Genetic basis, epidemiology, and future significance of antibiotic resistance in Staphylococcus aureus: a review

Analysis of antibiotic resistance patterns and detection of mecA gene in Staphylococcus aureus isolated from packaged hamburger

Presence of Staphylococcus aureus, antibiotic resistance pattern and PCR detection of mecA gene in isolated strains were investigated in total of 256 packaged hamburgers in Iran-Tehran. For this purpose we used standard disk-diffusion method and sensitive and specific PCR technique, respectively. Results showed that 25% of samples were positive for S. aureus. Resistance to meticillin, erythromycin, penicillin G, cefazolin, ciprofloxasin, vacomycin and amoxiclave was determined 89%, 20.3%, 18.7%, 15.6%, 14%, 26.6% and 12.5%, respectively. According to the obtained results from PCR analysis of methicillin-resistant S. aureus (MRSA), mecA gene was present in 100% of the resistant isolates, 0% of intermediate-resistance isolates and 25% of susceptible isolates. The results obtained from PCR detection of mecA gene showed high correlation with standard disk diffusion test.

Staphylococcus aureus: An old pathogen with new weapons

Staphylococcus aureus has been recognized as an important human pathogen for more than 100 years. S aureus has been able to adapt and evolve in terms of its resistance traits and virulence factors; it is among the most important causes of human infections in the twenty-first century. Rapid molecular identification in the clinical microbiology laboratory of these resistance and virulence factors expressed by S aureus will play an important role in the future in decreasing the morbidity and mortality of infections. This article addresses the emerging aspects of infections caused by S aureus, including microbiology, epidemiology, clinical presentation, pathogenesis, diagnosis, treatment and prognosis, and immunity.

[Staphylococcus aureus infections: new challenges from an old pathogen]

Staphylococcus aureus is a versatile organism with several virulent characteristics and resistance mechanisms at its disposal. It is also a significant cause of a wide range of infectious diseases in humans. S. aureus often causes life-threatening deep seated infections like bacteremia, endocarditis and pneumonia. While traditionally confined mostly to the hospital setting, methicillin-resistant S. aureus (MRSA) is now rapidly becoming rampant in the community. Community-acquired MRSA is particularly significant because of its potential for unchecked spread within households and its propensity for causing serious skin and pulmonary infections. Because of the unfavorable outcome of many MRSA infections with the standard glycopeptide therapy, new antimicrobial agents belonging to various classes have been introduced and have been evaluated in clinical trials for their efficacy in treating resistant staphylococcal infections. A number of preventive strategies have also been suggested to contain the spread of such infections. In this review, we address the recent changes in the epidemiology of S. aureus and their impact on the clinical manifestations and management of serious infections. We also discuss new treatment modalities for MRSA infections and emphasize the importance of preventive approaches.

[Problems with gram-positive bacteria: resistance in staphylococci, enterococci, and pneumococci to antimicrobial drugs]

The resistance in staphylococci, enterococci, and pneumococci is reviewed. The author also recalls the first cases, and presents an overview of the distribution of cases in the world, the genetic and molecular mechanisms of resistance, the importance in Brazil and therapeutic alternatives. The factors that contribute to the dissemination of these problem bacteria and the measures for their control are emphasized.

Nasal carriage and antibiotic susceptibility of Staphylococcus aureus in general practice

The incidence of nasal carriage of Staphylococcus aureus and the in vitro susceptibility of isolates to fusidic acid, penicillin, erythromycin, methicillin and tetracycline was determined in 204 patients who had been treated previously with a short course of a topical preparation of Fucidin for acute skin sepsis, and in an equal number of control subjects. Staphylococcus aureus was isolated from 36 per cent and 34 per cent of patients in the Fucidin and control groups respectively. Only one of the 144 isolates was resistant to fusidic acid. Short, single courses of topical therapy in general practice are unlikely to be epidemiologically hazardous in the long term. Evidence of possible cross-infection in general practice was obtained.

Lysogeny and other characteristics of Staphylococcus hyicus isolated from chickens

Lysogeny was readily demonstrated among strains of Staphylococcus hyicus that were isolated from chickens. Susceptibility to phage lysis was affected by prophage immunity, but lipase activity and erythromycin resistance were not affected by the presence of temperate phage. In contrast to previously published results, lipase-negative strains of S. hyicus were relatively common and the use of selective media based on lipase activity would have been unsuitable for detection of the S. hyicus strains examined.

