Antibiotic susceptibility and phage-type pattern of Staphylococcus aureus strains isolated from patients in general practice compared to strains from hospitalized patients

Distribution of toxin genes among different spa types and phage types of animal Staphylococcus aureus

We analyzed distribution of toxin genes (sea-seo, eta, etb, tst, lukS/lukF-PV) among spa types and phage types of 39 Staphylococcus aureus (S. aureus) isolates from healthy and diseased animals. All isolates turned out to be mecA negative (MSSA). Nine spa types were identified: t144 and t723 (dogs), t084 (dogs and pigs), t5447 (cat), t1491 and t008 (pigs), t002, t127 and t3478 (poultry). Seven phage types were detected, enclosed within four phage groups: I (cat), II (dogs), III (pigs) and mixed group (dogs and pigs). Three poultry spa types proved to be non-typeable by phages. Toxin genes were detected in 33 out of the 39 animal isolates. Our analysis revealed that the incidence of some toxin genes in S. aureus is host specific. Canine isolates t144 of phage group II harbored exfoliative toxin gene (eta), and porcine isolates type t1491 representing phage group III showed enterotoxin A gene (sea). The enterotoxin gene cluster (egc1) and enterotoxin gene seh were found in non-typeable isolates from chicken and in one feline isolate type t5447.

Rapid optical determination of β-lactamase and antibiotic activity

BACKGROUND

The absence of rapid tests evaluating antibiotic susceptibility results in the empirical prescription of antibiotics. This can lead to treatment failures due to escalating antibiotic resistance, and also furthers the emergence of drug-resistant bacteria. This study reports a rapid optical method to detect β-lactamase and thereby assess activity of β-lactam antibiotics, which could provide an approach for targeted prescription of antibiotics. The methodology is centred on a fluorescence quenching based probe (β-LEAF--β-Lactamase Enzyme Activated Fluorophore) that mimics the structure of β-lactam antibiotics.

RESULTS

The β-LEAF assay was performed for rapid determination of β-lactamase production and activity of β-lactam antibiotic (cefazolin) on a panel of Staphylococcus aureus ATCC strains and clinical isolates. Four of the clinical isolates were determined to be lactamase producers, with the capacity to inactivate cefazolin, out of the twenty-five isolates tested. These results were compared against gold standard methods, nitrocefin disk test for β-lactamase detection and disk diffusion for antibiotic susceptibility, showing results to be largely consistent. Furthermore, in the sub-set of β-lactamase producers, it was demonstrated and validated that multiple antibiotics (cefazolin, cefoxitin, cefepime) could be assessed simultaneously to predict the antibiotic that would be most active for a given bacterial isolate.

CONCLUSIONS

The study establishes the rapid β-LEAF assay for β-lactamase detection and prediction of antibiotic activity using S. aureus clinical isolates. Although the focus in the current study is β-lactamase-based resistance, the overall approach represents a broad diagnostic platform. In the long-term, these studies form the basis for the development of assays utilizing a broader variety of targets, pathogens and drugs.

Plasmid profile analysis and evaluation of antibiotic susceptibility of Staphylococcus aureus strains isolated from table chicken eggs

The aim of this study was to isolate and characterize Staphylococcus aureus bacteria present on the shell surfaces and in the contents of chicken eggs, taking into account their phenotypic properties, antibiotic susceptibility patterns, and the presence of plasmid DNA. The study included 90 table chicken eggs from laying farms situated in the vicinity of Lublin. A total of 105 bacterial strains identified as Staphylococcus were isolated from the material, of which 18 (17.14%) were of the species Staphylococcus aureus. All 18 S. aureus strains were found to be resistant to at least one of the antibiotics tested, while some (55.55%) showed resistance to five or more of the 17 therapeutic agents. The greatest number of strains showed resistance to erythromycin (66.66%), tetracycline (66.66%), oxytetracycline (61.11%), penicillin G (50%), and amoxicillin (44.44%). The plasmid profile analysis of the S. aureus strains made it possible to evaluate the dependence between antibiotic susceptibility and the presence of plasmids in particular isolates. The results showed that plasmids in various quantities and of varying molecular weights were isolated from 17 of the strains. Most often isolated were small plasmids, of 5.6 kb - from 11 of the S. aureus strains (61.11%), 2.5 kb - from 9 strains (50%), 4.1 kb - from 8 (44.44%), and 4.6 kb - from 7 (38.88%) of the strains.

