Antibiotic resistance of coagulase-negative staphylococci and micrococci

Antimicrobial resistance in coagulase-negative staphylococci from Nigerian traditional fermented foods

Background

Coagulase-negative staphylococci have become increasingly recognized as the etiological agent of some infections. A significant characteristic of coagulase-negative staphylococci especially strains isolated from animals and clinical samples is their resistance to routinely used antibiotics although, resistant strains isolated from fermented foods have not been fully reported.

Methods

A total of two hundred and fifty-five CoNS isolates were subjected to antimicrobial susceptibility test using the disc diffusion technique. The minimum inhibitory concentration of the isolates to the tested antibiotics was determined using the microbroth dilution method. Methicillin resistant strains were confirmed by detection of methicillin resistant genes (mecA) and also employing cefoxitin screening test.

Results

The isolates were confirmed to be methicillin resistant by the detection of mecA genes and the cefoxitin screening test. The isolates demonstrated appreciable resistance to ampicillin (86.7%), sulfomethoxazole–trimethoprim (74.9%), amoxicillin–clavulanic acid (52.5%) and oxacillin (35.7%). Methicillin resistance was exhibited by 13 out of the 255 isolates although no mecA gene was detected. It was also observed that the methicillin resistant isolates were prevalent in these traditional foods; iru, kindirmo, nono and wara.

Conclusion

This study has ameliorated the incidence of multiple antibiotic resistant coagulase-negative staphylococci in Nigerian fermented foods and if not tackled adequately might lead to horizontal transfer of antibiotic resistance from food to man.

Staphylococcus haemolyticus - an emerging threat in the twilight of the antibiotics age

Staphylococcus haemolyticus is one of the most frequent aetiological factors of staphylococcal infections. This species seems to lack the important virulence attributes described in other staphylococci. However, studies have shown that the presence of various enzymes, cytolysins and surface substances affects the virulence of S. haemolyticus. Nevertheless, none of them has been identified as crucial and determinative. Despite this, S. haemolyticus is, after Staphylococcus epidermidis, the second most frequently isolated coagulase-negative staphylococcus from clinical cases, notably from blood infections, including sepsis. This raises the question of what is the reason for the increasing clinical significance of S. haemolyticus? The most important factor might be the ability to acquire multiresistance against available antimicrobial agents, even glycopeptides. The unusual genome plasticity of S. haemolyticus strains manifested by a large number of insertion sequences and identified SNPs might contribute to its acquisition of antibiotic resistance. Interspecies transfer of SCCmec cassettes suggests that S. haemolyticus might also be the reservoir of resistance genes for other staphylococci, including Staphylococcus aureus. Taking into consideration the great adaptability and the ability to survive in the hospital environment, especially on medical devices, S. haemolyticus becomes a crucial factor in nosocomial infections caused by multiresistant staphylococci.

Mechanism of Chloramphenicol Resistance in Staphylococcus epidermidis

The mechanism of chloramphenicol resistance in several multiple-resistant Staphylococcus epidermidis strains has been studied and shown to be due to the presence of the enzyme, chloramphenicol acetyltransferase. As with S. aureus, the inactivating enzyme in S. epidermidis appears to be the product of a structural gene on the chloramphenicol plasmid because resistance and enzyme activity are concurcurrently lost after growth in acridine orange or at elevated temperatures. The synthesis of chloramphenicol acetyltransferase in S. epidermidis has been compared with the function of a similar enzyme in chloramphenicol-resistant S. aureus with the conclusion that the kinetics of induction, products of the reaction, and general properties of the enzymes are identical. The chloramphenicol acetylating enzyme from S. epidermidis has been purified to a state of homogeneity and compared with the analogous purified S. aureus enzyme. Both purified preparations consist of native enzymes with molecular weights of 80,000, and evidence is presented that is consistent with their being made up of four identical subunits of 20,000 each. The two staphylococcal enzymes are identical with respect to pH optimum, apparent affinity (K(m)) for chloramphenicol, heat denaturation, and immunological reactivity, but they differ in electrophoretic mobility, chromatographic behavior, substrate specificity, and sensitivity to inhibition by mercuric ion.

