilm formation is suggested to be the result of primary attachment of Staphylococcus epidermidis cells to a polymer surface followed by accumulation in multilayered cell clusters. Here we describe the further characterization of transposon (Tn917) mutants of Staphylococcus epidermidis O-47 having been biofilm-negative in a polystyrene microtiter plate adhesion assay. Among 5000 Tn917 insertion strains, we isolated four biofilm-negative mutants, each carrying one copy of Tn917. The mutants could be divided into two phenotypic classes: class A (mut1 and mut1a) and class B (mut2 and mut2a). Mutants of phenotype class A lacked four cell surface proteins and were affected in the primary attachment to polystyrene, but remained able to form multilayered cell clusters and to produce PIA. Mutants of phenotype class B were able to attach to polystyrene, but did not form multilayered cell clusters nor produce PIA. The cell surface protein pattern relative to the wild type was unchanged in class B mutants. On Congo red agar, the wild type and class A mutants formed black colonies (positive reaction on Congo red agar) while class B mutant colonies were red (negative reaction). The initial binding of cells to polystyrene and the ability to form multilayered cell clusters were found to be phenotypically and genetically distinct traits.

Molecular basis of intercellular adhesion in the biofilm-forming Staphylococcus epidermidis

The Staphylococcus epidermidis genes icaABC are involved in the synthesis of the polysaccharide intercellular adhesin (PIA), which is located mainly on the cell surface, as shown by immunofluorescence studies with PIA-specific antiserum. PIA was shown to be a linear beta-1,6-linked glucosaminoglycan composed of at least 130 2-deoxy-2-amino-D-glucopyranosyl residues of which 80-85% are N-acetylated, the rest being non-N-acetylated and positively charged. A transposon insertion in the icaABC gene cluster (ica, intercellular adhesion) led to the loss of several traits, such as the ability to form a biofilm on a polystyrene surface, cell aggregation, and PIA production. The mutant could be complemented by transformation with the icaABC-carrying plasmid pCN27. Transfer of pCN27 into the heterologous host Staphylococcus carnosus led to the formation of large cell aggregates, the formation of a biofilm on a glass surface, and PIA expression. The nucleotide sequence of icaABC suggests that the three genes are organized in an operon and that they are co-transcribed from the mapped icaA promoter. IcaA contains four potential transmembrane helices, indicative of a membrane location. The deduced IcaA sequence shows similarity to those of polysaccharide-polymerizing enzymes, the most pronounced being with a Rhizobium meliloti N-acetylglucosaminyltransferase involved in lipo-chitin biosynthesis (22.5% overall identity and 37.4% overall similarity). This similarity suggests that IcaA has N-acetylglucosaminyltransferase activity in the formation of the beta-1, 6-linked N-acetyl-D-glucosaminyl polymer. IcaB is secreted into the medium and contains a typical signal peptide. IcaC is hydrophobic and contains six predicted transmembrane helices distributed over its entire length, typical for an integral membrane protein. Neither IcaB nor IcaC shares similarity with known proteins, and their function is unknown. Inactivation of icaA, icaB, or icaC in pCN27 led to the complete loss of the intercellular adhesion phenotype in S. carnosus, suggesting that all three genes are involved in intercellular adhesion, PIA expression, and translocation.

Characterization of Tn917 insertion mutants of Staphylococcus epidermidis affected in biofilm formation

Biofilm formation is thought to result from the concerted action of primary attachment to a specific surface and accumulation in multilayered cell clusters. Here we describe the isolation and characterization of transposon (Tn917) mutants of Staphylococcus epidermidis O-47 which were biofilm negative in the polystyrene microtiter plate assay. Among 5,000 Tn917 insertion mutants, 4 biofilm-negative mutants were isolated. Each mutant carried one copy of Tn917. The mutants were divided into two phenotypic classes: class A (mut1 and mut1a) and class B (mut2 and mut2a). Mutants of phenotypic class A lacked four cell surface proteins, were less hydrophobic, and were affected in primary attachment to polystyrene, but were still able to form multilayered cell clusters. They were able to form a biofilm on a glass surface, a trait that was even more pronounced than in the wild-type stain O-47. Loss of several surface proteins might have led to the reduced surface hydrophilic structures, thus favoring primary attachment to a glass surface and leading to subsequent biofilm formation. Mutants of phenotype class B were able to attach to polystyrene but were unable to form multilayered cell clusters, had unchanged cell surface proteins and hydrophobicity, and were unable to form a biofilm on a glass surface, mut1 and mut2 could be complemented by wild-type DNA fragments containing the Tn917 insertion sites of mut1 and mut2, respectively. The complemented biofilm-positive clone mut1 (pRC20) produced a 60-kDa protein which is postulated to function as the adhesin for binding to plastic. The traits of binding to polystyrene and the ability to form multilayered cell clusters are phenotypically and genetically distinct.

