WILD-TYPE VARIANTS OF EXOPENICILLINASE FROM STAPHYLOCOCCUS AUREUS

1. Three variants of staphylococcal exopenicillinase (types A, B and C) can be distinguished on chemical, enzymological and immunological grounds. 2. Enzyme type A has a higher specific activity than that of type B, but has a similar combination affinity with anti-(exopenicillinase type A) serum. 3. Enzyme types A and C have a similar specific activity, but enzyme type C has a lower combination affinity for anti-(exopenicillinase type A) serum than has enzyme type A. 4. The sedimentation coefficients and amino acid analyses of the three enzyme types are similar. 5. All three enzyme types have small but significant differences in kinetics of action when hydrolysing benzylpenicillin, methicillin, cloxacillin and cephalosporin C. 6. Peptide maps, obtained from enzyme types A and C after digestion with trypsin, show that these two variants probably differ in the nature of only a very few amino acid residues. 7. Enzyme type B seems to be confined to staphylococci that are members of staphylococcal phage group II. Enzyme types A and C are produced by staphylococci that are members either of phage group I or III, but never group II. 8. The low specific enzyme activity and affinity of enzyme type B towards all penicillins tested suggest that this enzyme type has a lower ;efficiency' in hydrolysing penicillin and therefore in protecting bacteria from the action of penicillin. This could account for the low incidence among ;hospital staphylococci' of penicillin-resistant staphylococci that are members of phage group II.

CELL-WALL LYSINS OF STAPHYLOCOCCUS AUREUS STRAINS INDUCED BY SPECIFIC TYPING PHAGES

Ralston, Doris J. (University of California, Berkeley), and Mary McIvor. Cell-wall lysins of Staphylococcus aureus strains induced by specific typing phages. J. Bacteriol. 88:667-675. 1964.-At least 12 different phages induced the formation of soluble lysins (separable from the phages by ultracentrifugation). The lysins caused rapid clearing of heat-killed cells of all strains of Staphylococcus aureus tested, irrespective of the capacity of the phage to form plaques on living cells of the strain. The uninfected cells of the 12 strains contained a second lysin, an autolysin, released upon cellular autolysis. The autolysin preparations differed from the phage-induced lysins, in that they exhibited relatively high activity for lysing Micrococcus lysodeikticus and low activity for strain S. aureus K(1N), and were each specifically inhibited by antiserum prepared against purified autolysin from strain K(1). A third kind of lysin, virolysin, induced by polyvalent phage K, was differentiated from the lysins of the specific phages on the basis of its antigenic specificity and lack of action on M. lysodeikticus. All three kinds of lysins digested the mucopeptide portion of staphylococcal cell walls. No evidence was found that any of these lysins possessed specific host ranges which could be correlated with the lytic host range of the inducing phage.

STAPHYLOCOCCUS AUREUS STRAINS ASSOCIATED WITH THE HEDGEHOG, ERINACEUS EUROPAEUS

1. Strains ofStaphylococcus aureuswere obtained from the nostrils of twenty-three of fifty-eight hedgehogs; the skin of thirty-eight of fifty-six hedgehogs; the paws of thirty-six of fifty-seven hedgehogs and the anus of six of eleven hedgehogs.

2. Of 118 strains, 106 (90%) were typable with human staphylophages. Seventeen were phage group I, three phage group II, twenty-five phage group III, sixty-one were typable but unclassifiable into groups, and twelve were untypable.

3. Male hedgehogs were more heavily infected than females, while all ages of hedgehogs appeared equally susceptible to infection.

4. Of the 124 coagulase positive strains obtained, 107 (86·3%) were resistant to penicillin. Resistance to other antibiotics—chloramphenicol, streptomycin, tetracycline, erythromycin, celbenin—was not encountered.

5. Thirty-three (83%) of forty strains produced β-lysin.

6. Mites (Caparinia tripilis) and fungi (Trichophyton mentagrophytesvar.erinacei) did not appear to directly influence the carriage ofStaphylococcus aureuson the hedgehog skin.