PCR detection of toxic shock syndrome toxin of Staphylococcus aureus from Tripoli, Libya

Sixty-three Staphylococcus aureus strains (40 from clinical sources and 23 from food sources) were examined for toxic shock syndrome toxin-1 (TSST-1) using PCR, phage typed using the international phage set (IPS) and tested for their susceptibility to antibiotics. Only three strains (all from clinical sources) were positive for the TSST-1 gene (tst). The majority of S. aureus strains that were typeable by IPS belonged to group II. Resistance to one or more antibiotics was detected in 47.5 and 73.9 % of clinical and food strains, respectively. This is the first time that PCR detection of tst in S. aureus has been reported from Libya, and further studies are needed on the occurrence of toxic shock syndrome in the community and the role of TSST-1-producing S. aureus in this disease in Libya.

Role of the clinical microbiology laboratory in infection control--a Danish perspective

Clinical microbiology laboratories in Denmark are located in hospitals and staffed by clinical microbiologists who are clinically trained medical doctors. Each county has its own clinical microbiology unit, serving a population of 0.3-0.6 million. The responsibilities of clinical microbiology unit cover many different aspects of infection control. They include detection of outbreaks of hospital-acquired infections, screening for multi-resistant organisms, advice to clinicians about disinfection, sterilization and isolation procedures, and the rational use of antibiotics. Clinical microbiologists work closely with infection control nurses. Together they form the infection control team, which is the executive part of the local infection control committee. The infection control team is also the main body responsible for the development of guidelines, which are approved by the regional infection control committee. The local microbiology laboratories work in close contact with the National Department of Hospital Hygiene and other reference laboratories at the State Serum Institute. The present structure of infection control was established 25 years ago. The main aim at that time was to decentralize infection control and establish facilities as close to clinicians and patients as practically possible. This has solved most basic problems related to infection control, and compliance by clinicians has been fairly good. However, the present organization will not meet future requirements for standardization and documentation of quality. Currently a national standard for infection control is being prepared. It consists of a main standard defining requirements for the management system and 12 subsidiary standards defining requirements for specific areas of infection control. Adoption of the standard will undoubtedly require additional resources for infection control at a local level, and some organizational changes may also be needed. Infection control should be maintained as an integrated part of clinical microbiology.

Antimicrobial susceptibility and presence of resistance genes in staphylococci from poultry

The species distribution, susceptibility to 19 antimicrobial agents and presence of selected genes encoding resistance to macrolides, streptogramins and tetracyclines were examined among 118 staphylococcal isolates from infections of poultry in Denmark. Isolates were identified using a combination of conventional biochemical testing and 16S rDNA sequencing. The most common species were Staphylococcus aureus (83), Staphylococcus hyicus (11), Staphylococcus xylosus (9) and Staphylococcus cohnii (6). The isolates were susceptible to most antimicrobials tested. A high frequency of S. aureus (30%) was resistant to ciprofloxacin. Only six (7%) S. aureus isolates and one Staphylococcus saprophyticus were penicillin resistant. Resistance to sulphamethoxazole was observed among 16 (19%) of S. aureus isolates and two coagulase negative staphylococci (CNS). Twenty (24%) of the S. aureus isolates were resistant to erythromycin and 19 of these isolates contained the ermA gene, whereas the remaining isolate contained the ermC gene. Eleven (48%) of the novobiocin resistant CNS were resistant to erythromycin and all these isolates contained the ermA gene. Two isolates identified as S. xylosus, were found to be resistant to streptogramins and both contained the vatB- and the vgaB-genes. Thirty-nine (47%) of the S. aureus isolates, three of nine S. hyicus and eight of the 23 novobiocin resistant CNS were tetracycline resistant and all contained the tet(K) gene. A single S. aureus isolate also contained the tet(M) gene. The present study showed a frequent occurrence of resistance to fluoroquinolones, tetracycline and macrolides among staphylococci isolated from broilers in Denmark, whereas the occurrence of resistance to other antimicrobial agents remains low. Similar genes, encoding resistance to erythromycin, tetracycline and streptogramins to those previously observed, were detected.