The resistance to antimicrobial agents of Staphylococcus aureus isolated from the bovine udder

Isolates of Staphylococcus aureus (total 1657) from bovine mastitis were collected from 13 laboratories throughout Australia from 1974 to 1979. They were tested for resistance to antimicrobial agents using an agar dilution method. Resistance shown was mainly to penicillin and streptomycin. Occasional strains were resistant to neomycin, lincomycin, erythromycin, tetracycline, chloramphenicol and furazolidone but multiple resistance was rare. No strain showed resistance to methicillin. Resistance to penicillin declined from 35% in 1974-75 to 7.1% in 1979. Most strains (1395) were retested to allow induction of penicillinase; 62% produced the enzyme.

Gentamicin- and clindamycin-resistant Staphylococcus aureus

From 1975 through 1978 isolates from 21 of 230 (9%) Staphylococcus aureus bacteremias were resistant to gentamicin and clindamycin. Gentamicin- and clindamycin-resistant S aureus (GCRS) accounted for 23% of all S aureus isolates from 1977 compared with 2 to 6% in the two years immediately preceding, and the year following 1977. When compared with patients with gentamicin- and clindamycin-sensitive S aureus (GCSS) from 1977, GCRS were more often isolated from patients who acquired their infections in the hospital, particularly in the intensive care unit. A significant association existed between prior or concurrent therapy with gentamicin and/or clindamycin and the isolation of GCRS. Infection with GCRS was associated with a 73% mortality rate versus 28% with GCSS. GCRS were susceptible to oxacillin, cephalothin, tetracycline, and vancomycin. GCRS were resistant to kanamycin and tobramycin but were susceptible to amikacin (median MIC of GCRS, 4.0 microgram/ml). Multiple bacteriophage types of S aureus were involved, and resistance appeared to be plasmid-mediated. A survey of antibiotic usage showed that in comparison to January 1977, a mikacin usage increased and gentamicin usage decreased in March 1979. Because of the popularity of the combination of clindamycin and gentamicin for therapy of life-threatening infections, clinicians should be aware of potential gentamicin- and clindamycin-resistance in S aureus.

"Methicillin-resistant" Staphylococcus aureus: reassessment by controlled trial in burns unit

A controlled trial of oral flucloxacillin (250 mg six-hourly for four days) was performed in 34 patients treated by the covered method whose burns had yielded a heavy or moderate growth of Staphylococcus aureus resistant to methicillin at 30 degrees C but moderately sensitive at 37 degrees C. Staph aureus was eliminated in nine of the 17 patients treated with flucloxacillin but in none of the 17 controls; the proportion of patients from whose burns sensitive Staph aureus was eliminated in an earlier trial of cloxacillin was greater than this. Strains of Staph aureus commonly described as methicillin-resistant and showing heterogeneous growth at 37 degrees C of many sensitive and very few resistant bacterial cells should, in the light of these findings, be called moderately sensitive to flucloxacillin. Such "heteroresistant" strains showed consistent moderate sensitivity in replicate diffusion sensitivity tests at 37 degrees C, but very inconsistent results in replicate dilution tests, especially with flucloxacillin. These studies showed that 18-hour diffusion sensitivity tests indicate the clinical value of treatment with flucloxacillin for staphylococcal infections of moderate severity more correctly at 37 degrees C than at 30 degrees C.

A new look at erythromycin

This article reviews the current place of erythromycin in antibiotic therapy. Overall, erythromycin is thought to be underused because: (1) the fear of resistance has been exaggerated; (2) significant toxicity has been associated with only one derivative (the estolate); (3) newer antibiotics have very rarely been demonstrated to be superior to erythromycin. Erythromycin has an important place in treating acute upper and lower respiratory tract infections, acute otitis media, sinusitis, skin and soft tissue, osteomyelitis, prostatitis, infections due to Mycoplasma spp. and Chlamydia organisms, and infections due to anaerobes.