THE EVOLUTION OF NEW HOSPITAL STRAINS OF STAPHYLOCOCCUS AUREUS

The emergence of new groups of strains of Staph. aureus as important causes of endemic hospital infection in Great Britain has been followed by the phage typing method. Experiments are reported which suggest the possible origin of one of them.

[Use of bacteriophages as selective factors in bacteriological diagnosis of mixed infections]

A new method is proposed for detecting aerobic and anaerobic bacteria during diagnostic culturing by exposure of mixed microorganism populations to bacteriophages. By lysing homologous bacteria, the phages facilitate the detection and isolation of associates resistant to them in pure cultures. The proposed method is compared with the selective media techniques and a conclusion is made on the advantages of selective decontamination of biological samples by bacteriophages in experiments and diagnostic culturing of material from patients with pyo-inflammatory processes.

[Comparison of detection methods for the Staphylococcus aureus capsule]

Eleven methods for capsule detection of Staphylococcus aureus were compared. The most suitable of them were transmission electron microscopy, determination of the presence of clumping factor, determination of colonial morphology in serum-soft agar, estimation of cell volume and staining with safranine. The determination of clumping factor is a fast and effective method for presumptive diagnosis of capsulated strains, but need to be confirmed by another method. The cell volume estimation is useful for determination of capsule production in liquid cultures, while staining with safranine is suitable for genetic studies of capsule production. The other methods analyzed in this work (Indian ink staining, use of anticapsular antisera, determination of virulence for mice, lisostaphin susceptibility, resistance to phages and resistance to phagocytosis) were laborious, too slow, or need components and/or equipment not available in all laboratories. In addition, two methods of induction of capsule production were assayed, one in vitro by several passages in broth with 10% bovine serum and the other in vitro by intraperitoneal inoculation in mice. Both methods induced capsule production.

[Is methicillin better than cloxacillin in serious infections caused by strong penicillinase-producing staphylococci (phage-type 94/96)?]

An intravenous drug addict was treated with cloxacillin for septicaemia with Staphylococcus aureus because of pneumonia and suspected endocarditis. After 51 days of treatment Staphylococcus aureus was still found in blood and expectorate despite continued treatment with intravenous cloxacillin 1 g three and later four times daily and oral rifampicin. The staphylococcal isolates were all of phage type 94/96. Investigations have shown that Staphylococci aurei of phage type 94/96 produce large amounts of penicillinase, and that methicillin is the most penicillinase-resistant of the penicillinase-resistant penicillins followed by dicloxacillin and cloxacillin. The penicillinase production of the patient's Staphylococcus aureus strain was 304-362 units per mg bacteria which is high compared to typical values of 50-200. After 50 days of cloxacillin treatment, the treatment was changed to methicillin 2 g four times daily. Within a week the staphylococci had disappeared from the expectorate, and were never again recovered from the blood. It is suggested that methicillin should have superior efficiency in serious infections with Staphylococcus aureus of phage type 94/96.

Pulsed-field gel electrophoresis as a replacement for bacteriophage typing of Staphylococcus aureus

Bacteriophage typing (BT) (World Health Organization method) has been used at the Centers for Disease Control and Prevention for over 30 years to type isolates of Staphylococcus aureus. Since studies have shown that BT patterns have poor reproducibility and because BT fails to type a high percentage (15 to 20%) of isolates, the Centers for Disease Control and Prevention has converted from using BT to using pulsed-field gel electrophoresis (PFGE) for strain typing S. aureus. We compared the results of BT with results of PFGE for typing 300 isolates of S. aureus, including strains from several well-characterized outbreaks. Ninety-six isolates were BT group I, 19 were group II, 82 were group III, 7 were group V, and 96 were nontypeable. PFGE identified subgroups within each phage group and thus was more discriminating than BT, which identified no subgroups. PFGE was able to type all isolates and distinguish related from unrelated strains of S. aureus. Our modified, standardized PFGE methodology should enable typing laboratories to obtain rapid, reliable results in 3 to 4 days when starting with an isolated colony on agar media.