Influence of strain, biomaterial, proteins, and oncostatic chemotherapy on Staphylococcus epidermidis adhesion to intravascular catheters in vitro

Initial adhesion of four phenotypically different strains of Staphylococcus epidermidis to 16 silicone, polyurethane, or hydrophilic polyurethane catheters was assessed in vitro by a bacterial radiolabeling method. The effect of catheter exposure to plasma proteins, to an anticancer polychemotherapy (5-fluorouracil, doxorubicin, cyclophosphamide), or to both of them was determined. Bacterial adhesion on native catheters was dependent on the hydrophobicity of both bacteria and catheters. The four strains tested adhered preferentially to silicone catheters (p < 0.05); adhesion was moderate to polyurethane surfaces, whereas the least adhesion was obtained for hydrophilic polyurethane catheters. Adsorption of plasma proteins on the surface produced a marked decrease in adhesion on silicone (-66.2%; p < 0.001) and polyurethane (-32.8%; p < 0.01) catheters and a marked increase in adhesion on hydrophilic surfaces (+91.7%; p < 0.05). Chemotherapeutic treatment of the catheter produced a slight but not significant decrease in adhesion on silicone (-17.4%) and polyurethane (-19.8%) catheters and a marked increase in adhesion on hydrophilic polyurethanes (+148.2%; p < 0.001). The in vitro simulation of catheter use suggested that oncostatic drugs and plasma proteins play an important role in S. epidermidis adhesion to intravascular catheters. Overall, bacterial adhesion is lowest on hydrophilic polyurethane catheters before and after simulation of catheter use.

Activation of the human immunodeficiency virus long terminal repeat in THP-1 cells by a staphylococcal extracellular product

Staphylococcal strains can release a factor that strongly activates the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) in THP-1 cells transfected with the HIV-1 LTR-driven luciferase reporter gene (THP-1 LTRluc). The factor is present in the overnight culture fluid and is readily released from the organisms into aqueous medium by vigorous mixing. Staphylococcal extracellular material is a complex mixture of polysaccharide and protein containing peptidoglycan and teichoic acid, released in part by cell wall turnover. The importance of the carbohydrate component is emphasized by concanavalin A (Con A) inhibition of staphylococcal product-induced LTR activation but not of activation by phorbol 12-myristate 13-acetate or tumor necrosis factor. The effect of Con A was decreased or abolished by sugars in the order methyl alpha-D-mannopyranoside > methyl alpha-D-glucopyranoside > mannose > glucose = fructose > N-acetylglucosamine. Wheat germ agglutinin was less inhibitory than Con A; in this instance N-acetylglucosamine decreased inhibition, whereas methyl alpha-D-mannopyranoside or methyl alpha-D-glucopyranoside did not. The induction of luciferase activity in THP-1 LTRluc by the staphylococcal extracellular product also was inhibited by fetal bovine and normal human serum. A comparison of 31 staphylococcal isolates (9 Staphylococcus aureus, 11 Staphylococcus epidermidis, 2 Staphylococcus haemolyticus, 4 Staphylococcus hominis, 2 Staphylococcus capitis, 2 Staphylococcus warneri, 1 Staphylococcus saprophyticus) revealed wide variation in LTR activating activity that did not correlate closely with slime production. Our findings, using induction of luciferase in THP-1 LTRluc as a model for upregulation of HIV infection, raise the possibility that staphylococci, as well as certain other microorganisms, release carbohydrate-containing exopolymers, which can activate the HIV-1 LTR, thus influencing progression of HIV infection.

Variable fixation of staphylococcal slime by different histochemical fixatives

A variety of histochemical fixatives were used to compare the fixation of bacterial films produced by a standard slime-producing strain of Staphylococcus epidermidis on plastic tissue culture plates. Some reagents were completely ineffective in fixing the slime layer, whereas others gave variable results. The best alternative to the fixative of the reference method, the potentially explosive Bouin's reagent, was air drying.