An outbreak of infection caused by a gentamicin-resistant Staphylococcus aureus

An outbreak of infection caused by a strain of Staphylococcus aureus resistant to gentamicin and tobramycin and other antibiotics occurred in two wards in a hospital. Eight patients were colonized, of whom six had clinical infections. Previous administration of gentamicin appeared to predispose the patients to infection with the strain. Restriction of the use of gentamicin and tobramycin is essential to preserve their value in serious infections.

Staphylococcus aureus strains isolated in Danish hospitals from January 1st, 1966, to December 31st, 1974

During the years 1966-1974, 167,297 strains isolated from 167,297 patients or staff members in Danish hospitals were registered at Staten Seruminstitu. All the strains were phage-typed and examined for production of a 'Tween'-80-splitting enzyme and resistance to mercuric chloride. 158,236 strains were examined for resistance to antibiotics. Since 1968, a steep decrease in the number of strains resistant to three or more antibiotics (multiple-resistant) and in strains of the 83A complex was noticed. In recent years an increase in strains belonging to phage-group I and in those referred to as miscellaneous and non-identified was registered. The increase in the non-typable strains might be explained by the shift of the concentration of the typing phages from 1000 X RTD to 100 X RTD. It is concluded that at least two factors may have contributed to the reduction of the multiple-resistant strains: an altered antibiotic policy, restricting the use of streptomycin and tetracyclines, and an improved hospital hygiene, diminishing the spread of identical strains within the various departments. However, it is emphasized that the consumption of methicillin is still increasing.

Transduction of bacteriocin determinants in group A streptococci

Determinants of streptococcin A-FF22 (SA) production and host cell immunity have been transduced to three serologically distinct Group A streptococci. Streptomycin resistance markers were not cotransducible with bacteriocin determinants. SA+ transductants of strains unrelated to the parent SA+ strain were unstable but SA+ transductants of a spontaneous SA- derivative of the parent appeared to be stable.

Methicillin-sensitive variants in ageing broth cultures of methicillin-resistant Staphylococcus aureus

Methicillin-sensitive variants have been isolated from ageing broth cultures of the methicillin-resistant strain of Staphylococcus aureus NCTC 10442 and also from numerous other strains. There were wide variations and fluctuations in the incidence of sensitive variants from cultures incubated under uniform conditions.

Unusual skin sepsis due to a strain of multiresistant Staphylococcus aureus

A strain of Staphylococcus aureus resistant to as many as nine distinct antibiotics has shown unusally high virulence as indicated by its ability to cause an epidemic of furunculosis amongst hospital nurses.

Co-transduction of plasmids mediating resistance to tetracycline and chloramphenicol in Staphylococcus aureus

Independent plasmids mediating resistance either to tetracycline (Tc) or chloramphenicol (Cm) were transduced successively into Staphylococcus aureus strain 8325. From this doubly resistant donor strain, Tc was co-transduced with a frequency of 40 to 50% when Cm was selected. Co-transduction of Cm was 5 to 10% with Tc selection. Plasmid elimination was infrequent and restricted to the Cm plasmid. A variant, doubly resistant strain gave 100% co-transduction of Tc and Cm and a high rate of joint elimination of both plasmid markers. Co-transduction of the plasmids from recombination-deficient donor strains was much reduced if the plasmids had been introduced separately into the donor strain, but occurred at the normal high rate if they had been introduced jointly. The plasmids were co-transformed at relatively low rates with closed circular deoxyribonucleic acid (DNA) from doubly resistant donors, but not with DNA from a mixed lysate of singly resistant strains. Our evidence favored a hypothesis of recombination-dependent, reversible linkage between the two plasmids as the basis for their co-transduction. Examination of plasmid DNA from the doubly resistant strains by ultracentrifugal and electron microscopic methods did not disclose any physical differences between singly and doubly resistant strains that might account for the observed co-transduction.

Isolation and characterization of a kanamycin resistance plasmid from Staphylococcus aureus

A circular covalently closed duplex deoxyribonucleic acid plasmid carrying genes for resistance to kanamycin/neomycin has been identified in Staphylococcus aureus E419. The plasmid has a molecular size of 9.2 x 10(6) daltons and can be transduced into or can transform competent susceptible strains of S. aureus to kanamycin/neomycin resistance.