Increased typability of multiresistant Staphylococcus aureus by reverse phage typing

Sixty percent of Staphylococcus aureus isolates from patients in Israeli hospitals proved to be non typable by the conventional phage typing method. Heat pretreatment improved typability only to 54% while reverse typing increased typability to 75%. In general isolates typable by conventional phages belonged to group V, II, III, I, or to mixed groups. While isolates typable only by reverse typing belonged to group III, II, the extended group III + IIIa, or to mixed groups, but seldom to group I. Although most isolates were resistant to penicillin G, only one half were resistant to other antibiotics as well. While one third of these isolates could by typed by conventional phage typing, typability was significantly improved to over 80%, by the use of reverse typing as the additional typing method. Two main groups of oxacillin resistant isolates were identified. The partial resistant group consisting of isolates resistant to penicillin G and oxacillin with no or few other resistances. These isolates were mostly typable by conventional phage typing (group V) and dominated in the first study period (1989-1990) but were only seldom isolated in the second one (1991-1992). The multiresistant group consisted of isolates resistant to penicillin G and oxacillin accompanied by resistances to 3-5 other antibiotics (chloramphenicol, clindamycin, erythromycin, gentamicin and tetracycline). These isolates were mostly typable by reverse typing (the extended group III + IIIa) and showed no change in isolation frequencies during the entire study period. Reverse typing is proposed by us as a typing tool for these multiresistant S. aureus isolates.

Risk of resistance related to antibiotic use before admission in patients with community-acquired bacteraemia

We analysed the association of antibiotic therapy before admission and antibiotic resistance of blood isolates in a total of 1717 community-acquired bacteraemias in the County of Northern Jutland during 1992-96. Antibiotics had been prescribed to 14% of the patients during the 30 days before admission and to 37% during the 6 months. The most frequently prescribed antibiotics within 30 days were ampicillin (28%), penicillin G (27%), sulphonamides and/or trimethoprim (16%) and macrolides (14%). The most frequent blood isolates were Escherichia coli (33%), other Enterobacteriaceae (8%), Streptococcus pneumoniae (23%) and Staphylococcus aureus (10%). Of the 575 isolates of E. coli, 425 (74%), 432 (75%) and 518 (90%) were susceptible to ampicillin, sulphonamides and trimethoprim, respectively. Previous antibiotic prescriptions were strongly associated with resistance to ampicillin, sulphonamides and trimethoprim in E. coli. The association was less pronounced for S. aureus and enteric rods other than E. coli. Antibiotic prescriptions within the last 3 months predicted antibiotic resistance, and this should be taken into account when selecting empirical antibiotic therapy of severe community-acquired infections.

A study of phage- and ribotype patterns of Staphylococcus aureus isolated from bovine mastitis in the Nordic countries

This study was conducted to investigate the geographical distribution of phage and ribotypes of Staphylococcus aureus causing bovine mastitis in the 5 Nordic countries. A total of 403 isolates of S. aureus was isolated from 403 different dairy herds. One hundred five strains were isolated in Denmark, 81 in Finland, 17 in Iceland, 96 in Norway and 104 in Sweden. The isolates were phage typed and characterized for their EcoRI restriction fragment length polymorphisms of the genes encoding ribosomal RNA (ribotyping). A total of 351 (87%) of the 403 isolates could be typed by phages assigning them to 25 different phage types. Two to 3 different phage types predominated within each country. One type (29/52) accounted for 36% of all the isolates and was found in 4 of the countries. A total of 87 different ribotypes was found among the isolates investigated. As for phage typing 2 to 3 different types predominated within countries. However, except for one type (ribotype 1), which was commonly found in Denmark, Sweden and Finland, different ribotypes predominated within each country. The combination of phage and ribotyping assigned the isolates to 178 different types. Ninety-six percent of the isolates of ribotype 1 belonged to phage type 29/52. This combined type accounted for 17% of all the 403 isolates. These findings show that a large number of different types of S. aureus can be isolated from cases of bovine mastitis. However, few types predominate within different countries. These predominating types seem to be specific in each country, however, a single type was common for both Denmark, Sweden and Finland. This could suggest differences in the virulence or in modes of transmission of predominating and rare types of S. aureus associated with bovine mastitis.