Epidemic methicillin-resistant Staphylococcus aureus: controlling the spread outside hospital

Over a 21-month period an outbreak of methicillin-resistant Staphylococcus aureus infection occurred in east Northamptonshire. The outbreak was caused by a novel phage-type (EMRSA-16) and affected 400 patients. It was centred on three hospitals but spread was also detected in the community, particularly among clients of nursing and residential homes. Three hundred and fifty residents in 15 care homes were screened for MRSA. Cross-infection of MRSA was demonstrated in 14 patients in six different homes. A key aspect of the overall containment of the outbreak was the implementation of infection control measures in the community, together with treatment and screening of known positive patients following their discharge from hospital.

A major outbreak of methicillin-resistant Staphylococcus aureus caused by a new phage-type (EMRSA-16)

An outbreak of methicillin-resistant Staphylococcus aureus (MRSA) infection caused by a novel phage-type (now designated EMRSA-16) occurred in three hospitals in East Northamptonshire over a 21-month period (April 1991--December 1992). Four hundred patients were colonized or infected. Seven patients died as a direct result of infection. Chest infections were significantly associated with the outbreak strain when compared with methicillin-sensitive S. aureus. Twenty-seven staff and two relatives who cared for patients were also colonized. A 'search and destroy' strategy, as advocated in the current UK guidelines for control of epidemic MRSA was implemented after detection of the first case. Despite extensive screening of staff and patients and isolation of colonized and infected patients, the outbreak strain spread to all wards of the three hospitals except paediatrics and maternity. A high incidence of throat colonization (51%) was observed. Failure to recognize the importance of this until late in the outbreak contributed to the delay in containing its spread. Key parts of the strategy which eventually contained the local outbreak were the establishment of isolation wards in two hospitals, treatment of all colonized patients and staff to eradicate carriage and screening of all patients upon discharge from wards where MRSA had ever been detected. EMRSA-16 spread to neighbouring hospitals by early 1992 and to London and the South of England by 1993. It is distinguished from other epidemic strains by its characteristic phage-type, antibiogram (susceptibility to tetracycline and resistance to ciprofloxacin), and in the pattern given on pulse field electrophoresis.

Clonal dissemination of two MRSA strains in Germany

Clonal dissemination of two different MRSA strains, both clumping factor negative, has been observed in Germany for more than a year. Both strains possess the mec-A determinant and each exhibits a characteristic genomic DNA fragment pattern. One strain has spread in the north, the other in the south-west of Germany. Intensive care units are mainly affected by MRSA-infections and probably play a special role in further intra- and inter-hospital spread.

Epidemiology of Staphylococcus aureus bacteremia in Denmark

The number of Staphylococcus aureus bacteremia cases has increased annually in Denmark during the latest decades. This increase has occurred among older patients with hospital-acquired bacteremia. Methicillin-resistance, which earlier was a property of strains of the 83A phage-complex, has nearly disappeared, while the frequency of penicillin-resistance has increased. Today both the phage-type pattern and antibiotic resistance are nearly similar for strains from hospital-acquired and community-acquired cases. In hospitals the frequency of bacteremia after postoperative wound infections has decreased, while cases associated with intravascular catheters has increased, and these infections are now the most common cause of hospital-acquired S. aureus bacteremia. Endocarditis is most commonly found in community-acquired cases without an identified primary focus in patients between 21-50 years. Also hematogenous osteomyelitis is most common in community-acquired cases, but these infections have changed to having a high predilection for the vertebral column, and the prevalence of chronic cases has decreased.

[A new collection of phages for typing methicillin resistant Staphylococcus aureus]

A new collection of phages for typing methicillin-resistant S. aureus (MRSA) is proposed. The collection includes phage 85 (modified by the MRSA strain), capable of selecting strains with the similar specificity of the restriction-modification system, and 9 MRSA-induced phages. The latter differentiate MRSA strains according to the specificity of prophages present in bacterial cells. The use of this phage collection has permitted the typing of MRSA strains insensitive to the phages of the international collection. Among these cultures an epidemic strain has been detected and the source of its spread in the burn center has been established.

