Alison M. Vickery

Observations on the resistance to drying of staphylococcal strains

Death rates have been determined for staphylococcal strains dried on cotton blanket material and stored at room temperature in the dark and in the light. Methicillin-resistant Staphylococcus aureus (MRSA) strains that produced a golden pigment and had a wide distribution within the hospital survived for longer periods than MRSA strains that produced little pigment and had a restricted local distribution. Death rates of methicillin-sensitive strains of S. aureus at day 7 were similar to those of the general epidemic MRSA strains, and there was no significant difference between the death rates at day 7 of the local epidemic MRSA strains and the coagulase-negative strains.

Methicillin-resistant Staphylococcus aureus in a cystic fibrosis unit

Methicillin-resistant Staphylococcus aureus (MRSA) infection in a cystic fibrosis (CF) unit was investigated. Two typing methods, phage-typing and restriction fragment length polymorphism (RFLP) by pulsed-field gel electrophoresis (PFGE) and phylogenetic analysis, showed that nonsocomial transmission of MRSA from the general hospital population had occurred. One instance of possible transmission between two patients was identified. However, transmission between two family members did not occur indicating a minimal risk of MRSA acquisition from social contact compared with hospital admission. This study supports policies for limiting CF-patient admission to hospital but transmission of MRSA does not appear to be a reason for limiting social contact with other CF patients.

Nasal carriage of Staphylococcus aureus in Australian (pre-clinical and clinical) medical students

The nasal carriage of Staphylococcus aureus in 808 Australian medical students was studied. Five groups of students experienced varying degrees of clinical exposure in a hospital environment ranging from 0 to 42 months. The overall percentage of carriers among the five groups did not vary. However, with increasing clinical exposure there was a decrease in the percentage of isolates sensitive to all antibiotics tested, and an increase in the carriage of S. aureus resistant to three or more antibiotics. No carriers of methicillin-resistant S. aureus (MRSA) were detected. The comparative rates of S. aureus carriage between female and male students varied. The relevance of medical students as nasal carriers of S. aureus in the hospital environment today is discussed.

Phage-typing patterns and lysogenicity of methicillin -resistant strains of Staphylococcus aureus from Sydney, Australia, 1965-85

Methicillin-resistant strains of Staphylococcus aureus isolated at the Royal Prince Alfred Hospital since 1965 were differentiated by phage-typing and by their lysogenic status. Most of these strains were isolated during two periods, 1965-72 and 1976-85. Nearly all of the strains isolated in the first period had one of four phage-typing patterns. Strains with each typing pattern carried two prophages; these eight phages were all different, as characterised by serological grouping and lytic spectrum. Lysogenisation of the non-lysogenic strain 1489 with each of these phages narrowed its phage-typing pattern; the typing pattern of the double lysogens was generally similar to and occasionally identical with that of the host strain that had yielded the pair of phages. In the second period, strains with one of five other phage-typing patterns predominated. Representatives of each of these carried the lysogenic phage C. The first methicillin-resistant strain carrying this phage had been isolated in 1974. The current methicillin-resistant S. aureus strains thus appear to form a distinct group that can be differentiated from those seen in earlier years.

Phages for methicillin-resistant Staphylococcus aureus: an international trial.

An internationally agreed and validated set of phages is used worldwide for the typing of strains of Staphylococcus aureus of human origin. However, because of the sometimes reduced susceptibility of methicillin-resistant strains (MRSA) to these phages, some of the national typing centres use locally isolated and characterized sets of experimental phages. In this trial, 42 such phages were distributed to 6 centres and tested against 744 isolates of MRSA with the intention of defining a phage set to augment the international set. The use of these experimental phages increased the percentage typability from 75% with the international set to 93% and the number of identifiable lytic patterns from 192 to 424. A subset of 10 experimental phages was selected. When this subset was compared with the experimental panel, the typability rate was 91% and 370 distinct patterns were obtained. This subset of phages has been distributed for international trial.