Changes in reimbursement policy for antibiotics and prescribing patterns in general practice

OBJECTIVE: To study the effect of a reduction in reimbursement of the cost of antibiotics on the prescribing pattern in primary care in Denmark. METHOD: We analyzed the general practitioners' prescriptions of antibiotics during 1993--96 in relation to a reduction in reimbursement on the basis of national health service data in the county of North Jutland (population 488 000). On 1 January 1996 the reimbursement for tetracyclines was withdrawn, and for other antibiotics reimbursement was reduced from 75% to 50%. RESULTS: The total consumption of all antibiotic groups increased steadily in the county until 1995, and in 1996 a decrease of 13% was seen. A very marked reduction was noticed immediately after 1 January 1996 for the more expensive broad-spectrum antibiotics. The use of tetracyclines dropped by 42% during the first 3 months of 1996 after withdrawal of reimbursement. CONCLUSIONS: It is reasonable to assume that the new reimbursement policy has initiated a reduction and caused a shift in general practitioners' prescribing of antibiotics. Thus a differential reimbursement policy might influence general practitioners' prescribing behavior towards antibiotics, with desirable ecological consequences.

Characteristics of Staphylococcus aureus strains isolated from clinical and non-clinical human sources in Trinidad: susceptibility to bacteriophages and antimicrobial agents, and toxigenicity

The susceptibility of Staphylococcus aureus strains isolated from human clinical and non-clinical sources in Trinidad to bacteriophages and antimicrobial agents was determined. The ability of the strains to produce enterotoxins and toxic shock syndrome toxin-1 (TSST-1) was also investigated. Of the 554 strains tested, 454 (81.8%) were susceptible to international phage set (IPS) phages with strains isolated from bacteruria (57.1%) and bacteremia (53.3%) having a low sensitivity compared to isolates from aspirates (87.3%) and anterior nares (97.4%). All sources combined, strains were most susceptible to phages belonging to several groups (mixed). Overall, 419 (75.6%) strains were resistant to one or more of nine antimicrobial agents tested. Resistance to penicillin was most prevalent, with 413 (74.5%) strains found to be resistant. Prevalence of resistance to tetracycline, gentamicin, oxacillin, cefuroxime and ciprofloxacin was 5.1%, 2.0%, 0.7%, 0.4% and 0.4%, respectively. Of the 554 strains tested, 307 (55.4%) produced staphylococcal enterotoxins A (SEA), B (SEB), C (SEC) and D (SED) singly or in combination. Strains recovered from high vaginal swabs were least enterotoxigenic (40.0%) as compared to umbilical infection isolates which were most enterotoxigenic (78.9%). TSST-1 was produced by 95 (19.0%) out of 499 strains tested, with isolates from bacteruria found to be most toxigenic (33.3%). It was concluded that the S. aureus strains tested were highly susceptible to bacteriophages and antimicrobial agents (except penicillin) and that enterotoxigenic and TSST-1 producers were widespread and have an aetiologic potential.

Characteristics of Staphylococcus aureus strains isolated from bovine mastitic milk: bacteriophage and antimicrobial agent susceptibility, and enterotoxigenicity

