Epidemiology of resistance among gram-positive bacteria: with special reference to staphylococcal infections

During the past 27-30 years the antibiotic-resistance patterns of Danish Staphylococcus aureus strains have changed from penicillin-, streptomycin-resistance, to multiple-resistance ending up today with resistance to penicillin only. These changes have mainly been due to the introduction of different clones with characteristic phage-patterns and antibiotic-resistance patterns; respectively, the penicillin-, streptomycin-resistant strains of the 52, 52A, 80, 81 complex; multiple-resistant strains of the 83A complex and strains of the 94, 96 complex and of type 95 resistant to penicillin only. At the same time, however, changes in antibiotic-resistance pattern within the 52, 52A, 80, 81 and the 83A complex have taken place, and today strains of these complexes are mainly penicillin-resistant only or fully susceptible. Comparison of hospital-acquired strains with community-acquired strains proves that differences are only seen in periods with many resistant strains; today in Denmark these two groups have identical phage-patterns and antibiotic-resistance patterns. The investigations are based on 486412 strains isolated and phage-typed in 1960-86 and on further examination of 12852 strains isolated from blood.

Correlation between enterotoxigenicity, tested by different ELISA-techniques, antibiotic resistance patterns and phage groups of Staphylococcus aureus strains

A group of 596 Staphylococcus aureus strains isolated from various clinical sources or implicated in food poisoning was investigated for enterotoxins A and B (SEA and SEB) production. The conventional ELISA techniques (competitive and sandwich ELISA) were compared with a newly developed avidin-biotin ELISA in their ability to detect the enterotoxins. The avidin-biotin system was not remarkably influenced by SPA up to 10 micrograms/ml. A semi-quantitative competitive ELISA for the detection of staphylococcal protein A (SPA) in culture supernatants was carried out in parallel. The strains isolated in cases of food poisoning showed different antibiotic resistance patterns, whereas the strains from clinical sources were selected for either methicillin or penicillin resistance only. The strains isolated in food poisoning outbreaks (FP strains) were enterotoxin A positive in 22%, enterotoxin B positive in 11%, and SEA + SEB positive in 9% of cases. The strains with resistance to penicillin only (PER strains) produced SEB in 26%, SEA in 14%, and both toxins in 7% of the cases. The methicillin-resistant strains (MCR strains) produced SEA in 59% of cases, whereas SEB was produced in 6% only (SEA + SEB: 20%). 37% of the SEA producers belonged to phage group III (SEB: 30%; SEA + SEB: 25%) and 12% (SEB: 11%; SEA + SEB: 9%) to phage group I. 26% of the SEA-producing and 37% of the SEB-producing strains (SEA + SEB: 23%) were non-typable.

Heat shocking as a useful adjunct to routine phage typing of Staphylococcus aureus

The heat shock technique (heating a culture at 55 degrees C for 3 min immediately before phage typing) has been used in our laboratory as an adjunct to routine phage typing for 2 years. This has enabled phage typing patterns to be determined on isolates otherwise recorded as untypable. The method is easily performed and standardized. Phage patterns were found to be reproducible and adequate discrimination was achieved. We found the technique provided significant information which was not available by conventional typing.

Phage patterns of Staphylococcus hyicus subsp. hyicus isolated from chickens, cattle and pigs

Bacteriophage typing was performed on 285 strains of Staphylococcus hyicus subsp. hyicus isolated from pigs, chickens, and cattle, using the 5 S. hyicus subsp. hyicus phages, S9, S13, S39, S188 and CH11. One hundred and twenty-eight (64.3%) of the 199 swine strains, 62 (100%) of the 62 chicken strains, and 24 (100%) of the 24 cattle strains were typable at either routine test dilution (RTD) or 100 X RTD. Most (124/128) of the typable swine strains showed phage patterns consisting of lytic reactions with one or more of the phages S9, S13, S39 and S188. Phage patterns including phage CH11 were detected in only 4 swine strains. All of the typable chicken strains showed phage patterns consisting of lytic reactions with phage CH11. Cattle strains had the phage patterns that were found most frequently in swine and chicken strains. This study suggested that phage typing might be a useful marker for distinguishing ecovars within S. hyicus subsp. hyicus.

Phage typing of Staphylococcus aureus associated with subclinical bovine mastitis

Six hundred and seventeen isolates of Staphylococcus aureus from subclinical clinical mastitis cases in 63 dairy herds in Northern Ireland were typed using a set of 25 phages. Ninety-four per cent of the isolates were typable, with nine phages, predominantly from groups I and III, being responsible for almost all of the lysis. Although 68 phage patterns were found, six of them typed 47.2% of the isolates. One strain accounted for 14.7% of the isolates, but the largest number of strains (44) was restricted to individual farms. The epidemiological significance of these findings for on-farm mastitis control 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.