Prevalence of peritonitis-associated coagulase-negative staphylococci on the skin of continuous ambulatory peritoneal dialysis patients

The predominance of coagulase-negative staphylococci as normal skin flora is thought to be a factor in their association with episodes of peritonitis in patients undergoing continuous ambulatory peritoneal dialysis. We investigated the prevalence of peritonitis-associated strains on the skin of 28 patients undergoing peritoneal dialysis. Coagulase-negative staphylococci were the most frequently isolated organisms, comprising 47% of peritoneal dialysis fluid isolates and 59% of body site isolates. A total of 142 coagulase-negative staphylococci were speciated, tested for their antimicrobial sensitivity and slime production, and identified by phage typing and plasmid-profile analysis. Staphylococcus epidermidis was the most commonly identified species from both peritoneal dialysis fluid (73%) and body sites (53%). Multiple antibiotic resistance was common, and the greater proportion of isolates were resistant to methicillin; 63.6% of peritoneal dialysis fluid isolates and 61.7% of body-site isolates. S. haemolyticus isolates were significantly more resistant to methicillin than other species. By phage typing and plasmid-profile analysis it was shown that peritonitis was rarely caused by skin-colonizing strains. In only 3 of 14 patients were peritonitis-associated strains isolated as skin colonizers, and no patients developed peritonitis due to organisms previously isolated as skin colonizers.

Strain Differentiation in Methicillin-Resistant Staphylococcus Aureus

Summary Three different systems were used to test 236 isolates of methicillin‐resistant Staphylococcus aureusin an attempt to ascertain if more than one strain is responsible for the current problem of cross‐infection by this organism in N.S.W. hospitals. The biochemical tests used were of little assistance. Phage typing, using the Basic International Set of typing phages at 100 × routine test dilution (RTD), provided evidence of the presence of several different strains. Phage type 83A/85/95/90/88 was the typing pattern of the predominant strain and the next most frequent group was not typable. These results were often difficult to read. Five new phages were therefore isolated and found to be valuable as they produced easily identifiable patterns at RTD.

Non-multiresistant methicillin-resistant Staphylococcus aureus bacteraemia in Sydney, Australia: emergence of EMRSA-15, Oceania, Queensland and Western Australian MRSA strains

Aims: To describe clinical features and molecular epidemiology of non‐multiresistant methicillin‐resistant Staphylococcus aureus (MRSA) bacteraemia. Methods: Patients with non‐multiresistant MRSA isolated from blood at South Western Area Pathology Service from 1 January 1999 to 31 December 2001 were enrolled. Pulsed field gel electrophoresis, phage typing, and (selected instances) multilocus sequence and staphylococcal cassette chromosome typing was performed. PCR was used to detect Panton‐Valentine leukocidin (PVL), toxic shock syndrome toxin‐1 (TSST‐1), and enterotoxin genes. Results: Sixteen patients were detected: eight with UK EMRSA‐15 (ST22‐MRSA‐IV), three with Oceania (South‐West Pacific/Western Samoan phage pattern) (ST30‐MRSA‐IV), two with WA MRSA‐5 (ST8‐MRSA‐IV), and one each with WA MRSA‐1 (ST1‐MRSA‐IV), Queensland strain (ST93‐MRSA‐IV), and WA MRSA‐15 (ST59‐MRSA‐IV). Prior hospital admissions occurred with six of the eight patients with UK EMRSA‐15, none of the three with Oceania, and three of the five with other strains. Thirteen of 16 patients had underlying disease. Three of the three patients with Oceania strain bacteraemia were Polynesians; 11 of 13 of the others were Caucasians. PVL genes were detected in four of 16 isolates (all Oceania and Queensland strains). entC was detected in two EMRSA‐15 strains; entA in one Oceania, two WA MRSA‐5 and the WA MRSA‐1 strain, with entA and entB in the WA MRSA‐15 strain. tst was not detected. Conclusions: Multiple epidemic strains cause non‐multiresistant MRSA bacteraemia. Most patients had risk factors. Oceania and Queensland strains possess the PVL gene. Abbreviations: ccr, cassette chromosome recombinase; EMRSA‐15, epidemic methicillin‐resistant Staphylococcus aureus‐15 EMRSA‐16, epidemic methicillin‐resistant Staphylococcus aureus‐16; MLST, multilocus sequence typing; MRSA, Methicillin‐resistant Staphylococcus aureus; PCR, polymerase chain reaction; PFGE, pulsed‐field gel electrophoresis; PVL, Panton‐Valentine leukocidin; RFLP, restriction fragment length polymorphism; SCCmec, staphylococcal cassette chromosome mec; STx‐MRSA‐IV, multilocus sequence type x‐MRSA‐SCCmec type‐IV; SWP, South‐West Pacific; TSST‐1, (staphylococcal) toxic shock syndrome toxin‐1; WA MRSA, Western Australian MRSA; WSPP, Western Samoan phage pattern.