The slime of coagulase-negative staphylococci: biochemistry and relation to adherence

In recent years, infections of implanted plastic devices by coagulase-negative staphylococci have become a major cause of septicaemia in human patients. The causal bacterial species is usually Staphylococcus epidermidis and these organisms grow as a biofilm adherent to a solid surface. Several methods have been introduced to assess the mass of adherent bacteria and the slimy matrix in which they are embedded. Some methods measure total biofilm, others measure the organisms or the slime alone. In vitro, the type of medium, the atmosphere during incubation, and the nature of the solid surface, affect the quantity of biofilm that is formed. In most studies on the chemistry of the slime, the material used was formed on complex media solidified with agar. Contamination by ingredients of the media or by agar may not always have been recognised. Recent work with chemically defined medium (liquid or solidified with silica gel) shows that the slime is a mixture of about 80% (w/w) teichoic acid and 20% protein. Growth as a biofilm may protect the staphylococci from antibiotics. At present, the greatest success in preventing infection has come from improved surgical techniques during the insertion of implants.

Surface hydrophobicity of Staphylococcus intermedius and Staphylococcus hyicus

Surface hydrophobicity of 90 Staphylococcus intermedius and 55 S hyicus isolates was evaluated using the hexadecane adherence assay and the ammonium sulphate salt aggregation test. A strongly positive hydrocarbon adherence in the hexadecane adherence assay was demonstrated in 11 per cent of the S intermedius isolates and 7 per cent of the S hyicus isolates. Bacterial aggregation in 1.6 M, or less, ammonium sulphate was observed in 28 per cent of the S intermedius isolates and 37 per cent of the S hyicus isolates. There was no statistical correlation between the two assays. The adherence of both bacterial species to hexadecane was eliminated when the cells were first treated with pronase and trypsin, while it was mildly enhanced by prior heat treatment (60 degrees C and 95 degrees C for up to three hours). In contrast, aggregation of S intermedius in ammonium sulphate was not influenced by trypsin pretreatment, and aggregation of both bacterial species was diminished, or eliminated, with pronase or prior 95 degrees C heat treatment. Surface hydrophobicity, as measured in both assays, appeared to have no relationship with growth patterns in serum soft agar or production of slime. Similarly, the presence or absence of substantial surface receptor activity to fibrinogen, fibronectin or IgG did not appear to be related to surface hydrophobicity.

Slime production by Staphylococcus saprophyticus

Only 9 of 30 Staphylococcus saprophyticus strains produced slime in trypticase soy broth, while all did so in urine. It was found that urea was essential for the production of slime. The pH, the iron concentration, or the presence of sex hormones did not affect slime production.

Adherence measured by microtiter assay as a virulence marker for Staphylococcus epidermidis infections

Staphylococcus epidermidis strains isolated from clinical sources showed a wide range of abilities to adhere to glass and plastic materials. The degree of adherence depended on a number of factors, most notably, the composition of the growth medium. Adherence was enhanced by the addition of glucose or oleic acid to the growth medium and inhibited by serum. We have demonstrated a statistically significant association between the quantitative assessment of adherence to polystyrene tissue culture plates and clinical relevance. No such association was found when adherence was assessed by the qualitative adherence assay. Possible new approaches for assessing the clinical relevance of coagulase-negative staphylococcal isolates are discussed.

Laboratory, clinical, and epidemiological aspects of coagulase-negative staphylococci

Coagulase-negative staphylococci, particularly Staphylococcus epidermidis, are increasingly important causes of nosocomial infection. Microbiologists and clinicians no longer can afford to disregard clinical isolates of coagulase-negative staphylococci as contaminants. Accurate species identification and antimicrobial susceptibility testing, in a clinically relevant time frame, are important aids in the diagnosis and management of serious coagulase-negative staphylococcal infections. Emphasis in the clinical laboratory should be placed on the routine identification of S. epidermidis and Staphylococcus saprophyticus, with identification of other species of coagulase-negative staphylococci as clinically indicated. The application of newer techniques, such as plasmid analysis and tests for slime production and adherence, contribute to our understanding of the epidemiology and pathogenesis of coagulase-negative staphylococci and may also be helpful in establishing the diagnosis of infection.