Staphylococcus aureus strains isolated from bovine mastitic milk in Trinidad were examined for their susceptibility to bacteriophages and antimicrobial agents and their ability to produce enterotoxins. Phage 42D was used to screen for bovine strains of S. aureus in milk. Of 250 strains tested, 224 (89.6%) were sensitive to phages in the international phage set (IPS), 85 (34.0%) were resistant to antimicrobial agents and 134 (53.6%) were enterotoxigenic. Strains lysed by phages in various groups (mixed) were prevalent, 145 (58.0%), followed by strains sensitive to groups III (17.0%) and I (8.8%) phages. A total of 72 (28.8%) strains were lysed by phage 42D either alone or with others. Resistance to penicillin was most common with 59 (23.6%) strains while 44 (17.6%) and 43 (17.2%) strains were resistant to ampicillin and triple sulphur respectively. Only 3 (1.2%) strains were resistant to methicillin. Prevalence of resistance to penicillin (12.5%) amongst phage 42D-sensitive strains was significantly (P < or = 0.01; X2) lower than for strains not lysed by phage 42D (28.1%) but strains susceptible to phage 42D were significantly (P < or = 0.05; X2) more resistant (4.2%) to methicillin than those not lysed by the phage (0.0%). Amongst 134 enterotoxigenic strains, 32 (23.9%), 77 (57.5%), 67 (50.0%) and 21 (15.7%) produced staphylococcal enterotoxins A(SEA), B(SEB), C(SEC) and D(SED) respectively either alone or mixed. SEB and SEC were significantly (P < or = 0.01; X2) more produced than either SEA or SED. Strains lysed by groups IV, i.e. 42D (62.5%), and III (56.7%) were more enterotoxigenic than those sensitive to phages in groups II (45.5%) and non-typable (46.2%) but the differences were not statistically significant (P > or = 0.05; X2). Strains lysed by group II phages (72.7%) were significantly (P < or = 0.05; X2) more resistant to antimicrobial agents than those lysed by phage 42D (18.8%). It was concluded that bovine mastitis strains of S. aureus in Trinidad were highly susceptible to bacteriophages and antimicrobial agents and enterotoxigenic and less than one-third may be considered to be bovine strains.

Antibiotic treatment of sinusitis in general practice. A double-blind study comparing ofloxacin and erythromycin

The present study compared ofloxacin and erythromycin in a double-blind study with parallel groups for clinical efficacy and the number and severity of adverse reactions in patients treated in general practice for acute or chronic sinusitis. All patients lived in medium-sized to large towns and rural districts in the northern and western parts of Sealand, Funen and eastern Jutland, Denmark. Three hundred and nineteen patients were enrolled in the study, of whom 280 were clinically evaluable. From this total number, 136 patients were treated with ofloxacin (31 males and 105 females) and 144 patients were treated with erythromycin (40 males and 104 females). Following administration of either ofloxacin 400 mg once daily or erythromycin 500 mg twice daily for 7-14 days, 94.9% of the ofloxacin-treated group and 94.4% of the erythromycin-treated group were cured of their infections. There was no difference in clinical efficacy. Complications occurred in 18 of 155 patients in the ofloxacin-treated group and 32 of 164 in the erythromycin-treated group (P < 0.05), corresponding to 27 and 45 symptoms respectively (P < 0.01). This difference in adverse reactions principally involved gastrointestinal symptoms, i.e. 19 in the ofloxacin-treated group and 41 in the erythromycin-treated group (P < 0.01). Present findings show that the two antibiotics are comparable as to clinical efficacy, but the frequency of adverse reactions is significantly higher in the erythromycin-treated group due to the greater incidence of gastrointestinal adverse reactions.

Changing pattern of phage group II Staphylococcus aureus infections: from community to hospital

Changes in Staphylococcus aureus strains of phage group II were evaluated over a 30-year period. Strains of this group were previously known to be mainly community-acquired, to be rather sensitive to antibiotics and to occur in infections with better clinical outcome. During the period 1961 to 1990 a total of 551, 563 S. aureus strains was characterized according to antibiotic resistance, phage type and site of isolation. Clinical information was obtained on 16,781 bacteraemia cases. Strains of group II occurred until 1983 with a rather constant frequency around 16% of the S. aureus population. Since then, a constant increase in frequency has taken place and since 1990 they are the most frequently isolated phage pattern (22%). Bacteraemia caused by these strains occurs today with the same frequency in hospital and community as strains of other phage patterns. Moreover, these strains have changed from being highly susceptible, to being more resistant to penicillins and tetracycline than the rest of the population. Resistance to methicillin remained low in group II strains throughout the period (about 0.2%). Mortality rate and the proportion of patients with underlying diseases have been the same in recent years regarding group II strains as with other strains. This study indicates that the previous distinction between community-acquired and hospital-acquired S. aureus infections is no longer valid.