LYSOGENICITY OF METHICILLIN-RESISTANT STRAINS OF STAPHYLOCOCCUS AUREUS

The lysogenic status of 23 strains of methicillin-resistant Staphylococcus aureus, isolated at the Royal Prince Alfred Hospital, Sydney, since 1980, was studied. Twenty strains, belonging to the four predominant phage types isolated in this hospital, carried the same lysogenic phage which we have designated C. Three other phages were isolated from five strains belonging to phage type 84/85/90. The presence of phage C had little effect on the phage-typing pattern of the strains. Similarly, lysogenization with the other three phages did not result in a significant change in phage-typing patterns. However, when strain 1489, isolated in 1969, was lysogenized with these three phages, there was a change in phage-typing pattern. Lysogenization of this strain with phage 47T resulted in a marked loss of sensitivity to both group-I and group-III phages. The lysogenic status of these methicillin-resistant strains of S. aureus was compared with that of strains isolated between 1967 and 1970. There was no evidence that the strains isolated recently were either related to, or derived from, the earlier ones.

Clinical features, epidemiology, antimicrobial resistance, and exotoxin genes (including that of Panton-Valentine leukocidin) of gentamicin-susceptible methicillin-resistant Staphylococcus aureus (GS-MRSA) isolated at a paediatric teaching hospital in New South Wales, Australia

Aims: To describe the epidemiological, clinical, and laboratory features of gentamicin‐susceptible methicillin‐resistant Staphylococcus aureus (GS‐MRSA) seen at a paediatric teaching hospital. Methods: Patients from whom GS‐MRSA was isolated between 1 January 2001 and 31 December 2002 were enrolled. Retrospective chart review was performed. Susceptibility testing was performed with the Vitek2 system; PCR confirmed methicillin resistance. Phage typing and pulsed field gel electrophoresis (PFGE) was performed (utilising MLST/SCCmec ‐defined control strains). PCR detection of tst, luk–PV, and entA‐entE was performed. Results: Eighty‐five per cent of all Staphylococcus aureus isolates during the study period were methicillin‐sensitive, and 15% were MRSA (9% GS‐MRSA, 6% gentamicin resistant‐MRSA). 100 GS‐MRSA infections in 98 children were identified: 59 cases of skin/soft tissue, four bone and joint, four surgical site infections, three pneumonia, eight other types, and 22 represented colonisation. Ninety‐nine isolates were non‐multidrug resistant, but 17 strains were resistant to erythromycin, 7 to tetracyclines, 12 to ciprofloxacin, 11 to fusidic acid, 1 each to rifampicin and mupirocin. 44 isolates were Oceania strain (ST30‐MRSA‐IV), 20 were Queensland strain (ST93‐MRSA‐IV), ten were UK EMRSA‐15 (ST22‐MRSA‐IV), eight were WA MRSA‐1 (ST1‐MRSA‐IV), two were WA MRSA‐5 (ST8‐MRSA‐IV), one was WA MRSA‐2 (ST78slv‐MRSA‐IV), one was WA MRSA‐15 (ST59‐MRSA‐IV), and the remainder were sporadics. Twenty patients were Pacific Islanders, of whom 12 had the Oceania strain; ten were Aboriginal, of whom eight had the Queensland strain. Sixty‐eight isolates possessed luk–PV, including all Queensland strains and 91% of Oceania strains. Enterotoxin genes were detected in 25% of the isolates, and tst was detected in four isolates. Conclusions: GS‐MRSA is a significant paediatric problem in New South Wales: two minority groups are over‐represented, multiple epidemic strains were detected, most community strains possess luk–PV, and many isolates are multidrug resistant.