Microbiologic studies of coagulase-negative staphylococci isolated from patients with nosocomial bacteraemias

We studied 50 strains of coagulase-negative staphylococci (CNS) isolated from 50 patients with hospital-acquired bacteraemia, identified by prospective surveillance at the University of Virginia Hospital between March 1981 and September 1982. Using the Staph-Ident System for speciation, we found that 37 strains (74%) were Staphylococcus epidermidis, 7 (14%) Staph. hominis, 3 (6%) Staph. haemolyticus and 3 (6%) Staph. warneri. 33 (66%) of the strains produced slime and a higher proportion of the Staph. epidermidis group (75%) than the non-epidermidis group (46%), did so. Minimal inhibitory concentrations (MIC) were determined by a microdilution technique with 20 different antibiotics. There was no difference in geometric mean MICs between slime producers and non-slime producers within either the epidermidis or non-epidermidis group. The most potent antibiotics against Staph. epidermidis (MIC90 mg l-1) were rifampin (0.05), netilmicin (0.05), amikacin (2.9), thienamycin (0.75), teichomycin (0.85), vancomycin (1.0) and nafcillin (0.39). On the other hand strains were resistant to tobramycin (15), moxalactam (50), fosfomycin (greater than 64), and clindamycin (greater than 64). Overall, eight (16%) of the CNS strains were resistant to methicillin, three of which were Staph. haemolyticus. The non-epidermidis strains were more resistant than the Staph. epidermidis strains to most beta-lactam antibiotics. Differences in antibiograms indicate that speciation of CNS may prove useful for clinical and epidemiologic purposes.

Studies on coagulase-negative staphylococci in patients undergoing cardiac surgery. Different hypotheses for the origin of multiply-resistant isolates

Hypotheses for the origin of multiply-resistant coagulase-negative staphylococci from 146 patients undergoing cardiac surgery were tested. All received cephalothin per-operatively. Antibiotic susceptibility testing, phage-typing, bio-typing, and test for Tween-80-splitting enzyme were used to characterize 132 isolates from nose swabs. Seventy-five percent of the pre-operative susceptible isolates were of biotype 1, while biotypes 3 and 4 made up 59% of the post-operative, multiply-resistant isolates. Fifty-three percent of the isolates were typable by phage-typing. Typability of isolates of biotype 1 was high (56%) while almost 75% of biotype 4 were untypable. Susceptible isolates were more often typable than multiply-resistant ones. Of the 146 patients, 105 (72%) carried coagulase-negative staphylococci pre-operatively, only two of them carried multiply-resistant strains. Fifty-nine patients (41%) were colonized with multiply-resistant coagulase-negative staphylococci post-operatively. By combining the results of bio-typing, phage-typing, and test for Tween-splitting enzyme the study made it probable that a maximum of ten patients (6.8%) already carried multiply-resistant strains on admission to the hospital or were carriers of initially susceptible strains which developed multiple-resistance during administration of antibiotics. It therefore seemed likely that most of the patients were deprived of their natural bacterial flora by antibiotic treatment and subsequently colonized post-operatively with multiply-resistant coagulase-negative staphylococci from the environment.

Role of coagulase-negative staphylococci and micrococci in ocular disease

Forty-nine strains of coagulase-negative staphylococci and 26 strains of micrococci isolated from human eyes were classified by the Baird-Parker system of 1966. The staphylococci belonged to subgroups II, III, IV, and V with one strain each in subgroups III and IV. However, when biotyped by Baird-Parker's system of 1974, less than 50% (23/49) of strains were typable and they belonged to biotypes 1 and 2. With our proposed modified classification all strains could be classified into biotypes 1, 2, and 3. All the 26 strains of micrococci belonged to subgroup VII. Staphylococci isolated from diverse sources produced, qualitatively and quantitatively, different corneal pathology in rabbits when compared to those isolated from healthy conjunctiva. This bore no relation to the present system of subtyping based on biochemical reactions. Micrococci were incapable of producing experimental corneal lesions in the rabbit.