Phage susceptibility, enterotoxigenicity and antibiograms of Staphylococcus aureus strains isolated from human wounds and diarrhoea

The phage types, enterotoxigenicity and antibiograms of Staphylococcus aureus strains isolated from human diarrhoea and skin wounds in Nigeria were determined. Of 194 strains tested, 140 (72.2%) were typable using a combination of phages in the International Phage Set (IPS) for human strains of S. aureus and the bovine phage set. IPS phages lysed 118 (60.8%) strains while 96 (49.5%) were susceptible to bovine phages. S. aureus strains from adult diarrhoea were significantly (P less than or equal to 0.01; x2) more sensitive to bovine phages (52.8%) than to IPS human phages (16.7%). Strains isolated from wounds were however significantly (P less than or equal to 0.001; x2) more susceptible to IPS human phages (72.9%) than to bovine phages (41.5%). Phage group III strains were predominant amongst diarrhoeal isolates while wound strains were most susceptible to group II phages. Phage 119, a bovine phage, lysed all 19 strains of diarrhoeal origin sensitive to group M phages but all wound strains were resistant. Overall, 132 (68.0%) strains were enterotoxigenic producing staphylococcal enterotoxins A (SEA), B (SEB), C (SEC) or a combination of these. A majority of diarrhoeal strains elaborated SEC while SEB production was predominant amongst wound strains. Of the eight antimicrobial agents used, S. aureus strains were most resistant to penicillin (71.6%) and least to sulfamethoxazole/trimethoprim (1.0%). Occurrence of resistance to one or more antibiotics was higher amongst wound strains (97.5%) than amongst strains isolated from diarrhoea (52.6%). It was concluded that bovine phage 119 may be a useful epidemiologic marker for S. aureus strains of bovine origin associated with human diarrhoea in Nigeria. It is however difficult to ascribe any aetiological significance to these strains because other enteropathogens not assayed for may have been present.

Epidemiological studies of penicillin resistance in Danish Staphylococcus aureus strains in the period 1977-1990

During the period 1977-1990 the frequency of penicillin resistance increased from 78.7 to 87.5% among a total of 278,193 Danish Staphylococcus aureus strains from hospitalized patients. By combining these data with phage-type patterns the increase was shown to be caused by 1) the introduction and spread of mainly resistant strains of type 95 and the 94,96 complex; 2) an increased occurrence of strains of group II which during the observation period became more frequently penicillin resistant; and 3) a gradual disappearance of strains of group III and the 83A complex which showed a decreasing degree of penicillin resistance. During the observation period community acquired strains reached nearly the same level of penicillin resistance as the hospital-acquired strains, and the frequency of penicillin resistance did not increase during hospitalization among the predominant strains of type 95, group II and the 94,96 complex. S. aureus isolated from airways had a higher frequency of penicillin resistance mainly caused by increasing amount of penicillin resistant strains of group II. Strains from urine had a lower frequency of penicillin resistance. The total antibiotic consumption and the usage of beta-lactam antibiotics remained nearly unchanged during the observation period. The frequent use of beta-lactam antibiotics for airway infections might explain the possible selection of penicillin resistant strains of group II.

Evolution of Staphylococcus aureus resistance to erythromycin in Denmark, 1959 to 1988: comparison with erythromycin-susceptible strains

Between 1959 and 1988, all Staphylococcus aureus strains (15 168 patients) isolated from blood in Denmark have been collected, investigated and stored, and clinical data has been obtained. Erythromycin resistance was found in 4.9% of these strains. The frequency of erythromycin resistance peaked at 25% in 1966, due to the spread in hospitals of multiresistant strains of the 83A complex. When these strains dominated, an increased mortality rate was seen in patients infected with erythromycin-resistant S. aureus. In contrast to most countries, erythromycin resistance in S. aureus declined to less than 5% in 1971, continued to fall to 1.3% in 1983, and has increased slowly to 2.4% in 1988. The decline was only due to a decrease of multiresistant strains. Erythromycin-resistant strains isolated in recent years are predominantly resistant only to penicillin and erythromycin and belong to many different phage type patterns. In Denmark, inducible resistance has occurred at a stable high frequency of approximately 90% of the erythromycin-resistant strains during the last 30 years. Erythromycin-resistant strains isolated today, however, have higher minimum inhibitory concentrations, and are rarely resistant to spectinomycin, in contrast to the strains isolated in the first half of the observation period.