Treatment of experimental infections of mice with bacteriophages

Bacteriophages for Acinetobacter baumanii, Pseudomonas aeruginosa and Staphylococcus aureus were tested in experimental infections of mice to investigate their potential for the treatment of infections of man. As few as 10(2) particles of an acinetobacter phage protected mice against 5 LD50 (1 x 10(8)) of a virulent strain of A. baumanii, and phage was demonstrated to have multiplied in the mice. A pseudomonas phage protected mice against 5 LD50 of a virulent strain of P. aeruginosa, with a PD50 of 1.2 x 10(7) particles. A staphylococcal phage failed to protect mice infected with a strain of S. aureus. These studies support the view that bacteriophages could be useful in the treatment of human infections caused by antibiotic-resistant strains of bacteria.

Phage typing of coagulase-negative staphylococci

Seventy-nine staphylococcal strains isolated from blood cultures (57 coagulase-negative staphylococci (CNS) and 22 S. aureus) and 308 CNS isolated from the skin of healthy donors were phage typed. S. epidermidis and S. capitis were readily typed with 91 strains out of 124 and 24 strains out of 43 strains being successful. Species such as S. haemolyticus, S. hominis and S. simulans could be moderately phage typed. Others gave only a few strains capable of being typed, such as S. saprophyticus and S. sciuri. Under our experimental conditions the S. warneri, S. xylosus and S. cohnii could not be typed with our set of phages.

A new approach to establishing the set of phages for typing methicillin-resistant Staphylococcus aureus

A new approach to using experimental phages for typing methicillin-resistant S. aureus (MRSA) non-sensitive to the phages of International Basic Set (IBS) is described. The collection Includes phage 85, modified on a culture of MRSA, and 5 phages induced from MRSA strains isolated in clinics of Moscow in 1975-76. Firstly, the modified phage selects cultures according to the specific character of its restriction-modification system, then the induced phages differentiate the selected strains into 5 groups (1, 2, 3, 4, 5) based on the specificity of the prophages they contain. Group 1 strains can further be differentiated into 5 subgroups (A, B, C, D, E) by additional phages. Forty-one MRSA strains isolated in 1987-90 in various hospitals of Moscow showing no sensitivity to IBS phages, were lysed by the modified phage, 15 of them belonging to Group 2 and isolated in the traumatological hospital, 26 belonging to Group 1 and were circulating in the burn center. Twenty-three strains of Group 1 appertain to subgroup 1B and were isolated over a 4-year period from the burned surface of patients and from the throat of a medical staff carrier.

Phage types and drug susceptibility patterns of Staphylococcus aureus from two hospitals in northwest Ethiopia

Fifty-eight Staphylococcus aureus strains from Gonder College of Medical Sciences Hospital, (43 isolates from patients and 15 from carriers) and 28 from Debre Tabor Hospital (14 each from patients and carriers), both in northwest Ethiopia, were phage typed in 1988. Eighty-one of the 86 strains were recognized by their phage types. A multiresistant strain of type 29 was frequent among Gonder patients'. This strain was also recovered from the hospital personnel. Other well known multiresistant strains of phage type NT/A994 and 85/A994 were identified among patients from Gonder and phage type 85/A994 was recovered from 5 patients and 4 carriers from Debre Tabor. These findings suggest cross-infection with virulent strains of Staphylococcus aureus in both hospitals. All 86 phage-typed strains were tested for susceptibility to 7 antibiotics. A high frequency of multiple resistance was observed. Double resistance to penicillin and tetracycline was frequent among patients strains from Gonder. Among strains of phage type 85/A994 multiresistance to penicillin, chloramphenicol, tetracycline, streptomycin, erythromycin and oxacillin was found. Strains of phage type 85/A994 and NT/A994 were resistant to mercury. No plasmid DNA was detected in one strain of 85/A994 investigated.

A subdivision of strains of Staphylococcus aureus in the 94,96 complex by means of experimental phages

In order to facilitate epidemiological investigations a subdivision of Staphylococcus aureus strains belonging to the 94,96 complex by means of two experimental phages, 16 and 47A, was performed. These phages were selected from the nine experimental phages initially examined because they gave the greatest discrimination. On the basis of reactions with these two phages, 2199 isolates which reacted with phages 94 and 96, and 773 isolates which reacted with phage 96 alone, were each subdivided into two major and two minor groups. Strains with different phage patterns were in a few cases (2/64) isolated from the same deep body site in a patient, and lysogenisation experiments suggested that differences in phage patterns were determined by the presence of prophages. Strains with the phage patterns 94/96 and 96 were found to be unevenly distributed throughout Denmark. This regional distribution suggested that particular strains might predominate in some areas. The extended phage patterns with the experimental phages did not give any retrospectively useful epidemiological information. It is proposed that in future phages 16 and 47A be used for specific investigations into the sources and relatedness of strains involved in small incidents.