Antibiotic activity in vitro against methicillin-resistant Staphylococcus epidermidis and therapy of an experimental infection

Staphylococcus epidermidis is a major pathogen in early prosthetic valve endocarditis and cerebrospinal fluid shunt infections. Approximately 10 to 15% of hospital isolates are methicillin resistant. Ten clinically significant isolates of the latter were collected for antibiotic studies in vitro and in an experimental infection in animals. Time-kill studies of five strains showed gentamicin to be the single most effective antibiotic; however, dwarf colony variants emerged as survivors with two of these strains when challenged with gentamicin alone. The addition of a second antibiotic to gentamicin did not significantly improve the bactericidal rate but prevented the emergence of variant strains. A blood culture isolate of methicillin-resistant S. epidermidis combined with 5% hog gastric mucin was used to establish an experimental intraperitoneal infection in mice. Neither methicillin nor nafcillin treatment reduced mortality below that of untreated animals. Cephalothin treatment delayed early mortality but did not diminish overall mortality. Gentamicin was the most effective single antibiotic, and gentamicin in combination with vancomycin was the most effective regimen overall. The combination of rifampin plus vancomycin was as effective as gentamicin alone. The combinations of cephalothin or nafcillin with gentamicin and cephalothin with vancomycin demonstrated antagonism. The antagonism was not due to multiple injections or drug-drug inactivation.

Classification of staphylococci isolated from ocular tissues

A total of 145 strains of Gram-positive, catalase-positive, coagulase-positive, and coagulase-negative cocci isolated from the human eye were classified by the system of Baird-Parker (1966). These belonged to subgroups I, II, IV, and V and showed a wide range of antibiotic sensitivities unrelated to subgroup and category of lesion. The role of coagulase-negative staphylococci in producing postoperative ocular infections has been especially emphasised.

Micrococcus luteus pneumonia: a case report and review of the literature

The clinical course of a 69-year-old male with acute myelogenous leukemia is described who, while extremely leukopenic (less than 100 neutrophils/microliter) from chemotherapy, developed a cavitating pneumonia due to a gram-positive coccus, Micrococcus luteus. Aggressive antibiotic management and attainment of complete remission of his leukemia resulted in a successful outcome. A review of the literature regarding the pathogenicity of this organism and, in particular, its occurrence as a cause of pneumonia is presented.

Antimicrobial susceptibility and selection of resistance among Staphylococcus epidermidis isolates recovered from patients with infections of indwelling foreign devices

Twenty-seven isolates of Staphylococcus epidermidis from patients with prosthetic valve endocarditis or infected cerebrospinal fluid shunts were examined for susceptibility to antimicrobial agents. Subpopulations resistant to 20 and 100 mug of methicillin per ml were present in 63% of the isolates (methicillin-resistant isolates). Subpopulations resistant to 20 mug of nafcillin and cephalothin per ml were found in every methicillin-resistant isolate but with frequencies (10(-5.0 +/- 0.5) and 10(-6.4 +/- 0.9), respectively) which were not always detectable by susceptibility testing. Resistance to >/=1.6 mug of penicillin per ml was found in 80% of isolates. Cephalothin, cefazolin, and cefamandole were more active than cefoxitin or cephradine, and gentamicin was more active than tobramycin or amikacin; rifampin was the single most active agent against all isolates. There was no difference in susceptibility between prosthetic valve endocarditis and cerebrospinal fluid shunt infection isolates. Among methicillin-resistant isolates, the phenotypic expression of resistance to methicillin or nafcillin but not to cephalothin could be enhanced by 48 h of incubation with each drug. Isolates containing no methicillin-resistant subpopulations were killed by incubation with methicillin, nafcillin, or cephalothin. High-level resistance to rifampin emerged in both methicillin-resistant and methicillin-sensitive isolates after 8 to 24 h of incubation with this drug. The presence or absence of antibiotic-resistant subpopulations among S. epidermidis isolates and their selection during treatment should be considered when therapy is devised.

Significance of urinary isolates of coagulase-negative Micrococcaceae

Of 16,347 urine cultures submitted to the hospital laboratory, 68 (0.4%) specimens from 50 patients yielded greater than 10(4) coagulase-negative staphylococci/ml in pure culture. A total of 62 of 63 organisms available for study were staphylococci: 45 Staphylococcus epidermidis (predominantly subgroup 1), 15 Staphylococcus saprophyticus (subgroup 3), and 2 Staphylococcus aureus. Twenty-one patients had "probable" urine infections. Eight patients had two or more positive urine cultures, and all isolates from the same patients were identical (by morphology, antibiotic susceptibility, and hemolytic pattern). Nine (75%) of the 12 isolates of S. saprophyticus, which were novobiocin resistant and nonhemolytic on the synergistic hemolysis test, were from patients with probable urinary infection. Eight were young women with acute symptoms and pyuria. Differences in the glucose and mannitol fermentation tests with different media may lead to difficulties in identification. Novobiocin resistance cannot be relied upon to differentiate isolates of S. saprophyticus from S. epidermidis.