Biotyping and phage typing of coagulase-negative staphylococci from blood cultures of neonates

One hundred coagulase-negative staphylococci isolated from blood cultures of neonates have been biotyped and phage typed. These results have been compared with previous reports. The susceptibility of the strains to antimicrobial drugs has also been examined and a rise in resistance rates towards the end of the study was documented. The possible causes of this finding are discussed.

Microbial pathogens from goat mastitis and phage-typing of Staphylococcus aureus isolates

Examination of milk from goats yielded 41 strains from 40 clinically affected halves; 15 were Staphylococcus aureus, 6 Staph. epidermis, 1 Streptococcus agalactiae, 2 Strept. dysgalactiae, 5 Strept. uberis, 2 Corynebacterium pyogenes, 3 Escherichia coli, 3 Pasteurella spp. and 4 Mycoplasma spp. One half had dual infection of Staph. aureus and Strept. dysgalactiae. Twenty two of the 297 milk samples from apparently normal halves also harboured pathogens comprising of 9 Staph. aureus, 1 Strept. agalactiae, 2 E. coli, 2 Pasteurella spp., 2 Candida albicans and 6 Mycoplasma spp. Most of the bacterial isolates were sensitive to many broad spectrum antibiotics. Twenty of the 24 Staph. aureus isolates were phase typable by a set of 23 human Staphylococcal International Phages suggesting the utility of these phages for the typing of goat strains. The isolates were grouped into 15 phage-types, many of which have been reported from human infections in Iraq. This indicates the possibility of association of human strains of Staph. aureus in caprine mastitis. No definite correlation could be noted between antibiogram and phage types of Staph. aureus strains.

Phage types of Staphylococcus aureus received at the Quebec Public Health Laboratory from 1976 to 1983

Phage typing of 13,579 clinical and environmental strains of Staphylococcus aureus received at the Quebec Public Health Laboratory between 1976 and 1983 was routinely performed to assess the distribution of lytic groups. Strains susceptible to phages 94, 95, and 96 predominated and accounted for 25% of the specimens. The distribution of strains in lytic groups varied with time and specimen source.

The basic phage set for typing bovine staphylococci

Two hundred and sixty-nine Staphylococcus aureus cultures isolated from bovine milk were subjected to phage typing using the International basic set of 16 phages at Routine Test Dilution. In the current study 73.6% of cultures were 'typable' compared with 84-89% in 1972 when the set was first recommended. The set remains capable of typing the majority of bovine staphylococci but shows a reduction in lysogenicity of most of its phages.

Phage-typing of Staphylococcus aureus from cases of bacteraemia

Isolates of Staphylococcus aureus from 98 cases of bacteraemia from 16 different hospitals were phage-typed. Fifty-six isolates were associated with sporadic infections and 42 with hospital outbreaks. In the sporadic cases, group I strains, particularly types 29, 52, or 29/52, were very frequent (39.2%), followed by non-typable strains. Type 94/96 was also common (14.2%). In hospital outbreaks, mixed I and III strains (multiply-resistant) were found in 73.6% and non-typable strains in 21.4%.

Transfer of plasmid-borne aminoglycoside-resistance determinants in staphylococci

Aminoglycoside-resistance determinants in staphylococci are borne on conjugative and non-conjugative plasmids. The conjugative plasmids were found in methicillin-resistant strains of Staphylococcus aureus isolated recently in Darwin and Sydney, Australia and in Houston, Texas, USA. These plasmids and the class-2 conjugative plasmid reported by Archer and Johnston (1983) had similar patterns of EcoR1 restriction-endonuclease fragments, encoded resistance to gentamicin, kanamycin and neomycin, transferred to a non-lysogenic recipient in conditions that promoted close cell-to-cell contact and mobilised a small, non-conjugative plasmid. A further plasmid, pWG14, encoding resistance to kanamycin, neomycin, streptomycin, erythromycin and lincomycin, also displayed conjugative properties but did not mobilise the small, non-conjugative plasmid. The transfer frequency of all conjugative plasmids was stimulated by the addition of polyethylene glycol, particularly at concentrations above 20%, to mixtures of donor and recipient broth cultures. Polyethylene glycol appeared to promote close cell-to-cell contact between donor and recipient cells. A representative of the most common aminoglycoside-resistance plasmids in Australian isolates of methicillin-resistant S. aureus was non-conjugative and transferred by a bacteriophage-mediated system to a lysogenic recipient. With the exception of plasmid pWG14, the conjugative plasmids were also transferred by a bacteriophage-mediated system. Furthermore, cultural conditions that favoured conjugative transfer of plasmids inhibited bacteriophage-mediated transfer and vice versa. The efficacy of the two transfer systems for analysing the plasmids of gentamicin-resistant, methicillin-resistant isolates of S. aureus has been compared.