Phage-typing of coagulase-negative staphylococci. Factors influencing typability

Factors influencing the phage-typability of coagulase-negative Micrococcaceae have been studied in 2,778 clinical isolates comprising A) 209 consecutive isolates from one laboratory, B) 2,107 clinical strains submitted for phage-typing for epidemiological reasons, and C) 462 strains representing all isolates of presumed clinical significance found in two laboratories during one month. The reproducibility was acceptable at duplicate repeated typing of the same strains as well as by typing epidemiologically-related pairs of strains from the same patient. Strains of Staphylococcus haemolyticus were seldom typable, whereas strains of S. epidermidis and S. hominis had a higher typability. Methicillin-resistant strains and other multiple-resistant strains were rarely typable (11-13%). The typability was higher among susceptible strains (36%) and strains resistant to penicillin only (43-50%). The typability of strains of the same species and antibiotic-resistance pattern differed between hospitals compared and decreased markedly over the years for multiple-resistant S. epidermidis isolates.

Development of a new set of phages as an epidemiological marker in Staphylococcus epidermidis causing nosocomial infections

We describe the isolation of a new set of phages for typing Staphylococcus epidermidis. One hundred and eighty-two phages were obtained from S. epidermidis strains of human origin. Twelve phages were selected according to their potency and their lytic activity studied. Twenty phages of the Dean and Williams' set were also studied. Phage-typing was undertaken at 100 x RTD, 1000 x RTD and after heat treatment at 48 degrees C. When the two sets of phages were compared separately similar figures were obtained. When the two typing sets were combined, the percentage of typability for the 182 bacterial strains increased to 29.1% using 1000 x RTD and to 75.3% after heat treatment.

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

Phage-type patterns and antibiotic susceptibility have been examined in 904 Staphylococcus aureus strains from general practice in the Copenhagen municipality, in 1107 strains from hospitals in the Copenhagen municipality and in 18,028 strains isolated in 1988 from inpatients all over Denmark. The phage-type patterns of the 3 materials were very similar except for a slightly higher frequency of group II strains among isolates from general practice (24% compared to 19%). Penicillin resistance was high (86-87%) in all materials. Resistance to tetracycline and erythromycin was more frequent in strains from general practice (8.6% and 3.8%) than in strains both from hospitals in the same area (3.6% an 2.2%) and in all Danish hospitals (5.3% and 2.4%). This indicates that the restrictive use of antibiotics in hospitals seems to have eliminated the previous preponderance of multiresistant staphylococci in hospitals compared to community acquired staphylococci. It even seems as if the less restrictive use of tetracycline and erythromycin in general practice has now inversed the situation.

Restriction enzyme analysis of plasmid DNA and bacteriophage typing of paired Staphylococcus aureus blood culture isolates

We compared restriction enzyme analysis of plasmid (REAP) DNA profiling with bacteriophage typing for determination of similarities and differences among 50 pairs of Staphylococcus aureus blood isolates from patients with multiple positive blood cultures. Isolates from 17 pairs did not have detectable plasmids. Isolates from 33 pairs had plasmids classified into 17 distinct REAP DNA profiles. Paired isolates from 31 of these episodes were identical to one another. By phage typing, 35 pairs had strong lytic reactions to a phage(s), 9 pairs lacked strong reactions, and 6 pairs consisted of a strongly reactive isolate and an isolate with no strong reaction to a phage. When consolidated into 11 general phage groups, pairs from 44 of the 50 episodes were in the same general group. REAP DNA profiles were highly reproducible (99%), whereas phage typing was not. REAP DNA profiling is superior to phage typing as a technique for determining similarities and differences among S. aureus blood isolates.