The gram positive cocci

Recent changes in taxonomy of the gram positive cocci are discussed. Views on these changes and practical methods of differentiating the staphylococci, micrococci, streptococci, and aerococci are presented. Simplified schemes, using acceptable clinical laboratory techniques, are presented that either differentiate or categorize the pathologically important gram positive coccal species.

Gram-positive, motile, cluster-forming cocci as a cause of urinary infection

One hundred and thirteen strains of motile, Gram-positive, catalase-positive, cluster-forming cocci were isolated from patients with urinary infection attending a private surgery. They constituted 1% of the total 11 302 positive cultures. The biochemical characteristics and the drug sensitivities of the strains are described. The significance of motility for organisms which cause urinary infections is pointed out.At the present time the organisms isolated are orphans in the controversial classification of staphylococci and micrococci.

Coagulase-negative staphylococci causing endocarditis after cardiac surgery

The laboratory findings in seven cases of endocarditis caused by coagulase-negative staphylococci are presented. The usefulness of biochemical characterization of the strains in diagnosis and the selection of antibiotics for prophylaxis and treatment are discussed.

Phage typing of coagulase-negative staphylococci and micrococci

A total of 3217 strains of coagulase-negative staphylococci and micrococci were tested for susceptibility to a collection of phages isolated from coagulase-negative cocci; it was concluded that a useful typing scheme could be developed. Of the strains of Baird-Parker's biotype 1, 72% were lysed by one or more phages, although rather a large proportion of strains are lysed by many phages to give a complex typing pattern.Normal persons commonly yield 10 or more distinguishable strains of coagulase-negative cocci in cultures from the nose and the skin.

Plasmid for tetracycline resistance in Staphylococcus epidermidis

A plasmid determining tetracycline resistance was demonstrated for Staphylococcus epidermidis. Tetracycline resistance was spontaneously lost from a S. epidermidis strain at a frequency of <0.1 to 1.3%. Frequency of loss was not appreciably enhanced by growth at 42 C or in ethyl violet. The rate of transduction of tetracycline resistance in three S. epidermidis crosses was decreased as a function of ultraviolet irradiation of the transducing phage. Plasmid deoxyribonucleic acid (DNA) associated with tetracycline resistance was isolated by CsCl-ethidium bromide dye-buoyant density gradients. The tetracycline plasmids from S. aureus RN 1304 (molecular weight 2.66 Mdals) and S. epidermidis 367(phi367) (T(367)) cosedimented in 5 to 20% neutral and alkaline sucrose gradients and are therefore of similar molecular weights. An extrachromosomal element in the recipient strain, isolated as covalently closed circular DNA, did not retain its integrity in an alkaline sucrose gradient.

Staphylococcus epidermidis BV: antibiotic resistance patterns, physiological characteristics, and bacteriophage susceptibility

Staphylococcus epidermidis BV is a group of mannitol-fermenting coagulase-negative staphylococci characterized by multiple antibiotic resistance, very similar biochemical characteristics, and phage susceptibility. Clinical isolates belonging to this group are resistant to most antibiotics tested, including oxacillin, lincomycin, and novobiocin. The only antibiotic to which all tested strains are sensitive is vancomycin. Common biochemical traits of the tested S. epidermidis BV strains include fermentation of trehalose and ribose, phospho-beta-glucosidase activity, growth on synthetic medium with amino acids as carbon source, and lack of deoxyribonuclease, phosphatase, lipase, and gelatinase activity. Some of these characteristics appear more frequently in mannitol-positive control strains than in mannitol-negative strains. S. epidermidis BV strains carry lysogenic phages with a host range restricted to this group. These phages allow the differentiation of individual strains.

Selection of Staphylococcus aureus in cultures from air samples

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