Bacteriophage typing of Staphylococcus aureus strains isolated from Bloemfontein dairy herds

Bacteriophage typing was performed on 88 coagulase positive Staphylococcus aureus strains isolated during a survey of subclinical mastitis in Bloemfontein dairy herds. Phage typing was performed using two basic international phage typing sets, i.e. the human isolate phage set (HPS) and the bovine isolate phage set (BPS). The results clearly indicated that the BPS could be successfully applied for the phage typing of bovine mastitis S. aureus strains. The majority of the strains was typed as BPS phage group IV (78,4%) and HPS group III (47,7%). The high prevalence of BPS group IV strains is in agreement with other studies. The prevalence of non-typable strains was 3,4% for BPS and 28,4% for HPS. Phages 102, 117, 107, 81, 47, and 6 had high lytic activity. BPS group IV patterns (102/107/117 and 102/117) dominated. The incidence of unique phage patterns was 12,5% for BPS and 26,0% for HPS. A relatively high proportion (71,3%) of the strains was typable with the HPS. As these strains were of possible human origin it indicated the possibility of mutual human-animal transfer of the pathogens. No relationship could be found between phage groups on the one hand and multiple antibiotic resistance on the other, and no phage groups dominated within herds.

[Biological properties, phage typing and antimicrobial susceptibility of Staphylococcus aureus isolated from dermatitis in laboratory mice]

The characteristics of 167 isolates of S. aureus from 106 mice suffering dermatitis were examined. All 167 isolates coagulated both rabbit and human plasmas and 161 of them also coagulated bovine plasma. All the isolates produced heat-stable and heat-labile DNase, phosphatase and yellow pigment, reduced nitrate, hydrolysed egg yolk, Tween 80, and hippurate, and grew on crystal violet agar in colonies of the negative type C and on medium with 10% NaCl. The majority of them produced fibrinolysin, protease and acetoin. Fifty-three percent were gelatinase positive. In hemolysis tests, 25, 57 and 45 isolates showed alpha-, beta-, alpha beta-hemolysis, respectively. Forty isolates did not produce hemolysins in the rabbit and sheep blood agar. All of 75 isolates tested produced acid from fructose, galactose, glucose, glycerol and mannose, but did not from arabinose, dextrin, inulin, raffinose, salicin, sorbitol and xylose. Most of these isolates produced acid from lactose, mannitol, sucrose and trehalose. All of the 75 isolates were highly sensitive to penicillin, methylphenylisoxazolyl penicillin, erythromycin, spiramycin, lincomycin, chloramphenicol, tetracycline, kanamycin, gentamicin and cephaloridine, but were resistant to sulfisoxazole. With phages of human set, all 167 isolates were typable at 100 X RTD. All but one of the typable isolates belonged to mixed lytic groups. These were I + III (35 isolates), I + M (1), I + III + M (124) and I + II + III + M (6), with long phage patterns. When the 167 isolates were biotyped as described by Hájek and Marsálek [7, 8], 5 belonged to biotype A, 1 to biotype B and 60 to biotype C.(ABSTRACT TRUNCATED AT 250 WORDS)

Hospital infection caused by non-typable Staphylococcus aureus: application of reverse typing

Hospital infections caused by strains of Staphylococcus aureus non-typable (NT) by phages have occurred in three Spanish hospitals since 1981. Reverse typing allowed characterization of the strains in all three cases.

In-vitro activity of methicillin against clinical isolates of Staphylococcus aureus

Methicillin activity against 149 penicillin-resistant, methicillin-susceptible Staphylococcus aureus strains from bacteraemia cases with endocarditis (n = 89) or without endocarditis (n = 60), from the years 1976-1981, was studied with broth dilution and agar dilution. While no differences in methicillin susceptibility were found in relation to the origin of the strains, Staph. aureus of the phage type complex 94,96 showed significantly higher MIC and IC50 by agar dilution than strains of other phage groups/complexes. This difference probably has no clinical importance but is of epidemiological interest. Broth dilution MIC was generally one dilution higher than agar dilution MIC, possibly explained by methodological factors. The MBC/MIC ratios never exceeded two in any of the strains, indicating a lack of tolerance in these clinically important isolates.